Optimizing Prop Performance

I Optimizing Prop Pedormance Photos Author nrsohk necion Jill Ann Cavanaugh thought reached zenith performance souped-up Goldberg Electra sailplane designed new T tail airplane kept punching holes horizonal stabilizer breaking fuselage time landed tall grass improved thrust output kit stock motor 70 percent converting model direct-drive eight-inch prop gear drive 12-inch folding propeller folding prop installed readily available local hobby storea Master Airscrew model propeller durable relatively inexpensive greatly increased thrust available stock motor seven-cell battery 13 ounces direct drive 22 ounces Astrolight 035 gear box flew configuration several years enjoying increased thrust available found difference performance between direct-drive eight-inch gear-driven 12-inch prop exciting no longer launch Electra dead run Equipped gear box Master Airscrew 12 x 8 prop model climbed authority high field elevation 4740 feet flights days dead air still pretty short about four minutes new gear drive drew about 20 amperes U Don Brooks seven-cell batteryabout same running direct drive wondered could maintain high thrust increase full-power time-of-flight selecting different propeller thought process different prop less drag design smaller pitch might allow motor run faster efficiently drawing less current three propellers thought should compared 12 x 8 Master Airscrew prop using 12 x 7 Sonic-Tronics prop 12 x 7 Aero-naut Freudenthaler prop set about test objective way optimize performance entire system motor gear box propeller used method chapter ten Prop Talk Understanding Optimizing Propeller Peiformance Model Electric Aircraft called simultaneous measurements thrust current determine system efficiency factor used thrust calculator included book usable elevation sea level 7000 feet along tachometer determine thrust test runs measured current Astrolight inline volt/ammeter idea same thrust maintained highest ratio thrust current System Efficiency Factor SEF represents efficient combination prop drive system sport-type flying get thrust same current value can climb faster get same thrust reduced value current can fly longer higher thrust divided current better performance under criterion little tinkering workshop made objective choice props based available thrust current drain comparison have included thrust data current information operation direct drive 8 x 4 propeller April 1998 51 Authors Goldberg Electra reconfigured use T-tail geared drive embedded nose gear efficient folding Aero-naut prop Embedded nose gear Aero-naut prop improve Electras airframe streamlining drive system efficiency U workshop data appeared Aero-naut propeller best matched other system drive components optimized thrust efficient operation current draw operation 12 x 7 Aero-naut prop 40% less required 12 x 8 Master Airscrew represented potential increase full-power time-of-flight maintaining same thrust 22 ounces workshop test data shown Table 1 Ct column Table 1 shows static thrust coefficient propeller Coefficients reprinted appear Field Thrust Calculator Appendix C Prop Talk Consider SEF setups shown Table 1 direct drive SEF about 07 geared drive 12inch props best SEF twice 15 three 12-inch-diameter props produced about 22 ounces thrust Aero-naut 12 x 7 providing best match maximize system efficiency prop motor drew r current required Master Airscrew 12 x 8 prop Part extra power required 12 x 8 because its increased pitch Unfortunately unable match pitch commercially available propellers Regardless data Table 1 three 12-inch-diameter propellers shows example potential gain flight time case same amount thrust less current therefore longer flying time specific rpm thrust numbers will different other elevations However relative propeller performance motor gearbox drive system will same So much workshop bench tests longer flight times actually possible confirm bench results made four flights three propellers using same airplane same two seven-cell 1500 mAh batteries used twice propeller same motor gearbox test weight ready fly about 62 ounces used Astrolight peak charger ensure peak performance batteries flight flights made same flight profile 1 Climb 100 feet above ground full power 2 fly large ovals 100 feet full power until gearbox starts chatter thepp rapidly decreasing power end battery discharge 3 shut off power glide safe landing glide portion flight about 30Gush white7 seconds timeTornado 8 x 4 two sets six flightsstock prop air temperatures set relatively constant 700 620 Fahrenheit respectively onlyMaster racrew variables propeller my12 x 8 folder7 flying ability averaged flight time theAero-naut four flights propeller full12 x 7 folder7 power time-of-flight results Sonic-Tmnics propeller average flight times12 x 7 folder7 arc listed Table 2 Aero-naut propeller does indeed give best full-power endurance under test conditions described sailplane motor gearbox combination Other combinations motor gear box may give different results motor torque curve different torque characteristics motor will affect efficient rpm operation motor Ah longer flights always better Having seen possible gains performance difficult soup-up Electra much does cost job answers relatively simple modification less $65 have outlined three possible options associated costs below Option 1 Astro Flight 035 gear box Stk No 701 $3795 Aero-naut Freudenthaler 12 x 7 Folding Prop Hobby Lobby Part No HLAN3 148 $1520 Aero-naut Freudenthaler Middlepart Yoke42 mm Hobby Lobby Part No HLAN4222 $1080 Total Option 1 $6315 Option 2 Astrolight 035 gear box Stk No 701 $3795 Sonic-Tronics 12 x 7 Folding Prop Sonic-Tronics Stk No 182 $1595 Total essentials Option 2 $5390 Option 3 Master Airscrew Electric Flight Pack 251 $4295 includes Master Airscrew 12 x 8 Folding Prop Total essentials Option 3 $4295 Other materials needed Electra upgrade direct drive Option 1 piece 3A6 plywood about 1 1/ inches diameter make adapter plate Astrolight gear box two about 1/2-inch motor mounting bolts mount gearbox adapter plate motor Keep stock motor excellent motor use gear box Additional suggestions Replace electrical connector plugs Sermos connectors Ever feel stock connector plugs after motor run get hot heat could have used thrust instead waste heat good solid connection going get geared Electrics will need purchase pinion puller able change gears different gear ratios choose Option 1 purchase spinner Aero-naut prop Hobby Lobby Sermos Connectors $440 Hobby Lobby Stk No SEROOl two pair replace original battery connectors Pinion Puller 1895 Model Electronics Corporation Aero-naut Freudenthaler Spinner 40 mm $ 470 Hobby Lobby Part No HLAN5 140 selected Option 1 option yields highest overall system efficiency could choose less costly option would still give Electra almost twice thrust have direct drive Choose option soup-up Electra enjoy 4ARPI 900 Bower Dr Idaho Falls ID 83404 Astro Flight Inc 13311 Beach Ave Marina del Ray CA 90292 Hobby Lobby 5614 Franklin Pike Circle Brentwood TN 37027 Model Electronics Corporation 14550 20th Ave NE Seattle WA 98155 Windsor Propeller Co 4319 Monier Circle Rancho Cordova CA 95742 Sonic-Tronics Inc 7865 Mill Rd Elkins Park PA 19027 52 Model Aviation e 1 Battery Ct RPM ThrustCurrent SEF CeUsOunces Amperes Direct Dnve 0074 950013187069 Stock Kit Motor Equipped Astro Flight 0352381 Gearbox 0125430022200113 0085530022144153 0089520022157140 Table 2 PropellerFlight Times seconds Avg Time seconds Aero-naut 12 x 7355 345 340 348347 Sonic-Tronics 12x7315 312 325 310316 MasterAirscrewl2x8 235245265245248