Dr Robert Nagel prepares record reading test aircraft modified Miss Martha manufactured Model Engineering Raleigh NC passes over sound-level meter full throttle fixed flight speeds 90 120 km/hr meter captures peak value overall noise generated aircraft during pass Several types commonly used propellers employed flyover noise tests THE FIRST article series model propeller noise reviewed basic theoretical concepts concerning thrust drag air craft performance continued defi nitions sound frequency sound pressure level sound power level nonlinear manner sound lev els combinea result logarithmic na ture dB scalewas also explained helping reader understand relative contributions various noise sources to tal sound Finally data presented clearly demonstrate typical model aircraft equipped reasonably efficient muffler its propeller rather engine dominates noise sig nature Because specific additive behavior sound components mentioned above article concluded reducing dominant noise sourceie propelleris prop erly viewed critical task model air plane noise abatement noted propeller noise consists several sources components noise due thrust torque thickness effects oth ers Just reduction lesser engine noise may lower total noise re ducing lesser propeller noise component may bring no perceptible dimunition prop noise example eliminating 80 dB thrust noise acoustical power 904 dB total noise power slightly reduces sound level about 90 dB major challenge identify leading contributor model propeller noise Several methods determining domi nant source propeller noise available However approaches self clear-cut easy Conclusions must based several pieces information generally depend upon quality formation available ___wIINOIS second series articles reporting findings AMA-sponsored study propeller noise conducted North Carolina State University first installment explained na ture prop noise present discussion focuses methods determining some types sources prop-generated sound ER Vess D Heathcoat R Nagel 38 Model Aviation er theories carefully worked out over years published scien tific journals demonstrate various types propeller noise related mea surable quantities such thrust propeller tip speed etc propeller noise mea sured exhibits variances consistent theoretical pattern particular type noiseeg thrust torque etcone can identify reasonable confidence pri marily type noise example measurements show prop noise changes rpm thrust flight veloc ity etc fashion consistent pat tern described torque noise can sup pose latter major cause overall prop noise propeller noise sources thrust torque thickness effects etc exhibits characteristic distance noise radiates away propeller noise caused torque loading ex ample will strongest 90 degrees side plane propeller spe cific distance propeller noise caused thrust loads will little magnitude same location Thus care ful measurement directivity patterns noise can produce information about source sound difficulty again lies differentia ting among multiple noise components single out leading mechanism way circumventing problem might operate different propellers such manner thrust torque held con stant thereby eliminating thrust torque loading possible causes variations total noise pattern Such test could help us adduce primary noise source Finally physical differences among propellersin pitch diameter planform etccan affect relative dynamics prop noise Since such variations can exert enough influence alter dominant source noise propeller next should overlooked use ful source information Observed changes prop noise may provisionally related differences physical char acteristics Experimental Setup Two types experimental data used study Carefully controlled labora tory tests anechoic wind tunnel pro duced first set data phase props powered Astro Flight elec tric motors second type data de rived field tests experi mental model aircraft instrumented flown over microphone Anechoic wind tunnel wind tunnel uti lized research consisted openjet test section maximum flow veloc ity approximately 115 ft/sec about 78 mph entrance nozzle area control ling flow test section two feet square diagram general tunnel configuration shown Figure 1 Micro phones located outside flow paral lel wind tunnel centerline used measure noise level different loca tions indication directivity pat tern term anechoic refers use sound-absorbent material simulate free-field acoustic environment air craft flight eliminated distortion caused reflection would otherwise have present prop noise measure ments measurements also cor rected account sound wave propaga tion through flow shear layer streamlined housing supported aerodynamically smooth strut contained motor held propeller test sec tion wind tunnel force transducer mounted motor support structure measure thrust power determined monitoring voltage current motors arrangement permitted pro peller rpm simulated flight speed independently controlled fact higher ranges flight yeunnm locity propeller rpm model aircraft achieve flight cannot repro duced laboratory constituted builtin limitation wind tunnel tests Flight tests modified Miss Martha man ufactured Model Engineering Ra leigh NC used equipped stock OS Max 046 SF side exhaust en gine Isolation mounts utilized min imize airframe noise transmission Two different mufflers tested stock OS Max unit supplied engine Soundmaster muffler made Davis Diesel Development aircraft instrumented sensors allowed propeller rpm flight speed measured ground during flight aircraft flown full throttle fixed flight speeds 90 120 kilome ters per hour approximately 56 75 mph respectively aircraft two meters away microphone sound meter maximum noise level -..wIIuJ JET TURDULEEF NIXINS RESKIN 92m WJJU ENTRAIICE NOZZLE 4 6Gm9Gm12Gm I4 microphone -I Zzzzz 103 m FLOW EXIT MIZZLE T January 1990 39 test aircraft shown airspeed sensor mounted Its left wing tip rpm sensor mounted just behind propeller Also shown telemetry ground receiver alternate Soundmaster muffler used testing engine OS Max 046 SF Figure 1 Top View Anechoic Wind Tunnel OASPL recorded flyover data used both verify ex trapolate findings laboratory Data Base Since variety propellers often used model aircraft pilots several representa tive units selected testing Propel lers chosen being typical use today flight tests re quiring amount torque OS Max 046 SF engine provides See Table 1 list propellers no case does inclusion propeller study imply endorsement exclusion suggest criti cism validity results must care fully extended beyond range data base propellers tested establish general noise characteristics Acoustic data measured wind tunnel angles 45 60 90 120 135 degrees shown microphone locations Fig ure 1 acoustic data base deter mined simulated flight velocity 100 ft/sec 682 mph rpm 10500 Limitations electric motors deter mined criteria Two different Sound Pressure Levels SPLs recorded microphone location propeller level fundamental tone blade-passing fre quency BPF Overall Sound Pres sure Level OASPL between frequen cies 100 Hz 2000 Hz data obtained analysis narrow-band spec tra similar shown Figure 2 greatest peak about 350 Hz cor responds pressure pulse radiated sound time blade passes ie BPF other peaks may generally identified harmonics larger peak occur frequencies 2BPF 3BPF etc level peak yields SPL frequency sum harmonics between 100 2000 Hz gives OASPLthat acoustic noise levelbetween two fre quencies additive level signifi cantly higher peak level repre sented blade-passing frequency other words prop noise pro duced tone BPF first few harmonics will easily understood recalls explained Part 1 point spectrum falls 20 dB below peak level has negligible impact compared peak value Analysis spectrum shows propeller noise reaches crescendo blade-passing frequency problem determine Results link between propeller noise air craft performance discussed con text thrust torque Part 1 components can conveniently related comparing power generated thrust power obtained multiplying thrust flight velocity propel ler efficiency obtained dividing power produced engine thrust power propeller efficiency varies between 0 1 closer value 1 greater amount thrust per horsepower being generated propeller An efficient pro peller will perform thrust work same engine output will ineffi cient latter engine ex penditure will converted thrust work 0 Theory 0 0 0 Torque Noise 020406 Shaft Power HP I 0810 Figure 4- SPL vs Shaft Power Torque-Noise Theory nd Experimental Data 40 Model Aviation 900FundamentalOASPL dB BPF 10500 RPM 2BPF 700 m3BPF 0 -j 0 U 500 Noise 300 400800120016002000 Frequency Hz Figure 2 Acoustic Spectrum Zinger 10 x 6 Prop Microphone 1200 10 Propellers 08x 6 08-0 9x6 6 U C 06 0 U 44Id 04 0 0 000204060810 Advance Ratio J Figure 3 Effect Pitch/Diameter Ratio 10000 rpm 907 85t71 0 V r 800 -J 0 U 00 0 advance ratio denoted symbol J defined ratio flight veloc ity propeller tip speed expressed following equation flight velocity 314 x prop rpm x prop diameter Figure 3 shows typical plot efficien cy varying flight speeds since pro peller rotational speed held constant 10000 rpm Manipulating parameters according formula yields useful information simply examining raw data calculations show representa tive model propellers used study have less 50% efficiencies flight speeds indicates little work being performed engine being used generate thrust thrust noise dominant noise mechanism would dif ficult reduce propeller noise se verely compromising aircraft performance generally low values propeller effi ciency suggest however loading blades due torqueand hence torque noiseis high comparison thrust As indicated Figure 3 fixed rpm about 10000 propeller blades un load flight speed increases Little thrust generated such situation engines work must used torque maintain propeller rotation As general finding propellers higher pitch smaller diameter have creased efficiency high speeds Note example efficiency peak 8 x 6 propeller has higher pitch-todiameter ratio occurs higher flight veloc Continued page 148 January 1990 41 close-up view propeller test rig positioned outside flow entrance noz zle wind tunnel electric motor drives propeller thrust measure ment electronics rpm sensor mounted within streamlined fairing David Heathcoat checks propeller test rig within test section anechoic wind tunnel microphone visible base shaft hanging above Daves head 65- Relation between Sound Power Shaft Pawer Gutins Pormula Torque Noise 4L o 0 0 U 0 o II 000204060810 Shaft Power HP Figure 5 Sound Power vs Shaft Power Theory Experimental Data 06- 25 -20 05 jF C L Lu15U Ii0 _a 04 oJ 0100 U O Prop Efficiency o Sound Power 03-05 89101112 Prop Diameter Figure 6 Prop Efficiency Sound Power Variation Propeller Diameter FULL BODY PILOT KIT DARNED GOOD AIRMEN Lightest pilots available Lifelike vinyl latex rubber cap goggles full templates easy instruc Build Sportsman Barnstormer Full Body Bust V Contains pilot head hands boots helmet lions Easy assemble finish Some simple sewing required Fully BUST PILOT KITpositionable tool Pta Contains pilot head helmet apart cap goggles#206-A sca895 L#205hi jacket Easy assemble finishA scee995 Per-#204- sea1095 #108-1A scaleNEW#203-A scae695 #1061/ scale #l05-/n scale795 scale895* some scale 1495 mpie aew ng equ Gd JET PILOT KIT Pilot has molded jet helmet Contains face mask oxygen hose Extreme ly Realistic Weighs less V2 oz Pea #308-A scale 595 #307-V scale 695 ORDERING INSTRUCTIONS See dealer first order direct Add $100 shipping NYS residents add 7% lax Send check money order CODS OK Send $100 catalog See Dealer add Dollar direct otder handling vice modelers friend Les Shine doing business Bentley Electronics 106 Wedgewood Drive Hauppauge NY 11788 telephone 1800/634-6306 also available through SR Bat teries P-IK fuel Stock # 50A18107 can shipped air $5499 Fuel can purchased cigar counters shipped surface UPS Ask Colibri butane 34 fi oz Stock # 50A18106 $399 Scale Sailplane kit visiting Kotzebue AK tiny village above Arctic Cir cle right Bering Sea 65 miles Si beria made acquaintance Greg Harding doing business Triton Models Box 1157 Kot zebue AK 99752 telephone 1-707/442-2617 Kotzebue just about out-of-the-way place imaginable find model manu facturer time Greg offering nice fiberglass-bodied 4-scale model 1937 DFS Reicher gull-winged sailplane former ly flown Hanna Reicher Hanna Germanys foremost aviatrix es put name history books flew Focke-WuIf twin-rotor helicopter side Olympic Stadium Berlin about 1939 Scale enthusiasts might want give Greg call Time Kotzebue two hours earlier Pa cific Standard Time keep mind call ie 800 am New York 300 am Kotzebue Propeller Noise Continued page 41 ities Although 12 x 6 propeller has higher peak efficiency occurs lower flight speeds Such propeller would ef ficient near takeoff conditions perform poorly high flight speeds Equally impor tant assuming torque loading ma jor cause propeller noise props efficient high speeds will provide re duced noise levels no compromise performance Torque noise Several other findings impli cate torque loading dominant compo nent propeller noise Figure 4 shows plot SPL blade-passing fre quency BPF measured lab about 90 tant rotational speed Also shown curve generated using ac cepted empirical theory torque noise has shown correlate very closely experimental data Since havior SPL shaft power follows expected behavior torque noise can reasonably conjecture measured noise source fact torque noise broader view data obtained examining total acoustic power sound power radiated measurement de rived integration acoustic pres sure over space sound power can compared relation between sound power shaft power classical theory propeller noise developed years ago researcher named Gutin Figure 5 shows comparison 10500 rpm simulated flight speed 100 ft/sec Note agreement tween acoustic power data Gutin theory quite close correlation tween results shown Fig ure 4 view complications associ ated combining sufficient measure ments integrating data obtain acoustic power such consistency between two sets data unexpected Both re sults point torque-related noise leading element propeller sound reader will recall propeller efficiency low work engine must used overcome torque propeller rather produce thrust plot propulsive efficiency against sound power several different props assuming acoustic power derived primarily torque loads lat ter would rise propeller efficiency de clined Due variability thrustrelated noise however such plot would meaningful thrust held constant As shown plot Figure 6 noise due thrust held constant acoustic output varies propeller diameter ac cording propeller efficiency further corroborates dominant noise mechanism sound due torque loading propeller blades thrust-related noise dominant sound power vari ation Figure 6 would nearly con stant point can see constant thrust does lead constant noise Continued page 150 4 Championship Design Outstanding4 Strong & Stable New Combat/Sport4 FastEasyAssembly Plane4 High Performance Includes Complete Hardware ine Included Belicrank outs s 0 Hinges s & Nuts $100 catalog Precision Foam Wing Corescontrol-line combat specialties Dealer & Distributor inquiries Welcome 760 Waltonville Road 1-lummelatown PA 17036 66-3810 148 Model Aviation VINYLWRITE CUSTOM LETFERING Providing elegant time saving economical finishing touch modelers EZ TO APPLY ering comes prespaced prealignedsaving hours cutting fuss aligning individual letters decals text custom computer cut 3M PEEl PROTScTlVE BACKINGPremium cast vinyl l thin olors pe styles includinq Military B[ock high NOW AAILE Stencil Mask & 1 Color Outlining Priced right no minimum charge PSEL OFF THE CARRIER TAPE example AMA numbers i/i high 1 hi h high $125P&H Call write cornplete info U ordm procisied upon rectpack & sample ITS FREE nldpped vii kit cliii m VINYLWEITE CUSTOM LEFIERING 16043 Tulsa Street Granada Hills CA 91344 818363-7131 Nooo 6PM Pacihce Mail order CA res add taz Custom Letter Today VINVLWRITE Way Rather measured noise varies torque loads very good news modelers since main noise mecha nism fact caused torque loading use efficient propellers will lead better performance less noise Its ideal solution next article series will con tinue discussion thrust thickness noise will demonstrated strictly high tip speeds thickness noise makes small contribution total propeller sound output Finally flight test data will shown strongly support inferences drawn laboratory RC Giant Scale/de Vries Continued page 43 electric screwdrivers available reasonable pric es makes logical choices use re chargeable battery-powered electric motors big birds Theyre useful manner aux iliary applications An example F-14 Tomcat being built Chuck Bailey Fremont CA Chuck enlarged set Jim Gupton F-14 drawings 24% aims power ducted-fan model twin Picco 80s Dynamax fans disassembled electric screwdriver provide strong geared source power swing Tomcats wings initial reaction wonder mo tor affected radio reception motor has com mutator brushes could possibly source unacceptable radio noise ac cording Chuck ran exhaustive series radio range checks concluded simple diode across motor leads renders electroni cally silent design rack-and-pinion gear system sweep wings well re duction drive mechanism includes ball bear ing pivots aluminum mounts model thats expected weigh 27 30 lb wet talking true Giant herethe fully extended wingspan healthy 96/2 Applying electric screwdriver motors land ing gear retracts flaps seems gaining fa vor mechanisms complex take bit metalworking expertise Powerful RC race car electric motors being considered prime movers Giants well caution go electric motor route no matter what its original source make darn sure doesnt goof up radio reception dont know somebody didnt think before people Ace RIC Inc did Theyve come up southpaw single-stick RC transmitter Using Olympic V electron ics simply reversed everything came up transmitter specifically designed 15% RC community left-handed youre interested drop em line PO Box 511 Higginsville MO 64037 Sets include Aces 91 receiver standard receiver Ni-Cdsbut no servos allows use positive-pulse high-powered servos sincerely hope readers have Merry Happy RC Aerobatics/Van Putte Continued page 45 serious Pattern competitors flying twocycle engines again end story doubt Both engines have advantages disad vantages four-cycle engines can easily turn larger propellers vertical performance bet ter However also have problems caused higher torque finesse rudder necessary vertical maneuvers two-cycle engine uses fuel costs less fourcycle fuel Propeller cost really factor cause exotic two-cycle propellers cost just much big clubs four-cycle engines turn four-cycle engines bigger heavier difficult shoehorn fuse lage airplane balance changed Cost reli ability maintainability about same early maintenance problems four-cycle engines generally thing past think four-cycle engine will win world championships F3A competition unless Prettner decides curious thing happened t989 RC Aer obatics World Championships report prob ably issue wont go great lengths about it appears international read European judges let Prettner get away new personal style flying Apparently flew very fast airplane about 200 meters out judges rules say 150-175 ters USA s Steve Helms Tony Frack owiak flew fast way out two years ago Continued page 152 150 Model Aviation W ndihoetIa5 1/4 Scale Kits $12995 Epoxy/Glass/Foam Construction Drawings Date Formula 120 Pylon Sport Standoff ScaleKit Price ping Credit cards WelcomedOhio Residents Add 7% STEP BACK & ADMIRE YOUR WORK YOURE DONE responding advertisers mention read about ModelAviation
Edition: Model Aviation - 1990/01
Page Numbers: 38, 39, 40, 41, 148, 150
Dr Robert Nagel prepares record reading test aircraft modified Miss Martha manufactured Model Engineering Raleigh NC passes over sound-level meter full throttle fixed flight speeds 90 120 km/hr meter captures peak value overall noise generated aircraft during pass Several types commonly used propellers employed flyover noise tests THE FIRST article series model propeller noise reviewed basic theoretical concepts concerning thrust drag air craft performance continued defi nitions sound frequency sound pressure level sound power level nonlinear manner sound lev els combinea result logarithmic na ture dB scalewas also explained helping reader understand relative contributions various noise sources to tal sound Finally data presented clearly demonstrate typical model aircraft equipped reasonably efficient muffler its propeller rather engine dominates noise sig nature Because specific additive behavior sound components mentioned above article concluded reducing dominant noise sourceie propelleris prop erly viewed critical task model air plane noise abatement noted propeller noise consists several sources components noise due thrust torque thickness effects oth ers Just reduction lesser engine noise may lower total noise re ducing lesser propeller noise component may bring no perceptible dimunition prop noise example eliminating 80 dB thrust noise acoustical power 904 dB total noise power slightly reduces sound level about 90 dB major challenge identify leading contributor model propeller noise Several methods determining domi nant source propeller noise available However approaches self clear-cut easy Conclusions must based several pieces information generally depend upon quality formation available ___wIINOIS second series articles reporting findings AMA-sponsored study propeller noise conducted North Carolina State University first installment explained na ture prop noise present discussion focuses methods determining some types sources prop-generated sound ER Vess D Heathcoat R Nagel 38 Model Aviation er theories carefully worked out over years published scien tific journals demonstrate various types propeller noise related mea surable quantities such thrust propeller tip speed etc propeller noise mea sured exhibits variances consistent theoretical pattern particular type noiseeg thrust torque etcone can identify reasonable confidence pri marily type noise example measurements show prop noise changes rpm thrust flight veloc ity etc fashion consistent pat tern described torque noise can sup pose latter major cause overall prop noise propeller noise sources thrust torque thickness effects etc exhibits characteristic distance noise radiates away propeller noise caused torque loading ex ample will strongest 90 degrees side plane propeller spe cific distance propeller noise caused thrust loads will little magnitude same location Thus care ful measurement directivity patterns noise can produce information about source sound difficulty again lies differentia ting among multiple noise components single out leading mechanism way circumventing problem might operate different propellers such manner thrust torque held con stant thereby eliminating thrust torque loading possible causes variations total noise pattern Such test could help us adduce primary noise source Finally physical differences among propellersin pitch diameter planform etccan affect relative dynamics prop noise Since such variations can exert enough influence alter dominant source noise propeller next should overlooked use ful source information Observed changes prop noise may provisionally related differences physical char acteristics Experimental Setup Two types experimental data used study Carefully controlled labora tory tests anechoic wind tunnel pro duced first set data phase props powered Astro Flight elec tric motors second type data de rived field tests experi mental model aircraft instrumented flown over microphone Anechoic wind tunnel wind tunnel uti lized research consisted openjet test section maximum flow veloc ity approximately 115 ft/sec about 78 mph entrance nozzle area control ling flow test section two feet square diagram general tunnel configuration shown Figure 1 Micro phones located outside flow paral lel wind tunnel centerline used measure noise level different loca tions indication directivity pat tern term anechoic refers use sound-absorbent material simulate free-field acoustic environment air craft flight eliminated distortion caused reflection would otherwise have present prop noise measure ments measurements also cor rected account sound wave propaga tion through flow shear layer streamlined housing supported aerodynamically smooth strut contained motor held propeller test sec tion wind tunnel force transducer mounted motor support structure measure thrust power determined monitoring voltage current motors arrangement permitted pro peller rpm simulated flight speed independently controlled fact higher ranges flight yeunnm locity propeller rpm model aircraft achieve flight cannot repro duced laboratory constituted builtin limitation wind tunnel tests Flight tests modified Miss Martha man ufactured Model Engineering Ra leigh NC used equipped stock OS Max 046 SF side exhaust en gine Isolation mounts utilized min imize airframe noise transmission Two different mufflers tested stock OS Max unit supplied engine Soundmaster muffler made Davis Diesel Development aircraft instrumented sensors allowed propeller rpm flight speed measured ground during flight aircraft flown full throttle fixed flight speeds 90 120 kilome ters per hour approximately 56 75 mph respectively aircraft two meters away microphone sound meter maximum noise level -..wIIuJ JET TURDULEEF NIXINS RESKIN 92m WJJU ENTRAIICE NOZZLE 4 6Gm9Gm12Gm I4 microphone -I Zzzzz 103 m FLOW EXIT MIZZLE T January 1990 39 test aircraft shown airspeed sensor mounted Its left wing tip rpm sensor mounted just behind propeller Also shown telemetry ground receiver alternate Soundmaster muffler used testing engine OS Max 046 SF Figure 1 Top View Anechoic Wind Tunnel OASPL recorded flyover data used both verify ex trapolate findings laboratory Data Base Since variety propellers often used model aircraft pilots several representa tive units selected testing Propel lers chosen being typical use today flight tests re quiring amount torque OS Max 046 SF engine provides See Table 1 list propellers no case does inclusion propeller study imply endorsement exclusion suggest criti cism validity results must care fully extended beyond range data base propellers tested establish general noise characteristics Acoustic data measured wind tunnel angles 45 60 90 120 135 degrees shown microphone locations Fig ure 1 acoustic data base deter mined simulated flight velocity 100 ft/sec 682 mph rpm 10500 Limitations electric motors deter mined criteria Two different Sound Pressure Levels SPLs recorded microphone location propeller level fundamental tone blade-passing fre quency BPF Overall Sound Pres sure Level OASPL between frequen cies 100 Hz 2000 Hz data obtained analysis narrow-band spec tra similar shown Figure 2 greatest peak about 350 Hz cor responds pressure pulse radiated sound time blade passes ie BPF other peaks may generally identified harmonics larger peak occur frequencies 2BPF 3BPF etc level peak yields SPL frequency sum harmonics between 100 2000 Hz gives OASPLthat acoustic noise levelbetween two fre quencies additive level signifi cantly higher peak level repre sented blade-passing frequency other words prop noise pro duced tone BPF first few harmonics will easily understood recalls explained Part 1 point spectrum falls 20 dB below peak level has negligible impact compared peak value Analysis spectrum shows propeller noise reaches crescendo blade-passing frequency problem determine Results link between propeller noise air craft performance discussed con text thrust torque Part 1 components can conveniently related comparing power generated thrust power obtained multiplying thrust flight velocity propel ler efficiency obtained dividing power produced engine thrust power propeller efficiency varies between 0 1 closer value 1 greater amount thrust per horsepower being generated propeller An efficient pro peller will perform thrust work same engine output will ineffi cient latter engine ex penditure will converted thrust work 0 Theory 0 0 0 Torque Noise 020406 Shaft Power HP I 0810 Figure 4- SPL vs Shaft Power Torque-Noise Theory nd Experimental Data 40 Model Aviation 900FundamentalOASPL dB BPF 10500 RPM 2BPF 700 m3BPF 0 -j 0 U 500 Noise 300 400800120016002000 Frequency Hz Figure 2 Acoustic Spectrum Zinger 10 x 6 Prop Microphone 1200 10 Propellers 08x 6 08-0 9x6 6 U C 06 0 U 44Id 04 0 0 000204060810 Advance Ratio J Figure 3 Effect Pitch/Diameter Ratio 10000 rpm 907 85t71 0 V r 800 -J 0 U 00 0 advance ratio denoted symbol J defined ratio flight veloc ity propeller tip speed expressed following equation flight velocity 314 x prop rpm x prop diameter Figure 3 shows typical plot efficien cy varying flight speeds since pro peller rotational speed held constant 10000 rpm Manipulating parameters according formula yields useful information simply examining raw data calculations show representa tive model propellers used study have less 50% efficiencies flight speeds indicates little work being performed engine being used generate thrust thrust noise dominant noise mechanism would dif ficult reduce propeller noise se verely compromising aircraft performance generally low values propeller effi ciency suggest however loading blades due torqueand hence torque noiseis high comparison thrust As indicated Figure 3 fixed rpm about 10000 propeller blades un load flight speed increases Little thrust generated such situation engines work must used torque maintain propeller rotation As general finding propellers higher pitch smaller diameter have creased efficiency high speeds Note example efficiency peak 8 x 6 propeller has higher pitch-todiameter ratio occurs higher flight veloc Continued page 148 January 1990 41 close-up view propeller test rig positioned outside flow entrance noz zle wind tunnel electric motor drives propeller thrust measure ment electronics rpm sensor mounted within streamlined fairing David Heathcoat checks propeller test rig within test section anechoic wind tunnel microphone visible base shaft hanging above Daves head 65- Relation between Sound Power Shaft Pawer Gutins Pormula Torque Noise 4L o 0 0 U 0 o II 000204060810 Shaft Power HP Figure 5 Sound Power vs Shaft Power Theory Experimental Data 06- 25 -20 05 jF C L Lu15U Ii0 _a 04 oJ 0100 U O Prop Efficiency o Sound Power 03-05 89101112 Prop Diameter Figure 6 Prop Efficiency Sound Power Variation Propeller Diameter FULL BODY PILOT KIT DARNED GOOD AIRMEN Lightest pilots available Lifelike vinyl latex rubber cap goggles full templates easy instruc Build Sportsman Barnstormer Full Body Bust V Contains pilot head hands boots helmet lions Easy assemble finish Some simple sewing required Fully BUST PILOT KITpositionable tool Pta Contains pilot head helmet apart cap goggles#206-A sca895 L#205hi jacket Easy assemble finishA scee995 Per-#204- sea1095 #108-1A scaleNEW#203-A scae695 #1061/ scale #l05-/n scale795 scale895* some scale 1495 mpie aew ng equ Gd JET PILOT KIT Pilot has molded jet helmet Contains face mask oxygen hose Extreme ly Realistic Weighs less V2 oz Pea #308-A scale 595 #307-V scale 695 ORDERING INSTRUCTIONS See dealer first order direct Add $100 shipping NYS residents add 7% lax Send check money order CODS OK Send $100 catalog See Dealer add Dollar direct otder handling vice modelers friend Les Shine doing business Bentley Electronics 106 Wedgewood Drive Hauppauge NY 11788 telephone 1800/634-6306 also available through SR Bat teries P-IK fuel Stock # 50A18107 can shipped air $5499 Fuel can purchased cigar counters shipped surface UPS Ask Colibri butane 34 fi oz Stock # 50A18106 $399 Scale Sailplane kit visiting Kotzebue AK tiny village above Arctic Cir cle right Bering Sea 65 miles Si beria made acquaintance Greg Harding doing business Triton Models Box 1157 Kot zebue AK 99752 telephone 1-707/442-2617 Kotzebue just about out-of-the-way place imaginable find model manu facturer time Greg offering nice fiberglass-bodied 4-scale model 1937 DFS Reicher gull-winged sailplane former ly flown Hanna Reicher Hanna Germanys foremost aviatrix es put name history books flew Focke-WuIf twin-rotor helicopter side Olympic Stadium Berlin about 1939 Scale enthusiasts might want give Greg call Time Kotzebue two hours earlier Pa cific Standard Time keep mind call ie 800 am New York 300 am Kotzebue Propeller Noise Continued page 41 ities Although 12 x 6 propeller has higher peak efficiency occurs lower flight speeds Such propeller would ef ficient near takeoff conditions perform poorly high flight speeds Equally impor tant assuming torque loading ma jor cause propeller noise props efficient high speeds will provide re duced noise levels no compromise performance Torque noise Several other findings impli cate torque loading dominant compo nent propeller noise Figure 4 shows plot SPL blade-passing fre quency BPF measured lab about 90 tant rotational speed Also shown curve generated using ac cepted empirical theory torque noise has shown correlate very closely experimental data Since havior SPL shaft power follows expected behavior torque noise can reasonably conjecture measured noise source fact torque noise broader view data obtained examining total acoustic power sound power radiated measurement de rived integration acoustic pres sure over space sound power can compared relation between sound power shaft power classical theory propeller noise developed years ago researcher named Gutin Figure 5 shows comparison 10500 rpm simulated flight speed 100 ft/sec Note agreement tween acoustic power data Gutin theory quite close correlation tween results shown Fig ure 4 view complications associ ated combining sufficient measure ments integrating data obtain acoustic power such consistency between two sets data unexpected Both re sults point torque-related noise leading element propeller sound reader will recall propeller efficiency low work engine must used overcome torque propeller rather produce thrust plot propulsive efficiency against sound power several different props assuming acoustic power derived primarily torque loads lat ter would rise propeller efficiency de clined Due variability thrustrelated noise however such plot would meaningful thrust held constant As shown plot Figure 6 noise due thrust held constant acoustic output varies propeller diameter ac cording propeller efficiency further corroborates dominant noise mechanism sound due torque loading propeller blades thrust-related noise dominant sound power vari ation Figure 6 would nearly con stant point can see constant thrust does lead constant noise Continued page 150 4 Championship Design Outstanding4 Strong & Stable New Combat/Sport4 FastEasyAssembly Plane4 High Performance Includes Complete Hardware ine Included Belicrank outs s 0 Hinges s & Nuts $100 catalog Precision Foam Wing Corescontrol-line combat specialties Dealer & Distributor inquiries Welcome 760 Waltonville Road 1-lummelatown PA 17036 66-3810 148 Model Aviation VINYLWRITE CUSTOM LETFERING Providing elegant time saving economical finishing touch modelers EZ TO APPLY ering comes prespaced prealignedsaving hours cutting fuss aligning individual letters decals text custom computer cut 3M PEEl PROTScTlVE BACKINGPremium cast vinyl l thin olors pe styles includinq Military B[ock high NOW AAILE Stencil Mask & 1 Color Outlining Priced right no minimum charge PSEL OFF THE CARRIER TAPE example AMA numbers i/i high 1 hi h high $125P&H Call write cornplete info U ordm procisied upon rectpack & sample ITS FREE nldpped vii kit cliii m VINYLWEITE CUSTOM LEFIERING 16043 Tulsa Street Granada Hills CA 91344 818363-7131 Nooo 6PM Pacihce Mail order CA res add taz Custom Letter Today VINVLWRITE Way Rather measured noise varies torque loads very good news modelers since main noise mecha nism fact caused torque loading use efficient propellers will lead better performance less noise Its ideal solution next article series will con tinue discussion thrust thickness noise will demonstrated strictly high tip speeds thickness noise makes small contribution total propeller sound output Finally flight test data will shown strongly support inferences drawn laboratory RC Giant Scale/de Vries Continued page 43 electric screwdrivers available reasonable pric es makes logical choices use re chargeable battery-powered electric motors big birds Theyre useful manner aux iliary applications An example F-14 Tomcat being built Chuck Bailey Fremont CA Chuck enlarged set Jim Gupton F-14 drawings 24% aims power ducted-fan model twin Picco 80s Dynamax fans disassembled electric screwdriver provide strong geared source power swing Tomcats wings initial reaction wonder mo tor affected radio reception motor has com mutator brushes could possibly source unacceptable radio noise ac cording Chuck ran exhaustive series radio range checks concluded simple diode across motor leads renders electroni cally silent design rack-and-pinion gear system sweep wings well re duction drive mechanism includes ball bear ing pivots aluminum mounts model thats expected weigh 27 30 lb wet talking true Giant herethe fully extended wingspan healthy 96/2 Applying electric screwdriver motors land ing gear retracts flaps seems gaining fa vor mechanisms complex take bit metalworking expertise Powerful RC race car electric motors being considered prime movers Giants well caution go electric motor route no matter what its original source make darn sure doesnt goof up radio reception dont know somebody didnt think before people Ace RIC Inc did Theyve come up southpaw single-stick RC transmitter Using Olympic V electron ics simply reversed everything came up transmitter specifically designed 15% RC community left-handed youre interested drop em line PO Box 511 Higginsville MO 64037 Sets include Aces 91 receiver standard receiver Ni-Cdsbut no servos allows use positive-pulse high-powered servos sincerely hope readers have Merry Happy RC Aerobatics/Van Putte Continued page 45 serious Pattern competitors flying twocycle engines again end story doubt Both engines have advantages disad vantages four-cycle engines can easily turn larger propellers vertical performance bet ter However also have problems caused higher torque finesse rudder necessary vertical maneuvers two-cycle engine uses fuel costs less fourcycle fuel Propeller cost really factor cause exotic two-cycle propellers cost just much big clubs four-cycle engines turn four-cycle engines bigger heavier difficult shoehorn fuse lage airplane balance changed Cost reli ability maintainability about same early maintenance problems four-cycle engines generally thing past think four-cycle engine will win world championships F3A competition unless Prettner decides curious thing happened t989 RC Aer obatics World Championships report prob ably issue wont go great lengths about it appears international read European judges let Prettner get away new personal style flying Apparently flew very fast airplane about 200 meters out judges rules say 150-175 ters USA s Steve Helms Tony Frack owiak flew fast way out two years ago Continued page 152 150 Model Aviation W ndihoetIa5 1/4 Scale Kits $12995 Epoxy/Glass/Foam Construction Drawings Date Formula 120 Pylon Sport Standoff ScaleKit Price ping Credit cards WelcomedOhio Residents Add 7% STEP BACK & ADMIRE YOUR WORK YOURE DONE responding advertisers mention read about ModelAviation
Edition: Model Aviation - 1990/01
Page Numbers: 38, 39, 40, 41, 148, 150
Dr Robert Nagel prepares record reading test aircraft modified Miss Martha manufactured Model Engineering Raleigh NC passes over sound-level meter full throttle fixed flight speeds 90 120 km/hr meter captures peak value overall noise generated aircraft during pass Several types commonly used propellers employed flyover noise tests THE FIRST article series model propeller noise reviewed basic theoretical concepts concerning thrust drag air craft performance continued defi nitions sound frequency sound pressure level sound power level nonlinear manner sound lev els combinea result logarithmic na ture dB scalewas also explained helping reader understand relative contributions various noise sources to tal sound Finally data presented clearly demonstrate typical model aircraft equipped reasonably efficient muffler its propeller rather engine dominates noise sig nature Because specific additive behavior sound components mentioned above article concluded reducing dominant noise sourceie propelleris prop erly viewed critical task model air plane noise abatement noted propeller noise consists several sources components noise due thrust torque thickness effects oth ers Just reduction lesser engine noise may lower total noise re ducing lesser propeller noise component may bring no perceptible dimunition prop noise example eliminating 80 dB thrust noise acoustical power 904 dB total noise power slightly reduces sound level about 90 dB major challenge identify leading contributor model propeller noise Several methods determining domi nant source propeller noise available However approaches self clear-cut easy Conclusions must based several pieces information generally depend upon quality formation available ___wIINOIS second series articles reporting findings AMA-sponsored study propeller noise conducted North Carolina State University first installment explained na ture prop noise present discussion focuses methods determining some types sources prop-generated sound ER Vess D Heathcoat R Nagel 38 Model Aviation er theories carefully worked out over years published scien tific journals demonstrate various types propeller noise related mea surable quantities such thrust propeller tip speed etc propeller noise mea sured exhibits variances consistent theoretical pattern particular type noiseeg thrust torque etcone can identify reasonable confidence pri marily type noise example measurements show prop noise changes rpm thrust flight veloc ity etc fashion consistent pat tern described torque noise can sup pose latter major cause overall prop noise propeller noise sources thrust torque thickness effects etc exhibits characteristic distance noise radiates away propeller noise caused torque loading ex ample will strongest 90 degrees side plane propeller spe cific distance propeller noise caused thrust loads will little magnitude same location Thus care ful measurement directivity patterns noise can produce information about source sound difficulty again lies differentia ting among multiple noise components single out leading mechanism way circumventing problem might operate different propellers such manner thrust torque held con stant thereby eliminating thrust torque loading possible causes variations total noise pattern Such test could help us adduce primary noise source Finally physical differences among propellersin pitch diameter planform etccan affect relative dynamics prop noise Since such variations can exert enough influence alter dominant source noise propeller next should overlooked use ful source information Observed changes prop noise may provisionally related differences physical char acteristics Experimental Setup Two types experimental data used study Carefully controlled labora tory tests anechoic wind tunnel pro duced first set data phase props powered Astro Flight elec tric motors second type data de rived field tests experi mental model aircraft instrumented flown over microphone Anechoic wind tunnel wind tunnel uti lized research consisted openjet test section maximum flow veloc ity approximately 115 ft/sec about 78 mph entrance nozzle area control ling flow test section two feet square diagram general tunnel configuration shown Figure 1 Micro phones located outside flow paral lel wind tunnel centerline used measure noise level different loca tions indication directivity pat tern term anechoic refers use sound-absorbent material simulate free-field acoustic environment air craft flight eliminated distortion caused reflection would otherwise have present prop noise measure ments measurements also cor rected account sound wave propaga tion through flow shear layer streamlined housing supported aerodynamically smooth strut contained motor held propeller test sec tion wind tunnel force transducer mounted motor support structure measure thrust power determined monitoring voltage current motors arrangement permitted pro peller rpm simulated flight speed independently controlled fact higher ranges flight yeunnm locity propeller rpm model aircraft achieve flight cannot repro duced laboratory constituted builtin limitation wind tunnel tests Flight tests modified Miss Martha man ufactured Model Engineering Ra leigh NC used equipped stock OS Max 046 SF side exhaust en gine Isolation mounts utilized min imize airframe noise transmission Two different mufflers tested stock OS Max unit supplied engine Soundmaster muffler made Davis Diesel Development aircraft instrumented sensors allowed propeller rpm flight speed measured ground during flight aircraft flown full throttle fixed flight speeds 90 120 kilome ters per hour approximately 56 75 mph respectively aircraft two meters away microphone sound meter maximum noise level -..wIIuJ JET TURDULEEF NIXINS RESKIN 92m WJJU ENTRAIICE NOZZLE 4 6Gm9Gm12Gm I4 microphone -I Zzzzz 103 m FLOW EXIT MIZZLE T January 1990 39 test aircraft shown airspeed sensor mounted Its left wing tip rpm sensor mounted just behind propeller Also shown telemetry ground receiver alternate Soundmaster muffler used testing engine OS Max 046 SF Figure 1 Top View Anechoic Wind Tunnel OASPL recorded flyover data used both verify ex trapolate findings laboratory Data Base Since variety propellers often used model aircraft pilots several representa tive units selected testing Propel lers chosen being typical use today flight tests re quiring amount torque OS Max 046 SF engine provides See Table 1 list propellers no case does inclusion propeller study imply endorsement exclusion suggest criti cism validity results must care fully extended beyond range data base propellers tested establish general noise characteristics Acoustic data measured wind tunnel angles 45 60 90 120 135 degrees shown microphone locations Fig ure 1 acoustic data base deter mined simulated flight velocity 100 ft/sec 682 mph rpm 10500 Limitations electric motors deter mined criteria Two different Sound Pressure Levels SPLs recorded microphone location propeller level fundamental tone blade-passing fre quency BPF Overall Sound Pres sure Level OASPL between frequen cies 100 Hz 2000 Hz data obtained analysis narrow-band spec tra similar shown Figure 2 greatest peak about 350 Hz cor responds pressure pulse radiated sound time blade passes ie BPF other peaks may generally identified harmonics larger peak occur frequencies 2BPF 3BPF etc level peak yields SPL frequency sum harmonics between 100 2000 Hz gives OASPLthat acoustic noise levelbetween two fre quencies additive level signifi cantly higher peak level repre sented blade-passing frequency other words prop noise pro duced tone BPF first few harmonics will easily understood recalls explained Part 1 point spectrum falls 20 dB below peak level has negligible impact compared peak value Analysis spectrum shows propeller noise reaches crescendo blade-passing frequency problem determine Results link between propeller noise air craft performance discussed con text thrust torque Part 1 components can conveniently related comparing power generated thrust power obtained multiplying thrust flight velocity propel ler efficiency obtained dividing power produced engine thrust power propeller efficiency varies between 0 1 closer value 1 greater amount thrust per horsepower being generated propeller An efficient pro peller will perform thrust work same engine output will ineffi cient latter engine ex penditure will converted thrust work 0 Theory 0 0 0 Torque Noise 020406 Shaft Power HP I 0810 Figure 4- SPL vs Shaft Power Torque-Noise Theory nd Experimental Data 40 Model Aviation 900FundamentalOASPL dB BPF 10500 RPM 2BPF 700 m3BPF 0 -j 0 U 500 Noise 300 400800120016002000 Frequency Hz Figure 2 Acoustic Spectrum Zinger 10 x 6 Prop Microphone 1200 10 Propellers 08x 6 08-0 9x6 6 U C 06 0 U 44Id 04 0 0 000204060810 Advance Ratio J Figure 3 Effect Pitch/Diameter Ratio 10000 rpm 907 85t71 0 V r 800 -J 0 U 00 0 advance ratio denoted symbol J defined ratio flight veloc ity propeller tip speed expressed following equation flight velocity 314 x prop rpm x prop diameter Figure 3 shows typical plot efficien cy varying flight speeds since pro peller rotational speed held constant 10000 rpm Manipulating parameters according formula yields useful information simply examining raw data calculations show representa tive model propellers used study have less 50% efficiencies flight speeds indicates little work being performed engine being used generate thrust thrust noise dominant noise mechanism would dif ficult reduce propeller noise se verely compromising aircraft performance generally low values propeller effi ciency suggest however loading blades due torqueand hence torque noiseis high comparison thrust As indicated Figure 3 fixed rpm about 10000 propeller blades un load flight speed increases Little thrust generated such situation engines work must used torque maintain propeller rotation As general finding propellers higher pitch smaller diameter have creased efficiency high speeds Note example efficiency peak 8 x 6 propeller has higher pitch-todiameter ratio occurs higher flight veloc Continued page 148 January 1990 41 close-up view propeller test rig positioned outside flow entrance noz zle wind tunnel electric motor drives propeller thrust measure ment electronics rpm sensor mounted within streamlined fairing David Heathcoat checks propeller test rig within test section anechoic wind tunnel microphone visible base shaft hanging above Daves head 65- Relation between Sound Power Shaft Pawer Gutins Pormula Torque Noise 4L o 0 0 U 0 o II 000204060810 Shaft Power HP Figure 5 Sound Power vs Shaft Power Theory Experimental Data 06- 25 -20 05 jF C L Lu15U Ii0 _a 04 oJ 0100 U O Prop Efficiency o Sound Power 03-05 89101112 Prop Diameter Figure 6 Prop Efficiency Sound Power Variation Propeller Diameter FULL BODY PILOT KIT DARNED GOOD AIRMEN Lightest pilots available Lifelike vinyl latex rubber cap goggles full templates easy instruc Build Sportsman Barnstormer Full Body Bust V Contains pilot head hands boots helmet lions Easy assemble finish Some simple sewing required Fully BUST PILOT KITpositionable tool Pta Contains pilot head helmet apart cap goggles#206-A sca895 L#205hi jacket Easy assemble finishA scee995 Per-#204- sea1095 #108-1A scaleNEW#203-A scae695 #1061/ scale #l05-/n scale795 scale895* some scale 1495 mpie aew ng equ Gd JET PILOT KIT Pilot has molded jet helmet Contains face mask oxygen hose Extreme ly Realistic Weighs less V2 oz Pea #308-A scale 595 #307-V scale 695 ORDERING INSTRUCTIONS See dealer first order direct Add $100 shipping NYS residents add 7% lax Send check money order CODS OK Send $100 catalog See Dealer add Dollar direct otder handling vice modelers friend Les Shine doing business Bentley Electronics 106 Wedgewood Drive Hauppauge NY 11788 telephone 1800/634-6306 also available through SR Bat teries P-IK fuel Stock # 50A18107 can shipped air $5499 Fuel can purchased cigar counters shipped surface UPS Ask Colibri butane 34 fi oz Stock # 50A18106 $399 Scale Sailplane kit visiting Kotzebue AK tiny village above Arctic Cir cle right Bering Sea 65 miles Si beria made acquaintance Greg Harding doing business Triton Models Box 1157 Kot zebue AK 99752 telephone 1-707/442-2617 Kotzebue just about out-of-the-way place imaginable find model manu facturer time Greg offering nice fiberglass-bodied 4-scale model 1937 DFS Reicher gull-winged sailplane former ly flown Hanna Reicher Hanna Germanys foremost aviatrix es put name history books flew Focke-WuIf twin-rotor helicopter side Olympic Stadium Berlin about 1939 Scale enthusiasts might want give Greg call Time Kotzebue two hours earlier Pa cific Standard Time keep mind call ie 800 am New York 300 am Kotzebue Propeller Noise Continued page 41 ities Although 12 x 6 propeller has higher peak efficiency occurs lower flight speeds Such propeller would ef ficient near takeoff conditions perform poorly high flight speeds Equally impor tant assuming torque loading ma jor cause propeller noise props efficient high speeds will provide re duced noise levels no compromise performance Torque noise Several other findings impli cate torque loading dominant compo nent propeller noise Figure 4 shows plot SPL blade-passing fre quency BPF measured lab about 90 tant rotational speed Also shown curve generated using ac cepted empirical theory torque noise has shown correlate very closely experimental data Since havior SPL shaft power follows expected behavior torque noise can reasonably conjecture measured noise source fact torque noise broader view data obtained examining total acoustic power sound power radiated measurement de rived integration acoustic pres sure over space sound power can compared relation between sound power shaft power classical theory propeller noise developed years ago researcher named Gutin Figure 5 shows comparison 10500 rpm simulated flight speed 100 ft/sec Note agreement tween acoustic power data Gutin theory quite close correlation tween results shown Fig ure 4 view complications associ ated combining sufficient measure ments integrating data obtain acoustic power such consistency between two sets data unexpected Both re sults point torque-related noise leading element propeller sound reader will recall propeller efficiency low work engine must used overcome torque propeller rather produce thrust plot propulsive efficiency against sound power several different props assuming acoustic power derived primarily torque loads lat ter would rise propeller efficiency de clined Due variability thrustrelated noise however such plot would meaningful thrust held constant As shown plot Figure 6 noise due thrust held constant acoustic output varies propeller diameter ac cording propeller efficiency further corroborates dominant noise mechanism sound due torque loading propeller blades thrust-related noise dominant sound power vari ation Figure 6 would nearly con stant point can see constant thrust does lead constant noise Continued page 150 4 Championship Design Outstanding4 Strong & Stable New Combat/Sport4 FastEasyAssembly Plane4 High Performance Includes Complete Hardware ine Included Belicrank outs s 0 Hinges s & Nuts $100 catalog Precision Foam Wing Corescontrol-line combat specialties Dealer & Distributor inquiries Welcome 760 Waltonville Road 1-lummelatown PA 17036 66-3810 148 Model Aviation VINYLWRITE CUSTOM LETFERING Providing elegant time saving economical finishing touch modelers EZ TO APPLY ering comes prespaced prealignedsaving hours cutting fuss aligning individual letters decals text custom computer cut 3M PEEl PROTScTlVE BACKINGPremium cast vinyl l thin olors pe styles includinq Military B[ock high NOW AAILE Stencil Mask & 1 Color Outlining Priced right no minimum charge PSEL OFF THE CARRIER TAPE example AMA numbers i/i high 1 hi h high $125P&H Call write cornplete info U ordm procisied upon rectpack & sample ITS FREE nldpped vii kit cliii m VINYLWEITE CUSTOM LEFIERING 16043 Tulsa Street Granada Hills CA 91344 818363-7131 Nooo 6PM Pacihce Mail order CA res add taz Custom Letter Today VINVLWRITE Way Rather measured noise varies torque loads very good news modelers since main noise mecha nism fact caused torque loading use efficient propellers will lead better performance less noise Its ideal solution next article series will con tinue discussion thrust thickness noise will demonstrated strictly high tip speeds thickness noise makes small contribution total propeller sound output Finally flight test data will shown strongly support inferences drawn laboratory RC Giant Scale/de Vries Continued page 43 electric screwdrivers available reasonable pric es makes logical choices use re chargeable battery-powered electric motors big birds Theyre useful manner aux iliary applications An example F-14 Tomcat being built Chuck Bailey Fremont CA Chuck enlarged set Jim Gupton F-14 drawings 24% aims power ducted-fan model twin Picco 80s Dynamax fans disassembled electric screwdriver provide strong geared source power swing Tomcats wings initial reaction wonder mo tor affected radio reception motor has com mutator brushes could possibly source unacceptable radio noise ac cording Chuck ran exhaustive series radio range checks concluded simple diode across motor leads renders electroni cally silent design rack-and-pinion gear system sweep wings well re duction drive mechanism includes ball bear ing pivots aluminum mounts model thats expected weigh 27 30 lb wet talking true Giant herethe fully extended wingspan healthy 96/2 Applying electric screwdriver motors land ing gear retracts flaps seems gaining fa vor mechanisms complex take bit metalworking expertise Powerful RC race car electric motors being considered prime movers Giants well caution go electric motor route no matter what its original source make darn sure doesnt goof up radio reception dont know somebody didnt think before people Ace RIC Inc did Theyve come up southpaw single-stick RC transmitter Using Olympic V electron ics simply reversed everything came up transmitter specifically designed 15% RC community left-handed youre interested drop em line PO Box 511 Higginsville MO 64037 Sets include Aces 91 receiver standard receiver Ni-Cdsbut no servos allows use positive-pulse high-powered servos sincerely hope readers have Merry Happy RC Aerobatics/Van Putte Continued page 45 serious Pattern competitors flying twocycle engines again end story doubt Both engines have advantages disad vantages four-cycle engines can easily turn larger propellers vertical performance bet ter However also have problems caused higher torque finesse rudder necessary vertical maneuvers two-cycle engine uses fuel costs less fourcycle fuel Propeller cost really factor cause exotic two-cycle propellers cost just much big clubs four-cycle engines turn four-cycle engines bigger heavier difficult shoehorn fuse lage airplane balance changed Cost reli ability maintainability about same early maintenance problems four-cycle engines generally thing past think four-cycle engine will win world championships F3A competition unless Prettner decides curious thing happened t989 RC Aer obatics World Championships report prob ably issue wont go great lengths about it appears international read European judges let Prettner get away new personal style flying Apparently flew very fast airplane about 200 meters out judges rules say 150-175 ters USA s Steve Helms Tony Frack owiak flew fast way out two years ago Continued page 152 150 Model Aviation W ndihoetIa5 1/4 Scale Kits $12995 Epoxy/Glass/Foam Construction Drawings Date Formula 120 Pylon Sport Standoff ScaleKit Price ping Credit cards WelcomedOhio Residents Add 7% STEP BACK & ADMIRE YOUR WORK YOURE DONE responding advertisers mention read about ModelAviation
Edition: Model Aviation - 1990/01
Page Numbers: 38, 39, 40, 41, 148, 150
Dr Robert Nagel prepares record reading test aircraft modified Miss Martha manufactured Model Engineering Raleigh NC passes over sound-level meter full throttle fixed flight speeds 90 120 km/hr meter captures peak value overall noise generated aircraft during pass Several types commonly used propellers employed flyover noise tests THE FIRST article series model propeller noise reviewed basic theoretical concepts concerning thrust drag air craft performance continued defi nitions sound frequency sound pressure level sound power level nonlinear manner sound lev els combinea result logarithmic na ture dB scalewas also explained helping reader understand relative contributions various noise sources to tal sound Finally data presented clearly demonstrate typical model aircraft equipped reasonably efficient muffler its propeller rather engine dominates noise sig nature Because specific additive behavior sound components mentioned above article concluded reducing dominant noise sourceie propelleris prop erly viewed critical task model air plane noise abatement noted propeller noise consists several sources components noise due thrust torque thickness effects oth ers Just reduction lesser engine noise may lower total noise re ducing lesser propeller noise component may bring no perceptible dimunition prop noise example eliminating 80 dB thrust noise acoustical power 904 dB total noise power slightly reduces sound level about 90 dB major challenge identify leading contributor model propeller noise Several methods determining domi nant source propeller noise available However approaches self clear-cut easy Conclusions must based several pieces information generally depend upon quality formation available ___wIINOIS second series articles reporting findings AMA-sponsored study propeller noise conducted North Carolina State University first installment explained na ture prop noise present discussion focuses methods determining some types sources prop-generated sound ER Vess D Heathcoat R Nagel 38 Model Aviation er theories carefully worked out over years published scien tific journals demonstrate various types propeller noise related mea surable quantities such thrust propeller tip speed etc propeller noise mea sured exhibits variances consistent theoretical pattern particular type noiseeg thrust torque etcone can identify reasonable confidence pri marily type noise example measurements show prop noise changes rpm thrust flight veloc ity etc fashion consistent pat tern described torque noise can sup pose latter major cause overall prop noise propeller noise sources thrust torque thickness effects etc exhibits characteristic distance noise radiates away propeller noise caused torque loading ex ample will strongest 90 degrees side plane propeller spe cific distance propeller noise caused thrust loads will little magnitude same location Thus care ful measurement directivity patterns noise can produce information about source sound difficulty again lies differentia ting among multiple noise components single out leading mechanism way circumventing problem might operate different propellers such manner thrust torque held con stant thereby eliminating thrust torque loading possible causes variations total noise pattern Such test could help us adduce primary noise source Finally physical differences among propellersin pitch diameter planform etccan affect relative dynamics prop noise Since such variations can exert enough influence alter dominant source noise propeller next should overlooked use ful source information Observed changes prop noise may provisionally related differences physical char acteristics Experimental Setup Two types experimental data used study Carefully controlled labora tory tests anechoic wind tunnel pro duced first set data phase props powered Astro Flight elec tric motors second type data de rived field tests experi mental model aircraft instrumented flown over microphone Anechoic wind tunnel wind tunnel uti lized research consisted openjet test section maximum flow veloc ity approximately 115 ft/sec about 78 mph entrance nozzle area control ling flow test section two feet square diagram general tunnel configuration shown Figure 1 Micro phones located outside flow paral lel wind tunnel centerline used measure noise level different loca tions indication directivity pat tern term anechoic refers use sound-absorbent material simulate free-field acoustic environment air craft flight eliminated distortion caused reflection would otherwise have present prop noise measure ments measurements also cor rected account sound wave propaga tion through flow shear layer streamlined housing supported aerodynamically smooth strut contained motor held propeller test sec tion wind tunnel force transducer mounted motor support structure measure thrust power determined monitoring voltage current motors arrangement permitted pro peller rpm simulated flight speed independently controlled fact higher ranges flight yeunnm locity propeller rpm model aircraft achieve flight cannot repro duced laboratory constituted builtin limitation wind tunnel tests Flight tests modified Miss Martha man ufactured Model Engineering Ra leigh NC used equipped stock OS Max 046 SF side exhaust en gine Isolation mounts utilized min imize airframe noise transmission Two different mufflers tested stock OS Max unit supplied engine Soundmaster muffler made Davis Diesel Development aircraft instrumented sensors allowed propeller rpm flight speed measured ground during flight aircraft flown full throttle fixed flight speeds 90 120 kilome ters per hour approximately 56 75 mph respectively aircraft two meters away microphone sound meter maximum noise level -..wIIuJ JET TURDULEEF NIXINS RESKIN 92m WJJU ENTRAIICE NOZZLE 4 6Gm9Gm12Gm I4 microphone -I Zzzzz 103 m FLOW EXIT MIZZLE T January 1990 39 test aircraft shown airspeed sensor mounted Its left wing tip rpm sensor mounted just behind propeller Also shown telemetry ground receiver alternate Soundmaster muffler used testing engine OS Max 046 SF Figure 1 Top View Anechoic Wind Tunnel OASPL recorded flyover data used both verify ex trapolate findings laboratory Data Base Since variety propellers often used model aircraft pilots several representa tive units selected testing Propel lers chosen being typical use today flight tests re quiring amount torque OS Max 046 SF engine provides See Table 1 list propellers no case does inclusion propeller study imply endorsement exclusion suggest criti cism validity results must care fully extended beyond range data base propellers tested establish general noise characteristics Acoustic data measured wind tunnel angles 45 60 90 120 135 degrees shown microphone locations Fig ure 1 acoustic data base deter mined simulated flight velocity 100 ft/sec 682 mph rpm 10500 Limitations electric motors deter mined criteria Two different Sound Pressure Levels SPLs recorded microphone location propeller level fundamental tone blade-passing fre quency BPF Overall Sound Pres sure Level OASPL between frequen cies 100 Hz 2000 Hz data obtained analysis narrow-band spec tra similar shown Figure 2 greatest peak about 350 Hz cor responds pressure pulse radiated sound time blade passes ie BPF other peaks may generally identified harmonics larger peak occur frequencies 2BPF 3BPF etc level peak yields SPL frequency sum harmonics between 100 2000 Hz gives OASPLthat acoustic noise levelbetween two fre quencies additive level signifi cantly higher peak level repre sented blade-passing frequency other words prop noise pro duced tone BPF first few harmonics will easily understood recalls explained Part 1 point spectrum falls 20 dB below peak level has negligible impact compared peak value Analysis spectrum shows propeller noise reaches crescendo blade-passing frequency problem determine Results link between propeller noise air craft performance discussed con text thrust torque Part 1 components can conveniently related comparing power generated thrust power obtained multiplying thrust flight velocity propel ler efficiency obtained dividing power produced engine thrust power propeller efficiency varies between 0 1 closer value 1 greater amount thrust per horsepower being generated propeller An efficient pro peller will perform thrust work same engine output will ineffi cient latter engine ex penditure will converted thrust work 0 Theory 0 0 0 Torque Noise 020406 Shaft Power HP I 0810 Figure 4- SPL vs Shaft Power Torque-Noise Theory nd Experimental Data 40 Model Aviation 900FundamentalOASPL dB BPF 10500 RPM 2BPF 700 m3BPF 0 -j 0 U 500 Noise 300 400800120016002000 Frequency Hz Figure 2 Acoustic Spectrum Zinger 10 x 6 Prop Microphone 1200 10 Propellers 08x 6 08-0 9x6 6 U C 06 0 U 44Id 04 0 0 000204060810 Advance Ratio J Figure 3 Effect Pitch/Diameter Ratio 10000 rpm 907 85t71 0 V r 800 -J 0 U 00 0 advance ratio denoted symbol J defined ratio flight veloc ity propeller tip speed expressed following equation flight velocity 314 x prop rpm x prop diameter Figure 3 shows typical plot efficien cy varying flight speeds since pro peller rotational speed held constant 10000 rpm Manipulating parameters according formula yields useful information simply examining raw data calculations show representa tive model propellers used study have less 50% efficiencies flight speeds indicates little work being performed engine being used generate thrust thrust noise dominant noise mechanism would dif ficult reduce propeller noise se verely compromising aircraft performance generally low values propeller effi ciency suggest however loading blades due torqueand hence torque noiseis high comparison thrust As indicated Figure 3 fixed rpm about 10000 propeller blades un load flight speed increases Little thrust generated such situation engines work must used torque maintain propeller rotation As general finding propellers higher pitch smaller diameter have creased efficiency high speeds Note example efficiency peak 8 x 6 propeller has higher pitch-todiameter ratio occurs higher flight veloc Continued page 148 January 1990 41 close-up view propeller test rig positioned outside flow entrance noz zle wind tunnel electric motor drives propeller thrust measure ment electronics rpm sensor mounted within streamlined fairing David Heathcoat checks propeller test rig within test section anechoic wind tunnel microphone visible base shaft hanging above Daves head 65- Relation between Sound Power Shaft Pawer Gutins Pormula Torque Noise 4L o 0 0 U 0 o II 000204060810 Shaft Power HP Figure 5 Sound Power vs Shaft Power Theory Experimental Data 06- 25 -20 05 jF C L Lu15U Ii0 _a 04 oJ 0100 U O Prop Efficiency o Sound Power 03-05 89101112 Prop Diameter Figure 6 Prop Efficiency Sound Power Variation Propeller Diameter FULL BODY PILOT KIT DARNED GOOD AIRMEN Lightest pilots available Lifelike vinyl latex rubber cap goggles full templates easy instruc Build Sportsman Barnstormer Full Body Bust V Contains pilot head hands boots helmet lions Easy assemble finish Some simple sewing required Fully BUST PILOT KITpositionable tool Pta Contains pilot head helmet apart cap goggles#206-A sca895 L#205hi jacket Easy assemble finishA scee995 Per-#204- sea1095 #108-1A scaleNEW#203-A scae695 #1061/ scale #l05-/n scale795 scale895* some scale 1495 mpie aew ng equ Gd JET PILOT KIT Pilot has molded jet helmet Contains face mask oxygen hose Extreme ly Realistic Weighs less V2 oz Pea #308-A scale 595 #307-V scale 695 ORDERING INSTRUCTIONS See dealer first order direct Add $100 shipping NYS residents add 7% lax Send check money order CODS OK Send $100 catalog See Dealer add Dollar direct otder handling vice modelers friend Les Shine doing business Bentley Electronics 106 Wedgewood Drive Hauppauge NY 11788 telephone 1800/634-6306 also available through SR Bat teries P-IK fuel Stock # 50A18107 can shipped air $5499 Fuel can purchased cigar counters shipped surface UPS Ask Colibri butane 34 fi oz Stock # 50A18106 $399 Scale Sailplane kit visiting Kotzebue AK tiny village above Arctic Cir cle right Bering Sea 65 miles Si beria made acquaintance Greg Harding doing business Triton Models Box 1157 Kot zebue AK 99752 telephone 1-707/442-2617 Kotzebue just about out-of-the-way place imaginable find model manu facturer time Greg offering nice fiberglass-bodied 4-scale model 1937 DFS Reicher gull-winged sailplane former ly flown Hanna Reicher Hanna Germanys foremost aviatrix es put name history books flew Focke-WuIf twin-rotor helicopter side Olympic Stadium Berlin about 1939 Scale enthusiasts might want give Greg call Time Kotzebue two hours earlier Pa cific Standard Time keep mind call ie 800 am New York 300 am Kotzebue Propeller Noise Continued page 41 ities Although 12 x 6 propeller has higher peak efficiency occurs lower flight speeds Such propeller would ef ficient near takeoff conditions perform poorly high flight speeds Equally impor tant assuming torque loading ma jor cause propeller noise props efficient high speeds will provide re duced noise levels no compromise performance Torque noise Several other findings impli cate torque loading dominant compo nent propeller noise Figure 4 shows plot SPL blade-passing fre quency BPF measured lab about 90 tant rotational speed Also shown curve generated using ac cepted empirical theory torque noise has shown correlate very closely experimental data Since havior SPL shaft power follows expected behavior torque noise can reasonably conjecture measured noise source fact torque noise broader view data obtained examining total acoustic power sound power radiated measurement de rived integration acoustic pres sure over space sound power can compared relation between sound power shaft power classical theory propeller noise developed years ago researcher named Gutin Figure 5 shows comparison 10500 rpm simulated flight speed 100 ft/sec Note agreement tween acoustic power data Gutin theory quite close correlation tween results shown Fig ure 4 view complications associ ated combining sufficient measure ments integrating data obtain acoustic power such consistency between two sets data unexpected Both re sults point torque-related noise leading element propeller sound reader will recall propeller efficiency low work engine must used overcome torque propeller rather produce thrust plot propulsive efficiency against sound power several different props assuming acoustic power derived primarily torque loads lat ter would rise propeller efficiency de clined Due variability thrustrelated noise however such plot would meaningful thrust held constant As shown plot Figure 6 noise due thrust held constant acoustic output varies propeller diameter ac cording propeller efficiency further corroborates dominant noise mechanism sound due torque loading propeller blades thrust-related noise dominant sound power vari ation Figure 6 would nearly con stant point can see constant thrust does lead constant noise Continued page 150 4 Championship Design Outstanding4 Strong & Stable New Combat/Sport4 FastEasyAssembly Plane4 High Performance Includes Complete Hardware ine Included Belicrank outs s 0 Hinges s & Nuts $100 catalog Precision Foam Wing Corescontrol-line combat specialties Dealer & Distributor inquiries Welcome 760 Waltonville Road 1-lummelatown PA 17036 66-3810 148 Model Aviation VINYLWRITE CUSTOM LETFERING Providing elegant time saving economical finishing touch modelers EZ TO APPLY ering comes prespaced prealignedsaving hours cutting fuss aligning individual letters decals text custom computer cut 3M PEEl PROTScTlVE BACKINGPremium cast vinyl l thin olors pe styles includinq Military B[ock high NOW AAILE Stencil Mask & 1 Color Outlining Priced right no minimum charge PSEL OFF THE CARRIER TAPE example AMA numbers i/i high 1 hi h high $125P&H Call write cornplete info U ordm procisied upon rectpack & sample ITS FREE nldpped vii kit cliii m VINYLWEITE CUSTOM LEFIERING 16043 Tulsa Street Granada Hills CA 91344 818363-7131 Nooo 6PM Pacihce Mail order CA res add taz Custom Letter Today VINVLWRITE Way Rather measured noise varies torque loads very good news modelers since main noise mecha nism fact caused torque loading use efficient propellers will lead better performance less noise Its ideal solution next article series will con tinue discussion thrust thickness noise will demonstrated strictly high tip speeds thickness noise makes small contribution total propeller sound output Finally flight test data will shown strongly support inferences drawn laboratory RC Giant Scale/de Vries Continued page 43 electric screwdrivers available reasonable pric es makes logical choices use re chargeable battery-powered electric motors big birds Theyre useful manner aux iliary applications An example F-14 Tomcat being built Chuck Bailey Fremont CA Chuck enlarged set Jim Gupton F-14 drawings 24% aims power ducted-fan model twin Picco 80s Dynamax fans disassembled electric screwdriver provide strong geared source power swing Tomcats wings initial reaction wonder mo tor affected radio reception motor has com mutator brushes could possibly source unacceptable radio noise ac cording Chuck ran exhaustive series radio range checks concluded simple diode across motor leads renders electroni cally silent design rack-and-pinion gear system sweep wings well re duction drive mechanism includes ball bear ing pivots aluminum mounts model thats expected weigh 27 30 lb wet talking true Giant herethe fully extended wingspan healthy 96/2 Applying electric screwdriver motors land ing gear retracts flaps seems gaining fa vor mechanisms complex take bit metalworking expertise Powerful RC race car electric motors being considered prime movers Giants well caution go electric motor route no matter what its original source make darn sure doesnt goof up radio reception dont know somebody didnt think before people Ace RIC Inc did Theyve come up southpaw single-stick RC transmitter Using Olympic V electron ics simply reversed everything came up transmitter specifically designed 15% RC community left-handed youre interested drop em line PO Box 511 Higginsville MO 64037 Sets include Aces 91 receiver standard receiver Ni-Cdsbut no servos allows use positive-pulse high-powered servos sincerely hope readers have Merry Happy RC Aerobatics/Van Putte Continued page 45 serious Pattern competitors flying twocycle engines again end story doubt Both engines have advantages disad vantages four-cycle engines can easily turn larger propellers vertical performance bet ter However also have problems caused higher torque finesse rudder necessary vertical maneuvers two-cycle engine uses fuel costs less fourcycle fuel Propeller cost really factor cause exotic two-cycle propellers cost just much big clubs four-cycle engines turn four-cycle engines bigger heavier difficult shoehorn fuse lage airplane balance changed Cost reli ability maintainability about same early maintenance problems four-cycle engines generally thing past think four-cycle engine will win world championships F3A competition unless Prettner decides curious thing happened t989 RC Aer obatics World Championships report prob ably issue wont go great lengths about it appears international read European judges let Prettner get away new personal style flying Apparently flew very fast airplane about 200 meters out judges rules say 150-175 ters USA s Steve Helms Tony Frack owiak flew fast way out two years ago Continued page 152 150 Model Aviation W ndihoetIa5 1/4 Scale Kits $12995 Epoxy/Glass/Foam Construction Drawings Date Formula 120 Pylon Sport Standoff ScaleKit Price ping Credit cards WelcomedOhio Residents Add 7% STEP BACK & ADMIRE YOUR WORK YOURE DONE responding advertisers mention read about ModelAviation
Edition: Model Aviation - 1990/01
Page Numbers: 38, 39, 40, 41, 148, 150
Dr Robert Nagel prepares record reading test aircraft modified Miss Martha manufactured Model Engineering Raleigh NC passes over sound-level meter full throttle fixed flight speeds 90 120 km/hr meter captures peak value overall noise generated aircraft during pass Several types commonly used propellers employed flyover noise tests THE FIRST article series model propeller noise reviewed basic theoretical concepts concerning thrust drag air craft performance continued defi nitions sound frequency sound pressure level sound power level nonlinear manner sound lev els combinea result logarithmic na ture dB scalewas also explained helping reader understand relative contributions various noise sources to tal sound Finally data presented clearly demonstrate typical model aircraft equipped reasonably efficient muffler its propeller rather engine dominates noise sig nature Because specific additive behavior sound components mentioned above article concluded reducing dominant noise sourceie propelleris prop erly viewed critical task model air plane noise abatement noted propeller noise consists several sources components noise due thrust torque thickness effects oth ers Just reduction lesser engine noise may lower total noise re ducing lesser propeller noise component may bring no perceptible dimunition prop noise example eliminating 80 dB thrust noise acoustical power 904 dB total noise power slightly reduces sound level about 90 dB major challenge identify leading contributor model propeller noise Several methods determining domi nant source propeller noise available However approaches self clear-cut easy Conclusions must based several pieces information generally depend upon quality formation available ___wIINOIS second series articles reporting findings AMA-sponsored study propeller noise conducted North Carolina State University first installment explained na ture prop noise present discussion focuses methods determining some types sources prop-generated sound ER Vess D Heathcoat R Nagel 38 Model Aviation er theories carefully worked out over years published scien tific journals demonstrate various types propeller noise related mea surable quantities such thrust propeller tip speed etc propeller noise mea sured exhibits variances consistent theoretical pattern particular type noiseeg thrust torque etcone can identify reasonable confidence pri marily type noise example measurements show prop noise changes rpm thrust flight veloc ity etc fashion consistent pat tern described torque noise can sup pose latter major cause overall prop noise propeller noise sources thrust torque thickness effects etc exhibits characteristic distance noise radiates away propeller noise caused torque loading ex ample will strongest 90 degrees side plane propeller spe cific distance propeller noise caused thrust loads will little magnitude same location Thus care ful measurement directivity patterns noise can produce information about source sound difficulty again lies differentia ting among multiple noise components single out leading mechanism way circumventing problem might operate different propellers such manner thrust torque held con stant thereby eliminating thrust torque loading possible causes variations total noise pattern Such test could help us adduce primary noise source Finally physical differences among propellersin pitch diameter planform etccan affect relative dynamics prop noise Since such variations can exert enough influence alter dominant source noise propeller next should overlooked use ful source information Observed changes prop noise may provisionally related differences physical char acteristics Experimental Setup Two types experimental data used study Carefully controlled labora tory tests anechoic wind tunnel pro duced first set data phase props powered Astro Flight elec tric motors second type data de rived field tests experi mental model aircraft instrumented flown over microphone Anechoic wind tunnel wind tunnel uti lized research consisted openjet test section maximum flow veloc ity approximately 115 ft/sec about 78 mph entrance nozzle area control ling flow test section two feet square diagram general tunnel configuration shown Figure 1 Micro phones located outside flow paral lel wind tunnel centerline used measure noise level different loca tions indication directivity pat tern term anechoic refers use sound-absorbent material simulate free-field acoustic environment air craft flight eliminated distortion caused reflection would otherwise have present prop noise measure ments measurements also cor rected account sound wave propaga tion through flow shear layer streamlined housing supported aerodynamically smooth strut contained motor held propeller test sec tion wind tunnel force transducer mounted motor support structure measure thrust power determined monitoring voltage current motors arrangement permitted pro peller rpm simulated flight speed independently controlled fact higher ranges flight yeunnm locity propeller rpm model aircraft achieve flight cannot repro duced laboratory constituted builtin limitation wind tunnel tests Flight tests modified Miss Martha man ufactured Model Engineering Ra leigh NC used equipped stock OS Max 046 SF side exhaust en gine Isolation mounts utilized min imize airframe noise transmission Two different mufflers tested stock OS Max unit supplied engine Soundmaster muffler made Davis Diesel Development aircraft instrumented sensors allowed propeller rpm flight speed measured ground during flight aircraft flown full throttle fixed flight speeds 90 120 kilome ters per hour approximately 56 75 mph respectively aircraft two meters away microphone sound meter maximum noise level -..wIIuJ JET TURDULEEF NIXINS RESKIN 92m WJJU ENTRAIICE NOZZLE 4 6Gm9Gm12Gm I4 microphone -I Zzzzz 103 m FLOW EXIT MIZZLE T January 1990 39 test aircraft shown airspeed sensor mounted Its left wing tip rpm sensor mounted just behind propeller Also shown telemetry ground receiver alternate Soundmaster muffler used testing engine OS Max 046 SF Figure 1 Top View Anechoic Wind Tunnel OASPL recorded flyover data used both verify ex trapolate findings laboratory Data Base Since variety propellers often used model aircraft pilots several representa tive units selected testing Propel lers chosen being typical use today flight tests re quiring amount torque OS Max 046 SF engine provides See Table 1 list propellers no case does inclusion propeller study imply endorsement exclusion suggest criti cism validity results must care fully extended beyond range data base propellers tested establish general noise characteristics Acoustic data measured wind tunnel angles 45 60 90 120 135 degrees shown microphone locations Fig ure 1 acoustic data base deter mined simulated flight velocity 100 ft/sec 682 mph rpm 10500 Limitations electric motors deter mined criteria Two different Sound Pressure Levels SPLs recorded microphone location propeller level fundamental tone blade-passing fre quency BPF Overall Sound Pres sure Level OASPL between frequen cies 100 Hz 2000 Hz data obtained analysis narrow-band spec tra similar shown Figure 2 greatest peak about 350 Hz cor responds pressure pulse radiated sound time blade passes ie BPF other peaks may generally identified harmonics larger peak occur frequencies 2BPF 3BPF etc level peak yields SPL frequency sum harmonics between 100 2000 Hz gives OASPLthat acoustic noise levelbetween two fre quencies additive level signifi cantly higher peak level repre sented blade-passing frequency other words prop noise pro duced tone BPF first few harmonics will easily understood recalls explained Part 1 point spectrum falls 20 dB below peak level has negligible impact compared peak value Analysis spectrum shows propeller noise reaches crescendo blade-passing frequency problem determine Results link between propeller noise air craft performance discussed con text thrust torque Part 1 components can conveniently related comparing power generated thrust power obtained multiplying thrust flight velocity propel ler efficiency obtained dividing power produced engine thrust power propeller efficiency varies between 0 1 closer value 1 greater amount thrust per horsepower being generated propeller An efficient pro peller will perform thrust work same engine output will ineffi cient latter engine ex penditure will converted thrust work 0 Theory 0 0 0 Torque Noise 020406 Shaft Power HP I 0810 Figure 4- SPL vs Shaft Power Torque-Noise Theory nd Experimental Data 40 Model Aviation 900FundamentalOASPL dB BPF 10500 RPM 2BPF 700 m3BPF 0 -j 0 U 500 Noise 300 400800120016002000 Frequency Hz Figure 2 Acoustic Spectrum Zinger 10 x 6 Prop Microphone 1200 10 Propellers 08x 6 08-0 9x6 6 U C 06 0 U 44Id 04 0 0 000204060810 Advance Ratio J Figure 3 Effect Pitch/Diameter Ratio 10000 rpm 907 85t71 0 V r 800 -J 0 U 00 0 advance ratio denoted symbol J defined ratio flight veloc ity propeller tip speed expressed following equation flight velocity 314 x prop rpm x prop diameter Figure 3 shows typical plot efficien cy varying flight speeds since pro peller rotational speed held constant 10000 rpm Manipulating parameters according formula yields useful information simply examining raw data calculations show representa tive model propellers used study have less 50% efficiencies flight speeds indicates little work being performed engine being used generate thrust thrust noise dominant noise mechanism would dif ficult reduce propeller noise se verely compromising aircraft performance generally low values propeller effi ciency suggest however loading blades due torqueand hence torque noiseis high comparison thrust As indicated Figure 3 fixed rpm about 10000 propeller blades un load flight speed increases Little thrust generated such situation engines work must used torque maintain propeller rotation As general finding propellers higher pitch smaller diameter have creased efficiency high speeds Note example efficiency peak 8 x 6 propeller has higher pitch-todiameter ratio occurs higher flight veloc Continued page 148 January 1990 41 close-up view propeller test rig positioned outside flow entrance noz zle wind tunnel electric motor drives propeller thrust measure ment electronics rpm sensor mounted within streamlined fairing David Heathcoat checks propeller test rig within test section anechoic wind tunnel microphone visible base shaft hanging above Daves head 65- Relation between Sound Power Shaft Pawer Gutins Pormula Torque Noise 4L o 0 0 U 0 o II 000204060810 Shaft Power HP Figure 5 Sound Power vs Shaft Power Theory Experimental Data 06- 25 -20 05 jF C L Lu15U Ii0 _a 04 oJ 0100 U O Prop Efficiency o Sound Power 03-05 89101112 Prop Diameter Figure 6 Prop Efficiency Sound Power Variation Propeller Diameter FULL BODY PILOT KIT DARNED GOOD AIRMEN Lightest pilots available Lifelike vinyl latex rubber cap goggles full templates easy instruc Build Sportsman Barnstormer Full Body Bust V Contains pilot head hands boots helmet lions Easy assemble finish Some simple sewing required Fully BUST PILOT KITpositionable tool Pta Contains pilot head helmet apart cap goggles#206-A sca895 L#205hi jacket Easy assemble finishA scee995 Per-#204- sea1095 #108-1A scaleNEW#203-A scae695 #1061/ scale #l05-/n scale795 scale895* some scale 1495 mpie aew ng equ Gd JET PILOT KIT Pilot has molded jet helmet Contains face mask oxygen hose Extreme ly Realistic Weighs less V2 oz Pea #308-A scale 595 #307-V scale 695 ORDERING INSTRUCTIONS See dealer first order direct Add $100 shipping NYS residents add 7% lax Send check money order CODS OK Send $100 catalog See Dealer add Dollar direct otder handling vice modelers friend Les Shine doing business Bentley Electronics 106 Wedgewood Drive Hauppauge NY 11788 telephone 1800/634-6306 also available through SR Bat teries P-IK fuel Stock # 50A18107 can shipped air $5499 Fuel can purchased cigar counters shipped surface UPS Ask Colibri butane 34 fi oz Stock # 50A18106 $399 Scale Sailplane kit visiting Kotzebue AK tiny village above Arctic Cir cle right Bering Sea 65 miles Si beria made acquaintance Greg Harding doing business Triton Models Box 1157 Kot zebue AK 99752 telephone 1-707/442-2617 Kotzebue just about out-of-the-way place imaginable find model manu facturer time Greg offering nice fiberglass-bodied 4-scale model 1937 DFS Reicher gull-winged sailplane former ly flown Hanna Reicher Hanna Germanys foremost aviatrix es put name history books flew Focke-WuIf twin-rotor helicopter side Olympic Stadium Berlin about 1939 Scale enthusiasts might want give Greg call Time Kotzebue two hours earlier Pa cific Standard Time keep mind call ie 800 am New York 300 am Kotzebue Propeller Noise Continued page 41 ities Although 12 x 6 propeller has higher peak efficiency occurs lower flight speeds Such propeller would ef ficient near takeoff conditions perform poorly high flight speeds Equally impor tant assuming torque loading ma jor cause propeller noise props efficient high speeds will provide re duced noise levels no compromise performance Torque noise Several other findings impli cate torque loading dominant compo nent propeller noise Figure 4 shows plot SPL blade-passing fre quency BPF measured lab about 90 tant rotational speed Also shown curve generated using ac cepted empirical theory torque noise has shown correlate very closely experimental data Since havior SPL shaft power follows expected behavior torque noise can reasonably conjecture measured noise source fact torque noise broader view data obtained examining total acoustic power sound power radiated measurement de rived integration acoustic pres sure over space sound power can compared relation between sound power shaft power classical theory propeller noise developed years ago researcher named Gutin Figure 5 shows comparison 10500 rpm simulated flight speed 100 ft/sec Note agreement tween acoustic power data Gutin theory quite close correlation tween results shown Fig ure 4 view complications associ ated combining sufficient measure ments integrating data obtain acoustic power such consistency between two sets data unexpected Both re sults point torque-related noise leading element propeller sound reader will recall propeller efficiency low work engine must used overcome torque propeller rather produce thrust plot propulsive efficiency against sound power several different props assuming acoustic power derived primarily torque loads lat ter would rise propeller efficiency de clined Due variability thrustrelated noise however such plot would meaningful thrust held constant As shown plot Figure 6 noise due thrust held constant acoustic output varies propeller diameter ac cording propeller efficiency further corroborates dominant noise mechanism sound due torque loading propeller blades thrust-related noise dominant sound power vari ation Figure 6 would nearly con stant point can see constant thrust does lead constant noise Continued page 150 4 Championship Design Outstanding4 Strong & Stable New Combat/Sport4 FastEasyAssembly Plane4 High Performance Includes Complete Hardware ine Included Belicrank outs s 0 Hinges s & Nuts $100 catalog Precision Foam Wing Corescontrol-line combat specialties Dealer & Distributor inquiries Welcome 760 Waltonville Road 1-lummelatown PA 17036 66-3810 148 Model Aviation VINYLWRITE CUSTOM LETFERING Providing elegant time saving economical finishing touch modelers EZ TO APPLY ering comes prespaced prealignedsaving hours cutting fuss aligning individual letters decals text custom computer cut 3M PEEl PROTScTlVE BACKINGPremium cast vinyl l thin olors pe styles includinq Military B[ock high NOW AAILE Stencil Mask & 1 Color Outlining Priced right no minimum charge PSEL OFF THE CARRIER TAPE example AMA numbers i/i high 1 hi h high $125P&H Call write cornplete info U ordm procisied upon rectpack & sample ITS FREE nldpped vii kit cliii m VINYLWEITE CUSTOM LEFIERING 16043 Tulsa Street Granada Hills CA 91344 818363-7131 Nooo 6PM Pacihce Mail order CA res add taz Custom Letter Today VINVLWRITE Way Rather measured noise varies torque loads very good news modelers since main noise mecha nism fact caused torque loading use efficient propellers will lead better performance less noise Its ideal solution next article series will con tinue discussion thrust thickness noise will demonstrated strictly high tip speeds thickness noise makes small contribution total propeller sound output Finally flight test data will shown strongly support inferences drawn laboratory RC Giant Scale/de Vries Continued page 43 electric screwdrivers available reasonable pric es makes logical choices use re chargeable battery-powered electric motors big birds Theyre useful manner aux iliary applications An example F-14 Tomcat being built Chuck Bailey Fremont CA Chuck enlarged set Jim Gupton F-14 drawings 24% aims power ducted-fan model twin Picco 80s Dynamax fans disassembled electric screwdriver provide strong geared source power swing Tomcats wings initial reaction wonder mo tor affected radio reception motor has com mutator brushes could possibly source unacceptable radio noise ac cording Chuck ran exhaustive series radio range checks concluded simple diode across motor leads renders electroni cally silent design rack-and-pinion gear system sweep wings well re duction drive mechanism includes ball bear ing pivots aluminum mounts model thats expected weigh 27 30 lb wet talking true Giant herethe fully extended wingspan healthy 96/2 Applying electric screwdriver motors land ing gear retracts flaps seems gaining fa vor mechanisms complex take bit metalworking expertise Powerful RC race car electric motors being considered prime movers Giants well caution go electric motor route no matter what its original source make darn sure doesnt goof up radio reception dont know somebody didnt think before people Ace RIC Inc did Theyve come up southpaw single-stick RC transmitter Using Olympic V electron ics simply reversed everything came up transmitter specifically designed 15% RC community left-handed youre interested drop em line PO Box 511 Higginsville MO 64037 Sets include Aces 91 receiver standard receiver Ni-Cdsbut no servos allows use positive-pulse high-powered servos sincerely hope readers have Merry Happy RC Aerobatics/Van Putte Continued page 45 serious Pattern competitors flying twocycle engines again end story doubt Both engines have advantages disad vantages four-cycle engines can easily turn larger propellers vertical performance bet ter However also have problems caused higher torque finesse rudder necessary vertical maneuvers two-cycle engine uses fuel costs less fourcycle fuel Propeller cost really factor cause exotic two-cycle propellers cost just much big clubs four-cycle engines turn four-cycle engines bigger heavier difficult shoehorn fuse lage airplane balance changed Cost reli ability maintainability about same early maintenance problems four-cycle engines generally thing past think four-cycle engine will win world championships F3A competition unless Prettner decides curious thing happened t989 RC Aer obatics World Championships report prob ably issue wont go great lengths about it appears international read European judges let Prettner get away new personal style flying Apparently flew very fast airplane about 200 meters out judges rules say 150-175 ters USA s Steve Helms Tony Frack owiak flew fast way out two years ago Continued page 152 150 Model Aviation W ndihoetIa5 1/4 Scale Kits $12995 Epoxy/Glass/Foam Construction Drawings Date Formula 120 Pylon Sport Standoff ScaleKit Price ping Credit cards WelcomedOhio Residents Add 7% STEP BACK & ADMIRE YOUR WORK YOURE DONE responding advertisers mention read about ModelAviation
Edition: Model Aviation - 1990/01
Page Numbers: 38, 39, 40, 41, 148, 150
Dr Robert Nagel prepares record reading test aircraft modified Miss Martha manufactured Model Engineering Raleigh NC passes over sound-level meter full throttle fixed flight speeds 90 120 km/hr meter captures peak value overall noise generated aircraft during pass Several types commonly used propellers employed flyover noise tests THE FIRST article series model propeller noise reviewed basic theoretical concepts concerning thrust drag air craft performance continued defi nitions sound frequency sound pressure level sound power level nonlinear manner sound lev els combinea result logarithmic na ture dB scalewas also explained helping reader understand relative contributions various noise sources to tal sound Finally data presented clearly demonstrate typical model aircraft equipped reasonably efficient muffler its propeller rather engine dominates noise sig nature Because specific additive behavior sound components mentioned above article concluded reducing dominant noise sourceie propelleris prop erly viewed critical task model air plane noise abatement noted propeller noise consists several sources components noise due thrust torque thickness effects oth ers Just reduction lesser engine noise may lower total noise re ducing lesser propeller noise component may bring no perceptible dimunition prop noise example eliminating 80 dB thrust noise acoustical power 904 dB total noise power slightly reduces sound level about 90 dB major challenge identify leading contributor model propeller noise Several methods determining domi nant source propeller noise available However approaches self clear-cut easy Conclusions must based several pieces information generally depend upon quality formation available ___wIINOIS second series articles reporting findings AMA-sponsored study propeller noise conducted North Carolina State University first installment explained na ture prop noise present discussion focuses methods determining some types sources prop-generated sound ER Vess D Heathcoat R Nagel 38 Model Aviation er theories carefully worked out over years published scien tific journals demonstrate various types propeller noise related mea surable quantities such thrust propeller tip speed etc propeller noise mea sured exhibits variances consistent theoretical pattern particular type noiseeg thrust torque etcone can identify reasonable confidence pri marily type noise example measurements show prop noise changes rpm thrust flight veloc ity etc fashion consistent pat tern described torque noise can sup pose latter major cause overall prop noise propeller noise sources thrust torque thickness effects etc exhibits characteristic distance noise radiates away propeller noise caused torque loading ex ample will strongest 90 degrees side plane propeller spe cific distance propeller noise caused thrust loads will little magnitude same location Thus care ful measurement directivity patterns noise can produce information about source sound difficulty again lies differentia ting among multiple noise components single out leading mechanism way circumventing problem might operate different propellers such manner thrust torque held con stant thereby eliminating thrust torque loading possible causes variations total noise pattern Such test could help us adduce primary noise source Finally physical differences among propellersin pitch diameter planform etccan affect relative dynamics prop noise Since such variations can exert enough influence alter dominant source noise propeller next should overlooked use ful source information Observed changes prop noise may provisionally related differences physical char acteristics Experimental Setup Two types experimental data used study Carefully controlled labora tory tests anechoic wind tunnel pro duced first set data phase props powered Astro Flight elec tric motors second type data de rived field tests experi mental model aircraft instrumented flown over microphone Anechoic wind tunnel wind tunnel uti lized research consisted openjet test section maximum flow veloc ity approximately 115 ft/sec about 78 mph entrance nozzle area control ling flow test section two feet square diagram general tunnel configuration shown Figure 1 Micro phones located outside flow paral lel wind tunnel centerline used measure noise level different loca tions indication directivity pat tern term anechoic refers use sound-absorbent material simulate free-field acoustic environment air craft flight eliminated distortion caused reflection would otherwise have present prop noise measure ments measurements also cor rected account sound wave propaga tion through flow shear layer streamlined housing supported aerodynamically smooth strut contained motor held propeller test sec tion wind tunnel force transducer mounted motor support structure measure thrust power determined monitoring voltage current motors arrangement permitted pro peller rpm simulated flight speed independently controlled fact higher ranges flight yeunnm locity propeller rpm model aircraft achieve flight cannot repro duced laboratory constituted builtin limitation wind tunnel tests Flight tests modified Miss Martha man ufactured Model Engineering Ra leigh NC used equipped stock OS Max 046 SF side exhaust en gine Isolation mounts utilized min imize airframe noise transmission Two different mufflers tested stock OS Max unit supplied engine Soundmaster muffler made Davis Diesel Development aircraft instrumented sensors allowed propeller rpm flight speed measured ground during flight aircraft flown full throttle fixed flight speeds 90 120 kilome ters per hour approximately 56 75 mph respectively aircraft two meters away microphone sound meter maximum noise level -..wIIuJ JET TURDULEEF NIXINS RESKIN 92m WJJU ENTRAIICE NOZZLE 4 6Gm9Gm12Gm I4 microphone -I Zzzzz 103 m FLOW EXIT MIZZLE T January 1990 39 test aircraft shown airspeed sensor mounted Its left wing tip rpm sensor mounted just behind propeller Also shown telemetry ground receiver alternate Soundmaster muffler used testing engine OS Max 046 SF Figure 1 Top View Anechoic Wind Tunnel OASPL recorded flyover data used both verify ex trapolate findings laboratory Data Base Since variety propellers often used model aircraft pilots several representa tive units selected testing Propel lers chosen being typical use today flight tests re quiring amount torque OS Max 046 SF engine provides See Table 1 list propellers no case does inclusion propeller study imply endorsement exclusion suggest criti cism validity results must care fully extended beyond range data base propellers tested establish general noise characteristics Acoustic data measured wind tunnel angles 45 60 90 120 135 degrees shown microphone locations Fig ure 1 acoustic data base deter mined simulated flight velocity 100 ft/sec 682 mph rpm 10500 Limitations electric motors deter mined criteria Two different Sound Pressure Levels SPLs recorded microphone location propeller level fundamental tone blade-passing fre quency BPF Overall Sound Pres sure Level OASPL between frequen cies 100 Hz 2000 Hz data obtained analysis narrow-band spec tra similar shown Figure 2 greatest peak about 350 Hz cor responds pressure pulse radiated sound time blade passes ie BPF other peaks may generally identified harmonics larger peak occur frequencies 2BPF 3BPF etc level peak yields SPL frequency sum harmonics between 100 2000 Hz gives OASPLthat acoustic noise levelbetween two fre quencies additive level signifi cantly higher peak level repre sented blade-passing frequency other words prop noise pro duced tone BPF first few harmonics will easily understood recalls explained Part 1 point spectrum falls 20 dB below peak level has negligible impact compared peak value Analysis spectrum shows propeller noise reaches crescendo blade-passing frequency problem determine Results link between propeller noise air craft performance discussed con text thrust torque Part 1 components can conveniently related comparing power generated thrust power obtained multiplying thrust flight velocity propel ler efficiency obtained dividing power produced engine thrust power propeller efficiency varies between 0 1 closer value 1 greater amount thrust per horsepower being generated propeller An efficient pro peller will perform thrust work same engine output will ineffi cient latter engine ex penditure will converted thrust work 0 Theory 0 0 0 Torque Noise 020406 Shaft Power HP I 0810 Figure 4- SPL vs Shaft Power Torque-Noise Theory nd Experimental Data 40 Model Aviation 900FundamentalOASPL dB BPF 10500 RPM 2BPF 700 m3BPF 0 -j 0 U 500 Noise 300 400800120016002000 Frequency Hz Figure 2 Acoustic Spectrum Zinger 10 x 6 Prop Microphone 1200 10 Propellers 08x 6 08-0 9x6 6 U C 06 0 U 44Id 04 0 0 000204060810 Advance Ratio J Figure 3 Effect Pitch/Diameter Ratio 10000 rpm 907 85t71 0 V r 800 -J 0 U 00 0 advance ratio denoted symbol J defined ratio flight veloc ity propeller tip speed expressed following equation flight velocity 314 x prop rpm x prop diameter Figure 3 shows typical plot efficien cy varying flight speeds since pro peller rotational speed held constant 10000 rpm Manipulating parameters according formula yields useful information simply examining raw data calculations show representa tive model propellers used study have less 50% efficiencies flight speeds indicates little work being performed engine being used generate thrust thrust noise dominant noise mechanism would dif ficult reduce propeller noise se verely compromising aircraft performance generally low values propeller effi ciency suggest however loading blades due torqueand hence torque noiseis high comparison thrust As indicated Figure 3 fixed rpm about 10000 propeller blades un load flight speed increases Little thrust generated such situation engines work must used torque maintain propeller rotation As general finding propellers higher pitch smaller diameter have creased efficiency high speeds Note example efficiency peak 8 x 6 propeller has higher pitch-todiameter ratio occurs higher flight veloc Continued page 148 January 1990 41 close-up view propeller test rig positioned outside flow entrance noz zle wind tunnel electric motor drives propeller thrust measure ment electronics rpm sensor mounted within streamlined fairing David Heathcoat checks propeller test rig within test section anechoic wind tunnel microphone visible base shaft hanging above Daves head 65- Relation between Sound Power Shaft Pawer Gutins Pormula Torque Noise 4L o 0 0 U 0 o II 000204060810 Shaft Power HP Figure 5 Sound Power vs Shaft Power Theory Experimental Data 06- 25 -20 05 jF C L Lu15U Ii0 _a 04 oJ 0100 U O Prop Efficiency o Sound Power 03-05 89101112 Prop Diameter Figure 6 Prop Efficiency Sound Power Variation Propeller Diameter FULL BODY PILOT KIT DARNED GOOD AIRMEN Lightest pilots available Lifelike vinyl latex rubber cap goggles full templates easy instruc Build Sportsman Barnstormer Full Body Bust V Contains pilot head hands boots helmet lions Easy assemble finish Some simple sewing required Fully BUST PILOT KITpositionable tool Pta Contains pilot head helmet apart cap goggles#206-A sca895 L#205hi jacket Easy assemble finishA scee995 Per-#204- sea1095 #108-1A scaleNEW#203-A scae695 #1061/ scale #l05-/n scale795 scale895* some scale 1495 mpie aew ng equ Gd JET PILOT KIT Pilot has molded jet helmet Contains face mask oxygen hose Extreme ly Realistic Weighs less V2 oz Pea #308-A scale 595 #307-V scale 695 ORDERING INSTRUCTIONS See dealer first order direct Add $100 shipping NYS residents add 7% lax Send check money order CODS OK Send $100 catalog See Dealer add Dollar direct otder handling vice modelers friend Les Shine doing business Bentley Electronics 106 Wedgewood Drive Hauppauge NY 11788 telephone 1800/634-6306 also available through SR Bat teries P-IK fuel Stock # 50A18107 can shipped air $5499 Fuel can purchased cigar counters shipped surface UPS Ask Colibri butane 34 fi oz Stock # 50A18106 $399 Scale Sailplane kit visiting Kotzebue AK tiny village above Arctic Cir cle right Bering Sea 65 miles Si beria made acquaintance Greg Harding doing business Triton Models Box 1157 Kot zebue AK 99752 telephone 1-707/442-2617 Kotzebue just about out-of-the-way place imaginable find model manu facturer time Greg offering nice fiberglass-bodied 4-scale model 1937 DFS Reicher gull-winged sailplane former ly flown Hanna Reicher Hanna Germanys foremost aviatrix es put name history books flew Focke-WuIf twin-rotor helicopter side Olympic Stadium Berlin about 1939 Scale enthusiasts might want give Greg call Time Kotzebue two hours earlier Pa cific Standard Time keep mind call ie 800 am New York 300 am Kotzebue Propeller Noise Continued page 41 ities Although 12 x 6 propeller has higher peak efficiency occurs lower flight speeds Such propeller would ef ficient near takeoff conditions perform poorly high flight speeds Equally impor tant assuming torque loading ma jor cause propeller noise props efficient high speeds will provide re duced noise levels no compromise performance Torque noise Several other findings impli cate torque loading dominant compo nent propeller noise Figure 4 shows plot SPL blade-passing fre quency BPF measured lab about 90 tant rotational speed Also shown curve generated using ac cepted empirical theory torque noise has shown correlate very closely experimental data Since havior SPL shaft power follows expected behavior torque noise can reasonably conjecture measured noise source fact torque noise broader view data obtained examining total acoustic power sound power radiated measurement de rived integration acoustic pres sure over space sound power can compared relation between sound power shaft power classical theory propeller noise developed years ago researcher named Gutin Figure 5 shows comparison 10500 rpm simulated flight speed 100 ft/sec Note agreement tween acoustic power data Gutin theory quite close correlation tween results shown Fig ure 4 view complications associ ated combining sufficient measure ments integrating data obtain acoustic power such consistency between two sets data unexpected Both re sults point torque-related noise leading element propeller sound reader will recall propeller efficiency low work engine must used overcome torque propeller rather produce thrust plot propulsive efficiency against sound power several different props assuming acoustic power derived primarily torque loads lat ter would rise propeller efficiency de clined Due variability thrustrelated noise however such plot would meaningful thrust held constant As shown plot Figure 6 noise due thrust held constant acoustic output varies propeller diameter ac cording propeller efficiency further corroborates dominant noise mechanism sound due torque loading propeller blades thrust-related noise dominant sound power vari ation Figure 6 would nearly con stant point can see constant thrust does lead constant noise Continued page 150 4 Championship Design Outstanding4 Strong & Stable New Combat/Sport4 FastEasyAssembly Plane4 High Performance Includes Complete Hardware ine Included Belicrank outs s 0 Hinges s & Nuts $100 catalog Precision Foam Wing Corescontrol-line combat specialties Dealer & Distributor inquiries Welcome 760 Waltonville Road 1-lummelatown PA 17036 66-3810 148 Model Aviation VINYLWRITE CUSTOM LETFERING Providing elegant time saving economical finishing touch modelers EZ TO APPLY ering comes prespaced prealignedsaving hours cutting fuss aligning individual letters decals text custom computer cut 3M PEEl PROTScTlVE BACKINGPremium cast vinyl l thin olors pe styles includinq Military B[ock high NOW AAILE Stencil Mask & 1 Color Outlining Priced right no minimum charge PSEL OFF THE CARRIER TAPE example AMA numbers i/i high 1 hi h high $125P&H Call write cornplete info U ordm procisied upon rectpack & sample ITS FREE nldpped vii kit cliii m VINYLWEITE CUSTOM LEFIERING 16043 Tulsa Street Granada Hills CA 91344 818363-7131 Nooo 6PM Pacihce Mail order CA res add taz Custom Letter Today VINVLWRITE Way Rather measured noise varies torque loads very good news modelers since main noise mecha nism fact caused torque loading use efficient propellers will lead better performance less noise Its ideal solution next article series will con tinue discussion thrust thickness noise will demonstrated strictly high tip speeds thickness noise makes small contribution total propeller sound output Finally flight test data will shown strongly support inferences drawn laboratory RC Giant Scale/de Vries Continued page 43 electric screwdrivers available reasonable pric es makes logical choices use re chargeable battery-powered electric motors big birds Theyre useful manner aux iliary applications An example F-14 Tomcat being built Chuck Bailey Fremont CA Chuck enlarged set Jim Gupton F-14 drawings 24% aims power ducted-fan model twin Picco 80s Dynamax fans disassembled electric screwdriver provide strong geared source power swing Tomcats wings initial reaction wonder mo tor affected radio reception motor has com mutator brushes could possibly source unacceptable radio noise ac cording Chuck ran exhaustive series radio range checks concluded simple diode across motor leads renders electroni cally silent design rack-and-pinion gear system sweep wings well re duction drive mechanism includes ball bear ing pivots aluminum mounts model thats expected weigh 27 30 lb wet talking true Giant herethe fully extended wingspan healthy 96/2 Applying electric screwdriver motors land ing gear retracts flaps seems gaining fa vor mechanisms complex take bit metalworking expertise Powerful RC race car electric motors being considered prime movers Giants well caution go electric motor route no matter what its original source make darn sure doesnt goof up radio reception dont know somebody didnt think before people Ace RIC Inc did Theyve come up southpaw single-stick RC transmitter Using Olympic V electron ics simply reversed everything came up transmitter specifically designed 15% RC community left-handed youre interested drop em line PO Box 511 Higginsville MO 64037 Sets include Aces 91 receiver standard receiver Ni-Cdsbut no servos allows use positive-pulse high-powered servos sincerely hope readers have Merry Happy RC Aerobatics/Van Putte Continued page 45 serious Pattern competitors flying twocycle engines again end story doubt Both engines have advantages disad vantages four-cycle engines can easily turn larger propellers vertical performance bet ter However also have problems caused higher torque finesse rudder necessary vertical maneuvers two-cycle engine uses fuel costs less fourcycle fuel Propeller cost really factor cause exotic two-cycle propellers cost just much big clubs four-cycle engines turn four-cycle engines bigger heavier difficult shoehorn fuse lage airplane balance changed Cost reli ability maintainability about same early maintenance problems four-cycle engines generally thing past think four-cycle engine will win world championships F3A competition unless Prettner decides curious thing happened t989 RC Aer obatics World Championships report prob ably issue wont go great lengths about it appears international read European judges let Prettner get away new personal style flying Apparently flew very fast airplane about 200 meters out judges rules say 150-175 ters USA s Steve Helms Tony Frack owiak flew fast way out two years ago Continued page 152 150 Model Aviation W ndihoetIa5 1/4 Scale Kits $12995 Epoxy/Glass/Foam Construction Drawings Date Formula 120 Pylon Sport Standoff ScaleKit Price ping Credit cards WelcomedOhio Residents Add 7% STEP BACK & ADMIRE YOUR WORK YOURE DONE responding advertisers mention read about ModelAviation