Propellers

Theyre almost everything fly except gliders ducted-fan models much really know about props bolt onto engines article can provide us starting point determin ing prop works given application EGeorge Abbott FOR MOST MODELERS selection propeller usually matter fol lowing recommendation engine manufacturer airplane designer Later modeler may experiment dif ferent diameter pitch combinations seeking seems provide type performance desired advent larger chainsaw engines big glow engines four-cycle engines modeler faced power plants having characteristics quite different glow engines have standard hobby 30 years larger engines may develop up 5 hp around 10000 rpm fourcycle engines develop power some what lower rpm two-cycle coun terparts generally 10000 rpm less although some four-cycles now appearing run several thousand rpm faster Because four-cycle engines offer certain advantages such lower noise reduced fuel consumption often de sirable use airplanes designed two-cycle power plants An other advantage often claimed fourcycle engines improved vertical performance constant speed through ma neuvers Achieving advantages dependent upon selection proper propeller particular engine airplane combination example suppose has fourcycle engine expected develop 1 hp 13000 desired use engine airplane expected fly tween 50 60 mph nominal airspeed chart presented article can found 13000 rpm propeller 6-in pitch has nominal speed 74 mph 8-in pitch has speed 99 mph 5 62 mph Further power absorption chart shows 1 hp 13000 rpm represents power absorption Left big Kioritz swings 22 xl 0 prop transmit aii powerto prop six-boit hub used Right Saito 45 Ace 4-4Oturns 12 x 6 prop plane actuaiiy flew betterwith 13 x 5 ground ciearance pilot skiii made 12 x 6 economical choice 40 Model Aviation Theres commercially-avaliabie prop virtuaiiy diameter pitch can imagine choosing best particular engine airpiane can difficult 8/4 8/6 9/8 10/6 10/8 ** -~1p13/8 80 90 100 P14/8 16/6 16/8 ___418/6 18/8 90018/10 100020/8 -20/10 22/8 24/8 24/10 hf26/10 0/P - ----- 1000 4 ii~x--x 2 -- -77 i-- 7 - - 4 -7 25 HP PD4 RPM3 14 x 7 810 fourth power multiply pitch inches Find ersects rpm hp tines determine appropriate prop go n follow nearest diagonal line up diameter/plth value factor 60000 turn indicates suitable propellers would 9/8 10/6 11/5 actually 1045/5 power curve engine known easy make further selections Vihen relation ship between thrust rpmand thrust propeller diameterare understood selections may intelligently made must bear mind power absorption chart applies static condi tions flight engine will unload some extent will probably choose propeller will load engine toward low end its power curve under static conditions achieve close maxi mum power flight Except racing aircraft maximum power usually desired climb during vertical maneuvers time airspeed toward low end aircraft speed range An understanding interrelation ship between engine power rpm propeller pitch diameter thrust will valuable October 1986 41 12/6 12/8 * * Left Ziroll Morane Saulnier plain-bearing OS 35 uses 11 x 5 prop Generally engine uses lOx 6 airplanes performance noticeably better 11 x 5 Propeller choice isa matter matching engine airplane pilot preference Right nearly-finished 1/4-scale L-4 J-3 has OS 120 four-cycle twin 20 x6 prop will starting point 18 x6 mounted forthe photo both airplane designer modeler wishing select airframe/en gine combination will provide desired type performance Basics Everyone has pretty fair general understanding principles operation airplane propellers Its generally under stood propeller device serves convert power produced engine thrust cause airplane move through air screw analogy easily understood fact European countries propeller known airscrew generally well understood applications laws aerodynamics describe operation pro peller article way diameter pitch rpm propeller well velocity airplane affect thrust power absorption will dis cussed Also will presented way estimate brake horsepower required drive propeller particular rpm particularly useful selecting propeller particular engine airplane estimating effectiveness various fuels engine modifications Terminology number terms will used throughout article describe various physical character istics propellers well conditions under operate Most will familiar anyone experience airplanes several may Bear mind attempting provide understanding operation propellers exhaustive course aerody namics Most readers will buy commercial propellers rather design make own purpose article help make such selection informed way following definitions should sufficient qualitative discussion follows D Diameter measurement inches prop tip tip P h distance inches prop would move forward revolution no slippage J nce ratio measure 42 Model Aviation 50-year-old Brown Jr pioneering gas model engines isa 60 advertised produce 1/5 hp 5000-6000 rpm Since rather flat torque curve could handle large props uncommon inthe prewar Free Flight days see Browns enormous 7-and 8-ftwingspan airplanes happily swinging 17and 18-in props hp may have lower Brown Jr good thrust Ross twin 60no longer production seemed happiest swinging 12 x 6 TheOS Wankel 30 likesto run high rpm hence its best turning 9 x 6 Output strongest engine operating 12 14K range anything dictated best prop K&B 15 Schnuerle thoroughbred racing engine uses very thin highpitched prop art science finding optimum prop raceran example value experimentation 05 60 four-stroke flies stately slow bipe equally well either 13 x 5 14 x 4 612441818 6 629856 121 48294416 110 165536026 velocity V airspeed air plane divided rotational speed propeller its diameter J Xrpm consistent units ie in mm should clear will define angle attack propeller airfoil airspeed rpm Think about mo ment terms unloading engine occurs dive rpm speed rotation pro peller revolutions per minute hp horsepower produced engine absorbed propel ler Power defined force times distance per unit time hp 33000 foot-pounds per minute p Density air varies pressure temperature hu midity slugs per cubic foot standard sea level pressure 2992 Hg temperature 590F p 00237 Thrust term refers force ex erted rotating propeller di rection travel airplane whole purpose propellerto convert power engine appears rotating force torque linear force T p X rpm2 X J4 X Ct Ct thrust coefficient constant shape particular pro peller advance ratio J Rey nolds number Thus Ct will different different propellers under different condi tionsor same propeller under different conditions Since Ct includes advance ratio J determined airspeed its clear thrust will different different airspeeds model purposes very difficult get mean ingful value Ct What informative about formula fact thrust varies fourth power diameter square rpm because thrust developed consequence blade behaving airfoil will recall lift varies square velocity velocity part blade function distance center propeller finally area propeller disk goes square diameter Thus seems advantageous select largest prop consistent desired pitch rpm available power seems make tuitive sense greater volume air will influenced propeller greater thrust Power absorption Reciprocating internal combustion engines include vir tually model engines exhibit power output curve increases increas ing rpm certain peak dimin ishes further increases rpm October 1986 43 Spinners improve appearance reduce drag some extentand also provide place apply starter Spinners diameter up 20% prop diameter can used no reduction perform ance since center prop does convert powertothrust fact spinners im prove efficiency propeller elimi nating turbulence vicinity hub propel airplane formula thrust Continued page 132 Prather pitch gauge useful especially youre serious about racing finding out exactly what have pitch markings stamped prop always correct dontthinkourauthorisseriousabOut propellers take look mailbox AERO-PACER $8900 Span 64 1/2 Weight 55 7 lbs Engine 45 61 FS 5 TS ig 25 oz wing loading 4 channel Sport Trainer GIPSY $10900 MOTH Span 543/4 5475 Weight 5-6 lbs 787 sq inches 15 oz wing loading Engine 45 65 FS 0 TS 4 channel Both kits designed primarily Four-Stoke engine fly equally well Two-Stroke engine Add $450 shipping handling Direct SalesMichigan residents add 4B/0 sales tax Check money orderMastercard Visa Radio Techniq ue/MyersPropellers/Abbott Continued page 129Continued page 43 ratio problems Capture ratio refers characteristic FM receivers allows switch allegiance strongest transmitter vicinity FM Redundant Radio system possible rare possible someone operating vicinity channel take control airplane signal stronger receiver signal flying Redundant Radio system gain freedom interference having half system captured foreign transmitter doesnt help FM Error Switch has deal possibility tests Using oscilloscope set up Error Switch transmitter instructed ran few tests 1 The two receivers attached Error Switch attached via Red port Green port An LED light-emitting diode center device indicates system source signals being used control servo both transmitters working Green 72790 MHzRC5O Red old 72240 MHz servo worked normally Error Switch usually showed Green system control 2 When turned off Green transmitter LED indicated Red system 72240 MHz use servo acted normally 3 When turned off Red transmitter LED indicated Green system use servo acted normally 4 When turned off both transmitters LED indicated Red system select ed course servo did nothing 5 With both transmitters operating turned another RC5O Green transmitter LED flickered Green Red servo continued respond control inputs also exhibited some jitters oscilloscope showed pulses Green port erratic timing pulse widths Red pulses looked normal reset timing Error Switch get solid switch Red no jitters 6 Continuing interference turned off Red transmitter LED indicated Green system selected servo contin ued respond Green system though jittery fashion makes good sense Its better have some control jitters switch dead channel As can easily see addition redun dant radio made dual system almost bullet proof However using two 72 MHz channels leaves us vulnerable same defect mentioned earlier discussed splitting channels groups could used specific lo cationsyou cant sure everyone will cooperate system use right channel right location Working Bob Aberles ham rig Custom Electronics Transmitter T-Module Bobs AM module 534 MHz AM synthesizer module 72 MHz got same results high end six-meter band rarely used might have bit confidence used 53/72 T-Module think everyone should flying everything redundant radios AMA should now create Redundant Radio Phase-In Plan might happen Stay tuned next episode story Interference Fighters George M Myers 70 Froehlich Form Road Hilzksville NY 11801 because power product torque times rpm peak torque generally occurs rpm well below peak power As rpm increases engine produces less force torque because breathing diffi culties less fuel-air mixture gets cylinder stroke higher speeds advisable thus select propeller will permit engine operate just right rpm maximum power As will see moment examine expression power absorp tion speed airplane plays important part problem As matter fact adjustable-pitch pro pellers developed full-size aircraft have used some extent modelsThe formula propeller power power required drive pro peller hp rpm3 X D3 p power coefficient function shape propeller advance ratio Reynolds number Again advance ratio J factors airspeed airplane Note pitch propeller does specifically appear formula included Cp since pitch important factor shape propeller What really important realize propeller power varies cube rpm means twice rpm would require eight times power 10% increase rpm would reflect 33% increase power 20% increase rpm would require 73% increase power Its interesting understand re lationships would nice have some actual numbers stated section thrust its very difficult get useful values thrust coefficient Ct However can get some useful numbers propeller power coefficient Cp * SCALE DOCUMENTATION * SCALE DRAWINGSMODEL PLANS PHOTOS BOOKS EPLA-TECH 1986- INTERNATIONAL AIRPLANE CATALOG OVER 100 PAGES48500 MC KENZIE 1-IWY *300VIDA OREGON 97488 132Model Aviation 11 ATTENTION ERS EPOXY GLASS COWLS FOR NOSEN PICA SIS MORGAN BALSA USA PLATT CONCEPT FLEET HOSTETLER RCM TCRAPT SHEBER PuTS N & N SCALE SUPER CUB FOKKER 57 BOEING P12 P26 F4B2 P4B4 SPARROW HAWK GEE BEE MOO Y MACBRIENS TURBULENT CHRISTEN EAGLE BRISIGHELLAS STARDUSTER II IA SCALE J3Bl BABY FLYBABY N 0 TN E B S WHEEL PANTS FOR CITABRIA STARDUSTER II PIUS SKYBOLT LIBERTY SPORT CHRISTEN EAGLE P6E HAWK MULLIGAN H OTHERS LARGE SCALE PLANS AVAILABLE Please send $100 complete lIst WB supply Modelers fiberglass parts plans Write Call us T & D FIBERGLASS SPECIALTIES 30925 BLOCK GARDEN CITY MI 4B13B PHONE 1313421-6358 BRAZED -TREATED WIRE GEAR5 & CABANES PHONE 313 21-9064 WORLOS ClOSES SCALE enOTO SERVICE 5005 PHBrC PACrSr PLANS EWS PHOTO-PACKSPLANS ENLARGING 5*5E Enlarging coats Catalog 5300SCALE PlANS PHOTO SEll IJICE 3209 MadiSOn GeanSBoB N C 27403 Phone lB1B1292B239 NH CRIIEZII PAWU DIESELS Englands Finest 049 35 RIG STD Send $100 list Eric Clutton 913 Cedar Lane Tullahoma Tenn 37388 Model Magic Filler Balsa Foam & Fiberglasssands exactly like Balsa Super lightweight Superior adhesion Waterproof Nontoxic Use nicks gaps fillets fairings building up large areas8 fI oz $595 retail k. 0~~ CmQ 1 Model Magic Epoxy Plus 8 mm 25% lighter Sands & carves like Basswood Non sagging gap filling super strength Use anywhere \ atwo part epoxy used 6f1 oz $895 retail equal 8 oz regular epoxy Red Gas & Diesel Tubing fQ1Model Magic Gas & Diesel Fuel Tubing will swell tine products available dealer direct Magic Products PO Box 19784 C~del St Paul MN 55119 715/425-1397 d shrink turn brittle used gasoline diesel~1~ fuel offers clarity visual fuel flow Model Magic fuel tubing remains flexible plasticizer migration foul engines exhibits outstanding tear abrasion resistence Tubing tinted red easy identification gasoline & diesel use Available 5ft $249/pkg 1 Oft $479/pkg SOft spools $2190 Blue Gb-Fuel Tubing Made finest silicone tubing available Less 1% swelling after 150 hours 15% nitro fuel Available 21/2 5ft packages 5Oft spoolsy C& Inc under static conditions means can estimate hp produced engine driving particular propeller measuring rpm know hp produced engine particular rpm can select appropriate propeller propeller power chart Recall formula propeller power given above hp rpm3 X D5 X Cp density air p known Cp constant determined shape propeller advance ratio etc have know want find hp above formula tough problem However discovered some articles books published 50 60 years ago gave some values Cp full-size propellers days laws physics dont change publications gave some clues follow Among other things turns out model airplane propellers operate Reynolds numbers quite similar full-size lightplane props because although model props smaller operate much higher speeds researched engine reviews horsepower reported together pitch di ameter props used data able derive following expression accurate better adequate model work P D5rpm3 hp 1011 P D inches formula identical previous except numerical value Cp terms ratio pitch diameter including standard value p density air has introduced advance ratio J course zero since dealing static conditions should make sense Cp shape factor propeller pitch diameter obviously principle aspects shape propeller formula can re written little simpler form hp rpm3/l4x 1011 have calculator has exponential function engineering no tation denominator 14 17 zeros after its easy enough plug pitch diameter rpm get power Its nice have formula like its nicer able estimate power particular prop/rpm situation having lot calculations make possible Ive constructed graph permits chose combination pitch diameter might encounter modeling imedi ately find power rpm vice versa must make calculation PD4 dont want Ive indicated chart values PD4 number commonly-used model pro pellers use chart take diameter Continued page 136 CLEVELANDS GI NTSI MANY NEW FOR R/C BUFFS Decignod Ac BasIc Macnr Flying Modal Following BolltUp Prototype Fraction Wood Fabric Ropboo fiocIiinr Vt Thoi New Hictarical Bad 57 Cott JN4 Jan01 $27 81 8 14 Foklcan 07 Ftn$39 108 70 Boylec Gan-Bor $32 POSt 10 Hoorord Poto Rorn $32 99 N 05 Sopanononion S6B $24 71 5 B9 Sopannnonino 56$ $35 950 03Cont Honib F6E $42 068 94 Curt Hoork P6E $5464 St 74 Doolucrlac GB 11 $48r72 C 95 Mororoop Sport $36 109 80 Poll Opt Enildog $43OS Ooogloc 002 Mod $24 107 Aerooto C3 Syt $35r 68 Brictol Bnildog Fr 830 62 Bonrond Born $45 59 Broinfora McLA $54n 78 Tonnenc W-W tot $35 107 Groor Bnorrc F8F 054 63 Cor GochIr 7117 $42 69 Lirdbnngc NO211 $30 94 Cor Cochb Fl lC $54 91 [idbnrgc NO211 839 oNor Cornet $24 96 WnNWlNoo $48 62 BoroMrMolIigoO $35 74 C Hnlldrr SB2C-4 $55 94 HooiMnMolligon 84W 108 FoirrhFTt9 $S9 63 Boning F-26A Ftn $36 65 Worn TopanWing $36 84 8oaing P366 Frr $4890 Worn ToparWing $4B8 IO4Worn C-B Cobin $55r75 Wotl4 [tncordar 832 Booth 717$ Stog 830 lOS Wacrid Lycoodar $49r 96 Bonrb 717-B Slog $49n57 Ford Tninrln 4AT $36 * 55 [orb 11 Elantro $30 76 Ford Trinrtr 4AS $48 02 Lork II Elaorno 840 114 Ford Trionrr 4AS 865 * 62 SOocon T/W Sf7 $18 06 Bolloorn Ainrroc $40 81 Stincon 01W 087 $26 93 Looohng C2Anrplr $69 122 Stirrcorr 5/W Sf7 $38 50 Groin J3F Gorlr $29 59 Bnintol Ftr F2-8 $20 78 Grirnr J3F Sorb $56 118 Bristol FIr 7208 $45. 124 [orb Air Doyrocin $48 74Srnnanc P0cm $45 65 [orb Air Eopranc 824 56 Crr Worirk F-40 $24 02 [orb Air Erpreco $36 60 Vogt Corcoin P40 $35 77 WWrrnc 121 BadI 848 00 Vogt Corcoin F45 $69 637 Sooborinrlr F7C1 845 7$ Lork Liglrtrrg F38 $38 947 Snohoork 9771 $57.r 56 fnpSao-Bno Ant $24 158 Sibor 058 Annph $49 74 RnpSoo8aa Ant $39 65 Booing 100 Sport $36 70 Fion J3 Cob$29 95 Bonrrq 100 Sport $49 106 Pipan J3 Cob$39 75 Nonrlrrop Gonnrrro $40 90 [orb Hodono Oonb $38 96 Northro Goon o $75 * 63 Gino F6F Halloot 028 95 S 77 Bonino B17G Fort $35 60$ 153 Boo B17G Fort OSS too 68 Woctl Whirlnrind 832 78 C 68 N Amer Nonion 839 104 Corn Co FBY SA $56 68 BBononco VToiI $39 61007$ no C pyr 865 77 Locroroba Sadno $25 9700 7$ no C ppo $75 72 NA $25 Boonbor $49 05 Co cc NC 4 859 65 OtMonoodon B26 $49 94 Co cc NC 4 $69 iroro POICO ronicotoc oroonrono As 4. Goon 205 Otlnnnc 6 73 100 SOc Up Add 10% oil ondon chi p gA USA Con & Mao Elcanchana ir % Fiotoniol rotolog 8200 inrlod cnotion 01000 81 05 II nin fonogn odd $1 5$ r LEVELANDMODEL&SUPPLYCo 050 rorconnAoiorrnn c scc tIEeco. sicoc net lB305S DBT$OIT AVE CLEVELAND OHIO 44182 pnOrsocnre n 000 O OAro 981 0000 October 1986 133 Building repairs snap Model Magic Horn Old Timer fl{2t born 7&QVii LANZOS 8 GAS 900Cc cAdO deL S~ cr1 cs RECORD BREAKER -1941 BROOKLYN DODGER 36 Cabi EWEST0 Retail $529505INTRODUCTORY PRICE0 $3900 1938 Record Breaker 96 $6956 tO39Zipper 54$5356 1938 Kloud King 63 $42 36 1941 Brigidier 56 $4076 1941 Super Ouaker 78 $7276 1940 So Long 50$3036 1936 Buccaneer 84 $5996 1938 Clipper MKI 72$4156 1937 Dallaire 108 $75 16 1935 Miss America 84$7196 1941 Playboy Sr 80 $5116 1991 Playboy Jr 54$31 16 1938 Powerhouse 84 $5356 1990 Sailplane 76 $0479 1938 Trenton Terror 72 $90 76 1990 Ranger 46$31 96 1939 Korda Wake 44 $1916 1939 Mercury 72 6 kits gualify SAM evento EF & RIG ond feature highest quabty machine cut 6 sanded parts Superior Competition ott ahoet atrip wood mire & window material Ptana orig EF modela easily convertible Och RIG KITS Sailplanes Electric power Gas Hobby Horn SENSOAR Glider 78 $1600 Midway Model GNOME RIG Hand Launch Glider$2400 Jolly Models FLINGER RIG HLG 50 Span$2400 Midway Model FAST EDDIE Aerobatic /05 EIec$19 00 Jolly Models ELECTRICUS Electric Glider 05s93250 Leisure PLAYBOY SR 67 Gear 05 Elect $3800 Astro ASTRO SPORT 37 Direct 05 Elect $2250 Leisure WASP 37 Direct 05 Electrics$2210 Midway ULTRA MK IV 86 Geared 04 EP $3900 Midway FLYING OUAKER 84 40-454 stroke $6976 4kslMidway DENNY JR 72 Alum Comel$6396 4kslMidwav BUZZARD BOMBSHELL 7200196 FULL LINE OF ELECTRIC SYSTEMS S Parts Avail SHIIlllll & HANDLING Up $000 add $150 $801 $2000 add $220 $2001 $4500 add $301 $4501 $7000 add $350 over $7000 add $4 00 CA Addressees add 65 tax Send MO VisaIMC# Eap Check allow up 30 days CK clearance COD Exact Charges plus $158 HdI Cash Only Designs 06 DA 0 0 S C 21 0 0 18 C 01 1 91 2_________ 0 0 a_________________ C 21 01__________________ ___ __________ S 0 C 21 C 0 0 0 C Ct k4 Page UAaALUUUO $200 PP/tat Clxos copy will sent free--when requested-with order HOBBY HORN 15173 Moran St PO Bow 2212 Westminster Ca 92604 714 0938311 [AftHrs 714 0951203] . 0ce Deslgfls 0 0 IC 18 S 0 SPORT BIPE S $21 PPD 0 PPDZl S _______________0 ~s15 __________0 It ________________0 0 PHOTO DOCUMENTATION PACKS availableon Scale Plans ALL PLANS ROLLEDSHIPPED UPS Compleie wlnetrection Osokiet Send slOO Catalog New York OlaRe Residenie aoO 7% selee tax. Osndsheak . Allow 3 weeks aleckfoalxar QUARTER SCALE PLANSQuarter Master Sport BIpe0 Guadra 35. 73Span.E-Z build. Great PIyer.*Semitif Acailable DAVIS D-1K 905 Span. Ouadra 35 power similar. 1933 KINNER SPORTSTER Model K.ll7Span.035 power. 4-CYCLE PROJECTS aW AKRON FUNK ls Ocae 84span AO size 4 cesle. Faniasiic Flyer DAVIS D1K00 BOa Span. 40 4 cycle similar. Two losS wale 010th scale 1933 KINNER SPORTSTERRR Ce Model K. 79 Span. B1-75.4ny poo510 *e Photo roosoed ocr 1/4 Osele plans. Two loon scale Sloth seals DA Plans comino Propellers/Abbott Continued page 133 prop inches raise fourth power multiply pitch inches common model props will get number between 20000 5000000 find value upper right-hand part chart follow diagonal line down left rpm/hp combination will probably find value PD4 get particular prop does exactly agree values chart will have interpolate between given values need greater accuracy can always use formula other hand know power rpm engine wish select appropriate propeller find inter section hp rpm follow diagonal up right find value PD4 can use calculator find combinations pitch diameter equal value PD4 find diameter will have able find fourth root number must have scientific-type calculator least has exponential func tion have use exponen tial key usually labeled xy enter 25 exponent Finally Ive provided listing values PD4 some 32 typical model propellers chart works two-bladed props having aspect ratio between 61 91 typical props used RC CL models have tested thin toothpick props used racers also very useful have idea airspeed range may expected particular propeller given rpm will obvious higher pitch will result higher speed simple formula relates pitch airspeed rpm mph thousands X pitch nominal airspeed air speed would result propeller operating no slippage nominal airspeed chart shows relationship air speed rpm propeller pitches 3 12 rpm up 15000 covers model situations assumption no slippage course usually encountered actual flight However does give valuable insight selection propeller particular set conditions example suppose airplane planned fly 75 mph engine expected run 10000 rpm chart may immediately determined 10000 rpm propeller 8-in pitch will have nominal airspeed 75 mph Its therefore obvious propeller selected must have 8-in pitch greater airspeed 75 mph reached Its true under certain conditions speeds excess nominal airspeed may achieved due fact propeller blade airfoil may produce lift slightly negative angle attack Bear mind vail ables involved analysis propellers article have made number simplifying assumptions order provide fairly simple method estimating pro peller performance have found results better hp cases Ive checked method against data full-size aircraft engines propel lers well home-builts ultralights have always well within tha range Im confident method i adequate model purposes Conclusion discussed two formulac describe two important aspects 01 propeller behavior thrust power ab sorption formula thrust th importance diameter disk area came apparent discussion 01 power saw propeller powe varies third power rpm 2 fairly small change rpm indicates rathe larger change power chart pre sented makes possible estimate power required drive propeller particular rpm chart also pro vided find nominal airspeed function rpm propeller pitch RC Scale/Wischers Continued page 45 connecting link lined up directly across servo output shaft centerline will no load servo motor Current flow servo will drop idle flaps locked down securely course true full-flap position extra gear retract servo also helps reduce current con sumption intermediate flap positions Incidence angles again third time recent columns going dwell upon touchy subject disastrous crash club field model descended ver tically impact few feet pit area filled models fliers spectators Fortunately missed everyone thing destroying itself pilot us ing full up-elevator throughout dive several hundred feet no appar ent response plane Having built kit assumed incidence angles correct center gravity location concern its first flight case due building error stabilizer leading edge inad vertently raised bit too much providing lifting force Ordinarily sort thing causes no great problem model can readily flown trimming bit upelevator model ratio stabilizer area elevator area quite high large stab small elevator Elevator travel set near minimum prevent overcontrolling Whenever model built up speed tendency models nose tuck under required full upelevator recover level flight its final dive gathered excessive speed simply wouldnt pull out enough up-elevator travel say During its first flight 136 Model Aviation TOciarterMaster .ru 3] i 11

Theyre almost everything fly except gliders ducted-fan models much really know about props bolt onto engines article can provide us starting point determin ing prop works given application EGeorge Abbott FOR MOST MODELERS selection propeller usually matter fol lowing recommendation engine manufacturer airplane designer Later modeler may experiment dif ferent diameter pitch combinations seeking seems provide type performance desired advent larger chainsaw engines big glow engines four-cycle engines modeler faced power plants having characteristics quite different glow engines have standard hobby 30 years larger engines may develop up 5 hp around 10000 rpm fourcycle engines develop power some what lower rpm two-cycle coun terparts generally 10000 rpm less although some four-cycles now appearing run several thousand rpm faster Because four-cycle engines offer certain advantages such lower noise reduced fuel consumption often de sirable use airplanes designed two-cycle power plants An other advantage often claimed fourcycle engines improved vertical performance constant speed through ma neuvers Achieving advantages dependent upon selection proper propeller particular engine airplane combination example suppose has fourcycle engine expected develop 1 hp 13000 desired use engine airplane expected fly tween 50 60 mph nominal airspeed chart presented article can found 13000 rpm propeller 6-in pitch has nominal speed 74 mph 8-in pitch has speed 99 mph 5 62 mph Further power absorption chart shows 1 hp 13000 rpm represents power absorption Left big Kioritz swings 22 xl 0 prop transmit aii powerto prop six-boit hub used Right Saito 45 Ace 4-4Oturns 12 x 6 prop plane actuaiiy flew betterwith 13 x 5 ground ciearance pilot skiii made 12 x 6 economical choice 40 Model Aviation Theres commercially-avaliabie prop virtuaiiy diameter pitch can imagine choosing best particular engine airpiane can difficult 8/4 8/6 9/8 10/6 10/8 ** -~1p13/8 80 90 100 P14/8 16/6 16/8 ___418/6 18/8 90018/10 100020/8 -20/10 22/8 24/8 24/10 hf26/10 0/P - ----- 1000 4 ii~x--x 2 -- -77 i-- 7 - - 4 -7 25 HP PD4 RPM3 14 x 7 810 fourth power multiply pitch inches Find ersects rpm hp tines determine appropriate prop go n follow nearest diagonal line up diameter/plth value factor 60000 turn indicates suitable propellers would 9/8 10/6 11/5 actually 1045/5 power curve engine known easy make further selections Vihen relation ship between thrust rpmand thrust propeller diameterare understood selections may intelligently made must bear mind power absorption chart applies static condi tions flight engine will unload some extent will probably choose propeller will load engine toward low end its power curve under static conditions achieve close maxi mum power flight Except racing aircraft maximum power usually desired climb during vertical maneuvers time airspeed toward low end aircraft speed range An understanding interrelation ship between engine power rpm propeller pitch diameter thrust will valuable October 1986 41 12/6 12/8 * * Left Ziroll Morane Saulnier plain-bearing OS 35 uses 11 x 5 prop Generally engine uses lOx 6 airplanes performance noticeably better 11 x 5 Propeller choice isa matter matching engine airplane pilot preference Right nearly-finished 1/4-scale L-4 J-3 has OS 120 four-cycle twin 20 x6 prop will starting point 18 x6 mounted forthe photo both airplane designer modeler wishing select airframe/en gine combination will provide desired type performance Basics Everyone has pretty fair general understanding principles operation airplane propellers Its generally under stood propeller device serves convert power produced engine thrust cause airplane move through air screw analogy easily understood fact European countries propeller known airscrew generally well understood applications laws aerodynamics describe operation pro peller article way diameter pitch rpm propeller well velocity airplane affect thrust power absorption will dis cussed Also will presented way estimate brake horsepower required drive propeller particular rpm particularly useful selecting propeller particular engine airplane estimating effectiveness various fuels engine modifications Terminology number terms will used throughout article describe various physical character istics propellers well conditions under operate Most will familiar anyone experience airplanes several may Bear mind attempting provide understanding operation propellers exhaustive course aerody namics Most readers will buy commercial propellers rather design make own purpose article help make such selection informed way following definitions should sufficient qualitative discussion follows D Diameter measurement inches prop tip tip P h distance inches prop would move forward revolution no slippage J nce ratio measure 42 Model Aviation 50-year-old Brown Jr pioneering gas model engines isa 60 advertised produce 1/5 hp 5000-6000 rpm Since rather flat torque curve could handle large props uncommon inthe prewar Free Flight days see Browns enormous 7-and 8-ftwingspan airplanes happily swinging 17and 18-in props hp may have lower Brown Jr good thrust Ross twin 60no longer production seemed happiest swinging 12 x 6 TheOS Wankel 30 likesto run high rpm hence its best turning 9 x 6 Output strongest engine operating 12 14K range anything dictated best prop K&B 15 Schnuerle thoroughbred racing engine uses very thin highpitched prop art science finding optimum prop raceran example value experimentation 05 60 four-stroke flies stately slow bipe equally well either 13 x 5 14 x 4 612441818 6 629856 121 48294416 110 165536026 velocity V airspeed air plane divided rotational speed propeller its diameter J Xrpm consistent units ie in mm should clear will define angle attack propeller airfoil airspeed rpm Think about mo ment terms unloading engine occurs dive rpm speed rotation pro peller revolutions per minute hp horsepower produced engine absorbed propel ler Power defined force times distance per unit time hp 33000 foot-pounds per minute p Density air varies pressure temperature hu midity slugs per cubic foot standard sea level pressure 2992 Hg temperature 590F p 00237 Thrust term refers force ex erted rotating propeller di rection travel airplane whole purpose propellerto convert power engine appears rotating force torque linear force T p X rpm2 X J4 X Ct Ct thrust coefficient constant shape particular pro peller advance ratio J Rey nolds number Thus Ct will different different propellers under different condi tionsor same propeller under different conditions Since Ct includes advance ratio J determined airspeed its clear thrust will different different airspeeds model purposes very difficult get mean ingful value Ct What informative about formula fact thrust varies fourth power diameter square rpm because thrust developed consequence blade behaving airfoil will recall lift varies square velocity velocity part blade function distance center propeller finally area propeller disk goes square diameter Thus seems advantageous select largest prop consistent desired pitch rpm available power seems make tuitive sense greater volume air will influenced propeller greater thrust Power absorption Reciprocating internal combustion engines include vir tually model engines exhibit power output curve increases increas ing rpm certain peak dimin ishes further increases rpm October 1986 43 Spinners improve appearance reduce drag some extentand also provide place apply starter Spinners diameter up 20% prop diameter can used no reduction perform ance since center prop does convert powertothrust fact spinners im prove efficiency propeller elimi nating turbulence vicinity hub propel airplane formula thrust Continued page 132 Prather pitch gauge useful especially youre serious about racing finding out exactly what have pitch markings stamped prop always correct dontthinkourauthorisseriousabOut propellers take look mailbox AERO-PACER $8900 Span 64 1/2 Weight 55 7 lbs Engine 45 61 FS 5 TS ig 25 oz wing loading 4 channel Sport Trainer GIPSY $10900 MOTH Span 543/4 5475 Weight 5-6 lbs 787 sq inches 15 oz wing loading Engine 45 65 FS 0 TS 4 channel Both kits designed primarily Four-Stoke engine fly equally well Two-Stroke engine Add $450 shipping handling Direct SalesMichigan residents add 4B/0 sales tax Check money orderMastercard Visa Radio Techniq ue/MyersPropellers/Abbott Continued page 129Continued page 43 ratio problems Capture ratio refers characteristic FM receivers allows switch allegiance strongest transmitter vicinity FM Redundant Radio system possible rare possible someone operating vicinity channel take control airplane signal stronger receiver signal flying Redundant Radio system gain freedom interference having half system captured foreign transmitter doesnt help FM Error Switch has deal possibility tests Using oscilloscope set up Error Switch transmitter instructed ran few tests 1 The two receivers attached Error Switch attached via Red port Green port An LED light-emitting diode center device indicates system source signals being used control servo both transmitters working Green 72790 MHzRC5O Red old 72240 MHz servo worked normally Error Switch usually showed Green system control 2 When turned off Green transmitter LED indicated Red system 72240 MHz use servo acted normally 3 When turned off Red transmitter LED indicated Green system use servo acted normally 4 When turned off both transmitters LED indicated Red system select ed course servo did nothing 5 With both transmitters operating turned another RC5O Green transmitter LED flickered Green Red servo continued respond control inputs also exhibited some jitters oscilloscope showed pulses Green port erratic timing pulse widths Red pulses looked normal reset timing Error Switch get solid switch Red no jitters 6 Continuing interference turned off Red transmitter LED indicated Green system selected servo contin ued respond Green system though jittery fashion makes good sense Its better have some control jitters switch dead channel As can easily see addition redun dant radio made dual system almost bullet proof However using two 72 MHz channels leaves us vulnerable same defect mentioned earlier discussed splitting channels groups could used specific lo cationsyou cant sure everyone will cooperate system use right channel right location Working Bob Aberles ham rig Custom Electronics Transmitter T-Module Bobs AM module 534 MHz AM synthesizer module 72 MHz got same results high end six-meter band rarely used might have bit confidence used 53/72 T-Module think everyone should flying everything redundant radios AMA should now create Redundant Radio Phase-In Plan might happen Stay tuned next episode story Interference Fighters George M Myers 70 Froehlich Form Road Hilzksville NY 11801 because power product torque times rpm peak torque generally occurs rpm well below peak power As rpm increases engine produces less force torque because breathing diffi culties less fuel-air mixture gets cylinder stroke higher speeds advisable thus select propeller will permit engine operate just right rpm maximum power As will see moment examine expression power absorp tion speed airplane plays important part problem As matter fact adjustable-pitch pro pellers developed full-size aircraft have used some extent modelsThe formula propeller power power required drive pro peller hp rpm3 X D3 p power coefficient function shape propeller advance ratio Reynolds number Again advance ratio J factors airspeed airplane Note pitch propeller does specifically appear formula included Cp since pitch important factor shape propeller What really important realize propeller power varies cube rpm means twice rpm would require eight times power 10% increase rpm would reflect 33% increase power 20% increase rpm would require 73% increase power Its interesting understand re lationships would nice have some actual numbers stated section thrust its very difficult get useful values thrust coefficient Ct However can get some useful numbers propeller power coefficient Cp * SCALE DOCUMENTATION * SCALE DRAWINGSMODEL PLANS PHOTOS BOOKS EPLA-TECH 1986- INTERNATIONAL AIRPLANE CATALOG OVER 100 PAGES48500 MC KENZIE 1-IWY *300VIDA OREGON 97488 132Model Aviation 11 ATTENTION ERS EPOXY GLASS COWLS FOR NOSEN PICA SIS MORGAN BALSA USA PLATT CONCEPT FLEET HOSTETLER RCM TCRAPT SHEBER PuTS N & N SCALE SUPER CUB FOKKER 57 BOEING P12 P26 F4B2 P4B4 SPARROW HAWK GEE BEE MOO Y MACBRIENS TURBULENT CHRISTEN EAGLE BRISIGHELLAS STARDUSTER II IA SCALE J3Bl BABY FLYBABY N 0 TN E B S WHEEL PANTS FOR CITABRIA STARDUSTER II PIUS SKYBOLT LIBERTY SPORT CHRISTEN EAGLE P6E HAWK MULLIGAN H OTHERS LARGE SCALE PLANS AVAILABLE Please send $100 complete lIst WB supply Modelers fiberglass parts plans Write Call us T & D FIBERGLASS SPECIALTIES 30925 BLOCK GARDEN CITY MI 4B13B PHONE 1313421-6358 BRAZED -TREATED WIRE GEAR5 & CABANES PHONE 313 21-9064 WORLOS ClOSES SCALE enOTO SERVICE 5005 PHBrC PACrSr PLANS EWS PHOTO-PACKSPLANS ENLARGING 5*5E Enlarging coats Catalog 5300SCALE PlANS PHOTO SEll IJICE 3209 MadiSOn GeanSBoB N C 27403 Phone lB1B1292B239 NH CRIIEZII PAWU DIESELS Englands Finest 049 35 RIG STD Send $100 list Eric Clutton 913 Cedar Lane Tullahoma Tenn 37388 Model Magic Filler Balsa Foam & Fiberglasssands exactly like Balsa Super lightweight Superior adhesion Waterproof Nontoxic Use nicks gaps fillets fairings building up large areas8 fI oz $595 retail k. 0~~ CmQ 1 Model Magic Epoxy Plus 8 mm 25% lighter Sands & carves like Basswood Non sagging gap filling super strength Use anywhere \ atwo part epoxy used 6f1 oz $895 retail equal 8 oz regular epoxy Red Gas & Diesel Tubing fQ1Model Magic Gas & Diesel Fuel Tubing will swell tine products available dealer direct Magic Products PO Box 19784 C~del St Paul MN 55119 715/425-1397 d shrink turn brittle used gasoline diesel~1~ fuel offers clarity visual fuel flow Model Magic fuel tubing remains flexible plasticizer migration foul engines exhibits outstanding tear abrasion resistence Tubing tinted red easy identification gasoline & diesel use Available 5ft $249/pkg 1 Oft $479/pkg SOft spools $2190 Blue Gb-Fuel Tubing Made finest silicone tubing available Less 1% swelling after 150 hours 15% nitro fuel Available 21/2 5ft packages 5Oft spoolsy C& Inc under static conditions means can estimate hp produced engine driving particular propeller measuring rpm know hp produced engine particular rpm can select appropriate propeller propeller power chart Recall formula propeller power given above hp rpm3 X D5 X Cp density air p known Cp constant determined shape propeller advance ratio etc have know want find hp above formula tough problem However discovered some articles books published 50 60 years ago gave some values Cp full-size propellers days laws physics dont change publications gave some clues follow Among other things turns out model airplane propellers operate Reynolds numbers quite similar full-size lightplane props because although model props smaller operate much higher speeds researched engine reviews horsepower reported together pitch di ameter props used data able derive following expression accurate better adequate model work P D5rpm3 hp 1011 P D inches formula identical previous except numerical value Cp terms ratio pitch diameter including standard value p density air has introduced advance ratio J course zero since dealing static conditions should make sense Cp shape factor propeller pitch diameter obviously principle aspects shape propeller formula can re written little simpler form hp rpm3/l4x 1011 have calculator has exponential function engineering no tation denominator 14 17 zeros after its easy enough plug pitch diameter rpm get power Its nice have formula like its nicer able estimate power particular prop/rpm situation having lot calculations make possible Ive constructed graph permits chose combination pitch diameter might encounter modeling imedi ately find power rpm vice versa must make calculation PD4 dont want Ive indicated chart values PD4 number commonly-used model pro pellers use chart take diameter Continued page 136 CLEVELANDS GI NTSI MANY NEW FOR R/C BUFFS Decignod Ac BasIc Macnr Flying Modal Following BolltUp Prototype Fraction Wood Fabric Ropboo fiocIiinr Vt Thoi New Hictarical Bad 57 Cott JN4 Jan01 $27 81 8 14 Foklcan 07 Ftn$39 108 70 Boylec Gan-Bor $32 POSt 10 Hoorord Poto Rorn $32 99 N 05 Sopanononion S6B $24 71 5 B9 Sopannnonino 56$ $35 950 03Cont Honib F6E $42 068 94 Curt Hoork P6E $5464 St 74 Doolucrlac GB 11 $48r72 C 95 Mororoop Sport $36 109 80 Poll Opt Enildog $43OS Ooogloc 002 Mod $24 107 Aerooto C3 Syt $35r 68 Brictol Bnildog Fr 830 62 Bonrond Born $45 59 Broinfora McLA $54n 78 Tonnenc W-W tot $35 107 Groor Bnorrc F8F 054 63 Cor GochIr 7117 $42 69 Lirdbnngc NO211 $30 94 Cor Cochb Fl lC $54 91 [idbnrgc NO211 839 oNor Cornet $24 96 WnNWlNoo $48 62 BoroMrMolIigoO $35 74 C Hnlldrr SB2C-4 $55 94 HooiMnMolligon 84W 108 FoirrhFTt9 $S9 63 Boning F-26A Ftn $36 65 Worn TopanWing $36 84 8oaing P366 Frr $4890 Worn ToparWing $4B8 IO4Worn C-B Cobin $55r75 Wotl4 [tncordar 832 Booth 717$ Stog 830 lOS Wacrid Lycoodar $49r 96 Bonrb 717-B Slog $49n57 Ford Tninrln 4AT $36 * 55 [orb 11 Elantro $30 76 Ford Trinrtr 4AS $48 02 Lork II Elaorno 840 114 Ford Trionrr 4AS 865 * 62 SOocon T/W Sf7 $18 06 Bolloorn Ainrroc $40 81 Stincon 01W 087 $26 93 Looohng C2Anrplr $69 122 Stirrcorr 5/W Sf7 $38 50 Groin J3F Gorlr $29 59 Bnintol Ftr F2-8 $20 78 Grirnr J3F Sorb $56 118 Bristol FIr 7208 $45. 124 [orb Air Doyrocin $48 74Srnnanc P0cm $45 65 [orb Air Eopranc 824 56 Crr Worirk F-40 $24 02 [orb Air Erpreco $36 60 Vogt Corcoin P40 $35 77 WWrrnc 121 BadI 848 00 Vogt Corcoin F45 $69 637 Sooborinrlr F7C1 845 7$ Lork Liglrtrrg F38 $38 947 Snohoork 9771 $57.r 56 fnpSao-Bno Ant $24 158 Sibor 058 Annph $49 74 RnpSoo8aa Ant $39 65 Booing 100 Sport $36 70 Fion J3 Cob$29 95 Bonrrq 100 Sport $49 106 Pipan J3 Cob$39 75 Nonrlrrop Gonnrrro $40 90 [orb Hodono Oonb $38 96 Northro Goon o $75 * 63 Gino F6F Halloot 028 95 S 77 Bonino B17G Fort $35 60$ 153 Boo B17G Fort OSS too 68 Woctl Whirlnrind 832 78 C 68 N Amer Nonion 839 104 Corn Co FBY SA $56 68 BBononco VToiI $39 61007$ no C pyr 865 77 Locroroba Sadno $25 9700 7$ no C ppo $75 72 NA $25 Boonbor $49 05 Co cc NC 4 859 65 OtMonoodon B26 $49 94 Co cc NC 4 $69 iroro POICO ronicotoc oroonrono As 4. Goon 205 Otlnnnc 6 73 100 SOc Up Add 10% oil ondon chi p gA USA Con & Mao Elcanchana ir % Fiotoniol rotolog 8200 inrlod cnotion 01000 81 05 II nin fonogn odd $1 5$ r LEVELANDMODEL&SUPPLYCo 050 rorconnAoiorrnn c scc tIEeco. sicoc net lB305S DBT$OIT AVE CLEVELAND OHIO 44182 pnOrsocnre n 000 O OAro 981 0000 October 1986 133 Building repairs snap Model Magic Horn Old Timer fl{2t born 7&QVii LANZOS 8 GAS 900Cc cAdO deL S~ cr1 cs RECORD BREAKER -1941 BROOKLYN DODGER 36 Cabi EWEST0 Retail $529505INTRODUCTORY PRICE0 $3900 1938 Record Breaker 96 $6956 tO39Zipper 54$5356 1938 Kloud King 63 $42 36 1941 Brigidier 56 $4076 1941 Super Ouaker 78 $7276 1940 So Long 50$3036 1936 Buccaneer 84 $5996 1938 Clipper MKI 72$4156 1937 Dallaire 108 $75 16 1935 Miss America 84$7196 1941 Playboy Sr 80 $5116 1991 Playboy Jr 54$31 16 1938 Powerhouse 84 $5356 1990 Sailplane 76 $0479 1938 Trenton Terror 72 $90 76 1990 Ranger 46$31 96 1939 Korda Wake 44 $1916 1939 Mercury 72 6 kits gualify SAM evento EF & RIG ond feature highest quabty machine cut 6 sanded parts Superior Competition ott ahoet atrip wood mire & window material Ptana orig EF modela easily convertible Och RIG KITS Sailplanes Electric power Gas Hobby Horn SENSOAR Glider 78 $1600 Midway Model GNOME RIG Hand Launch Glider$2400 Jolly Models FLINGER RIG HLG 50 Span$2400 Midway Model FAST EDDIE Aerobatic /05 EIec$19 00 Jolly Models ELECTRICUS Electric Glider 05s93250 Leisure PLAYBOY SR 67 Gear 05 Elect $3800 Astro ASTRO SPORT 37 Direct 05 Elect $2250 Leisure WASP 37 Direct 05 Electrics$2210 Midway ULTRA MK IV 86 Geared 04 EP $3900 Midway FLYING OUAKER 84 40-454 stroke $6976 4kslMidway DENNY JR 72 Alum Comel$6396 4kslMidwav BUZZARD BOMBSHELL 7200196 FULL LINE OF ELECTRIC SYSTEMS S Parts Avail SHIIlllll & HANDLING Up $000 add $150 $801 $2000 add $220 $2001 $4500 add $301 $4501 $7000 add $350 over $7000 add $4 00 CA Addressees add 65 tax Send MO VisaIMC# Eap Check allow up 30 days CK clearance COD Exact Charges plus $158 HdI Cash Only Designs 06 DA 0 0 S C 21 0 0 18 C 01 1 91 2_________ 0 0 a_________________ C 21 01__________________ ___ __________ S 0 C 21 C 0 0 0 C Ct k4 Page UAaALUUUO $200 PP/tat Clxos copy will sent free--when requested-with order HOBBY HORN 15173 Moran St PO Bow 2212 Westminster Ca 92604 714 0938311 [AftHrs 714 0951203] . 0ce Deslgfls 0 0 IC 18 S 0 SPORT BIPE S $21 PPD 0 PPDZl S _______________0 ~s15 __________0 It ________________0 0 PHOTO DOCUMENTATION PACKS availableon Scale Plans ALL PLANS ROLLEDSHIPPED UPS Compleie wlnetrection Osokiet Send slOO Catalog New York OlaRe Residenie aoO 7% selee tax. Osndsheak . Allow 3 weeks aleckfoalxar QUARTER SCALE PLANSQuarter Master Sport BIpe0 Guadra 35. 73Span.E-Z build. Great PIyer.*Semitif Acailable DAVIS D-1K 905 Span. Ouadra 35 power similar. 1933 KINNER SPORTSTER Model K.ll7Span.035 power. 4-CYCLE PROJECTS aW AKRON FUNK ls Ocae 84span AO size 4 cesle. Faniasiic Flyer DAVIS D1K00 BOa Span. 40 4 cycle similar. Two losS wale 010th scale 1933 KINNER SPORTSTERRR Ce Model K. 79 Span. B1-75.4ny poo510 *e Photo roosoed ocr 1/4 Osele plans. Two loon scale Sloth seals DA Plans comino Propellers/Abbott Continued page 133 prop inches raise fourth power multiply pitch inches common model props will get number between 20000 5000000 find value upper right-hand part chart follow diagonal line down left rpm/hp combination will probably find value PD4 get particular prop does exactly agree values chart will have interpolate between given values need greater accuracy can always use formula other hand know power rpm engine wish select appropriate propeller find inter section hp rpm follow diagonal up right find value PD4 can use calculator find combinations pitch diameter equal value PD4 find diameter will have able find fourth root number must have scientific-type calculator least has exponential func tion have use exponen tial key usually labeled xy enter 25 exponent Finally Ive provided listing values PD4 some 32 typical model propellers chart works two-bladed props having aspect ratio between 61 91 typical props used RC CL models have tested thin toothpick props used racers also very useful have idea airspeed range may expected particular propeller given rpm will obvious higher pitch will result higher speed simple formula relates pitch airspeed rpm mph thousands X pitch nominal airspeed air speed would result propeller operating no slippage nominal airspeed chart shows relationship air speed rpm propeller pitches 3 12 rpm up 15000 covers model situations assumption no slippage course usually encountered actual flight However does give valuable insight selection propeller particular set conditions example suppose airplane planned fly 75 mph engine expected run 10000 rpm chart may immediately determined 10000 rpm propeller 8-in pitch will have nominal airspeed 75 mph Its therefore obvious propeller selected must have 8-in pitch greater airspeed 75 mph reached Its true under certain conditions speeds excess nominal airspeed may achieved due fact propeller blade airfoil may produce lift slightly negative angle attack Bear mind vail ables involved analysis propellers article have made number simplifying assumptions order provide fairly simple method estimating pro peller performance have found results better hp cases Ive checked method against data full-size aircraft engines propel lers well home-builts ultralights have always well within tha range Im confident method i adequate model purposes Conclusion discussed two formulac describe two important aspects 01 propeller behavior thrust power ab sorption formula thrust th importance diameter disk area came apparent discussion 01 power saw propeller powe varies third power rpm 2 fairly small change rpm indicates rathe larger change power chart pre sented makes possible estimate power required drive propeller particular rpm chart also pro vided find nominal airspeed function rpm propeller pitch RC Scale/Wischers Continued page 45 connecting link lined up directly across servo output shaft centerline will no load servo motor Current flow servo will drop idle flaps locked down securely course true full-flap position extra gear retract servo also helps reduce current con sumption intermediate flap positions Incidence angles again third time recent columns going dwell upon touchy subject disastrous crash club field model descended ver tically impact few feet pit area filled models fliers spectators Fortunately missed everyone thing destroying itself pilot us ing full up-elevator throughout dive several hundred feet no appar ent response plane Having built kit assumed incidence angles correct center gravity location concern its first flight case due building error stabilizer leading edge inad vertently raised bit too much providing lifting force Ordinarily sort thing causes no great problem model can readily flown trimming bit upelevator model ratio stabilizer area elevator area quite high large stab small elevator Elevator travel set near minimum prevent overcontrolling Whenever model built up speed tendency models nose tuck under required full upelevator recover level flight its final dive gathered excessive speed simply wouldnt pull out enough up-elevator travel say During its first flight 136 Model Aviation TOciarterMaster .ru 3] i 11

Theyre almost everything fly except gliders ducted-fan models much really know about props bolt onto engines article can provide us starting point determin ing prop works given application EGeorge Abbott FOR MOST MODELERS selection propeller usually matter fol lowing recommendation engine manufacturer airplane designer Later modeler may experiment dif ferent diameter pitch combinations seeking seems provide type performance desired advent larger chainsaw engines big glow engines four-cycle engines modeler faced power plants having characteristics quite different glow engines have standard hobby 30 years larger engines may develop up 5 hp around 10000 rpm fourcycle engines develop power some what lower rpm two-cycle coun terparts generally 10000 rpm less although some four-cycles now appearing run several thousand rpm faster Because four-cycle engines offer certain advantages such lower noise reduced fuel consumption often de sirable use airplanes designed two-cycle power plants An other advantage often claimed fourcycle engines improved vertical performance constant speed through ma neuvers Achieving advantages dependent upon selection proper propeller particular engine airplane combination example suppose has fourcycle engine expected develop 1 hp 13000 desired use engine airplane expected fly tween 50 60 mph nominal airspeed chart presented article can found 13000 rpm propeller 6-in pitch has nominal speed 74 mph 8-in pitch has speed 99 mph 5 62 mph Further power absorption chart shows 1 hp 13000 rpm represents power absorption Left big Kioritz swings 22 xl 0 prop transmit aii powerto prop six-boit hub used Right Saito 45 Ace 4-4Oturns 12 x 6 prop plane actuaiiy flew betterwith 13 x 5 ground ciearance pilot skiii made 12 x 6 economical choice 40 Model Aviation Theres commercially-avaliabie prop virtuaiiy diameter pitch can imagine choosing best particular engine airpiane can difficult 8/4 8/6 9/8 10/6 10/8 ** -~1p13/8 80 90 100 P14/8 16/6 16/8 ___418/6 18/8 90018/10 100020/8 -20/10 22/8 24/8 24/10 hf26/10 0/P - ----- 1000 4 ii~x--x 2 -- -77 i-- 7 - - 4 -7 25 HP PD4 RPM3 14 x 7 810 fourth power multiply pitch inches Find ersects rpm hp tines determine appropriate prop go n follow nearest diagonal line up diameter/plth value factor 60000 turn indicates suitable propellers would 9/8 10/6 11/5 actually 1045/5 power curve engine known easy make further selections Vihen relation ship between thrust rpmand thrust propeller diameterare understood selections may intelligently made must bear mind power absorption chart applies static condi tions flight engine will unload some extent will probably choose propeller will load engine toward low end its power curve under static conditions achieve close maxi mum power flight Except racing aircraft maximum power usually desired climb during vertical maneuvers time airspeed toward low end aircraft speed range An understanding interrelation ship between engine power rpm propeller pitch diameter thrust will valuable October 1986 41 12/6 12/8 * * Left Ziroll Morane Saulnier plain-bearing OS 35 uses 11 x 5 prop Generally engine uses lOx 6 airplanes performance noticeably better 11 x 5 Propeller choice isa matter matching engine airplane pilot preference Right nearly-finished 1/4-scale L-4 J-3 has OS 120 four-cycle twin 20 x6 prop will starting point 18 x6 mounted forthe photo both airplane designer modeler wishing select airframe/en gine combination will provide desired type performance Basics Everyone has pretty fair general understanding principles operation airplane propellers Its generally under stood propeller device serves convert power produced engine thrust cause airplane move through air screw analogy easily understood fact European countries propeller known airscrew generally well understood applications laws aerodynamics describe operation pro peller article way diameter pitch rpm propeller well velocity airplane affect thrust power absorption will dis cussed Also will presented way estimate brake horsepower required drive propeller particular rpm particularly useful selecting propeller particular engine airplane estimating effectiveness various fuels engine modifications Terminology number terms will used throughout article describe various physical character istics propellers well conditions under operate Most will familiar anyone experience airplanes several may Bear mind attempting provide understanding operation propellers exhaustive course aerody namics Most readers will buy commercial propellers rather design make own purpose article help make such selection informed way following definitions should sufficient qualitative discussion follows D Diameter measurement inches prop tip tip P h distance inches prop would move forward revolution no slippage J nce ratio measure 42 Model Aviation 50-year-old Brown Jr pioneering gas model engines isa 60 advertised produce 1/5 hp 5000-6000 rpm Since rather flat torque curve could handle large props uncommon inthe prewar Free Flight days see Browns enormous 7-and 8-ftwingspan airplanes happily swinging 17and 18-in props hp may have lower Brown Jr good thrust Ross twin 60no longer production seemed happiest swinging 12 x 6 TheOS Wankel 30 likesto run high rpm hence its best turning 9 x 6 Output strongest engine operating 12 14K range anything dictated best prop K&B 15 Schnuerle thoroughbred racing engine uses very thin highpitched prop art science finding optimum prop raceran example value experimentation 05 60 four-stroke flies stately slow bipe equally well either 13 x 5 14 x 4 612441818 6 629856 121 48294416 110 165536026 velocity V airspeed air plane divided rotational speed propeller its diameter J Xrpm consistent units ie in mm should clear will define angle attack propeller airfoil airspeed rpm Think about mo ment terms unloading engine occurs dive rpm speed rotation pro peller revolutions per minute hp horsepower produced engine absorbed propel ler Power defined force times distance per unit time hp 33000 foot-pounds per minute p Density air varies pressure temperature hu midity slugs per cubic foot standard sea level pressure 2992 Hg temperature 590F p 00237 Thrust term refers force ex erted rotating propeller di rection travel airplane whole purpose propellerto convert power engine appears rotating force torque linear force T p X rpm2 X J4 X Ct Ct thrust coefficient constant shape particular pro peller advance ratio J Rey nolds number Thus Ct will different different propellers under different condi tionsor same propeller under different conditions Since Ct includes advance ratio J determined airspeed its clear thrust will different different airspeeds model purposes very difficult get mean ingful value Ct What informative about formula fact thrust varies fourth power diameter square rpm because thrust developed consequence blade behaving airfoil will recall lift varies square velocity velocity part blade function distance center propeller finally area propeller disk goes square diameter Thus seems advantageous select largest prop consistent desired pitch rpm available power seems make tuitive sense greater volume air will influenced propeller greater thrust Power absorption Reciprocating internal combustion engines include vir tually model engines exhibit power output curve increases increas ing rpm certain peak dimin ishes further increases rpm October 1986 43 Spinners improve appearance reduce drag some extentand also provide place apply starter Spinners diameter up 20% prop diameter can used no reduction perform ance since center prop does convert powertothrust fact spinners im prove efficiency propeller elimi nating turbulence vicinity hub propel airplane formula thrust Continued page 132 Prather pitch gauge useful especially youre serious about racing finding out exactly what have pitch markings stamped prop always correct dontthinkourauthorisseriousabOut propellers take look mailbox AERO-PACER $8900 Span 64 1/2 Weight 55 7 lbs Engine 45 61 FS 5 TS ig 25 oz wing loading 4 channel Sport Trainer GIPSY $10900 MOTH Span 543/4 5475 Weight 5-6 lbs 787 sq inches 15 oz wing loading Engine 45 65 FS 0 TS 4 channel Both kits designed primarily Four-Stoke engine fly equally well Two-Stroke engine Add $450 shipping handling Direct SalesMichigan residents add 4B/0 sales tax Check money orderMastercard Visa Radio Techniq ue/MyersPropellers/Abbott Continued page 129Continued page 43 ratio problems Capture ratio refers characteristic FM receivers allows switch allegiance strongest transmitter vicinity FM Redundant Radio system possible rare possible someone operating vicinity channel take control airplane signal stronger receiver signal flying Redundant Radio system gain freedom interference having half system captured foreign transmitter doesnt help FM Error Switch has deal possibility tests Using oscilloscope set up Error Switch transmitter instructed ran few tests 1 The two receivers attached Error Switch attached via Red port Green port An LED light-emitting diode center device indicates system source signals being used control servo both transmitters working Green 72790 MHzRC5O Red old 72240 MHz servo worked normally Error Switch usually showed Green system control 2 When turned off Green transmitter LED indicated Red system 72240 MHz use servo acted normally 3 When turned off Red transmitter LED indicated Green system use servo acted normally 4 When turned off both transmitters LED indicated Red system select ed course servo did nothing 5 With both transmitters operating turned another RC5O Green transmitter LED flickered Green Red servo continued respond control inputs also exhibited some jitters oscilloscope showed pulses Green port erratic timing pulse widths Red pulses looked normal reset timing Error Switch get solid switch Red no jitters 6 Continuing interference turned off Red transmitter LED indicated Green system selected servo contin ued respond Green system though jittery fashion makes good sense Its better have some control jitters switch dead channel As can easily see addition redun dant radio made dual system almost bullet proof However using two 72 MHz channels leaves us vulnerable same defect mentioned earlier discussed splitting channels groups could used specific lo cationsyou cant sure everyone will cooperate system use right channel right location Working Bob Aberles ham rig Custom Electronics Transmitter T-Module Bobs AM module 534 MHz AM synthesizer module 72 MHz got same results high end six-meter band rarely used might have bit confidence used 53/72 T-Module think everyone should flying everything redundant radios AMA should now create Redundant Radio Phase-In Plan might happen Stay tuned next episode story Interference Fighters George M Myers 70 Froehlich Form Road Hilzksville NY 11801 because power product torque times rpm peak torque generally occurs rpm well below peak power As rpm increases engine produces less force torque because breathing diffi culties less fuel-air mixture gets cylinder stroke higher speeds advisable thus select propeller will permit engine operate just right rpm maximum power As will see moment examine expression power absorp tion speed airplane plays important part problem As matter fact adjustable-pitch pro pellers developed full-size aircraft have used some extent modelsThe formula propeller power power required drive pro peller hp rpm3 X D3 p power coefficient function shape propeller advance ratio Reynolds number Again advance ratio J factors airspeed airplane Note pitch propeller does specifically appear formula included Cp since pitch important factor shape propeller What really important realize propeller power varies cube rpm means twice rpm would require eight times power 10% increase rpm would reflect 33% increase power 20% increase rpm would require 73% increase power Its interesting understand re lationships would nice have some actual numbers stated section thrust its very difficult get useful values thrust coefficient Ct However can get some useful numbers propeller power coefficient Cp * SCALE DOCUMENTATION * SCALE DRAWINGSMODEL PLANS PHOTOS BOOKS EPLA-TECH 1986- INTERNATIONAL AIRPLANE CATALOG OVER 100 PAGES48500 MC KENZIE 1-IWY *300VIDA OREGON 97488 132Model Aviation 11 ATTENTION ERS EPOXY GLASS COWLS FOR NOSEN PICA SIS MORGAN BALSA USA PLATT CONCEPT FLEET HOSTETLER RCM TCRAPT SHEBER PuTS N & N SCALE SUPER CUB FOKKER 57 BOEING P12 P26 F4B2 P4B4 SPARROW HAWK GEE BEE MOO Y MACBRIENS TURBULENT CHRISTEN EAGLE BRISIGHELLAS STARDUSTER II IA SCALE J3Bl BABY FLYBABY N 0 TN E B S WHEEL PANTS FOR CITABRIA STARDUSTER II PIUS SKYBOLT LIBERTY SPORT CHRISTEN EAGLE P6E HAWK MULLIGAN H OTHERS LARGE SCALE PLANS AVAILABLE Please send $100 complete lIst WB supply Modelers fiberglass parts plans Write Call us T & D FIBERGLASS SPECIALTIES 30925 BLOCK GARDEN CITY MI 4B13B PHONE 1313421-6358 BRAZED -TREATED WIRE GEAR5 & CABANES PHONE 313 21-9064 WORLOS ClOSES SCALE enOTO SERVICE 5005 PHBrC PACrSr PLANS EWS PHOTO-PACKSPLANS ENLARGING 5*5E Enlarging coats Catalog 5300SCALE PlANS PHOTO SEll IJICE 3209 MadiSOn GeanSBoB N C 27403 Phone lB1B1292B239 NH CRIIEZII PAWU DIESELS Englands Finest 049 35 RIG STD Send $100 list Eric Clutton 913 Cedar Lane Tullahoma Tenn 37388 Model Magic Filler Balsa Foam & Fiberglasssands exactly like Balsa Super lightweight Superior adhesion Waterproof Nontoxic Use nicks gaps fillets fairings building up large areas8 fI oz $595 retail k. 0~~ CmQ 1 Model Magic Epoxy Plus 8 mm 25% lighter Sands & carves like Basswood Non sagging gap filling super strength Use anywhere \ atwo part epoxy used 6f1 oz $895 retail equal 8 oz regular epoxy Red Gas & Diesel Tubing fQ1Model Magic Gas & Diesel Fuel Tubing will swell tine products available dealer direct Magic Products PO Box 19784 C~del St Paul MN 55119 715/425-1397 d shrink turn brittle used gasoline diesel~1~ fuel offers clarity visual fuel flow Model Magic fuel tubing remains flexible plasticizer migration foul engines exhibits outstanding tear abrasion resistence Tubing tinted red easy identification gasoline & diesel use Available 5ft $249/pkg 1 Oft $479/pkg SOft spools $2190 Blue Gb-Fuel Tubing Made finest silicone tubing available Less 1% swelling after 150 hours 15% nitro fuel Available 21/2 5ft packages 5Oft spoolsy C& Inc under static conditions means can estimate hp produced engine driving particular propeller measuring rpm know hp produced engine particular rpm can select appropriate propeller propeller power chart Recall formula propeller power given above hp rpm3 X D5 X Cp density air p known Cp constant determined shape propeller advance ratio etc have know want find hp above formula tough problem However discovered some articles books published 50 60 years ago gave some values Cp full-size propellers days laws physics dont change publications gave some clues follow Among other things turns out model airplane propellers operate Reynolds numbers quite similar full-size lightplane props because although model props smaller operate much higher speeds researched engine reviews horsepower reported together pitch di ameter props used data able derive following expression accurate better adequate model work P D5rpm3 hp 1011 P D inches formula identical previous except numerical value Cp terms ratio pitch diameter including standard value p density air has introduced advance ratio J course zero since dealing static conditions should make sense Cp shape factor propeller pitch diameter obviously principle aspects shape propeller formula can re written little simpler form hp rpm3/l4x 1011 have calculator has exponential function engineering no tation denominator 14 17 zeros after its easy enough plug pitch diameter rpm get power Its nice have formula like its nicer able estimate power particular prop/rpm situation having lot calculations make possible Ive constructed graph permits chose combination pitch diameter might encounter modeling imedi ately find power rpm vice versa must make calculation PD4 dont want Ive indicated chart values PD4 number commonly-used model pro pellers use chart take diameter Continued page 136 CLEVELANDS GI NTSI MANY NEW FOR R/C BUFFS Decignod Ac BasIc Macnr Flying Modal Following BolltUp Prototype Fraction Wood Fabric Ropboo fiocIiinr Vt Thoi New Hictarical Bad 57 Cott JN4 Jan01 $27 81 8 14 Foklcan 07 Ftn$39 108 70 Boylec Gan-Bor $32 POSt 10 Hoorord Poto Rorn $32 99 N 05 Sopanononion S6B $24 71 5 B9 Sopannnonino 56$ $35 950 03Cont Honib F6E $42 068 94 Curt Hoork P6E $5464 St 74 Doolucrlac GB 11 $48r72 C 95 Mororoop Sport $36 109 80 Poll Opt Enildog $43OS Ooogloc 002 Mod $24 107 Aerooto C3 Syt $35r 68 Brictol Bnildog Fr 830 62 Bonrond Born $45 59 Broinfora McLA $54n 78 Tonnenc W-W tot $35 107 Groor Bnorrc F8F 054 63 Cor GochIr 7117 $42 69 Lirdbnngc NO211 $30 94 Cor Cochb Fl lC $54 91 [idbnrgc NO211 839 oNor Cornet $24 96 WnNWlNoo $48 62 BoroMrMolIigoO $35 74 C Hnlldrr SB2C-4 $55 94 HooiMnMolligon 84W 108 FoirrhFTt9 $S9 63 Boning F-26A Ftn $36 65 Worn TopanWing $36 84 8oaing P366 Frr $4890 Worn ToparWing $4B8 IO4Worn C-B Cobin $55r75 Wotl4 [tncordar 832 Booth 717$ Stog 830 lOS Wacrid Lycoodar $49r 96 Bonrb 717-B Slog $49n57 Ford Tninrln 4AT $36 * 55 [orb 11 Elantro $30 76 Ford Trinrtr 4AS $48 02 Lork II Elaorno 840 114 Ford Trionrr 4AS 865 * 62 SOocon T/W Sf7 $18 06 Bolloorn Ainrroc $40 81 Stincon 01W 087 $26 93 Looohng C2Anrplr $69 122 Stirrcorr 5/W Sf7 $38 50 Groin J3F Gorlr $29 59 Bnintol Ftr F2-8 $20 78 Grirnr J3F Sorb $56 118 Bristol FIr 7208 $45. 124 [orb Air Doyrocin $48 74Srnnanc P0cm $45 65 [orb Air Eopranc 824 56 Crr Worirk F-40 $24 02 [orb Air Erpreco $36 60 Vogt Corcoin P40 $35 77 WWrrnc 121 BadI 848 00 Vogt Corcoin F45 $69 637 Sooborinrlr F7C1 845 7$ Lork Liglrtrrg F38 $38 947 Snohoork 9771 $57.r 56 fnpSao-Bno Ant $24 158 Sibor 058 Annph $49 74 RnpSoo8aa Ant $39 65 Booing 100 Sport $36 70 Fion J3 Cob$29 95 Bonrrq 100 Sport $49 106 Pipan J3 Cob$39 75 Nonrlrrop Gonnrrro $40 90 [orb Hodono Oonb $38 96 Northro Goon o $75 * 63 Gino F6F Halloot 028 95 S 77 Bonino B17G Fort $35 60$ 153 Boo B17G Fort OSS too 68 Woctl Whirlnrind 832 78 C 68 N Amer Nonion 839 104 Corn Co FBY SA $56 68 BBononco VToiI $39 61007$ no C pyr 865 77 Locroroba Sadno $25 9700 7$ no C ppo $75 72 NA $25 Boonbor $49 05 Co cc NC 4 859 65 OtMonoodon B26 $49 94 Co cc NC 4 $69 iroro POICO ronicotoc oroonrono As 4. Goon 205 Otlnnnc 6 73 100 SOc Up Add 10% oil ondon chi p gA USA Con & Mao Elcanchana ir % Fiotoniol rotolog 8200 inrlod cnotion 01000 81 05 II nin fonogn odd $1 5$ r LEVELANDMODEL&SUPPLYCo 050 rorconnAoiorrnn c scc tIEeco. sicoc net lB305S DBT$OIT AVE CLEVELAND OHIO 44182 pnOrsocnre n 000 O OAro 981 0000 October 1986 133 Building repairs snap Model Magic Horn Old Timer fl{2t born 7&QVii LANZOS 8 GAS 900Cc cAdO deL S~ cr1 cs RECORD BREAKER -1941 BROOKLYN DODGER 36 Cabi EWEST0 Retail $529505INTRODUCTORY PRICE0 $3900 1938 Record Breaker 96 $6956 tO39Zipper 54$5356 1938 Kloud King 63 $42 36 1941 Brigidier 56 $4076 1941 Super Ouaker 78 $7276 1940 So Long 50$3036 1936 Buccaneer 84 $5996 1938 Clipper MKI 72$4156 1937 Dallaire 108 $75 16 1935 Miss America 84$7196 1941 Playboy Sr 80 $5116 1991 Playboy Jr 54$31 16 1938 Powerhouse 84 $5356 1990 Sailplane 76 $0479 1938 Trenton Terror 72 $90 76 1990 Ranger 46$31 96 1939 Korda Wake 44 $1916 1939 Mercury 72 6 kits gualify SAM evento EF & RIG ond feature highest quabty machine cut 6 sanded parts Superior Competition ott ahoet atrip wood mire & window material Ptana orig EF modela easily convertible Och RIG KITS Sailplanes Electric power Gas Hobby Horn SENSOAR Glider 78 $1600 Midway Model GNOME RIG Hand Launch Glider$2400 Jolly Models FLINGER RIG HLG 50 Span$2400 Midway Model FAST EDDIE Aerobatic /05 EIec$19 00 Jolly Models ELECTRICUS Electric Glider 05s93250 Leisure PLAYBOY SR 67 Gear 05 Elect $3800 Astro ASTRO SPORT 37 Direct 05 Elect $2250 Leisure WASP 37 Direct 05 Electrics$2210 Midway ULTRA MK IV 86 Geared 04 EP $3900 Midway FLYING OUAKER 84 40-454 stroke $6976 4kslMidway DENNY JR 72 Alum Comel$6396 4kslMidwav BUZZARD BOMBSHELL 7200196 FULL LINE OF ELECTRIC SYSTEMS S Parts Avail SHIIlllll & HANDLING Up $000 add $150 $801 $2000 add $220 $2001 $4500 add $301 $4501 $7000 add $350 over $7000 add $4 00 CA Addressees add 65 tax Send MO VisaIMC# Eap Check allow up 30 days CK clearance COD Exact Charges plus $158 HdI Cash Only Designs 06 DA 0 0 S C 21 0 0 18 C 01 1 91 2_________ 0 0 a_________________ C 21 01__________________ ___ __________ S 0 C 21 C 0 0 0 C Ct k4 Page UAaALUUUO $200 PP/tat Clxos copy will sent free--when requested-with order HOBBY HORN 15173 Moran St PO Bow 2212 Westminster Ca 92604 714 0938311 [AftHrs 714 0951203] . 0ce Deslgfls 0 0 IC 18 S 0 SPORT BIPE S $21 PPD 0 PPDZl S _______________0 ~s15 __________0 It ________________0 0 PHOTO DOCUMENTATION PACKS availableon Scale Plans ALL PLANS ROLLEDSHIPPED UPS Compleie wlnetrection Osokiet Send slOO Catalog New York OlaRe Residenie aoO 7% selee tax. Osndsheak . Allow 3 weeks aleckfoalxar QUARTER SCALE PLANSQuarter Master Sport BIpe0 Guadra 35. 73Span.E-Z build. Great PIyer.*Semitif Acailable DAVIS D-1K 905 Span. Ouadra 35 power similar. 1933 KINNER SPORTSTER Model K.ll7Span.035 power. 4-CYCLE PROJECTS aW AKRON FUNK ls Ocae 84span AO size 4 cesle. Faniasiic Flyer DAVIS D1K00 BOa Span. 40 4 cycle similar. Two losS wale 010th scale 1933 KINNER SPORTSTERRR Ce Model K. 79 Span. B1-75.4ny poo510 *e Photo roosoed ocr 1/4 Osele plans. Two loon scale Sloth seals DA Plans comino Propellers/Abbott Continued page 133 prop inches raise fourth power multiply pitch inches common model props will get number between 20000 5000000 find value upper right-hand part chart follow diagonal line down left rpm/hp combination will probably find value PD4 get particular prop does exactly agree values chart will have interpolate between given values need greater accuracy can always use formula other hand know power rpm engine wish select appropriate propeller find inter section hp rpm follow diagonal up right find value PD4 can use calculator find combinations pitch diameter equal value PD4 find diameter will have able find fourth root number must have scientific-type calculator least has exponential func tion have use exponen tial key usually labeled xy enter 25 exponent Finally Ive provided listing values PD4 some 32 typical model propellers chart works two-bladed props having aspect ratio between 61 91 typical props used RC CL models have tested thin toothpick props used racers also very useful have idea airspeed range may expected particular propeller given rpm will obvious higher pitch will result higher speed simple formula relates pitch airspeed rpm mph thousands X pitch nominal airspeed air speed would result propeller operating no slippage nominal airspeed chart shows relationship air speed rpm propeller pitches 3 12 rpm up 15000 covers model situations assumption no slippage course usually encountered actual flight However does give valuable insight selection propeller particular set conditions example suppose airplane planned fly 75 mph engine expected run 10000 rpm chart may immediately determined 10000 rpm propeller 8-in pitch will have nominal airspeed 75 mph Its therefore obvious propeller selected must have 8-in pitch greater airspeed 75 mph reached Its true under certain conditions speeds excess nominal airspeed may achieved due fact propeller blade airfoil may produce lift slightly negative angle attack Bear mind vail ables involved analysis propellers article have made number simplifying assumptions order provide fairly simple method estimating pro peller performance have found results better hp cases Ive checked method against data full-size aircraft engines propel lers well home-builts ultralights have always well within tha range Im confident method i adequate model purposes Conclusion discussed two formulac describe two important aspects 01 propeller behavior thrust power ab sorption formula thrust th importance diameter disk area came apparent discussion 01 power saw propeller powe varies third power rpm 2 fairly small change rpm indicates rathe larger change power chart pre sented makes possible estimate power required drive propeller particular rpm chart also pro vided find nominal airspeed function rpm propeller pitch RC Scale/Wischers Continued page 45 connecting link lined up directly across servo output shaft centerline will no load servo motor Current flow servo will drop idle flaps locked down securely course true full-flap position extra gear retract servo also helps reduce current con sumption intermediate flap positions Incidence angles again third time recent columns going dwell upon touchy subject disastrous crash club field model descended ver tically impact few feet pit area filled models fliers spectators Fortunately missed everyone thing destroying itself pilot us ing full up-elevator throughout dive several hundred feet no appar ent response plane Having built kit assumed incidence angles correct center gravity location concern its first flight case due building error stabilizer leading edge inad vertently raised bit too much providing lifting force Ordinarily sort thing causes no great problem model can readily flown trimming bit upelevator model ratio stabilizer area elevator area quite high large stab small elevator Elevator travel set near minimum prevent overcontrolling Whenever model built up speed tendency models nose tuck under required full upelevator recover level flight its final dive gathered excessive speed simply wouldnt pull out enough up-elevator travel say During its first flight 136 Model Aviation TOciarterMaster .ru 3] i 11