FOR variety reasons early speculation about future aviation painted rosy picture seaplanes During interval between two world wars seaplanes set speed records crossed oceans offered great promise future Since through out world almost city size situated near important body water feeling build expensive space consuming airports 1929 Claude Dornier building remarkable seaplane shown pic ture american industrial designer Nor man Bel Geddes busy collaboration Dr Otto Koller designer Ger man Pfalz biplane Together worked up design enormous flying boat wing span 528 feet deck below water line eight decks above have 20 1 900-hp engines includ ing engine repair shop root wing 22 feet thick gross weight 1275000 pounds would believe behemoth designed cruise fantastic speed 100 mph 5000 feet some reason never built Now discredit man Larry Williams taxies Supermarine S4 waters Lake Elsinora CA prior contest-winning flight powered K&8 front-rotor engine Warren Shipp photo Norman Bel Geddes true genius ideas kitchen ranges elevated freeways have become reality simply show fast actual progress can overtake wildest dreams gifted advent all-metal stressed skin monoplanes retractable gear landplanes suddenly stopped looking like Jennies began look today Seaplane designers other hand could never figure out way retract floats within sensible weight allowance density seawater just wasnt great enough floats hulls always too big invariably added up drag just simple landplane fuselage Since drag means fuel increased fuel meant corresponding reductions range pay load translated reductions reve nues wasnt until jet engine came along eliminating large clearances re quired propellers designers able create seaplanes such Skate shown model photo could compete drag-wise landplane time airports finally built Iandplanes stolen show 10 Model Aviation Larrys Supermarine overhead later lowwing Supermarines among beautiful ali aircraft laid groundwork Spit fire designed RJ Mitchell Shipp photo Other factors also determined de mise seaplane Rough seas landing areas werent always calm areas congested unsafe handling mooring maintenance difficulties say nothing severe corrosive effects sea water aluminum alloy hulls Numerous approaches problem operating aircraft water have made include variety floats varying shapes skis hydrofoils large hulls literally stabilized tip floats spon sons blended configuration Skate shown photo exception last item possibly hydrofoils think modelers have man aged adapt others models varying degrees success ducted fan makes both hydrofoils blended hull-wing attractive possibilities since out propeller clearances deal inter esting ideas suggest themselves will leave notions another time devote article understanding principles underlying simple scale type floats appropriate scale model will try use procedures learned evaluate excellent model type float given Irwin Ohlsson might think float piece functional sculpture must perform following 1 Provide adequate buoyancy rest 2 Provide minimum resistance motion through water during progressive stages takeoff 3 Provide smooth stable variations trim during takeoff landing since pilot has little no control over trim attitude low speeds water 4 Provide stable reasonably soft landing entry course minimum weight air drag well have ridden water skis aboard speedboat power cruiser familiar changing attitudes craft starts move nose begins rise untilif sufficient power available will gain enough speed level off plane An airplane floats does same thing As moves forward pushes sizeable volume water ahead itself creating large wave hump over OHLSSONS WIDGEON DURING preparation Mr Powers article both Brad editor con sulted Irwin Ohisson retired engine manufacturer AMA Hall Famer has considerable success floats hulls radio control Shown Irwins Grumman Widgeon data supplied Ohlsson Fol lowing Irwins comments hull table specifications configuration first step changed double concave also two sponsons added sides hull bow first step Small spray rails extend outboard length sponsons tunnel de sign gives smooth low power takeoff sponsons spray rails deflect water props original full-scale aircraft 2% degree positive wing incidence reduced 0 degrees model After first flightwith Joe Bridi test pilotit came off water before reached its flying speed stalled nose wing down landplane would have bought farm However bounced out water like basketballnot scratch Since day April 1974 about 50 flights have madenever has wet real good stable fast flying machine Specifications Twin-Engine Widgeon Span 80 chord center section 13% tip 8 hull overall 54 Weight empty 13 lbs weight fueled 15 lbs Power2 contra-rotation 61 Perry pumpsfuel 500cc nacelleprops 11 x 7Y2 left right handthrottles 2one nacelle Controls Flaps Aileron Rudder Elevator Construction Wing2 main spars balsa ribs 2 apart sheet balsa silk covered butyrate doped plywood engine mounts rear spar Hullspruce keel balsa sheeted bottom 3/32 balsa 1/32 x 3 plywood glassed top sides silk covered butyrate dope April1979 11 Noting jet engineno prop clearance problemsmade possible blended hull Powers cites Skate shown moaei tesi tow RACING AIRPLANE AVERAGE___ AIRPLANE LIGHTPLANE Lu 0 0 IL L - 7approx / S 1/ EXCESS THRUSTAVAILABLE FOR TAKE-OFF THRUST 2 L RESISTANCE HUMP 18 10 TAKE-OFF SPEED must literally climb order level off plane gather takeoff speed hump region operation critical regard power indicated Fig 1 Obviously airplane accelerate take off thrust must greater resistance Otherwise will just cruise around water until fuel gone Fig 1 racing airplane has very high water resistance presumably due small floats achieve low air drag since Fig 1 high speed design has sufficient thrust cope resistance As apparent thrust available average airplane used racer takeoff speed would impossible since airplane could never ride over hump Since model engines available appear adequate cases should justified applying average~ rather marginal criteria designing float As aspects airplane design VOLUME Lb2 VOL b b VOLL2b compromises between conflicting require ments generally being sought case hulls floats boils down finding nice balance betweeen size displacement Large floats have advan tage low immersion light spray weigh have higher air drag Small floats sink too deeply water makes heavy spray high water resistance So can say except refinements design actual float itself basic problem find proper size job keeping both float size spray minimum commensu rate power orother limiting factors Early float designers found after much experimentation floats having length beam ratios less about 6/1 didnt work very well seven seemed best average conditions acceptable per formance water achieved draft early floats such displacement value approx imating cubical container filled water having same dimensions side beam float Thus float beam 3 ft could expected perform satisfactorily displaced amount water could placed cubical container 3 ft side Such float would displace 33 27 cu ft sea water Since sea water has density 64 lb/cu ft weight water 1728 lbs pair such floats would right average airplane weighing about 3450 lbs As pointed out Fig 1 could vary considerably non average conditions Once relationship estab lished easy matter scale floats up down suit different gross weights long same family reasonably close being geome trically similar relationship came called beam loading expressed non-dimensional terms W 3andhadavalueoflOwhen wb length/beam ratio seven W equals Load Carried Floatlbs w equals Density Sea Water 4 lbs/cu ft b equals Beam FloatFeet criterion expressed graphically Fig2 Although shown simple cube Fig 2 applies L/b ratio seven L/b 6 value C of75 worked best since L/b decreased Beam increased same token increases L/b accompanied decreases beam requiring corresponding increases values C During WW II studies made configurations floats particularly hulls involving length/beam ratios order 8 10 higher 12 Model Aviation b.Kbb COMPARING CRITERIA found longer hulls less air drag less water resistance less way nasty characteristics like hobby horsing~ porp oising pitching back forth under way selecting length/beam ratio float strong consideration given value 8 finally ruled out due excessive length fact typical scale applications early seaplanes However after have finished article should able design float having high L/b wish float described will have value L/b investigation progressed became apparent immersion coefficient would useful contained provision beam length well Accordingly new term developed engineers called K2 w equal w L2 b Like C K2 nondimensional does indeed account length well beam Recom mended values K2 range 018 light spray low power 022 heavy spray high power 020 representing good criterion average~ conditions float therefore will based indirectly value 020 However look Fig 2 see volume portion term L2b resolves itself large cakepan 2 percent full bears little physical resemblance float So based K2 tried true parameter lets devise term just purpose multiply K2 length/beam ratio increase amount also get cakepan carton has same overall dimensions float follows K2so X K2 wL2bb Lx W — W c bwL2bwLb2 C1 ficient Immersion Lb2 gives us figure fits float like shoe box carton shown figure top Fig 2 So term C1 derived K2 constant like K2 varies length/beam ratio said float has value 7 X K2 7 X 020 140 shown figure 3 As can seen C really percent age displacement float bears its carton makes cozier relationship wish reconcile parameters fully correlation between C K2 shown Fig 4 Now lets proceed design float First must find beam whch turn requires value displacement W watch weight think can put pair floats Nosen Citabria already weighs 18 lbs about 32 lbs Thus gross weight will 25 lbs LENGTH/BEAM RATIO vs Cj 8-7 b 6bf LCi b 144 160 126140154HEAVY OUR FLOAT 101121314 dispi float W dispi artonwLb2 I0 L b 15161718 Fig 3 K2 COMPARED WITH 0 OUR FLOAT 0 . LIGHT SPRAY K2018 7 MODERATE 020 6 HEAVY 022 EXCESSIVE 025 5 2 Fig 4 34 5 68 CW 125 April 1979 13 20 Dornier X 12-engined flying boat built 1929 photo has radial engines arranged tandem pairs After transatlantic crossing turned turtle tropical storm CONVENTIONAL FLOAT t217 Al curve ares r2 7b 77 20 2022 / / 2 25 225 -2 10304222 IS oisoc. 926 [2 DeejI F24Ih0 02p2[ 942 W05N9044IIb25jyf 4404 h224&Ih1l 410 2STSP/C0NTROOISO40 t f J 0 10 42240 V Fig 5 float will carry 125 lbs So W equals 125 lbs C2 said 140 W C2 2 expression two unknowns b L So will have express L terms b making WW wLbbzw7b3 andbeamb3 W — w7 C 125 64 X 7 X 140 584 ft or7in Since length/beam ratio seven length 7 Now lets check results another way said C percentage displacement float carton 14 percent carton has displacement 7 X 7 X 4 8893 lbs 1728 14 percent 8893 1245 lbs close enough point might wise reassess things consider other values planning build model 3-lb camera may added later going fly fresh water lake having water density 624 lb/cu ft might wiser pick value C2 126 shown Fig 3 rather 140 reduce draft lighten spray give some room grow particularly think powerplant marginal beam will become 725 length 5075 However will add around 10 percent weight float Now some discussion before tackle details Obviously float should aerodynamically clean can make So might say Ok lets make streamlined like wing tip fuel tank sounds good streamlined bodies completely immersed tend suck under speak takeoff impossible final analysis wing generates lift deflecting thus accelerating mass air downward float completely streamlined partially immersed actually deflects water upward thus sinking deeper deeper power applied speed remains essentially constant displacement vessels sailing yachts have less fixed maximum speed no matter much extra power wind available just sink deeper deeper like bottom teaspoon suspended against water flowing faucet other hand hull bottom vicinity step transom flat like water ski v-shaped like speed boat water departs step float rides up skims over water deriving lift much same way wing slighting deflecting water down ward gaining lift thereby derived form dynamic pressure hull bottom Actually forebody its transom step does work afterbody primarily provide static buoyancy rest aircraft doesnt rock back its tail Indeed Lou Proctors Antic has forward floats really forebodies coupled small efficient afterbody form small float tail Minimum air drag critical matter models faithful attention detail scale models requires easy lines generous step depth needed assure clean departure wake doesnt tend reattach afterbody cause porpoising plus generous landing angle will handle problem forebody lines should sharp easy keep hull resistance minimum large aircraft ample deadrise needed minimize decelerations landing Deadrise should 14 Model Aviation 226 find center buoyancy Trace curve areas onto cardboard balance three ways edge ruler marking line time Intersection centroid area figurecenter buoyancy float 4 j3-I RAZOR SHARP CHINES Fig 6 TRUE AREAS SQ INf337 316 EI$II LIII -__ IPORT VIEW LEFT FLOAT OUTBOARD CHINE 16 r -eTAogrIb, VINBARD CHINE 0 11 FLOAT PROBLEMS Construct curve areas find 1 Displacement pounds 2 Center Bouyancy LSO 3 Length/Beam Ratio disregarding rounded ends tapered sides 4 Length Beam displacements 1 lb 5 lbs 10 lbs increase go forward along forebody sharpen hull lines provide stability trim Adequate buoyancy afterbody easier attain deadrise held constant initial application power takeoff produces powerful nose-down moment seaplanes must countered adequate forebody displacement will tend resist moment quickly smoothly avoid forebody porpoising char acteristic low length/beam ratio hulls having insufficient restoring moment standpoint L/b 8 would better float would begin get too long landing angle would suffercompro mises again Landing Angle No2 corresponds similar angle landplane Its purpose allow step wheels make initial contact angle close 90 percent stalling angle wing permit slowest possible 912 1 2 REOD PORT AND STARBOARD 17 16 15 114 13 12 1 II II 7k 8 14518 5 18 3 gPORT FLOAT SHOWN -. FLOAT OPPOSITE II 212426 Ti OHLSSON FLOAT 1213 WEIGHT W/ FLOAT. LBS landing speed Since impact forces vary square speed small reductions speed accompanied sizeable increases safety float landing angle 14 15 Fig 7 9 degrees coupled 3 degrees wing incidence 12 degrees Clark Y airfoil small Reynolds Numbers corresponds guidelines just mentioned 1 2 3 4 ANSWERS TO FLOAT PROBLEMS Fig 8 Displacement 298 say 3 lbs CB Station 134 just forward Step 1/B 26/4 equals 65 Dimensions vary cube root Ratio Displacements So 1 lb dimensions will Ohlsson float timesthe cube root 1/3 693 So equals 693 x 26 18 end B 593 x 4 277 Similarly 5 lbs 307 B 472 10 lbs L 3875 B 595 say 6 Note Since float different family conventional float geomet rically related values CW Ci would comparable VOLUME 4 CtiINV2SOLU OF OUYANC April1979 15 FLOAT TOO SMALL LOAT FLOAT TOO LARGE static trim CG complete airplane must obviously lie perpendic ular waterplane passes through Center Buoyancy float indicated Item 29 Fig 5 Item 2 Fig 5 shows landing angle mentioned above As can seen step centroidof V-step Item 22 Fig 5 should slightly aft Center Buoyancy place directly under CG landing 30 order keep float axis parallel fuselage usually desirable flight angle static trim Item 13 Fig 5 3 degrees producing slightly nose up attitude airplane static rest water undesirable have axis airplane parallel waterplane would mean placing floats slightly nose up else reducing forebody displacementneither good Flare No 12 directs spray helps control its effects Judicious use spray dams blinders metal strips flush sides float projecting about half inch below chine can reduce spray dramatically carried too far forward made too large can destabilizing flight probably best experiment little bit Because forward portions floats destabilizing flight necessary add substantial increment fin area compensate shown No 24 Since floats will also produce negative diving moment elevator trim order preferably some means adjusting horizontal stabilizer toe-in recommended procedure installing wheels landplane no-no floats very necessary mounted firmly accurately Water forces high unforgiving afterbody float tapers back flat transom large enough accomodate water rudder mounting brackets outlets internal pushrods water rudder should placed float its pivot line should 2530% its chord Its area critical make about size proportion shown respect size float So much generalities Now lets put Fig 5 front us study steps involved creating particular float Lay out 7 X 49 carton side view 3 X 49 half plan below 7 X 7 box left Note height float equals beam mainly simplify geometry article height could increased say used basis single hull design ever should decreased excess buoyancy very necessary Theoretically could slice float off just above waterline did extra ounce fuel added servo could sink whole kaboodle Draw center line 3 Draw upper deck lines shown forebody duplicate below plan view forebody shown above chine elliptical prolate spheroid anybody interested doesnt have Make shape matches picture favorite seaplane wish Locate Step 1 As first approxi mation lets assume Sta 26 26 aft nose Later might want change bit Lets hope Draw landing angle 2 heel step up center line Sta 49 Make step depth 8 afterbody keel 7 Draw forebody keel 6 Note carries well forward does match curve deck line top sharpen entry side view left draw circular cross sections upper forebody deck down center line drop vertical tangents circular cross section meets center line tangents Sta 6 forward should extend above 16 Model Aviation Mercury Racer Granger WIlliams repose La Costa CA sloughlntended Schneider Trophy race flown Al Williams real Mercury grossly overweight Brad Powers left Irwin Ohlsson latters highly successful twinfloat design using floats own design championship free-flighter Thirties later manufacturer engines exAMA president Hall Famer Irwin builds designs best center line Starting step Sta 26 draw deadrise angle 4 20 degrees Its inter section vertical tangent just drew determines aft point theoret ical chine 9 Draw theoretical chine 9 establishes smooth variation deadrise go forward Back step section again draw chine flare 12 Its intersection vertical tangent establishes aft end forebody chine 10 Draw forebody chine 10 shown Near Station 6 curve reverses lie fore aft direction make clean aerodynamic entry Assuming theoret ical chine lie curved surface touching side hull therefore intersecting vertical tangents drew draw deadrise Station add flare tangent deadrise horizontal chine flare should have generous radiusbut excessive Now draw afterbody deadrise Station other side end view plan view drew beginning establish afterbody chine both end side views 11 Using afterbody planform deter radii draw locus radii 18 side view complete sections afterbody end view point good idea draw some 'buttock lines' 'water lines' end view shown project other views see fair fair smooth fiddle drawing bit until 23 region between Sta 18 step bottom should have straight buttock lines insure stable planning other words hull bottom surfaces should have no fore aft curvature region Draw trial static load water line sloping up aft 3 degrees through point 3 above keel step 14 information end view water line construct sections shown hatched station Measure sections determine area section Since half sections dont forget multiply area 2 plot values shown 26 establish acurve areas Just volume deck cards sum cards area under curve summation infinite number cross sectional areas therefore represents volume immersed portion float Since before reproduction maga zine drawing made half scale areas have indicated obtained half scale drawing will have corrected full scale will shortly true well length curve areas drawn 1/5 scale expression shape curve areas could add up integrate mathematically since arbitrarily determined its slope choices deadrise flare chine chape etc no way establish slope area curve mathematically must integrate graphically can done close approximation adding areas successive steps 27 judiciously done better way use device called polar planimeter have done gives area under curve 169 sq just pointed out areas taken one-half scale drawing therefore have fourth full-size areas because areas varies scale squared Also said length figure one-fifth actual float must multiply 169 5 times 4 20 have correct figure since value volume cu must divide number cu in cu ft get cu ft can multiply 64 weight cu ft sea water we see float indeed displaces 1252 lbs indicated Fig 5 about draft 3 good guesstimate As shown Fig 7 float should loaded carry much over 13 pounds spray will get too heavy other hand float carry much less 11 pounds will too big heavy smaller float should used Well now know draft displacement what Before can screw floats onto airplane have know buoyancy concentrated way find Center Buoyancy trace curve areas onto piece cardboard no lumps cut out balance shown picture Balance least three ways mark time have careful marks will intersect point centroid area figure Center Buoyancy float 21 Incidentally good way find centroids such things elliptical wings centers lateral area other irregular shapes Now can relate float Nosen Citabria 19 above described earlier shown Fig 5 good stability control CG 20 should 25% mean aerody namic chord MAC wing Since Citabria has rectangular planform amounts 25 percent root chord indicated 17 Fortunately Center Buoyancy falls just want landing angle right step fortuitous because have struggling days get together Actually little both aerodynamically unfortunate carrying large appendages like floats way out arms length speak clearances shown 6 at31 learance 20-in propeller float spacing 3 beams 21 33 should reduced keep airplane its vitals being inun dated choppy water spray covers general way preliminary design float great other aspects covering water resistance trimming moments etc have left untouched felt really essential modeler putting floats pride joy intention article es tablish basic criteria Prelimi nary Design future article will presented Detail Design Continued page 98 April1979 17 Line-up RC seaplane models Lto R Bob Wisniewakis modIfied Lancer single pontoon wing-tip floats Granger Williams sport model similar configuration Granger Williams Mercury twin floats Gary Neelys modified sport biplane twin floats Main floats models same Mercury design molded foam plastic Openers/Winter continued page 72 have something tell As RCer FOs chief interest CL Racing frantic aerobatics pilots center circle will find Bill Lee CL Racing talking about home-made fibreglass props Bill Wynn Paul too guy endlessly seeks truth about tanks things like props doing experimenting finding para meters Dave Chesney writes beautifully RC Helicopters column existence now Bill Warner Sport/Scale will put humor life flying circus note others gang Without guys like us would never know about hundreds things add up sum total skills Brad Powers lead article floats quarter-scale landmark article Model aviation old century yet explosion knowledge techniques products never dared dream about what know about floats would fit smallest drawer field box So designer partook dozens famous pro jects made history modeler boot telling us design float virtually size modelas well monsters weve yet see water Note feed-inIrwin Ohlsson great Ernie Stout Convair fame What suggesting dear friend April issue however excep tional 12 year talking about magazine Within another yearGod willingit will thousand light years beyond April 1976 MA began July 1975 its modern form ask conscious magazine contro versial terms some other magazines have shown theyd like see deadbut inspect closely what speak especially minority members did subscribe MA past yours wed like proud AS WE GO TO PRESS sad news ar rives passing Myron Mike Schlesinger recent past president Top Flite Models Mike respected friend industry innumerable modelers true pioneer helped start Top Flite its way chaired trade show committee 1956 became member HIAAs board directors served nearly 10 years chairman co-chairman HIAAs Model Aeronautics Division Hu morous easy going always compassion ate understanding Mike Schlesinger will truly missed us Floats Powers continued page 17 actual floats installed Citabria model together summary results some photos Irwin Ohlsson thirties deve loped line famous Ohlsson engines now retired builds beautiful model seaplanes has given pair floats developed has found very satisfactory straightforward design have generous step landing angle embody progressive deadrise Rather present float complete its displacement Center Buoyancy etc ready determined will give its dimensions trim another guesstimate draft 16 40 percent its beam data procedures already discussed up find answers problems Fig 6 shows float answers will found illustration Answers Float Prob lems Finally wish express thanks Ernest G Stout former Chief Hydrody namics Convair worked interesting projects sistance providing data presented herein Now am going start building float build finish before write let know works can de cide whether stay leave Tierra Del Fuego RC Technique/Myers continued page 19 control thats going wrong way move pushrod hole opposite side output wheel frequently make such change field someone needs disadvantage approach pushrods usually get tangled you end up product review product review product review Radial Engines man has thingultra deluxe 57-cylinder scale-like engines /4 scale 4-cycle high-torque swing 16-8 through 20-6 props Low vibra tion low fuel consumption mild glow fuel 6-in diameter 23 oz weight 7cylinder engines offered 3 versionspol ished aluminum anodized black deluxe Collectors Gold Edition package trimmed 14K gold Manufacturer states fully opera tional warranted 90 dayssold direct Executive Engines Co 16650 S 104th Ave Orland Park IL 60462 product review product review product review swapping rudder elevator servos side-by-side using Nyrod often finds surgery neces sary because outer shell has anchored location doesnt allow shift connection other side wheel Wouldnt nice could just throw reversing switch servo point Bobs eyes lit up Ill bet Ace R/C Bantam Midget machinery will fit regular Bantam case says leave enough room servo reverser dont see what can idea George kicked around some possibilities until time get back work few days later Bantam case Bantam Midget servo appeared desk magic Christmas came bit early year thought until Bob told wanted back after youve finished rever sing switch first thought make use 16pin DIP switch After little consideration possibilities left open direct short across batteries dropped idea Besides switch too big Next tried 4PDT Noble switch commonly used switch harnesses RC systems can made fit little help Dremel problem will have take out servo get switch smaller switch could mounted right out open can get couldnt find Slightly later Bob left another goodie desk prototype servo reverser ACE R/C few mods could fit space available would left servo having two pigtails rotation Plug need configuration left project returned servo Bob must careful let unused plug short out metal parts because will short out batteries kill whole system As said before like idea having servo reverser receiver todays IC circuitry major configuration change would adding second set sockets other rotation Its fair mention Kraft has shipping sets 10 years have two servos set up direction Editors NoteLike feature Cox-Sanwa get what want swapping around dot no dot servos dot tiny circle molded mounting flange between cutouts grommets Once get flight pack set up right theres no way make mistake Thats way like things Over years have bought flight packs transmitters work plane until control trims throws right transmitter trim levers center position leave everything alone until needs service way can pick plane off wall go flying worrying its compatible 98 Model Aviation
Edition: Model Aviation - 1979/04
Page Numbers: 10, 11, 12, 13, 14, 15, 16, 17, 98
FOR variety reasons early speculation about future aviation painted rosy picture seaplanes During interval between two world wars seaplanes set speed records crossed oceans offered great promise future Since through out world almost city size situated near important body water feeling build expensive space consuming airports 1929 Claude Dornier building remarkable seaplane shown pic ture american industrial designer Nor man Bel Geddes busy collaboration Dr Otto Koller designer Ger man Pfalz biplane Together worked up design enormous flying boat wing span 528 feet deck below water line eight decks above have 20 1 900-hp engines includ ing engine repair shop root wing 22 feet thick gross weight 1275000 pounds would believe behemoth designed cruise fantastic speed 100 mph 5000 feet some reason never built Now discredit man Larry Williams taxies Supermarine S4 waters Lake Elsinora CA prior contest-winning flight powered K&8 front-rotor engine Warren Shipp photo Norman Bel Geddes true genius ideas kitchen ranges elevated freeways have become reality simply show fast actual progress can overtake wildest dreams gifted advent all-metal stressed skin monoplanes retractable gear landplanes suddenly stopped looking like Jennies began look today Seaplane designers other hand could never figure out way retract floats within sensible weight allowance density seawater just wasnt great enough floats hulls always too big invariably added up drag just simple landplane fuselage Since drag means fuel increased fuel meant corresponding reductions range pay load translated reductions reve nues wasnt until jet engine came along eliminating large clearances re quired propellers designers able create seaplanes such Skate shown model photo could compete drag-wise landplane time airports finally built Iandplanes stolen show 10 Model Aviation Larrys Supermarine overhead later lowwing Supermarines among beautiful ali aircraft laid groundwork Spit fire designed RJ Mitchell Shipp photo Other factors also determined de mise seaplane Rough seas landing areas werent always calm areas congested unsafe handling mooring maintenance difficulties say nothing severe corrosive effects sea water aluminum alloy hulls Numerous approaches problem operating aircraft water have made include variety floats varying shapes skis hydrofoils large hulls literally stabilized tip floats spon sons blended configuration Skate shown photo exception last item possibly hydrofoils think modelers have man aged adapt others models varying degrees success ducted fan makes both hydrofoils blended hull-wing attractive possibilities since out propeller clearances deal inter esting ideas suggest themselves will leave notions another time devote article understanding principles underlying simple scale type floats appropriate scale model will try use procedures learned evaluate excellent model type float given Irwin Ohlsson might think float piece functional sculpture must perform following 1 Provide adequate buoyancy rest 2 Provide minimum resistance motion through water during progressive stages takeoff 3 Provide smooth stable variations trim during takeoff landing since pilot has little no control over trim attitude low speeds water 4 Provide stable reasonably soft landing entry course minimum weight air drag well have ridden water skis aboard speedboat power cruiser familiar changing attitudes craft starts move nose begins rise untilif sufficient power available will gain enough speed level off plane An airplane floats does same thing As moves forward pushes sizeable volume water ahead itself creating large wave hump over OHLSSONS WIDGEON DURING preparation Mr Powers article both Brad editor con sulted Irwin Ohisson retired engine manufacturer AMA Hall Famer has considerable success floats hulls radio control Shown Irwins Grumman Widgeon data supplied Ohlsson Fol lowing Irwins comments hull table specifications configuration first step changed double concave also two sponsons added sides hull bow first step Small spray rails extend outboard length sponsons tunnel de sign gives smooth low power takeoff sponsons spray rails deflect water props original full-scale aircraft 2% degree positive wing incidence reduced 0 degrees model After first flightwith Joe Bridi test pilotit came off water before reached its flying speed stalled nose wing down landplane would have bought farm However bounced out water like basketballnot scratch Since day April 1974 about 50 flights have madenever has wet real good stable fast flying machine Specifications Twin-Engine Widgeon Span 80 chord center section 13% tip 8 hull overall 54 Weight empty 13 lbs weight fueled 15 lbs Power2 contra-rotation 61 Perry pumpsfuel 500cc nacelleprops 11 x 7Y2 left right handthrottles 2one nacelle Controls Flaps Aileron Rudder Elevator Construction Wing2 main spars balsa ribs 2 apart sheet balsa silk covered butyrate doped plywood engine mounts rear spar Hullspruce keel balsa sheeted bottom 3/32 balsa 1/32 x 3 plywood glassed top sides silk covered butyrate dope April1979 11 Noting jet engineno prop clearance problemsmade possible blended hull Powers cites Skate shown moaei tesi tow RACING AIRPLANE AVERAGE___ AIRPLANE LIGHTPLANE Lu 0 0 IL L - 7approx / S 1/ EXCESS THRUSTAVAILABLE FOR TAKE-OFF THRUST 2 L RESISTANCE HUMP 18 10 TAKE-OFF SPEED must literally climb order level off plane gather takeoff speed hump region operation critical regard power indicated Fig 1 Obviously airplane accelerate take off thrust must greater resistance Otherwise will just cruise around water until fuel gone Fig 1 racing airplane has very high water resistance presumably due small floats achieve low air drag since Fig 1 high speed design has sufficient thrust cope resistance As apparent thrust available average airplane used racer takeoff speed would impossible since airplane could never ride over hump Since model engines available appear adequate cases should justified applying average~ rather marginal criteria designing float As aspects airplane design VOLUME Lb2 VOL b b VOLL2b compromises between conflicting require ments generally being sought case hulls floats boils down finding nice balance betweeen size displacement Large floats have advan tage low immersion light spray weigh have higher air drag Small floats sink too deeply water makes heavy spray high water resistance So can say except refinements design actual float itself basic problem find proper size job keeping both float size spray minimum commensu rate power orother limiting factors Early float designers found after much experimentation floats having length beam ratios less about 6/1 didnt work very well seven seemed best average conditions acceptable per formance water achieved draft early floats such displacement value approx imating cubical container filled water having same dimensions side beam float Thus float beam 3 ft could expected perform satisfactorily displaced amount water could placed cubical container 3 ft side Such float would displace 33 27 cu ft sea water Since sea water has density 64 lb/cu ft weight water 1728 lbs pair such floats would right average airplane weighing about 3450 lbs As pointed out Fig 1 could vary considerably non average conditions Once relationship estab lished easy matter scale floats up down suit different gross weights long same family reasonably close being geome trically similar relationship came called beam loading expressed non-dimensional terms W 3andhadavalueoflOwhen wb length/beam ratio seven W equals Load Carried Floatlbs w equals Density Sea Water 4 lbs/cu ft b equals Beam FloatFeet criterion expressed graphically Fig2 Although shown simple cube Fig 2 applies L/b ratio seven L/b 6 value C of75 worked best since L/b decreased Beam increased same token increases L/b accompanied decreases beam requiring corresponding increases values C During WW II studies made configurations floats particularly hulls involving length/beam ratios order 8 10 higher 12 Model Aviation b.Kbb COMPARING CRITERIA found longer hulls less air drag less water resistance less way nasty characteristics like hobby horsing~ porp oising pitching back forth under way selecting length/beam ratio float strong consideration given value 8 finally ruled out due excessive length fact typical scale applications early seaplanes However after have finished article should able design float having high L/b wish float described will have value L/b investigation progressed became apparent immersion coefficient would useful contained provision beam length well Accordingly new term developed engineers called K2 w equal w L2 b Like C K2 nondimensional does indeed account length well beam Recom mended values K2 range 018 light spray low power 022 heavy spray high power 020 representing good criterion average~ conditions float therefore will based indirectly value 020 However look Fig 2 see volume portion term L2b resolves itself large cakepan 2 percent full bears little physical resemblance float So based K2 tried true parameter lets devise term just purpose multiply K2 length/beam ratio increase amount also get cakepan carton has same overall dimensions float follows K2so X K2 wL2bb Lx W — W c bwL2bwLb2 C1 ficient Immersion Lb2 gives us figure fits float like shoe box carton shown figure top Fig 2 So term C1 derived K2 constant like K2 varies length/beam ratio said float has value 7 X K2 7 X 020 140 shown figure 3 As can seen C really percent age displacement float bears its carton makes cozier relationship wish reconcile parameters fully correlation between C K2 shown Fig 4 Now lets proceed design float First must find beam whch turn requires value displacement W watch weight think can put pair floats Nosen Citabria already weighs 18 lbs about 32 lbs Thus gross weight will 25 lbs LENGTH/BEAM RATIO vs Cj 8-7 b 6bf LCi b 144 160 126140154HEAVY OUR FLOAT 101121314 dispi float W dispi artonwLb2 I0 L b 15161718 Fig 3 K2 COMPARED WITH 0 OUR FLOAT 0 . LIGHT SPRAY K2018 7 MODERATE 020 6 HEAVY 022 EXCESSIVE 025 5 2 Fig 4 34 5 68 CW 125 April 1979 13 20 Dornier X 12-engined flying boat built 1929 photo has radial engines arranged tandem pairs After transatlantic crossing turned turtle tropical storm CONVENTIONAL FLOAT t217 Al curve ares r2 7b 77 20 2022 / / 2 25 225 -2 10304222 IS oisoc. 926 [2 DeejI F24Ih0 02p2[ 942 W05N9044IIb25jyf 4404 h224&Ih1l 410 2STSP/C0NTROOISO40 t f J 0 10 42240 V Fig 5 float will carry 125 lbs So W equals 125 lbs C2 said 140 W C2 2 expression two unknowns b L So will have express L terms b making WW wLbbzw7b3 andbeamb3 W — w7 C 125 64 X 7 X 140 584 ft or7in Since length/beam ratio seven length 7 Now lets check results another way said C percentage displacement float carton 14 percent carton has displacement 7 X 7 X 4 8893 lbs 1728 14 percent 8893 1245 lbs close enough point might wise reassess things consider other values planning build model 3-lb camera may added later going fly fresh water lake having water density 624 lb/cu ft might wiser pick value C2 126 shown Fig 3 rather 140 reduce draft lighten spray give some room grow particularly think powerplant marginal beam will become 725 length 5075 However will add around 10 percent weight float Now some discussion before tackle details Obviously float should aerodynamically clean can make So might say Ok lets make streamlined like wing tip fuel tank sounds good streamlined bodies completely immersed tend suck under speak takeoff impossible final analysis wing generates lift deflecting thus accelerating mass air downward float completely streamlined partially immersed actually deflects water upward thus sinking deeper deeper power applied speed remains essentially constant displacement vessels sailing yachts have less fixed maximum speed no matter much extra power wind available just sink deeper deeper like bottom teaspoon suspended against water flowing faucet other hand hull bottom vicinity step transom flat like water ski v-shaped like speed boat water departs step float rides up skims over water deriving lift much same way wing slighting deflecting water down ward gaining lift thereby derived form dynamic pressure hull bottom Actually forebody its transom step does work afterbody primarily provide static buoyancy rest aircraft doesnt rock back its tail Indeed Lou Proctors Antic has forward floats really forebodies coupled small efficient afterbody form small float tail Minimum air drag critical matter models faithful attention detail scale models requires easy lines generous step depth needed assure clean departure wake doesnt tend reattach afterbody cause porpoising plus generous landing angle will handle problem forebody lines should sharp easy keep hull resistance minimum large aircraft ample deadrise needed minimize decelerations landing Deadrise should 14 Model Aviation 226 find center buoyancy Trace curve areas onto cardboard balance three ways edge ruler marking line time Intersection centroid area figurecenter buoyancy float 4 j3-I RAZOR SHARP CHINES Fig 6 TRUE AREAS SQ INf337 316 EI$II LIII -__ IPORT VIEW LEFT FLOAT OUTBOARD CHINE 16 r -eTAogrIb, VINBARD CHINE 0 11 FLOAT PROBLEMS Construct curve areas find 1 Displacement pounds 2 Center Bouyancy LSO 3 Length/Beam Ratio disregarding rounded ends tapered sides 4 Length Beam displacements 1 lb 5 lbs 10 lbs increase go forward along forebody sharpen hull lines provide stability trim Adequate buoyancy afterbody easier attain deadrise held constant initial application power takeoff produces powerful nose-down moment seaplanes must countered adequate forebody displacement will tend resist moment quickly smoothly avoid forebody porpoising char acteristic low length/beam ratio hulls having insufficient restoring moment standpoint L/b 8 would better float would begin get too long landing angle would suffercompro mises again Landing Angle No2 corresponds similar angle landplane Its purpose allow step wheels make initial contact angle close 90 percent stalling angle wing permit slowest possible 912 1 2 REOD PORT AND STARBOARD 17 16 15 114 13 12 1 II II 7k 8 14518 5 18 3 gPORT FLOAT SHOWN -. FLOAT OPPOSITE II 212426 Ti OHLSSON FLOAT 1213 WEIGHT W/ FLOAT. LBS landing speed Since impact forces vary square speed small reductions speed accompanied sizeable increases safety float landing angle 14 15 Fig 7 9 degrees coupled 3 degrees wing incidence 12 degrees Clark Y airfoil small Reynolds Numbers corresponds guidelines just mentioned 1 2 3 4 ANSWERS TO FLOAT PROBLEMS Fig 8 Displacement 298 say 3 lbs CB Station 134 just forward Step 1/B 26/4 equals 65 Dimensions vary cube root Ratio Displacements So 1 lb dimensions will Ohlsson float timesthe cube root 1/3 693 So equals 693 x 26 18 end B 593 x 4 277 Similarly 5 lbs 307 B 472 10 lbs L 3875 B 595 say 6 Note Since float different family conventional float geomet rically related values CW Ci would comparable VOLUME 4 CtiINV2SOLU OF OUYANC April1979 15 FLOAT TOO SMALL LOAT FLOAT TOO LARGE static trim CG complete airplane must obviously lie perpendic ular waterplane passes through Center Buoyancy float indicated Item 29 Fig 5 Item 2 Fig 5 shows landing angle mentioned above As can seen step centroidof V-step Item 22 Fig 5 should slightly aft Center Buoyancy place directly under CG landing 30 order keep float axis parallel fuselage usually desirable flight angle static trim Item 13 Fig 5 3 degrees producing slightly nose up attitude airplane static rest water undesirable have axis airplane parallel waterplane would mean placing floats slightly nose up else reducing forebody displacementneither good Flare No 12 directs spray helps control its effects Judicious use spray dams blinders metal strips flush sides float projecting about half inch below chine can reduce spray dramatically carried too far forward made too large can destabilizing flight probably best experiment little bit Because forward portions floats destabilizing flight necessary add substantial increment fin area compensate shown No 24 Since floats will also produce negative diving moment elevator trim order preferably some means adjusting horizontal stabilizer toe-in recommended procedure installing wheels landplane no-no floats very necessary mounted firmly accurately Water forces high unforgiving afterbody float tapers back flat transom large enough accomodate water rudder mounting brackets outlets internal pushrods water rudder should placed float its pivot line should 2530% its chord Its area critical make about size proportion shown respect size float So much generalities Now lets put Fig 5 front us study steps involved creating particular float Lay out 7 X 49 carton side view 3 X 49 half plan below 7 X 7 box left Note height float equals beam mainly simplify geometry article height could increased say used basis single hull design ever should decreased excess buoyancy very necessary Theoretically could slice float off just above waterline did extra ounce fuel added servo could sink whole kaboodle Draw center line 3 Draw upper deck lines shown forebody duplicate below plan view forebody shown above chine elliptical prolate spheroid anybody interested doesnt have Make shape matches picture favorite seaplane wish Locate Step 1 As first approxi mation lets assume Sta 26 26 aft nose Later might want change bit Lets hope Draw landing angle 2 heel step up center line Sta 49 Make step depth 8 afterbody keel 7 Draw forebody keel 6 Note carries well forward does match curve deck line top sharpen entry side view left draw circular cross sections upper forebody deck down center line drop vertical tangents circular cross section meets center line tangents Sta 6 forward should extend above 16 Model Aviation Mercury Racer Granger WIlliams repose La Costa CA sloughlntended Schneider Trophy race flown Al Williams real Mercury grossly overweight Brad Powers left Irwin Ohlsson latters highly successful twinfloat design using floats own design championship free-flighter Thirties later manufacturer engines exAMA president Hall Famer Irwin builds designs best center line Starting step Sta 26 draw deadrise angle 4 20 degrees Its inter section vertical tangent just drew determines aft point theoret ical chine 9 Draw theoretical chine 9 establishes smooth variation deadrise go forward Back step section again draw chine flare 12 Its intersection vertical tangent establishes aft end forebody chine 10 Draw forebody chine 10 shown Near Station 6 curve reverses lie fore aft direction make clean aerodynamic entry Assuming theoret ical chine lie curved surface touching side hull therefore intersecting vertical tangents drew draw deadrise Station add flare tangent deadrise horizontal chine flare should have generous radiusbut excessive Now draw afterbody deadrise Station other side end view plan view drew beginning establish afterbody chine both end side views 11 Using afterbody planform deter radii draw locus radii 18 side view complete sections afterbody end view point good idea draw some 'buttock lines' 'water lines' end view shown project other views see fair fair smooth fiddle drawing bit until 23 region between Sta 18 step bottom should have straight buttock lines insure stable planning other words hull bottom surfaces should have no fore aft curvature region Draw trial static load water line sloping up aft 3 degrees through point 3 above keel step 14 information end view water line construct sections shown hatched station Measure sections determine area section Since half sections dont forget multiply area 2 plot values shown 26 establish acurve areas Just volume deck cards sum cards area under curve summation infinite number cross sectional areas therefore represents volume immersed portion float Since before reproduction maga zine drawing made half scale areas have indicated obtained half scale drawing will have corrected full scale will shortly true well length curve areas drawn 1/5 scale expression shape curve areas could add up integrate mathematically since arbitrarily determined its slope choices deadrise flare chine chape etc no way establish slope area curve mathematically must integrate graphically can done close approximation adding areas successive steps 27 judiciously done better way use device called polar planimeter have done gives area under curve 169 sq just pointed out areas taken one-half scale drawing therefore have fourth full-size areas because areas varies scale squared Also said length figure one-fifth actual float must multiply 169 5 times 4 20 have correct figure since value volume cu must divide number cu in cu ft get cu ft can multiply 64 weight cu ft sea water we see float indeed displaces 1252 lbs indicated Fig 5 about draft 3 good guesstimate As shown Fig 7 float should loaded carry much over 13 pounds spray will get too heavy other hand float carry much less 11 pounds will too big heavy smaller float should used Well now know draft displacement what Before can screw floats onto airplane have know buoyancy concentrated way find Center Buoyancy trace curve areas onto piece cardboard no lumps cut out balance shown picture Balance least three ways mark time have careful marks will intersect point centroid area figure Center Buoyancy float 21 Incidentally good way find centroids such things elliptical wings centers lateral area other irregular shapes Now can relate float Nosen Citabria 19 above described earlier shown Fig 5 good stability control CG 20 should 25% mean aerody namic chord MAC wing Since Citabria has rectangular planform amounts 25 percent root chord indicated 17 Fortunately Center Buoyancy falls just want landing angle right step fortuitous because have struggling days get together Actually little both aerodynamically unfortunate carrying large appendages like floats way out arms length speak clearances shown 6 at31 learance 20-in propeller float spacing 3 beams 21 33 should reduced keep airplane its vitals being inun dated choppy water spray covers general way preliminary design float great other aspects covering water resistance trimming moments etc have left untouched felt really essential modeler putting floats pride joy intention article es tablish basic criteria Prelimi nary Design future article will presented Detail Design Continued page 98 April1979 17 Line-up RC seaplane models Lto R Bob Wisniewakis modIfied Lancer single pontoon wing-tip floats Granger Williams sport model similar configuration Granger Williams Mercury twin floats Gary Neelys modified sport biplane twin floats Main floats models same Mercury design molded foam plastic Openers/Winter continued page 72 have something tell As RCer FOs chief interest CL Racing frantic aerobatics pilots center circle will find Bill Lee CL Racing talking about home-made fibreglass props Bill Wynn Paul too guy endlessly seeks truth about tanks things like props doing experimenting finding para meters Dave Chesney writes beautifully RC Helicopters column existence now Bill Warner Sport/Scale will put humor life flying circus note others gang Without guys like us would never know about hundreds things add up sum total skills Brad Powers lead article floats quarter-scale landmark article Model aviation old century yet explosion knowledge techniques products never dared dream about what know about floats would fit smallest drawer field box So designer partook dozens famous pro jects made history modeler boot telling us design float virtually size modelas well monsters weve yet see water Note feed-inIrwin Ohlsson great Ernie Stout Convair fame What suggesting dear friend April issue however excep tional 12 year talking about magazine Within another yearGod willingit will thousand light years beyond April 1976 MA began July 1975 its modern form ask conscious magazine contro versial terms some other magazines have shown theyd like see deadbut inspect closely what speak especially minority members did subscribe MA past yours wed like proud AS WE GO TO PRESS sad news ar rives passing Myron Mike Schlesinger recent past president Top Flite Models Mike respected friend industry innumerable modelers true pioneer helped start Top Flite its way chaired trade show committee 1956 became member HIAAs board directors served nearly 10 years chairman co-chairman HIAAs Model Aeronautics Division Hu morous easy going always compassion ate understanding Mike Schlesinger will truly missed us Floats Powers continued page 17 actual floats installed Citabria model together summary results some photos Irwin Ohlsson thirties deve loped line famous Ohlsson engines now retired builds beautiful model seaplanes has given pair floats developed has found very satisfactory straightforward design have generous step landing angle embody progressive deadrise Rather present float complete its displacement Center Buoyancy etc ready determined will give its dimensions trim another guesstimate draft 16 40 percent its beam data procedures already discussed up find answers problems Fig 6 shows float answers will found illustration Answers Float Prob lems Finally wish express thanks Ernest G Stout former Chief Hydrody namics Convair worked interesting projects sistance providing data presented herein Now am going start building float build finish before write let know works can de cide whether stay leave Tierra Del Fuego RC Technique/Myers continued page 19 control thats going wrong way move pushrod hole opposite side output wheel frequently make such change field someone needs disadvantage approach pushrods usually get tangled you end up product review product review product review Radial Engines man has thingultra deluxe 57-cylinder scale-like engines /4 scale 4-cycle high-torque swing 16-8 through 20-6 props Low vibra tion low fuel consumption mild glow fuel 6-in diameter 23 oz weight 7cylinder engines offered 3 versionspol ished aluminum anodized black deluxe Collectors Gold Edition package trimmed 14K gold Manufacturer states fully opera tional warranted 90 dayssold direct Executive Engines Co 16650 S 104th Ave Orland Park IL 60462 product review product review product review swapping rudder elevator servos side-by-side using Nyrod often finds surgery neces sary because outer shell has anchored location doesnt allow shift connection other side wheel Wouldnt nice could just throw reversing switch servo point Bobs eyes lit up Ill bet Ace R/C Bantam Midget machinery will fit regular Bantam case says leave enough room servo reverser dont see what can idea George kicked around some possibilities until time get back work few days later Bantam case Bantam Midget servo appeared desk magic Christmas came bit early year thought until Bob told wanted back after youve finished rever sing switch first thought make use 16pin DIP switch After little consideration possibilities left open direct short across batteries dropped idea Besides switch too big Next tried 4PDT Noble switch commonly used switch harnesses RC systems can made fit little help Dremel problem will have take out servo get switch smaller switch could mounted right out open can get couldnt find Slightly later Bob left another goodie desk prototype servo reverser ACE R/C few mods could fit space available would left servo having two pigtails rotation Plug need configuration left project returned servo Bob must careful let unused plug short out metal parts because will short out batteries kill whole system As said before like idea having servo reverser receiver todays IC circuitry major configuration change would adding second set sockets other rotation Its fair mention Kraft has shipping sets 10 years have two servos set up direction Editors NoteLike feature Cox-Sanwa get what want swapping around dot no dot servos dot tiny circle molded mounting flange between cutouts grommets Once get flight pack set up right theres no way make mistake Thats way like things Over years have bought flight packs transmitters work plane until control trims throws right transmitter trim levers center position leave everything alone until needs service way can pick plane off wall go flying worrying its compatible 98 Model Aviation
Edition: Model Aviation - 1979/04
Page Numbers: 10, 11, 12, 13, 14, 15, 16, 17, 98
FOR variety reasons early speculation about future aviation painted rosy picture seaplanes During interval between two world wars seaplanes set speed records crossed oceans offered great promise future Since through out world almost city size situated near important body water feeling build expensive space consuming airports 1929 Claude Dornier building remarkable seaplane shown pic ture american industrial designer Nor man Bel Geddes busy collaboration Dr Otto Koller designer Ger man Pfalz biplane Together worked up design enormous flying boat wing span 528 feet deck below water line eight decks above have 20 1 900-hp engines includ ing engine repair shop root wing 22 feet thick gross weight 1275000 pounds would believe behemoth designed cruise fantastic speed 100 mph 5000 feet some reason never built Now discredit man Larry Williams taxies Supermarine S4 waters Lake Elsinora CA prior contest-winning flight powered K&8 front-rotor engine Warren Shipp photo Norman Bel Geddes true genius ideas kitchen ranges elevated freeways have become reality simply show fast actual progress can overtake wildest dreams gifted advent all-metal stressed skin monoplanes retractable gear landplanes suddenly stopped looking like Jennies began look today Seaplane designers other hand could never figure out way retract floats within sensible weight allowance density seawater just wasnt great enough floats hulls always too big invariably added up drag just simple landplane fuselage Since drag means fuel increased fuel meant corresponding reductions range pay load translated reductions reve nues wasnt until jet engine came along eliminating large clearances re quired propellers designers able create seaplanes such Skate shown model photo could compete drag-wise landplane time airports finally built Iandplanes stolen show 10 Model Aviation Larrys Supermarine overhead later lowwing Supermarines among beautiful ali aircraft laid groundwork Spit fire designed RJ Mitchell Shipp photo Other factors also determined de mise seaplane Rough seas landing areas werent always calm areas congested unsafe handling mooring maintenance difficulties say nothing severe corrosive effects sea water aluminum alloy hulls Numerous approaches problem operating aircraft water have made include variety floats varying shapes skis hydrofoils large hulls literally stabilized tip floats spon sons blended configuration Skate shown photo exception last item possibly hydrofoils think modelers have man aged adapt others models varying degrees success ducted fan makes both hydrofoils blended hull-wing attractive possibilities since out propeller clearances deal inter esting ideas suggest themselves will leave notions another time devote article understanding principles underlying simple scale type floats appropriate scale model will try use procedures learned evaluate excellent model type float given Irwin Ohlsson might think float piece functional sculpture must perform following 1 Provide adequate buoyancy rest 2 Provide minimum resistance motion through water during progressive stages takeoff 3 Provide smooth stable variations trim during takeoff landing since pilot has little no control over trim attitude low speeds water 4 Provide stable reasonably soft landing entry course minimum weight air drag well have ridden water skis aboard speedboat power cruiser familiar changing attitudes craft starts move nose begins rise untilif sufficient power available will gain enough speed level off plane An airplane floats does same thing As moves forward pushes sizeable volume water ahead itself creating large wave hump over OHLSSONS WIDGEON DURING preparation Mr Powers article both Brad editor con sulted Irwin Ohisson retired engine manufacturer AMA Hall Famer has considerable success floats hulls radio control Shown Irwins Grumman Widgeon data supplied Ohlsson Fol lowing Irwins comments hull table specifications configuration first step changed double concave also two sponsons added sides hull bow first step Small spray rails extend outboard length sponsons tunnel de sign gives smooth low power takeoff sponsons spray rails deflect water props original full-scale aircraft 2% degree positive wing incidence reduced 0 degrees model After first flightwith Joe Bridi test pilotit came off water before reached its flying speed stalled nose wing down landplane would have bought farm However bounced out water like basketballnot scratch Since day April 1974 about 50 flights have madenever has wet real good stable fast flying machine Specifications Twin-Engine Widgeon Span 80 chord center section 13% tip 8 hull overall 54 Weight empty 13 lbs weight fueled 15 lbs Power2 contra-rotation 61 Perry pumpsfuel 500cc nacelleprops 11 x 7Y2 left right handthrottles 2one nacelle Controls Flaps Aileron Rudder Elevator Construction Wing2 main spars balsa ribs 2 apart sheet balsa silk covered butyrate doped plywood engine mounts rear spar Hullspruce keel balsa sheeted bottom 3/32 balsa 1/32 x 3 plywood glassed top sides silk covered butyrate dope April1979 11 Noting jet engineno prop clearance problemsmade possible blended hull Powers cites Skate shown moaei tesi tow RACING AIRPLANE AVERAGE___ AIRPLANE LIGHTPLANE Lu 0 0 IL L - 7approx / S 1/ EXCESS THRUSTAVAILABLE FOR TAKE-OFF THRUST 2 L RESISTANCE HUMP 18 10 TAKE-OFF SPEED must literally climb order level off plane gather takeoff speed hump region operation critical regard power indicated Fig 1 Obviously airplane accelerate take off thrust must greater resistance Otherwise will just cruise around water until fuel gone Fig 1 racing airplane has very high water resistance presumably due small floats achieve low air drag since Fig 1 high speed design has sufficient thrust cope resistance As apparent thrust available average airplane used racer takeoff speed would impossible since airplane could never ride over hump Since model engines available appear adequate cases should justified applying average~ rather marginal criteria designing float As aspects airplane design VOLUME Lb2 VOL b b VOLL2b compromises between conflicting require ments generally being sought case hulls floats boils down finding nice balance betweeen size displacement Large floats have advan tage low immersion light spray weigh have higher air drag Small floats sink too deeply water makes heavy spray high water resistance So can say except refinements design actual float itself basic problem find proper size job keeping both float size spray minimum commensu rate power orother limiting factors Early float designers found after much experimentation floats having length beam ratios less about 6/1 didnt work very well seven seemed best average conditions acceptable per formance water achieved draft early floats such displacement value approx imating cubical container filled water having same dimensions side beam float Thus float beam 3 ft could expected perform satisfactorily displaced amount water could placed cubical container 3 ft side Such float would displace 33 27 cu ft sea water Since sea water has density 64 lb/cu ft weight water 1728 lbs pair such floats would right average airplane weighing about 3450 lbs As pointed out Fig 1 could vary considerably non average conditions Once relationship estab lished easy matter scale floats up down suit different gross weights long same family reasonably close being geome trically similar relationship came called beam loading expressed non-dimensional terms W 3andhadavalueoflOwhen wb length/beam ratio seven W equals Load Carried Floatlbs w equals Density Sea Water 4 lbs/cu ft b equals Beam FloatFeet criterion expressed graphically Fig2 Although shown simple cube Fig 2 applies L/b ratio seven L/b 6 value C of75 worked best since L/b decreased Beam increased same token increases L/b accompanied decreases beam requiring corresponding increases values C During WW II studies made configurations floats particularly hulls involving length/beam ratios order 8 10 higher 12 Model Aviation b.Kbb COMPARING CRITERIA found longer hulls less air drag less water resistance less way nasty characteristics like hobby horsing~ porp oising pitching back forth under way selecting length/beam ratio float strong consideration given value 8 finally ruled out due excessive length fact typical scale applications early seaplanes However after have finished article should able design float having high L/b wish float described will have value L/b investigation progressed became apparent immersion coefficient would useful contained provision beam length well Accordingly new term developed engineers called K2 w equal w L2 b Like C K2 nondimensional does indeed account length well beam Recom mended values K2 range 018 light spray low power 022 heavy spray high power 020 representing good criterion average~ conditions float therefore will based indirectly value 020 However look Fig 2 see volume portion term L2b resolves itself large cakepan 2 percent full bears little physical resemblance float So based K2 tried true parameter lets devise term just purpose multiply K2 length/beam ratio increase amount also get cakepan carton has same overall dimensions float follows K2so X K2 wL2bb Lx W — W c bwL2bwLb2 C1 ficient Immersion Lb2 gives us figure fits float like shoe box carton shown figure top Fig 2 So term C1 derived K2 constant like K2 varies length/beam ratio said float has value 7 X K2 7 X 020 140 shown figure 3 As can seen C really percent age displacement float bears its carton makes cozier relationship wish reconcile parameters fully correlation between C K2 shown Fig 4 Now lets proceed design float First must find beam whch turn requires value displacement W watch weight think can put pair floats Nosen Citabria already weighs 18 lbs about 32 lbs Thus gross weight will 25 lbs LENGTH/BEAM RATIO vs Cj 8-7 b 6bf LCi b 144 160 126140154HEAVY OUR FLOAT 101121314 dispi float W dispi artonwLb2 I0 L b 15161718 Fig 3 K2 COMPARED WITH 0 OUR FLOAT 0 . LIGHT SPRAY K2018 7 MODERATE 020 6 HEAVY 022 EXCESSIVE 025 5 2 Fig 4 34 5 68 CW 125 April 1979 13 20 Dornier X 12-engined flying boat built 1929 photo has radial engines arranged tandem pairs After transatlantic crossing turned turtle tropical storm CONVENTIONAL FLOAT t217 Al curve ares r2 7b 77 20 2022 / / 2 25 225 -2 10304222 IS oisoc. 926 [2 DeejI F24Ih0 02p2[ 942 W05N9044IIb25jyf 4404 h224&Ih1l 410 2STSP/C0NTROOISO40 t f J 0 10 42240 V Fig 5 float will carry 125 lbs So W equals 125 lbs C2 said 140 W C2 2 expression two unknowns b L So will have express L terms b making WW wLbbzw7b3 andbeamb3 W — w7 C 125 64 X 7 X 140 584 ft or7in Since length/beam ratio seven length 7 Now lets check results another way said C percentage displacement float carton 14 percent carton has displacement 7 X 7 X 4 8893 lbs 1728 14 percent 8893 1245 lbs close enough point might wise reassess things consider other values planning build model 3-lb camera may added later going fly fresh water lake having water density 624 lb/cu ft might wiser pick value C2 126 shown Fig 3 rather 140 reduce draft lighten spray give some room grow particularly think powerplant marginal beam will become 725 length 5075 However will add around 10 percent weight float Now some discussion before tackle details Obviously float should aerodynamically clean can make So might say Ok lets make streamlined like wing tip fuel tank sounds good streamlined bodies completely immersed tend suck under speak takeoff impossible final analysis wing generates lift deflecting thus accelerating mass air downward float completely streamlined partially immersed actually deflects water upward thus sinking deeper deeper power applied speed remains essentially constant displacement vessels sailing yachts have less fixed maximum speed no matter much extra power wind available just sink deeper deeper like bottom teaspoon suspended against water flowing faucet other hand hull bottom vicinity step transom flat like water ski v-shaped like speed boat water departs step float rides up skims over water deriving lift much same way wing slighting deflecting water down ward gaining lift thereby derived form dynamic pressure hull bottom Actually forebody its transom step does work afterbody primarily provide static buoyancy rest aircraft doesnt rock back its tail Indeed Lou Proctors Antic has forward floats really forebodies coupled small efficient afterbody form small float tail Minimum air drag critical matter models faithful attention detail scale models requires easy lines generous step depth needed assure clean departure wake doesnt tend reattach afterbody cause porpoising plus generous landing angle will handle problem forebody lines should sharp easy keep hull resistance minimum large aircraft ample deadrise needed minimize decelerations landing Deadrise should 14 Model Aviation 226 find center buoyancy Trace curve areas onto cardboard balance three ways edge ruler marking line time Intersection centroid area figurecenter buoyancy float 4 j3-I RAZOR SHARP CHINES Fig 6 TRUE AREAS SQ INf337 316 EI$II LIII -__ IPORT VIEW LEFT FLOAT OUTBOARD CHINE 16 r -eTAogrIb, VINBARD CHINE 0 11 FLOAT PROBLEMS Construct curve areas find 1 Displacement pounds 2 Center Bouyancy LSO 3 Length/Beam Ratio disregarding rounded ends tapered sides 4 Length Beam displacements 1 lb 5 lbs 10 lbs increase go forward along forebody sharpen hull lines provide stability trim Adequate buoyancy afterbody easier attain deadrise held constant initial application power takeoff produces powerful nose-down moment seaplanes must countered adequate forebody displacement will tend resist moment quickly smoothly avoid forebody porpoising char acteristic low length/beam ratio hulls having insufficient restoring moment standpoint L/b 8 would better float would begin get too long landing angle would suffercompro mises again Landing Angle No2 corresponds similar angle landplane Its purpose allow step wheels make initial contact angle close 90 percent stalling angle wing permit slowest possible 912 1 2 REOD PORT AND STARBOARD 17 16 15 114 13 12 1 II II 7k 8 14518 5 18 3 gPORT FLOAT SHOWN -. FLOAT OPPOSITE II 212426 Ti OHLSSON FLOAT 1213 WEIGHT W/ FLOAT. LBS landing speed Since impact forces vary square speed small reductions speed accompanied sizeable increases safety float landing angle 14 15 Fig 7 9 degrees coupled 3 degrees wing incidence 12 degrees Clark Y airfoil small Reynolds Numbers corresponds guidelines just mentioned 1 2 3 4 ANSWERS TO FLOAT PROBLEMS Fig 8 Displacement 298 say 3 lbs CB Station 134 just forward Step 1/B 26/4 equals 65 Dimensions vary cube root Ratio Displacements So 1 lb dimensions will Ohlsson float timesthe cube root 1/3 693 So equals 693 x 26 18 end B 593 x 4 277 Similarly 5 lbs 307 B 472 10 lbs L 3875 B 595 say 6 Note Since float different family conventional float geomet rically related values CW Ci would comparable VOLUME 4 CtiINV2SOLU OF OUYANC April1979 15 FLOAT TOO SMALL LOAT FLOAT TOO LARGE static trim CG complete airplane must obviously lie perpendic ular waterplane passes through Center Buoyancy float indicated Item 29 Fig 5 Item 2 Fig 5 shows landing angle mentioned above As can seen step centroidof V-step Item 22 Fig 5 should slightly aft Center Buoyancy place directly under CG landing 30 order keep float axis parallel fuselage usually desirable flight angle static trim Item 13 Fig 5 3 degrees producing slightly nose up attitude airplane static rest water undesirable have axis airplane parallel waterplane would mean placing floats slightly nose up else reducing forebody displacementneither good Flare No 12 directs spray helps control its effects Judicious use spray dams blinders metal strips flush sides float projecting about half inch below chine can reduce spray dramatically carried too far forward made too large can destabilizing flight probably best experiment little bit Because forward portions floats destabilizing flight necessary add substantial increment fin area compensate shown No 24 Since floats will also produce negative diving moment elevator trim order preferably some means adjusting horizontal stabilizer toe-in recommended procedure installing wheels landplane no-no floats very necessary mounted firmly accurately Water forces high unforgiving afterbody float tapers back flat transom large enough accomodate water rudder mounting brackets outlets internal pushrods water rudder should placed float its pivot line should 2530% its chord Its area critical make about size proportion shown respect size float So much generalities Now lets put Fig 5 front us study steps involved creating particular float Lay out 7 X 49 carton side view 3 X 49 half plan below 7 X 7 box left Note height float equals beam mainly simplify geometry article height could increased say used basis single hull design ever should decreased excess buoyancy very necessary Theoretically could slice float off just above waterline did extra ounce fuel added servo could sink whole kaboodle Draw center line 3 Draw upper deck lines shown forebody duplicate below plan view forebody shown above chine elliptical prolate spheroid anybody interested doesnt have Make shape matches picture favorite seaplane wish Locate Step 1 As first approxi mation lets assume Sta 26 26 aft nose Later might want change bit Lets hope Draw landing angle 2 heel step up center line Sta 49 Make step depth 8 afterbody keel 7 Draw forebody keel 6 Note carries well forward does match curve deck line top sharpen entry side view left draw circular cross sections upper forebody deck down center line drop vertical tangents circular cross section meets center line tangents Sta 6 forward should extend above 16 Model Aviation Mercury Racer Granger WIlliams repose La Costa CA sloughlntended Schneider Trophy race flown Al Williams real Mercury grossly overweight Brad Powers left Irwin Ohlsson latters highly successful twinfloat design using floats own design championship free-flighter Thirties later manufacturer engines exAMA president Hall Famer Irwin builds designs best center line Starting step Sta 26 draw deadrise angle 4 20 degrees Its inter section vertical tangent just drew determines aft point theoret ical chine 9 Draw theoretical chine 9 establishes smooth variation deadrise go forward Back step section again draw chine flare 12 Its intersection vertical tangent establishes aft end forebody chine 10 Draw forebody chine 10 shown Near Station 6 curve reverses lie fore aft direction make clean aerodynamic entry Assuming theoret ical chine lie curved surface touching side hull therefore intersecting vertical tangents drew draw deadrise Station add flare tangent deadrise horizontal chine flare should have generous radiusbut excessive Now draw afterbody deadrise Station other side end view plan view drew beginning establish afterbody chine both end side views 11 Using afterbody planform deter radii draw locus radii 18 side view complete sections afterbody end view point good idea draw some 'buttock lines' 'water lines' end view shown project other views see fair fair smooth fiddle drawing bit until 23 region between Sta 18 step bottom should have straight buttock lines insure stable planning other words hull bottom surfaces should have no fore aft curvature region Draw trial static load water line sloping up aft 3 degrees through point 3 above keel step 14 information end view water line construct sections shown hatched station Measure sections determine area section Since half sections dont forget multiply area 2 plot values shown 26 establish acurve areas Just volume deck cards sum cards area under curve summation infinite number cross sectional areas therefore represents volume immersed portion float Since before reproduction maga zine drawing made half scale areas have indicated obtained half scale drawing will have corrected full scale will shortly true well length curve areas drawn 1/5 scale expression shape curve areas could add up integrate mathematically since arbitrarily determined its slope choices deadrise flare chine chape etc no way establish slope area curve mathematically must integrate graphically can done close approximation adding areas successive steps 27 judiciously done better way use device called polar planimeter have done gives area under curve 169 sq just pointed out areas taken one-half scale drawing therefore have fourth full-size areas because areas varies scale squared Also said length figure one-fifth actual float must multiply 169 5 times 4 20 have correct figure since value volume cu must divide number cu in cu ft get cu ft can multiply 64 weight cu ft sea water we see float indeed displaces 1252 lbs indicated Fig 5 about draft 3 good guesstimate As shown Fig 7 float should loaded carry much over 13 pounds spray will get too heavy other hand float carry much less 11 pounds will too big heavy smaller float should used Well now know draft displacement what Before can screw floats onto airplane have know buoyancy concentrated way find Center Buoyancy trace curve areas onto piece cardboard no lumps cut out balance shown picture Balance least three ways mark time have careful marks will intersect point centroid area figure Center Buoyancy float 21 Incidentally good way find centroids such things elliptical wings centers lateral area other irregular shapes Now can relate float Nosen Citabria 19 above described earlier shown Fig 5 good stability control CG 20 should 25% mean aerody namic chord MAC wing Since Citabria has rectangular planform amounts 25 percent root chord indicated 17 Fortunately Center Buoyancy falls just want landing angle right step fortuitous because have struggling days get together Actually little both aerodynamically unfortunate carrying large appendages like floats way out arms length speak clearances shown 6 at31 learance 20-in propeller float spacing 3 beams 21 33 should reduced keep airplane its vitals being inun dated choppy water spray covers general way preliminary design float great other aspects covering water resistance trimming moments etc have left untouched felt really essential modeler putting floats pride joy intention article es tablish basic criteria Prelimi nary Design future article will presented Detail Design Continued page 98 April1979 17 Line-up RC seaplane models Lto R Bob Wisniewakis modIfied Lancer single pontoon wing-tip floats Granger Williams sport model similar configuration Granger Williams Mercury twin floats Gary Neelys modified sport biplane twin floats Main floats models same Mercury design molded foam plastic Openers/Winter continued page 72 have something tell As RCer FOs chief interest CL Racing frantic aerobatics pilots center circle will find Bill Lee CL Racing talking about home-made fibreglass props Bill Wynn Paul too guy endlessly seeks truth about tanks things like props doing experimenting finding para meters Dave Chesney writes beautifully RC Helicopters column existence now Bill Warner Sport/Scale will put humor life flying circus note others gang Without guys like us would never know about hundreds things add up sum total skills Brad Powers lead article floats quarter-scale landmark article Model aviation old century yet explosion knowledge techniques products never dared dream about what know about floats would fit smallest drawer field box So designer partook dozens famous pro jects made history modeler boot telling us design float virtually size modelas well monsters weve yet see water Note feed-inIrwin Ohlsson great Ernie Stout Convair fame What suggesting dear friend April issue however excep tional 12 year talking about magazine Within another yearGod willingit will thousand light years beyond April 1976 MA began July 1975 its modern form ask conscious magazine contro versial terms some other magazines have shown theyd like see deadbut inspect closely what speak especially minority members did subscribe MA past yours wed like proud AS WE GO TO PRESS sad news ar rives passing Myron Mike Schlesinger recent past president Top Flite Models Mike respected friend industry innumerable modelers true pioneer helped start Top Flite its way chaired trade show committee 1956 became member HIAAs board directors served nearly 10 years chairman co-chairman HIAAs Model Aeronautics Division Hu morous easy going always compassion ate understanding Mike Schlesinger will truly missed us Floats Powers continued page 17 actual floats installed Citabria model together summary results some photos Irwin Ohlsson thirties deve loped line famous Ohlsson engines now retired builds beautiful model seaplanes has given pair floats developed has found very satisfactory straightforward design have generous step landing angle embody progressive deadrise Rather present float complete its displacement Center Buoyancy etc ready determined will give its dimensions trim another guesstimate draft 16 40 percent its beam data procedures already discussed up find answers problems Fig 6 shows float answers will found illustration Answers Float Prob lems Finally wish express thanks Ernest G Stout former Chief Hydrody namics Convair worked interesting projects sistance providing data presented herein Now am going start building float build finish before write let know works can de cide whether stay leave Tierra Del Fuego RC Technique/Myers continued page 19 control thats going wrong way move pushrod hole opposite side output wheel frequently make such change field someone needs disadvantage approach pushrods usually get tangled you end up product review product review product review Radial Engines man has thingultra deluxe 57-cylinder scale-like engines /4 scale 4-cycle high-torque swing 16-8 through 20-6 props Low vibra tion low fuel consumption mild glow fuel 6-in diameter 23 oz weight 7cylinder engines offered 3 versionspol ished aluminum anodized black deluxe Collectors Gold Edition package trimmed 14K gold Manufacturer states fully opera tional warranted 90 dayssold direct Executive Engines Co 16650 S 104th Ave Orland Park IL 60462 product review product review product review swapping rudder elevator servos side-by-side using Nyrod often finds surgery neces sary because outer shell has anchored location doesnt allow shift connection other side wheel Wouldnt nice could just throw reversing switch servo point Bobs eyes lit up Ill bet Ace R/C Bantam Midget machinery will fit regular Bantam case says leave enough room servo reverser dont see what can idea George kicked around some possibilities until time get back work few days later Bantam case Bantam Midget servo appeared desk magic Christmas came bit early year thought until Bob told wanted back after youve finished rever sing switch first thought make use 16pin DIP switch After little consideration possibilities left open direct short across batteries dropped idea Besides switch too big Next tried 4PDT Noble switch commonly used switch harnesses RC systems can made fit little help Dremel problem will have take out servo get switch smaller switch could mounted right out open can get couldnt find Slightly later Bob left another goodie desk prototype servo reverser ACE R/C few mods could fit space available would left servo having two pigtails rotation Plug need configuration left project returned servo Bob must careful let unused plug short out metal parts because will short out batteries kill whole system As said before like idea having servo reverser receiver todays IC circuitry major configuration change would adding second set sockets other rotation Its fair mention Kraft has shipping sets 10 years have two servos set up direction Editors NoteLike feature Cox-Sanwa get what want swapping around dot no dot servos dot tiny circle molded mounting flange between cutouts grommets Once get flight pack set up right theres no way make mistake Thats way like things Over years have bought flight packs transmitters work plane until control trims throws right transmitter trim levers center position leave everything alone until needs service way can pick plane off wall go flying worrying its compatible 98 Model Aviation
Edition: Model Aviation - 1979/04
Page Numbers: 10, 11, 12, 13, 14, 15, 16, 17, 98
FOR variety reasons early speculation about future aviation painted rosy picture seaplanes During interval between two world wars seaplanes set speed records crossed oceans offered great promise future Since through out world almost city size situated near important body water feeling build expensive space consuming airports 1929 Claude Dornier building remarkable seaplane shown pic ture american industrial designer Nor man Bel Geddes busy collaboration Dr Otto Koller designer Ger man Pfalz biplane Together worked up design enormous flying boat wing span 528 feet deck below water line eight decks above have 20 1 900-hp engines includ ing engine repair shop root wing 22 feet thick gross weight 1275000 pounds would believe behemoth designed cruise fantastic speed 100 mph 5000 feet some reason never built Now discredit man Larry Williams taxies Supermarine S4 waters Lake Elsinora CA prior contest-winning flight powered K&8 front-rotor engine Warren Shipp photo Norman Bel Geddes true genius ideas kitchen ranges elevated freeways have become reality simply show fast actual progress can overtake wildest dreams gifted advent all-metal stressed skin monoplanes retractable gear landplanes suddenly stopped looking like Jennies began look today Seaplane designers other hand could never figure out way retract floats within sensible weight allowance density seawater just wasnt great enough floats hulls always too big invariably added up drag just simple landplane fuselage Since drag means fuel increased fuel meant corresponding reductions range pay load translated reductions reve nues wasnt until jet engine came along eliminating large clearances re quired propellers designers able create seaplanes such Skate shown model photo could compete drag-wise landplane time airports finally built Iandplanes stolen show 10 Model Aviation Larrys Supermarine overhead later lowwing Supermarines among beautiful ali aircraft laid groundwork Spit fire designed RJ Mitchell Shipp photo Other factors also determined de mise seaplane Rough seas landing areas werent always calm areas congested unsafe handling mooring maintenance difficulties say nothing severe corrosive effects sea water aluminum alloy hulls Numerous approaches problem operating aircraft water have made include variety floats varying shapes skis hydrofoils large hulls literally stabilized tip floats spon sons blended configuration Skate shown photo exception last item possibly hydrofoils think modelers have man aged adapt others models varying degrees success ducted fan makes both hydrofoils blended hull-wing attractive possibilities since out propeller clearances deal inter esting ideas suggest themselves will leave notions another time devote article understanding principles underlying simple scale type floats appropriate scale model will try use procedures learned evaluate excellent model type float given Irwin Ohlsson might think float piece functional sculpture must perform following 1 Provide adequate buoyancy rest 2 Provide minimum resistance motion through water during progressive stages takeoff 3 Provide smooth stable variations trim during takeoff landing since pilot has little no control over trim attitude low speeds water 4 Provide stable reasonably soft landing entry course minimum weight air drag well have ridden water skis aboard speedboat power cruiser familiar changing attitudes craft starts move nose begins rise untilif sufficient power available will gain enough speed level off plane An airplane floats does same thing As moves forward pushes sizeable volume water ahead itself creating large wave hump over OHLSSONS WIDGEON DURING preparation Mr Powers article both Brad editor con sulted Irwin Ohisson retired engine manufacturer AMA Hall Famer has considerable success floats hulls radio control Shown Irwins Grumman Widgeon data supplied Ohlsson Fol lowing Irwins comments hull table specifications configuration first step changed double concave also two sponsons added sides hull bow first step Small spray rails extend outboard length sponsons tunnel de sign gives smooth low power takeoff sponsons spray rails deflect water props original full-scale aircraft 2% degree positive wing incidence reduced 0 degrees model After first flightwith Joe Bridi test pilotit came off water before reached its flying speed stalled nose wing down landplane would have bought farm However bounced out water like basketballnot scratch Since day April 1974 about 50 flights have madenever has wet real good stable fast flying machine Specifications Twin-Engine Widgeon Span 80 chord center section 13% tip 8 hull overall 54 Weight empty 13 lbs weight fueled 15 lbs Power2 contra-rotation 61 Perry pumpsfuel 500cc nacelleprops 11 x 7Y2 left right handthrottles 2one nacelle Controls Flaps Aileron Rudder Elevator Construction Wing2 main spars balsa ribs 2 apart sheet balsa silk covered butyrate doped plywood engine mounts rear spar Hullspruce keel balsa sheeted bottom 3/32 balsa 1/32 x 3 plywood glassed top sides silk covered butyrate dope April1979 11 Noting jet engineno prop clearance problemsmade possible blended hull Powers cites Skate shown moaei tesi tow RACING AIRPLANE AVERAGE___ AIRPLANE LIGHTPLANE Lu 0 0 IL L - 7approx / S 1/ EXCESS THRUSTAVAILABLE FOR TAKE-OFF THRUST 2 L RESISTANCE HUMP 18 10 TAKE-OFF SPEED must literally climb order level off plane gather takeoff speed hump region operation critical regard power indicated Fig 1 Obviously airplane accelerate take off thrust must greater resistance Otherwise will just cruise around water until fuel gone Fig 1 racing airplane has very high water resistance presumably due small floats achieve low air drag since Fig 1 high speed design has sufficient thrust cope resistance As apparent thrust available average airplane used racer takeoff speed would impossible since airplane could never ride over hump Since model engines available appear adequate cases should justified applying average~ rather marginal criteria designing float As aspects airplane design VOLUME Lb2 VOL b b VOLL2b compromises between conflicting require ments generally being sought case hulls floats boils down finding nice balance betweeen size displacement Large floats have advan tage low immersion light spray weigh have higher air drag Small floats sink too deeply water makes heavy spray high water resistance So can say except refinements design actual float itself basic problem find proper size job keeping both float size spray minimum commensu rate power orother limiting factors Early float designers found after much experimentation floats having length beam ratios less about 6/1 didnt work very well seven seemed best average conditions acceptable per formance water achieved draft early floats such displacement value approx imating cubical container filled water having same dimensions side beam float Thus float beam 3 ft could expected perform satisfactorily displaced amount water could placed cubical container 3 ft side Such float would displace 33 27 cu ft sea water Since sea water has density 64 lb/cu ft weight water 1728 lbs pair such floats would right average airplane weighing about 3450 lbs As pointed out Fig 1 could vary considerably non average conditions Once relationship estab lished easy matter scale floats up down suit different gross weights long same family reasonably close being geome trically similar relationship came called beam loading expressed non-dimensional terms W 3andhadavalueoflOwhen wb length/beam ratio seven W equals Load Carried Floatlbs w equals Density Sea Water 4 lbs/cu ft b equals Beam FloatFeet criterion expressed graphically Fig2 Although shown simple cube Fig 2 applies L/b ratio seven L/b 6 value C of75 worked best since L/b decreased Beam increased same token increases L/b accompanied decreases beam requiring corresponding increases values C During WW II studies made configurations floats particularly hulls involving length/beam ratios order 8 10 higher 12 Model Aviation b.Kbb COMPARING CRITERIA found longer hulls less air drag less water resistance less way nasty characteristics like hobby horsing~ porp oising pitching back forth under way selecting length/beam ratio float strong consideration given value 8 finally ruled out due excessive length fact typical scale applications early seaplanes However after have finished article should able design float having high L/b wish float described will have value L/b investigation progressed became apparent immersion coefficient would useful contained provision beam length well Accordingly new term developed engineers called K2 w equal w L2 b Like C K2 nondimensional does indeed account length well beam Recom mended values K2 range 018 light spray low power 022 heavy spray high power 020 representing good criterion average~ conditions float therefore will based indirectly value 020 However look Fig 2 see volume portion term L2b resolves itself large cakepan 2 percent full bears little physical resemblance float So based K2 tried true parameter lets devise term just purpose multiply K2 length/beam ratio increase amount also get cakepan carton has same overall dimensions float follows K2so X K2 wL2bb Lx W — W c bwL2bwLb2 C1 ficient Immersion Lb2 gives us figure fits float like shoe box carton shown figure top Fig 2 So term C1 derived K2 constant like K2 varies length/beam ratio said float has value 7 X K2 7 X 020 140 shown figure 3 As can seen C really percent age displacement float bears its carton makes cozier relationship wish reconcile parameters fully correlation between C K2 shown Fig 4 Now lets proceed design float First must find beam whch turn requires value displacement W watch weight think can put pair floats Nosen Citabria already weighs 18 lbs about 32 lbs Thus gross weight will 25 lbs LENGTH/BEAM RATIO vs Cj 8-7 b 6bf LCi b 144 160 126140154HEAVY OUR FLOAT 101121314 dispi float W dispi artonwLb2 I0 L b 15161718 Fig 3 K2 COMPARED WITH 0 OUR FLOAT 0 . LIGHT SPRAY K2018 7 MODERATE 020 6 HEAVY 022 EXCESSIVE 025 5 2 Fig 4 34 5 68 CW 125 April 1979 13 20 Dornier X 12-engined flying boat built 1929 photo has radial engines arranged tandem pairs After transatlantic crossing turned turtle tropical storm CONVENTIONAL FLOAT t217 Al curve ares r2 7b 77 20 2022 / / 2 25 225 -2 10304222 IS oisoc. 926 [2 DeejI F24Ih0 02p2[ 942 W05N9044IIb25jyf 4404 h224&Ih1l 410 2STSP/C0NTROOISO40 t f J 0 10 42240 V Fig 5 float will carry 125 lbs So W equals 125 lbs C2 said 140 W C2 2 expression two unknowns b L So will have express L terms b making WW wLbbzw7b3 andbeamb3 W — w7 C 125 64 X 7 X 140 584 ft or7in Since length/beam ratio seven length 7 Now lets check results another way said C percentage displacement float carton 14 percent carton has displacement 7 X 7 X 4 8893 lbs 1728 14 percent 8893 1245 lbs close enough point might wise reassess things consider other values planning build model 3-lb camera may added later going fly fresh water lake having water density 624 lb/cu ft might wiser pick value C2 126 shown Fig 3 rather 140 reduce draft lighten spray give some room grow particularly think powerplant marginal beam will become 725 length 5075 However will add around 10 percent weight float Now some discussion before tackle details Obviously float should aerodynamically clean can make So might say Ok lets make streamlined like wing tip fuel tank sounds good streamlined bodies completely immersed tend suck under speak takeoff impossible final analysis wing generates lift deflecting thus accelerating mass air downward float completely streamlined partially immersed actually deflects water upward thus sinking deeper deeper power applied speed remains essentially constant displacement vessels sailing yachts have less fixed maximum speed no matter much extra power wind available just sink deeper deeper like bottom teaspoon suspended against water flowing faucet other hand hull bottom vicinity step transom flat like water ski v-shaped like speed boat water departs step float rides up skims over water deriving lift much same way wing slighting deflecting water down ward gaining lift thereby derived form dynamic pressure hull bottom Actually forebody its transom step does work afterbody primarily provide static buoyancy rest aircraft doesnt rock back its tail Indeed Lou Proctors Antic has forward floats really forebodies coupled small efficient afterbody form small float tail Minimum air drag critical matter models faithful attention detail scale models requires easy lines generous step depth needed assure clean departure wake doesnt tend reattach afterbody cause porpoising plus generous landing angle will handle problem forebody lines should sharp easy keep hull resistance minimum large aircraft ample deadrise needed minimize decelerations landing Deadrise should 14 Model Aviation 226 find center buoyancy Trace curve areas onto cardboard balance three ways edge ruler marking line time Intersection centroid area figurecenter buoyancy float 4 j3-I RAZOR SHARP CHINES Fig 6 TRUE AREAS SQ INf337 316 EI$II LIII -__ IPORT VIEW LEFT FLOAT OUTBOARD CHINE 16 r -eTAogrIb, VINBARD CHINE 0 11 FLOAT PROBLEMS Construct curve areas find 1 Displacement pounds 2 Center Bouyancy LSO 3 Length/Beam Ratio disregarding rounded ends tapered sides 4 Length Beam displacements 1 lb 5 lbs 10 lbs increase go forward along forebody sharpen hull lines provide stability trim Adequate buoyancy afterbody easier attain deadrise held constant initial application power takeoff produces powerful nose-down moment seaplanes must countered adequate forebody displacement will tend resist moment quickly smoothly avoid forebody porpoising char acteristic low length/beam ratio hulls having insufficient restoring moment standpoint L/b 8 would better float would begin get too long landing angle would suffercompro mises again Landing Angle No2 corresponds similar angle landplane Its purpose allow step wheels make initial contact angle close 90 percent stalling angle wing permit slowest possible 912 1 2 REOD PORT AND STARBOARD 17 16 15 114 13 12 1 II II 7k 8 14518 5 18 3 gPORT FLOAT SHOWN -. FLOAT OPPOSITE II 212426 Ti OHLSSON FLOAT 1213 WEIGHT W/ FLOAT. LBS landing speed Since impact forces vary square speed small reductions speed accompanied sizeable increases safety float landing angle 14 15 Fig 7 9 degrees coupled 3 degrees wing incidence 12 degrees Clark Y airfoil small Reynolds Numbers corresponds guidelines just mentioned 1 2 3 4 ANSWERS TO FLOAT PROBLEMS Fig 8 Displacement 298 say 3 lbs CB Station 134 just forward Step 1/B 26/4 equals 65 Dimensions vary cube root Ratio Displacements So 1 lb dimensions will Ohlsson float timesthe cube root 1/3 693 So equals 693 x 26 18 end B 593 x 4 277 Similarly 5 lbs 307 B 472 10 lbs L 3875 B 595 say 6 Note Since float different family conventional float geomet rically related values CW Ci would comparable VOLUME 4 CtiINV2SOLU OF OUYANC April1979 15 FLOAT TOO SMALL LOAT FLOAT TOO LARGE static trim CG complete airplane must obviously lie perpendic ular waterplane passes through Center Buoyancy float indicated Item 29 Fig 5 Item 2 Fig 5 shows landing angle mentioned above As can seen step centroidof V-step Item 22 Fig 5 should slightly aft Center Buoyancy place directly under CG landing 30 order keep float axis parallel fuselage usually desirable flight angle static trim Item 13 Fig 5 3 degrees producing slightly nose up attitude airplane static rest water undesirable have axis airplane parallel waterplane would mean placing floats slightly nose up else reducing forebody displacementneither good Flare No 12 directs spray helps control its effects Judicious use spray dams blinders metal strips flush sides float projecting about half inch below chine can reduce spray dramatically carried too far forward made too large can destabilizing flight probably best experiment little bit Because forward portions floats destabilizing flight necessary add substantial increment fin area compensate shown No 24 Since floats will also produce negative diving moment elevator trim order preferably some means adjusting horizontal stabilizer toe-in recommended procedure installing wheels landplane no-no floats very necessary mounted firmly accurately Water forces high unforgiving afterbody float tapers back flat transom large enough accomodate water rudder mounting brackets outlets internal pushrods water rudder should placed float its pivot line should 2530% its chord Its area critical make about size proportion shown respect size float So much generalities Now lets put Fig 5 front us study steps involved creating particular float Lay out 7 X 49 carton side view 3 X 49 half plan below 7 X 7 box left Note height float equals beam mainly simplify geometry article height could increased say used basis single hull design ever should decreased excess buoyancy very necessary Theoretically could slice float off just above waterline did extra ounce fuel added servo could sink whole kaboodle Draw center line 3 Draw upper deck lines shown forebody duplicate below plan view forebody shown above chine elliptical prolate spheroid anybody interested doesnt have Make shape matches picture favorite seaplane wish Locate Step 1 As first approxi mation lets assume Sta 26 26 aft nose Later might want change bit Lets hope Draw landing angle 2 heel step up center line Sta 49 Make step depth 8 afterbody keel 7 Draw forebody keel 6 Note carries well forward does match curve deck line top sharpen entry side view left draw circular cross sections upper forebody deck down center line drop vertical tangents circular cross section meets center line tangents Sta 6 forward should extend above 16 Model Aviation Mercury Racer Granger WIlliams repose La Costa CA sloughlntended Schneider Trophy race flown Al Williams real Mercury grossly overweight Brad Powers left Irwin Ohlsson latters highly successful twinfloat design using floats own design championship free-flighter Thirties later manufacturer engines exAMA president Hall Famer Irwin builds designs best center line Starting step Sta 26 draw deadrise angle 4 20 degrees Its inter section vertical tangent just drew determines aft point theoret ical chine 9 Draw theoretical chine 9 establishes smooth variation deadrise go forward Back step section again draw chine flare 12 Its intersection vertical tangent establishes aft end forebody chine 10 Draw forebody chine 10 shown Near Station 6 curve reverses lie fore aft direction make clean aerodynamic entry Assuming theoret ical chine lie curved surface touching side hull therefore intersecting vertical tangents drew draw deadrise Station add flare tangent deadrise horizontal chine flare should have generous radiusbut excessive Now draw afterbody deadrise Station other side end view plan view drew beginning establish afterbody chine both end side views 11 Using afterbody planform deter radii draw locus radii 18 side view complete sections afterbody end view point good idea draw some 'buttock lines' 'water lines' end view shown project other views see fair fair smooth fiddle drawing bit until 23 region between Sta 18 step bottom should have straight buttock lines insure stable planning other words hull bottom surfaces should have no fore aft curvature region Draw trial static load water line sloping up aft 3 degrees through point 3 above keel step 14 information end view water line construct sections shown hatched station Measure sections determine area section Since half sections dont forget multiply area 2 plot values shown 26 establish acurve areas Just volume deck cards sum cards area under curve summation infinite number cross sectional areas therefore represents volume immersed portion float Since before reproduction maga zine drawing made half scale areas have indicated obtained half scale drawing will have corrected full scale will shortly true well length curve areas drawn 1/5 scale expression shape curve areas could add up integrate mathematically since arbitrarily determined its slope choices deadrise flare chine chape etc no way establish slope area curve mathematically must integrate graphically can done close approximation adding areas successive steps 27 judiciously done better way use device called polar planimeter have done gives area under curve 169 sq just pointed out areas taken one-half scale drawing therefore have fourth full-size areas because areas varies scale squared Also said length figure one-fifth actual float must multiply 169 5 times 4 20 have correct figure since value volume cu must divide number cu in cu ft get cu ft can multiply 64 weight cu ft sea water we see float indeed displaces 1252 lbs indicated Fig 5 about draft 3 good guesstimate As shown Fig 7 float should loaded carry much over 13 pounds spray will get too heavy other hand float carry much less 11 pounds will too big heavy smaller float should used Well now know draft displacement what Before can screw floats onto airplane have know buoyancy concentrated way find Center Buoyancy trace curve areas onto piece cardboard no lumps cut out balance shown picture Balance least three ways mark time have careful marks will intersect point centroid area figure Center Buoyancy float 21 Incidentally good way find centroids such things elliptical wings centers lateral area other irregular shapes Now can relate float Nosen Citabria 19 above described earlier shown Fig 5 good stability control CG 20 should 25% mean aerody namic chord MAC wing Since Citabria has rectangular planform amounts 25 percent root chord indicated 17 Fortunately Center Buoyancy falls just want landing angle right step fortuitous because have struggling days get together Actually little both aerodynamically unfortunate carrying large appendages like floats way out arms length speak clearances shown 6 at31 learance 20-in propeller float spacing 3 beams 21 33 should reduced keep airplane its vitals being inun dated choppy water spray covers general way preliminary design float great other aspects covering water resistance trimming moments etc have left untouched felt really essential modeler putting floats pride joy intention article es tablish basic criteria Prelimi nary Design future article will presented Detail Design Continued page 98 April1979 17 Line-up RC seaplane models Lto R Bob Wisniewakis modIfied Lancer single pontoon wing-tip floats Granger Williams sport model similar configuration Granger Williams Mercury twin floats Gary Neelys modified sport biplane twin floats Main floats models same Mercury design molded foam plastic Openers/Winter continued page 72 have something tell As RCer FOs chief interest CL Racing frantic aerobatics pilots center circle will find Bill Lee CL Racing talking about home-made fibreglass props Bill Wynn Paul too guy endlessly seeks truth about tanks things like props doing experimenting finding para meters Dave Chesney writes beautifully RC Helicopters column existence now Bill Warner Sport/Scale will put humor life flying circus note others gang Without guys like us would never know about hundreds things add up sum total skills Brad Powers lead article floats quarter-scale landmark article Model aviation old century yet explosion knowledge techniques products never dared dream about what know about floats would fit smallest drawer field box So designer partook dozens famous pro jects made history modeler boot telling us design float virtually size modelas well monsters weve yet see water Note feed-inIrwin Ohlsson great Ernie Stout Convair fame What suggesting dear friend April issue however excep tional 12 year talking about magazine Within another yearGod willingit will thousand light years beyond April 1976 MA began July 1975 its modern form ask conscious magazine contro versial terms some other magazines have shown theyd like see deadbut inspect closely what speak especially minority members did subscribe MA past yours wed like proud AS WE GO TO PRESS sad news ar rives passing Myron Mike Schlesinger recent past president Top Flite Models Mike respected friend industry innumerable modelers true pioneer helped start Top Flite its way chaired trade show committee 1956 became member HIAAs board directors served nearly 10 years chairman co-chairman HIAAs Model Aeronautics Division Hu morous easy going always compassion ate understanding Mike Schlesinger will truly missed us Floats Powers continued page 17 actual floats installed Citabria model together summary results some photos Irwin Ohlsson thirties deve loped line famous Ohlsson engines now retired builds beautiful model seaplanes has given pair floats developed has found very satisfactory straightforward design have generous step landing angle embody progressive deadrise Rather present float complete its displacement Center Buoyancy etc ready determined will give its dimensions trim another guesstimate draft 16 40 percent its beam data procedures already discussed up find answers problems Fig 6 shows float answers will found illustration Answers Float Prob lems Finally wish express thanks Ernest G Stout former Chief Hydrody namics Convair worked interesting projects sistance providing data presented herein Now am going start building float build finish before write let know works can de cide whether stay leave Tierra Del Fuego RC Technique/Myers continued page 19 control thats going wrong way move pushrod hole opposite side output wheel frequently make such change field someone needs disadvantage approach pushrods usually get tangled you end up product review product review product review Radial Engines man has thingultra deluxe 57-cylinder scale-like engines /4 scale 4-cycle high-torque swing 16-8 through 20-6 props Low vibra tion low fuel consumption mild glow fuel 6-in diameter 23 oz weight 7cylinder engines offered 3 versionspol ished aluminum anodized black deluxe Collectors Gold Edition package trimmed 14K gold Manufacturer states fully opera tional warranted 90 dayssold direct Executive Engines Co 16650 S 104th Ave Orland Park IL 60462 product review product review product review swapping rudder elevator servos side-by-side using Nyrod often finds surgery neces sary because outer shell has anchored location doesnt allow shift connection other side wheel Wouldnt nice could just throw reversing switch servo point Bobs eyes lit up Ill bet Ace R/C Bantam Midget machinery will fit regular Bantam case says leave enough room servo reverser dont see what can idea George kicked around some possibilities until time get back work few days later Bantam case Bantam Midget servo appeared desk magic Christmas came bit early year thought until Bob told wanted back after youve finished rever sing switch first thought make use 16pin DIP switch After little consideration possibilities left open direct short across batteries dropped idea Besides switch too big Next tried 4PDT Noble switch commonly used switch harnesses RC systems can made fit little help Dremel problem will have take out servo get switch smaller switch could mounted right out open can get couldnt find Slightly later Bob left another goodie desk prototype servo reverser ACE R/C few mods could fit space available would left servo having two pigtails rotation Plug need configuration left project returned servo Bob must careful let unused plug short out metal parts because will short out batteries kill whole system As said before like idea having servo reverser receiver todays IC circuitry major configuration change would adding second set sockets other rotation Its fair mention Kraft has shipping sets 10 years have two servos set up direction Editors NoteLike feature Cox-Sanwa get what want swapping around dot no dot servos dot tiny circle molded mounting flange between cutouts grommets Once get flight pack set up right theres no way make mistake Thats way like things Over years have bought flight packs transmitters work plane until control trims throws right transmitter trim levers center position leave everything alone until needs service way can pick plane off wall go flying worrying its compatible 98 Model Aviation
Edition: Model Aviation - 1979/04
Page Numbers: 10, 11, 12, 13, 14, 15, 16, 17, 98
FOR variety reasons early speculation about future aviation painted rosy picture seaplanes During interval between two world wars seaplanes set speed records crossed oceans offered great promise future Since through out world almost city size situated near important body water feeling build expensive space consuming airports 1929 Claude Dornier building remarkable seaplane shown pic ture american industrial designer Nor man Bel Geddes busy collaboration Dr Otto Koller designer Ger man Pfalz biplane Together worked up design enormous flying boat wing span 528 feet deck below water line eight decks above have 20 1 900-hp engines includ ing engine repair shop root wing 22 feet thick gross weight 1275000 pounds would believe behemoth designed cruise fantastic speed 100 mph 5000 feet some reason never built Now discredit man Larry Williams taxies Supermarine S4 waters Lake Elsinora CA prior contest-winning flight powered K&8 front-rotor engine Warren Shipp photo Norman Bel Geddes true genius ideas kitchen ranges elevated freeways have become reality simply show fast actual progress can overtake wildest dreams gifted advent all-metal stressed skin monoplanes retractable gear landplanes suddenly stopped looking like Jennies began look today Seaplane designers other hand could never figure out way retract floats within sensible weight allowance density seawater just wasnt great enough floats hulls always too big invariably added up drag just simple landplane fuselage Since drag means fuel increased fuel meant corresponding reductions range pay load translated reductions reve nues wasnt until jet engine came along eliminating large clearances re quired propellers designers able create seaplanes such Skate shown model photo could compete drag-wise landplane time airports finally built Iandplanes stolen show 10 Model Aviation Larrys Supermarine overhead later lowwing Supermarines among beautiful ali aircraft laid groundwork Spit fire designed RJ Mitchell Shipp photo Other factors also determined de mise seaplane Rough seas landing areas werent always calm areas congested unsafe handling mooring maintenance difficulties say nothing severe corrosive effects sea water aluminum alloy hulls Numerous approaches problem operating aircraft water have made include variety floats varying shapes skis hydrofoils large hulls literally stabilized tip floats spon sons blended configuration Skate shown photo exception last item possibly hydrofoils think modelers have man aged adapt others models varying degrees success ducted fan makes both hydrofoils blended hull-wing attractive possibilities since out propeller clearances deal inter esting ideas suggest themselves will leave notions another time devote article understanding principles underlying simple scale type floats appropriate scale model will try use procedures learned evaluate excellent model type float given Irwin Ohlsson might think float piece functional sculpture must perform following 1 Provide adequate buoyancy rest 2 Provide minimum resistance motion through water during progressive stages takeoff 3 Provide smooth stable variations trim during takeoff landing since pilot has little no control over trim attitude low speeds water 4 Provide stable reasonably soft landing entry course minimum weight air drag well have ridden water skis aboard speedboat power cruiser familiar changing attitudes craft starts move nose begins rise untilif sufficient power available will gain enough speed level off plane An airplane floats does same thing As moves forward pushes sizeable volume water ahead itself creating large wave hump over OHLSSONS WIDGEON DURING preparation Mr Powers article both Brad editor con sulted Irwin Ohisson retired engine manufacturer AMA Hall Famer has considerable success floats hulls radio control Shown Irwins Grumman Widgeon data supplied Ohlsson Fol lowing Irwins comments hull table specifications configuration first step changed double concave also two sponsons added sides hull bow first step Small spray rails extend outboard length sponsons tunnel de sign gives smooth low power takeoff sponsons spray rails deflect water props original full-scale aircraft 2% degree positive wing incidence reduced 0 degrees model After first flightwith Joe Bridi test pilotit came off water before reached its flying speed stalled nose wing down landplane would have bought farm However bounced out water like basketballnot scratch Since day April 1974 about 50 flights have madenever has wet real good stable fast flying machine Specifications Twin-Engine Widgeon Span 80 chord center section 13% tip 8 hull overall 54 Weight empty 13 lbs weight fueled 15 lbs Power2 contra-rotation 61 Perry pumpsfuel 500cc nacelleprops 11 x 7Y2 left right handthrottles 2one nacelle Controls Flaps Aileron Rudder Elevator Construction Wing2 main spars balsa ribs 2 apart sheet balsa silk covered butyrate doped plywood engine mounts rear spar Hullspruce keel balsa sheeted bottom 3/32 balsa 1/32 x 3 plywood glassed top sides silk covered butyrate dope April1979 11 Noting jet engineno prop clearance problemsmade possible blended hull Powers cites Skate shown moaei tesi tow RACING AIRPLANE AVERAGE___ AIRPLANE LIGHTPLANE Lu 0 0 IL L - 7approx / S 1/ EXCESS THRUSTAVAILABLE FOR TAKE-OFF THRUST 2 L RESISTANCE HUMP 18 10 TAKE-OFF SPEED must literally climb order level off plane gather takeoff speed hump region operation critical regard power indicated Fig 1 Obviously airplane accelerate take off thrust must greater resistance Otherwise will just cruise around water until fuel gone Fig 1 racing airplane has very high water resistance presumably due small floats achieve low air drag since Fig 1 high speed design has sufficient thrust cope resistance As apparent thrust available average airplane used racer takeoff speed would impossible since airplane could never ride over hump Since model engines available appear adequate cases should justified applying average~ rather marginal criteria designing float As aspects airplane design VOLUME Lb2 VOL b b VOLL2b compromises between conflicting require ments generally being sought case hulls floats boils down finding nice balance betweeen size displacement Large floats have advan tage low immersion light spray weigh have higher air drag Small floats sink too deeply water makes heavy spray high water resistance So can say except refinements design actual float itself basic problem find proper size job keeping both float size spray minimum commensu rate power orother limiting factors Early float designers found after much experimentation floats having length beam ratios less about 6/1 didnt work very well seven seemed best average conditions acceptable per formance water achieved draft early floats such displacement value approx imating cubical container filled water having same dimensions side beam float Thus float beam 3 ft could expected perform satisfactorily displaced amount water could placed cubical container 3 ft side Such float would displace 33 27 cu ft sea water Since sea water has density 64 lb/cu ft weight water 1728 lbs pair such floats would right average airplane weighing about 3450 lbs As pointed out Fig 1 could vary considerably non average conditions Once relationship estab lished easy matter scale floats up down suit different gross weights long same family reasonably close being geome trically similar relationship came called beam loading expressed non-dimensional terms W 3andhadavalueoflOwhen wb length/beam ratio seven W equals Load Carried Floatlbs w equals Density Sea Water 4 lbs/cu ft b equals Beam FloatFeet criterion expressed graphically Fig2 Although shown simple cube Fig 2 applies L/b ratio seven L/b 6 value C of75 worked best since L/b decreased Beam increased same token increases L/b accompanied decreases beam requiring corresponding increases values C During WW II studies made configurations floats particularly hulls involving length/beam ratios order 8 10 higher 12 Model Aviation b.Kbb COMPARING CRITERIA found longer hulls less air drag less water resistance less way nasty characteristics like hobby horsing~ porp oising pitching back forth under way selecting length/beam ratio float strong consideration given value 8 finally ruled out due excessive length fact typical scale applications early seaplanes However after have finished article should able design float having high L/b wish float described will have value L/b investigation progressed became apparent immersion coefficient would useful contained provision beam length well Accordingly new term developed engineers called K2 w equal w L2 b Like C K2 nondimensional does indeed account length well beam Recom mended values K2 range 018 light spray low power 022 heavy spray high power 020 representing good criterion average~ conditions float therefore will based indirectly value 020 However look Fig 2 see volume portion term L2b resolves itself large cakepan 2 percent full bears little physical resemblance float So based K2 tried true parameter lets devise term just purpose multiply K2 length/beam ratio increase amount also get cakepan carton has same overall dimensions float follows K2so X K2 wL2bb Lx W — W c bwL2bwLb2 C1 ficient Immersion Lb2 gives us figure fits float like shoe box carton shown figure top Fig 2 So term C1 derived K2 constant like K2 varies length/beam ratio said float has value 7 X K2 7 X 020 140 shown figure 3 As can seen C really percent age displacement float bears its carton makes cozier relationship wish reconcile parameters fully correlation between C K2 shown Fig 4 Now lets proceed design float First must find beam whch turn requires value displacement W watch weight think can put pair floats Nosen Citabria already weighs 18 lbs about 32 lbs Thus gross weight will 25 lbs LENGTH/BEAM RATIO vs Cj 8-7 b 6bf LCi b 144 160 126140154HEAVY OUR FLOAT 101121314 dispi float W dispi artonwLb2 I0 L b 15161718 Fig 3 K2 COMPARED WITH 0 OUR FLOAT 0 . LIGHT SPRAY K2018 7 MODERATE 020 6 HEAVY 022 EXCESSIVE 025 5 2 Fig 4 34 5 68 CW 125 April 1979 13 20 Dornier X 12-engined flying boat built 1929 photo has radial engines arranged tandem pairs After transatlantic crossing turned turtle tropical storm CONVENTIONAL FLOAT t217 Al curve ares r2 7b 77 20 2022 / / 2 25 225 -2 10304222 IS oisoc. 926 [2 DeejI F24Ih0 02p2[ 942 W05N9044IIb25jyf 4404 h224&Ih1l 410 2STSP/C0NTROOISO40 t f J 0 10 42240 V Fig 5 float will carry 125 lbs So W equals 125 lbs C2 said 140 W C2 2 expression two unknowns b L So will have express L terms b making WW wLbbzw7b3 andbeamb3 W — w7 C 125 64 X 7 X 140 584 ft or7in Since length/beam ratio seven length 7 Now lets check results another way said C percentage displacement float carton 14 percent carton has displacement 7 X 7 X 4 8893 lbs 1728 14 percent 8893 1245 lbs close enough point might wise reassess things consider other values planning build model 3-lb camera may added later going fly fresh water lake having water density 624 lb/cu ft might wiser pick value C2 126 shown Fig 3 rather 140 reduce draft lighten spray give some room grow particularly think powerplant marginal beam will become 725 length 5075 However will add around 10 percent weight float Now some discussion before tackle details Obviously float should aerodynamically clean can make So might say Ok lets make streamlined like wing tip fuel tank sounds good streamlined bodies completely immersed tend suck under speak takeoff impossible final analysis wing generates lift deflecting thus accelerating mass air downward float completely streamlined partially immersed actually deflects water upward thus sinking deeper deeper power applied speed remains essentially constant displacement vessels sailing yachts have less fixed maximum speed no matter much extra power wind available just sink deeper deeper like bottom teaspoon suspended against water flowing faucet other hand hull bottom vicinity step transom flat like water ski v-shaped like speed boat water departs step float rides up skims over water deriving lift much same way wing slighting deflecting water down ward gaining lift thereby derived form dynamic pressure hull bottom Actually forebody its transom step does work afterbody primarily provide static buoyancy rest aircraft doesnt rock back its tail Indeed Lou Proctors Antic has forward floats really forebodies coupled small efficient afterbody form small float tail Minimum air drag critical matter models faithful attention detail scale models requires easy lines generous step depth needed assure clean departure wake doesnt tend reattach afterbody cause porpoising plus generous landing angle will handle problem forebody lines should sharp easy keep hull resistance minimum large aircraft ample deadrise needed minimize decelerations landing Deadrise should 14 Model Aviation 226 find center buoyancy Trace curve areas onto cardboard balance three ways edge ruler marking line time Intersection centroid area figurecenter buoyancy float 4 j3-I RAZOR SHARP CHINES Fig 6 TRUE AREAS SQ INf337 316 EI$II LIII -__ IPORT VIEW LEFT FLOAT OUTBOARD CHINE 16 r -eTAogrIb, VINBARD CHINE 0 11 FLOAT PROBLEMS Construct curve areas find 1 Displacement pounds 2 Center Bouyancy LSO 3 Length/Beam Ratio disregarding rounded ends tapered sides 4 Length Beam displacements 1 lb 5 lbs 10 lbs increase go forward along forebody sharpen hull lines provide stability trim Adequate buoyancy afterbody easier attain deadrise held constant initial application power takeoff produces powerful nose-down moment seaplanes must countered adequate forebody displacement will tend resist moment quickly smoothly avoid forebody porpoising char acteristic low length/beam ratio hulls having insufficient restoring moment standpoint L/b 8 would better float would begin get too long landing angle would suffercompro mises again Landing Angle No2 corresponds similar angle landplane Its purpose allow step wheels make initial contact angle close 90 percent stalling angle wing permit slowest possible 912 1 2 REOD PORT AND STARBOARD 17 16 15 114 13 12 1 II II 7k 8 14518 5 18 3 gPORT FLOAT SHOWN -. FLOAT OPPOSITE II 212426 Ti OHLSSON FLOAT 1213 WEIGHT W/ FLOAT. LBS landing speed Since impact forces vary square speed small reductions speed accompanied sizeable increases safety float landing angle 14 15 Fig 7 9 degrees coupled 3 degrees wing incidence 12 degrees Clark Y airfoil small Reynolds Numbers corresponds guidelines just mentioned 1 2 3 4 ANSWERS TO FLOAT PROBLEMS Fig 8 Displacement 298 say 3 lbs CB Station 134 just forward Step 1/B 26/4 equals 65 Dimensions vary cube root Ratio Displacements So 1 lb dimensions will Ohlsson float timesthe cube root 1/3 693 So equals 693 x 26 18 end B 593 x 4 277 Similarly 5 lbs 307 B 472 10 lbs L 3875 B 595 say 6 Note Since float different family conventional float geomet rically related values CW Ci would comparable VOLUME 4 CtiINV2SOLU OF OUYANC April1979 15 FLOAT TOO SMALL LOAT FLOAT TOO LARGE static trim CG complete airplane must obviously lie perpendic ular waterplane passes through Center Buoyancy float indicated Item 29 Fig 5 Item 2 Fig 5 shows landing angle mentioned above As can seen step centroidof V-step Item 22 Fig 5 should slightly aft Center Buoyancy place directly under CG landing 30 order keep float axis parallel fuselage usually desirable flight angle static trim Item 13 Fig 5 3 degrees producing slightly nose up attitude airplane static rest water undesirable have axis airplane parallel waterplane would mean placing floats slightly nose up else reducing forebody displacementneither good Flare No 12 directs spray helps control its effects Judicious use spray dams blinders metal strips flush sides float projecting about half inch below chine can reduce spray dramatically carried too far forward made too large can destabilizing flight probably best experiment little bit Because forward portions floats destabilizing flight necessary add substantial increment fin area compensate shown No 24 Since floats will also produce negative diving moment elevator trim order preferably some means adjusting horizontal stabilizer toe-in recommended procedure installing wheels landplane no-no floats very necessary mounted firmly accurately Water forces high unforgiving afterbody float tapers back flat transom large enough accomodate water rudder mounting brackets outlets internal pushrods water rudder should placed float its pivot line should 2530% its chord Its area critical make about size proportion shown respect size float So much generalities Now lets put Fig 5 front us study steps involved creating particular float Lay out 7 X 49 carton side view 3 X 49 half plan below 7 X 7 box left Note height float equals beam mainly simplify geometry article height could increased say used basis single hull design ever should decreased excess buoyancy very necessary Theoretically could slice float off just above waterline did extra ounce fuel added servo could sink whole kaboodle Draw center line 3 Draw upper deck lines shown forebody duplicate below plan view forebody shown above chine elliptical prolate spheroid anybody interested doesnt have Make shape matches picture favorite seaplane wish Locate Step 1 As first approxi mation lets assume Sta 26 26 aft nose Later might want change bit Lets hope Draw landing angle 2 heel step up center line Sta 49 Make step depth 8 afterbody keel 7 Draw forebody keel 6 Note carries well forward does match curve deck line top sharpen entry side view left draw circular cross sections upper forebody deck down center line drop vertical tangents circular cross section meets center line tangents Sta 6 forward should extend above 16 Model Aviation Mercury Racer Granger WIlliams repose La Costa CA sloughlntended Schneider Trophy race flown Al Williams real Mercury grossly overweight Brad Powers left Irwin Ohlsson latters highly successful twinfloat design using floats own design championship free-flighter Thirties later manufacturer engines exAMA president Hall Famer Irwin builds designs best center line Starting step Sta 26 draw deadrise angle 4 20 degrees Its inter section vertical tangent just drew determines aft point theoret ical chine 9 Draw theoretical chine 9 establishes smooth variation deadrise go forward Back step section again draw chine flare 12 Its intersection vertical tangent establishes aft end forebody chine 10 Draw forebody chine 10 shown Near Station 6 curve reverses lie fore aft direction make clean aerodynamic entry Assuming theoret ical chine lie curved surface touching side hull therefore intersecting vertical tangents drew draw deadrise Station add flare tangent deadrise horizontal chine flare should have generous radiusbut excessive Now draw afterbody deadrise Station other side end view plan view drew beginning establish afterbody chine both end side views 11 Using afterbody planform deter radii draw locus radii 18 side view complete sections afterbody end view point good idea draw some 'buttock lines' 'water lines' end view shown project other views see fair fair smooth fiddle drawing bit until 23 region between Sta 18 step bottom should have straight buttock lines insure stable planning other words hull bottom surfaces should have no fore aft curvature region Draw trial static load water line sloping up aft 3 degrees through point 3 above keel step 14 information end view water line construct sections shown hatched station Measure sections determine area section Since half sections dont forget multiply area 2 plot values shown 26 establish acurve areas Just volume deck cards sum cards area under curve summation infinite number cross sectional areas therefore represents volume immersed portion float Since before reproduction maga zine drawing made half scale areas have indicated obtained half scale drawing will have corrected full scale will shortly true well length curve areas drawn 1/5 scale expression shape curve areas could add up integrate mathematically since arbitrarily determined its slope choices deadrise flare chine chape etc no way establish slope area curve mathematically must integrate graphically can done close approximation adding areas successive steps 27 judiciously done better way use device called polar planimeter have done gives area under curve 169 sq just pointed out areas taken one-half scale drawing therefore have fourth full-size areas because areas varies scale squared Also said length figure one-fifth actual float must multiply 169 5 times 4 20 have correct figure since value volume cu must divide number cu in cu ft get cu ft can multiply 64 weight cu ft sea water we see float indeed displaces 1252 lbs indicated Fig 5 about draft 3 good guesstimate As shown Fig 7 float should loaded carry much over 13 pounds spray will get too heavy other hand float carry much less 11 pounds will too big heavy smaller float should used Well now know draft displacement what Before can screw floats onto airplane have know buoyancy concentrated way find Center Buoyancy trace curve areas onto piece cardboard no lumps cut out balance shown picture Balance least three ways mark time have careful marks will intersect point centroid area figure Center Buoyancy float 21 Incidentally good way find centroids such things elliptical wings centers lateral area other irregular shapes Now can relate float Nosen Citabria 19 above described earlier shown Fig 5 good stability control CG 20 should 25% mean aerody namic chord MAC wing Since Citabria has rectangular planform amounts 25 percent root chord indicated 17 Fortunately Center Buoyancy falls just want landing angle right step fortuitous because have struggling days get together Actually little both aerodynamically unfortunate carrying large appendages like floats way out arms length speak clearances shown 6 at31 learance 20-in propeller float spacing 3 beams 21 33 should reduced keep airplane its vitals being inun dated choppy water spray covers general way preliminary design float great other aspects covering water resistance trimming moments etc have left untouched felt really essential modeler putting floats pride joy intention article es tablish basic criteria Prelimi nary Design future article will presented Detail Design Continued page 98 April1979 17 Line-up RC seaplane models Lto R Bob Wisniewakis modIfied Lancer single pontoon wing-tip floats Granger Williams sport model similar configuration Granger Williams Mercury twin floats Gary Neelys modified sport biplane twin floats Main floats models same Mercury design molded foam plastic Openers/Winter continued page 72 have something tell As RCer FOs chief interest CL Racing frantic aerobatics pilots center circle will find Bill Lee CL Racing talking about home-made fibreglass props Bill Wynn Paul too guy endlessly seeks truth about tanks things like props doing experimenting finding para meters Dave Chesney writes beautifully RC Helicopters column existence now Bill Warner Sport/Scale will put humor life flying circus note others gang Without guys like us would never know about hundreds things add up sum total skills Brad Powers lead article floats quarter-scale landmark article Model aviation old century yet explosion knowledge techniques products never dared dream about what know about floats would fit smallest drawer field box So designer partook dozens famous pro jects made history modeler boot telling us design float virtually size modelas well monsters weve yet see water Note feed-inIrwin Ohlsson great Ernie Stout Convair fame What suggesting dear friend April issue however excep tional 12 year talking about magazine Within another yearGod willingit will thousand light years beyond April 1976 MA began July 1975 its modern form ask conscious magazine contro versial terms some other magazines have shown theyd like see deadbut inspect closely what speak especially minority members did subscribe MA past yours wed like proud AS WE GO TO PRESS sad news ar rives passing Myron Mike Schlesinger recent past president Top Flite Models Mike respected friend industry innumerable modelers true pioneer helped start Top Flite its way chaired trade show committee 1956 became member HIAAs board directors served nearly 10 years chairman co-chairman HIAAs Model Aeronautics Division Hu morous easy going always compassion ate understanding Mike Schlesinger will truly missed us Floats Powers continued page 17 actual floats installed Citabria model together summary results some photos Irwin Ohlsson thirties deve loped line famous Ohlsson engines now retired builds beautiful model seaplanes has given pair floats developed has found very satisfactory straightforward design have generous step landing angle embody progressive deadrise Rather present float complete its displacement Center Buoyancy etc ready determined will give its dimensions trim another guesstimate draft 16 40 percent its beam data procedures already discussed up find answers problems Fig 6 shows float answers will found illustration Answers Float Prob lems Finally wish express thanks Ernest G Stout former Chief Hydrody namics Convair worked interesting projects sistance providing data presented herein Now am going start building float build finish before write let know works can de cide whether stay leave Tierra Del Fuego RC Technique/Myers continued page 19 control thats going wrong way move pushrod hole opposite side output wheel frequently make such change field someone needs disadvantage approach pushrods usually get tangled you end up product review product review product review Radial Engines man has thingultra deluxe 57-cylinder scale-like engines /4 scale 4-cycle high-torque swing 16-8 through 20-6 props Low vibra tion low fuel consumption mild glow fuel 6-in diameter 23 oz weight 7cylinder engines offered 3 versionspol ished aluminum anodized black deluxe Collectors Gold Edition package trimmed 14K gold Manufacturer states fully opera tional warranted 90 dayssold direct Executive Engines Co 16650 S 104th Ave Orland Park IL 60462 product review product review product review swapping rudder elevator servos side-by-side using Nyrod often finds surgery neces sary because outer shell has anchored location doesnt allow shift connection other side wheel Wouldnt nice could just throw reversing switch servo point Bobs eyes lit up Ill bet Ace R/C Bantam Midget machinery will fit regular Bantam case says leave enough room servo reverser dont see what can idea George kicked around some possibilities until time get back work few days later Bantam case Bantam Midget servo appeared desk magic Christmas came bit early year thought until Bob told wanted back after youve finished rever sing switch first thought make use 16pin DIP switch After little consideration possibilities left open direct short across batteries dropped idea Besides switch too big Next tried 4PDT Noble switch commonly used switch harnesses RC systems can made fit little help Dremel problem will have take out servo get switch smaller switch could mounted right out open can get couldnt find Slightly later Bob left another goodie desk prototype servo reverser ACE R/C few mods could fit space available would left servo having two pigtails rotation Plug need configuration left project returned servo Bob must careful let unused plug short out metal parts because will short out batteries kill whole system As said before like idea having servo reverser receiver todays IC circuitry major configuration change would adding second set sockets other rotation Its fair mention Kraft has shipping sets 10 years have two servos set up direction Editors NoteLike feature Cox-Sanwa get what want swapping around dot no dot servos dot tiny circle molded mounting flange between cutouts grommets Once get flight pack set up right theres no way make mistake Thats way like things Over years have bought flight packs transmitters work plane until control trims throws right transmitter trim levers center position leave everything alone until needs service way can pick plane off wall go flying worrying its compatible 98 Model Aviation
Edition: Model Aviation - 1979/04
Page Numbers: 10, 11, 12, 13, 14, 15, 16, 17, 98
FOR variety reasons early speculation about future aviation painted rosy picture seaplanes During interval between two world wars seaplanes set speed records crossed oceans offered great promise future Since through out world almost city size situated near important body water feeling build expensive space consuming airports 1929 Claude Dornier building remarkable seaplane shown pic ture american industrial designer Nor man Bel Geddes busy collaboration Dr Otto Koller designer Ger man Pfalz biplane Together worked up design enormous flying boat wing span 528 feet deck below water line eight decks above have 20 1 900-hp engines includ ing engine repair shop root wing 22 feet thick gross weight 1275000 pounds would believe behemoth designed cruise fantastic speed 100 mph 5000 feet some reason never built Now discredit man Larry Williams taxies Supermarine S4 waters Lake Elsinora CA prior contest-winning flight powered K&8 front-rotor engine Warren Shipp photo Norman Bel Geddes true genius ideas kitchen ranges elevated freeways have become reality simply show fast actual progress can overtake wildest dreams gifted advent all-metal stressed skin monoplanes retractable gear landplanes suddenly stopped looking like Jennies began look today Seaplane designers other hand could never figure out way retract floats within sensible weight allowance density seawater just wasnt great enough floats hulls always too big invariably added up drag just simple landplane fuselage Since drag means fuel increased fuel meant corresponding reductions range pay load translated reductions reve nues wasnt until jet engine came along eliminating large clearances re quired propellers designers able create seaplanes such Skate shown model photo could compete drag-wise landplane time airports finally built Iandplanes stolen show 10 Model Aviation Larrys Supermarine overhead later lowwing Supermarines among beautiful ali aircraft laid groundwork Spit fire designed RJ Mitchell Shipp photo Other factors also determined de mise seaplane Rough seas landing areas werent always calm areas congested unsafe handling mooring maintenance difficulties say nothing severe corrosive effects sea water aluminum alloy hulls Numerous approaches problem operating aircraft water have made include variety floats varying shapes skis hydrofoils large hulls literally stabilized tip floats spon sons blended configuration Skate shown photo exception last item possibly hydrofoils think modelers have man aged adapt others models varying degrees success ducted fan makes both hydrofoils blended hull-wing attractive possibilities since out propeller clearances deal inter esting ideas suggest themselves will leave notions another time devote article understanding principles underlying simple scale type floats appropriate scale model will try use procedures learned evaluate excellent model type float given Irwin Ohlsson might think float piece functional sculpture must perform following 1 Provide adequate buoyancy rest 2 Provide minimum resistance motion through water during progressive stages takeoff 3 Provide smooth stable variations trim during takeoff landing since pilot has little no control over trim attitude low speeds water 4 Provide stable reasonably soft landing entry course minimum weight air drag well have ridden water skis aboard speedboat power cruiser familiar changing attitudes craft starts move nose begins rise untilif sufficient power available will gain enough speed level off plane An airplane floats does same thing As moves forward pushes sizeable volume water ahead itself creating large wave hump over OHLSSONS WIDGEON DURING preparation Mr Powers article both Brad editor con sulted Irwin Ohisson retired engine manufacturer AMA Hall Famer has considerable success floats hulls radio control Shown Irwins Grumman Widgeon data supplied Ohlsson Fol lowing Irwins comments hull table specifications configuration first step changed double concave also two sponsons added sides hull bow first step Small spray rails extend outboard length sponsons tunnel de sign gives smooth low power takeoff sponsons spray rails deflect water props original full-scale aircraft 2% degree positive wing incidence reduced 0 degrees model After first flightwith Joe Bridi test pilotit came off water before reached its flying speed stalled nose wing down landplane would have bought farm However bounced out water like basketballnot scratch Since day April 1974 about 50 flights have madenever has wet real good stable fast flying machine Specifications Twin-Engine Widgeon Span 80 chord center section 13% tip 8 hull overall 54 Weight empty 13 lbs weight fueled 15 lbs Power2 contra-rotation 61 Perry pumpsfuel 500cc nacelleprops 11 x 7Y2 left right handthrottles 2one nacelle Controls Flaps Aileron Rudder Elevator Construction Wing2 main spars balsa ribs 2 apart sheet balsa silk covered butyrate doped plywood engine mounts rear spar Hullspruce keel balsa sheeted bottom 3/32 balsa 1/32 x 3 plywood glassed top sides silk covered butyrate dope April1979 11 Noting jet engineno prop clearance problemsmade possible blended hull Powers cites Skate shown moaei tesi tow RACING AIRPLANE AVERAGE___ AIRPLANE LIGHTPLANE Lu 0 0 IL L - 7approx / S 1/ EXCESS THRUSTAVAILABLE FOR TAKE-OFF THRUST 2 L RESISTANCE HUMP 18 10 TAKE-OFF SPEED must literally climb order level off plane gather takeoff speed hump region operation critical regard power indicated Fig 1 Obviously airplane accelerate take off thrust must greater resistance Otherwise will just cruise around water until fuel gone Fig 1 racing airplane has very high water resistance presumably due small floats achieve low air drag since Fig 1 high speed design has sufficient thrust cope resistance As apparent thrust available average airplane used racer takeoff speed would impossible since airplane could never ride over hump Since model engines available appear adequate cases should justified applying average~ rather marginal criteria designing float As aspects airplane design VOLUME Lb2 VOL b b VOLL2b compromises between conflicting require ments generally being sought case hulls floats boils down finding nice balance betweeen size displacement Large floats have advan tage low immersion light spray weigh have higher air drag Small floats sink too deeply water makes heavy spray high water resistance So can say except refinements design actual float itself basic problem find proper size job keeping both float size spray minimum commensu rate power orother limiting factors Early float designers found after much experimentation floats having length beam ratios less about 6/1 didnt work very well seven seemed best average conditions acceptable per formance water achieved draft early floats such displacement value approx imating cubical container filled water having same dimensions side beam float Thus float beam 3 ft could expected perform satisfactorily displaced amount water could placed cubical container 3 ft side Such float would displace 33 27 cu ft sea water Since sea water has density 64 lb/cu ft weight water 1728 lbs pair such floats would right average airplane weighing about 3450 lbs As pointed out Fig 1 could vary considerably non average conditions Once relationship estab lished easy matter scale floats up down suit different gross weights long same family reasonably close being geome trically similar relationship came called beam loading expressed non-dimensional terms W 3andhadavalueoflOwhen wb length/beam ratio seven W equals Load Carried Floatlbs w equals Density Sea Water 4 lbs/cu ft b equals Beam FloatFeet criterion expressed graphically Fig2 Although shown simple cube Fig 2 applies L/b ratio seven L/b 6 value C of75 worked best since L/b decreased Beam increased same token increases L/b accompanied decreases beam requiring corresponding increases values C During WW II studies made configurations floats particularly hulls involving length/beam ratios order 8 10 higher 12 Model Aviation b.Kbb COMPARING CRITERIA found longer hulls less air drag less water resistance less way nasty characteristics like hobby horsing~ porp oising pitching back forth under way selecting length/beam ratio float strong consideration given value 8 finally ruled out due excessive length fact typical scale applications early seaplanes However after have finished article should able design float having high L/b wish float described will have value L/b investigation progressed became apparent immersion coefficient would useful contained provision beam length well Accordingly new term developed engineers called K2 w equal w L2 b Like C K2 nondimensional does indeed account length well beam Recom mended values K2 range 018 light spray low power 022 heavy spray high power 020 representing good criterion average~ conditions float therefore will based indirectly value 020 However look Fig 2 see volume portion term L2b resolves itself large cakepan 2 percent full bears little physical resemblance float So based K2 tried true parameter lets devise term just purpose multiply K2 length/beam ratio increase amount also get cakepan carton has same overall dimensions float follows K2so X K2 wL2bb Lx W — W c bwL2bwLb2 C1 ficient Immersion Lb2 gives us figure fits float like shoe box carton shown figure top Fig 2 So term C1 derived K2 constant like K2 varies length/beam ratio said float has value 7 X K2 7 X 020 140 shown figure 3 As can seen C really percent age displacement float bears its carton makes cozier relationship wish reconcile parameters fully correlation between C K2 shown Fig 4 Now lets proceed design float First must find beam whch turn requires value displacement W watch weight think can put pair floats Nosen Citabria already weighs 18 lbs about 32 lbs Thus gross weight will 25 lbs LENGTH/BEAM RATIO vs Cj 8-7 b 6bf LCi b 144 160 126140154HEAVY OUR FLOAT 101121314 dispi float W dispi artonwLb2 I0 L b 15161718 Fig 3 K2 COMPARED WITH 0 OUR FLOAT 0 . LIGHT SPRAY K2018 7 MODERATE 020 6 HEAVY 022 EXCESSIVE 025 5 2 Fig 4 34 5 68 CW 125 April 1979 13 20 Dornier X 12-engined flying boat built 1929 photo has radial engines arranged tandem pairs After transatlantic crossing turned turtle tropical storm CONVENTIONAL FLOAT t217 Al curve ares r2 7b 77 20 2022 / / 2 25 225 -2 10304222 IS oisoc. 926 [2 DeejI F24Ih0 02p2[ 942 W05N9044IIb25jyf 4404 h224&Ih1l 410 2STSP/C0NTROOISO40 t f J 0 10 42240 V Fig 5 float will carry 125 lbs So W equals 125 lbs C2 said 140 W C2 2 expression two unknowns b L So will have express L terms b making WW wLbbzw7b3 andbeamb3 W — w7 C 125 64 X 7 X 140 584 ft or7in Since length/beam ratio seven length 7 Now lets check results another way said C percentage displacement float carton 14 percent carton has displacement 7 X 7 X 4 8893 lbs 1728 14 percent 8893 1245 lbs close enough point might wise reassess things consider other values planning build model 3-lb camera may added later going fly fresh water lake having water density 624 lb/cu ft might wiser pick value C2 126 shown Fig 3 rather 140 reduce draft lighten spray give some room grow particularly think powerplant marginal beam will become 725 length 5075 However will add around 10 percent weight float Now some discussion before tackle details Obviously float should aerodynamically clean can make So might say Ok lets make streamlined like wing tip fuel tank sounds good streamlined bodies completely immersed tend suck under speak takeoff impossible final analysis wing generates lift deflecting thus accelerating mass air downward float completely streamlined partially immersed actually deflects water upward thus sinking deeper deeper power applied speed remains essentially constant displacement vessels sailing yachts have less fixed maximum speed no matter much extra power wind available just sink deeper deeper like bottom teaspoon suspended against water flowing faucet other hand hull bottom vicinity step transom flat like water ski v-shaped like speed boat water departs step float rides up skims over water deriving lift much same way wing slighting deflecting water down ward gaining lift thereby derived form dynamic pressure hull bottom Actually forebody its transom step does work afterbody primarily provide static buoyancy rest aircraft doesnt rock back its tail Indeed Lou Proctors Antic has forward floats really forebodies coupled small efficient afterbody form small float tail Minimum air drag critical matter models faithful attention detail scale models requires easy lines generous step depth needed assure clean departure wake doesnt tend reattach afterbody cause porpoising plus generous landing angle will handle problem forebody lines should sharp easy keep hull resistance minimum large aircraft ample deadrise needed minimize decelerations landing Deadrise should 14 Model Aviation 226 find center buoyancy Trace curve areas onto cardboard balance three ways edge ruler marking line time Intersection centroid area figurecenter buoyancy float 4 j3-I RAZOR SHARP CHINES Fig 6 TRUE AREAS SQ INf337 316 EI$II LIII -__ IPORT VIEW LEFT FLOAT OUTBOARD CHINE 16 r -eTAogrIb, VINBARD CHINE 0 11 FLOAT PROBLEMS Construct curve areas find 1 Displacement pounds 2 Center Bouyancy LSO 3 Length/Beam Ratio disregarding rounded ends tapered sides 4 Length Beam displacements 1 lb 5 lbs 10 lbs increase go forward along forebody sharpen hull lines provide stability trim Adequate buoyancy afterbody easier attain deadrise held constant initial application power takeoff produces powerful nose-down moment seaplanes must countered adequate forebody displacement will tend resist moment quickly smoothly avoid forebody porpoising char acteristic low length/beam ratio hulls having insufficient restoring moment standpoint L/b 8 would better float would begin get too long landing angle would suffercompro mises again Landing Angle No2 corresponds similar angle landplane Its purpose allow step wheels make initial contact angle close 90 percent stalling angle wing permit slowest possible 912 1 2 REOD PORT AND STARBOARD 17 16 15 114 13 12 1 II II 7k 8 14518 5 18 3 gPORT FLOAT SHOWN -. FLOAT OPPOSITE II 212426 Ti OHLSSON FLOAT 1213 WEIGHT W/ FLOAT. LBS landing speed Since impact forces vary square speed small reductions speed accompanied sizeable increases safety float landing angle 14 15 Fig 7 9 degrees coupled 3 degrees wing incidence 12 degrees Clark Y airfoil small Reynolds Numbers corresponds guidelines just mentioned 1 2 3 4 ANSWERS TO FLOAT PROBLEMS Fig 8 Displacement 298 say 3 lbs CB Station 134 just forward Step 1/B 26/4 equals 65 Dimensions vary cube root Ratio Displacements So 1 lb dimensions will Ohlsson float timesthe cube root 1/3 693 So equals 693 x 26 18 end B 593 x 4 277 Similarly 5 lbs 307 B 472 10 lbs L 3875 B 595 say 6 Note Since float different family conventional float geomet rically related values CW Ci would comparable VOLUME 4 CtiINV2SOLU OF OUYANC April1979 15 FLOAT TOO SMALL LOAT FLOAT TOO LARGE static trim CG complete airplane must obviously lie perpendic ular waterplane passes through Center Buoyancy float indicated Item 29 Fig 5 Item 2 Fig 5 shows landing angle mentioned above As can seen step centroidof V-step Item 22 Fig 5 should slightly aft Center Buoyancy place directly under CG landing 30 order keep float axis parallel fuselage usually desirable flight angle static trim Item 13 Fig 5 3 degrees producing slightly nose up attitude airplane static rest water undesirable have axis airplane parallel waterplane would mean placing floats slightly nose up else reducing forebody displacementneither good Flare No 12 directs spray helps control its effects Judicious use spray dams blinders metal strips flush sides float projecting about half inch below chine can reduce spray dramatically carried too far forward made too large can destabilizing flight probably best experiment little bit Because forward portions floats destabilizing flight necessary add substantial increment fin area compensate shown No 24 Since floats will also produce negative diving moment elevator trim order preferably some means adjusting horizontal stabilizer toe-in recommended procedure installing wheels landplane no-no floats very necessary mounted firmly accurately Water forces high unforgiving afterbody float tapers back flat transom large enough accomodate water rudder mounting brackets outlets internal pushrods water rudder should placed float its pivot line should 2530% its chord Its area critical make about size proportion shown respect size float So much generalities Now lets put Fig 5 front us study steps involved creating particular float Lay out 7 X 49 carton side view 3 X 49 half plan below 7 X 7 box left Note height float equals beam mainly simplify geometry article height could increased say used basis single hull design ever should decreased excess buoyancy very necessary Theoretically could slice float off just above waterline did extra ounce fuel added servo could sink whole kaboodle Draw center line 3 Draw upper deck lines shown forebody duplicate below plan view forebody shown above chine elliptical prolate spheroid anybody interested doesnt have Make shape matches picture favorite seaplane wish Locate Step 1 As first approxi mation lets assume Sta 26 26 aft nose Later might want change bit Lets hope Draw landing angle 2 heel step up center line Sta 49 Make step depth 8 afterbody keel 7 Draw forebody keel 6 Note carries well forward does match curve deck line top sharpen entry side view left draw circular cross sections upper forebody deck down center line drop vertical tangents circular cross section meets center line tangents Sta 6 forward should extend above 16 Model Aviation Mercury Racer Granger WIlliams repose La Costa CA sloughlntended Schneider Trophy race flown Al Williams real Mercury grossly overweight Brad Powers left Irwin Ohlsson latters highly successful twinfloat design using floats own design championship free-flighter Thirties later manufacturer engines exAMA president Hall Famer Irwin builds designs best center line Starting step Sta 26 draw deadrise angle 4 20 degrees Its inter section vertical tangent just drew determines aft point theoret ical chine 9 Draw theoretical chine 9 establishes smooth variation deadrise go forward Back step section again draw chine flare 12 Its intersection vertical tangent establishes aft end forebody chine 10 Draw forebody chine 10 shown Near Station 6 curve reverses lie fore aft direction make clean aerodynamic entry Assuming theoret ical chine lie curved surface touching side hull therefore intersecting vertical tangents drew draw deadrise Station add flare tangent deadrise horizontal chine flare should have generous radiusbut excessive Now draw afterbody deadrise Station other side end view plan view drew beginning establish afterbody chine both end side views 11 Using afterbody planform deter radii draw locus radii 18 side view complete sections afterbody end view point good idea draw some 'buttock lines' 'water lines' end view shown project other views see fair fair smooth fiddle drawing bit until 23 region between Sta 18 step bottom should have straight buttock lines insure stable planning other words hull bottom surfaces should have no fore aft curvature region Draw trial static load water line sloping up aft 3 degrees through point 3 above keel step 14 information end view water line construct sections shown hatched station Measure sections determine area section Since half sections dont forget multiply area 2 plot values shown 26 establish acurve areas Just volume deck cards sum cards area under curve summation infinite number cross sectional areas therefore represents volume immersed portion float Since before reproduction maga zine drawing made half scale areas have indicated obtained half scale drawing will have corrected full scale will shortly true well length curve areas drawn 1/5 scale expression shape curve areas could add up integrate mathematically since arbitrarily determined its slope choices deadrise flare chine chape etc no way establish slope area curve mathematically must integrate graphically can done close approximation adding areas successive steps 27 judiciously done better way use device called polar planimeter have done gives area under curve 169 sq just pointed out areas taken one-half scale drawing therefore have fourth full-size areas because areas varies scale squared Also said length figure one-fifth actual float must multiply 169 5 times 4 20 have correct figure since value volume cu must divide number cu in cu ft get cu ft can multiply 64 weight cu ft sea water we see float indeed displaces 1252 lbs indicated Fig 5 about draft 3 good guesstimate As shown Fig 7 float should loaded carry much over 13 pounds spray will get too heavy other hand float carry much less 11 pounds will too big heavy smaller float should used Well now know draft displacement what Before can screw floats onto airplane have know buoyancy concentrated way find Center Buoyancy trace curve areas onto piece cardboard no lumps cut out balance shown picture Balance least three ways mark time have careful marks will intersect point centroid area figure Center Buoyancy float 21 Incidentally good way find centroids such things elliptical wings centers lateral area other irregular shapes Now can relate float Nosen Citabria 19 above described earlier shown Fig 5 good stability control CG 20 should 25% mean aerody namic chord MAC wing Since Citabria has rectangular planform amounts 25 percent root chord indicated 17 Fortunately Center Buoyancy falls just want landing angle right step fortuitous because have struggling days get together Actually little both aerodynamically unfortunate carrying large appendages like floats way out arms length speak clearances shown 6 at31 learance 20-in propeller float spacing 3 beams 21 33 should reduced keep airplane its vitals being inun dated choppy water spray covers general way preliminary design float great other aspects covering water resistance trimming moments etc have left untouched felt really essential modeler putting floats pride joy intention article es tablish basic criteria Prelimi nary Design future article will presented Detail Design Continued page 98 April1979 17 Line-up RC seaplane models Lto R Bob Wisniewakis modIfied Lancer single pontoon wing-tip floats Granger Williams sport model similar configuration Granger Williams Mercury twin floats Gary Neelys modified sport biplane twin floats Main floats models same Mercury design molded foam plastic Openers/Winter continued page 72 have something tell As RCer FOs chief interest CL Racing frantic aerobatics pilots center circle will find Bill Lee CL Racing talking about home-made fibreglass props Bill Wynn Paul too guy endlessly seeks truth about tanks things like props doing experimenting finding para meters Dave Chesney writes beautifully RC Helicopters column existence now Bill Warner Sport/Scale will put humor life flying circus note others gang Without guys like us would never know about hundreds things add up sum total skills Brad Powers lead article floats quarter-scale landmark article Model aviation old century yet explosion knowledge techniques products never dared dream about what know about floats would fit smallest drawer field box So designer partook dozens famous pro jects made history modeler boot telling us design float virtually size modelas well monsters weve yet see water Note feed-inIrwin Ohlsson great Ernie Stout Convair fame What suggesting dear friend April issue however excep tional 12 year talking about magazine Within another yearGod willingit will thousand light years beyond April 1976 MA began July 1975 its modern form ask conscious magazine contro versial terms some other magazines have shown theyd like see deadbut inspect closely what speak especially minority members did subscribe MA past yours wed like proud AS WE GO TO PRESS sad news ar rives passing Myron Mike Schlesinger recent past president Top Flite Models Mike respected friend industry innumerable modelers true pioneer helped start Top Flite its way chaired trade show committee 1956 became member HIAAs board directors served nearly 10 years chairman co-chairman HIAAs Model Aeronautics Division Hu morous easy going always compassion ate understanding Mike Schlesinger will truly missed us Floats Powers continued page 17 actual floats installed Citabria model together summary results some photos Irwin Ohlsson thirties deve loped line famous Ohlsson engines now retired builds beautiful model seaplanes has given pair floats developed has found very satisfactory straightforward design have generous step landing angle embody progressive deadrise Rather present float complete its displacement Center Buoyancy etc ready determined will give its dimensions trim another guesstimate draft 16 40 percent its beam data procedures already discussed up find answers problems Fig 6 shows float answers will found illustration Answers Float Prob lems Finally wish express thanks Ernest G Stout former Chief Hydrody namics Convair worked interesting projects sistance providing data presented herein Now am going start building float build finish before write let know works can de cide whether stay leave Tierra Del Fuego RC Technique/Myers continued page 19 control thats going wrong way move pushrod hole opposite side output wheel frequently make such change field someone needs disadvantage approach pushrods usually get tangled you end up product review product review product review Radial Engines man has thingultra deluxe 57-cylinder scale-like engines /4 scale 4-cycle high-torque swing 16-8 through 20-6 props Low vibra tion low fuel consumption mild glow fuel 6-in diameter 23 oz weight 7cylinder engines offered 3 versionspol ished aluminum anodized black deluxe Collectors Gold Edition package trimmed 14K gold Manufacturer states fully opera tional warranted 90 dayssold direct Executive Engines Co 16650 S 104th Ave Orland Park IL 60462 product review product review product review swapping rudder elevator servos side-by-side using Nyrod often finds surgery neces sary because outer shell has anchored location doesnt allow shift connection other side wheel Wouldnt nice could just throw reversing switch servo point Bobs eyes lit up Ill bet Ace R/C Bantam Midget machinery will fit regular Bantam case says leave enough room servo reverser dont see what can idea George kicked around some possibilities until time get back work few days later Bantam case Bantam Midget servo appeared desk magic Christmas came bit early year thought until Bob told wanted back after youve finished rever sing switch first thought make use 16pin DIP switch After little consideration possibilities left open direct short across batteries dropped idea Besides switch too big Next tried 4PDT Noble switch commonly used switch harnesses RC systems can made fit little help Dremel problem will have take out servo get switch smaller switch could mounted right out open can get couldnt find Slightly later Bob left another goodie desk prototype servo reverser ACE R/C few mods could fit space available would left servo having two pigtails rotation Plug need configuration left project returned servo Bob must careful let unused plug short out metal parts because will short out batteries kill whole system As said before like idea having servo reverser receiver todays IC circuitry major configuration change would adding second set sockets other rotation Its fair mention Kraft has shipping sets 10 years have two servos set up direction Editors NoteLike feature Cox-Sanwa get what want swapping around dot no dot servos dot tiny circle molded mounting flange between cutouts grommets Once get flight pack set up right theres no way make mistake Thats way like things Over years have bought flight packs transmitters work plane until control trims throws right transmitter trim levers center position leave everything alone until needs service way can pick plane off wall go flying worrying its compatible 98 Model Aviation
Edition: Model Aviation - 1979/04
Page Numbers: 10, 11, 12, 13, 14, 15, 16, 17, 98
FOR variety reasons early speculation about future aviation painted rosy picture seaplanes During interval between two world wars seaplanes set speed records crossed oceans offered great promise future Since through out world almost city size situated near important body water feeling build expensive space consuming airports 1929 Claude Dornier building remarkable seaplane shown pic ture american industrial designer Nor man Bel Geddes busy collaboration Dr Otto Koller designer Ger man Pfalz biplane Together worked up design enormous flying boat wing span 528 feet deck below water line eight decks above have 20 1 900-hp engines includ ing engine repair shop root wing 22 feet thick gross weight 1275000 pounds would believe behemoth designed cruise fantastic speed 100 mph 5000 feet some reason never built Now discredit man Larry Williams taxies Supermarine S4 waters Lake Elsinora CA prior contest-winning flight powered K&8 front-rotor engine Warren Shipp photo Norman Bel Geddes true genius ideas kitchen ranges elevated freeways have become reality simply show fast actual progress can overtake wildest dreams gifted advent all-metal stressed skin monoplanes retractable gear landplanes suddenly stopped looking like Jennies began look today Seaplane designers other hand could never figure out way retract floats within sensible weight allowance density seawater just wasnt great enough floats hulls always too big invariably added up drag just simple landplane fuselage Since drag means fuel increased fuel meant corresponding reductions range pay load translated reductions reve nues wasnt until jet engine came along eliminating large clearances re quired propellers designers able create seaplanes such Skate shown model photo could compete drag-wise landplane time airports finally built Iandplanes stolen show 10 Model Aviation Larrys Supermarine overhead later lowwing Supermarines among beautiful ali aircraft laid groundwork Spit fire designed RJ Mitchell Shipp photo Other factors also determined de mise seaplane Rough seas landing areas werent always calm areas congested unsafe handling mooring maintenance difficulties say nothing severe corrosive effects sea water aluminum alloy hulls Numerous approaches problem operating aircraft water have made include variety floats varying shapes skis hydrofoils large hulls literally stabilized tip floats spon sons blended configuration Skate shown photo exception last item possibly hydrofoils think modelers have man aged adapt others models varying degrees success ducted fan makes both hydrofoils blended hull-wing attractive possibilities since out propeller clearances deal inter esting ideas suggest themselves will leave notions another time devote article understanding principles underlying simple scale type floats appropriate scale model will try use procedures learned evaluate excellent model type float given Irwin Ohlsson might think float piece functional sculpture must perform following 1 Provide adequate buoyancy rest 2 Provide minimum resistance motion through water during progressive stages takeoff 3 Provide smooth stable variations trim during takeoff landing since pilot has little no control over trim attitude low speeds water 4 Provide stable reasonably soft landing entry course minimum weight air drag well have ridden water skis aboard speedboat power cruiser familiar changing attitudes craft starts move nose begins rise untilif sufficient power available will gain enough speed level off plane An airplane floats does same thing As moves forward pushes sizeable volume water ahead itself creating large wave hump over OHLSSONS WIDGEON DURING preparation Mr Powers article both Brad editor con sulted Irwin Ohisson retired engine manufacturer AMA Hall Famer has considerable success floats hulls radio control Shown Irwins Grumman Widgeon data supplied Ohlsson Fol lowing Irwins comments hull table specifications configuration first step changed double concave also two sponsons added sides hull bow first step Small spray rails extend outboard length sponsons tunnel de sign gives smooth low power takeoff sponsons spray rails deflect water props original full-scale aircraft 2% degree positive wing incidence reduced 0 degrees model After first flightwith Joe Bridi test pilotit came off water before reached its flying speed stalled nose wing down landplane would have bought farm However bounced out water like basketballnot scratch Since day April 1974 about 50 flights have madenever has wet real good stable fast flying machine Specifications Twin-Engine Widgeon Span 80 chord center section 13% tip 8 hull overall 54 Weight empty 13 lbs weight fueled 15 lbs Power2 contra-rotation 61 Perry pumpsfuel 500cc nacelleprops 11 x 7Y2 left right handthrottles 2one nacelle Controls Flaps Aileron Rudder Elevator Construction Wing2 main spars balsa ribs 2 apart sheet balsa silk covered butyrate doped plywood engine mounts rear spar Hullspruce keel balsa sheeted bottom 3/32 balsa 1/32 x 3 plywood glassed top sides silk covered butyrate dope April1979 11 Noting jet engineno prop clearance problemsmade possible blended hull Powers cites Skate shown moaei tesi tow RACING AIRPLANE AVERAGE___ AIRPLANE LIGHTPLANE Lu 0 0 IL L - 7approx / S 1/ EXCESS THRUSTAVAILABLE FOR TAKE-OFF THRUST 2 L RESISTANCE HUMP 18 10 TAKE-OFF SPEED must literally climb order level off plane gather takeoff speed hump region operation critical regard power indicated Fig 1 Obviously airplane accelerate take off thrust must greater resistance Otherwise will just cruise around water until fuel gone Fig 1 racing airplane has very high water resistance presumably due small floats achieve low air drag since Fig 1 high speed design has sufficient thrust cope resistance As apparent thrust available average airplane used racer takeoff speed would impossible since airplane could never ride over hump Since model engines available appear adequate cases should justified applying average~ rather marginal criteria designing float As aspects airplane design VOLUME Lb2 VOL b b VOLL2b compromises between conflicting require ments generally being sought case hulls floats boils down finding nice balance betweeen size displacement Large floats have advan tage low immersion light spray weigh have higher air drag Small floats sink too deeply water makes heavy spray high water resistance So can say except refinements design actual float itself basic problem find proper size job keeping both float size spray minimum commensu rate power orother limiting factors Early float designers found after much experimentation floats having length beam ratios less about 6/1 didnt work very well seven seemed best average conditions acceptable per formance water achieved draft early floats such displacement value approx imating cubical container filled water having same dimensions side beam float Thus float beam 3 ft could expected perform satisfactorily displaced amount water could placed cubical container 3 ft side Such float would displace 33 27 cu ft sea water Since sea water has density 64 lb/cu ft weight water 1728 lbs pair such floats would right average airplane weighing about 3450 lbs As pointed out Fig 1 could vary considerably non average conditions Once relationship estab lished easy matter scale floats up down suit different gross weights long same family reasonably close being geome trically similar relationship came called beam loading expressed non-dimensional terms W 3andhadavalueoflOwhen wb length/beam ratio seven W equals Load Carried Floatlbs w equals Density Sea Water 4 lbs/cu ft b equals Beam FloatFeet criterion expressed graphically Fig2 Although shown simple cube Fig 2 applies L/b ratio seven L/b 6 value C of75 worked best since L/b decreased Beam increased same token increases L/b accompanied decreases beam requiring corresponding increases values C During WW II studies made configurations floats particularly hulls involving length/beam ratios order 8 10 higher 12 Model Aviation b.Kbb COMPARING CRITERIA found longer hulls less air drag less water resistance less way nasty characteristics like hobby horsing~ porp oising pitching back forth under way selecting length/beam ratio float strong consideration given value 8 finally ruled out due excessive length fact typical scale applications early seaplanes However after have finished article should able design float having high L/b wish float described will have value L/b investigation progressed became apparent immersion coefficient would useful contained provision beam length well Accordingly new term developed engineers called K2 w equal w L2 b Like C K2 nondimensional does indeed account length well beam Recom mended values K2 range 018 light spray low power 022 heavy spray high power 020 representing good criterion average~ conditions float therefore will based indirectly value 020 However look Fig 2 see volume portion term L2b resolves itself large cakepan 2 percent full bears little physical resemblance float So based K2 tried true parameter lets devise term just purpose multiply K2 length/beam ratio increase amount also get cakepan carton has same overall dimensions float follows K2so X K2 wL2bb Lx W — W c bwL2bwLb2 C1 ficient Immersion Lb2 gives us figure fits float like shoe box carton shown figure top Fig 2 So term C1 derived K2 constant like K2 varies length/beam ratio said float has value 7 X K2 7 X 020 140 shown figure 3 As can seen C really percent age displacement float bears its carton makes cozier relationship wish reconcile parameters fully correlation between C K2 shown Fig 4 Now lets proceed design float First must find beam whch turn requires value displacement W watch weight think can put pair floats Nosen Citabria already weighs 18 lbs about 32 lbs Thus gross weight will 25 lbs LENGTH/BEAM RATIO vs Cj 8-7 b 6bf LCi b 144 160 126140154HEAVY OUR FLOAT 101121314 dispi float W dispi artonwLb2 I0 L b 15161718 Fig 3 K2 COMPARED WITH 0 OUR FLOAT 0 . LIGHT SPRAY K2018 7 MODERATE 020 6 HEAVY 022 EXCESSIVE 025 5 2 Fig 4 34 5 68 CW 125 April 1979 13 20 Dornier X 12-engined flying boat built 1929 photo has radial engines arranged tandem pairs After transatlantic crossing turned turtle tropical storm CONVENTIONAL FLOAT t217 Al curve ares r2 7b 77 20 2022 / / 2 25 225 -2 10304222 IS oisoc. 926 [2 DeejI F24Ih0 02p2[ 942 W05N9044IIb25jyf 4404 h224&Ih1l 410 2STSP/C0NTROOISO40 t f J 0 10 42240 V Fig 5 float will carry 125 lbs So W equals 125 lbs C2 said 140 W C2 2 expression two unknowns b L So will have express L terms b making WW wLbbzw7b3 andbeamb3 W — w7 C 125 64 X 7 X 140 584 ft or7in Since length/beam ratio seven length 7 Now lets check results another way said C percentage displacement float carton 14 percent carton has displacement 7 X 7 X 4 8893 lbs 1728 14 percent 8893 1245 lbs close enough point might wise reassess things consider other values planning build model 3-lb camera may added later going fly fresh water lake having water density 624 lb/cu ft might wiser pick value C2 126 shown Fig 3 rather 140 reduce draft lighten spray give some room grow particularly think powerplant marginal beam will become 725 length 5075 However will add around 10 percent weight float Now some discussion before tackle details Obviously float should aerodynamically clean can make So might say Ok lets make streamlined like wing tip fuel tank sounds good streamlined bodies completely immersed tend suck under speak takeoff impossible final analysis wing generates lift deflecting thus accelerating mass air downward float completely streamlined partially immersed actually deflects water upward thus sinking deeper deeper power applied speed remains essentially constant displacement vessels sailing yachts have less fixed maximum speed no matter much extra power wind available just sink deeper deeper like bottom teaspoon suspended against water flowing faucet other hand hull bottom vicinity step transom flat like water ski v-shaped like speed boat water departs step float rides up skims over water deriving lift much same way wing slighting deflecting water down ward gaining lift thereby derived form dynamic pressure hull bottom Actually forebody its transom step does work afterbody primarily provide static buoyancy rest aircraft doesnt rock back its tail Indeed Lou Proctors Antic has forward floats really forebodies coupled small efficient afterbody form small float tail Minimum air drag critical matter models faithful attention detail scale models requires easy lines generous step depth needed assure clean departure wake doesnt tend reattach afterbody cause porpoising plus generous landing angle will handle problem forebody lines should sharp easy keep hull resistance minimum large aircraft ample deadrise needed minimize decelerations landing Deadrise should 14 Model Aviation 226 find center buoyancy Trace curve areas onto cardboard balance three ways edge ruler marking line time Intersection centroid area figurecenter buoyancy float 4 j3-I RAZOR SHARP CHINES Fig 6 TRUE AREAS SQ INf337 316 EI$II LIII -__ IPORT VIEW LEFT FLOAT OUTBOARD CHINE 16 r -eTAogrIb, VINBARD CHINE 0 11 FLOAT PROBLEMS Construct curve areas find 1 Displacement pounds 2 Center Bouyancy LSO 3 Length/Beam Ratio disregarding rounded ends tapered sides 4 Length Beam displacements 1 lb 5 lbs 10 lbs increase go forward along forebody sharpen hull lines provide stability trim Adequate buoyancy afterbody easier attain deadrise held constant initial application power takeoff produces powerful nose-down moment seaplanes must countered adequate forebody displacement will tend resist moment quickly smoothly avoid forebody porpoising char acteristic low length/beam ratio hulls having insufficient restoring moment standpoint L/b 8 would better float would begin get too long landing angle would suffercompro mises again Landing Angle No2 corresponds similar angle landplane Its purpose allow step wheels make initial contact angle close 90 percent stalling angle wing permit slowest possible 912 1 2 REOD PORT AND STARBOARD 17 16 15 114 13 12 1 II II 7k 8 14518 5 18 3 gPORT FLOAT SHOWN -. FLOAT OPPOSITE II 212426 Ti OHLSSON FLOAT 1213 WEIGHT W/ FLOAT. LBS landing speed Since impact forces vary square speed small reductions speed accompanied sizeable increases safety float landing angle 14 15 Fig 7 9 degrees coupled 3 degrees wing incidence 12 degrees Clark Y airfoil small Reynolds Numbers corresponds guidelines just mentioned 1 2 3 4 ANSWERS TO FLOAT PROBLEMS Fig 8 Displacement 298 say 3 lbs CB Station 134 just forward Step 1/B 26/4 equals 65 Dimensions vary cube root Ratio Displacements So 1 lb dimensions will Ohlsson float timesthe cube root 1/3 693 So equals 693 x 26 18 end B 593 x 4 277 Similarly 5 lbs 307 B 472 10 lbs L 3875 B 595 say 6 Note Since float different family conventional float geomet rically related values CW Ci would comparable VOLUME 4 CtiINV2SOLU OF OUYANC April1979 15 FLOAT TOO SMALL LOAT FLOAT TOO LARGE static trim CG complete airplane must obviously lie perpendic ular waterplane passes through Center Buoyancy float indicated Item 29 Fig 5 Item 2 Fig 5 shows landing angle mentioned above As can seen step centroidof V-step Item 22 Fig 5 should slightly aft Center Buoyancy place directly under CG landing 30 order keep float axis parallel fuselage usually desirable flight angle static trim Item 13 Fig 5 3 degrees producing slightly nose up attitude airplane static rest water undesirable have axis airplane parallel waterplane would mean placing floats slightly nose up else reducing forebody displacementneither good Flare No 12 directs spray helps control its effects Judicious use spray dams blinders metal strips flush sides float projecting about half inch below chine can reduce spray dramatically carried too far forward made too large can destabilizing flight probably best experiment little bit Because forward portions floats destabilizing flight necessary add substantial increment fin area compensate shown No 24 Since floats will also produce negative diving moment elevator trim order preferably some means adjusting horizontal stabilizer toe-in recommended procedure installing wheels landplane no-no floats very necessary mounted firmly accurately Water forces high unforgiving afterbody float tapers back flat transom large enough accomodate water rudder mounting brackets outlets internal pushrods water rudder should placed float its pivot line should 2530% its chord Its area critical make about size proportion shown respect size float So much generalities Now lets put Fig 5 front us study steps involved creating particular float Lay out 7 X 49 carton side view 3 X 49 half plan below 7 X 7 box left Note height float equals beam mainly simplify geometry article height could increased say used basis single hull design ever should decreased excess buoyancy very necessary Theoretically could slice float off just above waterline did extra ounce fuel added servo could sink whole kaboodle Draw center line 3 Draw upper deck lines shown forebody duplicate below plan view forebody shown above chine elliptical prolate spheroid anybody interested doesnt have Make shape matches picture favorite seaplane wish Locate Step 1 As first approxi mation lets assume Sta 26 26 aft nose Later might want change bit Lets hope Draw landing angle 2 heel step up center line Sta 49 Make step depth 8 afterbody keel 7 Draw forebody keel 6 Note carries well forward does match curve deck line top sharpen entry side view left draw circular cross sections upper forebody deck down center line drop vertical tangents circular cross section meets center line tangents Sta 6 forward should extend above 16 Model Aviation Mercury Racer Granger WIlliams repose La Costa CA sloughlntended Schneider Trophy race flown Al Williams real Mercury grossly overweight Brad Powers left Irwin Ohlsson latters highly successful twinfloat design using floats own design championship free-flighter Thirties later manufacturer engines exAMA president Hall Famer Irwin builds designs best center line Starting step Sta 26 draw deadrise angle 4 20 degrees Its inter section vertical tangent just drew determines aft point theoret ical chine 9 Draw theoretical chine 9 establishes smooth variation deadrise go forward Back step section again draw chine flare 12 Its intersection vertical tangent establishes aft end forebody chine 10 Draw forebody chine 10 shown Near Station 6 curve reverses lie fore aft direction make clean aerodynamic entry Assuming theoret ical chine lie curved surface touching side hull therefore intersecting vertical tangents drew draw deadrise Station add flare tangent deadrise horizontal chine flare should have generous radiusbut excessive Now draw afterbody deadrise Station other side end view plan view drew beginning establish afterbody chine both end side views 11 Using afterbody planform deter radii draw locus radii 18 side view complete sections afterbody end view point good idea draw some 'buttock lines' 'water lines' end view shown project other views see fair fair smooth fiddle drawing bit until 23 region between Sta 18 step bottom should have straight buttock lines insure stable planning other words hull bottom surfaces should have no fore aft curvature region Draw trial static load water line sloping up aft 3 degrees through point 3 above keel step 14 information end view water line construct sections shown hatched station Measure sections determine area section Since half sections dont forget multiply area 2 plot values shown 26 establish acurve areas Just volume deck cards sum cards area under curve summation infinite number cross sectional areas therefore represents volume immersed portion float Since before reproduction maga zine drawing made half scale areas have indicated obtained half scale drawing will have corrected full scale will shortly true well length curve areas drawn 1/5 scale expression shape curve areas could add up integrate mathematically since arbitrarily determined its slope choices deadrise flare chine chape etc no way establish slope area curve mathematically must integrate graphically can done close approximation adding areas successive steps 27 judiciously done better way use device called polar planimeter have done gives area under curve 169 sq just pointed out areas taken one-half scale drawing therefore have fourth full-size areas because areas varies scale squared Also said length figure one-fifth actual float must multiply 169 5 times 4 20 have correct figure since value volume cu must divide number cu in cu ft get cu ft can multiply 64 weight cu ft sea water we see float indeed displaces 1252 lbs indicated Fig 5 about draft 3 good guesstimate As shown Fig 7 float should loaded carry much over 13 pounds spray will get too heavy other hand float carry much less 11 pounds will too big heavy smaller float should used Well now know draft displacement what Before can screw floats onto airplane have know buoyancy concentrated way find Center Buoyancy trace curve areas onto piece cardboard no lumps cut out balance shown picture Balance least three ways mark time have careful marks will intersect point centroid area figure Center Buoyancy float 21 Incidentally good way find centroids such things elliptical wings centers lateral area other irregular shapes Now can relate float Nosen Citabria 19 above described earlier shown Fig 5 good stability control CG 20 should 25% mean aerody namic chord MAC wing Since Citabria has rectangular planform amounts 25 percent root chord indicated 17 Fortunately Center Buoyancy falls just want landing angle right step fortuitous because have struggling days get together Actually little both aerodynamically unfortunate carrying large appendages like floats way out arms length speak clearances shown 6 at31 learance 20-in propeller float spacing 3 beams 21 33 should reduced keep airplane its vitals being inun dated choppy water spray covers general way preliminary design float great other aspects covering water resistance trimming moments etc have left untouched felt really essential modeler putting floats pride joy intention article es tablish basic criteria Prelimi nary Design future article will presented Detail Design Continued page 98 April1979 17 Line-up RC seaplane models Lto R Bob Wisniewakis modIfied Lancer single pontoon wing-tip floats Granger Williams sport model similar configuration Granger Williams Mercury twin floats Gary Neelys modified sport biplane twin floats Main floats models same Mercury design molded foam plastic Openers/Winter continued page 72 have something tell As RCer FOs chief interest CL Racing frantic aerobatics pilots center circle will find Bill Lee CL Racing talking about home-made fibreglass props Bill Wynn Paul too guy endlessly seeks truth about tanks things like props doing experimenting finding para meters Dave Chesney writes beautifully RC Helicopters column existence now Bill Warner Sport/Scale will put humor life flying circus note others gang Without guys like us would never know about hundreds things add up sum total skills Brad Powers lead article floats quarter-scale landmark article Model aviation old century yet explosion knowledge techniques products never dared dream about what know about floats would fit smallest drawer field box So designer partook dozens famous pro jects made history modeler boot telling us design float virtually size modelas well monsters weve yet see water Note feed-inIrwin Ohlsson great Ernie Stout Convair fame What suggesting dear friend April issue however excep tional 12 year talking about magazine Within another yearGod willingit will thousand light years beyond April 1976 MA began July 1975 its modern form ask conscious magazine contro versial terms some other magazines have shown theyd like see deadbut inspect closely what speak especially minority members did subscribe MA past yours wed like proud AS WE GO TO PRESS sad news ar rives passing Myron Mike Schlesinger recent past president Top Flite Models Mike respected friend industry innumerable modelers true pioneer helped start Top Flite its way chaired trade show committee 1956 became member HIAAs board directors served nearly 10 years chairman co-chairman HIAAs Model Aeronautics Division Hu morous easy going always compassion ate understanding Mike Schlesinger will truly missed us Floats Powers continued page 17 actual floats installed Citabria model together summary results some photos Irwin Ohlsson thirties deve loped line famous Ohlsson engines now retired builds beautiful model seaplanes has given pair floats developed has found very satisfactory straightforward design have generous step landing angle embody progressive deadrise Rather present float complete its displacement Center Buoyancy etc ready determined will give its dimensions trim another guesstimate draft 16 40 percent its beam data procedures already discussed up find answers problems Fig 6 shows float answers will found illustration Answers Float Prob lems Finally wish express thanks Ernest G Stout former Chief Hydrody namics Convair worked interesting projects sistance providing data presented herein Now am going start building float build finish before write let know works can de cide whether stay leave Tierra Del Fuego RC Technique/Myers continued page 19 control thats going wrong way move pushrod hole opposite side output wheel frequently make such change field someone needs disadvantage approach pushrods usually get tangled you end up product review product review product review Radial Engines man has thingultra deluxe 57-cylinder scale-like engines /4 scale 4-cycle high-torque swing 16-8 through 20-6 props Low vibra tion low fuel consumption mild glow fuel 6-in diameter 23 oz weight 7cylinder engines offered 3 versionspol ished aluminum anodized black deluxe Collectors Gold Edition package trimmed 14K gold Manufacturer states fully opera tional warranted 90 dayssold direct Executive Engines Co 16650 S 104th Ave Orland Park IL 60462 product review product review product review swapping rudder elevator servos side-by-side using Nyrod often finds surgery neces sary because outer shell has anchored location doesnt allow shift connection other side wheel Wouldnt nice could just throw reversing switch servo point Bobs eyes lit up Ill bet Ace R/C Bantam Midget machinery will fit regular Bantam case says leave enough room servo reverser dont see what can idea George kicked around some possibilities until time get back work few days later Bantam case Bantam Midget servo appeared desk magic Christmas came bit early year thought until Bob told wanted back after youve finished rever sing switch first thought make use 16pin DIP switch After little consideration possibilities left open direct short across batteries dropped idea Besides switch too big Next tried 4PDT Noble switch commonly used switch harnesses RC systems can made fit little help Dremel problem will have take out servo get switch smaller switch could mounted right out open can get couldnt find Slightly later Bob left another goodie desk prototype servo reverser ACE R/C few mods could fit space available would left servo having two pigtails rotation Plug need configuration left project returned servo Bob must careful let unused plug short out metal parts because will short out batteries kill whole system As said before like idea having servo reverser receiver todays IC circuitry major configuration change would adding second set sockets other rotation Its fair mention Kraft has shipping sets 10 years have two servos set up direction Editors NoteLike feature Cox-Sanwa get what want swapping around dot no dot servos dot tiny circle molded mounting flange between cutouts grommets Once get flight pack set up right theres no way make mistake Thats way like things Over years have bought flight packs transmitters work plane until control trims throws right transmitter trim levers center position leave everything alone until needs service way can pick plane off wall go flying worrying its compatible 98 Model Aviation
Edition: Model Aviation - 1979/04
Page Numbers: 10, 11, 12, 13, 14, 15, 16, 17, 98
FOR variety reasons early speculation about future aviation painted rosy picture seaplanes During interval between two world wars seaplanes set speed records crossed oceans offered great promise future Since through out world almost city size situated near important body water feeling build expensive space consuming airports 1929 Claude Dornier building remarkable seaplane shown pic ture american industrial designer Nor man Bel Geddes busy collaboration Dr Otto Koller designer Ger man Pfalz biplane Together worked up design enormous flying boat wing span 528 feet deck below water line eight decks above have 20 1 900-hp engines includ ing engine repair shop root wing 22 feet thick gross weight 1275000 pounds would believe behemoth designed cruise fantastic speed 100 mph 5000 feet some reason never built Now discredit man Larry Williams taxies Supermarine S4 waters Lake Elsinora CA prior contest-winning flight powered K&8 front-rotor engine Warren Shipp photo Norman Bel Geddes true genius ideas kitchen ranges elevated freeways have become reality simply show fast actual progress can overtake wildest dreams gifted advent all-metal stressed skin monoplanes retractable gear landplanes suddenly stopped looking like Jennies began look today Seaplane designers other hand could never figure out way retract floats within sensible weight allowance density seawater just wasnt great enough floats hulls always too big invariably added up drag just simple landplane fuselage Since drag means fuel increased fuel meant corresponding reductions range pay load translated reductions reve nues wasnt until jet engine came along eliminating large clearances re quired propellers designers able create seaplanes such Skate shown model photo could compete drag-wise landplane time airports finally built Iandplanes stolen show 10 Model Aviation Larrys Supermarine overhead later lowwing Supermarines among beautiful ali aircraft laid groundwork Spit fire designed RJ Mitchell Shipp photo Other factors also determined de mise seaplane Rough seas landing areas werent always calm areas congested unsafe handling mooring maintenance difficulties say nothing severe corrosive effects sea water aluminum alloy hulls Numerous approaches problem operating aircraft water have made include variety floats varying shapes skis hydrofoils large hulls literally stabilized tip floats spon sons blended configuration Skate shown photo exception last item possibly hydrofoils think modelers have man aged adapt others models varying degrees success ducted fan makes both hydrofoils blended hull-wing attractive possibilities since out propeller clearances deal inter esting ideas suggest themselves will leave notions another time devote article understanding principles underlying simple scale type floats appropriate scale model will try use procedures learned evaluate excellent model type float given Irwin Ohlsson might think float piece functional sculpture must perform following 1 Provide adequate buoyancy rest 2 Provide minimum resistance motion through water during progressive stages takeoff 3 Provide smooth stable variations trim during takeoff landing since pilot has little no control over trim attitude low speeds water 4 Provide stable reasonably soft landing entry course minimum weight air drag well have ridden water skis aboard speedboat power cruiser familiar changing attitudes craft starts move nose begins rise untilif sufficient power available will gain enough speed level off plane An airplane floats does same thing As moves forward pushes sizeable volume water ahead itself creating large wave hump over OHLSSONS WIDGEON DURING preparation Mr Powers article both Brad editor con sulted Irwin Ohisson retired engine manufacturer AMA Hall Famer has considerable success floats hulls radio control Shown Irwins Grumman Widgeon data supplied Ohlsson Fol lowing Irwins comments hull table specifications configuration first step changed double concave also two sponsons added sides hull bow first step Small spray rails extend outboard length sponsons tunnel de sign gives smooth low power takeoff sponsons spray rails deflect water props original full-scale aircraft 2% degree positive wing incidence reduced 0 degrees model After first flightwith Joe Bridi test pilotit came off water before reached its flying speed stalled nose wing down landplane would have bought farm However bounced out water like basketballnot scratch Since day April 1974 about 50 flights have madenever has wet real good stable fast flying machine Specifications Twin-Engine Widgeon Span 80 chord center section 13% tip 8 hull overall 54 Weight empty 13 lbs weight fueled 15 lbs Power2 contra-rotation 61 Perry pumpsfuel 500cc nacelleprops 11 x 7Y2 left right handthrottles 2one nacelle Controls Flaps Aileron Rudder Elevator Construction Wing2 main spars balsa ribs 2 apart sheet balsa silk covered butyrate doped plywood engine mounts rear spar Hullspruce keel balsa sheeted bottom 3/32 balsa 1/32 x 3 plywood glassed top sides silk covered butyrate dope April1979 11 Noting jet engineno prop clearance problemsmade possible blended hull Powers cites Skate shown moaei tesi tow RACING AIRPLANE AVERAGE___ AIRPLANE LIGHTPLANE Lu 0 0 IL L - 7approx / S 1/ EXCESS THRUSTAVAILABLE FOR TAKE-OFF THRUST 2 L RESISTANCE HUMP 18 10 TAKE-OFF SPEED must literally climb order level off plane gather takeoff speed hump region operation critical regard power indicated Fig 1 Obviously airplane accelerate take off thrust must greater resistance Otherwise will just cruise around water until fuel gone Fig 1 racing airplane has very high water resistance presumably due small floats achieve low air drag since Fig 1 high speed design has sufficient thrust cope resistance As apparent thrust available average airplane used racer takeoff speed would impossible since airplane could never ride over hump Since model engines available appear adequate cases should justified applying average~ rather marginal criteria designing float As aspects airplane design VOLUME Lb2 VOL b b VOLL2b compromises between conflicting require ments generally being sought case hulls floats boils down finding nice balance betweeen size displacement Large floats have advan tage low immersion light spray weigh have higher air drag Small floats sink too deeply water makes heavy spray high water resistance So can say except refinements design actual float itself basic problem find proper size job keeping both float size spray minimum commensu rate power orother limiting factors Early float designers found after much experimentation floats having length beam ratios less about 6/1 didnt work very well seven seemed best average conditions acceptable per formance water achieved draft early floats such displacement value approx imating cubical container filled water having same dimensions side beam float Thus float beam 3 ft could expected perform satisfactorily displaced amount water could placed cubical container 3 ft side Such float would displace 33 27 cu ft sea water Since sea water has density 64 lb/cu ft weight water 1728 lbs pair such floats would right average airplane weighing about 3450 lbs As pointed out Fig 1 could vary considerably non average conditions Once relationship estab lished easy matter scale floats up down suit different gross weights long same family reasonably close being geome trically similar relationship came called beam loading expressed non-dimensional terms W 3andhadavalueoflOwhen wb length/beam ratio seven W equals Load Carried Floatlbs w equals Density Sea Water 4 lbs/cu ft b equals Beam FloatFeet criterion expressed graphically Fig2 Although shown simple cube Fig 2 applies L/b ratio seven L/b 6 value C of75 worked best since L/b decreased Beam increased same token increases L/b accompanied decreases beam requiring corresponding increases values C During WW II studies made configurations floats particularly hulls involving length/beam ratios order 8 10 higher 12 Model Aviation b.Kbb COMPARING CRITERIA found longer hulls less air drag less water resistance less way nasty characteristics like hobby horsing~ porp oising pitching back forth under way selecting length/beam ratio float strong consideration given value 8 finally ruled out due excessive length fact typical scale applications early seaplanes However after have finished article should able design float having high L/b wish float described will have value L/b investigation progressed became apparent immersion coefficient would useful contained provision beam length well Accordingly new term developed engineers called K2 w equal w L2 b Like C K2 nondimensional does indeed account length well beam Recom mended values K2 range 018 light spray low power 022 heavy spray high power 020 representing good criterion average~ conditions float therefore will based indirectly value 020 However look Fig 2 see volume portion term L2b resolves itself large cakepan 2 percent full bears little physical resemblance float So based K2 tried true parameter lets devise term just purpose multiply K2 length/beam ratio increase amount also get cakepan carton has same overall dimensions float follows K2so X K2 wL2bb Lx W — W c bwL2bwLb2 C1 ficient Immersion Lb2 gives us figure fits float like shoe box carton shown figure top Fig 2 So term C1 derived K2 constant like K2 varies length/beam ratio said float has value 7 X K2 7 X 020 140 shown figure 3 As can seen C really percent age displacement float bears its carton makes cozier relationship wish reconcile parameters fully correlation between C K2 shown Fig 4 Now lets proceed design float First must find beam whch turn requires value displacement W watch weight think can put pair floats Nosen Citabria already weighs 18 lbs about 32 lbs Thus gross weight will 25 lbs LENGTH/BEAM RATIO vs Cj 8-7 b 6bf LCi b 144 160 126140154HEAVY OUR FLOAT 101121314 dispi float W dispi artonwLb2 I0 L b 15161718 Fig 3 K2 COMPARED WITH 0 OUR FLOAT 0 . LIGHT SPRAY K2018 7 MODERATE 020 6 HEAVY 022 EXCESSIVE 025 5 2 Fig 4 34 5 68 CW 125 April 1979 13 20 Dornier X 12-engined flying boat built 1929 photo has radial engines arranged tandem pairs After transatlantic crossing turned turtle tropical storm CONVENTIONAL FLOAT t217 Al curve ares r2 7b 77 20 2022 / / 2 25 225 -2 10304222 IS oisoc. 926 [2 DeejI F24Ih0 02p2[ 942 W05N9044IIb25jyf 4404 h224&Ih1l 410 2STSP/C0NTROOISO40 t f J 0 10 42240 V Fig 5 float will carry 125 lbs So W equals 125 lbs C2 said 140 W C2 2 expression two unknowns b L So will have express L terms b making WW wLbbzw7b3 andbeamb3 W — w7 C 125 64 X 7 X 140 584 ft or7in Since length/beam ratio seven length 7 Now lets check results another way said C percentage displacement float carton 14 percent carton has displacement 7 X 7 X 4 8893 lbs 1728 14 percent 8893 1245 lbs close enough point might wise reassess things consider other values planning build model 3-lb camera may added later going fly fresh water lake having water density 624 lb/cu ft might wiser pick value C2 126 shown Fig 3 rather 140 reduce draft lighten spray give some room grow particularly think powerplant marginal beam will become 725 length 5075 However will add around 10 percent weight float Now some discussion before tackle details Obviously float should aerodynamically clean can make So might say Ok lets make streamlined like wing tip fuel tank sounds good streamlined bodies completely immersed tend suck under speak takeoff impossible final analysis wing generates lift deflecting thus accelerating mass air downward float completely streamlined partially immersed actually deflects water upward thus sinking deeper deeper power applied speed remains essentially constant displacement vessels sailing yachts have less fixed maximum speed no matter much extra power wind available just sink deeper deeper like bottom teaspoon suspended against water flowing faucet other hand hull bottom vicinity step transom flat like water ski v-shaped like speed boat water departs step float rides up skims over water deriving lift much same way wing slighting deflecting water down ward gaining lift thereby derived form dynamic pressure hull bottom Actually forebody its transom step does work afterbody primarily provide static buoyancy rest aircraft doesnt rock back its tail Indeed Lou Proctors Antic has forward floats really forebodies coupled small efficient afterbody form small float tail Minimum air drag critical matter models faithful attention detail scale models requires easy lines generous step depth needed assure clean departure wake doesnt tend reattach afterbody cause porpoising plus generous landing angle will handle problem forebody lines should sharp easy keep hull resistance minimum large aircraft ample deadrise needed minimize decelerations landing Deadrise should 14 Model Aviation 226 find center buoyancy Trace curve areas onto cardboard balance three ways edge ruler marking line time Intersection centroid area figurecenter buoyancy float 4 j3-I RAZOR SHARP CHINES Fig 6 TRUE AREAS SQ INf337 316 EI$II LIII -__ IPORT VIEW LEFT FLOAT OUTBOARD CHINE 16 r -eTAogrIb, VINBARD CHINE 0 11 FLOAT PROBLEMS Construct curve areas find 1 Displacement pounds 2 Center Bouyancy LSO 3 Length/Beam Ratio disregarding rounded ends tapered sides 4 Length Beam displacements 1 lb 5 lbs 10 lbs increase go forward along forebody sharpen hull lines provide stability trim Adequate buoyancy afterbody easier attain deadrise held constant initial application power takeoff produces powerful nose-down moment seaplanes must countered adequate forebody displacement will tend resist moment quickly smoothly avoid forebody porpoising char acteristic low length/beam ratio hulls having insufficient restoring moment standpoint L/b 8 would better float would begin get too long landing angle would suffercompro mises again Landing Angle No2 corresponds similar angle landplane Its purpose allow step wheels make initial contact angle close 90 percent stalling angle wing permit slowest possible 912 1 2 REOD PORT AND STARBOARD 17 16 15 114 13 12 1 II II 7k 8 14518 5 18 3 gPORT FLOAT SHOWN -. FLOAT OPPOSITE II 212426 Ti OHLSSON FLOAT 1213 WEIGHT W/ FLOAT. LBS landing speed Since impact forces vary square speed small reductions speed accompanied sizeable increases safety float landing angle 14 15 Fig 7 9 degrees coupled 3 degrees wing incidence 12 degrees Clark Y airfoil small Reynolds Numbers corresponds guidelines just mentioned 1 2 3 4 ANSWERS TO FLOAT PROBLEMS Fig 8 Displacement 298 say 3 lbs CB Station 134 just forward Step 1/B 26/4 equals 65 Dimensions vary cube root Ratio Displacements So 1 lb dimensions will Ohlsson float timesthe cube root 1/3 693 So equals 693 x 26 18 end B 593 x 4 277 Similarly 5 lbs 307 B 472 10 lbs L 3875 B 595 say 6 Note Since float different family conventional float geomet rically related values CW Ci would comparable VOLUME 4 CtiINV2SOLU OF OUYANC April1979 15 FLOAT TOO SMALL LOAT FLOAT TOO LARGE static trim CG complete airplane must obviously lie perpendic ular waterplane passes through Center Buoyancy float indicated Item 29 Fig 5 Item 2 Fig 5 shows landing angle mentioned above As can seen step centroidof V-step Item 22 Fig 5 should slightly aft Center Buoyancy place directly under CG landing 30 order keep float axis parallel fuselage usually desirable flight angle static trim Item 13 Fig 5 3 degrees producing slightly nose up attitude airplane static rest water undesirable have axis airplane parallel waterplane would mean placing floats slightly nose up else reducing forebody displacementneither good Flare No 12 directs spray helps control its effects Judicious use spray dams blinders metal strips flush sides float projecting about half inch below chine can reduce spray dramatically carried too far forward made too large can destabilizing flight probably best experiment little bit Because forward portions floats destabilizing flight necessary add substantial increment fin area compensate shown No 24 Since floats will also produce negative diving moment elevator trim order preferably some means adjusting horizontal stabilizer toe-in recommended procedure installing wheels landplane no-no floats very necessary mounted firmly accurately Water forces high unforgiving afterbody float tapers back flat transom large enough accomodate water rudder mounting brackets outlets internal pushrods water rudder should placed float its pivot line should 2530% its chord Its area critical make about size proportion shown respect size float So much generalities Now lets put Fig 5 front us study steps involved creating particular float Lay out 7 X 49 carton side view 3 X 49 half plan below 7 X 7 box left Note height float equals beam mainly simplify geometry article height could increased say used basis single hull design ever should decreased excess buoyancy very necessary Theoretically could slice float off just above waterline did extra ounce fuel added servo could sink whole kaboodle Draw center line 3 Draw upper deck lines shown forebody duplicate below plan view forebody shown above chine elliptical prolate spheroid anybody interested doesnt have Make shape matches picture favorite seaplane wish Locate Step 1 As first approxi mation lets assume Sta 26 26 aft nose Later might want change bit Lets hope Draw landing angle 2 heel step up center line Sta 49 Make step depth 8 afterbody keel 7 Draw forebody keel 6 Note carries well forward does match curve deck line top sharpen entry side view left draw circular cross sections upper forebody deck down center line drop vertical tangents circular cross section meets center line tangents Sta 6 forward should extend above 16 Model Aviation Mercury Racer Granger WIlliams repose La Costa CA sloughlntended Schneider Trophy race flown Al Williams real Mercury grossly overweight Brad Powers left Irwin Ohlsson latters highly successful twinfloat design using floats own design championship free-flighter Thirties later manufacturer engines exAMA president Hall Famer Irwin builds designs best center line Starting step Sta 26 draw deadrise angle 4 20 degrees Its inter section vertical tangent just drew determines aft point theoret ical chine 9 Draw theoretical chine 9 establishes smooth variation deadrise go forward Back step section again draw chine flare 12 Its intersection vertical tangent establishes aft end forebody chine 10 Draw forebody chine 10 shown Near Station 6 curve reverses lie fore aft direction make clean aerodynamic entry Assuming theoret ical chine lie curved surface touching side hull therefore intersecting vertical tangents drew draw deadrise Station add flare tangent deadrise horizontal chine flare should have generous radiusbut excessive Now draw afterbody deadrise Station other side end view plan view drew beginning establish afterbody chine both end side views 11 Using afterbody planform deter radii draw locus radii 18 side view complete sections afterbody end view point good idea draw some 'buttock lines' 'water lines' end view shown project other views see fair fair smooth fiddle drawing bit until 23 region between Sta 18 step bottom should have straight buttock lines insure stable planning other words hull bottom surfaces should have no fore aft curvature region Draw trial static load water line sloping up aft 3 degrees through point 3 above keel step 14 information end view water line construct sections shown hatched station Measure sections determine area section Since half sections dont forget multiply area 2 plot values shown 26 establish acurve areas Just volume deck cards sum cards area under curve summation infinite number cross sectional areas therefore represents volume immersed portion float Since before reproduction maga zine drawing made half scale areas have indicated obtained half scale drawing will have corrected full scale will shortly true well length curve areas drawn 1/5 scale expression shape curve areas could add up integrate mathematically since arbitrarily determined its slope choices deadrise flare chine chape etc no way establish slope area curve mathematically must integrate graphically can done close approximation adding areas successive steps 27 judiciously done better way use device called polar planimeter have done gives area under curve 169 sq just pointed out areas taken one-half scale drawing therefore have fourth full-size areas because areas varies scale squared Also said length figure one-fifth actual float must multiply 169 5 times 4 20 have correct figure since value volume cu must divide number cu in cu ft get cu ft can multiply 64 weight cu ft sea water we see float indeed displaces 1252 lbs indicated Fig 5 about draft 3 good guesstimate As shown Fig 7 float should loaded carry much over 13 pounds spray will get too heavy other hand float carry much less 11 pounds will too big heavy smaller float should used Well now know draft displacement what Before can screw floats onto airplane have know buoyancy concentrated way find Center Buoyancy trace curve areas onto piece cardboard no lumps cut out balance shown picture Balance least three ways mark time have careful marks will intersect point centroid area figure Center Buoyancy float 21 Incidentally good way find centroids such things elliptical wings centers lateral area other irregular shapes Now can relate float Nosen Citabria 19 above described earlier shown Fig 5 good stability control CG 20 should 25% mean aerody namic chord MAC wing Since Citabria has rectangular planform amounts 25 percent root chord indicated 17 Fortunately Center Buoyancy falls just want landing angle right step fortuitous because have struggling days get together Actually little both aerodynamically unfortunate carrying large appendages like floats way out arms length speak clearances shown 6 at31 learance 20-in propeller float spacing 3 beams 21 33 should reduced keep airplane its vitals being inun dated choppy water spray covers general way preliminary design float great other aspects covering water resistance trimming moments etc have left untouched felt really essential modeler putting floats pride joy intention article es tablish basic criteria Prelimi nary Design future article will presented Detail Design Continued page 98 April1979 17 Line-up RC seaplane models Lto R Bob Wisniewakis modIfied Lancer single pontoon wing-tip floats Granger Williams sport model similar configuration Granger Williams Mercury twin floats Gary Neelys modified sport biplane twin floats Main floats models same Mercury design molded foam plastic Openers/Winter continued page 72 have something tell As RCer FOs chief interest CL Racing frantic aerobatics pilots center circle will find Bill Lee CL Racing talking about home-made fibreglass props Bill Wynn Paul too guy endlessly seeks truth about tanks things like props doing experimenting finding para meters Dave Chesney writes beautifully RC Helicopters column existence now Bill Warner Sport/Scale will put humor life flying circus note others gang Without guys like us would never know about hundreds things add up sum total skills Brad Powers lead article floats quarter-scale landmark article Model aviation old century yet explosion knowledge techniques products never dared dream about what know about floats would fit smallest drawer field box So designer partook dozens famous pro jects made history modeler boot telling us design float virtually size modelas well monsters weve yet see water Note feed-inIrwin Ohlsson great Ernie Stout Convair fame What suggesting dear friend April issue however excep tional 12 year talking about magazine Within another yearGod willingit will thousand light years beyond April 1976 MA began July 1975 its modern form ask conscious magazine contro versial terms some other magazines have shown theyd like see deadbut inspect closely what speak especially minority members did subscribe MA past yours wed like proud AS WE GO TO PRESS sad news ar rives passing Myron Mike Schlesinger recent past president Top Flite Models Mike respected friend industry innumerable modelers true pioneer helped start Top Flite its way chaired trade show committee 1956 became member HIAAs board directors served nearly 10 years chairman co-chairman HIAAs Model Aeronautics Division Hu morous easy going always compassion ate understanding Mike Schlesinger will truly missed us Floats Powers continued page 17 actual floats installed Citabria model together summary results some photos Irwin Ohlsson thirties deve loped line famous Ohlsson engines now retired builds beautiful model seaplanes has given pair floats developed has found very satisfactory straightforward design have generous step landing angle embody progressive deadrise Rather present float complete its displacement Center Buoyancy etc ready determined will give its dimensions trim another guesstimate draft 16 40 percent its beam data procedures already discussed up find answers problems Fig 6 shows float answers will found illustration Answers Float Prob lems Finally wish express thanks Ernest G Stout former Chief Hydrody namics Convair worked interesting projects sistance providing data presented herein Now am going start building float build finish before write let know works can de cide whether stay leave Tierra Del Fuego RC Technique/Myers continued page 19 control thats going wrong way move pushrod hole opposite side output wheel frequently make such change field someone needs disadvantage approach pushrods usually get tangled you end up product review product review product review Radial Engines man has thingultra deluxe 57-cylinder scale-like engines /4 scale 4-cycle high-torque swing 16-8 through 20-6 props Low vibra tion low fuel consumption mild glow fuel 6-in diameter 23 oz weight 7cylinder engines offered 3 versionspol ished aluminum anodized black deluxe Collectors Gold Edition package trimmed 14K gold Manufacturer states fully opera tional warranted 90 dayssold direct Executive Engines Co 16650 S 104th Ave Orland Park IL 60462 product review product review product review swapping rudder elevator servos side-by-side using Nyrod often finds surgery neces sary because outer shell has anchored location doesnt allow shift connection other side wheel Wouldnt nice could just throw reversing switch servo point Bobs eyes lit up Ill bet Ace R/C Bantam Midget machinery will fit regular Bantam case says leave enough room servo reverser dont see what can idea George kicked around some possibilities until time get back work few days later Bantam case Bantam Midget servo appeared desk magic Christmas came bit early year thought until Bob told wanted back after youve finished rever sing switch first thought make use 16pin DIP switch After little consideration possibilities left open direct short across batteries dropped idea Besides switch too big Next tried 4PDT Noble switch commonly used switch harnesses RC systems can made fit little help Dremel problem will have take out servo get switch smaller switch could mounted right out open can get couldnt find Slightly later Bob left another goodie desk prototype servo reverser ACE R/C few mods could fit space available would left servo having two pigtails rotation Plug need configuration left project returned servo Bob must careful let unused plug short out metal parts because will short out batteries kill whole system As said before like idea having servo reverser receiver todays IC circuitry major configuration change would adding second set sockets other rotation Its fair mention Kraft has shipping sets 10 years have two servos set up direction Editors NoteLike feature Cox-Sanwa get what want swapping around dot no dot servos dot tiny circle molded mounting flange between cutouts grommets Once get flight pack set up right theres no way make mistake Thats way like things Over years have bought flight packs transmitters work plane until control trims throws right transmitter trim levers center position leave everything alone until needs service way can pick plane off wall go flying worrying its compatible 98 Model Aviation
Edition: Model Aviation - 1979/04
Page Numbers: 10, 11, 12, 13, 14, 15, 16, 17, 98
FOR variety reasons early speculation about future aviation painted rosy picture seaplanes During interval between two world wars seaplanes set speed records crossed oceans offered great promise future Since through out world almost city size situated near important body water feeling build expensive space consuming airports 1929 Claude Dornier building remarkable seaplane shown pic ture american industrial designer Nor man Bel Geddes busy collaboration Dr Otto Koller designer Ger man Pfalz biplane Together worked up design enormous flying boat wing span 528 feet deck below water line eight decks above have 20 1 900-hp engines includ ing engine repair shop root wing 22 feet thick gross weight 1275000 pounds would believe behemoth designed cruise fantastic speed 100 mph 5000 feet some reason never built Now discredit man Larry Williams taxies Supermarine S4 waters Lake Elsinora CA prior contest-winning flight powered K&8 front-rotor engine Warren Shipp photo Norman Bel Geddes true genius ideas kitchen ranges elevated freeways have become reality simply show fast actual progress can overtake wildest dreams gifted advent all-metal stressed skin monoplanes retractable gear landplanes suddenly stopped looking like Jennies began look today Seaplane designers other hand could never figure out way retract floats within sensible weight allowance density seawater just wasnt great enough floats hulls always too big invariably added up drag just simple landplane fuselage Since drag means fuel increased fuel meant corresponding reductions range pay load translated reductions reve nues wasnt until jet engine came along eliminating large clearances re quired propellers designers able create seaplanes such Skate shown model photo could compete drag-wise landplane time airports finally built Iandplanes stolen show 10 Model Aviation Larrys Supermarine overhead later lowwing Supermarines among beautiful ali aircraft laid groundwork Spit fire designed RJ Mitchell Shipp photo Other factors also determined de mise seaplane Rough seas landing areas werent always calm areas congested unsafe handling mooring maintenance difficulties say nothing severe corrosive effects sea water aluminum alloy hulls Numerous approaches problem operating aircraft water have made include variety floats varying shapes skis hydrofoils large hulls literally stabilized tip floats spon sons blended configuration Skate shown photo exception last item possibly hydrofoils think modelers have man aged adapt others models varying degrees success ducted fan makes both hydrofoils blended hull-wing attractive possibilities since out propeller clearances deal inter esting ideas suggest themselves will leave notions another time devote article understanding principles underlying simple scale type floats appropriate scale model will try use procedures learned evaluate excellent model type float given Irwin Ohlsson might think float piece functional sculpture must perform following 1 Provide adequate buoyancy rest 2 Provide minimum resistance motion through water during progressive stages takeoff 3 Provide smooth stable variations trim during takeoff landing since pilot has little no control over trim attitude low speeds water 4 Provide stable reasonably soft landing entry course minimum weight air drag well have ridden water skis aboard speedboat power cruiser familiar changing attitudes craft starts move nose begins rise untilif sufficient power available will gain enough speed level off plane An airplane floats does same thing As moves forward pushes sizeable volume water ahead itself creating large wave hump over OHLSSONS WIDGEON DURING preparation Mr Powers article both Brad editor con sulted Irwin Ohisson retired engine manufacturer AMA Hall Famer has considerable success floats hulls radio control Shown Irwins Grumman Widgeon data supplied Ohlsson Fol lowing Irwins comments hull table specifications configuration first step changed double concave also two sponsons added sides hull bow first step Small spray rails extend outboard length sponsons tunnel de sign gives smooth low power takeoff sponsons spray rails deflect water props original full-scale aircraft 2% degree positive wing incidence reduced 0 degrees model After first flightwith Joe Bridi test pilotit came off water before reached its flying speed stalled nose wing down landplane would have bought farm However bounced out water like basketballnot scratch Since day April 1974 about 50 flights have madenever has wet real good stable fast flying machine Specifications Twin-Engine Widgeon Span 80 chord center section 13% tip 8 hull overall 54 Weight empty 13 lbs weight fueled 15 lbs Power2 contra-rotation 61 Perry pumpsfuel 500cc nacelleprops 11 x 7Y2 left right handthrottles 2one nacelle Controls Flaps Aileron Rudder Elevator Construction Wing2 main spars balsa ribs 2 apart sheet balsa silk covered butyrate doped plywood engine mounts rear spar Hullspruce keel balsa sheeted bottom 3/32 balsa 1/32 x 3 plywood glassed top sides silk covered butyrate dope April1979 11 Noting jet engineno prop clearance problemsmade possible blended hull Powers cites Skate shown moaei tesi tow RACING AIRPLANE AVERAGE___ AIRPLANE LIGHTPLANE Lu 0 0 IL L - 7approx / S 1/ EXCESS THRUSTAVAILABLE FOR TAKE-OFF THRUST 2 L RESISTANCE HUMP 18 10 TAKE-OFF SPEED must literally climb order level off plane gather takeoff speed hump region operation critical regard power indicated Fig 1 Obviously airplane accelerate take off thrust must greater resistance Otherwise will just cruise around water until fuel gone Fig 1 racing airplane has very high water resistance presumably due small floats achieve low air drag since Fig 1 high speed design has sufficient thrust cope resistance As apparent thrust available average airplane used racer takeoff speed would impossible since airplane could never ride over hump Since model engines available appear adequate cases should justified applying average~ rather marginal criteria designing float As aspects airplane design VOLUME Lb2 VOL b b VOLL2b compromises between conflicting require ments generally being sought case hulls floats boils down finding nice balance betweeen size displacement Large floats have advan tage low immersion light spray weigh have higher air drag Small floats sink too deeply water makes heavy spray high water resistance So can say except refinements design actual float itself basic problem find proper size job keeping both float size spray minimum commensu rate power orother limiting factors Early float designers found after much experimentation floats having length beam ratios less about 6/1 didnt work very well seven seemed best average conditions acceptable per formance water achieved draft early floats such displacement value approx imating cubical container filled water having same dimensions side beam float Thus float beam 3 ft could expected perform satisfactorily displaced amount water could placed cubical container 3 ft side Such float would displace 33 27 cu ft sea water Since sea water has density 64 lb/cu ft weight water 1728 lbs pair such floats would right average airplane weighing about 3450 lbs As pointed out Fig 1 could vary considerably non average conditions Once relationship estab lished easy matter scale floats up down suit different gross weights long same family reasonably close being geome trically similar relationship came called beam loading expressed non-dimensional terms W 3andhadavalueoflOwhen wb length/beam ratio seven W equals Load Carried Floatlbs w equals Density Sea Water 4 lbs/cu ft b equals Beam FloatFeet criterion expressed graphically Fig2 Although shown simple cube Fig 2 applies L/b ratio seven L/b 6 value C of75 worked best since L/b decreased Beam increased same token increases L/b accompanied decreases beam requiring corresponding increases values C During WW II studies made configurations floats particularly hulls involving length/beam ratios order 8 10 higher 12 Model Aviation b.Kbb COMPARING CRITERIA found longer hulls less air drag less water resistance less way nasty characteristics like hobby horsing~ porp oising pitching back forth under way selecting length/beam ratio float strong consideration given value 8 finally ruled out due excessive length fact typical scale applications early seaplanes However after have finished article should able design float having high L/b wish float described will have value L/b investigation progressed became apparent immersion coefficient would useful contained provision beam length well Accordingly new term developed engineers called K2 w equal w L2 b Like C K2 nondimensional does indeed account length well beam Recom mended values K2 range 018 light spray low power 022 heavy spray high power 020 representing good criterion average~ conditions float therefore will based indirectly value 020 However look Fig 2 see volume portion term L2b resolves itself large cakepan 2 percent full bears little physical resemblance float So based K2 tried true parameter lets devise term just purpose multiply K2 length/beam ratio increase amount also get cakepan carton has same overall dimensions float follows K2so X K2 wL2bb Lx W — W c bwL2bwLb2 C1 ficient Immersion Lb2 gives us figure fits float like shoe box carton shown figure top Fig 2 So term C1 derived K2 constant like K2 varies length/beam ratio said float has value 7 X K2 7 X 020 140 shown figure 3 As can seen C really percent age displacement float bears its carton makes cozier relationship wish reconcile parameters fully correlation between C K2 shown Fig 4 Now lets proceed design float First must find beam whch turn requires value displacement W watch weight think can put pair floats Nosen Citabria already weighs 18 lbs about 32 lbs Thus gross weight will 25 lbs LENGTH/BEAM RATIO vs Cj 8-7 b 6bf LCi b 144 160 126140154HEAVY OUR FLOAT 101121314 dispi float W dispi artonwLb2 I0 L b 15161718 Fig 3 K2 COMPARED WITH 0 OUR FLOAT 0 . LIGHT SPRAY K2018 7 MODERATE 020 6 HEAVY 022 EXCESSIVE 025 5 2 Fig 4 34 5 68 CW 125 April 1979 13 20 Dornier X 12-engined flying boat built 1929 photo has radial engines arranged tandem pairs After transatlantic crossing turned turtle tropical storm CONVENTIONAL FLOAT t217 Al curve ares r2 7b 77 20 2022 / / 2 25 225 -2 10304222 IS oisoc. 926 [2 DeejI F24Ih0 02p2[ 942 W05N9044IIb25jyf 4404 h224&Ih1l 410 2STSP/C0NTROOISO40 t f J 0 10 42240 V Fig 5 float will carry 125 lbs So W equals 125 lbs C2 said 140 W C2 2 expression two unknowns b L So will have express L terms b making WW wLbbzw7b3 andbeamb3 W — w7 C 125 64 X 7 X 140 584 ft or7in Since length/beam ratio seven length 7 Now lets check results another way said C percentage displacement float carton 14 percent carton has displacement 7 X 7 X 4 8893 lbs 1728 14 percent 8893 1245 lbs close enough point might wise reassess things consider other values planning build model 3-lb camera may added later going fly fresh water lake having water density 624 lb/cu ft might wiser pick value C2 126 shown Fig 3 rather 140 reduce draft lighten spray give some room grow particularly think powerplant marginal beam will become 725 length 5075 However will add around 10 percent weight float Now some discussion before tackle details Obviously float should aerodynamically clean can make So might say Ok lets make streamlined like wing tip fuel tank sounds good streamlined bodies completely immersed tend suck under speak takeoff impossible final analysis wing generates lift deflecting thus accelerating mass air downward float completely streamlined partially immersed actually deflects water upward thus sinking deeper deeper power applied speed remains essentially constant displacement vessels sailing yachts have less fixed maximum speed no matter much extra power wind available just sink deeper deeper like bottom teaspoon suspended against water flowing faucet other hand hull bottom vicinity step transom flat like water ski v-shaped like speed boat water departs step float rides up skims over water deriving lift much same way wing slighting deflecting water down ward gaining lift thereby derived form dynamic pressure hull bottom Actually forebody its transom step does work afterbody primarily provide static buoyancy rest aircraft doesnt rock back its tail Indeed Lou Proctors Antic has forward floats really forebodies coupled small efficient afterbody form small float tail Minimum air drag critical matter models faithful attention detail scale models requires easy lines generous step depth needed assure clean departure wake doesnt tend reattach afterbody cause porpoising plus generous landing angle will handle problem forebody lines should sharp easy keep hull resistance minimum large aircraft ample deadrise needed minimize decelerations landing Deadrise should 14 Model Aviation 226 find center buoyancy Trace curve areas onto cardboard balance three ways edge ruler marking line time Intersection centroid area figurecenter buoyancy float 4 j3-I RAZOR SHARP CHINES Fig 6 TRUE AREAS SQ INf337 316 EI$II LIII -__ IPORT VIEW LEFT FLOAT OUTBOARD CHINE 16 r -eTAogrIb, VINBARD CHINE 0 11 FLOAT PROBLEMS Construct curve areas find 1 Displacement pounds 2 Center Bouyancy LSO 3 Length/Beam Ratio disregarding rounded ends tapered sides 4 Length Beam displacements 1 lb 5 lbs 10 lbs increase go forward along forebody sharpen hull lines provide stability trim Adequate buoyancy afterbody easier attain deadrise held constant initial application power takeoff produces powerful nose-down moment seaplanes must countered adequate forebody displacement will tend resist moment quickly smoothly avoid forebody porpoising char acteristic low length/beam ratio hulls having insufficient restoring moment standpoint L/b 8 would better float would begin get too long landing angle would suffercompro mises again Landing Angle No2 corresponds similar angle landplane Its purpose allow step wheels make initial contact angle close 90 percent stalling angle wing permit slowest possible 912 1 2 REOD PORT AND STARBOARD 17 16 15 114 13 12 1 II II 7k 8 14518 5 18 3 gPORT FLOAT SHOWN -. FLOAT OPPOSITE II 212426 Ti OHLSSON FLOAT 1213 WEIGHT W/ FLOAT. LBS landing speed Since impact forces vary square speed small reductions speed accompanied sizeable increases safety float landing angle 14 15 Fig 7 9 degrees coupled 3 degrees wing incidence 12 degrees Clark Y airfoil small Reynolds Numbers corresponds guidelines just mentioned 1 2 3 4 ANSWERS TO FLOAT PROBLEMS Fig 8 Displacement 298 say 3 lbs CB Station 134 just forward Step 1/B 26/4 equals 65 Dimensions vary cube root Ratio Displacements So 1 lb dimensions will Ohlsson float timesthe cube root 1/3 693 So equals 693 x 26 18 end B 593 x 4 277 Similarly 5 lbs 307 B 472 10 lbs L 3875 B 595 say 6 Note Since float different family conventional float geomet rically related values CW Ci would comparable VOLUME 4 CtiINV2SOLU OF OUYANC April1979 15 FLOAT TOO SMALL LOAT FLOAT TOO LARGE static trim CG complete airplane must obviously lie perpendic ular waterplane passes through Center Buoyancy float indicated Item 29 Fig 5 Item 2 Fig 5 shows landing angle mentioned above As can seen step centroidof V-step Item 22 Fig 5 should slightly aft Center Buoyancy place directly under CG landing 30 order keep float axis parallel fuselage usually desirable flight angle static trim Item 13 Fig 5 3 degrees producing slightly nose up attitude airplane static rest water undesirable have axis airplane parallel waterplane would mean placing floats slightly nose up else reducing forebody displacementneither good Flare No 12 directs spray helps control its effects Judicious use spray dams blinders metal strips flush sides float projecting about half inch below chine can reduce spray dramatically carried too far forward made too large can destabilizing flight probably best experiment little bit Because forward portions floats destabilizing flight necessary add substantial increment fin area compensate shown No 24 Since floats will also produce negative diving moment elevator trim order preferably some means adjusting horizontal stabilizer toe-in recommended procedure installing wheels landplane no-no floats very necessary mounted firmly accurately Water forces high unforgiving afterbody float tapers back flat transom large enough accomodate water rudder mounting brackets outlets internal pushrods water rudder should placed float its pivot line should 2530% its chord Its area critical make about size proportion shown respect size float So much generalities Now lets put Fig 5 front us study steps involved creating particular float Lay out 7 X 49 carton side view 3 X 49 half plan below 7 X 7 box left Note height float equals beam mainly simplify geometry article height could increased say used basis single hull design ever should decreased excess buoyancy very necessary Theoretically could slice float off just above waterline did extra ounce fuel added servo could sink whole kaboodle Draw center line 3 Draw upper deck lines shown forebody duplicate below plan view forebody shown above chine elliptical prolate spheroid anybody interested doesnt have Make shape matches picture favorite seaplane wish Locate Step 1 As first approxi mation lets assume Sta 26 26 aft nose Later might want change bit Lets hope Draw landing angle 2 heel step up center line Sta 49 Make step depth 8 afterbody keel 7 Draw forebody keel 6 Note carries well forward does match curve deck line top sharpen entry side view left draw circular cross sections upper forebody deck down center line drop vertical tangents circular cross section meets center line tangents Sta 6 forward should extend above 16 Model Aviation Mercury Racer Granger WIlliams repose La Costa CA sloughlntended Schneider Trophy race flown Al Williams real Mercury grossly overweight Brad Powers left Irwin Ohlsson latters highly successful twinfloat design using floats own design championship free-flighter Thirties later manufacturer engines exAMA president Hall Famer Irwin builds designs best center line Starting step Sta 26 draw deadrise angle 4 20 degrees Its inter section vertical tangent just drew determines aft point theoret ical chine 9 Draw theoretical chine 9 establishes smooth variation deadrise go forward Back step section again draw chine flare 12 Its intersection vertical tangent establishes aft end forebody chine 10 Draw forebody chine 10 shown Near Station 6 curve reverses lie fore aft direction make clean aerodynamic entry Assuming theoret ical chine lie curved surface touching side hull therefore intersecting vertical tangents drew draw deadrise Station add flare tangent deadrise horizontal chine flare should have generous radiusbut excessive Now draw afterbody deadrise Station other side end view plan view drew beginning establish afterbody chine both end side views 11 Using afterbody planform deter radii draw locus radii 18 side view complete sections afterbody end view point good idea draw some 'buttock lines' 'water lines' end view shown project other views see fair fair smooth fiddle drawing bit until 23 region between Sta 18 step bottom should have straight buttock lines insure stable planning other words hull bottom surfaces should have no fore aft curvature region Draw trial static load water line sloping up aft 3 degrees through point 3 above keel step 14 information end view water line construct sections shown hatched station Measure sections determine area section Since half sections dont forget multiply area 2 plot values shown 26 establish acurve areas Just volume deck cards sum cards area under curve summation infinite number cross sectional areas therefore represents volume immersed portion float Since before reproduction maga zine drawing made half scale areas have indicated obtained half scale drawing will have corrected full scale will shortly true well length curve areas drawn 1/5 scale expression shape curve areas could add up integrate mathematically since arbitrarily determined its slope choices deadrise flare chine chape etc no way establish slope area curve mathematically must integrate graphically can done close approximation adding areas successive steps 27 judiciously done better way use device called polar planimeter have done gives area under curve 169 sq just pointed out areas taken one-half scale drawing therefore have fourth full-size areas because areas varies scale squared Also said length figure one-fifth actual float must multiply 169 5 times 4 20 have correct figure since value volume cu must divide number cu in cu ft get cu ft can multiply 64 weight cu ft sea water we see float indeed displaces 1252 lbs indicated Fig 5 about draft 3 good guesstimate As shown Fig 7 float should loaded carry much over 13 pounds spray will get too heavy other hand float carry much less 11 pounds will too big heavy smaller float should used Well now know draft displacement what Before can screw floats onto airplane have know buoyancy concentrated way find Center Buoyancy trace curve areas onto piece cardboard no lumps cut out balance shown picture Balance least three ways mark time have careful marks will intersect point centroid area figure Center Buoyancy float 21 Incidentally good way find centroids such things elliptical wings centers lateral area other irregular shapes Now can relate float Nosen Citabria 19 above described earlier shown Fig 5 good stability control CG 20 should 25% mean aerody namic chord MAC wing Since Citabria has rectangular planform amounts 25 percent root chord indicated 17 Fortunately Center Buoyancy falls just want landing angle right step fortuitous because have struggling days get together Actually little both aerodynamically unfortunate carrying large appendages like floats way out arms length speak clearances shown 6 at31 learance 20-in propeller float spacing 3 beams 21 33 should reduced keep airplane its vitals being inun dated choppy water spray covers general way preliminary design float great other aspects covering water resistance trimming moments etc have left untouched felt really essential modeler putting floats pride joy intention article es tablish basic criteria Prelimi nary Design future article will presented Detail Design Continued page 98 April1979 17 Line-up RC seaplane models Lto R Bob Wisniewakis modIfied Lancer single pontoon wing-tip floats Granger Williams sport model similar configuration Granger Williams Mercury twin floats Gary Neelys modified sport biplane twin floats Main floats models same Mercury design molded foam plastic Openers/Winter continued page 72 have something tell As RCer FOs chief interest CL Racing frantic aerobatics pilots center circle will find Bill Lee CL Racing talking about home-made fibreglass props Bill Wynn Paul too guy endlessly seeks truth about tanks things like props doing experimenting finding para meters Dave Chesney writes beautifully RC Helicopters column existence now Bill Warner Sport/Scale will put humor life flying circus note others gang Without guys like us would never know about hundreds things add up sum total skills Brad Powers lead article floats quarter-scale landmark article Model aviation old century yet explosion knowledge techniques products never dared dream about what know about floats would fit smallest drawer field box So designer partook dozens famous pro jects made history modeler boot telling us design float virtually size modelas well monsters weve yet see water Note feed-inIrwin Ohlsson great Ernie Stout Convair fame What suggesting dear friend April issue however excep tional 12 year talking about magazine Within another yearGod willingit will thousand light years beyond April 1976 MA began July 1975 its modern form ask conscious magazine contro versial terms some other magazines have shown theyd like see deadbut inspect closely what speak especially minority members did subscribe MA past yours wed like proud AS WE GO TO PRESS sad news ar rives passing Myron Mike Schlesinger recent past president Top Flite Models Mike respected friend industry innumerable modelers true pioneer helped start Top Flite its way chaired trade show committee 1956 became member HIAAs board directors served nearly 10 years chairman co-chairman HIAAs Model Aeronautics Division Hu morous easy going always compassion ate understanding Mike Schlesinger will truly missed us Floats Powers continued page 17 actual floats installed Citabria model together summary results some photos Irwin Ohlsson thirties deve loped line famous Ohlsson engines now retired builds beautiful model seaplanes has given pair floats developed has found very satisfactory straightforward design have generous step landing angle embody progressive deadrise Rather present float complete its displacement Center Buoyancy etc ready determined will give its dimensions trim another guesstimate draft 16 40 percent its beam data procedures already discussed up find answers problems Fig 6 shows float answers will found illustration Answers Float Prob lems Finally wish express thanks Ernest G Stout former Chief Hydrody namics Convair worked interesting projects sistance providing data presented herein Now am going start building float build finish before write let know works can de cide whether stay leave Tierra Del Fuego RC Technique/Myers continued page 19 control thats going wrong way move pushrod hole opposite side output wheel frequently make such change field someone needs disadvantage approach pushrods usually get tangled you end up product review product review product review Radial Engines man has thingultra deluxe 57-cylinder scale-like engines /4 scale 4-cycle high-torque swing 16-8 through 20-6 props Low vibra tion low fuel consumption mild glow fuel 6-in diameter 23 oz weight 7cylinder engines offered 3 versionspol ished aluminum anodized black deluxe Collectors Gold Edition package trimmed 14K gold Manufacturer states fully opera tional warranted 90 dayssold direct Executive Engines Co 16650 S 104th Ave Orland Park IL 60462 product review product review product review swapping rudder elevator servos side-by-side using Nyrod often finds surgery neces sary because outer shell has anchored location doesnt allow shift connection other side wheel Wouldnt nice could just throw reversing switch servo point Bobs eyes lit up Ill bet Ace R/C Bantam Midget machinery will fit regular Bantam case says leave enough room servo reverser dont see what can idea George kicked around some possibilities until time get back work few days later Bantam case Bantam Midget servo appeared desk magic Christmas came bit early year thought until Bob told wanted back after youve finished rever sing switch first thought make use 16pin DIP switch After little consideration possibilities left open direct short across batteries dropped idea Besides switch too big Next tried 4PDT Noble switch commonly used switch harnesses RC systems can made fit little help Dremel problem will have take out servo get switch smaller switch could mounted right out open can get couldnt find Slightly later Bob left another goodie desk prototype servo reverser ACE R/C few mods could fit space available would left servo having two pigtails rotation Plug need configuration left project returned servo Bob must careful let unused plug short out metal parts because will short out batteries kill whole system As said before like idea having servo reverser receiver todays IC circuitry major configuration change would adding second set sockets other rotation Its fair mention Kraft has shipping sets 10 years have two servos set up direction Editors NoteLike feature Cox-Sanwa get what want swapping around dot no dot servos dot tiny circle molded mounting flange between cutouts grommets Once get flight pack set up right theres no way make mistake Thats way like things Over years have bought flight packs transmitters work plane until control trims throws right transmitter trim levers center position leave everything alone until needs service way can pick plane off wall go flying worrying its compatible 98 Model Aviation