Engine Technique Don Jehulk PROPS AND SPINNERS first props model engines like pictured Brown Jr engine cour tesy Dave Elias quite large diameter rotated slowly 4-8000 rpm made soft woods like bass gum subjected high cen trifugal forces shock loads mod ern engines produce Second generation props typically smaller diameter rotated faster 14000 rpm made harder woods like oak walnut maple Horsepower increased 1/4 60-size en gines end World War II brought desire things including hob bies Model planes cars enjoyed popPostwar engines increased power requiring hardwood props sophisticated design became smaller rotated faster up 14000 rpm made harder woodslike oak walnut maple Photo BugI diesel shows three test props used measure flight performance horsepower standard identical engine manufacturers test data selection props bench running author outlines procedure does require tachometer 46 Model Aviation first generation propellerslike Brown Jr ignition enginewere large diameter rotated slowly between 4-8000 rpm made soft woods like bass gum urnor Deuleves mis leblane propel ler first serious effort evaluate prop performance parameters Huth may have seen pictures pitch gauge illustrates its use better Matthews shown Hornet 60 designed just pitch gauge indispensable tool fliers certain events notably racing speed prior WW II race car competition ularity next few years has equalled since High performance engines like Hornet 60 pictured Huth-Matthews designed one-blade prop Edco Skydevil hardwood props designed period just prior WW II race car application Modified new control-line style flying speed performance race Looking back believe Irwin Huth Wayne Mathews one-blade prop adjustable pitch first serious effort made competition fliers optimize propeller/horsepower application privelege talking 1949 Nats learned single-blade prop re-shaped blade area optimized airfoil blade modified pitch adjusted allow combination turn rpm matched maximum hp engine last sentence says before talk about optimum prop want mention uses props sounds simple believe props have several uses applications placing different demand first Bench Running dont really need fancy props just ones appropriate safe previous col umn discussed selection props bench running run props allow engine initially turn at least rpm expect run air continue reduce prop size until en gine runs consistently throughout rpm envelope intend use model plus 2-3000 rpm top end Dont have tach Heres general rule First prop engines 5-10 cc displacement select prop same pitch inch less diameter used flight reduce diameter once again usually trim ming inch off prop 25cc engines start prop 2 less pitch same diameter flight prop trim off diameter final test Props engines reduced 1/4 original diameter first runs final runs second Power Performance Testing photo BugI diesel en gine shows three test props Another photo shows array props cut various sizes hp tests hp tests swingweight dynanometer use series props place maximum minimum practical loads engine allows plot power curve engine well engine response different fuels plugs etc gets rather esoteric Ill reserve future article discussion sensible use special props area performance testing Remember Ive said before bench running its performance mod eler Briefly performance testing lots things BugI engine has three per formance test props because exactly duplicates load placed engine flight b another allows enConunued page 97 July1978 47 Through use 01 test propellers tne autnor awe piot norsepower curves oy corlcuueflCe deBolt article page 42 also goes importance matching propeller engine running high rpm high-quality metal spinners recommended tip wobble 1/16 in. spinner may cost speed model much 3 mph spinner should balanced Careful propeller balancing vital both life engine plane static balanced prop unequal blade lengths and/or areas will unbalanced runs nual Taft Gary Medley towing A-2 towline glider attempt 14 max line slipped out hand model took off downwind good air line still attached Thinking better chasing foot Gary ran back got motorcycle chase model got low enough abandoned cycle grabbed towline towed model back field foot launched maxed Sandwiched between stormy weekends all-FAI annual meet blessed two days excellent flying weather Most Southern California regulars there good represen tation Northern Cal too Competi tors came Michigan Colorado Oklahoma too Peter Allnutt wife Canada Peters parents England Five 14 entrants A-2 Glider maxed out Bob Isaacson won 14 maxes two max-outs both Wakefield Power top honors finally going Bob Piserchio Roger Simpson Among five top fliers three events five previous US Team mem bers plus ex-World Champion Quite meet Official Manhattan Formula Rules long last perhaps rules event nailed down Until now pub lished version differed slightly other published version rules pub lished based iden tical versions published MIAMA club also con siderably different Ed Whittens orig inal rules decade ago rules under event will flown active New York group will un doubtedly local variations 1 Airframe weight less rubber 4 grams minimum 2 Overall length measured front prop bearing 20 maximum 3 Fuselage Must support enclose single rubber motor No motor sticks b Must include excede box 2 X 4 x 2 c Must havea windshield 2 sq minimum area plust window side 1 sq minimum area covered cellophane similar transparent material 4 Prop wood direct drive fixed pitch 5 Wing Monoplane maximum pro jected span 20 maximum chord 4 Wood bracing allowed 6 Stab Monoplane stab maximum projected span 8 maximum chord 3 Wood bracing allowed 7 Landing gear Rigid fixed least two wheels minimum diameter Must able support model 8 Covering Except windshield windows paper including condenser paper allowed No film Microlite 9 Flying flights least two-point ROG Best single flight counts Un limited number official flights MARIAH 300 Latest well-worn workbench Vic Cunnyngham Jr 300-square-incher intended competi tion Classes Similar Vics Sirocco published Flying Models three years ago Vic says Mariah 300 much better features three rudders following old Fast Richard concept good two better Three should just about right Vics models have parts require greater building time typical designs geodetic ribs take little time get right wing built way unlikely warp under severe conditions wing Vics recent models has over 300 parts Compare typical Nordic A-2 glider has about three times Regarding A-2 wings Bob Hatschek claims hates build models recently remarked wing looks ready cover realize still have 200 parts go Vic regards complexity thera peutic exercise end working day Built during winter Mariah has yet experience rigors competi tion history repeats well probably still hearing about 1988 Bob Meuser 4200 Gregory St Oak land CA 94619 gine turn 19000 rpm 3000 over flight rpm c third prop stand ard exactly matches test prop Paul BugI uses tests three props am able reproduce flight loads bench will able pre dict exactly engine will perform model within 1 lap 1 rpm verify performance figures another experimenter BugI FAI Team Race performance testing refined form testing currently being done rapid advances helicopter ducted fan models benefiting similar experiments development appropriate props performance testing will enable modeler predict performance Racing eventslaps speed CL Aerobatics engine response duration run Throttled enginesengine response throttle characteristics third use props flying may seem odd think flying props last Really three uses props synergistic Ive put flight props last impress upon importance break-in power performance testing procedures Flight props fall several categories applications will discussed separately Moderate Performance Props used sport flying competition flying does place exacting demands design match engine power Scale precision aerobatics sport flying examples basic rule selection props use props recom mended engine manufacturer b select available props best suits requirements c stick off-the-shelf props High Performance Special Applica tion Props used events involve high stress loads and/or special design requirements achieve optimum performance Speed racing events com bat high performance FF events place special demands props demands typically operate July1978 97 Engine Technique/Jehlik continued page 47 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
Edition: Model Aviation - 1978/07
Page Numbers: 46, 47, 97, 98
Engine Technique Don Jehulk PROPS AND SPINNERS first props model engines like pictured Brown Jr engine cour tesy Dave Elias quite large diameter rotated slowly 4-8000 rpm made soft woods like bass gum subjected high cen trifugal forces shock loads mod ern engines produce Second generation props typically smaller diameter rotated faster 14000 rpm made harder woods like oak walnut maple Horsepower increased 1/4 60-size en gines end World War II brought desire things including hob bies Model planes cars enjoyed popPostwar engines increased power requiring hardwood props sophisticated design became smaller rotated faster up 14000 rpm made harder woodslike oak walnut maple Photo BugI diesel shows three test props used measure flight performance horsepower standard identical engine manufacturers test data selection props bench running author outlines procedure does require tachometer 46 Model Aviation first generation propellerslike Brown Jr ignition enginewere large diameter rotated slowly between 4-8000 rpm made soft woods like bass gum urnor Deuleves mis leblane propel ler first serious effort evaluate prop performance parameters Huth may have seen pictures pitch gauge illustrates its use better Matthews shown Hornet 60 designed just pitch gauge indispensable tool fliers certain events notably racing speed prior WW II race car competition ularity next few years has equalled since High performance engines like Hornet 60 pictured Huth-Matthews designed one-blade prop Edco Skydevil hardwood props designed period just prior WW II race car application Modified new control-line style flying speed performance race Looking back believe Irwin Huth Wayne Mathews one-blade prop adjustable pitch first serious effort made competition fliers optimize propeller/horsepower application privelege talking 1949 Nats learned single-blade prop re-shaped blade area optimized airfoil blade modified pitch adjusted allow combination turn rpm matched maximum hp engine last sentence says before talk about optimum prop want mention uses props sounds simple believe props have several uses applications placing different demand first Bench Running dont really need fancy props just ones appropriate safe previous col umn discussed selection props bench running run props allow engine initially turn at least rpm expect run air continue reduce prop size until en gine runs consistently throughout rpm envelope intend use model plus 2-3000 rpm top end Dont have tach Heres general rule First prop engines 5-10 cc displacement select prop same pitch inch less diameter used flight reduce diameter once again usually trim ming inch off prop 25cc engines start prop 2 less pitch same diameter flight prop trim off diameter final test Props engines reduced 1/4 original diameter first runs final runs second Power Performance Testing photo BugI diesel en gine shows three test props Another photo shows array props cut various sizes hp tests hp tests swingweight dynanometer use series props place maximum minimum practical loads engine allows plot power curve engine well engine response different fuels plugs etc gets rather esoteric Ill reserve future article discussion sensible use special props area performance testing Remember Ive said before bench running its performance mod eler Briefly performance testing lots things BugI engine has three per formance test props because exactly duplicates load placed engine flight b another allows enConunued page 97 July1978 47 Through use 01 test propellers tne autnor awe piot norsepower curves oy corlcuueflCe deBolt article page 42 also goes importance matching propeller engine running high rpm high-quality metal spinners recommended tip wobble 1/16 in. spinner may cost speed model much 3 mph spinner should balanced Careful propeller balancing vital both life engine plane static balanced prop unequal blade lengths and/or areas will unbalanced runs nual Taft Gary Medley towing A-2 towline glider attempt 14 max line slipped out hand model took off downwind good air line still attached Thinking better chasing foot Gary ran back got motorcycle chase model got low enough abandoned cycle grabbed towline towed model back field foot launched maxed Sandwiched between stormy weekends all-FAI annual meet blessed two days excellent flying weather Most Southern California regulars there good represen tation Northern Cal too Competi tors came Michigan Colorado Oklahoma too Peter Allnutt wife Canada Peters parents England Five 14 entrants A-2 Glider maxed out Bob Isaacson won 14 maxes two max-outs both Wakefield Power top honors finally going Bob Piserchio Roger Simpson Among five top fliers three events five previous US Team mem bers plus ex-World Champion Quite meet Official Manhattan Formula Rules long last perhaps rules event nailed down Until now pub lished version differed slightly other published version rules pub lished based iden tical versions published MIAMA club also con siderably different Ed Whittens orig inal rules decade ago rules under event will flown active New York group will un doubtedly local variations 1 Airframe weight less rubber 4 grams minimum 2 Overall length measured front prop bearing 20 maximum 3 Fuselage Must support enclose single rubber motor No motor sticks b Must include excede box 2 X 4 x 2 c Must havea windshield 2 sq minimum area plust window side 1 sq minimum area covered cellophane similar transparent material 4 Prop wood direct drive fixed pitch 5 Wing Monoplane maximum pro jected span 20 maximum chord 4 Wood bracing allowed 6 Stab Monoplane stab maximum projected span 8 maximum chord 3 Wood bracing allowed 7 Landing gear Rigid fixed least two wheels minimum diameter Must able support model 8 Covering Except windshield windows paper including condenser paper allowed No film Microlite 9 Flying flights least two-point ROG Best single flight counts Un limited number official flights MARIAH 300 Latest well-worn workbench Vic Cunnyngham Jr 300-square-incher intended competi tion Classes Similar Vics Sirocco published Flying Models three years ago Vic says Mariah 300 much better features three rudders following old Fast Richard concept good two better Three should just about right Vics models have parts require greater building time typical designs geodetic ribs take little time get right wing built way unlikely warp under severe conditions wing Vics recent models has over 300 parts Compare typical Nordic A-2 glider has about three times Regarding A-2 wings Bob Hatschek claims hates build models recently remarked wing looks ready cover realize still have 200 parts go Vic regards complexity thera peutic exercise end working day Built during winter Mariah has yet experience rigors competi tion history repeats well probably still hearing about 1988 Bob Meuser 4200 Gregory St Oak land CA 94619 gine turn 19000 rpm 3000 over flight rpm c third prop stand ard exactly matches test prop Paul BugI uses tests three props am able reproduce flight loads bench will able pre dict exactly engine will perform model within 1 lap 1 rpm verify performance figures another experimenter BugI FAI Team Race performance testing refined form testing currently being done rapid advances helicopter ducted fan models benefiting similar experiments development appropriate props performance testing will enable modeler predict performance Racing eventslaps speed CL Aerobatics engine response duration run Throttled enginesengine response throttle characteristics third use props flying may seem odd think flying props last Really three uses props synergistic Ive put flight props last impress upon importance break-in power performance testing procedures Flight props fall several categories applications will discussed separately Moderate Performance Props used sport flying competition flying does place exacting demands design match engine power Scale precision aerobatics sport flying examples basic rule selection props use props recom mended engine manufacturer b select available props best suits requirements c stick off-the-shelf props High Performance Special Applica tion Props used events involve high stress loads and/or special design requirements achieve optimum performance Speed racing events com bat high performance FF events place special demands props demands typically operate July1978 97 Engine Technique/Jehlik continued page 47 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
Edition: Model Aviation - 1978/07
Page Numbers: 46, 47, 97, 98
Engine Technique Don Jehulk PROPS AND SPINNERS first props model engines like pictured Brown Jr engine cour tesy Dave Elias quite large diameter rotated slowly 4-8000 rpm made soft woods like bass gum subjected high cen trifugal forces shock loads mod ern engines produce Second generation props typically smaller diameter rotated faster 14000 rpm made harder woods like oak walnut maple Horsepower increased 1/4 60-size en gines end World War II brought desire things including hob bies Model planes cars enjoyed popPostwar engines increased power requiring hardwood props sophisticated design became smaller rotated faster up 14000 rpm made harder woodslike oak walnut maple Photo BugI diesel shows three test props used measure flight performance horsepower standard identical engine manufacturers test data selection props bench running author outlines procedure does require tachometer 46 Model Aviation first generation propellerslike Brown Jr ignition enginewere large diameter rotated slowly between 4-8000 rpm made soft woods like bass gum urnor Deuleves mis leblane propel ler first serious effort evaluate prop performance parameters Huth may have seen pictures pitch gauge illustrates its use better Matthews shown Hornet 60 designed just pitch gauge indispensable tool fliers certain events notably racing speed prior WW II race car competition ularity next few years has equalled since High performance engines like Hornet 60 pictured Huth-Matthews designed one-blade prop Edco Skydevil hardwood props designed period just prior WW II race car application Modified new control-line style flying speed performance race Looking back believe Irwin Huth Wayne Mathews one-blade prop adjustable pitch first serious effort made competition fliers optimize propeller/horsepower application privelege talking 1949 Nats learned single-blade prop re-shaped blade area optimized airfoil blade modified pitch adjusted allow combination turn rpm matched maximum hp engine last sentence says before talk about optimum prop want mention uses props sounds simple believe props have several uses applications placing different demand first Bench Running dont really need fancy props just ones appropriate safe previous col umn discussed selection props bench running run props allow engine initially turn at least rpm expect run air continue reduce prop size until en gine runs consistently throughout rpm envelope intend use model plus 2-3000 rpm top end Dont have tach Heres general rule First prop engines 5-10 cc displacement select prop same pitch inch less diameter used flight reduce diameter once again usually trim ming inch off prop 25cc engines start prop 2 less pitch same diameter flight prop trim off diameter final test Props engines reduced 1/4 original diameter first runs final runs second Power Performance Testing photo BugI diesel en gine shows three test props Another photo shows array props cut various sizes hp tests hp tests swingweight dynanometer use series props place maximum minimum practical loads engine allows plot power curve engine well engine response different fuels plugs etc gets rather esoteric Ill reserve future article discussion sensible use special props area performance testing Remember Ive said before bench running its performance mod eler Briefly performance testing lots things BugI engine has three per formance test props because exactly duplicates load placed engine flight b another allows enConunued page 97 July1978 47 Through use 01 test propellers tne autnor awe piot norsepower curves oy corlcuueflCe deBolt article page 42 also goes importance matching propeller engine running high rpm high-quality metal spinners recommended tip wobble 1/16 in. spinner may cost speed model much 3 mph spinner should balanced Careful propeller balancing vital both life engine plane static balanced prop unequal blade lengths and/or areas will unbalanced runs nual Taft Gary Medley towing A-2 towline glider attempt 14 max line slipped out hand model took off downwind good air line still attached Thinking better chasing foot Gary ran back got motorcycle chase model got low enough abandoned cycle grabbed towline towed model back field foot launched maxed Sandwiched between stormy weekends all-FAI annual meet blessed two days excellent flying weather Most Southern California regulars there good represen tation Northern Cal too Competi tors came Michigan Colorado Oklahoma too Peter Allnutt wife Canada Peters parents England Five 14 entrants A-2 Glider maxed out Bob Isaacson won 14 maxes two max-outs both Wakefield Power top honors finally going Bob Piserchio Roger Simpson Among five top fliers three events five previous US Team mem bers plus ex-World Champion Quite meet Official Manhattan Formula Rules long last perhaps rules event nailed down Until now pub lished version differed slightly other published version rules pub lished based iden tical versions published MIAMA club also con siderably different Ed Whittens orig inal rules decade ago rules under event will flown active New York group will un doubtedly local variations 1 Airframe weight less rubber 4 grams minimum 2 Overall length measured front prop bearing 20 maximum 3 Fuselage Must support enclose single rubber motor No motor sticks b Must include excede box 2 X 4 x 2 c Must havea windshield 2 sq minimum area plust window side 1 sq minimum area covered cellophane similar transparent material 4 Prop wood direct drive fixed pitch 5 Wing Monoplane maximum pro jected span 20 maximum chord 4 Wood bracing allowed 6 Stab Monoplane stab maximum projected span 8 maximum chord 3 Wood bracing allowed 7 Landing gear Rigid fixed least two wheels minimum diameter Must able support model 8 Covering Except windshield windows paper including condenser paper allowed No film Microlite 9 Flying flights least two-point ROG Best single flight counts Un limited number official flights MARIAH 300 Latest well-worn workbench Vic Cunnyngham Jr 300-square-incher intended competi tion Classes Similar Vics Sirocco published Flying Models three years ago Vic says Mariah 300 much better features three rudders following old Fast Richard concept good two better Three should just about right Vics models have parts require greater building time typical designs geodetic ribs take little time get right wing built way unlikely warp under severe conditions wing Vics recent models has over 300 parts Compare typical Nordic A-2 glider has about three times Regarding A-2 wings Bob Hatschek claims hates build models recently remarked wing looks ready cover realize still have 200 parts go Vic regards complexity thera peutic exercise end working day Built during winter Mariah has yet experience rigors competi tion history repeats well probably still hearing about 1988 Bob Meuser 4200 Gregory St Oak land CA 94619 gine turn 19000 rpm 3000 over flight rpm c third prop stand ard exactly matches test prop Paul BugI uses tests three props am able reproduce flight loads bench will able pre dict exactly engine will perform model within 1 lap 1 rpm verify performance figures another experimenter BugI FAI Team Race performance testing refined form testing currently being done rapid advances helicopter ducted fan models benefiting similar experiments development appropriate props performance testing will enable modeler predict performance Racing eventslaps speed CL Aerobatics engine response duration run Throttled enginesengine response throttle characteristics third use props flying may seem odd think flying props last Really three uses props synergistic Ive put flight props last impress upon importance break-in power performance testing procedures Flight props fall several categories applications will discussed separately Moderate Performance Props used sport flying competition flying does place exacting demands design match engine power Scale precision aerobatics sport flying examples basic rule selection props use props recom mended engine manufacturer b select available props best suits requirements c stick off-the-shelf props High Performance Special Applica tion Props used events involve high stress loads and/or special design requirements achieve optimum performance Speed racing events com bat high performance FF events place special demands props demands typically operate July1978 97 Engine Technique/Jehlik continued page 47 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
Edition: Model Aviation - 1978/07
Page Numbers: 46, 47, 97, 98
Engine Technique Don Jehulk PROPS AND SPINNERS first props model engines like pictured Brown Jr engine cour tesy Dave Elias quite large diameter rotated slowly 4-8000 rpm made soft woods like bass gum subjected high cen trifugal forces shock loads mod ern engines produce Second generation props typically smaller diameter rotated faster 14000 rpm made harder woods like oak walnut maple Horsepower increased 1/4 60-size en gines end World War II brought desire things including hob bies Model planes cars enjoyed popPostwar engines increased power requiring hardwood props sophisticated design became smaller rotated faster up 14000 rpm made harder woodslike oak walnut maple Photo BugI diesel shows three test props used measure flight performance horsepower standard identical engine manufacturers test data selection props bench running author outlines procedure does require tachometer 46 Model Aviation first generation propellerslike Brown Jr ignition enginewere large diameter rotated slowly between 4-8000 rpm made soft woods like bass gum urnor Deuleves mis leblane propel ler first serious effort evaluate prop performance parameters Huth may have seen pictures pitch gauge illustrates its use better Matthews shown Hornet 60 designed just pitch gauge indispensable tool fliers certain events notably racing speed prior WW II race car competition ularity next few years has equalled since High performance engines like Hornet 60 pictured Huth-Matthews designed one-blade prop Edco Skydevil hardwood props designed period just prior WW II race car application Modified new control-line style flying speed performance race Looking back believe Irwin Huth Wayne Mathews one-blade prop adjustable pitch first serious effort made competition fliers optimize propeller/horsepower application privelege talking 1949 Nats learned single-blade prop re-shaped blade area optimized airfoil blade modified pitch adjusted allow combination turn rpm matched maximum hp engine last sentence says before talk about optimum prop want mention uses props sounds simple believe props have several uses applications placing different demand first Bench Running dont really need fancy props just ones appropriate safe previous col umn discussed selection props bench running run props allow engine initially turn at least rpm expect run air continue reduce prop size until en gine runs consistently throughout rpm envelope intend use model plus 2-3000 rpm top end Dont have tach Heres general rule First prop engines 5-10 cc displacement select prop same pitch inch less diameter used flight reduce diameter once again usually trim ming inch off prop 25cc engines start prop 2 less pitch same diameter flight prop trim off diameter final test Props engines reduced 1/4 original diameter first runs final runs second Power Performance Testing photo BugI diesel en gine shows three test props Another photo shows array props cut various sizes hp tests hp tests swingweight dynanometer use series props place maximum minimum practical loads engine allows plot power curve engine well engine response different fuels plugs etc gets rather esoteric Ill reserve future article discussion sensible use special props area performance testing Remember Ive said before bench running its performance mod eler Briefly performance testing lots things BugI engine has three per formance test props because exactly duplicates load placed engine flight b another allows enConunued page 97 July1978 47 Through use 01 test propellers tne autnor awe piot norsepower curves oy corlcuueflCe deBolt article page 42 also goes importance matching propeller engine running high rpm high-quality metal spinners recommended tip wobble 1/16 in. spinner may cost speed model much 3 mph spinner should balanced Careful propeller balancing vital both life engine plane static balanced prop unequal blade lengths and/or areas will unbalanced runs nual Taft Gary Medley towing A-2 towline glider attempt 14 max line slipped out hand model took off downwind good air line still attached Thinking better chasing foot Gary ran back got motorcycle chase model got low enough abandoned cycle grabbed towline towed model back field foot launched maxed Sandwiched between stormy weekends all-FAI annual meet blessed two days excellent flying weather Most Southern California regulars there good represen tation Northern Cal too Competi tors came Michigan Colorado Oklahoma too Peter Allnutt wife Canada Peters parents England Five 14 entrants A-2 Glider maxed out Bob Isaacson won 14 maxes two max-outs both Wakefield Power top honors finally going Bob Piserchio Roger Simpson Among five top fliers three events five previous US Team mem bers plus ex-World Champion Quite meet Official Manhattan Formula Rules long last perhaps rules event nailed down Until now pub lished version differed slightly other published version rules pub lished based iden tical versions published MIAMA club also con siderably different Ed Whittens orig inal rules decade ago rules under event will flown active New York group will un doubtedly local variations 1 Airframe weight less rubber 4 grams minimum 2 Overall length measured front prop bearing 20 maximum 3 Fuselage Must support enclose single rubber motor No motor sticks b Must include excede box 2 X 4 x 2 c Must havea windshield 2 sq minimum area plust window side 1 sq minimum area covered cellophane similar transparent material 4 Prop wood direct drive fixed pitch 5 Wing Monoplane maximum pro jected span 20 maximum chord 4 Wood bracing allowed 6 Stab Monoplane stab maximum projected span 8 maximum chord 3 Wood bracing allowed 7 Landing gear Rigid fixed least two wheels minimum diameter Must able support model 8 Covering Except windshield windows paper including condenser paper allowed No film Microlite 9 Flying flights least two-point ROG Best single flight counts Un limited number official flights MARIAH 300 Latest well-worn workbench Vic Cunnyngham Jr 300-square-incher intended competi tion Classes Similar Vics Sirocco published Flying Models three years ago Vic says Mariah 300 much better features three rudders following old Fast Richard concept good two better Three should just about right Vics models have parts require greater building time typical designs geodetic ribs take little time get right wing built way unlikely warp under severe conditions wing Vics recent models has over 300 parts Compare typical Nordic A-2 glider has about three times Regarding A-2 wings Bob Hatschek claims hates build models recently remarked wing looks ready cover realize still have 200 parts go Vic regards complexity thera peutic exercise end working day Built during winter Mariah has yet experience rigors competi tion history repeats well probably still hearing about 1988 Bob Meuser 4200 Gregory St Oak land CA 94619 gine turn 19000 rpm 3000 over flight rpm c third prop stand ard exactly matches test prop Paul BugI uses tests three props am able reproduce flight loads bench will able pre dict exactly engine will perform model within 1 lap 1 rpm verify performance figures another experimenter BugI FAI Team Race performance testing refined form testing currently being done rapid advances helicopter ducted fan models benefiting similar experiments development appropriate props performance testing will enable modeler predict performance Racing eventslaps speed CL Aerobatics engine response duration run Throttled enginesengine response throttle characteristics third use props flying may seem odd think flying props last Really three uses props synergistic Ive put flight props last impress upon importance break-in power performance testing procedures Flight props fall several categories applications will discussed separately Moderate Performance Props used sport flying competition flying does place exacting demands design match engine power Scale precision aerobatics sport flying examples basic rule selection props use props recom mended engine manufacturer b select available props best suits requirements c stick off-the-shelf props High Performance Special Applica tion Props used events involve high stress loads and/or special design requirements achieve optimum performance Speed racing events com bat high performance FF events place special demands props demands typically operate July1978 97 Engine Technique/Jehlik continued page 47 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