LAST month gave parametric equa tion picking size servo need based usual aileron elevator situation tapered wood strip attached trailing edge wing stabilizer some kind hinge gap month will extend discussion mass- aerodynamicallybalanced surfaces some discussion dynamics First lets look various kinds servo loads Loads Servos Static overloads throttle control should least likely damage servo yet due carelessness frequently eats cause simply owner doesnt test setup carefully enough before committing service test ridiculously easy Set High motor plus High trim Disconnect clevis throttle Push throttle arm should free go little farther High direction Go Low motor plus Low trim throttle arm should have little freedom direction too Now hook up go flying Shock No can calculate shock results nose gear dropping gopher hole standard approach isolate servo behind spring spongy pushrod servo has enough control steer plane protected shock damage work up answer starting weak spring cutting off coil time until its stiff enough theres elevator tail-dragger air plane such Norm Rosenstocks Waco HKS 7 cant see mass balance because echniquc inside aerodynamic balance area tip elevator Consider landing mass balance plane comes nose-high fully-stalled condition drops frequently tail-first Onto runway elevator heavy wants keep coming down after tail bumper has stopped result shock pulse down pushrod magnitude pulse depends things weight elevator location its center-of-gravity length control horn stiffness pushrod buckles its shock absorber stiffness servo mounts amount ofup airload elevator Unbalanced elevators thats what us using have known take teeth off servo gears kick ends intermediate gear shafts right out sockets add weight forward hinge line ie mass balance Norm did bad things go away rudder can get too Frequently tail draggers have tail wheels mounted directly connected tail wheel plane lands yawed crosswind rudder kicked downwind side last minute W iOn Che Bojoge Weigh take out yaw tail wheel takes shot tries straighten out does shock go Right down trail described elevator Mass balances wont help situation youd better make connection rudder pretty soft Use some kind spring work up nose wheel Flaps bit like elevators though work through larger angles parametric equa tion wont accurate found often bottom plane contact runway significant hazard hand want stiff pushrod system ensure flaps go down against airload other something has got give flap hits runway Most folks make flap flimsy Being outside theyre pretty easy repair fixing necessary Flaps naturally unbalanced Flutter Ailerons live world own first place likely problem flutter lot area controlled servo side going up other going down can add aerodynamic balance tabs like WW Fokker few people Mass balances common Torsion-bar strip ailerons suffer fact twist easily Barn Door ailerons inset tip suffer spongy pushrods linkages Strip allerons benefit balance weights out tip can get knocked about bad landings Barn Door ailerons can balanced anywhere usual location middle near control horn minimize structural support weight balance weights ailerons willflutter Control ever-present flutter obtained use stiff pushrod systems transfers oscillating load right servos gear box Theres thing can help ailerons Run engine through its full range rpm friends hold plane up off ground grasping wing panel about halfway out panel Watch ailerons carefully Ifyou notice go resonance engine rpm change something aileron system get rid Something can mean better support servo pushrods and/or bellcranks can try mass balances whatever must get rid resonance resonance later Ailerons flutter because something vibrating make flutter biggest forcing function have propeller hand engine gives swat once during revolution due engine vibration torsional vibration ailerons resist producing airloads opposite direction airplane flying Also twice rotation two-bladed prop blade will pass leading edge wing panel Since airflow off propeller moves spiral blade passage also puts torsional vibration Both vibrations revealed hold-it-up test just described Ive got interrupt aileron discussion moment Theres thing called resonance deal Stretch flat rubberband Blow edge 22 Model Aviation Tony Srakowiak flies iiis Nusn D19 lCj using ror etevajor ruooernosewneel -i ron S-il throttle another choke/kill switch servos serviced World Engines 1 6 Amp-Hour battery pack has demonstrated sufficient capacity provide two hours safe flying main purposes AMAs existence share kind data rubber near middle stretched length see effect resonance force breath puts rubberband small response large Pull down rubberband youll get idea large Go outside wind blowing may see rubberband stretched 12 inches vibrating through arc three inches What about Take ruler out desk Blow its edge much happens right Stiffness helps So does added weight trouble weight interferes flying So wed better stick stiffness de-resonate model Now back aileron Another forcing function called vortex shedding result properties air shape wing aileron best example can give famous movie Galloping Gertie bridge shook itself down torsional reson ance bridge acted exactly did rubberband blew ailerons will too whenever airspeed gets high enough forcing function always waiting destroy airplane minimize seal ing gap between wing aileron balancing aileron its hinge overhanging weights keeping servo drive system stiff possible Choose Servo Ive included test results some servos borrowed purpose order give idea range available table includes Performance Factor PF may help choose Performance Factor stall torque divided product stall current 9Q0 free-transit time Its similar horsepower per Watt pretty sensitive measure work can get out charged set batteries knowing charge servos use mission flown High numbers give longer missions other considerations being equal Servos higher PF numbers resist gear tooth damage better comparing gears same size made same material called upon resist same loads vibrations qualifications should make clear Im giving tools make choice making cho ice Wear Servo Gears Im going td digress moment talk about servo gears themselves Most servos use straight-cut gears look like triangles points knocked off slide over another flutter causes rub together briskly under high loads teeth get hot Ive seen aileron gears actually got hot enough soften extrude due flutter Normally have trouble getting piece paper between meshing gear teeth Ive seen situations could get straight pin after flutter has done its work situation feeds itself need stiff ness control amplitude flutter gears soften extrude pivot holes bellcranks wear enlarge amplitude allowed increase impact loads system get larger Larger loads create damage end destruction system Help available form various geartooth profiles roll another rather sliding gears set may use such profile gears higher PF number Given identical flutter situations improved gears will run cooler Bottom Line said Id tell pick servo considermg ShOCK uno viurahull IL S CSY P iguie OUL 110W much shock want resistand pick servo has higher stall torque Servo gears designed inside-out means motor cant hurt gears pushes against locked output opposite situation true push against output arm trying make motor turn backwards against electricity will likely break something gear train Friction reason Pushing output wheel requires put torque equal motor torque plus twice friction gear train Inside-out frictions subtract output torque Outside-in must added Dont try push servos backwards dont let shock either Safety involved What would happen control systems bound up same time ice storm maybe ended up pushing same direction Will pushrods servo mounts take pull tests Control Line models dont Should RCer less Lock controls try pop servos out mounts own power might learn something Better wait learn middle pullout things youre likely learn servo push test pushrods work fine tension compression often build grid balsa sticks tailcone support pushrods middle length touch pushrod tries bend Otherwise its like arent Ron Van Putte gave few hints about pushrod installations Jan 81 issue p28 et seq Enough Already Well leave story shock vibration pushrods right present Unfor tunately no simple formula calculat ing such forces know As Ive tried Next month well go batteries support use larger servos meantime keep mind attend trade shows see something think would support column write tell about As promised last month well close solving problem Norm Rosenstocks elevator Waco HKS-7 Incidently dont write Norm plans plane due kitted Orlando Aircraft Manufacturing Co Ill Bed ford Ave Belmore NY 11710 sometime 1981 82 Write about Sample Problem No 2 Elevator Norm Rosenstocks Waco HKS-7 Total elevator area S sq Area balance tab 13 1Oi x 4 x will assume balance tab removes equal area behind hinge calcula tion Net elevator area 152- 4 x 647 sq C Weight airplane 32 lbs Cross section area 1865 see Problem #1 last months column procedure Q 32/1865 psi Vdive hfrom last months graph Norm flying KPS-15 servos using outside hole long arm elevator control horn measures long half-inch thick Continued page 102 April1981 23 show limited shock levels safe servos Ive shown establish limits Flutter vibration elastic phenomena control destructive characteristics using stiff systems Stiff systems have natural resonances high frequencies amplitudes small difficult excite both instances shock vibration avoid problem rather solving Radio Technique/Myers Continued page 23 elevator Therefore L~ 525 J 12125 D 371/125 0 Servo torque required T CF F 5 last months chart T--- x94x94x 126x525xoooo5 867 125 In-oz Better use World Engines S-16 Norm George M Myers 70 Froehlich Farm Road Hicksville NY 11801 bulky look engine due rectangular portions crankcase casting can removed turns out weight saved less three ounces doesnt justify machining cost An unusual feature Kawasaki engines cylinder can repositioned 180 degrees normal configuration carb side exhaust other cylinder test engine rotated carb exhaust same side makes horizontal mounting snap cowl like Pitts Kawasaki high quality cool running smooth engine Kioritz engine makes best first impres sion pretty well lives up Like blower-derived engines designed long periods high-speed running opposed chain-saws short bursts addition Kengines usual application requires low vibration Both design goals fit requirements perfectly significantly different respects Kioritz shares characteristic Quadra carburetors have built-in chokes Hand-choking can awkward downright dangerous un-cowled engine practically impossible inside cowl Dario Brisighella has available add-on choke Quadra probably will fit just well Kioritz relatively high fuel consumption figure suspect due noticeable amount fuel drawn out carb air intake running ram-air scoop carb should result slightly leaner mixture settings better fuel consumption Kioritz smooth cool running high quality engine Roper maximum displacement engine current test series would expect measurements maxi mum also did have maximum thrust measurements werent really able identify peak props available did have maximum weight physical dimensions didnt have maximum fuel consumption see Kioritz notes did have maximum vibration levels first time ran engine shaking much couldnt get screwdriver otherwise easily accessible mixture screws stop engine make changes low-speed mixture until got things calmed down Once mixture set properly engine warmed up smoothed out nicely Ropers vibration relatively high especially idle does detract significantly engines usefulness struck size-to-displacement ratio engine requires very little space Quadra large flywheel close behind prop does mean need fairly flat-faced cowl longer prop adapter would simplify getting engine tapering cowl carb has external pressure pick-up can rotated 180 degrees places mixture adjustments face forward would accessible cowled engine though could accessed engine running completes Part report Unfortun 102 Model Aviation .yASINII AIRSCIU lIT PRESENTS BALSA STRIPPER PRECISION STRIP WOOD TO x INS FROM BALSA SHEET ALSO FOR DRAFTING AND PHOTO MATS USES TYPE II BLADE SUPER TOOL T PRICE WINDSOR PROPELLER CO PO BOX 112 WINDSOR CA 95492 Heres equipment need give psur props toe very best balance--balance directions Carefully crafted top grade materials BUBBLE BALArtJCER accomodates 3/161/49/32 prop holes Other sizes available special order Dealers oivited $1495 Add $150 HOWARD B HUEBL DEPT 055 postage handling ft Mien add 4% sales tax No CD0s Boo 193 Route 4 Mankato Mn 56931 Big Bangers/Beckman Continued page 28
Edition: Model Aviation - 1981/04
Page Numbers: 22, 23, 102
Edition: Model Aviation - 1981/04
Page Numbers: 22, 23, 102
LAST month gave parametric equa tion picking size servo need based usual aileron elevator situation tapered wood strip attached trailing edge wing stabilizer some kind hinge gap month will extend discussion mass- aerodynamicallybalanced surfaces some discussion dynamics First lets look various kinds servo loads Loads Servos Static overloads throttle control should least likely damage servo yet due carelessness frequently eats cause simply owner doesnt test setup carefully enough before committing service test ridiculously easy Set High motor plus High trim Disconnect clevis throttle Push throttle arm should free go little farther High direction Go Low motor plus Low trim throttle arm should have little freedom direction too Now hook up go flying Shock No can calculate shock results nose gear dropping gopher hole standard approach isolate servo behind spring spongy pushrod servo has enough control steer plane protected shock damage work up answer starting weak spring cutting off coil time until its stiff enough theres elevator tail-dragger air plane such Norm Rosenstocks Waco HKS 7 cant see mass balance because echniquc inside aerodynamic balance area tip elevator Consider landing mass balance plane comes nose-high fully-stalled condition drops frequently tail-first Onto runway elevator heavy wants keep coming down after tail bumper has stopped result shock pulse down pushrod magnitude pulse depends things weight elevator location its center-of-gravity length control horn stiffness pushrod buckles its shock absorber stiffness servo mounts amount ofup airload elevator Unbalanced elevators thats what us using have known take teeth off servo gears kick ends intermediate gear shafts right out sockets add weight forward hinge line ie mass balance Norm did bad things go away rudder can get too Frequently tail draggers have tail wheels mounted directly connected tail wheel plane lands yawed crosswind rudder kicked downwind side last minute W iOn Che Bojoge Weigh take out yaw tail wheel takes shot tries straighten out does shock go Right down trail described elevator Mass balances wont help situation youd better make connection rudder pretty soft Use some kind spring work up nose wheel Flaps bit like elevators though work through larger angles parametric equa tion wont accurate found often bottom plane contact runway significant hazard hand want stiff pushrod system ensure flaps go down against airload other something has got give flap hits runway Most folks make flap flimsy Being outside theyre pretty easy repair fixing necessary Flaps naturally unbalanced Flutter Ailerons live world own first place likely problem flutter lot area controlled servo side going up other going down can add aerodynamic balance tabs like WW Fokker few people Mass balances common Torsion-bar strip ailerons suffer fact twist easily Barn Door ailerons inset tip suffer spongy pushrods linkages Strip allerons benefit balance weights out tip can get knocked about bad landings Barn Door ailerons can balanced anywhere usual location middle near control horn minimize structural support weight balance weights ailerons willflutter Control ever-present flutter obtained use stiff pushrod systems transfers oscillating load right servos gear box Theres thing can help ailerons Run engine through its full range rpm friends hold plane up off ground grasping wing panel about halfway out panel Watch ailerons carefully Ifyou notice go resonance engine rpm change something aileron system get rid Something can mean better support servo pushrods and/or bellcranks can try mass balances whatever must get rid resonance resonance later Ailerons flutter because something vibrating make flutter biggest forcing function have propeller hand engine gives swat once during revolution due engine vibration torsional vibration ailerons resist producing airloads opposite direction airplane flying Also twice rotation two-bladed prop blade will pass leading edge wing panel Since airflow off propeller moves spiral blade passage also puts torsional vibration Both vibrations revealed hold-it-up test just described Ive got interrupt aileron discussion moment Theres thing called resonance deal Stretch flat rubberband Blow edge 22 Model Aviation Tony Srakowiak flies iiis Nusn D19 lCj using ror etevajor ruooernosewneel -i ron S-il throttle another choke/kill switch servos serviced World Engines 1 6 Amp-Hour battery pack has demonstrated sufficient capacity provide two hours safe flying main purposes AMAs existence share kind data rubber near middle stretched length see effect resonance force breath puts rubberband small response large Pull down rubberband youll get idea large Go outside wind blowing may see rubberband stretched 12 inches vibrating through arc three inches What about Take ruler out desk Blow its edge much happens right Stiffness helps So does added weight trouble weight interferes flying So wed better stick stiffness de-resonate model Now back aileron Another forcing function called vortex shedding result properties air shape wing aileron best example can give famous movie Galloping Gertie bridge shook itself down torsional reson ance bridge acted exactly did rubberband blew ailerons will too whenever airspeed gets high enough forcing function always waiting destroy airplane minimize seal ing gap between wing aileron balancing aileron its hinge overhanging weights keeping servo drive system stiff possible Choose Servo Ive included test results some servos borrowed purpose order give idea range available table includes Performance Factor PF may help choose Performance Factor stall torque divided product stall current 9Q0 free-transit time Its similar horsepower per Watt pretty sensitive measure work can get out charged set batteries knowing charge servos use mission flown High numbers give longer missions other considerations being equal Servos higher PF numbers resist gear tooth damage better comparing gears same size made same material called upon resist same loads vibrations qualifications should make clear Im giving tools make choice making cho ice Wear Servo Gears Im going td digress moment talk about servo gears themselves Most servos use straight-cut gears look like triangles points knocked off slide over another flutter causes rub together briskly under high loads teeth get hot Ive seen aileron gears actually got hot enough soften extrude due flutter Normally have trouble getting piece paper between meshing gear teeth Ive seen situations could get straight pin after flutter has done its work situation feeds itself need stiff ness control amplitude flutter gears soften extrude pivot holes bellcranks wear enlarge amplitude allowed increase impact loads system get larger Larger loads create damage end destruction system Help available form various geartooth profiles roll another rather sliding gears set may use such profile gears higher PF number Given identical flutter situations improved gears will run cooler Bottom Line said Id tell pick servo considermg ShOCK uno viurahull IL S CSY P iguie OUL 110W much shock want resistand pick servo has higher stall torque Servo gears designed inside-out means motor cant hurt gears pushes against locked output opposite situation true push against output arm trying make motor turn backwards against electricity will likely break something gear train Friction reason Pushing output wheel requires put torque equal motor torque plus twice friction gear train Inside-out frictions subtract output torque Outside-in must added Dont try push servos backwards dont let shock either Safety involved What would happen control systems bound up same time ice storm maybe ended up pushing same direction Will pushrods servo mounts take pull tests Control Line models dont Should RCer less Lock controls try pop servos out mounts own power might learn something Better wait learn middle pullout things youre likely learn servo push test pushrods work fine tension compression often build grid balsa sticks tailcone support pushrods middle length touch pushrod tries bend Otherwise its like arent Ron Van Putte gave few hints about pushrod installations Jan 81 issue p28 et seq Enough Already Well leave story shock vibration pushrods right present Unfor tunately no simple formula calculat ing such forces know As Ive tried Next month well go batteries support use larger servos meantime keep mind attend trade shows see something think would support column write tell about As promised last month well close solving problem Norm Rosenstocks elevator Waco HKS-7 Incidently dont write Norm plans plane due kitted Orlando Aircraft Manufacturing Co Ill Bed ford Ave Belmore NY 11710 sometime 1981 82 Write about Sample Problem No 2 Elevator Norm Rosenstocks Waco HKS-7 Total elevator area S sq Area balance tab 13 1Oi x 4 x will assume balance tab removes equal area behind hinge calcula tion Net elevator area 152- 4 x 647 sq C Weight airplane 32 lbs Cross section area 1865 see Problem #1 last months column procedure Q 32/1865 psi Vdive hfrom last months graph Norm flying KPS-15 servos using outside hole long arm elevator control horn measures long half-inch thick Continued page 102 April1981 23 show limited shock levels safe servos Ive shown establish limits Flutter vibration elastic phenomena control destructive characteristics using stiff systems Stiff systems have natural resonances high frequencies amplitudes small difficult excite both instances shock vibration avoid problem rather solving Radio Technique/Myers Continued page 23 elevator Therefore L~ 525 J 12125 D 371/125 0 Servo torque required T CF F 5 last months chart T--- x94x94x 126x525xoooo5 867 125 In-oz Better use World Engines S-16 Norm George M Myers 70 Froehlich Farm Road Hicksville NY 11801 bulky look engine due rectangular portions crankcase casting can removed turns out weight saved less three ounces doesnt justify machining cost An unusual feature Kawasaki engines cylinder can repositioned 180 degrees normal configuration carb side exhaust other cylinder test engine rotated carb exhaust same side makes horizontal mounting snap cowl like Pitts Kawasaki high quality cool running smooth engine Kioritz engine makes best first impres sion pretty well lives up Like blower-derived engines designed long periods high-speed running opposed chain-saws short bursts addition Kengines usual application requires low vibration Both design goals fit requirements perfectly significantly different respects Kioritz shares characteristic Quadra carburetors have built-in chokes Hand-choking can awkward downright dangerous un-cowled engine practically impossible inside cowl Dario Brisighella has available add-on choke Quadra probably will fit just well Kioritz relatively high fuel consumption figure suspect due noticeable amount fuel drawn out carb air intake running ram-air scoop carb should result slightly leaner mixture settings better fuel consumption Kioritz smooth cool running high quality engine Roper maximum displacement engine current test series would expect measurements maxi mum also did have maximum thrust measurements werent really able identify peak props available did have maximum weight physical dimensions didnt have maximum fuel consumption see Kioritz notes did have maximum vibration levels first time ran engine shaking much couldnt get screwdriver otherwise easily accessible mixture screws stop engine make changes low-speed mixture until got things calmed down Once mixture set properly engine warmed up smoothed out nicely Ropers vibration relatively high especially idle does detract significantly engines usefulness struck size-to-displacement ratio engine requires very little space Quadra large flywheel close behind prop does mean need fairly flat-faced cowl longer prop adapter would simplify getting engine tapering cowl carb has external pressure pick-up can rotated 180 degrees places mixture adjustments face forward would accessible cowled engine though could accessed engine running completes Part report Unfortun 102 Model Aviation .yASINII AIRSCIU lIT PRESENTS BALSA STRIPPER PRECISION STRIP WOOD TO x INS FROM BALSA SHEET ALSO FOR DRAFTING AND PHOTO MATS USES TYPE II BLADE SUPER TOOL T PRICE WINDSOR PROPELLER CO PO BOX 112 WINDSOR CA 95492 Heres equipment need give psur props toe very best balance--balance directions Carefully crafted top grade materials BUBBLE BALArtJCER accomodates 3/161/49/32 prop holes Other sizes available special order Dealers oivited $1495 Add $150 HOWARD B HUEBL DEPT 055 postage handling ft Mien add 4% sales tax No CD0s Boo 193 Route 4 Mankato Mn 56931 Big Bangers/Beckman Continued page 28
Edition: Model Aviation - 1981/04
Page Numbers: 22, 23, 102
LAST month gave parametric equa tion picking size servo need based usual aileron elevator situation tapered wood strip attached trailing edge wing stabilizer some kind hinge gap month will extend discussion mass- aerodynamicallybalanced surfaces some discussion dynamics First lets look various kinds servo loads Loads Servos Static overloads throttle control should least likely damage servo yet due carelessness frequently eats cause simply owner doesnt test setup carefully enough before committing service test ridiculously easy Set High motor plus High trim Disconnect clevis throttle Push throttle arm should free go little farther High direction Go Low motor plus Low trim throttle arm should have little freedom direction too Now hook up go flying Shock No can calculate shock results nose gear dropping gopher hole standard approach isolate servo behind spring spongy pushrod servo has enough control steer plane protected shock damage work up answer starting weak spring cutting off coil time until its stiff enough theres elevator tail-dragger air plane such Norm Rosenstocks Waco HKS 7 cant see mass balance because echniquc inside aerodynamic balance area tip elevator Consider landing mass balance plane comes nose-high fully-stalled condition drops frequently tail-first Onto runway elevator heavy wants keep coming down after tail bumper has stopped result shock pulse down pushrod magnitude pulse depends things weight elevator location its center-of-gravity length control horn stiffness pushrod buckles its shock absorber stiffness servo mounts amount ofup airload elevator Unbalanced elevators thats what us using have known take teeth off servo gears kick ends intermediate gear shafts right out sockets add weight forward hinge line ie mass balance Norm did bad things go away rudder can get too Frequently tail draggers have tail wheels mounted directly connected tail wheel plane lands yawed crosswind rudder kicked downwind side last minute W iOn Che Bojoge Weigh take out yaw tail wheel takes shot tries straighten out does shock go Right down trail described elevator Mass balances wont help situation youd better make connection rudder pretty soft Use some kind spring work up nose wheel Flaps bit like elevators though work through larger angles parametric equa tion wont accurate found often bottom plane contact runway significant hazard hand want stiff pushrod system ensure flaps go down against airload other something has got give flap hits runway Most folks make flap flimsy Being outside theyre pretty easy repair fixing necessary Flaps naturally unbalanced Flutter Ailerons live world own first place likely problem flutter lot area controlled servo side going up other going down can add aerodynamic balance tabs like WW Fokker few people Mass balances common Torsion-bar strip ailerons suffer fact twist easily Barn Door ailerons inset tip suffer spongy pushrods linkages Strip allerons benefit balance weights out tip can get knocked about bad landings Barn Door ailerons can balanced anywhere usual location middle near control horn minimize structural support weight balance weights ailerons willflutter Control ever-present flutter obtained use stiff pushrod systems transfers oscillating load right servos gear box Theres thing can help ailerons Run engine through its full range rpm friends hold plane up off ground grasping wing panel about halfway out panel Watch ailerons carefully Ifyou notice go resonance engine rpm change something aileron system get rid Something can mean better support servo pushrods and/or bellcranks can try mass balances whatever must get rid resonance resonance later Ailerons flutter because something vibrating make flutter biggest forcing function have propeller hand engine gives swat once during revolution due engine vibration torsional vibration ailerons resist producing airloads opposite direction airplane flying Also twice rotation two-bladed prop blade will pass leading edge wing panel Since airflow off propeller moves spiral blade passage also puts torsional vibration Both vibrations revealed hold-it-up test just described Ive got interrupt aileron discussion moment Theres thing called resonance deal Stretch flat rubberband Blow edge 22 Model Aviation Tony Srakowiak flies iiis Nusn D19 lCj using ror etevajor ruooernosewneel -i ron S-il throttle another choke/kill switch servos serviced World Engines 1 6 Amp-Hour battery pack has demonstrated sufficient capacity provide two hours safe flying main purposes AMAs existence share kind data rubber near middle stretched length see effect resonance force breath puts rubberband small response large Pull down rubberband youll get idea large Go outside wind blowing may see rubberband stretched 12 inches vibrating through arc three inches What about Take ruler out desk Blow its edge much happens right Stiffness helps So does added weight trouble weight interferes flying So wed better stick stiffness de-resonate model Now back aileron Another forcing function called vortex shedding result properties air shape wing aileron best example can give famous movie Galloping Gertie bridge shook itself down torsional reson ance bridge acted exactly did rubberband blew ailerons will too whenever airspeed gets high enough forcing function always waiting destroy airplane minimize seal ing gap between wing aileron balancing aileron its hinge overhanging weights keeping servo drive system stiff possible Choose Servo Ive included test results some servos borrowed purpose order give idea range available table includes Performance Factor PF may help choose Performance Factor stall torque divided product stall current 9Q0 free-transit time Its similar horsepower per Watt pretty sensitive measure work can get out charged set batteries knowing charge servos use mission flown High numbers give longer missions other considerations being equal Servos higher PF numbers resist gear tooth damage better comparing gears same size made same material called upon resist same loads vibrations qualifications should make clear Im giving tools make choice making cho ice Wear Servo Gears Im going td digress moment talk about servo gears themselves Most servos use straight-cut gears look like triangles points knocked off slide over another flutter causes rub together briskly under high loads teeth get hot Ive seen aileron gears actually got hot enough soften extrude due flutter Normally have trouble getting piece paper between meshing gear teeth Ive seen situations could get straight pin after flutter has done its work situation feeds itself need stiff ness control amplitude flutter gears soften extrude pivot holes bellcranks wear enlarge amplitude allowed increase impact loads system get larger Larger loads create damage end destruction system Help available form various geartooth profiles roll another rather sliding gears set may use such profile gears higher PF number Given identical flutter situations improved gears will run cooler Bottom Line said Id tell pick servo considermg ShOCK uno viurahull IL S CSY P iguie OUL 110W much shock want resistand pick servo has higher stall torque Servo gears designed inside-out means motor cant hurt gears pushes against locked output opposite situation true push against output arm trying make motor turn backwards against electricity will likely break something gear train Friction reason Pushing output wheel requires put torque equal motor torque plus twice friction gear train Inside-out frictions subtract output torque Outside-in must added Dont try push servos backwards dont let shock either Safety involved What would happen control systems bound up same time ice storm maybe ended up pushing same direction Will pushrods servo mounts take pull tests Control Line models dont Should RCer less Lock controls try pop servos out mounts own power might learn something Better wait learn middle pullout things youre likely learn servo push test pushrods work fine tension compression often build grid balsa sticks tailcone support pushrods middle length touch pushrod tries bend Otherwise its like arent Ron Van Putte gave few hints about pushrod installations Jan 81 issue p28 et seq Enough Already Well leave story shock vibration pushrods right present Unfor tunately no simple formula calculat ing such forces know As Ive tried Next month well go batteries support use larger servos meantime keep mind attend trade shows see something think would support column write tell about As promised last month well close solving problem Norm Rosenstocks elevator Waco HKS-7 Incidently dont write Norm plans plane due kitted Orlando Aircraft Manufacturing Co Ill Bed ford Ave Belmore NY 11710 sometime 1981 82 Write about Sample Problem No 2 Elevator Norm Rosenstocks Waco HKS-7 Total elevator area S sq Area balance tab 13 1Oi x 4 x will assume balance tab removes equal area behind hinge calcula tion Net elevator area 152- 4 x 647 sq C Weight airplane 32 lbs Cross section area 1865 see Problem #1 last months column procedure Q 32/1865 psi Vdive hfrom last months graph Norm flying KPS-15 servos using outside hole long arm elevator control horn measures long half-inch thick Continued page 102 April1981 23 show limited shock levels safe servos Ive shown establish limits Flutter vibration elastic phenomena control destructive characteristics using stiff systems Stiff systems have natural resonances high frequencies amplitudes small difficult excite both instances shock vibration avoid problem rather solving Radio Technique/Myers Continued page 23 elevator Therefore L~ 525 J 12125 D 371/125 0 Servo torque required T CF F 5 last months chart T--- x94x94x 126x525xoooo5 867 125 In-oz Better use World Engines S-16 Norm George M Myers 70 Froehlich Farm Road Hicksville NY 11801 bulky look engine due rectangular portions crankcase casting can removed turns out weight saved less three ounces doesnt justify machining cost An unusual feature Kawasaki engines cylinder can repositioned 180 degrees normal configuration carb side exhaust other cylinder test engine rotated carb exhaust same side makes horizontal mounting snap cowl like Pitts Kawasaki high quality cool running smooth engine Kioritz engine makes best first impres sion pretty well lives up Like blower-derived engines designed long periods high-speed running opposed chain-saws short bursts addition Kengines usual application requires low vibration Both design goals fit requirements perfectly significantly different respects Kioritz shares characteristic Quadra carburetors have built-in chokes Hand-choking can awkward downright dangerous un-cowled engine practically impossible inside cowl Dario Brisighella has available add-on choke Quadra probably will fit just well Kioritz relatively high fuel consumption figure suspect due noticeable amount fuel drawn out carb air intake running ram-air scoop carb should result slightly leaner mixture settings better fuel consumption Kioritz smooth cool running high quality engine Roper maximum displacement engine current test series would expect measurements maxi mum also did have maximum thrust measurements werent really able identify peak props available did have maximum weight physical dimensions didnt have maximum fuel consumption see Kioritz notes did have maximum vibration levels first time ran engine shaking much couldnt get screwdriver otherwise easily accessible mixture screws stop engine make changes low-speed mixture until got things calmed down Once mixture set properly engine warmed up smoothed out nicely Ropers vibration relatively high especially idle does detract significantly engines usefulness struck size-to-displacement ratio engine requires very little space Quadra large flywheel close behind prop does mean need fairly flat-faced cowl longer prop adapter would simplify getting engine tapering cowl carb has external pressure pick-up can rotated 180 degrees places mixture adjustments face forward would accessible cowled engine though could accessed engine running completes Part report Unfortun 102 Model Aviation .yASINII AIRSCIU lIT PRESENTS BALSA STRIPPER PRECISION STRIP WOOD TO x INS FROM BALSA SHEET ALSO FOR DRAFTING AND PHOTO MATS USES TYPE II BLADE SUPER TOOL T PRICE WINDSOR PROPELLER CO PO BOX 112 WINDSOR CA 95492 Heres equipment need give psur props toe very best balance--balance directions Carefully crafted top grade materials BUBBLE BALArtJCER accomodates 3/161/49/32 prop holes Other sizes available special order Dealers oivited $1495 Add $150 HOWARD B HUEBL DEPT 055 postage handling ft Mien add 4% sales tax No CD0s Boo 193 Route 4 Mankato Mn 56931 Big Bangers/Beckman Continued page 28
