IN PART discussion described apply various design factors ob tain superior performance through intelli gent prop design also explained fabricate propeller scratch ac cording block method templates point should have decided desired design features first tempt will have fabricated tem plates needed produce prop block will find templates useful design changes wanted Quite ten design change does affect drasti cally shape block interpolation can made easily purpose now transform useful propeller First consider ation choice material may other materials besides wood work experimental stage nothing easier work wood home workshops proper choice kind wood important propeller compares favorably propellers made other materials Wood varies greatly its characteristics variations can affect production per formance props can made easily-worked light soft wood faster turn propeller stronger wood must So better prop requires wood stiff possible pos sessing great shear strength yet can easily worked Manufacturers use wide variety woods mostly ease production Woods bass popular families easy machine have proven useable lower rpm engines metal prop would probably yield ultimate perfor formance wood comes closest metal characteristics maple Since method fabrication allow its use settle anything less best maple maple cut strips slightly oversize templates used After cutting length crankshaft hole drilled center block top-view outline drawn block sawed desired shape next step machine outline exact size band jig saw disc belt sander helpful no great effort re quired work hand tools important tolerance outside outline keep sides parallel Once top outline completed draw center line side blank side view outline drawn about side view machined same manner top view Carving blades shape time consuming project proper tools pro cedures used tools required 42 Model Aviation .part2 procedures actual carving experimental Make Concluding two-part discussion Hal details efficient props importantly match engine U Harold deBolt Propellers 1 6note small numbers hubsrough finished oversized condition reedy match engines Props 4 5 matched engine now ready flight evaluation Prop 4 helical constant pitch No 5 has progressive pitch symmetrical airfoil High-Performance Pron $ simple good 8-in half-round wood rasp 8-in half-round bastard file necessary common l motor wood cutting bit important better hardware store wood-working supply house would have stock router bit works well about iameter about long has 9 10 flutes spiral fashion rather fine flutes metal cutting bit used electric drill motor will hog away excess maple ease main piece equipment hold ing fixture prop blank Though special simple make nec essary secret fast production small pieces anchor solidly can attacked quickcutting tools holding fixture illus trated need fancy toler ances liberal sturdier better prop blank bolted fixture blade worked sup ported shims indicated di rection rotation prop must determined doing Most props so-called right-hand rotation As suming prop right-handed blank bolted fixture such man ner rear side blank upper blade receive first work right hold-down bolt face fixture allows rear bottom side airfoil formed first airfoil flat bottom remove excess material until lower front leading edge blade has straight line upper rear trailing edge blank careful re move no material necessary connect edges station blade correct pitch will come out SIDE TEMPLATE FOR SWEEPBACK SIDE- PROP NO6 t BLOCK SIZE 3/4 X 7/8 X9 0 TOP SIDE- PROP NO1 BLOCK SIZE11/16X7/8X9 VI 0 FULL SIZE PROPELLER BLANK TEMPLATES July1978 43 Itompletea prop maicned engine flight eval uated ready racing Following advice article can easily duplicated Prop blank mounted holding fixture ready carving Fixture should solid order keep blank moving vibrating being attacked cutting tools I/4 X 20 BOLT HEAVY WOOD X7XI2NOM CLAMP TO BENCH PROP BLANK HOLDING AND CARVING FIXTURE automatically Removing too much mate- First step rough blade shape rial leading edge increases pitch done drill motor too much off trailing edge decreases cutting bit number quick light cuts pitch either case blade area lost will job easier trying take off 44 Model Aviation too much time will find can take material off right down within about 1/32 finished size Watch twist desired shape prop tip Because blade angle changes tip hub can make straight cut tool careful follow contour cut ting toll Because direction rotation drill motor start cut tip prop danger catching tip router bit destroying Therefore always start cut about I/ tip excess removed wood rasp later Once blade roughed down size leave blank fixture complete joining edges files airfoil flat bottom slightly different approach necessary case blade length line drawn blank high point airfoil falls line replaces lower leading edge blank reference roughing out airfoil router cutting done down line trailing edge Once point airfoil shaped files using lower leading edge prop blank center line airfoil either case note approach hub prop pitch blade no longer can held still have smooth flow hub blade change should occur within spinner no aerodynamic effect created Once bottom first blade has completed blank revolved same procedure followed second blade Once rear bottom blades completed can check pitch gauge adjust ments amount pitch equal ize two blades can made top airfoil completed similar manner case no matter whether airfoil flat bottom airfoil high-point center line will have used order have enough material form airfoil Again final shaping airfoil done files flowing airfoil top leading edge prop bank Remember long flow airfoil used top leading edge prop blank lower trailing edge prop blank amount pitch will correct no matter what shape airfoil has top side both blades has shaped propeller completed except balancing finishing balancing should no problem used wood consistent grain struc ture followed same procedure shaped airfoil will come out almost automatically balanced check will usually show airfoil heavier blade bit thicker other Adjustments simple point propeller tailored engine before doing will Prop blank mounted fixture wood-working router bit drill motor ready commence shaping Router bit will hog off excess material Shaping completed just few minutes note hub probably too thick con veniently fit crankshaft Remove enough thickness rear side prop within spinner area hub suitable engine Remove material files drill press end-mill cutting bit adjusting height end-mill bit drill press table match desired hub thickness using table ref erence excess material can accu rately routed away Recall props deliberately designed oversize can tailored engine As prop came off shaping fix ture engine probably will turn far under desired rmpwhich exactly what wanted objective strive tailoring prop obtain de sired engine rpm removing material prop areas least effi ciency general means close hub tip Therefore proce dure should bring size down minimum two areas remove material other portions prop Providing desired rpm has already reached propeller adjusted allow engine reach its required ground rpmwhich should about 10% below its peak horsepower speedthe prop ready flight resting Look in-flight aircraft speed working rac ing models pattern type look pull ing power maneuvers speed pulling power appears good determine well prop unloads flight Un loading very important operational characteristic 2-cycle engines pro pellers Simply stated means rpm crease flight compared static rpm engine ability unload determined engines breathing char acteristics design allows fuel-air mixture enter venturi greatest possible volume flow through passages easily exit exhaust re striction engine has maximum unload ing ability Such engine will have ab normally high maximum rpm potential engine would normally operated load better engine will re spond larger rpm increases portion load removed general racing engine design considers factor propeller also has unloading charac teristics Any propeller forward motion revolving disturbed air creates excessive drag holds rpm down given power Once propeller moves forward bites air less less disturbed until maximum velocity determined its pitch reached Max/V propeller will operating practically undisturbed air Drag source will gone Drag created propeller itself disturbs air disturbance added disturbance created lack forward movement compounds total drag propeller least inherent drag will create least disturbance low Max/V Such propeller will get its Max/V quickly Max/V also will higher Unloading propeller engine accumulative engines Max/rpm will higher desired operating rpm propeller un loads the engine also unloads thus increasing developed horsepower allows us design low-drag propel ler larger size will unload specified in-air rpm efficient unloading propeller Formula example engine rpm will decrease turns air plane recovers proceeds down straight-away rpm will seem crease continuously until maximum reached just next turn started caused quick acceleration low-drag propeller design As speed airplane increases load becomes less propeller thus engine will tend turn faster lower drag prop quicker increase rpm power speed process repeat ing until terminal velocity reached important racing quicker can accelerate maximum speed out turns better will over-all speed pattern coming out maneuvers should increase engine rpm moment acceleration ma neuver completed characteristics apparent test flights can assumed propeller either best de sign else can stand some reduction drag inefficient areas can accomplished several waysa change lower drag airfoil reduction blade width possible reduc tion diameter Try until Continued page 98 July1978 45 propeller blank ready carving developed procedures outlined articles Sheet plastic templates shown R Standard No 1 prop see drawings last issue sideview template top view No 6 prop precession progressive pitch added Propeller blank rough shaped ready attached xne engine Maple useu props maximum engine horsepower rpm 2030000 plus b capable achieving max imum model velocity c maximum ac celeration d compromise between b c order really discuss parameters involved would take space available Ill outline basic areas propeller evaluation development I Propeller rpm vs engine hp curve match prop rpm range max hp available achieved testing individual engines dyno ac cepting published rpm/hp figure given engine 2 Relation torque rpm some spe cial applications require prop turn less max hp/rpm figures FAI TR example RPM averages 16000 tested engines typically produce max hpat 19000 3 Propeller designed terminal ve locity model under controlled condi tions CL Speed event 4 Propeller designed produce max imum acceleration/velocity under limiting conditions FF event 5 Propeller designed produce op timum total flight performance under variety conditions FAI TR scale racing pylon racing examples should give example racing events analogous auto races accel eration top speed variable loads affect total performance Herb Stock ton flew props 2 mph slower fastest props TRs because total race times lower least 5 sec compromise prop used accelerated better starts re gained top speed quicker after in-flight maneuvers General Propeller Evaluation Procedures interested experimenting props models can several things will improve re sults require sophisticated work first step experiment prop diameter Use same pitch design now using select prop next larger diameter Fly ob serve measure results begin reduce diameter prop ements until same diameter original prop Take original prop reduce in crements until sure model does perform well second step experiment propeller blade width same diam eter tests props have wider narrower blades same pitch third step select props same brand blade configuration higher lower pitch Trim diameter higher pitch prop best diam eter achieved steps 2 fly carefully reduce diameter / 16 /8 time determine better first best prop Take lower pitch prop begin larger diameter work down carefully tests basic method used match prop/engine/model improved performance configuration use pitch gauges see photo other techniques will discussed future want conclude brief dis cussion props few reminders turn use simple prop balancers pictured Prather Products sells similar universal balance under two bucks balance props engine model will appreciate have enough trouble coping primary vibrations generated one-cylinder engines secondary vibrations induced unbal anced props reduce engine life add stress model high performance applications use best metal spinners balance same reasons note about spinners modern spinners run true dont wobble Wobbling spinners have cost speed models up 3 mph tip wobble approximately 1/16 Look spinner tip carefully run engine focuses sharply vision its okay may want correct problem clipped propeller picture carefully balanced blades equal length balance props removing ma terial top side blade trimming tips unequal lengths Blades unequal length area etc produce unequal dynamic loads engine What Im trying say prop static balancedbut has un equal blade area bladeis un balanced runs blade produces thrust other unequal load transferred engine model Safety activity power modeling has its safety aspects Rotating propellers statistically hazardous Prop blades stressed beyond structural limits fly off speeds several hundred mph Such projectile can fatal Balanced props safer unbalanced props 2 order apparent hazard molded plastic nylon similar hazardous followed soft wood hardwood molded-strand fiberglass props safest gen eral statement does pretend evaluate physical/safety aspects specific prop 3 Talk yourself time operate engine Ive learned over years am safe unless remind myself time keep fingers self under control away prop stand line prop wear ear protectors Ear protectors two things protect hearing isolate thinking processes noise can actually disorient mind judgment last item eye protection Wear glasses protect eyes broken blades frequently fuel oil thrown prop prop blast aware yourself relation engines operate operated others think safety Next column will airframes power train engine mount tank prop interact previous articles including this series concerned Power Systems point considering last model element system airframe Don Jehlik 438A Sch weer Dr Star Route 1 Hawthorne NV 89415 Make Props/de Bolt continued page 45 greatest benefit found final step apply finish record exact blade shape duplicates can made further testing high speeds blades travel sur face friction can create considerable drag reduction surface drag can add just much performance can reduction drag some design improve ment good finish important can finish prop normal ways using paints epoxies excellent However require time apply should changes desired prop later much work involved replac ing finish simple effective prop finish nothing wax propeller smoothly finished fine sandpaper paste wax Simonize Blue Coral etc rubbed wood wax dried buffed cloth high lustre An advantage other time saving prop can altered will finish quickly easily re placed using same method first custom prop gives desired results can easily duplicate second time around believe bet ter results can experiment various design parameters note re sults obtained Keep simple records results will soon have some solid facts base further experiments Since writing additional interesting 98 Model Aviation Dayg low Pem USE IT FOR TRIM & ALL BOTTOM SUR FACES mont Ave Huntingdon Valley Pa 19006 CAN SEE IT M AWAY results have become available spoke prop unloading its benefit na ture benefit can made clear comparison two props identical size unloads latter al lows engine rpm increase cause operate engine below its maxi mum rpm Any increase rpm result additional horsepower can used turn larger prop bring en gine back down its Max/hp/rpm prop unloads obviously add ing aircrafts efficiency two propellers identical size un loads other can because propeller reaches higher rpm has less drag present work aims towards removing drag propel lers felt drag controls unload ing ability great extent work unloading engines props area greatest potential improved perfor mance Both horsepower curve engine thrust curve prop rise steeply maximum ap proached Any increase rpm top end can equal times rpm near low end Also should considered few mph increase midspeed range means nothing added what top becomes very important results current work excellent-size normal pro peller Formula scratch pro duced similar size lower drag pro peller using ideas article Most normal props will unload about 10% air rpm 20K ground can expect 22K air new lower-drag prop showed 25% pick up decided increase race course amounted nearly 10 seconds As can seen 15% increase put rpm ter minal velocity over Max/hp/rpm engine point weather curtailed flight testing until 1978 season ever larger props already fabricated ap pear have good potential bench tests Only flight will offer proof course question increase prop area diameter blade width Perhaps increasing pitch combination pitch area would prove best Some interesting experiments appear order s suggested reader refer Mr deBolts article Better Props Formula published May 1977 issue Glider Flying/Wilson continued page 41 end up around armpits can run backwards faster people can run forward would make pretty good NFL cornerback After Thursdays opening ceremonies weather best Danish stayclear skies buoyant air low wind would take models 400500 meters three minutes Practice same before fliers working air-picking launches Launches good zooms doubly rewarded Ros kildes light air elevating ships hotter part thermal better climb plus extra flight time due climb itself calm-air launch sequence same medium wind se quence Run five six quick strides after ship turns wind hand-over hand two three arm lengths quickly turn loose line release Friday Wakefield flown glider team helped downwind re trieval group After contest three Soviet fliers busiest practice getting about 20 flights time spent flying techniqueno trim ming Only eight hours before start contest other contestants packing resting Russians however out working hardest difference previous sessions longer span fly-off models inconsistent launches compared shorter span models Whether due design construction quirks particular models dont know During practices neither fliers nor team manager talked very much fliers worked own ships didnt pay much attention other countries competitors saw camera Lepps out short time flying fin ished left either eat go back rooms short pretty seri ous business model processing serious entire team showed up fore processing officially began Thurs day ran ships through no crowds around dont know arranged effective Saturday morning team out early made about five short flights warm up test air Field condi tions affected flying greatly air port surrounded grass areas crops forest Upwind launch line large depression upwind rough little hills irregular terrain temperature between 5565o F sun directly visible until late day Some strong thermals generated right after 7 am otherwise lift weak Most rounds thermals just strong enough maintain ships line height slow descent last round especially ten 82 fliers maxed air conditions dead map field shows general layout Initials L C refer Lepp Chop lssaenko launch point particular flight LI instance Lepps first-round launch point Rus sians mobile fliers field although majority fliers circle towing did get fairly spread out Russians have simple strategy get downwind back good selec tion other fliers wait air someone hand over thermal July1978 99 Designed 2 channel R/C tether control 15 35 engines Maintaining top quality simple con struction Balsa Plywood parts accurately diecui precision vacuum formed Plastic hull cabin Hardware package including R/C hardware Full sized Plans plus Decals Sport model Coast Guard version STERLING MODELS G ST PI411A PA 19134 no dealer availaSle d,ect odes accepted tO additiOeai cflage handling shipping leo minimum U S SI 25 ninirnun Outside US Catalog 01 entie line Ot airplane Control line Train kit boat ero Secet otUOdplAiplanet cowering tinisking ricing enclosed C Seces ot Contnl Line Ca,ie Flying snIping stunting Carrer ruleS eguletionn oontul line installation instroctinni 2SC er NO checks OnioUS moneourde orcorrenut
Edition: Model Aviation - 1978/07
Page Numbers: 42, 43, 44, 45, 98, 99
IN PART discussion described apply various design factors ob tain superior performance through intelli gent prop design also explained fabricate propeller scratch ac cording block method templates point should have decided desired design features first tempt will have fabricated tem plates needed produce prop block will find templates useful design changes wanted Quite ten design change does affect drasti cally shape block interpolation can made easily purpose now transform useful propeller First consider ation choice material may other materials besides wood work experimental stage nothing easier work wood home workshops proper choice kind wood important propeller compares favorably propellers made other materials Wood varies greatly its characteristics variations can affect production per formance props can made easily-worked light soft wood faster turn propeller stronger wood must So better prop requires wood stiff possible pos sessing great shear strength yet can easily worked Manufacturers use wide variety woods mostly ease production Woods bass popular families easy machine have proven useable lower rpm engines metal prop would probably yield ultimate perfor formance wood comes closest metal characteristics maple Since method fabrication allow its use settle anything less best maple maple cut strips slightly oversize templates used After cutting length crankshaft hole drilled center block top-view outline drawn block sawed desired shape next step machine outline exact size band jig saw disc belt sander helpful no great effort re quired work hand tools important tolerance outside outline keep sides parallel Once top outline completed draw center line side blank side view outline drawn about side view machined same manner top view Carving blades shape time consuming project proper tools pro cedures used tools required 42 Model Aviation .part2 procedures actual carving experimental Make Concluding two-part discussion Hal details efficient props importantly match engine U Harold deBolt Propellers 1 6note small numbers hubsrough finished oversized condition reedy match engines Props 4 5 matched engine now ready flight evaluation Prop 4 helical constant pitch No 5 has progressive pitch symmetrical airfoil High-Performance Pron $ simple good 8-in half-round wood rasp 8-in half-round bastard file necessary common l motor wood cutting bit important better hardware store wood-working supply house would have stock router bit works well about iameter about long has 9 10 flutes spiral fashion rather fine flutes metal cutting bit used electric drill motor will hog away excess maple ease main piece equipment hold ing fixture prop blank Though special simple make nec essary secret fast production small pieces anchor solidly can attacked quickcutting tools holding fixture illus trated need fancy toler ances liberal sturdier better prop blank bolted fixture blade worked sup ported shims indicated di rection rotation prop must determined doing Most props so-called right-hand rotation As suming prop right-handed blank bolted fixture such man ner rear side blank upper blade receive first work right hold-down bolt face fixture allows rear bottom side airfoil formed first airfoil flat bottom remove excess material until lower front leading edge blade has straight line upper rear trailing edge blank careful re move no material necessary connect edges station blade correct pitch will come out SIDE TEMPLATE FOR SWEEPBACK SIDE- PROP NO6 t BLOCK SIZE 3/4 X 7/8 X9 0 TOP SIDE- PROP NO1 BLOCK SIZE11/16X7/8X9 VI 0 FULL SIZE PROPELLER BLANK TEMPLATES July1978 43 Itompletea prop maicned engine flight eval uated ready racing Following advice article can easily duplicated Prop blank mounted holding fixture ready carving Fixture should solid order keep blank moving vibrating being attacked cutting tools I/4 X 20 BOLT HEAVY WOOD X7XI2NOM CLAMP TO BENCH PROP BLANK HOLDING AND CARVING FIXTURE automatically Removing too much mate- First step rough blade shape rial leading edge increases pitch done drill motor too much off trailing edge decreases cutting bit number quick light cuts pitch either case blade area lost will job easier trying take off 44 Model Aviation too much time will find can take material off right down within about 1/32 finished size Watch twist desired shape prop tip Because blade angle changes tip hub can make straight cut tool careful follow contour cut ting toll Because direction rotation drill motor start cut tip prop danger catching tip router bit destroying Therefore always start cut about I/ tip excess removed wood rasp later Once blade roughed down size leave blank fixture complete joining edges files airfoil flat bottom slightly different approach necessary case blade length line drawn blank high point airfoil falls line replaces lower leading edge blank reference roughing out airfoil router cutting done down line trailing edge Once point airfoil shaped files using lower leading edge prop blank center line airfoil either case note approach hub prop pitch blade no longer can held still have smooth flow hub blade change should occur within spinner no aerodynamic effect created Once bottom first blade has completed blank revolved same procedure followed second blade Once rear bottom blades completed can check pitch gauge adjust ments amount pitch equal ize two blades can made top airfoil completed similar manner case no matter whether airfoil flat bottom airfoil high-point center line will have used order have enough material form airfoil Again final shaping airfoil done files flowing airfoil top leading edge prop bank Remember long flow airfoil used top leading edge prop blank lower trailing edge prop blank amount pitch will correct no matter what shape airfoil has top side both blades has shaped propeller completed except balancing finishing balancing should no problem used wood consistent grain struc ture followed same procedure shaped airfoil will come out almost automatically balanced check will usually show airfoil heavier blade bit thicker other Adjustments simple point propeller tailored engine before doing will Prop blank mounted fixture wood-working router bit drill motor ready commence shaping Router bit will hog off excess material Shaping completed just few minutes note hub probably too thick con veniently fit crankshaft Remove enough thickness rear side prop within spinner area hub suitable engine Remove material files drill press end-mill cutting bit adjusting height end-mill bit drill press table match desired hub thickness using table ref erence excess material can accu rately routed away Recall props deliberately designed oversize can tailored engine As prop came off shaping fix ture engine probably will turn far under desired rmpwhich exactly what wanted objective strive tailoring prop obtain de sired engine rpm removing material prop areas least effi ciency general means close hub tip Therefore proce dure should bring size down minimum two areas remove material other portions prop Providing desired rpm has already reached propeller adjusted allow engine reach its required ground rpmwhich should about 10% below its peak horsepower speedthe prop ready flight resting Look in-flight aircraft speed working rac ing models pattern type look pull ing power maneuvers speed pulling power appears good determine well prop unloads flight Un loading very important operational characteristic 2-cycle engines pro pellers Simply stated means rpm crease flight compared static rpm engine ability unload determined engines breathing char acteristics design allows fuel-air mixture enter venturi greatest possible volume flow through passages easily exit exhaust re striction engine has maximum unload ing ability Such engine will have ab normally high maximum rpm potential engine would normally operated load better engine will re spond larger rpm increases portion load removed general racing engine design considers factor propeller also has unloading charac teristics Any propeller forward motion revolving disturbed air creates excessive drag holds rpm down given power Once propeller moves forward bites air less less disturbed until maximum velocity determined its pitch reached Max/V propeller will operating practically undisturbed air Drag source will gone Drag created propeller itself disturbs air disturbance added disturbance created lack forward movement compounds total drag propeller least inherent drag will create least disturbance low Max/V Such propeller will get its Max/V quickly Max/V also will higher Unloading propeller engine accumulative engines Max/rpm will higher desired operating rpm propeller un loads the engine also unloads thus increasing developed horsepower allows us design low-drag propel ler larger size will unload specified in-air rpm efficient unloading propeller Formula example engine rpm will decrease turns air plane recovers proceeds down straight-away rpm will seem crease continuously until maximum reached just next turn started caused quick acceleration low-drag propeller design As speed airplane increases load becomes less propeller thus engine will tend turn faster lower drag prop quicker increase rpm power speed process repeat ing until terminal velocity reached important racing quicker can accelerate maximum speed out turns better will over-all speed pattern coming out maneuvers should increase engine rpm moment acceleration ma neuver completed characteristics apparent test flights can assumed propeller either best de sign else can stand some reduction drag inefficient areas can accomplished several waysa change lower drag airfoil reduction blade width possible reduc tion diameter Try until Continued page 98 July1978 45 propeller blank ready carving developed procedures outlined articles Sheet plastic templates shown R Standard No 1 prop see drawings last issue sideview template top view No 6 prop precession progressive pitch added Propeller blank rough shaped ready attached xne engine Maple useu props maximum engine horsepower rpm 2030000 plus b capable achieving max imum model velocity c maximum ac celeration d compromise between b c order really discuss parameters involved would take space available Ill outline basic areas propeller evaluation development I Propeller rpm vs engine hp curve match prop rpm range max hp available achieved testing individual engines dyno ac cepting published rpm/hp figure given engine 2 Relation torque rpm some spe cial applications require prop turn less max hp/rpm figures FAI TR example RPM averages 16000 tested engines typically produce max hpat 19000 3 Propeller designed terminal ve locity model under controlled condi tions CL Speed event 4 Propeller designed produce max imum acceleration/velocity under limiting conditions FF event 5 Propeller designed produce op timum total flight performance under variety conditions FAI TR scale racing pylon racing examples should give example racing events analogous auto races accel eration top speed variable loads affect total performance Herb Stock ton flew props 2 mph slower fastest props TRs because total race times lower least 5 sec compromise prop used accelerated better starts re gained top speed quicker after in-flight maneuvers General Propeller Evaluation Procedures interested experimenting props models can several things will improve re sults require sophisticated work first step experiment prop diameter Use same pitch design now using select prop next larger diameter Fly ob serve measure results begin reduce diameter prop ements until same diameter original prop Take original prop reduce in crements until sure model does perform well second step experiment propeller blade width same diam eter tests props have wider narrower blades same pitch third step select props same brand blade configuration higher lower pitch Trim diameter higher pitch prop best diam eter achieved steps 2 fly carefully reduce diameter / 16 /8 time determine better first best prop Take lower pitch prop begin larger diameter work down carefully tests basic method used match prop/engine/model improved performance configuration use pitch gauges see photo other techniques will discussed future want conclude brief dis cussion props few reminders turn use simple prop balancers pictured Prather Products sells similar universal balance under two bucks balance props engine model will appreciate have enough trouble coping primary vibrations generated one-cylinder engines secondary vibrations induced unbal anced props reduce engine life add stress model high performance applications use best metal spinners balance same reasons note about spinners modern spinners run true dont wobble Wobbling spinners have cost speed models up 3 mph tip wobble approximately 1/16 Look spinner tip carefully run engine focuses sharply vision its okay may want correct problem clipped propeller picture carefully balanced blades equal length balance props removing ma terial top side blade trimming tips unequal lengths Blades unequal length area etc produce unequal dynamic loads engine What Im trying say prop static balancedbut has un equal blade area bladeis un balanced runs blade produces thrust other unequal load transferred engine model Safety activity power modeling has its safety aspects Rotating propellers statistically hazardous Prop blades stressed beyond structural limits fly off speeds several hundred mph Such projectile can fatal Balanced props safer unbalanced props 2 order apparent hazard molded plastic nylon similar hazardous followed soft wood hardwood molded-strand fiberglass props safest gen eral statement does pretend evaluate physical/safety aspects specific prop 3 Talk yourself time operate engine Ive learned over years am safe unless remind myself time keep fingers self under control away prop stand line prop wear ear protectors Ear protectors two things protect hearing isolate thinking processes noise can actually disorient mind judgment last item eye protection Wear glasses protect eyes broken blades frequently fuel oil thrown prop prop blast aware yourself relation engines operate operated others think safety Next column will airframes power train engine mount tank prop interact previous articles including this series concerned Power Systems point considering last model element system airframe Don Jehlik 438A Sch weer Dr Star Route 1 Hawthorne NV 89415 Make Props/de Bolt continued page 45 greatest benefit found final step apply finish record exact blade shape duplicates can made further testing high speeds blades travel sur face friction can create considerable drag reduction surface drag can add just much performance can reduction drag some design improve ment good finish important can finish prop normal ways using paints epoxies excellent However require time apply should changes desired prop later much work involved replac ing finish simple effective prop finish nothing wax propeller smoothly finished fine sandpaper paste wax Simonize Blue Coral etc rubbed wood wax dried buffed cloth high lustre An advantage other time saving prop can altered will finish quickly easily re placed using same method first custom prop gives desired results can easily duplicate second time around believe bet ter results can experiment various design parameters note re sults obtained Keep simple records results will soon have some solid facts base further experiments Since writing additional interesting 98 Model Aviation Dayg low Pem USE IT FOR TRIM & ALL BOTTOM SUR FACES mont Ave Huntingdon Valley Pa 19006 CAN SEE IT M AWAY results have become available spoke prop unloading its benefit na ture benefit can made clear comparison two props identical size unloads latter al lows engine rpm increase cause operate engine below its maxi mum rpm Any increase rpm result additional horsepower can used turn larger prop bring en gine back down its Max/hp/rpm prop unloads obviously add ing aircrafts efficiency two propellers identical size un loads other can because propeller reaches higher rpm has less drag present work aims towards removing drag propel lers felt drag controls unload ing ability great extent work unloading engines props area greatest potential improved perfor mance Both horsepower curve engine thrust curve prop rise steeply maximum ap proached Any increase rpm top end can equal times rpm near low end Also should considered few mph increase midspeed range means nothing added what top becomes very important results current work excellent-size normal pro peller Formula scratch pro duced similar size lower drag pro peller using ideas article Most normal props will unload about 10% air rpm 20K ground can expect 22K air new lower-drag prop showed 25% pick up decided increase race course amounted nearly 10 seconds As can seen 15% increase put rpm ter minal velocity over Max/hp/rpm engine point weather curtailed flight testing until 1978 season ever larger props already fabricated ap pear have good potential bench tests Only flight will offer proof course question increase prop area diameter blade width Perhaps increasing pitch combination pitch area would prove best Some interesting experiments appear order s suggested reader refer Mr deBolts article Better Props Formula published May 1977 issue Glider Flying/Wilson continued page 41 end up around armpits can run backwards faster people can run forward would make pretty good NFL cornerback After Thursdays opening ceremonies weather best Danish stayclear skies buoyant air low wind would take models 400500 meters three minutes Practice same before fliers working air-picking launches Launches good zooms doubly rewarded Ros kildes light air elevating ships hotter part thermal better climb plus extra flight time due climb itself calm-air launch sequence same medium wind se quence Run five six quick strides after ship turns wind hand-over hand two three arm lengths quickly turn loose line release Friday Wakefield flown glider team helped downwind re trieval group After contest three Soviet fliers busiest practice getting about 20 flights time spent flying techniqueno trim ming Only eight hours before start contest other contestants packing resting Russians however out working hardest difference previous sessions longer span fly-off models inconsistent launches compared shorter span models Whether due design construction quirks particular models dont know During practices neither fliers nor team manager talked very much fliers worked own ships didnt pay much attention other countries competitors saw camera Lepps out short time flying fin ished left either eat go back rooms short pretty seri ous business model processing serious entire team showed up fore processing officially began Thurs day ran ships through no crowds around dont know arranged effective Saturday morning team out early made about five short flights warm up test air Field condi tions affected flying greatly air port surrounded grass areas crops forest Upwind launch line large depression upwind rough little hills irregular terrain temperature between 5565o F sun directly visible until late day Some strong thermals generated right after 7 am otherwise lift weak Most rounds thermals just strong enough maintain ships line height slow descent last round especially ten 82 fliers maxed air conditions dead map field shows general layout Initials L C refer Lepp Chop lssaenko launch point particular flight LI instance Lepps first-round launch point Rus sians mobile fliers field although majority fliers circle towing did get fairly spread out Russians have simple strategy get downwind back good selec tion other fliers wait air someone hand over thermal July1978 99 Designed 2 channel R/C tether control 15 35 engines Maintaining top quality simple con struction Balsa Plywood parts accurately diecui precision vacuum formed Plastic hull cabin Hardware package including R/C hardware Full sized Plans plus Decals Sport model Coast Guard version STERLING MODELS G ST PI411A PA 19134 no dealer availaSle d,ect odes accepted tO additiOeai cflage handling shipping leo minimum U S SI 25 ninirnun Outside US Catalog 01 entie line Ot airplane Control line Train kit boat ero Secet otUOdplAiplanet cowering tinisking ricing enclosed C Seces ot Contnl Line Ca,ie Flying snIping stunting Carrer ruleS eguletionn oontul line installation instroctinni 2SC er NO checks OnioUS moneourde orcorrenut
Edition: Model Aviation - 1978/07
Page Numbers: 42, 43, 44, 45, 98, 99
IN PART discussion described apply various design factors ob tain superior performance through intelli gent prop design also explained fabricate propeller scratch ac cording block method templates point should have decided desired design features first tempt will have fabricated tem plates needed produce prop block will find templates useful design changes wanted Quite ten design change does affect drasti cally shape block interpolation can made easily purpose now transform useful propeller First consider ation choice material may other materials besides wood work experimental stage nothing easier work wood home workshops proper choice kind wood important propeller compares favorably propellers made other materials Wood varies greatly its characteristics variations can affect production per formance props can made easily-worked light soft wood faster turn propeller stronger wood must So better prop requires wood stiff possible pos sessing great shear strength yet can easily worked Manufacturers use wide variety woods mostly ease production Woods bass popular families easy machine have proven useable lower rpm engines metal prop would probably yield ultimate perfor formance wood comes closest metal characteristics maple Since method fabrication allow its use settle anything less best maple maple cut strips slightly oversize templates used After cutting length crankshaft hole drilled center block top-view outline drawn block sawed desired shape next step machine outline exact size band jig saw disc belt sander helpful no great effort re quired work hand tools important tolerance outside outline keep sides parallel Once top outline completed draw center line side blank side view outline drawn about side view machined same manner top view Carving blades shape time consuming project proper tools pro cedures used tools required 42 Model Aviation .part2 procedures actual carving experimental Make Concluding two-part discussion Hal details efficient props importantly match engine U Harold deBolt Propellers 1 6note small numbers hubsrough finished oversized condition reedy match engines Props 4 5 matched engine now ready flight evaluation Prop 4 helical constant pitch No 5 has progressive pitch symmetrical airfoil High-Performance Pron $ simple good 8-in half-round wood rasp 8-in half-round bastard file necessary common l motor wood cutting bit important better hardware store wood-working supply house would have stock router bit works well about iameter about long has 9 10 flutes spiral fashion rather fine flutes metal cutting bit used electric drill motor will hog away excess maple ease main piece equipment hold ing fixture prop blank Though special simple make nec essary secret fast production small pieces anchor solidly can attacked quickcutting tools holding fixture illus trated need fancy toler ances liberal sturdier better prop blank bolted fixture blade worked sup ported shims indicated di rection rotation prop must determined doing Most props so-called right-hand rotation As suming prop right-handed blank bolted fixture such man ner rear side blank upper blade receive first work right hold-down bolt face fixture allows rear bottom side airfoil formed first airfoil flat bottom remove excess material until lower front leading edge blade has straight line upper rear trailing edge blank careful re move no material necessary connect edges station blade correct pitch will come out SIDE TEMPLATE FOR SWEEPBACK SIDE- PROP NO6 t BLOCK SIZE 3/4 X 7/8 X9 0 TOP SIDE- PROP NO1 BLOCK SIZE11/16X7/8X9 VI 0 FULL SIZE PROPELLER BLANK TEMPLATES July1978 43 Itompletea prop maicned engine flight eval uated ready racing Following advice article can easily duplicated Prop blank mounted holding fixture ready carving Fixture should solid order keep blank moving vibrating being attacked cutting tools I/4 X 20 BOLT HEAVY WOOD X7XI2NOM CLAMP TO BENCH PROP BLANK HOLDING AND CARVING FIXTURE automatically Removing too much mate- First step rough blade shape rial leading edge increases pitch done drill motor too much off trailing edge decreases cutting bit number quick light cuts pitch either case blade area lost will job easier trying take off 44 Model Aviation too much time will find can take material off right down within about 1/32 finished size Watch twist desired shape prop tip Because blade angle changes tip hub can make straight cut tool careful follow contour cut ting toll Because direction rotation drill motor start cut tip prop danger catching tip router bit destroying Therefore always start cut about I/ tip excess removed wood rasp later Once blade roughed down size leave blank fixture complete joining edges files airfoil flat bottom slightly different approach necessary case blade length line drawn blank high point airfoil falls line replaces lower leading edge blank reference roughing out airfoil router cutting done down line trailing edge Once point airfoil shaped files using lower leading edge prop blank center line airfoil either case note approach hub prop pitch blade no longer can held still have smooth flow hub blade change should occur within spinner no aerodynamic effect created Once bottom first blade has completed blank revolved same procedure followed second blade Once rear bottom blades completed can check pitch gauge adjust ments amount pitch equal ize two blades can made top airfoil completed similar manner case no matter whether airfoil flat bottom airfoil high-point center line will have used order have enough material form airfoil Again final shaping airfoil done files flowing airfoil top leading edge prop bank Remember long flow airfoil used top leading edge prop blank lower trailing edge prop blank amount pitch will correct no matter what shape airfoil has top side both blades has shaped propeller completed except balancing finishing balancing should no problem used wood consistent grain struc ture followed same procedure shaped airfoil will come out almost automatically balanced check will usually show airfoil heavier blade bit thicker other Adjustments simple point propeller tailored engine before doing will Prop blank mounted fixture wood-working router bit drill motor ready commence shaping Router bit will hog off excess material Shaping completed just few minutes note hub probably too thick con veniently fit crankshaft Remove enough thickness rear side prop within spinner area hub suitable engine Remove material files drill press end-mill cutting bit adjusting height end-mill bit drill press table match desired hub thickness using table ref erence excess material can accu rately routed away Recall props deliberately designed oversize can tailored engine As prop came off shaping fix ture engine probably will turn far under desired rmpwhich exactly what wanted objective strive tailoring prop obtain de sired engine rpm removing material prop areas least effi ciency general means close hub tip Therefore proce dure should bring size down minimum two areas remove material other portions prop Providing desired rpm has already reached propeller adjusted allow engine reach its required ground rpmwhich should about 10% below its peak horsepower speedthe prop ready flight resting Look in-flight aircraft speed working rac ing models pattern type look pull ing power maneuvers speed pulling power appears good determine well prop unloads flight Un loading very important operational characteristic 2-cycle engines pro pellers Simply stated means rpm crease flight compared static rpm engine ability unload determined engines breathing char acteristics design allows fuel-air mixture enter venturi greatest possible volume flow through passages easily exit exhaust re striction engine has maximum unload ing ability Such engine will have ab normally high maximum rpm potential engine would normally operated load better engine will re spond larger rpm increases portion load removed general racing engine design considers factor propeller also has unloading charac teristics Any propeller forward motion revolving disturbed air creates excessive drag holds rpm down given power Once propeller moves forward bites air less less disturbed until maximum velocity determined its pitch reached Max/V propeller will operating practically undisturbed air Drag source will gone Drag created propeller itself disturbs air disturbance added disturbance created lack forward movement compounds total drag propeller least inherent drag will create least disturbance low Max/V Such propeller will get its Max/V quickly Max/V also will higher Unloading propeller engine accumulative engines Max/rpm will higher desired operating rpm propeller un loads the engine also unloads thus increasing developed horsepower allows us design low-drag propel ler larger size will unload specified in-air rpm efficient unloading propeller Formula example engine rpm will decrease turns air plane recovers proceeds down straight-away rpm will seem crease continuously until maximum reached just next turn started caused quick acceleration low-drag propeller design As speed airplane increases load becomes less propeller thus engine will tend turn faster lower drag prop quicker increase rpm power speed process repeat ing until terminal velocity reached important racing quicker can accelerate maximum speed out turns better will over-all speed pattern coming out maneuvers should increase engine rpm moment acceleration ma neuver completed characteristics apparent test flights can assumed propeller either best de sign else can stand some reduction drag inefficient areas can accomplished several waysa change lower drag airfoil reduction blade width possible reduc tion diameter Try until Continued page 98 July1978 45 propeller blank ready carving developed procedures outlined articles Sheet plastic templates shown R Standard No 1 prop see drawings last issue sideview template top view No 6 prop precession progressive pitch added Propeller blank rough shaped ready attached xne engine Maple useu props maximum engine horsepower rpm 2030000 plus b capable achieving max imum model velocity c maximum ac celeration d compromise between b c order really discuss parameters involved would take space available Ill outline basic areas propeller evaluation development I Propeller rpm vs engine hp curve match prop rpm range max hp available achieved testing individual engines dyno ac cepting published rpm/hp figure given engine 2 Relation torque rpm some spe cial applications require prop turn less max hp/rpm figures FAI TR example RPM averages 16000 tested engines typically produce max hpat 19000 3 Propeller designed terminal ve locity model under controlled condi tions CL Speed event 4 Propeller designed produce max imum acceleration/velocity under limiting conditions FF event 5 Propeller designed produce op timum total flight performance under variety conditions FAI TR scale racing pylon racing examples should give example racing events analogous auto races accel eration top speed variable loads affect total performance Herb Stock ton flew props 2 mph slower fastest props TRs because total race times lower least 5 sec compromise prop used accelerated better starts re gained top speed quicker after in-flight maneuvers General Propeller Evaluation Procedures interested experimenting props models can several things will improve re sults require sophisticated work first step experiment prop diameter Use same pitch design now using select prop next larger diameter Fly ob serve measure results begin reduce diameter prop ements until same diameter original prop Take original prop reduce in crements until sure model does perform well second step experiment propeller blade width same diam eter tests props have wider narrower blades same pitch third step select props same brand blade configuration higher lower pitch Trim diameter higher pitch prop best diam eter achieved steps 2 fly carefully reduce diameter / 16 /8 time determine better first best prop Take lower pitch prop begin larger diameter work down carefully tests basic method used match prop/engine/model improved performance configuration use pitch gauges see photo other techniques will discussed future want conclude brief dis cussion props few reminders turn use simple prop balancers pictured Prather Products sells similar universal balance under two bucks balance props engine model will appreciate have enough trouble coping primary vibrations generated one-cylinder engines secondary vibrations induced unbal anced props reduce engine life add stress model high performance applications use best metal spinners balance same reasons note about spinners modern spinners run true dont wobble Wobbling spinners have cost speed models up 3 mph tip wobble approximately 1/16 Look spinner tip carefully run engine focuses sharply vision its okay may want correct problem clipped propeller picture carefully balanced blades equal length balance props removing ma terial top side blade trimming tips unequal lengths Blades unequal length area etc produce unequal dynamic loads engine What Im trying say prop static balancedbut has un equal blade area bladeis un balanced runs blade produces thrust other unequal load transferred engine model Safety activity power modeling has its safety aspects Rotating propellers statistically hazardous Prop blades stressed beyond structural limits fly off speeds several hundred mph Such projectile can fatal Balanced props safer unbalanced props 2 order apparent hazard molded plastic nylon similar hazardous followed soft wood hardwood molded-strand fiberglass props safest gen eral statement does pretend evaluate physical/safety aspects specific prop 3 Talk yourself time operate engine Ive learned over years am safe unless remind myself time keep fingers self under control away prop stand line prop wear ear protectors Ear protectors two things protect hearing isolate thinking processes noise can actually disorient mind judgment last item eye protection Wear glasses protect eyes broken blades frequently fuel oil thrown prop prop blast aware yourself relation engines operate operated others think safety Next column will airframes power train engine mount tank prop interact previous articles including this series concerned Power Systems point considering last model element system airframe Don Jehlik 438A Sch weer Dr Star Route 1 Hawthorne NV 89415 Make Props/de Bolt continued page 45 greatest benefit found final step apply finish record exact blade shape duplicates can made further testing high speeds blades travel sur face friction can create considerable drag reduction surface drag can add just much performance can reduction drag some design improve ment good finish important can finish prop normal ways using paints epoxies excellent However require time apply should changes desired prop later much work involved replac ing finish simple effective prop finish nothing wax propeller smoothly finished fine sandpaper paste wax Simonize Blue Coral etc rubbed wood wax dried buffed cloth high lustre An advantage other time saving prop can altered will finish quickly easily re placed using same method first custom prop gives desired results can easily duplicate second time around believe bet ter results can experiment various design parameters note re sults obtained Keep simple records results will soon have some solid facts base further experiments Since writing additional interesting 98 Model Aviation Dayg low Pem USE IT FOR TRIM & ALL BOTTOM SUR FACES mont Ave Huntingdon Valley Pa 19006 CAN SEE IT M AWAY results have become available spoke prop unloading its benefit na ture benefit can made clear comparison two props identical size unloads latter al lows engine rpm increase cause operate engine below its maxi mum rpm Any increase rpm result additional horsepower can used turn larger prop bring en gine back down its Max/hp/rpm prop unloads obviously add ing aircrafts efficiency two propellers identical size un loads other can because propeller reaches higher rpm has less drag present work aims towards removing drag propel lers felt drag controls unload ing ability great extent work unloading engines props area greatest potential improved perfor mance Both horsepower curve engine thrust curve prop rise steeply maximum ap proached Any increase rpm top end can equal times rpm near low end Also should considered few mph increase midspeed range means nothing added what top becomes very important results current work excellent-size normal pro peller Formula scratch pro duced similar size lower drag pro peller using ideas article Most normal props will unload about 10% air rpm 20K ground can expect 22K air new lower-drag prop showed 25% pick up decided increase race course amounted nearly 10 seconds As can seen 15% increase put rpm ter minal velocity over Max/hp/rpm engine point weather curtailed flight testing until 1978 season ever larger props already fabricated ap pear have good potential bench tests Only flight will offer proof course question increase prop area diameter blade width Perhaps increasing pitch combination pitch area would prove best Some interesting experiments appear order s suggested reader refer Mr deBolts article Better Props Formula published May 1977 issue Glider Flying/Wilson continued page 41 end up around armpits can run backwards faster people can run forward would make pretty good NFL cornerback After Thursdays opening ceremonies weather best Danish stayclear skies buoyant air low wind would take models 400500 meters three minutes Practice same before fliers working air-picking launches Launches good zooms doubly rewarded Ros kildes light air elevating ships hotter part thermal better climb plus extra flight time due climb itself calm-air launch sequence same medium wind se quence Run five six quick strides after ship turns wind hand-over hand two three arm lengths quickly turn loose line release Friday Wakefield flown glider team helped downwind re trieval group After contest three Soviet fliers busiest practice getting about 20 flights time spent flying techniqueno trim ming Only eight hours before start contest other contestants packing resting Russians however out working hardest difference previous sessions longer span fly-off models inconsistent launches compared shorter span models Whether due design construction quirks particular models dont know During practices neither fliers nor team manager talked very much fliers worked own ships didnt pay much attention other countries competitors saw camera Lepps out short time flying fin ished left either eat go back rooms short pretty seri ous business model processing serious entire team showed up fore processing officially began Thurs day ran ships through no crowds around dont know arranged effective Saturday morning team out early made about five short flights warm up test air Field condi tions affected flying greatly air port surrounded grass areas crops forest Upwind launch line large depression upwind rough little hills irregular terrain temperature between 5565o F sun directly visible until late day Some strong thermals generated right after 7 am otherwise lift weak Most rounds thermals just strong enough maintain ships line height slow descent last round especially ten 82 fliers maxed air conditions dead map field shows general layout Initials L C refer Lepp Chop lssaenko launch point particular flight LI instance Lepps first-round launch point Rus sians mobile fliers field although majority fliers circle towing did get fairly spread out Russians have simple strategy get downwind back good selec tion other fliers wait air someone hand over thermal July1978 99 Designed 2 channel R/C tether control 15 35 engines Maintaining top quality simple con struction Balsa Plywood parts accurately diecui precision vacuum formed Plastic hull cabin Hardware package including R/C hardware Full sized Plans plus Decals Sport model Coast Guard version STERLING MODELS G ST PI411A PA 19134 no dealer availaSle d,ect odes accepted tO additiOeai cflage handling shipping leo minimum U S SI 25 ninirnun Outside US Catalog 01 entie line Ot airplane Control line Train kit boat ero Secet otUOdplAiplanet cowering tinisking ricing enclosed C Seces ot Contnl Line Ca,ie Flying snIping stunting Carrer ruleS eguletionn oontul line installation instroctinni 2SC er NO checks OnioUS moneourde orcorrenut
Edition: Model Aviation - 1978/07
Page Numbers: 42, 43, 44, 45, 98, 99
IN PART discussion described apply various design factors ob tain superior performance through intelli gent prop design also explained fabricate propeller scratch ac cording block method templates point should have decided desired design features first tempt will have fabricated tem plates needed produce prop block will find templates useful design changes wanted Quite ten design change does affect drasti cally shape block interpolation can made easily purpose now transform useful propeller First consider ation choice material may other materials besides wood work experimental stage nothing easier work wood home workshops proper choice kind wood important propeller compares favorably propellers made other materials Wood varies greatly its characteristics variations can affect production per formance props can made easily-worked light soft wood faster turn propeller stronger wood must So better prop requires wood stiff possible pos sessing great shear strength yet can easily worked Manufacturers use wide variety woods mostly ease production Woods bass popular families easy machine have proven useable lower rpm engines metal prop would probably yield ultimate perfor formance wood comes closest metal characteristics maple Since method fabrication allow its use settle anything less best maple maple cut strips slightly oversize templates used After cutting length crankshaft hole drilled center block top-view outline drawn block sawed desired shape next step machine outline exact size band jig saw disc belt sander helpful no great effort re quired work hand tools important tolerance outside outline keep sides parallel Once top outline completed draw center line side blank side view outline drawn about side view machined same manner top view Carving blades shape time consuming project proper tools pro cedures used tools required 42 Model Aviation .part2 procedures actual carving experimental Make Concluding two-part discussion Hal details efficient props importantly match engine U Harold deBolt Propellers 1 6note small numbers hubsrough finished oversized condition reedy match engines Props 4 5 matched engine now ready flight evaluation Prop 4 helical constant pitch No 5 has progressive pitch symmetrical airfoil High-Performance Pron $ simple good 8-in half-round wood rasp 8-in half-round bastard file necessary common l motor wood cutting bit important better hardware store wood-working supply house would have stock router bit works well about iameter about long has 9 10 flutes spiral fashion rather fine flutes metal cutting bit used electric drill motor will hog away excess maple ease main piece equipment hold ing fixture prop blank Though special simple make nec essary secret fast production small pieces anchor solidly can attacked quickcutting tools holding fixture illus trated need fancy toler ances liberal sturdier better prop blank bolted fixture blade worked sup ported shims indicated di rection rotation prop must determined doing Most props so-called right-hand rotation As suming prop right-handed blank bolted fixture such man ner rear side blank upper blade receive first work right hold-down bolt face fixture allows rear bottom side airfoil formed first airfoil flat bottom remove excess material until lower front leading edge blade has straight line upper rear trailing edge blank careful re move no material necessary connect edges station blade correct pitch will come out SIDE TEMPLATE FOR SWEEPBACK SIDE- PROP NO6 t BLOCK SIZE 3/4 X 7/8 X9 0 TOP SIDE- PROP NO1 BLOCK SIZE11/16X7/8X9 VI 0 FULL SIZE PROPELLER BLANK TEMPLATES July1978 43 Itompletea prop maicned engine flight eval uated ready racing Following advice article can easily duplicated Prop blank mounted holding fixture ready carving Fixture should solid order keep blank moving vibrating being attacked cutting tools I/4 X 20 BOLT HEAVY WOOD X7XI2NOM CLAMP TO BENCH PROP BLANK HOLDING AND CARVING FIXTURE automatically Removing too much mate- First step rough blade shape rial leading edge increases pitch done drill motor too much off trailing edge decreases cutting bit number quick light cuts pitch either case blade area lost will job easier trying take off 44 Model Aviation too much time will find can take material off right down within about 1/32 finished size Watch twist desired shape prop tip Because blade angle changes tip hub can make straight cut tool careful follow contour cut ting toll Because direction rotation drill motor start cut tip prop danger catching tip router bit destroying Therefore always start cut about I/ tip excess removed wood rasp later Once blade roughed down size leave blank fixture complete joining edges files airfoil flat bottom slightly different approach necessary case blade length line drawn blank high point airfoil falls line replaces lower leading edge blank reference roughing out airfoil router cutting done down line trailing edge Once point airfoil shaped files using lower leading edge prop blank center line airfoil either case note approach hub prop pitch blade no longer can held still have smooth flow hub blade change should occur within spinner no aerodynamic effect created Once bottom first blade has completed blank revolved same procedure followed second blade Once rear bottom blades completed can check pitch gauge adjust ments amount pitch equal ize two blades can made top airfoil completed similar manner case no matter whether airfoil flat bottom airfoil high-point center line will have used order have enough material form airfoil Again final shaping airfoil done files flowing airfoil top leading edge prop bank Remember long flow airfoil used top leading edge prop blank lower trailing edge prop blank amount pitch will correct no matter what shape airfoil has top side both blades has shaped propeller completed except balancing finishing balancing should no problem used wood consistent grain struc ture followed same procedure shaped airfoil will come out almost automatically balanced check will usually show airfoil heavier blade bit thicker other Adjustments simple point propeller tailored engine before doing will Prop blank mounted fixture wood-working router bit drill motor ready commence shaping Router bit will hog off excess material Shaping completed just few minutes note hub probably too thick con veniently fit crankshaft Remove enough thickness rear side prop within spinner area hub suitable engine Remove material files drill press end-mill cutting bit adjusting height end-mill bit drill press table match desired hub thickness using table ref erence excess material can accu rately routed away Recall props deliberately designed oversize can tailored engine As prop came off shaping fix ture engine probably will turn far under desired rmpwhich exactly what wanted objective strive tailoring prop obtain de sired engine rpm removing material prop areas least effi ciency general means close hub tip Therefore proce dure should bring size down minimum two areas remove material other portions prop Providing desired rpm has already reached propeller adjusted allow engine reach its required ground rpmwhich should about 10% below its peak horsepower speedthe prop ready flight resting Look in-flight aircraft speed working rac ing models pattern type look pull ing power maneuvers speed pulling power appears good determine well prop unloads flight Un loading very important operational characteristic 2-cycle engines pro pellers Simply stated means rpm crease flight compared static rpm engine ability unload determined engines breathing char acteristics design allows fuel-air mixture enter venturi greatest possible volume flow through passages easily exit exhaust re striction engine has maximum unload ing ability Such engine will have ab normally high maximum rpm potential engine would normally operated load better engine will re spond larger rpm increases portion load removed general racing engine design considers factor propeller also has unloading charac teristics Any propeller forward motion revolving disturbed air creates excessive drag holds rpm down given power Once propeller moves forward bites air less less disturbed until maximum velocity determined its pitch reached Max/V propeller will operating practically undisturbed air Drag source will gone Drag created propeller itself disturbs air disturbance added disturbance created lack forward movement compounds total drag propeller least inherent drag will create least disturbance low Max/V Such propeller will get its Max/V quickly Max/V also will higher Unloading propeller engine accumulative engines Max/rpm will higher desired operating rpm propeller un loads the engine also unloads thus increasing developed horsepower allows us design low-drag propel ler larger size will unload specified in-air rpm efficient unloading propeller Formula example engine rpm will decrease turns air plane recovers proceeds down straight-away rpm will seem crease continuously until maximum reached just next turn started caused quick acceleration low-drag propeller design As speed airplane increases load becomes less propeller thus engine will tend turn faster lower drag prop quicker increase rpm power speed process repeat ing until terminal velocity reached important racing quicker can accelerate maximum speed out turns better will over-all speed pattern coming out maneuvers should increase engine rpm moment acceleration ma neuver completed characteristics apparent test flights can assumed propeller either best de sign else can stand some reduction drag inefficient areas can accomplished several waysa change lower drag airfoil reduction blade width possible reduc tion diameter Try until Continued page 98 July1978 45 propeller blank ready carving developed procedures outlined articles Sheet plastic templates shown R Standard No 1 prop see drawings last issue sideview template top view No 6 prop precession progressive pitch added Propeller blank rough shaped ready attached xne engine Maple useu props maximum engine horsepower rpm 2030000 plus b capable achieving max imum model velocity c maximum ac celeration d compromise between b c order really discuss parameters involved would take space available Ill outline basic areas propeller evaluation development I Propeller rpm vs engine hp curve match prop rpm range max hp available achieved testing individual engines dyno ac cepting published rpm/hp figure given engine 2 Relation torque rpm some spe cial applications require prop turn less max hp/rpm figures FAI TR example RPM averages 16000 tested engines typically produce max hpat 19000 3 Propeller designed terminal ve locity model under controlled condi tions CL Speed event 4 Propeller designed produce max imum acceleration/velocity under limiting conditions FF event 5 Propeller designed produce op timum total flight performance under variety conditions FAI TR scale racing pylon racing examples should give example racing events analogous auto races accel eration top speed variable loads affect total performance Herb Stock ton flew props 2 mph slower fastest props TRs because total race times lower least 5 sec compromise prop used accelerated better starts re gained top speed quicker after in-flight maneuvers General Propeller Evaluation Procedures interested experimenting props models can several things will improve re sults require sophisticated work first step experiment prop diameter Use same pitch design now using select prop next larger diameter Fly ob serve measure results begin reduce diameter prop ements until same diameter original prop Take original prop reduce in crements until sure model does perform well second step experiment propeller blade width same diam eter tests props have wider narrower blades same pitch third step select props same brand blade configuration higher lower pitch Trim diameter higher pitch prop best diam eter achieved steps 2 fly carefully reduce diameter / 16 /8 time determine better first best prop Take lower pitch prop begin larger diameter work down carefully tests basic method used match prop/engine/model improved performance configuration use pitch gauges see photo other techniques will discussed future want conclude brief dis cussion props few reminders turn use simple prop balancers pictured Prather Products sells similar universal balance under two bucks balance props engine model will appreciate have enough trouble coping primary vibrations generated one-cylinder engines secondary vibrations induced unbal anced props reduce engine life add stress model high performance applications use best metal spinners balance same reasons note about spinners modern spinners run true dont wobble Wobbling spinners have cost speed models up 3 mph tip wobble approximately 1/16 Look spinner tip carefully run engine focuses sharply vision its okay may want correct problem clipped propeller picture carefully balanced blades equal length balance props removing ma terial top side blade trimming tips unequal lengths Blades unequal length area etc produce unequal dynamic loads engine What Im trying say prop static balancedbut has un equal blade area bladeis un balanced runs blade produces thrust other unequal load transferred engine model Safety activity power modeling has its safety aspects Rotating propellers statistically hazardous Prop blades stressed beyond structural limits fly off speeds several hundred mph Such projectile can fatal Balanced props safer unbalanced props 2 order apparent hazard molded plastic nylon similar hazardous followed soft wood hardwood molded-strand fiberglass props safest gen eral statement does pretend evaluate physical/safety aspects specific prop 3 Talk yourself time operate engine Ive learned over years am safe unless remind myself time keep fingers self under control away prop stand line prop wear ear protectors Ear protectors two things protect hearing isolate thinking processes noise can actually disorient mind judgment last item eye protection Wear glasses protect eyes broken blades frequently fuel oil thrown prop prop blast aware yourself relation engines operate operated others think safety Next column will airframes power train engine mount tank prop interact previous articles including this series concerned Power Systems point considering last model element system airframe Don Jehlik 438A Sch weer Dr Star Route 1 Hawthorne NV 89415 Make Props/de Bolt continued page 45 greatest benefit found final step apply finish record exact blade shape duplicates can made further testing high speeds blades travel sur face friction can create considerable drag reduction surface drag can add just much performance can reduction drag some design improve ment good finish important can finish prop normal ways using paints epoxies excellent However require time apply should changes desired prop later much work involved replac ing finish simple effective prop finish nothing wax propeller smoothly finished fine sandpaper paste wax Simonize Blue Coral etc rubbed wood wax dried buffed cloth high lustre An advantage other time saving prop can altered will finish quickly easily re placed using same method first custom prop gives desired results can easily duplicate second time around believe bet ter results can experiment various design parameters note re sults obtained Keep simple records results will soon have some solid facts base further experiments Since writing additional interesting 98 Model Aviation Dayg low Pem USE IT FOR TRIM & ALL BOTTOM SUR FACES mont Ave Huntingdon Valley Pa 19006 CAN SEE IT M AWAY results have become available spoke prop unloading its benefit na ture benefit can made clear comparison two props identical size unloads latter al lows engine rpm increase cause operate engine below its maxi mum rpm Any increase rpm result additional horsepower can used turn larger prop bring en gine back down its Max/hp/rpm prop unloads obviously add ing aircrafts efficiency two propellers identical size un loads other can because propeller reaches higher rpm has less drag present work aims towards removing drag propel lers felt drag controls unload ing ability great extent work unloading engines props area greatest potential improved perfor mance Both horsepower curve engine thrust curve prop rise steeply maximum ap proached Any increase rpm top end can equal times rpm near low end Also should considered few mph increase midspeed range means nothing added what top becomes very important results current work excellent-size normal pro peller Formula scratch pro duced similar size lower drag pro peller using ideas article Most normal props will unload about 10% air rpm 20K ground can expect 22K air new lower-drag prop showed 25% pick up decided increase race course amounted nearly 10 seconds As can seen 15% increase put rpm ter minal velocity over Max/hp/rpm engine point weather curtailed flight testing until 1978 season ever larger props already fabricated ap pear have good potential bench tests Only flight will offer proof course question increase prop area diameter blade width Perhaps increasing pitch combination pitch area would prove best Some interesting experiments appear order s suggested reader refer Mr deBolts article Better Props Formula published May 1977 issue Glider Flying/Wilson continued page 41 end up around armpits can run backwards faster people can run forward would make pretty good NFL cornerback After Thursdays opening ceremonies weather best Danish stayclear skies buoyant air low wind would take models 400500 meters three minutes Practice same before fliers working air-picking launches Launches good zooms doubly rewarded Ros kildes light air elevating ships hotter part thermal better climb plus extra flight time due climb itself calm-air launch sequence same medium wind se quence Run five six quick strides after ship turns wind hand-over hand two three arm lengths quickly turn loose line release Friday Wakefield flown glider team helped downwind re trieval group After contest three Soviet fliers busiest practice getting about 20 flights time spent flying techniqueno trim ming Only eight hours before start contest other contestants packing resting Russians however out working hardest difference previous sessions longer span fly-off models inconsistent launches compared shorter span models Whether due design construction quirks particular models dont know During practices neither fliers nor team manager talked very much fliers worked own ships didnt pay much attention other countries competitors saw camera Lepps out short time flying fin ished left either eat go back rooms short pretty seri ous business model processing serious entire team showed up fore processing officially began Thurs day ran ships through no crowds around dont know arranged effective Saturday morning team out early made about five short flights warm up test air Field condi tions affected flying greatly air port surrounded grass areas crops forest Upwind launch line large depression upwind rough little hills irregular terrain temperature between 5565o F sun directly visible until late day Some strong thermals generated right after 7 am otherwise lift weak Most rounds thermals just strong enough maintain ships line height slow descent last round especially ten 82 fliers maxed air conditions dead map field shows general layout Initials L C refer Lepp Chop lssaenko launch point particular flight LI instance Lepps first-round launch point Rus sians mobile fliers field although majority fliers circle towing did get fairly spread out Russians have simple strategy get downwind back good selec tion other fliers wait air someone hand over thermal July1978 99 Designed 2 channel R/C tether control 15 35 engines Maintaining top quality simple con struction Balsa Plywood parts accurately diecui precision vacuum formed Plastic hull cabin Hardware package including R/C hardware Full sized Plans plus Decals Sport model Coast Guard version STERLING MODELS G ST PI411A PA 19134 no dealer availaSle d,ect odes accepted tO additiOeai cflage handling shipping leo minimum U S SI 25 ninirnun Outside US Catalog 01 entie line Ot airplane Control line Train kit boat ero Secet otUOdplAiplanet cowering tinisking ricing enclosed C Seces ot Contnl Line Ca,ie Flying snIping stunting Carrer ruleS eguletionn oontul line installation instroctinni 2SC er NO checks OnioUS moneourde orcorrenut
Edition: Model Aviation - 1978/07
Page Numbers: 42, 43, 44, 45, 98, 99
IN PART discussion described apply various design factors ob tain superior performance through intelli gent prop design also explained fabricate propeller scratch ac cording block method templates point should have decided desired design features first tempt will have fabricated tem plates needed produce prop block will find templates useful design changes wanted Quite ten design change does affect drasti cally shape block interpolation can made easily purpose now transform useful propeller First consider ation choice material may other materials besides wood work experimental stage nothing easier work wood home workshops proper choice kind wood important propeller compares favorably propellers made other materials Wood varies greatly its characteristics variations can affect production per formance props can made easily-worked light soft wood faster turn propeller stronger wood must So better prop requires wood stiff possible pos sessing great shear strength yet can easily worked Manufacturers use wide variety woods mostly ease production Woods bass popular families easy machine have proven useable lower rpm engines metal prop would probably yield ultimate perfor formance wood comes closest metal characteristics maple Since method fabrication allow its use settle anything less best maple maple cut strips slightly oversize templates used After cutting length crankshaft hole drilled center block top-view outline drawn block sawed desired shape next step machine outline exact size band jig saw disc belt sander helpful no great effort re quired work hand tools important tolerance outside outline keep sides parallel Once top outline completed draw center line side blank side view outline drawn about side view machined same manner top view Carving blades shape time consuming project proper tools pro cedures used tools required 42 Model Aviation .part2 procedures actual carving experimental Make Concluding two-part discussion Hal details efficient props importantly match engine U Harold deBolt Propellers 1 6note small numbers hubsrough finished oversized condition reedy match engines Props 4 5 matched engine now ready flight evaluation Prop 4 helical constant pitch No 5 has progressive pitch symmetrical airfoil High-Performance Pron $ simple good 8-in half-round wood rasp 8-in half-round bastard file necessary common l motor wood cutting bit important better hardware store wood-working supply house would have stock router bit works well about iameter about long has 9 10 flutes spiral fashion rather fine flutes metal cutting bit used electric drill motor will hog away excess maple ease main piece equipment hold ing fixture prop blank Though special simple make nec essary secret fast production small pieces anchor solidly can attacked quickcutting tools holding fixture illus trated need fancy toler ances liberal sturdier better prop blank bolted fixture blade worked sup ported shims indicated di rection rotation prop must determined doing Most props so-called right-hand rotation As suming prop right-handed blank bolted fixture such man ner rear side blank upper blade receive first work right hold-down bolt face fixture allows rear bottom side airfoil formed first airfoil flat bottom remove excess material until lower front leading edge blade has straight line upper rear trailing edge blank careful re move no material necessary connect edges station blade correct pitch will come out SIDE TEMPLATE FOR SWEEPBACK SIDE- PROP NO6 t BLOCK SIZE 3/4 X 7/8 X9 0 TOP SIDE- PROP NO1 BLOCK SIZE11/16X7/8X9 VI 0 FULL SIZE PROPELLER BLANK TEMPLATES July1978 43 Itompletea prop maicned engine flight eval uated ready racing Following advice article can easily duplicated Prop blank mounted holding fixture ready carving Fixture should solid order keep blank moving vibrating being attacked cutting tools I/4 X 20 BOLT HEAVY WOOD X7XI2NOM CLAMP TO BENCH PROP BLANK HOLDING AND CARVING FIXTURE automatically Removing too much mate- First step rough blade shape rial leading edge increases pitch done drill motor too much off trailing edge decreases cutting bit number quick light cuts pitch either case blade area lost will job easier trying take off 44 Model Aviation too much time will find can take material off right down within about 1/32 finished size Watch twist desired shape prop tip Because blade angle changes tip hub can make straight cut tool careful follow contour cut ting toll Because direction rotation drill motor start cut tip prop danger catching tip router bit destroying Therefore always start cut about I/ tip excess removed wood rasp later Once blade roughed down size leave blank fixture complete joining edges files airfoil flat bottom slightly different approach necessary case blade length line drawn blank high point airfoil falls line replaces lower leading edge blank reference roughing out airfoil router cutting done down line trailing edge Once point airfoil shaped files using lower leading edge prop blank center line airfoil either case note approach hub prop pitch blade no longer can held still have smooth flow hub blade change should occur within spinner no aerodynamic effect created Once bottom first blade has completed blank revolved same procedure followed second blade Once rear bottom blades completed can check pitch gauge adjust ments amount pitch equal ize two blades can made top airfoil completed similar manner case no matter whether airfoil flat bottom airfoil high-point center line will have used order have enough material form airfoil Again final shaping airfoil done files flowing airfoil top leading edge prop bank Remember long flow airfoil used top leading edge prop blank lower trailing edge prop blank amount pitch will correct no matter what shape airfoil has top side both blades has shaped propeller completed except balancing finishing balancing should no problem used wood consistent grain struc ture followed same procedure shaped airfoil will come out almost automatically balanced check will usually show airfoil heavier blade bit thicker other Adjustments simple point propeller tailored engine before doing will Prop blank mounted fixture wood-working router bit drill motor ready commence shaping Router bit will hog off excess material Shaping completed just few minutes note hub probably too thick con veniently fit crankshaft Remove enough thickness rear side prop within spinner area hub suitable engine Remove material files drill press end-mill cutting bit adjusting height end-mill bit drill press table match desired hub thickness using table ref erence excess material can accu rately routed away Recall props deliberately designed oversize can tailored engine As prop came off shaping fix ture engine probably will turn far under desired rmpwhich exactly what wanted objective strive tailoring prop obtain de sired engine rpm removing material prop areas least effi ciency general means close hub tip Therefore proce dure should bring size down minimum two areas remove material other portions prop Providing desired rpm has already reached propeller adjusted allow engine reach its required ground rpmwhich should about 10% below its peak horsepower speedthe prop ready flight resting Look in-flight aircraft speed working rac ing models pattern type look pull ing power maneuvers speed pulling power appears good determine well prop unloads flight Un loading very important operational characteristic 2-cycle engines pro pellers Simply stated means rpm crease flight compared static rpm engine ability unload determined engines breathing char acteristics design allows fuel-air mixture enter venturi greatest possible volume flow through passages easily exit exhaust re striction engine has maximum unload ing ability Such engine will have ab normally high maximum rpm potential engine would normally operated load better engine will re spond larger rpm increases portion load removed general racing engine design considers factor propeller also has unloading charac teristics Any propeller forward motion revolving disturbed air creates excessive drag holds rpm down given power Once propeller moves forward bites air less less disturbed until maximum velocity determined its pitch reached Max/V propeller will operating practically undisturbed air Drag source will gone Drag created propeller itself disturbs air disturbance added disturbance created lack forward movement compounds total drag propeller least inherent drag will create least disturbance low Max/V Such propeller will get its Max/V quickly Max/V also will higher Unloading propeller engine accumulative engines Max/rpm will higher desired operating rpm propeller un loads the engine also unloads thus increasing developed horsepower allows us design low-drag propel ler larger size will unload specified in-air rpm efficient unloading propeller Formula example engine rpm will decrease turns air plane recovers proceeds down straight-away rpm will seem crease continuously until maximum reached just next turn started caused quick acceleration low-drag propeller design As speed airplane increases load becomes less propeller thus engine will tend turn faster lower drag prop quicker increase rpm power speed process repeat ing until terminal velocity reached important racing quicker can accelerate maximum speed out turns better will over-all speed pattern coming out maneuvers should increase engine rpm moment acceleration ma neuver completed characteristics apparent test flights can assumed propeller either best de sign else can stand some reduction drag inefficient areas can accomplished several waysa change lower drag airfoil reduction blade width possible reduc tion diameter Try until Continued page 98 July1978 45 propeller blank ready carving developed procedures outlined articles Sheet plastic templates shown R Standard No 1 prop see drawings last issue sideview template top view No 6 prop precession progressive pitch added Propeller blank rough shaped ready attached xne engine Maple useu props maximum engine horsepower rpm 2030000 plus b capable achieving max imum model velocity c maximum ac celeration d compromise between b c order really discuss parameters involved would take space available Ill outline basic areas propeller evaluation development I Propeller rpm vs engine hp curve match prop rpm range max hp available achieved testing individual engines dyno ac cepting published rpm/hp figure given engine 2 Relation torque rpm some spe cial applications require prop turn less max hp/rpm figures FAI TR example RPM averages 16000 tested engines typically produce max hpat 19000 3 Propeller designed terminal ve locity model under controlled condi tions CL Speed event 4 Propeller designed produce max imum acceleration/velocity under limiting conditions FF event 5 Propeller designed produce op timum total flight performance under variety conditions FAI TR scale racing pylon racing examples should give example racing events analogous auto races accel eration top speed variable loads affect total performance Herb Stock ton flew props 2 mph slower fastest props TRs because total race times lower least 5 sec compromise prop used accelerated better starts re gained top speed quicker after in-flight maneuvers General Propeller Evaluation Procedures interested experimenting props models can several things will improve re sults require sophisticated work first step experiment prop diameter Use same pitch design now using select prop next larger diameter Fly ob serve measure results begin reduce diameter prop ements until same diameter original prop Take original prop reduce in crements until sure model does perform well second step experiment propeller blade width same diam eter tests props have wider narrower blades same pitch third step select props same brand blade configuration higher lower pitch Trim diameter higher pitch prop best diam eter achieved steps 2 fly carefully reduce diameter / 16 /8 time determine better first best prop Take lower pitch prop begin larger diameter work down carefully tests basic method used match prop/engine/model improved performance configuration use pitch gauges see photo other techniques will discussed future want conclude brief dis cussion props few reminders turn use simple prop balancers pictured Prather Products sells similar universal balance under two bucks balance props engine model will appreciate have enough trouble coping primary vibrations generated one-cylinder engines secondary vibrations induced unbal anced props reduce engine life add stress model high performance applications use best metal spinners balance same reasons note about spinners modern spinners run true dont wobble Wobbling spinners have cost speed models up 3 mph tip wobble approximately 1/16 Look spinner tip carefully run engine focuses sharply vision its okay may want correct problem clipped propeller picture carefully balanced blades equal length balance props removing ma terial top side blade trimming tips unequal lengths Blades unequal length area etc produce unequal dynamic loads engine What Im trying say prop static balancedbut has un equal blade area bladeis un balanced runs blade produces thrust other unequal load transferred engine model Safety activity power modeling has its safety aspects Rotating propellers statistically hazardous Prop blades stressed beyond structural limits fly off speeds several hundred mph Such projectile can fatal Balanced props safer unbalanced props 2 order apparent hazard molded plastic nylon similar hazardous followed soft wood hardwood molded-strand fiberglass props safest gen eral statement does pretend evaluate physical/safety aspects specific prop 3 Talk yourself time operate engine Ive learned over years am safe unless remind myself time keep fingers self under control away prop stand line prop wear ear protectors Ear protectors two things protect hearing isolate thinking processes noise can actually disorient mind judgment last item eye protection Wear glasses protect eyes broken blades frequently fuel oil thrown prop prop blast aware yourself relation engines operate operated others think safety Next column will airframes power train engine mount tank prop interact previous articles including this series concerned Power Systems point considering last model element system airframe Don Jehlik 438A Sch weer Dr Star Route 1 Hawthorne NV 89415 Make Props/de Bolt continued page 45 greatest benefit found final step apply finish record exact blade shape duplicates can made further testing high speeds blades travel sur face friction can create considerable drag reduction surface drag can add just much performance can reduction drag some design improve ment good finish important can finish prop normal ways using paints epoxies excellent However require time apply should changes desired prop later much work involved replac ing finish simple effective prop finish nothing wax propeller smoothly finished fine sandpaper paste wax Simonize Blue Coral etc rubbed wood wax dried buffed cloth high lustre An advantage other time saving prop can altered will finish quickly easily re placed using same method first custom prop gives desired results can easily duplicate second time around believe bet ter results can experiment various design parameters note re sults obtained Keep simple records results will soon have some solid facts base further experiments Since writing additional interesting 98 Model Aviation Dayg low Pem USE IT FOR TRIM & ALL BOTTOM SUR FACES mont Ave Huntingdon Valley Pa 19006 CAN SEE IT M AWAY results have become available spoke prop unloading its benefit na ture benefit can made clear comparison two props identical size unloads latter al lows engine rpm increase cause operate engine below its maxi mum rpm Any increase rpm result additional horsepower can used turn larger prop bring en gine back down its Max/hp/rpm prop unloads obviously add ing aircrafts efficiency two propellers identical size un loads other can because propeller reaches higher rpm has less drag present work aims towards removing drag propel lers felt drag controls unload ing ability great extent work unloading engines props area greatest potential improved perfor mance Both horsepower curve engine thrust curve prop rise steeply maximum ap proached Any increase rpm top end can equal times rpm near low end Also should considered few mph increase midspeed range means nothing added what top becomes very important results current work excellent-size normal pro peller Formula scratch pro duced similar size lower drag pro peller using ideas article Most normal props will unload about 10% air rpm 20K ground can expect 22K air new lower-drag prop showed 25% pick up decided increase race course amounted nearly 10 seconds As can seen 15% increase put rpm ter minal velocity over Max/hp/rpm engine point weather curtailed flight testing until 1978 season ever larger props already fabricated ap pear have good potential bench tests Only flight will offer proof course question increase prop area diameter blade width Perhaps increasing pitch combination pitch area would prove best Some interesting experiments appear order s suggested reader refer Mr deBolts article Better Props Formula published May 1977 issue Glider Flying/Wilson continued page 41 end up around armpits can run backwards faster people can run forward would make pretty good NFL cornerback After Thursdays opening ceremonies weather best Danish stayclear skies buoyant air low wind would take models 400500 meters three minutes Practice same before fliers working air-picking launches Launches good zooms doubly rewarded Ros kildes light air elevating ships hotter part thermal better climb plus extra flight time due climb itself calm-air launch sequence same medium wind se quence Run five six quick strides after ship turns wind hand-over hand two three arm lengths quickly turn loose line release Friday Wakefield flown glider team helped downwind re trieval group After contest three Soviet fliers busiest practice getting about 20 flights time spent flying techniqueno trim ming Only eight hours before start contest other contestants packing resting Russians however out working hardest difference previous sessions longer span fly-off models inconsistent launches compared shorter span models Whether due design construction quirks particular models dont know During practices neither fliers nor team manager talked very much fliers worked own ships didnt pay much attention other countries competitors saw camera Lepps out short time flying fin ished left either eat go back rooms short pretty seri ous business model processing serious entire team showed up fore processing officially began Thurs day ran ships through no crowds around dont know arranged effective Saturday morning team out early made about five short flights warm up test air Field condi tions affected flying greatly air port surrounded grass areas crops forest Upwind launch line large depression upwind rough little hills irregular terrain temperature between 5565o F sun directly visible until late day Some strong thermals generated right after 7 am otherwise lift weak Most rounds thermals just strong enough maintain ships line height slow descent last round especially ten 82 fliers maxed air conditions dead map field shows general layout Initials L C refer Lepp Chop lssaenko launch point particular flight LI instance Lepps first-round launch point Rus sians mobile fliers field although majority fliers circle towing did get fairly spread out Russians have simple strategy get downwind back good selec tion other fliers wait air someone hand over thermal July1978 99 Designed 2 channel R/C tether control 15 35 engines Maintaining top quality simple con struction Balsa Plywood parts accurately diecui precision vacuum formed Plastic hull cabin Hardware package including R/C hardware Full sized Plans plus Decals Sport model Coast Guard version STERLING MODELS G ST PI411A PA 19134 no dealer availaSle d,ect odes accepted tO additiOeai cflage handling shipping leo minimum U S SI 25 ninirnun Outside US Catalog 01 entie line Ot airplane Control line Train kit boat ero Secet otUOdplAiplanet cowering tinisking ricing enclosed C Seces ot Contnl Line Ca,ie Flying snIping stunting Carrer ruleS eguletionn oontul line installation instroctinni 2SC er NO checks OnioUS moneourde orcorrenut
Edition: Model Aviation - 1978/07
Page Numbers: 42, 43, 44, 45, 98, 99
IN PART discussion described apply various design factors ob tain superior performance through intelli gent prop design also explained fabricate propeller scratch ac cording block method templates point should have decided desired design features first tempt will have fabricated tem plates needed produce prop block will find templates useful design changes wanted Quite ten design change does affect drasti cally shape block interpolation can made easily purpose now transform useful propeller First consider ation choice material may other materials besides wood work experimental stage nothing easier work wood home workshops proper choice kind wood important propeller compares favorably propellers made other materials Wood varies greatly its characteristics variations can affect production per formance props can made easily-worked light soft wood faster turn propeller stronger wood must So better prop requires wood stiff possible pos sessing great shear strength yet can easily worked Manufacturers use wide variety woods mostly ease production Woods bass popular families easy machine have proven useable lower rpm engines metal prop would probably yield ultimate perfor formance wood comes closest metal characteristics maple Since method fabrication allow its use settle anything less best maple maple cut strips slightly oversize templates used After cutting length crankshaft hole drilled center block top-view outline drawn block sawed desired shape next step machine outline exact size band jig saw disc belt sander helpful no great effort re quired work hand tools important tolerance outside outline keep sides parallel Once top outline completed draw center line side blank side view outline drawn about side view machined same manner top view Carving blades shape time consuming project proper tools pro cedures used tools required 42 Model Aviation .part2 procedures actual carving experimental Make Concluding two-part discussion Hal details efficient props importantly match engine U Harold deBolt Propellers 1 6note small numbers hubsrough finished oversized condition reedy match engines Props 4 5 matched engine now ready flight evaluation Prop 4 helical constant pitch No 5 has progressive pitch symmetrical airfoil High-Performance Pron $ simple good 8-in half-round wood rasp 8-in half-round bastard file necessary common l motor wood cutting bit important better hardware store wood-working supply house would have stock router bit works well about iameter about long has 9 10 flutes spiral fashion rather fine flutes metal cutting bit used electric drill motor will hog away excess maple ease main piece equipment hold ing fixture prop blank Though special simple make nec essary secret fast production small pieces anchor solidly can attacked quickcutting tools holding fixture illus trated need fancy toler ances liberal sturdier better prop blank bolted fixture blade worked sup ported shims indicated di rection rotation prop must determined doing Most props so-called right-hand rotation As suming prop right-handed blank bolted fixture such man ner rear side blank upper blade receive first work right hold-down bolt face fixture allows rear bottom side airfoil formed first airfoil flat bottom remove excess material until lower front leading edge blade has straight line upper rear trailing edge blank careful re move no material necessary connect edges station blade correct pitch will come out SIDE TEMPLATE FOR SWEEPBACK SIDE- PROP NO6 t BLOCK SIZE 3/4 X 7/8 X9 0 TOP SIDE- PROP NO1 BLOCK SIZE11/16X7/8X9 VI 0 FULL SIZE PROPELLER BLANK TEMPLATES July1978 43 Itompletea prop maicned engine flight eval uated ready racing Following advice article can easily duplicated Prop blank mounted holding fixture ready carving Fixture should solid order keep blank moving vibrating being attacked cutting tools I/4 X 20 BOLT HEAVY WOOD X7XI2NOM CLAMP TO BENCH PROP BLANK HOLDING AND CARVING FIXTURE automatically Removing too much mate- First step rough blade shape rial leading edge increases pitch done drill motor too much off trailing edge decreases cutting bit number quick light cuts pitch either case blade area lost will job easier trying take off 44 Model Aviation too much time will find can take material off right down within about 1/32 finished size Watch twist desired shape prop tip Because blade angle changes tip hub can make straight cut tool careful follow contour cut ting toll Because direction rotation drill motor start cut tip prop danger catching tip router bit destroying Therefore always start cut about I/ tip excess removed wood rasp later Once blade roughed down size leave blank fixture complete joining edges files airfoil flat bottom slightly different approach necessary case blade length line drawn blank high point airfoil falls line replaces lower leading edge blank reference roughing out airfoil router cutting done down line trailing edge Once point airfoil shaped files using lower leading edge prop blank center line airfoil either case note approach hub prop pitch blade no longer can held still have smooth flow hub blade change should occur within spinner no aerodynamic effect created Once bottom first blade has completed blank revolved same procedure followed second blade Once rear bottom blades completed can check pitch gauge adjust ments amount pitch equal ize two blades can made top airfoil completed similar manner case no matter whether airfoil flat bottom airfoil high-point center line will have used order have enough material form airfoil Again final shaping airfoil done files flowing airfoil top leading edge prop bank Remember long flow airfoil used top leading edge prop blank lower trailing edge prop blank amount pitch will correct no matter what shape airfoil has top side both blades has shaped propeller completed except balancing finishing balancing should no problem used wood consistent grain struc ture followed same procedure shaped airfoil will come out almost automatically balanced check will usually show airfoil heavier blade bit thicker other Adjustments simple point propeller tailored engine before doing will Prop blank mounted fixture wood-working router bit drill motor ready commence shaping Router bit will hog off excess material Shaping completed just few minutes note hub probably too thick con veniently fit crankshaft Remove enough thickness rear side prop within spinner area hub suitable engine Remove material files drill press end-mill cutting bit adjusting height end-mill bit drill press table match desired hub thickness using table ref erence excess material can accu rately routed away Recall props deliberately designed oversize can tailored engine As prop came off shaping fix ture engine probably will turn far under desired rmpwhich exactly what wanted objective strive tailoring prop obtain de sired engine rpm removing material prop areas least effi ciency general means close hub tip Therefore proce dure should bring size down minimum two areas remove material other portions prop Providing desired rpm has already reached propeller adjusted allow engine reach its required ground rpmwhich should about 10% below its peak horsepower speedthe prop ready flight resting Look in-flight aircraft speed working rac ing models pattern type look pull ing power maneuvers speed pulling power appears good determine well prop unloads flight Un loading very important operational characteristic 2-cycle engines pro pellers Simply stated means rpm crease flight compared static rpm engine ability unload determined engines breathing char acteristics design allows fuel-air mixture enter venturi greatest possible volume flow through passages easily exit exhaust re striction engine has maximum unload ing ability Such engine will have ab normally high maximum rpm potential engine would normally operated load better engine will re spond larger rpm increases portion load removed general racing engine design considers factor propeller also has unloading charac teristics Any propeller forward motion revolving disturbed air creates excessive drag holds rpm down given power Once propeller moves forward bites air less less disturbed until maximum velocity determined its pitch reached Max/V propeller will operating practically undisturbed air Drag source will gone Drag created propeller itself disturbs air disturbance added disturbance created lack forward movement compounds total drag propeller least inherent drag will create least disturbance low Max/V Such propeller will get its Max/V quickly Max/V also will higher Unloading propeller engine accumulative engines Max/rpm will higher desired operating rpm propeller un loads the engine also unloads thus increasing developed horsepower allows us design low-drag propel ler larger size will unload specified in-air rpm efficient unloading propeller Formula example engine rpm will decrease turns air plane recovers proceeds down straight-away rpm will seem crease continuously until maximum reached just next turn started caused quick acceleration low-drag propeller design As speed airplane increases load becomes less propeller thus engine will tend turn faster lower drag prop quicker increase rpm power speed process repeat ing until terminal velocity reached important racing quicker can accelerate maximum speed out turns better will over-all speed pattern coming out maneuvers should increase engine rpm moment acceleration ma neuver completed characteristics apparent test flights can assumed propeller either best de sign else can stand some reduction drag inefficient areas can accomplished several waysa change lower drag airfoil reduction blade width possible reduc tion diameter Try until Continued page 98 July1978 45 propeller blank ready carving developed procedures outlined articles Sheet plastic templates shown R Standard No 1 prop see drawings last issue sideview template top view No 6 prop precession progressive pitch added Propeller blank rough shaped ready attached xne engine Maple useu props maximum engine horsepower rpm 2030000 plus b capable achieving max imum model velocity c maximum ac celeration d compromise between b c order really discuss parameters involved would take space available Ill outline basic areas propeller evaluation development I Propeller rpm vs engine hp curve match prop rpm range max hp available achieved testing individual engines dyno ac cepting published rpm/hp figure given engine 2 Relation torque rpm some spe cial applications require prop turn less max hp/rpm figures FAI TR example RPM averages 16000 tested engines typically produce max hpat 19000 3 Propeller designed terminal ve locity model under controlled condi tions CL Speed event 4 Propeller designed produce max imum acceleration/velocity under limiting conditions FF event 5 Propeller designed produce op timum total flight performance under variety conditions FAI TR scale racing pylon racing examples should give example racing events analogous auto races accel eration top speed variable loads affect total performance Herb Stock ton flew props 2 mph slower fastest props TRs because total race times lower least 5 sec compromise prop used accelerated better starts re gained top speed quicker after in-flight maneuvers General Propeller Evaluation Procedures interested experimenting props models can several things will improve re sults require sophisticated work first step experiment prop diameter Use same pitch design now using select prop next larger diameter Fly ob serve measure results begin reduce diameter prop ements until same diameter original prop Take original prop reduce in crements until sure model does perform well second step experiment propeller blade width same diam eter tests props have wider narrower blades same pitch third step select props same brand blade configuration higher lower pitch Trim diameter higher pitch prop best diam eter achieved steps 2 fly carefully reduce diameter / 16 /8 time determine better first best prop Take lower pitch prop begin larger diameter work down carefully tests basic method used match prop/engine/model improved performance configuration use pitch gauges see photo other techniques will discussed future want conclude brief dis cussion props few reminders turn use simple prop balancers pictured Prather Products sells similar universal balance under two bucks balance props engine model will appreciate have enough trouble coping primary vibrations generated one-cylinder engines secondary vibrations induced unbal anced props reduce engine life add stress model high performance applications use best metal spinners balance same reasons note about spinners modern spinners run true dont wobble Wobbling spinners have cost speed models up 3 mph tip wobble approximately 1/16 Look spinner tip carefully run engine focuses sharply vision its okay may want correct problem clipped propeller picture carefully balanced blades equal length balance props removing ma terial top side blade trimming tips unequal lengths Blades unequal length area etc produce unequal dynamic loads engine What Im trying say prop static balancedbut has un equal blade area bladeis un balanced runs blade produces thrust other unequal load transferred engine model Safety activity power modeling has its safety aspects Rotating propellers statistically hazardous Prop blades stressed beyond structural limits fly off speeds several hundred mph Such projectile can fatal Balanced props safer unbalanced props 2 order apparent hazard molded plastic nylon similar hazardous followed soft wood hardwood molded-strand fiberglass props safest gen eral statement does pretend evaluate physical/safety aspects specific prop 3 Talk yourself time operate engine Ive learned over years am safe unless remind myself time keep fingers self under control away prop stand line prop wear ear protectors Ear protectors two things protect hearing isolate thinking processes noise can actually disorient mind judgment last item eye protection Wear glasses protect eyes broken blades frequently fuel oil thrown prop prop blast aware yourself relation engines operate operated others think safety Next column will airframes power train engine mount tank prop interact previous articles including this series concerned Power Systems point considering last model element system airframe Don Jehlik 438A Sch weer Dr Star Route 1 Hawthorne NV 89415 Make Props/de Bolt continued page 45 greatest benefit found final step apply finish record exact blade shape duplicates can made further testing high speeds blades travel sur face friction can create considerable drag reduction surface drag can add just much performance can reduction drag some design improve ment good finish important can finish prop normal ways using paints epoxies excellent However require time apply should changes desired prop later much work involved replac ing finish simple effective prop finish nothing wax propeller smoothly finished fine sandpaper paste wax Simonize Blue Coral etc rubbed wood wax dried buffed cloth high lustre An advantage other time saving prop can altered will finish quickly easily re placed using same method first custom prop gives desired results can easily duplicate second time around believe bet ter results can experiment various design parameters note re sults obtained Keep simple records results will soon have some solid facts base further experiments Since writing additional interesting 98 Model Aviation Dayg low Pem USE IT FOR TRIM & ALL BOTTOM SUR FACES mont Ave Huntingdon Valley Pa 19006 CAN SEE IT M AWAY results have become available spoke prop unloading its benefit na ture benefit can made clear comparison two props identical size unloads latter al lows engine rpm increase cause operate engine below its maxi mum rpm Any increase rpm result additional horsepower can used turn larger prop bring en gine back down its Max/hp/rpm prop unloads obviously add ing aircrafts efficiency two propellers identical size un loads other can because propeller reaches higher rpm has less drag present work aims towards removing drag propel lers felt drag controls unload ing ability great extent work unloading engines props area greatest potential improved perfor mance Both horsepower curve engine thrust curve prop rise steeply maximum ap proached Any increase rpm top end can equal times rpm near low end Also should considered few mph increase midspeed range means nothing added what top becomes very important results current work excellent-size normal pro peller Formula scratch pro duced similar size lower drag pro peller using ideas article Most normal props will unload about 10% air rpm 20K ground can expect 22K air new lower-drag prop showed 25% pick up decided increase race course amounted nearly 10 seconds As can seen 15% increase put rpm ter minal velocity over Max/hp/rpm engine point weather curtailed flight testing until 1978 season ever larger props already fabricated ap pear have good potential bench tests Only flight will offer proof course question increase prop area diameter blade width Perhaps increasing pitch combination pitch area would prove best Some interesting experiments appear order s suggested reader refer Mr deBolts article Better Props Formula published May 1977 issue Glider Flying/Wilson continued page 41 end up around armpits can run backwards faster people can run forward would make pretty good NFL cornerback After Thursdays opening ceremonies weather best Danish stayclear skies buoyant air low wind would take models 400500 meters three minutes Practice same before fliers working air-picking launches Launches good zooms doubly rewarded Ros kildes light air elevating ships hotter part thermal better climb plus extra flight time due climb itself calm-air launch sequence same medium wind se quence Run five six quick strides after ship turns wind hand-over hand two three arm lengths quickly turn loose line release Friday Wakefield flown glider team helped downwind re trieval group After contest three Soviet fliers busiest practice getting about 20 flights time spent flying techniqueno trim ming Only eight hours before start contest other contestants packing resting Russians however out working hardest difference previous sessions longer span fly-off models inconsistent launches compared shorter span models Whether due design construction quirks particular models dont know During practices neither fliers nor team manager talked very much fliers worked own ships didnt pay much attention other countries competitors saw camera Lepps out short time flying fin ished left either eat go back rooms short pretty seri ous business model processing serious entire team showed up fore processing officially began Thurs day ran ships through no crowds around dont know arranged effective Saturday morning team out early made about five short flights warm up test air Field condi tions affected flying greatly air port surrounded grass areas crops forest Upwind launch line large depression upwind rough little hills irregular terrain temperature between 5565o F sun directly visible until late day Some strong thermals generated right after 7 am otherwise lift weak Most rounds thermals just strong enough maintain ships line height slow descent last round especially ten 82 fliers maxed air conditions dead map field shows general layout Initials L C refer Lepp Chop lssaenko launch point particular flight LI instance Lepps first-round launch point Rus sians mobile fliers field although majority fliers circle towing did get fairly spread out Russians have simple strategy get downwind back good selec tion other fliers wait air someone hand over thermal July1978 99 Designed 2 channel R/C tether control 15 35 engines Maintaining top quality simple con struction Balsa Plywood parts accurately diecui precision vacuum formed Plastic hull cabin Hardware package including R/C hardware Full sized Plans plus Decals Sport model Coast Guard version STERLING MODELS G ST PI411A PA 19134 no dealer availaSle d,ect odes accepted tO additiOeai cflage handling shipping leo minimum U S SI 25 ninirnun Outside US Catalog 01 entie line Ot airplane Control line Train kit boat ero Secet otUOdplAiplanet cowering tinisking ricing enclosed C Seces ot Contnl Line Ca,ie Flying snIping stunting Carrer ruleS eguletionn oontul line installation instroctinni 2SC er NO checks OnioUS moneourde orcorrenut