Every Electric modeler knows its important keep light offset weight heavy motor-andbattery combination better fundamental rule might Maximize thrustto-weight ratio rule still calls keeping things light ft also emphasizes thrust side equation going tolerate hea vier power train least can ask ft deliver much thrust possible techniques materials can used keep things lighta lot modelers have developed use fine art select power-train components maximize thrust Its easy task Most catalogs sales brochures woefully short accurate specifications ratings left buy-it-and-try method tempered judgment experience static-thrust tests can help provide better idea airplanes potential performance before build fly Static-thrust tests also reduce number cut-and-try tests field Static tests can run shopday night weather prevents flying test stand described inexpensive easy build Its probably new approachthe principle simple must have used before test stand shown photo Figure 1 nothing pendulum thats deflected its vertical rest position thrust vector Using values weight carrier platform angle deflection simple trigonometric relationship yields thrust value test rig photo consists 2 x 4 carrier platform suspended 2 x 4 support arm four aluminum-strap hangers carrier platform swings aluminum straps like pendulum protractor measures platform deflection angle typical thrust test using rig shown photo actual test setup using 035 motor 7 x 4 prop six-cell 1500 mAh battery rig photo includes some additional instrumentationit provides data motor voltage current well prop speed 1 Weigh pendulum platform motor battery receiver other equipment place weight hanger brackets can ignored long its less 2-3% total weight brackets heavier want precise add P2 total hanger weight carrier platform weight Dont forget include bolts shafts connect platform hangers total weight rig photo 3575 ounces 2 Run motor full thrust whatever level desire note deflection angle protractor example shown photo angle 250 THRUST L WG platform wi motor other p 52 Model Aviation n motor aII thrust note teflection angle icated prot U aQAL 35-75 1680 oz FULL THRUST Now ath multiply penduIuIW4VUElIf tangenalue October 1995 53 A. I~ 0 TOTAL WFIII-IT FORM HANGER LINK WGT Photo author Graphic nur run A2IY / 350 4O 450 3 Use calculator handles trig functions math handbook table curve shown Figure 2 find tangent deflection angle 250 deflection shown photo tangent 047 4 Multiply total pendulum weight tangent value photo example equation would 3575 oz x 047 oz full thrust generally accepted thrust-to-grossweight ratio 13 shows thrust adequate trainer weighing 45-50 ounces 13 ratio used conventional designs re contemplating Electric glider 14 ratio 60-ounce gross weight will probably fine high-performance airframe ratio will have lowered 125 12 Knowing static thrust gives feel capability power train can also adjust parameters before build model instance what will happen propeller _____ pitch size changed battery size adequate much thrust lost speed-controller voltage drop Will heavier-gauge power wiring add thrust other questions can worked out shop allowing finetune maximum thrust Also theres no need push secondary variables such rpm amps ohms through questionable calculations answers come out thrust can run entire simulated flight applying full throttle 30-45 seconds simulate takeoff climbout cutting back 1/3 1i2 thrust see long battery lasts Running tests helps develop feel power train helps youre building modelit makes better fit between airframe power-train components course static-thrust tests have limitations Thrust values will valid zero very low speed propeller thats churning still air efficient screwing itself through air equilibrium speed will require factoring-in judgement interpret some test results However results will conservative side part due lower prop efficiency during static testing may have some pleasant surprises finished model flies test stand can scaled up down easily fit larger smaller power systems Building stand fairly straightforward have few hints might helpful Keep pendulum geometry close squarethe length hangers should approximately equal distance between hangers suspension points hanger suspension should swing freely thrust plane binding moving sideways minimize back-thrust prop stream keep frontal area stand behind prop small possible Use thin material hangers same reason Ideally total carrier weight should approximately two three times anticipated thrust keeps pendulums swing within convenient 2530O range odel Aviation 4I p Ekv ouu Gear * Complete tiardwure Pok Send $1 catalog outside USA $2 ____ 4ff WaW41% 4 A/C MoeI~ 4251 LMieran Church Technical ormqt1on Wing Span Length &l*aq Wlrrg Orea S igIb Flying Wght 9 to lA 2 StrOke 12 to 1 Stroke
Edition: Model Aviation - 1995/10
Page Numbers: 52, 53, 54
Every Electric modeler knows its important keep light offset weight heavy motor-andbattery combination better fundamental rule might Maximize thrustto-weight ratio rule still calls keeping things light ft also emphasizes thrust side equation going tolerate hea vier power train least can ask ft deliver much thrust possible techniques materials can used keep things lighta lot modelers have developed use fine art select power-train components maximize thrust Its easy task Most catalogs sales brochures woefully short accurate specifications ratings left buy-it-and-try method tempered judgment experience static-thrust tests can help provide better idea airplanes potential performance before build fly Static-thrust tests also reduce number cut-and-try tests field Static tests can run shopday night weather prevents flying test stand described inexpensive easy build Its probably new approachthe principle simple must have used before test stand shown photo Figure 1 nothing pendulum thats deflected its vertical rest position thrust vector Using values weight carrier platform angle deflection simple trigonometric relationship yields thrust value test rig photo consists 2 x 4 carrier platform suspended 2 x 4 support arm four aluminum-strap hangers carrier platform swings aluminum straps like pendulum protractor measures platform deflection angle typical thrust test using rig shown photo actual test setup using 035 motor 7 x 4 prop six-cell 1500 mAh battery rig photo includes some additional instrumentationit provides data motor voltage current well prop speed 1 Weigh pendulum platform motor battery receiver other equipment place weight hanger brackets can ignored long its less 2-3% total weight brackets heavier want precise add P2 total hanger weight carrier platform weight Dont forget include bolts shafts connect platform hangers total weight rig photo 3575 ounces 2 Run motor full thrust whatever level desire note deflection angle protractor example shown photo angle 250 THRUST L WG platform wi motor other p 52 Model Aviation n motor aII thrust note teflection angle icated prot U aQAL 35-75 1680 oz FULL THRUST Now ath multiply penduIuIW4VUElIf tangenalue October 1995 53 A. I~ 0 TOTAL WFIII-IT FORM HANGER LINK WGT Photo author Graphic nur run A2IY / 350 4O 450 3 Use calculator handles trig functions math handbook table curve shown Figure 2 find tangent deflection angle 250 deflection shown photo tangent 047 4 Multiply total pendulum weight tangent value photo example equation would 3575 oz x 047 oz full thrust generally accepted thrust-to-grossweight ratio 13 shows thrust adequate trainer weighing 45-50 ounces 13 ratio used conventional designs re contemplating Electric glider 14 ratio 60-ounce gross weight will probably fine high-performance airframe ratio will have lowered 125 12 Knowing static thrust gives feel capability power train can also adjust parameters before build model instance what will happen propeller _____ pitch size changed battery size adequate much thrust lost speed-controller voltage drop Will heavier-gauge power wiring add thrust other questions can worked out shop allowing finetune maximum thrust Also theres no need push secondary variables such rpm amps ohms through questionable calculations answers come out thrust can run entire simulated flight applying full throttle 30-45 seconds simulate takeoff climbout cutting back 1/3 1i2 thrust see long battery lasts Running tests helps develop feel power train helps youre building modelit makes better fit between airframe power-train components course static-thrust tests have limitations Thrust values will valid zero very low speed propeller thats churning still air efficient screwing itself through air equilibrium speed will require factoring-in judgement interpret some test results However results will conservative side part due lower prop efficiency during static testing may have some pleasant surprises finished model flies test stand can scaled up down easily fit larger smaller power systems Building stand fairly straightforward have few hints might helpful Keep pendulum geometry close squarethe length hangers should approximately equal distance between hangers suspension points hanger suspension should swing freely thrust plane binding moving sideways minimize back-thrust prop stream keep frontal area stand behind prop small possible Use thin material hangers same reason Ideally total carrier weight should approximately two three times anticipated thrust keeps pendulums swing within convenient 2530O range odel Aviation 4I p Ekv ouu Gear * Complete tiardwure Pok Send $1 catalog outside USA $2 ____ 4ff WaW41% 4 A/C MoeI~ 4251 LMieran Church Technical ormqt1on Wing Span Length &l*aq Wlrrg Orea S igIb Flying Wght 9 to lA 2 StrOke 12 to 1 Stroke
Edition: Model Aviation - 1995/10
Page Numbers: 52, 53, 54
Every Electric modeler knows its important keep light offset weight heavy motor-andbattery combination better fundamental rule might Maximize thrustto-weight ratio rule still calls keeping things light ft also emphasizes thrust side equation going tolerate hea vier power train least can ask ft deliver much thrust possible techniques materials can used keep things lighta lot modelers have developed use fine art select power-train components maximize thrust Its easy task Most catalogs sales brochures woefully short accurate specifications ratings left buy-it-and-try method tempered judgment experience static-thrust tests can help provide better idea airplanes potential performance before build fly Static-thrust tests also reduce number cut-and-try tests field Static tests can run shopday night weather prevents flying test stand described inexpensive easy build Its probably new approachthe principle simple must have used before test stand shown photo Figure 1 nothing pendulum thats deflected its vertical rest position thrust vector Using values weight carrier platform angle deflection simple trigonometric relationship yields thrust value test rig photo consists 2 x 4 carrier platform suspended 2 x 4 support arm four aluminum-strap hangers carrier platform swings aluminum straps like pendulum protractor measures platform deflection angle typical thrust test using rig shown photo actual test setup using 035 motor 7 x 4 prop six-cell 1500 mAh battery rig photo includes some additional instrumentationit provides data motor voltage current well prop speed 1 Weigh pendulum platform motor battery receiver other equipment place weight hanger brackets can ignored long its less 2-3% total weight brackets heavier want precise add P2 total hanger weight carrier platform weight Dont forget include bolts shafts connect platform hangers total weight rig photo 3575 ounces 2 Run motor full thrust whatever level desire note deflection angle protractor example shown photo angle 250 THRUST L WG platform wi motor other p 52 Model Aviation n motor aII thrust note teflection angle icated prot U aQAL 35-75 1680 oz FULL THRUST Now ath multiply penduIuIW4VUElIf tangenalue October 1995 53 A. I~ 0 TOTAL WFIII-IT FORM HANGER LINK WGT Photo author Graphic nur run A2IY / 350 4O 450 3 Use calculator handles trig functions math handbook table curve shown Figure 2 find tangent deflection angle 250 deflection shown photo tangent 047 4 Multiply total pendulum weight tangent value photo example equation would 3575 oz x 047 oz full thrust generally accepted thrust-to-grossweight ratio 13 shows thrust adequate trainer weighing 45-50 ounces 13 ratio used conventional designs re contemplating Electric glider 14 ratio 60-ounce gross weight will probably fine high-performance airframe ratio will have lowered 125 12 Knowing static thrust gives feel capability power train can also adjust parameters before build model instance what will happen propeller _____ pitch size changed battery size adequate much thrust lost speed-controller voltage drop Will heavier-gauge power wiring add thrust other questions can worked out shop allowing finetune maximum thrust Also theres no need push secondary variables such rpm amps ohms through questionable calculations answers come out thrust can run entire simulated flight applying full throttle 30-45 seconds simulate takeoff climbout cutting back 1/3 1i2 thrust see long battery lasts Running tests helps develop feel power train helps youre building modelit makes better fit between airframe power-train components course static-thrust tests have limitations Thrust values will valid zero very low speed propeller thats churning still air efficient screwing itself through air equilibrium speed will require factoring-in judgement interpret some test results However results will conservative side part due lower prop efficiency during static testing may have some pleasant surprises finished model flies test stand can scaled up down easily fit larger smaller power systems Building stand fairly straightforward have few hints might helpful Keep pendulum geometry close squarethe length hangers should approximately equal distance between hangers suspension points hanger suspension should swing freely thrust plane binding moving sideways minimize back-thrust prop stream keep frontal area stand behind prop small possible Use thin material hangers same reason Ideally total carrier weight should approximately two three times anticipated thrust keeps pendulums swing within convenient 2530O range odel Aviation 4I p Ekv ouu Gear * Complete tiardwure Pok Send $1 catalog outside USA $2 ____ 4ff WaW41% 4 A/C MoeI~ 4251 LMieran Church Technical ormqt1on Wing Span Length &l*aq Wlrrg Orea S igIb Flying Wght 9 to lA 2 StrOke 12 to 1 Stroke