FREE FLIGHT SPORT SCALE U AT LAST YEARS FAC Flying Aces Club Nats made observation watching beautifully crafted Scale models fly overhead Although almost rubber-powered model flying rails flying much faster should have attributable too much power prop pulling model through sky Most FACers build light side rather too heavy couldnt models overpowered Most models saw flying too fast propelled plastic props am badmouth plastic props obvious reason using save time having carve break very easily generally speaking plastic props have enough pitch therefore spin faster necessary Most have probably seen pure Indoor models covered film lightness props use built up covered film props make revolution model moves forward substantial amount delicate models can stay up nearly hour time Wouldnt nice able get Scale models flying longer time aid thermal Most top competitors FAC Nats use carved prop cottage cheese variety blade area pitch can altered fairly easily essence article Fulton Hungerford very astute almost phase modeling time always winners box some unusual Scale model put forth article props can consider parameters involved next project Most have read articles dealing propellers have actually put information practice Competitive Free Flighters fly Wakefield Mulvihill models know great deal about propellers about average Rubber Scale modeler Too often much easier use plastic prop comes kit carve laminate model have just completed Yet order competitive propeller important considerations does start What size block should used What size block gives what pitch Take look Figure 1 Assume wanted carve prop 1 x 11/2 x 10 block wood carved conventional manner shown sketches referring Table 1 would get 340 pitch center blade Now complete revolution prop center blade would describe helix diameter L/2 assuming zero slippage formula pitch P x L12 x tangent pitch angle case 314 x 5 x 67 inches Therefore finished prop would have diameter 10 inches pitch l0/2 inches Okay know what thinking world want mess around math stuff Just hang will see numbers will make some sense isnt tough appears Besides can expound info friends he/she will think genius propeller blade derives its thrust exactly same formula wing derives its lift However fastest-moving part propeller tip center blade traveling about half speed 5-inch North Pacific plastic propeller will unwind 1000 turns -inch rubber loop about 40 seconds fact assumption Assume propeller rpm decreases steady rate turning say 3000 rpm moment release reaching 0 rpm 40 seconds average would 1500 rpm Assume also North Pacific prop has 300 pitch midblade position maximum attainable airplane speed zero drag slippage would 3000 x L12 x x Tan 300 t/sec 14mph Prop Tip Speed equation propeller tip speed follows rpmxitxLx 1mm x 1 cos pitch angle 60 secimin 12 inift 5-inch North Pacific prop would have maximum tip speed 3000 x [1727/866] x [1 min/60 sec] x [1/12 in/ft] t/sec Fulton compiled data doing static tests shop flight testing propellers used North Pacific props some Fulton s own handcarved props up six inches diameter equation propeller tip speed slightly different larger props such used Wakefield models Larger props efficient slippage major factor model actually gets up flying speed matter two seconds usually launched speed greater normal flying 132 Model Aviation 60 80 ft/sec ZIZIli 30 40 ft/sec 20 ft/sec 450Fig 2 speed During its powered flight Wakefield very close its flying speed will good assumption take average rpm get flying speed Wakefield prop 24 inches diameter 24 inches pitch unwinds 400 turns approximately 40 seconds translates average 600 rpm 10 rps models flying speed would 10 rps x 24-inch pitch t/sec equation propeller tip speed large props follows rpm Dia x it2 h2 60 secimin x 12 inift case average 659 ftisec course higher torque fully wound rubber motor would yield greater tip speed immediately after launch doubt would double average Maximum tip speed probably 80 90 ftisec Propeller Blade Airfoils above calculations guesses appears rubberpowered models travel nearly 20 ftIsec propeller tip speeds order 60 80 ftisec effective speeds tips should undercambered much middle blade can undercambered some trailing edge near hub prop does need undercamber see Fig 2 appears area close hub very inefficient required strength case folding props area reinforced metal wire etc best shape appears sharp-edged symmetrical airfoil does create drag IIKY ABC D Blade shape must have something performance Refer Fig 4 similar hand-carved balsa props really very good all-around prop shape B intended like pistonpowered full-scale airplanes Tip speeds higher possible rubber power Very efficient high speeds Fulton believes slippage causes unwind too fast models Never much luck props C contradiction uses Very similar shape turboprop propellers speed approaches supersonic velocity yet same shape commercial plastic props small rubber models North Pacific prop blades similar shape Tip speeds probably around 80 ft/sec D common shape rubber-power yet Fulton has better performance shapes C E scimitar blade George Perryman well-known competitive Rubber flier hard beat uses has probably won anyone Perrymans reason scimitar blade increase area tip F should studied too Perryman right G would inferior E F has pleasing shape area lists toward center blade Summary Using tables knowing what pitch prop diameter desire can select rectangular cross-section area need achieve proper pitch Example A 1 x 1 /2-inch block wood \ EFG Fig 3 will give 340 350 pitch regardless length prop pitch angle 350 midblade position will give 10-inch prop 10/2 inches pitch length other 10 inches simply multiply pitch factor last column Table II get inches pitch x 1 /2-inch block balsa too big six-inch prop six-inch diameter six-inch pitch prop wanted go Table II select pitch factor 100 Since lines up 1 x Is/s multiply dimension 610 get 5/ x 1 inch carving Fulton believes full-scale airplanes measure pitch angle hub tip used halfway hub tip Table gives Degrees Pitch vs Block Cross-Section midpoint blade carving blade shapes through D G Table okay watch out forE F instance wide-tip blade Lay blank out like Fig 4 Now suppose wanted 10-inch prop 10 inches pitch would need block 1 x 3 inches just exactly twice wide block 10 x 10 prop shape like C Maybe C popular Check charts carefully pick out what need next project Use plastic prop first switch over hand-carved beauty Ill bet will very happy effort chance review new video Harding Aero Productions Rubber Power Scale Construction Techniques 4782 Unity Line Rd New Waterford OH 44445 principally geared neophyte Rubber Scale lot good information just getting started would very useful teacher might have school model club cost $1995 plus $3 shipping handling Ohio residents need add $120 sales tax E TW Pitch Angle Mid-Blade Prop Blank Dim 1145lxi 110444lxl/6 110743lxl/I6 111142lxl/s 1115411x1/s 1119401x13/s 112339lxlA 1128381x1 1133371 x 1138361x13/s TABLE II TWLPitch inches Pitch Factor P/L 111015157 Il/s 1014140 I1 1012/2125 Ili/s 10l1/2115 1l/2 10l0/2110 Il/ 1010100 11 10990 September 1999 133 T Fig 4
Edition: Model Aviation - 1999/09
Page Numbers: 132, 133
Edition: Model Aviation - 1999/09
Page Numbers: 132, 133
FREE FLIGHT SPORT SCALE U AT LAST YEARS FAC Flying Aces Club Nats made observation watching beautifully crafted Scale models fly overhead Although almost rubber-powered model flying rails flying much faster should have attributable too much power prop pulling model through sky Most FACers build light side rather too heavy couldnt models overpowered Most models saw flying too fast propelled plastic props am badmouth plastic props obvious reason using save time having carve break very easily generally speaking plastic props have enough pitch therefore spin faster necessary Most have probably seen pure Indoor models covered film lightness props use built up covered film props make revolution model moves forward substantial amount delicate models can stay up nearly hour time Wouldnt nice able get Scale models flying longer time aid thermal Most top competitors FAC Nats use carved prop cottage cheese variety blade area pitch can altered fairly easily essence article Fulton Hungerford very astute almost phase modeling time always winners box some unusual Scale model put forth article props can consider parameters involved next project Most have read articles dealing propellers have actually put information practice Competitive Free Flighters fly Wakefield Mulvihill models know great deal about propellers about average Rubber Scale modeler Too often much easier use plastic prop comes kit carve laminate model have just completed Yet order competitive propeller important considerations does start What size block should used What size block gives what pitch Take look Figure 1 Assume wanted carve prop 1 x 11/2 x 10 block wood carved conventional manner shown sketches referring Table 1 would get 340 pitch center blade Now complete revolution prop center blade would describe helix diameter L/2 assuming zero slippage formula pitch P x L12 x tangent pitch angle case 314 x 5 x 67 inches Therefore finished prop would have diameter 10 inches pitch l0/2 inches Okay know what thinking world want mess around math stuff Just hang will see numbers will make some sense isnt tough appears Besides can expound info friends he/she will think genius propeller blade derives its thrust exactly same formula wing derives its lift However fastest-moving part propeller tip center blade traveling about half speed 5-inch North Pacific plastic propeller will unwind 1000 turns -inch rubber loop about 40 seconds fact assumption Assume propeller rpm decreases steady rate turning say 3000 rpm moment release reaching 0 rpm 40 seconds average would 1500 rpm Assume also North Pacific prop has 300 pitch midblade position maximum attainable airplane speed zero drag slippage would 3000 x L12 x x Tan 300 t/sec 14mph Prop Tip Speed equation propeller tip speed follows rpmxitxLx 1mm x 1 cos pitch angle 60 secimin 12 inift 5-inch North Pacific prop would have maximum tip speed 3000 x [1727/866] x [1 min/60 sec] x [1/12 in/ft] t/sec Fulton compiled data doing static tests shop flight testing propellers used North Pacific props some Fulton s own handcarved props up six inches diameter equation propeller tip speed slightly different larger props such used Wakefield models Larger props efficient slippage major factor model actually gets up flying speed matter two seconds usually launched speed greater normal flying 132 Model Aviation 60 80 ft/sec ZIZIli 30 40 ft/sec 20 ft/sec 450Fig 2 speed During its powered flight Wakefield very close its flying speed will good assumption take average rpm get flying speed Wakefield prop 24 inches diameter 24 inches pitch unwinds 400 turns approximately 40 seconds translates average 600 rpm 10 rps models flying speed would 10 rps x 24-inch pitch t/sec equation propeller tip speed large props follows rpm Dia x it2 h2 60 secimin x 12 inift case average 659 ftisec course higher torque fully wound rubber motor would yield greater tip speed immediately after launch doubt would double average Maximum tip speed probably 80 90 ftisec Propeller Blade Airfoils above calculations guesses appears rubberpowered models travel nearly 20 ftIsec propeller tip speeds order 60 80 ftisec effective speeds tips should undercambered much middle blade can undercambered some trailing edge near hub prop does need undercamber see Fig 2 appears area close hub very inefficient required strength case folding props area reinforced metal wire etc best shape appears sharp-edged symmetrical airfoil does create drag IIKY ABC D Blade shape must have something performance Refer Fig 4 similar hand-carved balsa props really very good all-around prop shape B intended like pistonpowered full-scale airplanes Tip speeds higher possible rubber power Very efficient high speeds Fulton believes slippage causes unwind too fast models Never much luck props C contradiction uses Very similar shape turboprop propellers speed approaches supersonic velocity yet same shape commercial plastic props small rubber models North Pacific prop blades similar shape Tip speeds probably around 80 ft/sec D common shape rubber-power yet Fulton has better performance shapes C E scimitar blade George Perryman well-known competitive Rubber flier hard beat uses has probably won anyone Perrymans reason scimitar blade increase area tip F should studied too Perryman right G would inferior E F has pleasing shape area lists toward center blade Summary Using tables knowing what pitch prop diameter desire can select rectangular cross-section area need achieve proper pitch Example A 1 x 1 /2-inch block wood \ EFG Fig 3 will give 340 350 pitch regardless length prop pitch angle 350 midblade position will give 10-inch prop 10/2 inches pitch length other 10 inches simply multiply pitch factor last column Table II get inches pitch x 1 /2-inch block balsa too big six-inch prop six-inch diameter six-inch pitch prop wanted go Table II select pitch factor 100 Since lines up 1 x Is/s multiply dimension 610 get 5/ x 1 inch carving Fulton believes full-scale airplanes measure pitch angle hub tip used halfway hub tip Table gives Degrees Pitch vs Block Cross-Section midpoint blade carving blade shapes through D G Table okay watch out forE F instance wide-tip blade Lay blank out like Fig 4 Now suppose wanted 10-inch prop 10 inches pitch would need block 1 x 3 inches just exactly twice wide block 10 x 10 prop shape like C Maybe C popular Check charts carefully pick out what need next project Use plastic prop first switch over hand-carved beauty Ill bet will very happy effort chance review new video Harding Aero Productions Rubber Power Scale Construction Techniques 4782 Unity Line Rd New Waterford OH 44445 principally geared neophyte Rubber Scale lot good information just getting started would very useful teacher might have school model club cost $1995 plus $3 shipping handling Ohio residents need add $120 sales tax E TW Pitch Angle Mid-Blade Prop Blank Dim 1145lxi 110444lxl/6 110743lxl/I6 111142lxl/s 1115411x1/s 1119401x13/s 112339lxlA 1128381x1 1133371 x 1138361x13/s TABLE II TWLPitch inches Pitch Factor P/L 111015157 Il/s 1014140 I1 1012/2125 Ili/s 10l1/2115 1l/2 10l0/2110 Il/ 1010100 11 10990 September 1999 133 T Fig 4
