D Heathcoat R Nagel Model Propeller NOISEc first series articles describes in-depth research spon sored AMA conducted North Carolina State Univer sity severity sources reduction propeller noise findings some unprecedented could have ma jor impact model airplane_flying community ADVANCES model aviation over past decade have spurred tremendous growth hobby year thousands people across US becoming ac tive participants weekend sessions local flying field greatest influx newcomers sport naturally occurs near large cities population con centrated flying sites tend lo cated suburban areas allows easy access fliers also subjects uninterested neighbor characteris tic whine model aircraft surprisingly greatest activity model field occurs weekends weekday evenings just peo ple living nearby home expecting chance relax involved sport well aware bitter confrontation scenario sometimes provokes ten modelers lose battle begin search another suitable flying site Losing established flying site hav ing search new can frustrat ing costly experience Ultimately has negative effect organization continued growth sport Its clear continuously relocating flying fields farther farther away populated ar eas isnt answer rate rural de velopment flying site relocation will lit tle postpone inevitable return problem solution instead develop model aircraft operate lower sound levels quite evident commonly accepted model aircraft noise generated propulsion system casual observer obvious sources intake combustion exhaust noise generated power plantand airframe noise re sulting its characteristic vibration However propeller too impor tant source noiseone misunder stood consequently overlooked fact acoustic research full-scale aircraft indicates propeller noise dominates over other sources sound illustrated following quote Journal Aircraft has well known years propellerdriven aircraft propeller primary source noise observation may 36 Model Aviation gu hold true model aircraft well effort better understand model pro Di recti Ro tat peller noise establish guidelines ultimately will lead quieter model aircraft AMA sponsored research pro Table 1Selected Flight Test Data Prop Velocity RPM QASPI kmphdBA Group 1 11 x5180160001110 9x7519516400960 9x719016250934 Group 2 10x615013500878 11 x614312000990 Group 3 10x712011000840 9x7512011250810 10x612010800764 Group 4 11 x 5908500925 9 x 7908700830 gram conducted North Carolina State Uni versity principal investigators include Dr Robert T Nagel associate professor nearly 15 years research experience aeroacoustics Robert Vess aero space engineer six years experience coordinator NC State University aerospace laboratories 18 years activ ity Radio Control including Pattern Hel icopter fun fly competition David M Heathcoat received bachelors degree physics NC State University 1986 participated propeller noise research masters degree thesis article first series will describe tests performed explain results make recommendations toward reducing model aircraft noise Im proving noise problem means averting loss flying sites will depend largely having knowledgeable fliers Due technical nature mate rial will precede discussion test program details brief explanation basic propeller theory Introducing some important aspects propeller per formance section will lead better understanding both current study propellers general Since formulas scientific jargon tend limit interest type article effort has made avoid use Basic Propeller Theory order aircraft move through air propelling force must work propeller essentially small rotating wing produces required thrust speed aircraft level flight deter mined relating thrust available power plant total aircraft drag Note both forces vary signifi cantly airspeed depicted typi cal aircraft Figure 1 example moving left right along horizontal axis Figure 1 represents increasing airspeed notes aircraft drag increases eventually exceeds thrust Point 1 figure represents case air craft accelerating since thrust pro duced propeller much greater aircraft drag Conversely aircraft operating point 2 predominance drag over thrust causes decelerate cases airspeed will stabi lize point 3 thrust drag equal Since engine example full throttle point 3 represents maximum tainable airspeed aircraft/engine/ propeller combination level flight re duction power below full throttle ef fectively shifts thrust curve downward resulting reduction maximum airspeed see dashed curve Figure 1 Similarly anything can done pro duce thrust less drag will shift December 1989 37 Figu curves allowing greater flight speeds Figure 1 has shown thrust produced power plant actually decreases yond certain threshold airspeed phenomenon results changes air flow around propeller high airspeeds As propeller rotates flow approaches its leading edge speed depends rotational speed rpm engine However forward movement aircraft creates additional flow ap proaches propeller disc speed equal forces acting propeller best explained examining thin slice blade such shown cross section Figure 2 Once again explanation simplified differentiating effects due blade rotation caused forward speed Figure 3 depicts flow action sec tion typical propeller blade due its ro tation alone would case engine being run model re strained flow approaches prop angle dictated blade pitch Just wing produces lift drag certain gle attack propeller produces sim ilar forces depend engine rpm shape blade airfoil lift force example acts along axis rotation force axial direction termed thrust Similarly drag force acts plane rotation pro peller resists its rotation defined torque Figure 4 illustrates condition after aircraft released acquires addi tional flow field its forward move ment simple way graphically depict combination two flows use special arrows called vectors flow represented single vector relative speed flow given length its vector flow direction rep resented direction vec tor pointing two propeller flow vectors arranged nose-to-tail Fig ure 4 rotation forward flight other vector completes triangle represents flow field resulting combination Notice speed direction resultant vector can al tered changing length speed original vectors Therefore flow around propeller indeed does depend both engine rpm forward flight speed flow vectors combine shown Figure 4 forces acting propel ler diminish Hence blade airfoil angle attack Figure 4 decreased com pared Figure 3 addition since lift drag forces measured respect altered flow angle slanted away axis rotation propel ler Therefore net thrust decreased further since lift force acting pre cisely thrust direction misdirection lift also shown Figure 4 reality thrust lost due slanting lift force becomes ad ditional torque load engine must overcome effectively demonstrates propeller performance very different flight ground better understanding engine turns propeller under varying load conditions can gained referring Fig ure 5 Assume drag forces acting point blade propeller example added together sum found lso assume net drag force determined act ing through point 12 center crankshaft product lb 12-in distance represents 6 in-lb b torque load blade propeller Since two blades net torque load power plant must produce order turn blades constant rotational speed 12 38 Model Aviation 0 flight velocity Figure 2 illustrates relative directions simultaneous flows respect propeller ro tating counterclockwise in-lb 1 ft-lb engine capable producing torque under condi tions rotational speed will increase cant produce enough torque rotational speed will achieved power available engine simply rotational speed multiplied amount torque can applied propeller given rpm example engine can produce 33 ft-lb torque 10000 rpm 16667 rev/sec power rotational speed 550 ft lb/sec example chosen order put value power recogniz able units Since horsepower 1 hp equivalent 550 ft-lb/sec engine producing exactly horsepower under operating conditions Figure 6 illustrates way horsepower output torque typical model engine vary rotational speed Most engines available modelers have curves resemble example actual magnitude power torque rotational speed depends physi cal design particular engine As mentioned above power required turn propeller product torque rotational speed power produced propeller proportional product thrust forward speed ratio power produced propeller required turn known propeller efficiency An efficient propeller capable producing given amount thrust using less power inefficient Equivalently efficient propeller can produce greater thrust therefore greater ward speed using same engine power Rather being fixed value efficien cy depends physical design opera ting rpm flight speed specific pro peller therefore improper categori cally call prop efficient other unless advantage holds true rotational forward speeds Propeller ef ficiency plays major role increasing air craft performance reducing noise Basic Noise Definitions Sound waves simply minute pressure fluctuations propagate air characterized two parameters frequency amplitude Frequency refers number pressure pulses pres sure fluctuations occur sec ond perceived ear pitch Like higher notes piano keyboard higher frequencies actually sound higher pitched Pressure amplitude measure size acoustical disturbance corresponds loudness sound simple tone characterized single frequency single amplitude Complex sounds composed different fre quencies Pressure amplitude measured deci bels dB measured referred sound pressure level SPL Continued page 40 Order direct Add $1500 shipping Use VISA MC check money order COD GOLIDW AGE MODELS RO box 807 Ienn Vcilleq CA 95946 916 432-2928 B&P Associates Gives Total FlIgbt Line FREEDOM battery needs call write B&P Associates PO Box 22054 Waco TX 76702-2054 817662-5587 new electric starter battery pack cuts cord has always tied starter power panel Discover freedom being able start plane wherever added safety less wire get caught prop charge hefty 4 Amp/hour pack will take through weekend flying power enough spare dont stop have Ni-Cads virtually size imaginable cut experimenter free design whatever ii takes make yours best setup field December 1989 39 h C, qusrter scale com plete deluxe kit features exact scale outlines balsa plywo, onstruction light epoxy cowl wheel pants selected wood complete hardware flying wires full cockpit details 3-views photos decals extensive instruction manual 20 cu ne lighL upoxy glass uuiage cowl wheel pants complete hardware selected wood decals 3-views cu engliw epoxy glass fudy owl wheel pants light foam wing cores con test wood complete hardware decals Satisfaction Guaranteed1 EA~ HINELZ SH-710 Pkg 24-52 95 THE HIGH-TECH HINGE DESIGNED FOR THE CYANOACRYLATE AGE Easier install other hinge No gouging picking messy epoxies Simply cut single knife slot hinge slide hinges place apply few drops favorite CA glue youre donel SUPER FAST SUPER EASY SUPER STRONG SIG MFG CO INC401-7 So Front St.Montezuma IA 50171 23-5154 LANDER INDUST 1005 19TH ST CT HAVRE MONTANA 59501 406265-6529 PRICES INCLUDE FREIGHT CANADIAN ORDERS ADD 25% ViSA Pwtakeet SUpeJL Po4 PO4JIWkQ 40. FREE CATALOG Ti4ewaiwt I4otoluj eIdWIIAi*e 392SC SE 13th Court Scala FImna 32571 904 6943531 sound pressure level corresponds dis crete frequency range frequencies overall sound pressure level' OASPL also measured decibels measure sound obtained adding SPLs frequency spectrum decibel reflecting fact human ear perceives very wide range sound pressure based loga rithmic scale rather linear compresses sonic data ease inter pretation Still another measure noise sound power level PWL based quantity acoustical power pro duced given source rather pres sure amplitude given location Since sound power level also measured dB its important keep track whether mea surements given units PWLs SPLs Sounds certain frequency ranges perceived being louder sounds other frequencies Weighted sound level curves have developed take fact account weighted scale used almost industrial commu nity noise standards US Sound lev els measured according scale ex pressed units called dBA significance relative contribu tions various components noise cannot appreciated general understanding manner sound levels combined two equal sound pressure levels SPLs added together combined sound level will 6dB higher orig inal value Adding together two equal sound power levels PWLs produces level 3 dB higher phenome non result logarithmic nature dB scale means levels separated few dB fact very different ab solute values acoustic power level PWL expressed dB adding two powers differ 10 dB pro duces no significant increase power yond higher two Consider ex ample adding 80 dB 90 dB powers dB1 B dB2 B total dBtotai given follow ing formula dBtotai og[l0dB/o 2/1O] dB Sound pressure levels SPLs behave similar fashion two SPLs com bined variance between acoustic levels addition becomes insignificant about 20 dB adds SPLs 80 dB 100 dB result 1008 dB practical implications will become clear realizes model aircraft noise derives several sourcesthe engine airframe propellerand propeller noise itself blends several components Often reducing lesser noise source fails produce noticeably quieter aircraft Consider example aircraft 80 dB engine noise 90 dB propeller noise As have seen formula given above able completely elim inate engine noise lesser source resulting acoustic power would discernibly reduced hypothetical example subtracting 80 dB engine noise acoustical power 904 dB total noise power slightly lowers total output about 90 dBnot significant change achieve meaningful reduction model air craft sound necessary reduce dominant source noise Justification Propeller Noise Reduction fundamental objective research project has verify sound pro duced propeller fact domi nant noise mechanism model aviation project assumes reasonable offthe-shelf muffler used aircraft since absence such use use poor muffler engine sounds likely dominate noise signature Measure ments acquired during different phases research provide several pieces evi dence indicate propeller noise dominates over produced properly muffled engine Flight test data provides first bit ev idence An instrumented aircraft flown fixed height over microphone peak OASPL measured dBA flight speed rpm throttle setting also recorded data compared obtained same propellers driven electric motor wind tunnel laboratory thereby eliminating power plant significant source noise Although flight velocities precisely duplicated lab several cases offer reasonable basis compari son such case SPL bladepassing frequency lab 78 dB simulated flight velocity 100 kmph ki lometers per hour microphone dis tance corrected same distance used flight tests flight test 120 kmph resulted OASPL 764 dBA OASPL includes frequencies spectrum whereas lab data ob tained blade-passing frequency Since engine airframe noise absent lab data would have ex pected flight test noise louder results support inference engine airframe noise did reach significant level flight tests done would have tended dominate rais ing OASPL above SPL measured lab fact propeller noise alone approximately equal total noise mea sured flight Table 1 shows data selected tests operating conditions nearly identical Group 1 contains propel lers same manufacturer tal variation mean rpm less 1% total variation flight velocity approximately 5% Groups 2 3 in40 Model Aviation RIG SKY CRADLES FIELD BOX MODEL$1595 BENCH MODEL$1995 FLOOR MODEL$2395 CEILING HANGERS SMALL20-40 .$995 MEDIUM 40- 60 95 LARGE 50-BO. $1195 nvur HAIFt FITS ALL PICKUPS . 5 cluded propellers two different manu facturers Group 4 propellers sin gle manufacturer Since flight speed rpm nearly same group aircraft always level flight measure ment point thrust produced likewise nearly same data groups Table 1 Clearly engine airframe having almost identically groups can therefore inferred observed large variations OASPL between cases within group rather being caused engine airframe noise result dif ferences sound levels among propellers Further assuming situation en gine noise closely approximated level propeller noise completely eliminating engine noise would effect noise re duction 6 dBa value ex ceeded differences noted among props particular group final piece evidence yielded data obtained two different mufflers during flight tests stock muffler re placed high-quality state-of-the-art muf fler data recorded two different flight speeds using same propeller 120 kmph difference OASPL measured 02 dBA 90 kmph difference 03 dBA Such ex tremely small variance suggests given flight speed advanced muffler no effect total noise output ever full throttle engine performed better upgraded muffler ad ditional rpm permitted latter creased noise levels improved engine performance advanced muffler did significantly impact noise level long flight speed remained constant test results clearly establish pro peller dominant source model air craft noise remainder discus sion will assume case Propeller Noise Sources sound produced model propel ler compounded several elements important include noise due thrust torque noise thickness noise referred discrete fre quency noise sources because sound produced occurs bladepassing frequency its harmonics blade-passing frequency rate blade passes given point propel ler disc product number blades rotational speed rev/sec understand noise mecha nisms operate imagine fixed point rotational disc propeller time blade near point air pressure its ordinary value Air pres sure changes blade passes through pushes air aside amount dis placed air depending thickness blade noise produced periodic displacement air known thickness noise Continued page 42 VJO ds best Sel 09 Spak osen ByTan Odginds TItG Mfg ml AM Aircraft Saqiply its outstenhg ruimhity Comp e e s ng e cyl nder system nclud ng ho e couped spark advance kt spark gead25 p ug ba e y pack charger 900 sh elded Much kmger 1gm hIs Easy haid sterts-no kickback 1AUO-12000 RPM rubble ii 0% power few strokers oni nutubbmi mviii Lower pricad fuels no okra neededMqleeduul9Fphagcovw FormumyuapaesI0&p2ft4strokeslegieudtwlsctulrs Klotzaioahactsaviule Splc cub aperk ded ibm bed ft tbi*ag hits avabbis CAT NO 106 Proof Switch Retail S995 Add $125 shipping Send $150 catalog Michigan residents add 4% sales tax IMPROVE YOUR 1991 SWITCH OVER ej Proof Switch Positive Locking Prevents Arriving field dead batteries Accidental switching off before take-off Will vibrate apart causing loss radio Does require special mounts Works radios Ideal seaplanes completely water proof SEE YOUR LOCAL HOBBY DEALER unavailable locally send Bru Line Industries Inc 4.. PO Box 3786 Center Line MI 48015 WASHINGTON S AMA BASE. $ An50 1 per couple per night Check day Minimum stay 2 nights Free Parking Cars Free Full Breakfasts Free Merropass Sat Sun Free Harrington Hawk Cafeteria avA 11th & E Streets NW Washington DC 20004G9 0-424-8532 628 8140T70 omm December 1989 41 Em 0AMA MEMBER RATE Tax no included A Radio South Batteries 500 ma Pack 48V Futaba conn 800 ma Pack 48V Futaba conn 1200 ma Pack 48V Futaba conn TX batt Futaba G-Series PCM 1300 1550 2200 2475 2400 2700 2995 RADIO SOUTH __ AUTHORIZED SERVICE CENTER Call Tony Stiliman Ken Dudley custom work competition needs stock complete hobby line specializing competition accessoriesall discounted prices bS ______ __ FREQUENCY CONVERSIONS _______9jgCY~ Frequency Comnnuee Approved @0__ stock Futaba JR radios Featuring fast service byOAYS engines parts qualified people thePhHatori headers pipes latest equipment Including aGh$tIWe Repair Heli Sets Gyros SPECTRUM ANA YZER Al Orders COD VISA MC American Express OPEN 8-5 CST P rices subject change notice 9003 N Davis Hwy Pensacola FL 32514 904 478-6745 As propeller blade passes through given point disc also exerts thrust torque forces cause pressure fluc tuation As air pressure displacement pressure fluctuation propagates sound known thrust torque noise point propeller disc pres sure fluctuates time blade passes total pressure disturbance sum disturbances caused thrust torque thickness certain other effects disturbances vary strength travels its own preferred direction combined effect pressure fluc tuations perceived propeller noise pressure amplitudes of components propeller noise depen dent relative amounts thrust torque well propeller tip speed itself proportional product rotational speed propeller di ameter Thrust torque noise generally significant sources propeller sound should noted ever since thickness noise consider ably affected tip speed thrust torque noise its relative impor tance will increase increasing rota tional speed Any attempt make sense propel ler noise problem complicated overlapping often interdependent ef fects acoustic sources example Figure 4 shows propeller blade lift does point exactly thrust direc tion means blade lift contrib utes both thrust torque hence both thrust torque noise Additionally noise various sources radiates away propeller overlapping pat terns difficult distinguish reduce propeller noise must dis cover dominant noise mechanism work can directed toward lessening source cant done some knowledge intricate makeup pro peller noise Its important understand its interplay factors associ ated aircraft operationengine per formance aircraft drag flight speed rpm propeller diameter pitch etcwhich pro duces noise perceived human ear Conducting scientific study such truly complicated system ridden variables difficult structured building block approach being used North Carolina State University laboratory data correlated both flight test data classical mathematical propel ler theory Although quite time-consuming process does provide direct path final answers research findings suggest propel ler noise may dominant acoustic source model aircraft may deed possible diminish leading Continued page 156 TO ORDER CALL 1406 265-4828 IT-i TRANSMITTER TRAY * Recommended especially handicaps beginners.experienced pilots love also * Pays itself times over airplanes saved l With set Gimbal Extenders $350 Postage & Handling Make Flying Breeze~ BJ ENTERPRISES 1100 Center Havre Montana 59501 42 Model Aviation GATOR RIC PRODUCTS DELUX ALL BALSA KIT An new Tiger Tail 120 four strokes piped 60 two strokes beautiful performer competition just showing offI balsa kit machined wood parts complete lsardware package includes plug-in djustable stab parts new wing mounts Wing Span- 72 inWing Ara 860 sq Complete Delux KitSI 5995 TRANSMITTER CASE An inexpensive rugged molded case protect expensive transmitter both two stick single stick transmitters Black leather grain aluminum trim locking 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smother fire towel rag blanket Cub Yellow engine cowling first RC model powered Cox 09 began turn first orange brown able smother fire wrap ping rag around front model Have safe month Keytwo/Randoiph Continued page 30 der everything place range check equipmentand its time fly Flying has wide performance en velope compared Paskey Keytwo basically quite gentle flier Whether upright inverted stall shows abso lutely no tendency snap fact model balanced correctly its very diffi cult make snap snaps bag move center-of-gravity aft about /2 increase elevator throw rate /16 up down movement trailing edge aile rons about right comfortable flying Landings can made nose-high slow full aileron control way touch down problem knife-edge flight first airplane persistently climbed half-loop until learned nose stayed up just little rudder Once Id mastered technique knife-edge loops included Keytwos repertoire tricks what did Eddie Williams have say about latest re-creation see youve built another Paskey said unsung maestro drunken pilot routine Its about time Play again Eddie Radio Technique/Myers Continued page 34 Failsafe Flight System small 15 sq light less ounce inexpensive has very low operating current 70 mA works no doubt nine-volt transistor radio batteries expensive about $250 Duracells live will last long time some chance will get care less let run down some critical time unit meets its claims follow admonition use fresh batteries check servo speed during preflight inspection careless youll probably crash some other reason anyway Failsafe Flight System @ $3995 list T&D Flight Systems PO Box 1782 Staten Island NY 10314 additional information call Alex Kronfeld l-7t8/984-9121 Propeller Noise Continued page 42 cause poor community relations Much cure will depend upon education Modelers need understand nature problem order properly utilize solu tions article has introduced propel ler noise problem provided some neces sary background Subsequent articles will explain test results greater detail describe what modeler can achieve better aircraft performance less noise RC Soaring/Blakeslee Continued page 49 down hes hoping arrange factur ers demonstrations during meet would flying demos followed show-andtell sessions guys like Byron Bruce Combat Models Marty Silberstein Steve Peacock Cliff Hangar Models Brian Laird Paul Masura Slope Scale Models Other Id imagine itll much like fabulously suc cessful Richland Scale Slope Fun Flyie fly want long have pin Info available writing Charley SSN 2601 E 19th 51 #29 Signal Hill CA 90804 Better call him 1-213/494-3712 1990 Soaring contests Ray Hayes Vice Presi dent LSF wrote remind us now time plan next years big contests Spe cifically Ray talking about every-evenyear LSF Regionals annual NSS Soar-Ins put go-ahead clubs around coun try Theyre bit expensive Ray hoping Continue tradition awarding beautiful LSF plaques LSF Regionals Theyre worth winning Ray also hoping three super con tests NSS Masters LSF Nationals AMA Nats can spread around country 1990 contests West Coast 89 Ray afraid guys east Kansas beginning feel left out youd like info LSF Regionals check Ray 69598 Brookhill Dr Romeo MI 48065 phone 1-313/ 752-6163 NSS Soar-Ins have handled Marshall Long past few years assume youre 90 Marshall Marshalls address 824 Garden Meadow Universal City TX 78148 worry East Coasters hear Nats will Lawrenceville IL 90 RC Aerobatics/Van Putte Continued page 51 aerodynamic center segment wing Youll note root segment tip another segment Figure 4 shows geometric technique solu tion Remember aerodynamic center panel 25% point mean aerody namic chord panel Once youve determined aerodynamic cen ter panel must calculate area panel using Equation 2 measure distance convenient line aerody namic centers panels Figure 4 shows con venient reference line distance re spective aerodynamic centers distance back reference line aerodynamic center wing located determined Equation 3 mean aerodynamic chord complete wing calculated individual values shown Equation 4 looks just like equa tion determining distance wing aero dynamic center doesnt should since 156 Model Aviation
Edition: Model Aviation - 1989/12
Page Numbers: 36, 37, 38, 39, 40, 41, 42, 156
D Heathcoat R Nagel Model Propeller NOISEc first series articles describes in-depth research spon sored AMA conducted North Carolina State Univer sity severity sources reduction propeller noise findings some unprecedented could have ma jor impact model airplane_flying community ADVANCES model aviation over past decade have spurred tremendous growth hobby year thousands people across US becoming ac tive participants weekend sessions local flying field greatest influx newcomers sport naturally occurs near large cities population con centrated flying sites tend lo cated suburban areas allows easy access fliers also subjects uninterested neighbor characteris tic whine model aircraft surprisingly greatest activity model field occurs weekends weekday evenings just peo ple living nearby home expecting chance relax involved sport well aware bitter confrontation scenario sometimes provokes ten modelers lose battle begin search another suitable flying site Losing established flying site hav ing search new can frustrat ing costly experience Ultimately has negative effect organization continued growth sport Its clear continuously relocating flying fields farther farther away populated ar eas isnt answer rate rural de velopment flying site relocation will lit tle postpone inevitable return problem solution instead develop model aircraft operate lower sound levels quite evident commonly accepted model aircraft noise generated propulsion system casual observer obvious sources intake combustion exhaust noise generated power plantand airframe noise re sulting its characteristic vibration However propeller too impor tant source noiseone misunder stood consequently overlooked fact acoustic research full-scale aircraft indicates propeller noise dominates over other sources sound illustrated following quote Journal Aircraft has well known years propellerdriven aircraft propeller primary source noise observation may 36 Model Aviation gu hold true model aircraft well effort better understand model pro Di recti Ro tat peller noise establish guidelines ultimately will lead quieter model aircraft AMA sponsored research pro Table 1Selected Flight Test Data Prop Velocity RPM QASPI kmphdBA Group 1 11 x5180160001110 9x7519516400960 9x719016250934 Group 2 10x615013500878 11 x614312000990 Group 3 10x712011000840 9x7512011250810 10x612010800764 Group 4 11 x 5908500925 9 x 7908700830 gram conducted North Carolina State Uni versity principal investigators include Dr Robert T Nagel associate professor nearly 15 years research experience aeroacoustics Robert Vess aero space engineer six years experience coordinator NC State University aerospace laboratories 18 years activ ity Radio Control including Pattern Hel icopter fun fly competition David M Heathcoat received bachelors degree physics NC State University 1986 participated propeller noise research masters degree thesis article first series will describe tests performed explain results make recommendations toward reducing model aircraft noise Im proving noise problem means averting loss flying sites will depend largely having knowledgeable fliers Due technical nature mate rial will precede discussion test program details brief explanation basic propeller theory Introducing some important aspects propeller per formance section will lead better understanding both current study propellers general Since formulas scientific jargon tend limit interest type article effort has made avoid use Basic Propeller Theory order aircraft move through air propelling force must work propeller essentially small rotating wing produces required thrust speed aircraft level flight deter mined relating thrust available power plant total aircraft drag Note both forces vary signifi cantly airspeed depicted typi cal aircraft Figure 1 example moving left right along horizontal axis Figure 1 represents increasing airspeed notes aircraft drag increases eventually exceeds thrust Point 1 figure represents case air craft accelerating since thrust pro duced propeller much greater aircraft drag Conversely aircraft operating point 2 predominance drag over thrust causes decelerate cases airspeed will stabi lize point 3 thrust drag equal Since engine example full throttle point 3 represents maximum tainable airspeed aircraft/engine/ propeller combination level flight re duction power below full throttle ef fectively shifts thrust curve downward resulting reduction maximum airspeed see dashed curve Figure 1 Similarly anything can done pro duce thrust less drag will shift December 1989 37 Figu curves allowing greater flight speeds Figure 1 has shown thrust produced power plant actually decreases yond certain threshold airspeed phenomenon results changes air flow around propeller high airspeeds As propeller rotates flow approaches its leading edge speed depends rotational speed rpm engine However forward movement aircraft creates additional flow ap proaches propeller disc speed equal forces acting propeller best explained examining thin slice blade such shown cross section Figure 2 Once again explanation simplified differentiating effects due blade rotation caused forward speed Figure 3 depicts flow action sec tion typical propeller blade due its ro tation alone would case engine being run model re strained flow approaches prop angle dictated blade pitch Just wing produces lift drag certain gle attack propeller produces sim ilar forces depend engine rpm shape blade airfoil lift force example acts along axis rotation force axial direction termed thrust Similarly drag force acts plane rotation pro peller resists its rotation defined torque Figure 4 illustrates condition after aircraft released acquires addi tional flow field its forward move ment simple way graphically depict combination two flows use special arrows called vectors flow represented single vector relative speed flow given length its vector flow direction rep resented direction vec tor pointing two propeller flow vectors arranged nose-to-tail Fig ure 4 rotation forward flight other vector completes triangle represents flow field resulting combination Notice speed direction resultant vector can al tered changing length speed original vectors Therefore flow around propeller indeed does depend both engine rpm forward flight speed flow vectors combine shown Figure 4 forces acting propel ler diminish Hence blade airfoil angle attack Figure 4 decreased com pared Figure 3 addition since lift drag forces measured respect altered flow angle slanted away axis rotation propel ler Therefore net thrust decreased further since lift force acting pre cisely thrust direction misdirection lift also shown Figure 4 reality thrust lost due slanting lift force becomes ad ditional torque load engine must overcome effectively demonstrates propeller performance very different flight ground better understanding engine turns propeller under varying load conditions can gained referring Fig ure 5 Assume drag forces acting point blade propeller example added together sum found lso assume net drag force determined act ing through point 12 center crankshaft product lb 12-in distance represents 6 in-lb b torque load blade propeller Since two blades net torque load power plant must produce order turn blades constant rotational speed 12 38 Model Aviation 0 flight velocity Figure 2 illustrates relative directions simultaneous flows respect propeller ro tating counterclockwise in-lb 1 ft-lb engine capable producing torque under condi tions rotational speed will increase cant produce enough torque rotational speed will achieved power available engine simply rotational speed multiplied amount torque can applied propeller given rpm example engine can produce 33 ft-lb torque 10000 rpm 16667 rev/sec power rotational speed 550 ft lb/sec example chosen order put value power recogniz able units Since horsepower 1 hp equivalent 550 ft-lb/sec engine producing exactly horsepower under operating conditions Figure 6 illustrates way horsepower output torque typical model engine vary rotational speed Most engines available modelers have curves resemble example actual magnitude power torque rotational speed depends physi cal design particular engine As mentioned above power required turn propeller product torque rotational speed power produced propeller proportional product thrust forward speed ratio power produced propeller required turn known propeller efficiency An efficient propeller capable producing given amount thrust using less power inefficient Equivalently efficient propeller can produce greater thrust therefore greater ward speed using same engine power Rather being fixed value efficien cy depends physical design opera ting rpm flight speed specific pro peller therefore improper categori cally call prop efficient other unless advantage holds true rotational forward speeds Propeller ef ficiency plays major role increasing air craft performance reducing noise Basic Noise Definitions Sound waves simply minute pressure fluctuations propagate air characterized two parameters frequency amplitude Frequency refers number pressure pulses pres sure fluctuations occur sec ond perceived ear pitch Like higher notes piano keyboard higher frequencies actually sound higher pitched Pressure amplitude measure size acoustical disturbance corresponds loudness sound simple tone characterized single frequency single amplitude Complex sounds composed different fre quencies Pressure amplitude measured deci bels dB measured referred sound pressure level SPL Continued page 40 Order direct Add $1500 shipping Use VISA MC check money order COD GOLIDW AGE MODELS RO box 807 Ienn Vcilleq CA 95946 916 432-2928 B&P Associates Gives Total FlIgbt Line FREEDOM battery needs call write B&P Associates PO Box 22054 Waco TX 76702-2054 817662-5587 new electric starter battery pack cuts cord has always tied starter power panel Discover freedom being able start plane wherever added safety less wire get caught prop charge hefty 4 Amp/hour pack will take through weekend flying power enough spare dont stop have Ni-Cads virtually size imaginable cut experimenter free design whatever ii takes make yours best setup field December 1989 39 h C, qusrter scale com plete deluxe kit features exact scale outlines balsa plywo, onstruction light epoxy cowl wheel pants selected wood complete hardware flying wires full cockpit details 3-views photos decals extensive instruction manual 20 cu ne lighL upoxy glass uuiage cowl wheel pants complete hardware selected wood decals 3-views cu engliw epoxy glass fudy owl wheel pants light foam wing cores con test wood complete hardware decals Satisfaction Guaranteed1 EA~ HINELZ SH-710 Pkg 24-52 95 THE HIGH-TECH HINGE DESIGNED FOR THE CYANOACRYLATE AGE Easier install other hinge No gouging picking messy epoxies Simply cut single knife slot hinge slide hinges place apply few drops favorite CA glue youre donel SUPER FAST SUPER EASY SUPER STRONG SIG MFG CO INC401-7 So Front St.Montezuma IA 50171 23-5154 LANDER INDUST 1005 19TH ST CT HAVRE MONTANA 59501 406265-6529 PRICES INCLUDE FREIGHT CANADIAN ORDERS ADD 25% ViSA Pwtakeet SUpeJL Po4 PO4JIWkQ 40. FREE CATALOG Ti4ewaiwt I4otoluj eIdWIIAi*e 392SC SE 13th Court Scala FImna 32571 904 6943531 sound pressure level corresponds dis crete frequency range frequencies overall sound pressure level' OASPL also measured decibels measure sound obtained adding SPLs frequency spectrum decibel reflecting fact human ear perceives very wide range sound pressure based loga rithmic scale rather linear compresses sonic data ease inter pretation Still another measure noise sound power level PWL based quantity acoustical power pro duced given source rather pres sure amplitude given location Since sound power level also measured dB its important keep track whether mea surements given units PWLs SPLs Sounds certain frequency ranges perceived being louder sounds other frequencies Weighted sound level curves have developed take fact account weighted scale used almost industrial commu nity noise standards US Sound lev els measured according scale ex pressed units called dBA significance relative contribu tions various components noise cannot appreciated general understanding manner sound levels combined two equal sound pressure levels SPLs added together combined sound level will 6dB higher orig inal value Adding together two equal sound power levels PWLs produces level 3 dB higher phenome non result logarithmic nature dB scale means levels separated few dB fact very different ab solute values acoustic power level PWL expressed dB adding two powers differ 10 dB pro duces no significant increase power yond higher two Consider ex ample adding 80 dB 90 dB powers dB1 B dB2 B total dBtotai given follow ing formula dBtotai og[l0dB/o 2/1O] dB Sound pressure levels SPLs behave similar fashion two SPLs com bined variance between acoustic levels addition becomes insignificant about 20 dB adds SPLs 80 dB 100 dB result 1008 dB practical implications will become clear realizes model aircraft noise derives several sourcesthe engine airframe propellerand propeller noise itself blends several components Often reducing lesser noise source fails produce noticeably quieter aircraft Consider example aircraft 80 dB engine noise 90 dB propeller noise As have seen formula given above able completely elim inate engine noise lesser source resulting acoustic power would discernibly reduced hypothetical example subtracting 80 dB engine noise acoustical power 904 dB total noise power slightly lowers total output about 90 dBnot significant change achieve meaningful reduction model air craft sound necessary reduce dominant source noise Justification Propeller Noise Reduction fundamental objective research project has verify sound pro duced propeller fact domi nant noise mechanism model aviation project assumes reasonable offthe-shelf muffler used aircraft since absence such use use poor muffler engine sounds likely dominate noise signature Measure ments acquired during different phases research provide several pieces evi dence indicate propeller noise dominates over produced properly muffled engine Flight test data provides first bit ev idence An instrumented aircraft flown fixed height over microphone peak OASPL measured dBA flight speed rpm throttle setting also recorded data compared obtained same propellers driven electric motor wind tunnel laboratory thereby eliminating power plant significant source noise Although flight velocities precisely duplicated lab several cases offer reasonable basis compari son such case SPL bladepassing frequency lab 78 dB simulated flight velocity 100 kmph ki lometers per hour microphone dis tance corrected same distance used flight tests flight test 120 kmph resulted OASPL 764 dBA OASPL includes frequencies spectrum whereas lab data ob tained blade-passing frequency Since engine airframe noise absent lab data would have ex pected flight test noise louder results support inference engine airframe noise did reach significant level flight tests done would have tended dominate rais ing OASPL above SPL measured lab fact propeller noise alone approximately equal total noise mea sured flight Table 1 shows data selected tests operating conditions nearly identical Group 1 contains propel lers same manufacturer tal variation mean rpm less 1% total variation flight velocity approximately 5% Groups 2 3 in40 Model Aviation RIG SKY CRADLES FIELD BOX MODEL$1595 BENCH MODEL$1995 FLOOR MODEL$2395 CEILING HANGERS SMALL20-40 .$995 MEDIUM 40- 60 95 LARGE 50-BO. $1195 nvur HAIFt FITS ALL PICKUPS . 5 cluded propellers two different manu facturers Group 4 propellers sin gle manufacturer Since flight speed rpm nearly same group aircraft always level flight measure ment point thrust produced likewise nearly same data groups Table 1 Clearly engine airframe having almost identically groups can therefore inferred observed large variations OASPL between cases within group rather being caused engine airframe noise result dif ferences sound levels among propellers Further assuming situation en gine noise closely approximated level propeller noise completely eliminating engine noise would effect noise re duction 6 dBa value ex ceeded differences noted among props particular group final piece evidence yielded data obtained two different mufflers during flight tests stock muffler re placed high-quality state-of-the-art muf fler data recorded two different flight speeds using same propeller 120 kmph difference OASPL measured 02 dBA 90 kmph difference 03 dBA Such ex tremely small variance suggests given flight speed advanced muffler no effect total noise output ever full throttle engine performed better upgraded muffler ad ditional rpm permitted latter creased noise levels improved engine performance advanced muffler did significantly impact noise level long flight speed remained constant test results clearly establish pro peller dominant source model air craft noise remainder discus sion will assume case Propeller Noise Sources sound produced model propel ler compounded several elements important include noise due thrust torque noise thickness noise referred discrete fre quency noise sources because sound produced occurs bladepassing frequency its harmonics blade-passing frequency rate blade passes given point propel ler disc product number blades rotational speed rev/sec understand noise mecha nisms operate imagine fixed point rotational disc propeller time blade near point air pressure its ordinary value Air pres sure changes blade passes through pushes air aside amount dis placed air depending thickness blade noise produced periodic displacement air known thickness noise Continued page 42 VJO ds best Sel 09 Spak osen ByTan Odginds TItG Mfg ml AM Aircraft Saqiply its outstenhg ruimhity Comp e e s ng e cyl nder system nclud ng ho e couped spark advance kt spark gead25 p ug ba e y pack charger 900 sh elded Much kmger 1gm hIs Easy haid sterts-no kickback 1AUO-12000 RPM rubble ii 0% power few strokers oni nutubbmi mviii Lower pricad fuels no okra neededMqleeduul9Fphagcovw FormumyuapaesI0&p2ft4strokeslegieudtwlsctulrs Klotzaioahactsaviule Splc cub aperk ded ibm bed ft tbi*ag hits avabbis CAT NO 106 Proof Switch Retail S995 Add $125 shipping Send $150 catalog Michigan residents add 4% sales tax IMPROVE YOUR 1991 SWITCH OVER ej Proof Switch Positive Locking Prevents Arriving field dead batteries Accidental switching off before take-off Will vibrate apart causing loss radio Does require special mounts Works radios Ideal seaplanes completely water proof SEE YOUR LOCAL HOBBY DEALER unavailable locally send Bru Line Industries Inc 4.. PO Box 3786 Center Line MI 48015 WASHINGTON S AMA BASE. $ An50 1 per couple per night Check day Minimum stay 2 nights Free Parking Cars Free Full Breakfasts Free Merropass Sat Sun Free Harrington Hawk Cafeteria avA 11th & E Streets NW Washington DC 20004G9 0-424-8532 628 8140T70 omm December 1989 41 Em 0AMA MEMBER RATE Tax no included A Radio South Batteries 500 ma Pack 48V Futaba conn 800 ma Pack 48V Futaba conn 1200 ma Pack 48V Futaba conn TX batt Futaba G-Series PCM 1300 1550 2200 2475 2400 2700 2995 RADIO SOUTH __ AUTHORIZED SERVICE CENTER Call Tony Stiliman Ken Dudley custom work competition needs stock complete hobby line specializing competition accessoriesall discounted prices bS ______ __ FREQUENCY CONVERSIONS _______9jgCY~ Frequency Comnnuee Approved @0__ stock Futaba JR radios Featuring fast service byOAYS engines parts qualified people thePhHatori headers pipes latest equipment Including aGh$tIWe Repair Heli Sets Gyros SPECTRUM ANA YZER Al Orders COD VISA MC American Express OPEN 8-5 CST P rices subject change notice 9003 N Davis Hwy Pensacola FL 32514 904 478-6745 As propeller blade passes through given point disc also exerts thrust torque forces cause pressure fluc tuation As air pressure displacement pressure fluctuation propagates sound known thrust torque noise point propeller disc pres sure fluctuates time blade passes total pressure disturbance sum disturbances caused thrust torque thickness certain other effects disturbances vary strength travels its own preferred direction combined effect pressure fluc tuations perceived propeller noise pressure amplitudes of components propeller noise depen dent relative amounts thrust torque well propeller tip speed itself proportional product rotational speed propeller di ameter Thrust torque noise generally significant sources propeller sound should noted ever since thickness noise consider ably affected tip speed thrust torque noise its relative impor tance will increase increasing rota tional speed Any attempt make sense propel ler noise problem complicated overlapping often interdependent ef fects acoustic sources example Figure 4 shows propeller blade lift does point exactly thrust direc tion means blade lift contrib utes both thrust torque hence both thrust torque noise Additionally noise various sources radiates away propeller overlapping pat terns difficult distinguish reduce propeller noise must dis cover dominant noise mechanism work can directed toward lessening source cant done some knowledge intricate makeup pro peller noise Its important understand its interplay factors associ ated aircraft operationengine per formance aircraft drag flight speed rpm propeller diameter pitch etcwhich pro duces noise perceived human ear Conducting scientific study such truly complicated system ridden variables difficult structured building block approach being used North Carolina State University laboratory data correlated both flight test data classical mathematical propel ler theory Although quite time-consuming process does provide direct path final answers research findings suggest propel ler noise may dominant acoustic source model aircraft may deed possible diminish leading Continued page 156 TO ORDER CALL 1406 265-4828 IT-i TRANSMITTER TRAY * Recommended especially handicaps beginners.experienced pilots love also * Pays itself times over airplanes saved l With set Gimbal Extenders $350 Postage & Handling Make Flying Breeze~ BJ ENTERPRISES 1100 Center Havre Montana 59501 42 Model Aviation GATOR RIC PRODUCTS DELUX ALL BALSA KIT An new Tiger Tail 120 four strokes piped 60 two strokes beautiful performer competition just showing offI balsa kit machined wood parts complete lsardware package includes plug-in djustable stab parts new wing mounts Wing Span- 72 inWing Ara 860 sq Complete Delux KitSI 5995 TRANSMITTER CASE An inexpensive rugged molded case protect expensive transmitter both two stick single stick transmitters Black leather grain aluminum trim locking clasp SI 995 MV-I TYPHOON New F3A competition Big beautiful flyer balsa construction plug-in wings 120 four stroke 60 two stroke power Plans-two sheets S 1495 Fiberglass cowl Si 595 Clear butyrate canopy. 5 995 OTHER PLANS Tiger Tail 4S-two sheets 120 four strokesS 1495 TAR baby 120 four strokes51195 Alley Kat 40 size trainer sportS 895 Gator Flea 40 size sport5 895 Bobcat 40 size sportS 895 feather Ilte glass cloth 7 ozsq yd est weave Fastest Filling test Finished Weight Big 3 Sq Yard Pkg Oetailed Instructions- $895 Include $2 SOlItem UPS esidents Add 6% Sales Tax GATOR RIC PRODUCTS 3713 Pompano Dr acola FL 32514 4768639 Letters Editor Continued page 12 Ken opened hobby shop Burk & Company Department Store after World War II worked him full-time year until started college After worked part-time until completing college Milton H Fanning Nashville TN Safety/Preston Continued page 22 some MonoKote repairs moral tale wise keep small extinguisher field box As alter native may possible smother fire towel rag blanket Cub Yellow engine cowling first RC model powered Cox 09 began turn first orange brown able smother fire wrap ping rag around front model Have safe month Keytwo/Randoiph Continued page 30 der everything place range check equipmentand its time fly Flying has wide performance en velope compared Paskey Keytwo basically quite gentle flier Whether upright inverted stall shows abso lutely no tendency snap fact model balanced correctly its very diffi cult make snap snaps bag move center-of-gravity aft about /2 increase elevator throw rate /16 up down movement trailing edge aile rons about right comfortable flying Landings can made nose-high slow full aileron control way touch down problem knife-edge flight first airplane persistently climbed half-loop until learned nose stayed up just little rudder Once Id mastered technique knife-edge loops included Keytwos repertoire tricks what did Eddie Williams have say about latest re-creation see youve built another Paskey said unsung maestro drunken pilot routine Its about time Play again Eddie Radio Technique/Myers Continued page 34 Failsafe Flight System small 15 sq light less ounce inexpensive has very low operating current 70 mA works no doubt nine-volt transistor radio batteries expensive about $250 Duracells live will last long time some chance will get care less let run down some critical time unit meets its claims follow admonition use fresh batteries check servo speed during preflight inspection careless youll probably crash some other reason anyway Failsafe Flight System @ $3995 list T&D Flight Systems PO Box 1782 Staten Island NY 10314 additional information call Alex Kronfeld l-7t8/984-9121 Propeller Noise Continued page 42 cause poor community relations Much cure will depend upon education Modelers need understand nature problem order properly utilize solu tions article has introduced propel ler noise problem provided some neces sary background Subsequent articles will explain test results greater detail describe what modeler can achieve better aircraft performance less noise RC Soaring/Blakeslee Continued page 49 down hes hoping arrange factur ers demonstrations during meet would flying demos followed show-andtell sessions guys like Byron Bruce Combat Models Marty Silberstein Steve Peacock Cliff Hangar Models Brian Laird Paul Masura Slope Scale Models Other Id imagine itll much like fabulously suc cessful Richland Scale Slope Fun Flyie fly want long have pin Info available writing Charley SSN 2601 E 19th 51 #29 Signal Hill CA 90804 Better call him 1-213/494-3712 1990 Soaring contests Ray Hayes Vice Presi dent LSF wrote remind us now time plan next years big contests Spe cifically Ray talking about every-evenyear LSF Regionals annual NSS Soar-Ins put go-ahead clubs around coun try Theyre bit expensive Ray hoping Continue tradition awarding beautiful LSF plaques LSF Regionals Theyre worth winning Ray also hoping three super con tests NSS Masters LSF Nationals AMA Nats can spread around country 1990 contests West Coast 89 Ray afraid guys east Kansas beginning feel left out youd like info LSF Regionals check Ray 69598 Brookhill Dr Romeo MI 48065 phone 1-313/ 752-6163 NSS Soar-Ins have handled Marshall Long past few years assume youre 90 Marshall Marshalls address 824 Garden Meadow Universal City TX 78148 worry East Coasters hear Nats will Lawrenceville IL 90 RC Aerobatics/Van Putte Continued page 51 aerodynamic center segment wing Youll note root segment tip another segment Figure 4 shows geometric technique solu tion Remember aerodynamic center panel 25% point mean aerody namic chord panel Once youve determined aerodynamic cen ter panel must calculate area panel using Equation 2 measure distance convenient line aerody namic centers panels Figure 4 shows con venient reference line distance re spective aerodynamic centers distance back reference line aerodynamic center wing located determined Equation 3 mean aerodynamic chord complete wing calculated individual values shown Equation 4 looks just like equa tion determining distance wing aero dynamic center doesnt should since 156 Model Aviation
Edition: Model Aviation - 1989/12
Page Numbers: 36, 37, 38, 39, 40, 41, 42, 156
D Heathcoat R Nagel Model Propeller NOISEc first series articles describes in-depth research spon sored AMA conducted North Carolina State Univer sity severity sources reduction propeller noise findings some unprecedented could have ma jor impact model airplane_flying community ADVANCES model aviation over past decade have spurred tremendous growth hobby year thousands people across US becoming ac tive participants weekend sessions local flying field greatest influx newcomers sport naturally occurs near large cities population con centrated flying sites tend lo cated suburban areas allows easy access fliers also subjects uninterested neighbor characteris tic whine model aircraft surprisingly greatest activity model field occurs weekends weekday evenings just peo ple living nearby home expecting chance relax involved sport well aware bitter confrontation scenario sometimes provokes ten modelers lose battle begin search another suitable flying site Losing established flying site hav ing search new can frustrat ing costly experience Ultimately has negative effect organization continued growth sport Its clear continuously relocating flying fields farther farther away populated ar eas isnt answer rate rural de velopment flying site relocation will lit tle postpone inevitable return problem solution instead develop model aircraft operate lower sound levels quite evident commonly accepted model aircraft noise generated propulsion system casual observer obvious sources intake combustion exhaust noise generated power plantand airframe noise re sulting its characteristic vibration However propeller too impor tant source noiseone misunder stood consequently overlooked fact acoustic research full-scale aircraft indicates propeller noise dominates over other sources sound illustrated following quote Journal Aircraft has well known years propellerdriven aircraft propeller primary source noise observation may 36 Model Aviation gu hold true model aircraft well effort better understand model pro Di recti Ro tat peller noise establish guidelines ultimately will lead quieter model aircraft AMA sponsored research pro Table 1Selected Flight Test Data Prop Velocity RPM QASPI kmphdBA Group 1 11 x5180160001110 9x7519516400960 9x719016250934 Group 2 10x615013500878 11 x614312000990 Group 3 10x712011000840 9x7512011250810 10x612010800764 Group 4 11 x 5908500925 9 x 7908700830 gram conducted North Carolina State Uni versity principal investigators include Dr Robert T Nagel associate professor nearly 15 years research experience aeroacoustics Robert Vess aero space engineer six years experience coordinator NC State University aerospace laboratories 18 years activ ity Radio Control including Pattern Hel icopter fun fly competition David M Heathcoat received bachelors degree physics NC State University 1986 participated propeller noise research masters degree thesis article first series will describe tests performed explain results make recommendations toward reducing model aircraft noise Im proving noise problem means averting loss flying sites will depend largely having knowledgeable fliers Due technical nature mate rial will precede discussion test program details brief explanation basic propeller theory Introducing some important aspects propeller per formance section will lead better understanding both current study propellers general Since formulas scientific jargon tend limit interest type article effort has made avoid use Basic Propeller Theory order aircraft move through air propelling force must work propeller essentially small rotating wing produces required thrust speed aircraft level flight deter mined relating thrust available power plant total aircraft drag Note both forces vary signifi cantly airspeed depicted typi cal aircraft Figure 1 example moving left right along horizontal axis Figure 1 represents increasing airspeed notes aircraft drag increases eventually exceeds thrust Point 1 figure represents case air craft accelerating since thrust pro duced propeller much greater aircraft drag Conversely aircraft operating point 2 predominance drag over thrust causes decelerate cases airspeed will stabi lize point 3 thrust drag equal Since engine example full throttle point 3 represents maximum tainable airspeed aircraft/engine/ propeller combination level flight re duction power below full throttle ef fectively shifts thrust curve downward resulting reduction maximum airspeed see dashed curve Figure 1 Similarly anything can done pro duce thrust less drag will shift December 1989 37 Figu curves allowing greater flight speeds Figure 1 has shown thrust produced power plant actually decreases yond certain threshold airspeed phenomenon results changes air flow around propeller high airspeeds As propeller rotates flow approaches its leading edge speed depends rotational speed rpm engine However forward movement aircraft creates additional flow ap proaches propeller disc speed equal forces acting propeller best explained examining thin slice blade such shown cross section Figure 2 Once again explanation simplified differentiating effects due blade rotation caused forward speed Figure 3 depicts flow action sec tion typical propeller blade due its ro tation alone would case engine being run model re strained flow approaches prop angle dictated blade pitch Just wing produces lift drag certain gle attack propeller produces sim ilar forces depend engine rpm shape blade airfoil lift force example acts along axis rotation force axial direction termed thrust Similarly drag force acts plane rotation pro peller resists its rotation defined torque Figure 4 illustrates condition after aircraft released acquires addi tional flow field its forward move ment simple way graphically depict combination two flows use special arrows called vectors flow represented single vector relative speed flow given length its vector flow direction rep resented direction vec tor pointing two propeller flow vectors arranged nose-to-tail Fig ure 4 rotation forward flight other vector completes triangle represents flow field resulting combination Notice speed direction resultant vector can al tered changing length speed original vectors Therefore flow around propeller indeed does depend both engine rpm forward flight speed flow vectors combine shown Figure 4 forces acting propel ler diminish Hence blade airfoil angle attack Figure 4 decreased com pared Figure 3 addition since lift drag forces measured respect altered flow angle slanted away axis rotation propel ler Therefore net thrust decreased further since lift force acting pre cisely thrust direction misdirection lift also shown Figure 4 reality thrust lost due slanting lift force becomes ad ditional torque load engine must overcome effectively demonstrates propeller performance very different flight ground better understanding engine turns propeller under varying load conditions can gained referring Fig ure 5 Assume drag forces acting point blade propeller example added together sum found lso assume net drag force determined act ing through point 12 center crankshaft product lb 12-in distance represents 6 in-lb b torque load blade propeller Since two blades net torque load power plant must produce order turn blades constant rotational speed 12 38 Model Aviation 0 flight velocity Figure 2 illustrates relative directions simultaneous flows respect propeller ro tating counterclockwise in-lb 1 ft-lb engine capable producing torque under condi tions rotational speed will increase cant produce enough torque rotational speed will achieved power available engine simply rotational speed multiplied amount torque can applied propeller given rpm example engine can produce 33 ft-lb torque 10000 rpm 16667 rev/sec power rotational speed 550 ft lb/sec example chosen order put value power recogniz able units Since horsepower 1 hp equivalent 550 ft-lb/sec engine producing exactly horsepower under operating conditions Figure 6 illustrates way horsepower output torque typical model engine vary rotational speed Most engines available modelers have curves resemble example actual magnitude power torque rotational speed depends physi cal design particular engine As mentioned above power required turn propeller product torque rotational speed power produced propeller proportional product thrust forward speed ratio power produced propeller required turn known propeller efficiency An efficient propeller capable producing given amount thrust using less power inefficient Equivalently efficient propeller can produce greater thrust therefore greater ward speed using same engine power Rather being fixed value efficien cy depends physical design opera ting rpm flight speed specific pro peller therefore improper categori cally call prop efficient other unless advantage holds true rotational forward speeds Propeller ef ficiency plays major role increasing air craft performance reducing noise Basic Noise Definitions Sound waves simply minute pressure fluctuations propagate air characterized two parameters frequency amplitude Frequency refers number pressure pulses pres sure fluctuations occur sec ond perceived ear pitch Like higher notes piano keyboard higher frequencies actually sound higher pitched Pressure amplitude measure size acoustical disturbance corresponds loudness sound simple tone characterized single frequency single amplitude Complex sounds composed different fre quencies Pressure amplitude measured deci bels dB measured referred sound pressure level SPL Continued page 40 Order direct Add $1500 shipping Use VISA MC check money order COD GOLIDW AGE MODELS RO box 807 Ienn Vcilleq CA 95946 916 432-2928 B&P Associates Gives Total FlIgbt Line FREEDOM battery needs call write B&P Associates PO Box 22054 Waco TX 76702-2054 817662-5587 new electric starter battery pack cuts cord has always tied starter power panel Discover freedom being able start plane wherever added safety less wire get caught prop charge hefty 4 Amp/hour pack will take through weekend flying power enough spare dont stop have Ni-Cads virtually size imaginable cut experimenter free design whatever ii takes make yours best setup field December 1989 39 h C, qusrter scale com plete deluxe kit features exact scale outlines balsa plywo, onstruction light epoxy cowl wheel pants selected wood complete hardware flying wires full cockpit details 3-views photos decals extensive instruction manual 20 cu ne lighL upoxy glass uuiage cowl wheel pants complete hardware selected wood decals 3-views cu engliw epoxy glass fudy owl wheel pants light foam wing cores con test wood complete hardware decals Satisfaction Guaranteed1 EA~ HINELZ SH-710 Pkg 24-52 95 THE HIGH-TECH HINGE DESIGNED FOR THE CYANOACRYLATE AGE Easier install other hinge No gouging picking messy epoxies Simply cut single knife slot hinge slide hinges place apply few drops favorite CA glue youre donel SUPER FAST SUPER EASY SUPER STRONG SIG MFG CO INC401-7 So Front St.Montezuma IA 50171 23-5154 LANDER INDUST 1005 19TH ST CT HAVRE MONTANA 59501 406265-6529 PRICES INCLUDE FREIGHT CANADIAN ORDERS ADD 25% ViSA Pwtakeet SUpeJL Po4 PO4JIWkQ 40. FREE CATALOG Ti4ewaiwt I4otoluj eIdWIIAi*e 392SC SE 13th Court Scala FImna 32571 904 6943531 sound pressure level corresponds dis crete frequency range frequencies overall sound pressure level' OASPL also measured decibels measure sound obtained adding SPLs frequency spectrum decibel reflecting fact human ear perceives very wide range sound pressure based loga rithmic scale rather linear compresses sonic data ease inter pretation Still another measure noise sound power level PWL based quantity acoustical power pro duced given source rather pres sure amplitude given location Since sound power level also measured dB its important keep track whether mea surements given units PWLs SPLs Sounds certain frequency ranges perceived being louder sounds other frequencies Weighted sound level curves have developed take fact account weighted scale used almost industrial commu nity noise standards US Sound lev els measured according scale ex pressed units called dBA significance relative contribu tions various components noise cannot appreciated general understanding manner sound levels combined two equal sound pressure levels SPLs added together combined sound level will 6dB higher orig inal value Adding together two equal sound power levels PWLs produces level 3 dB higher phenome non result logarithmic nature dB scale means levels separated few dB fact very different ab solute values acoustic power level PWL expressed dB adding two powers differ 10 dB pro duces no significant increase power yond higher two Consider ex ample adding 80 dB 90 dB powers dB1 B dB2 B total dBtotai given follow ing formula dBtotai og[l0dB/o 2/1O] dB Sound pressure levels SPLs behave similar fashion two SPLs com bined variance between acoustic levels addition becomes insignificant about 20 dB adds SPLs 80 dB 100 dB result 1008 dB practical implications will become clear realizes model aircraft noise derives several sourcesthe engine airframe propellerand propeller noise itself blends several components Often reducing lesser noise source fails produce noticeably quieter aircraft Consider example aircraft 80 dB engine noise 90 dB propeller noise As have seen formula given above able completely elim inate engine noise lesser source resulting acoustic power would discernibly reduced hypothetical example subtracting 80 dB engine noise acoustical power 904 dB total noise power slightly lowers total output about 90 dBnot significant change achieve meaningful reduction model air craft sound necessary reduce dominant source noise Justification Propeller Noise Reduction fundamental objective research project has verify sound pro duced propeller fact domi nant noise mechanism model aviation project assumes reasonable offthe-shelf muffler used aircraft since absence such use use poor muffler engine sounds likely dominate noise signature Measure ments acquired during different phases research provide several pieces evi dence indicate propeller noise dominates over produced properly muffled engine Flight test data provides first bit ev idence An instrumented aircraft flown fixed height over microphone peak OASPL measured dBA flight speed rpm throttle setting also recorded data compared obtained same propellers driven electric motor wind tunnel laboratory thereby eliminating power plant significant source noise Although flight velocities precisely duplicated lab several cases offer reasonable basis compari son such case SPL bladepassing frequency lab 78 dB simulated flight velocity 100 kmph ki lometers per hour microphone dis tance corrected same distance used flight tests flight test 120 kmph resulted OASPL 764 dBA OASPL includes frequencies spectrum whereas lab data ob tained blade-passing frequency Since engine airframe noise absent lab data would have ex pected flight test noise louder results support inference engine airframe noise did reach significant level flight tests done would have tended dominate rais ing OASPL above SPL measured lab fact propeller noise alone approximately equal total noise mea sured flight Table 1 shows data selected tests operating conditions nearly identical Group 1 contains propel lers same manufacturer tal variation mean rpm less 1% total variation flight velocity approximately 5% Groups 2 3 in40 Model Aviation RIG SKY CRADLES FIELD BOX MODEL$1595 BENCH MODEL$1995 FLOOR MODEL$2395 CEILING HANGERS SMALL20-40 .$995 MEDIUM 40- 60 95 LARGE 50-BO. $1195 nvur HAIFt FITS ALL PICKUPS . 5 cluded propellers two different manu facturers Group 4 propellers sin gle manufacturer Since flight speed rpm nearly same group aircraft always level flight measure ment point thrust produced likewise nearly same data groups Table 1 Clearly engine airframe having almost identically groups can therefore inferred observed large variations OASPL between cases within group rather being caused engine airframe noise result dif ferences sound levels among propellers Further assuming situation en gine noise closely approximated level propeller noise completely eliminating engine noise would effect noise re duction 6 dBa value ex ceeded differences noted among props particular group final piece evidence yielded data obtained two different mufflers during flight tests stock muffler re placed high-quality state-of-the-art muf fler data recorded two different flight speeds using same propeller 120 kmph difference OASPL measured 02 dBA 90 kmph difference 03 dBA Such ex tremely small variance suggests given flight speed advanced muffler no effect total noise output ever full throttle engine performed better upgraded muffler ad ditional rpm permitted latter creased noise levels improved engine performance advanced muffler did significantly impact noise level long flight speed remained constant test results clearly establish pro peller dominant source model air craft noise remainder discus sion will assume case Propeller Noise Sources sound produced model propel ler compounded several elements important include noise due thrust torque noise thickness noise referred discrete fre quency noise sources because sound produced occurs bladepassing frequency its harmonics blade-passing frequency rate blade passes given point propel ler disc product number blades rotational speed rev/sec understand noise mecha nisms operate imagine fixed point rotational disc propeller time blade near point air pressure its ordinary value Air pres sure changes blade passes through pushes air aside amount dis placed air depending thickness blade noise produced periodic displacement air known thickness noise Continued page 42 VJO ds best Sel 09 Spak osen ByTan Odginds TItG Mfg ml AM Aircraft Saqiply its outstenhg ruimhity Comp e e s ng e cyl nder system nclud ng ho e couped spark advance kt spark gead25 p ug ba e y pack charger 900 sh elded Much kmger 1gm hIs Easy haid sterts-no kickback 1AUO-12000 RPM rubble ii 0% power few strokers oni nutubbmi mviii Lower pricad fuels no okra neededMqleeduul9Fphagcovw FormumyuapaesI0&p2ft4strokeslegieudtwlsctulrs Klotzaioahactsaviule Splc cub aperk ded ibm bed ft tbi*ag hits avabbis CAT NO 106 Proof Switch Retail S995 Add $125 shipping Send $150 catalog Michigan residents add 4% sales tax IMPROVE YOUR 1991 SWITCH OVER ej Proof Switch Positive Locking Prevents Arriving field dead batteries Accidental switching off before take-off Will vibrate apart causing loss radio Does require special mounts Works radios Ideal seaplanes completely water proof SEE YOUR LOCAL HOBBY DEALER unavailable locally send Bru Line Industries Inc 4.. PO Box 3786 Center Line MI 48015 WASHINGTON S AMA BASE. $ An50 1 per couple per night Check day Minimum stay 2 nights Free Parking Cars Free Full Breakfasts Free Merropass Sat Sun Free Harrington Hawk Cafeteria avA 11th & E Streets NW Washington DC 20004G9 0-424-8532 628 8140T70 omm December 1989 41 Em 0AMA MEMBER RATE Tax no included A Radio South Batteries 500 ma Pack 48V Futaba conn 800 ma Pack 48V Futaba conn 1200 ma Pack 48V Futaba conn TX batt Futaba G-Series PCM 1300 1550 2200 2475 2400 2700 2995 RADIO SOUTH __ AUTHORIZED SERVICE CENTER Call Tony Stiliman Ken Dudley custom work competition needs stock complete hobby line specializing competition accessoriesall discounted prices bS ______ __ FREQUENCY CONVERSIONS _______9jgCY~ Frequency Comnnuee Approved @0__ stock Futaba JR radios Featuring fast service byOAYS engines parts qualified people thePhHatori headers pipes latest equipment Including aGh$tIWe Repair Heli Sets Gyros SPECTRUM ANA YZER Al Orders COD VISA MC American Express OPEN 8-5 CST P rices subject change notice 9003 N Davis Hwy Pensacola FL 32514 904 478-6745 As propeller blade passes through given point disc also exerts thrust torque forces cause pressure fluc tuation As air pressure displacement pressure fluctuation propagates sound known thrust torque noise point propeller disc pres sure fluctuates time blade passes total pressure disturbance sum disturbances caused thrust torque thickness certain other effects disturbances vary strength travels its own preferred direction combined effect pressure fluc tuations perceived propeller noise pressure amplitudes of components propeller noise depen dent relative amounts thrust torque well propeller tip speed itself proportional product rotational speed propeller di ameter Thrust torque noise generally significant sources propeller sound should noted ever since thickness noise consider ably affected tip speed thrust torque noise its relative impor tance will increase increasing rota tional speed Any attempt make sense propel ler noise problem complicated overlapping often interdependent ef fects acoustic sources example Figure 4 shows propeller blade lift does point exactly thrust direc tion means blade lift contrib utes both thrust torque hence both thrust torque noise Additionally noise various sources radiates away propeller overlapping pat terns difficult distinguish reduce propeller noise must dis cover dominant noise mechanism work can directed toward lessening source cant done some knowledge intricate makeup pro peller noise Its important understand its interplay factors associ ated aircraft operationengine per formance aircraft drag flight speed rpm propeller diameter pitch etcwhich pro duces noise perceived human ear Conducting scientific study such truly complicated system ridden variables difficult structured building block approach being used North Carolina State University laboratory data correlated both flight test data classical mathematical propel ler theory Although quite time-consuming process does provide direct path final answers research findings suggest propel ler noise may dominant acoustic source model aircraft may deed possible diminish leading Continued page 156 TO ORDER CALL 1406 265-4828 IT-i TRANSMITTER TRAY * Recommended especially handicaps beginners.experienced pilots love also * Pays itself times over airplanes saved l With set Gimbal Extenders $350 Postage & Handling Make Flying Breeze~ BJ ENTERPRISES 1100 Center Havre Montana 59501 42 Model Aviation GATOR RIC PRODUCTS DELUX ALL BALSA KIT An new Tiger Tail 120 four strokes piped 60 two strokes beautiful performer competition just showing offI balsa kit machined wood parts complete lsardware package includes plug-in djustable stab parts new wing mounts Wing Span- 72 inWing Ara 860 sq Complete Delux KitSI 5995 TRANSMITTER CASE An inexpensive rugged molded case protect expensive transmitter both two stick single stick transmitters Black leather grain aluminum trim locking clasp SI 995 MV-I TYPHOON New F3A competition Big beautiful flyer balsa construction plug-in wings 120 four stroke 60 two stroke power Plans-two sheets S 1495 Fiberglass cowl Si 595 Clear butyrate canopy. 5 995 OTHER PLANS Tiger Tail 4S-two sheets 120 four strokesS 1495 TAR baby 120 four strokes51195 Alley Kat 40 size trainer sportS 895 Gator Flea 40 size sport5 895 Bobcat 40 size sportS 895 feather Ilte glass cloth 7 ozsq yd est weave Fastest Filling test Finished Weight Big 3 Sq Yard Pkg Oetailed Instructions- $895 Include $2 SOlItem UPS esidents Add 6% Sales Tax GATOR RIC PRODUCTS 3713 Pompano Dr acola FL 32514 4768639 Letters Editor Continued page 12 Ken opened hobby shop Burk & Company Department Store after World War II worked him full-time year until started college After worked part-time until completing college Milton H Fanning Nashville TN Safety/Preston Continued page 22 some MonoKote repairs moral tale wise keep small extinguisher field box As alter native may possible smother fire towel rag blanket Cub Yellow engine cowling first RC model powered Cox 09 began turn first orange brown able smother fire wrap ping rag around front model Have safe month Keytwo/Randoiph Continued page 30 der everything place range check equipmentand its time fly Flying has wide performance en velope compared Paskey Keytwo basically quite gentle flier Whether upright inverted stall shows abso lutely no tendency snap fact model balanced correctly its very diffi cult make snap snaps bag move center-of-gravity aft about /2 increase elevator throw rate /16 up down movement trailing edge aile rons about right comfortable flying Landings can made nose-high slow full aileron control way touch down problem knife-edge flight first airplane persistently climbed half-loop until learned nose stayed up just little rudder Once Id mastered technique knife-edge loops included Keytwos repertoire tricks what did Eddie Williams have say about latest re-creation see youve built another Paskey said unsung maestro drunken pilot routine Its about time Play again Eddie Radio Technique/Myers Continued page 34 Failsafe Flight System small 15 sq light less ounce inexpensive has very low operating current 70 mA works no doubt nine-volt transistor radio batteries expensive about $250 Duracells live will last long time some chance will get care less let run down some critical time unit meets its claims follow admonition use fresh batteries check servo speed during preflight inspection careless youll probably crash some other reason anyway Failsafe Flight System @ $3995 list T&D Flight Systems PO Box 1782 Staten Island NY 10314 additional information call Alex Kronfeld l-7t8/984-9121 Propeller Noise Continued page 42 cause poor community relations Much cure will depend upon education Modelers need understand nature problem order properly utilize solu tions article has introduced propel ler noise problem provided some neces sary background Subsequent articles will explain test results greater detail describe what modeler can achieve better aircraft performance less noise RC Soaring/Blakeslee Continued page 49 down hes hoping arrange factur ers demonstrations during meet would flying demos followed show-andtell sessions guys like Byron Bruce Combat Models Marty Silberstein Steve Peacock Cliff Hangar Models Brian Laird Paul Masura Slope Scale Models Other Id imagine itll much like fabulously suc cessful Richland Scale Slope Fun Flyie fly want long have pin Info available writing Charley SSN 2601 E 19th 51 #29 Signal Hill CA 90804 Better call him 1-213/494-3712 1990 Soaring contests Ray Hayes Vice Presi dent LSF wrote remind us now time plan next years big contests Spe cifically Ray talking about every-evenyear LSF Regionals annual NSS Soar-Ins put go-ahead clubs around coun try Theyre bit expensive Ray hoping Continue tradition awarding beautiful LSF plaques LSF Regionals Theyre worth winning Ray also hoping three super con tests NSS Masters LSF Nationals AMA Nats can spread around country 1990 contests West Coast 89 Ray afraid guys east Kansas beginning feel left out youd like info LSF Regionals check Ray 69598 Brookhill Dr Romeo MI 48065 phone 1-313/ 752-6163 NSS Soar-Ins have handled Marshall Long past few years assume youre 90 Marshall Marshalls address 824 Garden Meadow Universal City TX 78148 worry East Coasters hear Nats will Lawrenceville IL 90 RC Aerobatics/Van Putte Continued page 51 aerodynamic center segment wing Youll note root segment tip another segment Figure 4 shows geometric technique solu tion Remember aerodynamic center panel 25% point mean aerody namic chord panel Once youve determined aerodynamic cen ter panel must calculate area panel using Equation 2 measure distance convenient line aerody namic centers panels Figure 4 shows con venient reference line distance re spective aerodynamic centers distance back reference line aerodynamic center wing located determined Equation 3 mean aerodynamic chord complete wing calculated individual values shown Equation 4 looks just like equa tion determining distance wing aero dynamic center doesnt should since 156 Model Aviation
Edition: Model Aviation - 1989/12
Page Numbers: 36, 37, 38, 39, 40, 41, 42, 156
D Heathcoat R Nagel Model Propeller NOISEc first series articles describes in-depth research spon sored AMA conducted North Carolina State Univer sity severity sources reduction propeller noise findings some unprecedented could have ma jor impact model airplane_flying community ADVANCES model aviation over past decade have spurred tremendous growth hobby year thousands people across US becoming ac tive participants weekend sessions local flying field greatest influx newcomers sport naturally occurs near large cities population con centrated flying sites tend lo cated suburban areas allows easy access fliers also subjects uninterested neighbor characteris tic whine model aircraft surprisingly greatest activity model field occurs weekends weekday evenings just peo ple living nearby home expecting chance relax involved sport well aware bitter confrontation scenario sometimes provokes ten modelers lose battle begin search another suitable flying site Losing established flying site hav ing search new can frustrat ing costly experience Ultimately has negative effect organization continued growth sport Its clear continuously relocating flying fields farther farther away populated ar eas isnt answer rate rural de velopment flying site relocation will lit tle postpone inevitable return problem solution instead develop model aircraft operate lower sound levels quite evident commonly accepted model aircraft noise generated propulsion system casual observer obvious sources intake combustion exhaust noise generated power plantand airframe noise re sulting its characteristic vibration However propeller too impor tant source noiseone misunder stood consequently overlooked fact acoustic research full-scale aircraft indicates propeller noise dominates over other sources sound illustrated following quote Journal Aircraft has well known years propellerdriven aircraft propeller primary source noise observation may 36 Model Aviation gu hold true model aircraft well effort better understand model pro Di recti Ro tat peller noise establish guidelines ultimately will lead quieter model aircraft AMA sponsored research pro Table 1Selected Flight Test Data Prop Velocity RPM QASPI kmphdBA Group 1 11 x5180160001110 9x7519516400960 9x719016250934 Group 2 10x615013500878 11 x614312000990 Group 3 10x712011000840 9x7512011250810 10x612010800764 Group 4 11 x 5908500925 9 x 7908700830 gram conducted North Carolina State Uni versity principal investigators include Dr Robert T Nagel associate professor nearly 15 years research experience aeroacoustics Robert Vess aero space engineer six years experience coordinator NC State University aerospace laboratories 18 years activ ity Radio Control including Pattern Hel icopter fun fly competition David M Heathcoat received bachelors degree physics NC State University 1986 participated propeller noise research masters degree thesis article first series will describe tests performed explain results make recommendations toward reducing model aircraft noise Im proving noise problem means averting loss flying sites will depend largely having knowledgeable fliers Due technical nature mate rial will precede discussion test program details brief explanation basic propeller theory Introducing some important aspects propeller per formance section will lead better understanding both current study propellers general Since formulas scientific jargon tend limit interest type article effort has made avoid use Basic Propeller Theory order aircraft move through air propelling force must work propeller essentially small rotating wing produces required thrust speed aircraft level flight deter mined relating thrust available power plant total aircraft drag Note both forces vary signifi cantly airspeed depicted typi cal aircraft Figure 1 example moving left right along horizontal axis Figure 1 represents increasing airspeed notes aircraft drag increases eventually exceeds thrust Point 1 figure represents case air craft accelerating since thrust pro duced propeller much greater aircraft drag Conversely aircraft operating point 2 predominance drag over thrust causes decelerate cases airspeed will stabi lize point 3 thrust drag equal Since engine example full throttle point 3 represents maximum tainable airspeed aircraft/engine/ propeller combination level flight re duction power below full throttle ef fectively shifts thrust curve downward resulting reduction maximum airspeed see dashed curve Figure 1 Similarly anything can done pro duce thrust less drag will shift December 1989 37 Figu curves allowing greater flight speeds Figure 1 has shown thrust produced power plant actually decreases yond certain threshold airspeed phenomenon results changes air flow around propeller high airspeeds As propeller rotates flow approaches its leading edge speed depends rotational speed rpm engine However forward movement aircraft creates additional flow ap proaches propeller disc speed equal forces acting propeller best explained examining thin slice blade such shown cross section Figure 2 Once again explanation simplified differentiating effects due blade rotation caused forward speed Figure 3 depicts flow action sec tion typical propeller blade due its ro tation alone would case engine being run model re strained flow approaches prop angle dictated blade pitch Just wing produces lift drag certain gle attack propeller produces sim ilar forces depend engine rpm shape blade airfoil lift force example acts along axis rotation force axial direction termed thrust Similarly drag force acts plane rotation pro peller resists its rotation defined torque Figure 4 illustrates condition after aircraft released acquires addi tional flow field its forward move ment simple way graphically depict combination two flows use special arrows called vectors flow represented single vector relative speed flow given length its vector flow direction rep resented direction vec tor pointing two propeller flow vectors arranged nose-to-tail Fig ure 4 rotation forward flight other vector completes triangle represents flow field resulting combination Notice speed direction resultant vector can al tered changing length speed original vectors Therefore flow around propeller indeed does depend both engine rpm forward flight speed flow vectors combine shown Figure 4 forces acting propel ler diminish Hence blade airfoil angle attack Figure 4 decreased com pared Figure 3 addition since lift drag forces measured respect altered flow angle slanted away axis rotation propel ler Therefore net thrust decreased further since lift force acting pre cisely thrust direction misdirection lift also shown Figure 4 reality thrust lost due slanting lift force becomes ad ditional torque load engine must overcome effectively demonstrates propeller performance very different flight ground better understanding engine turns propeller under varying load conditions can gained referring Fig ure 5 Assume drag forces acting point blade propeller example added together sum found lso assume net drag force determined act ing through point 12 center crankshaft product lb 12-in distance represents 6 in-lb b torque load blade propeller Since two blades net torque load power plant must produce order turn blades constant rotational speed 12 38 Model Aviation 0 flight velocity Figure 2 illustrates relative directions simultaneous flows respect propeller ro tating counterclockwise in-lb 1 ft-lb engine capable producing torque under condi tions rotational speed will increase cant produce enough torque rotational speed will achieved power available engine simply rotational speed multiplied amount torque can applied propeller given rpm example engine can produce 33 ft-lb torque 10000 rpm 16667 rev/sec power rotational speed 550 ft lb/sec example chosen order put value power recogniz able units Since horsepower 1 hp equivalent 550 ft-lb/sec engine producing exactly horsepower under operating conditions Figure 6 illustrates way horsepower output torque typical model engine vary rotational speed Most engines available modelers have curves resemble example actual magnitude power torque rotational speed depends physi cal design particular engine As mentioned above power required turn propeller product torque rotational speed power produced propeller proportional product thrust forward speed ratio power produced propeller required turn known propeller efficiency An efficient propeller capable producing given amount thrust using less power inefficient Equivalently efficient propeller can produce greater thrust therefore greater ward speed using same engine power Rather being fixed value efficien cy depends physical design opera ting rpm flight speed specific pro peller therefore improper categori cally call prop efficient other unless advantage holds true rotational forward speeds Propeller ef ficiency plays major role increasing air craft performance reducing noise Basic Noise Definitions Sound waves simply minute pressure fluctuations propagate air characterized two parameters frequency amplitude Frequency refers number pressure pulses pres sure fluctuations occur sec ond perceived ear pitch Like higher notes piano keyboard higher frequencies actually sound higher pitched Pressure amplitude measure size acoustical disturbance corresponds loudness sound simple tone characterized single frequency single amplitude Complex sounds composed different fre quencies Pressure amplitude measured deci bels dB measured referred sound pressure level SPL Continued page 40 Order direct Add $1500 shipping Use VISA MC check money order COD GOLIDW AGE MODELS RO box 807 Ienn Vcilleq CA 95946 916 432-2928 B&P Associates Gives Total FlIgbt Line FREEDOM battery needs call write B&P Associates PO Box 22054 Waco TX 76702-2054 817662-5587 new electric starter battery pack cuts cord has always tied starter power panel Discover freedom being able start plane wherever added safety less wire get caught prop charge hefty 4 Amp/hour pack will take through weekend flying power enough spare dont stop have Ni-Cads virtually size imaginable cut experimenter free design whatever ii takes make yours best setup field December 1989 39 h C, qusrter scale com plete deluxe kit features exact scale outlines balsa plywo, onstruction light epoxy cowl wheel pants selected wood complete hardware flying wires full cockpit details 3-views photos decals extensive instruction manual 20 cu ne lighL upoxy glass uuiage cowl wheel pants complete hardware selected wood decals 3-views cu engliw epoxy glass fudy owl wheel pants light foam wing cores con test wood complete hardware decals Satisfaction Guaranteed1 EA~ HINELZ SH-710 Pkg 24-52 95 THE HIGH-TECH HINGE DESIGNED FOR THE CYANOACRYLATE AGE Easier install other hinge No gouging picking messy epoxies Simply cut single knife slot hinge slide hinges place apply few drops favorite CA glue youre donel SUPER FAST SUPER EASY SUPER STRONG SIG MFG CO INC401-7 So Front St.Montezuma IA 50171 23-5154 LANDER INDUST 1005 19TH ST CT HAVRE MONTANA 59501 406265-6529 PRICES INCLUDE FREIGHT CANADIAN ORDERS ADD 25% ViSA Pwtakeet SUpeJL Po4 PO4JIWkQ 40. FREE CATALOG Ti4ewaiwt I4otoluj eIdWIIAi*e 392SC SE 13th Court Scala FImna 32571 904 6943531 sound pressure level corresponds dis crete frequency range frequencies overall sound pressure level' OASPL also measured decibels measure sound obtained adding SPLs frequency spectrum decibel reflecting fact human ear perceives very wide range sound pressure based loga rithmic scale rather linear compresses sonic data ease inter pretation Still another measure noise sound power level PWL based quantity acoustical power pro duced given source rather pres sure amplitude given location Since sound power level also measured dB its important keep track whether mea surements given units PWLs SPLs Sounds certain frequency ranges perceived being louder sounds other frequencies Weighted sound level curves have developed take fact account weighted scale used almost industrial commu nity noise standards US Sound lev els measured according scale ex pressed units called dBA significance relative contribu tions various components noise cannot appreciated general understanding manner sound levels combined two equal sound pressure levels SPLs added together combined sound level will 6dB higher orig inal value Adding together two equal sound power levels PWLs produces level 3 dB higher phenome non result logarithmic nature dB scale means levels separated few dB fact very different ab solute values acoustic power level PWL expressed dB adding two powers differ 10 dB pro duces no significant increase power yond higher two Consider ex ample adding 80 dB 90 dB powers dB1 B dB2 B total dBtotai given follow ing formula dBtotai og[l0dB/o 2/1O] dB Sound pressure levels SPLs behave similar fashion two SPLs com bined variance between acoustic levels addition becomes insignificant about 20 dB adds SPLs 80 dB 100 dB result 1008 dB practical implications will become clear realizes model aircraft noise derives several sourcesthe engine airframe propellerand propeller noise itself blends several components Often reducing lesser noise source fails produce noticeably quieter aircraft Consider example aircraft 80 dB engine noise 90 dB propeller noise As have seen formula given above able completely elim inate engine noise lesser source resulting acoustic power would discernibly reduced hypothetical example subtracting 80 dB engine noise acoustical power 904 dB total noise power slightly lowers total output about 90 dBnot significant change achieve meaningful reduction model air craft sound necessary reduce dominant source noise Justification Propeller Noise Reduction fundamental objective research project has verify sound pro duced propeller fact domi nant noise mechanism model aviation project assumes reasonable offthe-shelf muffler used aircraft since absence such use use poor muffler engine sounds likely dominate noise signature Measure ments acquired during different phases research provide several pieces evi dence indicate propeller noise dominates over produced properly muffled engine Flight test data provides first bit ev idence An instrumented aircraft flown fixed height over microphone peak OASPL measured dBA flight speed rpm throttle setting also recorded data compared obtained same propellers driven electric motor wind tunnel laboratory thereby eliminating power plant significant source noise Although flight velocities precisely duplicated lab several cases offer reasonable basis compari son such case SPL bladepassing frequency lab 78 dB simulated flight velocity 100 kmph ki lometers per hour microphone dis tance corrected same distance used flight tests flight test 120 kmph resulted OASPL 764 dBA OASPL includes frequencies spectrum whereas lab data ob tained blade-passing frequency Since engine airframe noise absent lab data would have ex pected flight test noise louder results support inference engine airframe noise did reach significant level flight tests done would have tended dominate rais ing OASPL above SPL measured lab fact propeller noise alone approximately equal total noise mea sured flight Table 1 shows data selected tests operating conditions nearly identical Group 1 contains propel lers same manufacturer tal variation mean rpm less 1% total variation flight velocity approximately 5% Groups 2 3 in40 Model Aviation RIG SKY CRADLES FIELD BOX MODEL$1595 BENCH MODEL$1995 FLOOR MODEL$2395 CEILING HANGERS SMALL20-40 .$995 MEDIUM 40- 60 95 LARGE 50-BO. $1195 nvur HAIFt FITS ALL PICKUPS . 5 cluded propellers two different manu facturers Group 4 propellers sin gle manufacturer Since flight speed rpm nearly same group aircraft always level flight measure ment point thrust produced likewise nearly same data groups Table 1 Clearly engine airframe having almost identically groups can therefore inferred observed large variations OASPL between cases within group rather being caused engine airframe noise result dif ferences sound levels among propellers Further assuming situation en gine noise closely approximated level propeller noise completely eliminating engine noise would effect noise re duction 6 dBa value ex ceeded differences noted among props particular group final piece evidence yielded data obtained two different mufflers during flight tests stock muffler re placed high-quality state-of-the-art muf fler data recorded two different flight speeds using same propeller 120 kmph difference OASPL measured 02 dBA 90 kmph difference 03 dBA Such ex tremely small variance suggests given flight speed advanced muffler no effect total noise output ever full throttle engine performed better upgraded muffler ad ditional rpm permitted latter creased noise levels improved engine performance advanced muffler did significantly impact noise level long flight speed remained constant test results clearly establish pro peller dominant source model air craft noise remainder discus sion will assume case Propeller Noise Sources sound produced model propel ler compounded several elements important include noise due thrust torque noise thickness noise referred discrete fre quency noise sources because sound produced occurs bladepassing frequency its harmonics blade-passing frequency rate blade passes given point propel ler disc product number blades rotational speed rev/sec understand noise mecha nisms operate imagine fixed point rotational disc propeller time blade near point air pressure its ordinary value Air pres sure changes blade passes through pushes air aside amount dis placed air depending thickness blade noise produced periodic displacement air known thickness noise Continued page 42 VJO ds best Sel 09 Spak osen ByTan Odginds TItG Mfg ml AM Aircraft Saqiply its outstenhg ruimhity Comp e e s ng e cyl nder system nclud ng ho e couped spark advance kt spark gead25 p ug ba e y pack charger 900 sh elded Much kmger 1gm hIs Easy haid sterts-no kickback 1AUO-12000 RPM rubble ii 0% power few strokers oni nutubbmi mviii Lower pricad fuels no okra neededMqleeduul9Fphagcovw FormumyuapaesI0&p2ft4strokeslegieudtwlsctulrs Klotzaioahactsaviule Splc cub aperk ded ibm bed ft tbi*ag hits avabbis CAT NO 106 Proof Switch Retail S995 Add $125 shipping Send $150 catalog Michigan residents add 4% sales tax IMPROVE YOUR 1991 SWITCH OVER ej Proof Switch Positive Locking Prevents Arriving field dead batteries Accidental switching off before take-off Will vibrate apart causing loss radio Does require special mounts Works radios Ideal seaplanes completely water proof SEE YOUR LOCAL HOBBY DEALER unavailable locally send Bru Line Industries Inc 4.. PO Box 3786 Center Line MI 48015 WASHINGTON S AMA BASE. $ An50 1 per couple per night Check day Minimum stay 2 nights Free Parking Cars Free Full Breakfasts Free Merropass Sat Sun Free Harrington Hawk Cafeteria avA 11th & E Streets NW Washington DC 20004G9 0-424-8532 628 8140T70 omm December 1989 41 Em 0AMA MEMBER RATE Tax no included A Radio South Batteries 500 ma Pack 48V Futaba conn 800 ma Pack 48V Futaba conn 1200 ma Pack 48V Futaba conn TX batt Futaba G-Series PCM 1300 1550 2200 2475 2400 2700 2995 RADIO SOUTH __ AUTHORIZED SERVICE CENTER Call Tony Stiliman Ken Dudley custom work competition needs stock complete hobby line specializing competition accessoriesall discounted prices bS ______ __ FREQUENCY CONVERSIONS _______9jgCY~ Frequency Comnnuee Approved @0__ stock Futaba JR radios Featuring fast service byOAYS engines parts qualified people thePhHatori headers pipes latest equipment Including aGh$tIWe Repair Heli Sets Gyros SPECTRUM ANA YZER Al Orders COD VISA MC American Express OPEN 8-5 CST P rices subject change notice 9003 N Davis Hwy Pensacola FL 32514 904 478-6745 As propeller blade passes through given point disc also exerts thrust torque forces cause pressure fluc tuation As air pressure displacement pressure fluctuation propagates sound known thrust torque noise point propeller disc pres sure fluctuates time blade passes total pressure disturbance sum disturbances caused thrust torque thickness certain other effects disturbances vary strength travels its own preferred direction combined effect pressure fluc tuations perceived propeller noise pressure amplitudes of components propeller noise depen dent relative amounts thrust torque well propeller tip speed itself proportional product rotational speed propeller di ameter Thrust torque noise generally significant sources propeller sound should noted ever since thickness noise consider ably affected tip speed thrust torque noise its relative impor tance will increase increasing rota tional speed Any attempt make sense propel ler noise problem complicated overlapping often interdependent ef fects acoustic sources example Figure 4 shows propeller blade lift does point exactly thrust direc tion means blade lift contrib utes both thrust torque hence both thrust torque noise Additionally noise various sources radiates away propeller overlapping pat terns difficult distinguish reduce propeller noise must dis cover dominant noise mechanism work can directed toward lessening source cant done some knowledge intricate makeup pro peller noise Its important understand its interplay factors associ ated aircraft operationengine per formance aircraft drag flight speed rpm propeller diameter pitch etcwhich pro duces noise perceived human ear Conducting scientific study such truly complicated system ridden variables difficult structured building block approach being used North Carolina State University laboratory data correlated both flight test data classical mathematical propel ler theory Although quite time-consuming process does provide direct path final answers research findings suggest propel ler noise may dominant acoustic source model aircraft may deed possible diminish leading Continued page 156 TO ORDER CALL 1406 265-4828 IT-i TRANSMITTER TRAY * Recommended especially handicaps beginners.experienced pilots love also * Pays itself times over airplanes saved l With set Gimbal Extenders $350 Postage & Handling Make Flying Breeze~ BJ ENTERPRISES 1100 Center Havre Montana 59501 42 Model Aviation GATOR RIC PRODUCTS DELUX ALL BALSA KIT An new Tiger Tail 120 four strokes piped 60 two strokes beautiful performer competition just showing offI balsa kit machined wood parts complete lsardware package includes plug-in djustable stab parts new wing mounts Wing Span- 72 inWing Ara 860 sq Complete Delux KitSI 5995 TRANSMITTER CASE An inexpensive rugged molded case protect expensive transmitter both two stick single stick transmitters Black leather grain aluminum trim locking clasp SI 995 MV-I TYPHOON New F3A competition Big beautiful flyer balsa construction plug-in wings 120 four stroke 60 two stroke power Plans-two sheets S 1495 Fiberglass cowl Si 595 Clear butyrate canopy. 5 995 OTHER PLANS Tiger Tail 4S-two sheets 120 four strokesS 1495 TAR baby 120 four strokes51195 Alley Kat 40 size trainer sportS 895 Gator Flea 40 size sport5 895 Bobcat 40 size sportS 895 feather Ilte glass cloth 7 ozsq yd est weave Fastest Filling test Finished Weight Big 3 Sq Yard Pkg Oetailed Instructions- $895 Include $2 SOlItem UPS esidents Add 6% Sales Tax GATOR RIC PRODUCTS 3713 Pompano Dr acola FL 32514 4768639 Letters Editor Continued page 12 Ken opened hobby shop Burk & Company Department Store after World War II worked him full-time year until started college After worked part-time until completing college Milton H Fanning Nashville TN Safety/Preston Continued page 22 some MonoKote repairs moral tale wise keep small extinguisher field box As alter native may possible smother fire towel rag blanket Cub Yellow engine cowling first RC model powered Cox 09 began turn first orange brown able smother fire wrap ping rag around front model Have safe month Keytwo/Randoiph Continued page 30 der everything place range check equipmentand its time fly Flying has wide performance en velope compared Paskey Keytwo basically quite gentle flier Whether upright inverted stall shows abso lutely no tendency snap fact model balanced correctly its very diffi cult make snap snaps bag move center-of-gravity aft about /2 increase elevator throw rate /16 up down movement trailing edge aile rons about right comfortable flying Landings can made nose-high slow full aileron control way touch down problem knife-edge flight first airplane persistently climbed half-loop until learned nose stayed up just little rudder Once Id mastered technique knife-edge loops included Keytwos repertoire tricks what did Eddie Williams have say about latest re-creation see youve built another Paskey said unsung maestro drunken pilot routine Its about time Play again Eddie Radio Technique/Myers Continued page 34 Failsafe Flight System small 15 sq light less ounce inexpensive has very low operating current 70 mA works no doubt nine-volt transistor radio batteries expensive about $250 Duracells live will last long time some chance will get care less let run down some critical time unit meets its claims follow admonition use fresh batteries check servo speed during preflight inspection careless youll probably crash some other reason anyway Failsafe Flight System @ $3995 list T&D Flight Systems PO Box 1782 Staten Island NY 10314 additional information call Alex Kronfeld l-7t8/984-9121 Propeller Noise Continued page 42 cause poor community relations Much cure will depend upon education Modelers need understand nature problem order properly utilize solu tions article has introduced propel ler noise problem provided some neces sary background Subsequent articles will explain test results greater detail describe what modeler can achieve better aircraft performance less noise RC Soaring/Blakeslee Continued page 49 down hes hoping arrange factur ers demonstrations during meet would flying demos followed show-andtell sessions guys like Byron Bruce Combat Models Marty Silberstein Steve Peacock Cliff Hangar Models Brian Laird Paul Masura Slope Scale Models Other Id imagine itll much like fabulously suc cessful Richland Scale Slope Fun Flyie fly want long have pin Info available writing Charley SSN 2601 E 19th 51 #29 Signal Hill CA 90804 Better call him 1-213/494-3712 1990 Soaring contests Ray Hayes Vice Presi dent LSF wrote remind us now time plan next years big contests Spe cifically Ray talking about every-evenyear LSF Regionals annual NSS Soar-Ins put go-ahead clubs around coun try Theyre bit expensive Ray hoping Continue tradition awarding beautiful LSF plaques LSF Regionals Theyre worth winning Ray also hoping three super con tests NSS Masters LSF Nationals AMA Nats can spread around country 1990 contests West Coast 89 Ray afraid guys east Kansas beginning feel left out youd like info LSF Regionals check Ray 69598 Brookhill Dr Romeo MI 48065 phone 1-313/ 752-6163 NSS Soar-Ins have handled Marshall Long past few years assume youre 90 Marshall Marshalls address 824 Garden Meadow Universal City TX 78148 worry East Coasters hear Nats will Lawrenceville IL 90 RC Aerobatics/Van Putte Continued page 51 aerodynamic center segment wing Youll note root segment tip another segment Figure 4 shows geometric technique solu tion Remember aerodynamic center panel 25% point mean aerody namic chord panel Once youve determined aerodynamic cen ter panel must calculate area panel using Equation 2 measure distance convenient line aerody namic centers panels Figure 4 shows con venient reference line distance re spective aerodynamic centers distance back reference line aerodynamic center wing located determined Equation 3 mean aerodynamic chord complete wing calculated individual values shown Equation 4 looks just like equa tion determining distance wing aero dynamic center doesnt should since 156 Model Aviation
Edition: Model Aviation - 1989/12
Page Numbers: 36, 37, 38, 39, 40, 41, 42, 156
D Heathcoat R Nagel Model Propeller NOISEc first series articles describes in-depth research spon sored AMA conducted North Carolina State Univer sity severity sources reduction propeller noise findings some unprecedented could have ma jor impact model airplane_flying community ADVANCES model aviation over past decade have spurred tremendous growth hobby year thousands people across US becoming ac tive participants weekend sessions local flying field greatest influx newcomers sport naturally occurs near large cities population con centrated flying sites tend lo cated suburban areas allows easy access fliers also subjects uninterested neighbor characteris tic whine model aircraft surprisingly greatest activity model field occurs weekends weekday evenings just peo ple living nearby home expecting chance relax involved sport well aware bitter confrontation scenario sometimes provokes ten modelers lose battle begin search another suitable flying site Losing established flying site hav ing search new can frustrat ing costly experience Ultimately has negative effect organization continued growth sport Its clear continuously relocating flying fields farther farther away populated ar eas isnt answer rate rural de velopment flying site relocation will lit tle postpone inevitable return problem solution instead develop model aircraft operate lower sound levels quite evident commonly accepted model aircraft noise generated propulsion system casual observer obvious sources intake combustion exhaust noise generated power plantand airframe noise re sulting its characteristic vibration However propeller too impor tant source noiseone misunder stood consequently overlooked fact acoustic research full-scale aircraft indicates propeller noise dominates over other sources sound illustrated following quote Journal Aircraft has well known years propellerdriven aircraft propeller primary source noise observation may 36 Model Aviation gu hold true model aircraft well effort better understand model pro Di recti Ro tat peller noise establish guidelines ultimately will lead quieter model aircraft AMA sponsored research pro Table 1Selected Flight Test Data Prop Velocity RPM QASPI kmphdBA Group 1 11 x5180160001110 9x7519516400960 9x719016250934 Group 2 10x615013500878 11 x614312000990 Group 3 10x712011000840 9x7512011250810 10x612010800764 Group 4 11 x 5908500925 9 x 7908700830 gram conducted North Carolina State Uni versity principal investigators include Dr Robert T Nagel associate professor nearly 15 years research experience aeroacoustics Robert Vess aero space engineer six years experience coordinator NC State University aerospace laboratories 18 years activ ity Radio Control including Pattern Hel icopter fun fly competition David M Heathcoat received bachelors degree physics NC State University 1986 participated propeller noise research masters degree thesis article first series will describe tests performed explain results make recommendations toward reducing model aircraft noise Im proving noise problem means averting loss flying sites will depend largely having knowledgeable fliers Due technical nature mate rial will precede discussion test program details brief explanation basic propeller theory Introducing some important aspects propeller per formance section will lead better understanding both current study propellers general Since formulas scientific jargon tend limit interest type article effort has made avoid use Basic Propeller Theory order aircraft move through air propelling force must work propeller essentially small rotating wing produces required thrust speed aircraft level flight deter mined relating thrust available power plant total aircraft drag Note both forces vary signifi cantly airspeed depicted typi cal aircraft Figure 1 example moving left right along horizontal axis Figure 1 represents increasing airspeed notes aircraft drag increases eventually exceeds thrust Point 1 figure represents case air craft accelerating since thrust pro duced propeller much greater aircraft drag Conversely aircraft operating point 2 predominance drag over thrust causes decelerate cases airspeed will stabi lize point 3 thrust drag equal Since engine example full throttle point 3 represents maximum tainable airspeed aircraft/engine/ propeller combination level flight re duction power below full throttle ef fectively shifts thrust curve downward resulting reduction maximum airspeed see dashed curve Figure 1 Similarly anything can done pro duce thrust less drag will shift December 1989 37 Figu curves allowing greater flight speeds Figure 1 has shown thrust produced power plant actually decreases yond certain threshold airspeed phenomenon results changes air flow around propeller high airspeeds As propeller rotates flow approaches its leading edge speed depends rotational speed rpm engine However forward movement aircraft creates additional flow ap proaches propeller disc speed equal forces acting propeller best explained examining thin slice blade such shown cross section Figure 2 Once again explanation simplified differentiating effects due blade rotation caused forward speed Figure 3 depicts flow action sec tion typical propeller blade due its ro tation alone would case engine being run model re strained flow approaches prop angle dictated blade pitch Just wing produces lift drag certain gle attack propeller produces sim ilar forces depend engine rpm shape blade airfoil lift force example acts along axis rotation force axial direction termed thrust Similarly drag force acts plane rotation pro peller resists its rotation defined torque Figure 4 illustrates condition after aircraft released acquires addi tional flow field its forward move ment simple way graphically depict combination two flows use special arrows called vectors flow represented single vector relative speed flow given length its vector flow direction rep resented direction vec tor pointing two propeller flow vectors arranged nose-to-tail Fig ure 4 rotation forward flight other vector completes triangle represents flow field resulting combination Notice speed direction resultant vector can al tered changing length speed original vectors Therefore flow around propeller indeed does depend both engine rpm forward flight speed flow vectors combine shown Figure 4 forces acting propel ler diminish Hence blade airfoil angle attack Figure 4 decreased com pared Figure 3 addition since lift drag forces measured respect altered flow angle slanted away axis rotation propel ler Therefore net thrust decreased further since lift force acting pre cisely thrust direction misdirection lift also shown Figure 4 reality thrust lost due slanting lift force becomes ad ditional torque load engine must overcome effectively demonstrates propeller performance very different flight ground better understanding engine turns propeller under varying load conditions can gained referring Fig ure 5 Assume drag forces acting point blade propeller example added together sum found lso assume net drag force determined act ing through point 12 center crankshaft product lb 12-in distance represents 6 in-lb b torque load blade propeller Since two blades net torque load power plant must produce order turn blades constant rotational speed 12 38 Model Aviation 0 flight velocity Figure 2 illustrates relative directions simultaneous flows respect propeller ro tating counterclockwise in-lb 1 ft-lb engine capable producing torque under condi tions rotational speed will increase cant produce enough torque rotational speed will achieved power available engine simply rotational speed multiplied amount torque can applied propeller given rpm example engine can produce 33 ft-lb torque 10000 rpm 16667 rev/sec power rotational speed 550 ft lb/sec example chosen order put value power recogniz able units Since horsepower 1 hp equivalent 550 ft-lb/sec engine producing exactly horsepower under operating conditions Figure 6 illustrates way horsepower output torque typical model engine vary rotational speed Most engines available modelers have curves resemble example actual magnitude power torque rotational speed depends physi cal design particular engine As mentioned above power required turn propeller product torque rotational speed power produced propeller proportional product thrust forward speed ratio power produced propeller required turn known propeller efficiency An efficient propeller capable producing given amount thrust using less power inefficient Equivalently efficient propeller can produce greater thrust therefore greater ward speed using same engine power Rather being fixed value efficien cy depends physical design opera ting rpm flight speed specific pro peller therefore improper categori cally call prop efficient other unless advantage holds true rotational forward speeds Propeller ef ficiency plays major role increasing air craft performance reducing noise Basic Noise Definitions Sound waves simply minute pressure fluctuations propagate air characterized two parameters frequency amplitude Frequency refers number pressure pulses pres sure fluctuations occur sec ond perceived ear pitch Like higher notes piano keyboard higher frequencies actually sound higher pitched Pressure amplitude measure size acoustical disturbance corresponds loudness sound simple tone characterized single frequency single amplitude Complex sounds composed different fre quencies Pressure amplitude measured deci bels dB measured referred sound pressure level SPL Continued page 40 Order direct Add $1500 shipping Use VISA MC check money order COD GOLIDW AGE MODELS RO box 807 Ienn Vcilleq CA 95946 916 432-2928 B&P Associates Gives Total FlIgbt Line FREEDOM battery needs call write B&P Associates PO Box 22054 Waco TX 76702-2054 817662-5587 new electric starter battery pack cuts cord has always tied starter power panel Discover freedom being able start plane wherever added safety less wire get caught prop charge hefty 4 Amp/hour pack will take through weekend flying power enough spare dont stop have Ni-Cads virtually size imaginable cut experimenter free design whatever ii takes make yours best setup field December 1989 39 h C, qusrter scale com plete deluxe kit features exact scale outlines balsa plywo, onstruction light epoxy cowl wheel pants selected wood complete hardware flying wires full cockpit details 3-views photos decals extensive instruction manual 20 cu ne lighL upoxy glass uuiage cowl wheel pants complete hardware selected wood decals 3-views cu engliw epoxy glass fudy owl wheel pants light foam wing cores con test wood complete hardware decals Satisfaction Guaranteed1 EA~ HINELZ SH-710 Pkg 24-52 95 THE HIGH-TECH HINGE DESIGNED FOR THE CYANOACRYLATE AGE Easier install other hinge No gouging picking messy epoxies Simply cut single knife slot hinge slide hinges place apply few drops favorite CA glue youre donel SUPER FAST SUPER EASY SUPER STRONG SIG MFG CO INC401-7 So Front St.Montezuma IA 50171 23-5154 LANDER INDUST 1005 19TH ST CT HAVRE MONTANA 59501 406265-6529 PRICES INCLUDE FREIGHT CANADIAN ORDERS ADD 25% ViSA Pwtakeet SUpeJL Po4 PO4JIWkQ 40. FREE CATALOG Ti4ewaiwt I4otoluj eIdWIIAi*e 392SC SE 13th Court Scala FImna 32571 904 6943531 sound pressure level corresponds dis crete frequency range frequencies overall sound pressure level' OASPL also measured decibels measure sound obtained adding SPLs frequency spectrum decibel reflecting fact human ear perceives very wide range sound pressure based loga rithmic scale rather linear compresses sonic data ease inter pretation Still another measure noise sound power level PWL based quantity acoustical power pro duced given source rather pres sure amplitude given location Since sound power level also measured dB its important keep track whether mea surements given units PWLs SPLs Sounds certain frequency ranges perceived being louder sounds other frequencies Weighted sound level curves have developed take fact account weighted scale used almost industrial commu nity noise standards US Sound lev els measured according scale ex pressed units called dBA significance relative contribu tions various components noise cannot appreciated general understanding manner sound levels combined two equal sound pressure levels SPLs added together combined sound level will 6dB higher orig inal value Adding together two equal sound power levels PWLs produces level 3 dB higher phenome non result logarithmic nature dB scale means levels separated few dB fact very different ab solute values acoustic power level PWL expressed dB adding two powers differ 10 dB pro duces no significant increase power yond higher two Consider ex ample adding 80 dB 90 dB powers dB1 B dB2 B total dBtotai given follow ing formula dBtotai og[l0dB/o 2/1O] dB Sound pressure levels SPLs behave similar fashion two SPLs com bined variance between acoustic levels addition becomes insignificant about 20 dB adds SPLs 80 dB 100 dB result 1008 dB practical implications will become clear realizes model aircraft noise derives several sourcesthe engine airframe propellerand propeller noise itself blends several components Often reducing lesser noise source fails produce noticeably quieter aircraft Consider example aircraft 80 dB engine noise 90 dB propeller noise As have seen formula given above able completely elim inate engine noise lesser source resulting acoustic power would discernibly reduced hypothetical example subtracting 80 dB engine noise acoustical power 904 dB total noise power slightly lowers total output about 90 dBnot significant change achieve meaningful reduction model air craft sound necessary reduce dominant source noise Justification Propeller Noise Reduction fundamental objective research project has verify sound pro duced propeller fact domi nant noise mechanism model aviation project assumes reasonable offthe-shelf muffler used aircraft since absence such use use poor muffler engine sounds likely dominate noise signature Measure ments acquired during different phases research provide several pieces evi dence indicate propeller noise dominates over produced properly muffled engine Flight test data provides first bit ev idence An instrumented aircraft flown fixed height over microphone peak OASPL measured dBA flight speed rpm throttle setting also recorded data compared obtained same propellers driven electric motor wind tunnel laboratory thereby eliminating power plant significant source noise Although flight velocities precisely duplicated lab several cases offer reasonable basis compari son such case SPL bladepassing frequency lab 78 dB simulated flight velocity 100 kmph ki lometers per hour microphone dis tance corrected same distance used flight tests flight test 120 kmph resulted OASPL 764 dBA OASPL includes frequencies spectrum whereas lab data ob tained blade-passing frequency Since engine airframe noise absent lab data would have ex pected flight test noise louder results support inference engine airframe noise did reach significant level flight tests done would have tended dominate rais ing OASPL above SPL measured lab fact propeller noise alone approximately equal total noise mea sured flight Table 1 shows data selected tests operating conditions nearly identical Group 1 contains propel lers same manufacturer tal variation mean rpm less 1% total variation flight velocity approximately 5% Groups 2 3 in40 Model Aviation RIG SKY CRADLES FIELD BOX MODEL$1595 BENCH MODEL$1995 FLOOR MODEL$2395 CEILING HANGERS SMALL20-40 .$995 MEDIUM 40- 60 95 LARGE 50-BO. $1195 nvur HAIFt FITS ALL PICKUPS . 5 cluded propellers two different manu facturers Group 4 propellers sin gle manufacturer Since flight speed rpm nearly same group aircraft always level flight measure ment point thrust produced likewise nearly same data groups Table 1 Clearly engine airframe having almost identically groups can therefore inferred observed large variations OASPL between cases within group rather being caused engine airframe noise result dif ferences sound levels among propellers Further assuming situation en gine noise closely approximated level propeller noise completely eliminating engine noise would effect noise re duction 6 dBa value ex ceeded differences noted among props particular group final piece evidence yielded data obtained two different mufflers during flight tests stock muffler re placed high-quality state-of-the-art muf fler data recorded two different flight speeds using same propeller 120 kmph difference OASPL measured 02 dBA 90 kmph difference 03 dBA Such ex tremely small variance suggests given flight speed advanced muffler no effect total noise output ever full throttle engine performed better upgraded muffler ad ditional rpm permitted latter creased noise levels improved engine performance advanced muffler did significantly impact noise level long flight speed remained constant test results clearly establish pro peller dominant source model air craft noise remainder discus sion will assume case Propeller Noise Sources sound produced model propel ler compounded several elements important include noise due thrust torque noise thickness noise referred discrete fre quency noise sources because sound produced occurs bladepassing frequency its harmonics blade-passing frequency rate blade passes given point propel ler disc product number blades rotational speed rev/sec understand noise mecha nisms operate imagine fixed point rotational disc propeller time blade near point air pressure its ordinary value Air pres sure changes blade passes through pushes air aside amount dis placed air depending thickness blade noise produced periodic displacement air known thickness noise Continued page 42 VJO ds best Sel 09 Spak osen ByTan Odginds TItG Mfg ml AM Aircraft Saqiply its outstenhg ruimhity Comp e e s ng e cyl nder system nclud ng ho e couped spark advance kt spark gead25 p ug ba e y pack charger 900 sh elded Much kmger 1gm hIs Easy haid sterts-no kickback 1AUO-12000 RPM rubble ii 0% power few strokers oni nutubbmi mviii Lower pricad fuels no okra neededMqleeduul9Fphagcovw FormumyuapaesI0&p2ft4strokeslegieudtwlsctulrs Klotzaioahactsaviule Splc cub aperk ded ibm bed ft tbi*ag hits avabbis CAT NO 106 Proof Switch Retail S995 Add $125 shipping Send $150 catalog Michigan residents add 4% sales tax IMPROVE YOUR 1991 SWITCH OVER ej Proof Switch Positive Locking Prevents Arriving field dead batteries Accidental switching off before take-off Will vibrate apart causing loss radio Does require special mounts Works radios Ideal seaplanes completely water proof SEE YOUR LOCAL HOBBY DEALER unavailable locally send Bru Line Industries Inc 4.. PO Box 3786 Center Line MI 48015 WASHINGTON S AMA BASE. $ An50 1 per couple per night Check day Minimum stay 2 nights Free Parking Cars Free Full Breakfasts Free Merropass Sat Sun Free Harrington Hawk Cafeteria avA 11th & E Streets NW Washington DC 20004G9 0-424-8532 628 8140T70 omm December 1989 41 Em 0AMA MEMBER RATE Tax no included A Radio South Batteries 500 ma Pack 48V Futaba conn 800 ma Pack 48V Futaba conn 1200 ma Pack 48V Futaba conn TX batt Futaba G-Series PCM 1300 1550 2200 2475 2400 2700 2995 RADIO SOUTH __ AUTHORIZED SERVICE CENTER Call Tony Stiliman Ken Dudley custom work competition needs stock complete hobby line specializing competition accessoriesall discounted prices bS ______ __ FREQUENCY CONVERSIONS _______9jgCY~ Frequency Comnnuee Approved @0__ stock Futaba JR radios Featuring fast service byOAYS engines parts qualified people thePhHatori headers pipes latest equipment Including aGh$tIWe Repair Heli Sets Gyros SPECTRUM ANA YZER Al Orders COD VISA MC American Express OPEN 8-5 CST P rices subject change notice 9003 N Davis Hwy Pensacola FL 32514 904 478-6745 As propeller blade passes through given point disc also exerts thrust torque forces cause pressure fluc tuation As air pressure displacement pressure fluctuation propagates sound known thrust torque noise point propeller disc pres sure fluctuates time blade passes total pressure disturbance sum disturbances caused thrust torque thickness certain other effects disturbances vary strength travels its own preferred direction combined effect pressure fluc tuations perceived propeller noise pressure amplitudes of components propeller noise depen dent relative amounts thrust torque well propeller tip speed itself proportional product rotational speed propeller di ameter Thrust torque noise generally significant sources propeller sound should noted ever since thickness noise consider ably affected tip speed thrust torque noise its relative impor tance will increase increasing rota tional speed Any attempt make sense propel ler noise problem complicated overlapping often interdependent ef fects acoustic sources example Figure 4 shows propeller blade lift does point exactly thrust direc tion means blade lift contrib utes both thrust torque hence both thrust torque noise Additionally noise various sources radiates away propeller overlapping pat terns difficult distinguish reduce propeller noise must dis cover dominant noise mechanism work can directed toward lessening source cant done some knowledge intricate makeup pro peller noise Its important understand its interplay factors associ ated aircraft operationengine per formance aircraft drag flight speed rpm propeller diameter pitch etcwhich pro duces noise perceived human ear Conducting scientific study such truly complicated system ridden variables difficult structured building block approach being used North Carolina State University laboratory data correlated both flight test data classical mathematical propel ler theory Although quite time-consuming process does provide direct path final answers research findings suggest propel ler noise may dominant acoustic source model aircraft may deed possible diminish leading Continued page 156 TO ORDER CALL 1406 265-4828 IT-i TRANSMITTER TRAY * Recommended especially handicaps beginners.experienced pilots love also * Pays itself times over airplanes saved l With set Gimbal Extenders $350 Postage & Handling Make Flying Breeze~ BJ ENTERPRISES 1100 Center Havre Montana 59501 42 Model Aviation GATOR RIC PRODUCTS DELUX ALL BALSA KIT An new Tiger Tail 120 four strokes piped 60 two strokes beautiful performer competition just showing offI balsa kit machined wood parts complete lsardware package includes plug-in djustable stab parts new wing mounts Wing Span- 72 inWing Ara 860 sq Complete Delux KitSI 5995 TRANSMITTER CASE An inexpensive rugged molded case protect expensive transmitter both two stick single stick transmitters Black leather grain aluminum trim locking clasp SI 995 MV-I TYPHOON New F3A competition Big beautiful flyer balsa construction plug-in wings 120 four stroke 60 two stroke power Plans-two sheets S 1495 Fiberglass cowl Si 595 Clear butyrate canopy. 5 995 OTHER PLANS Tiger Tail 4S-two sheets 120 four strokesS 1495 TAR baby 120 four strokes51195 Alley Kat 40 size trainer sportS 895 Gator Flea 40 size sport5 895 Bobcat 40 size sportS 895 feather Ilte glass cloth 7 ozsq yd est weave Fastest Filling test Finished Weight Big 3 Sq Yard Pkg Oetailed Instructions- $895 Include $2 SOlItem UPS esidents Add 6% Sales Tax GATOR RIC PRODUCTS 3713 Pompano Dr acola FL 32514 4768639 Letters Editor Continued page 12 Ken opened hobby shop Burk & Company Department Store after World War II worked him full-time year until started college After worked part-time until completing college Milton H Fanning Nashville TN Safety/Preston Continued page 22 some MonoKote repairs moral tale wise keep small extinguisher field box As alter native may possible smother fire towel rag blanket Cub Yellow engine cowling first RC model powered Cox 09 began turn first orange brown able smother fire wrap ping rag around front model Have safe month Keytwo/Randoiph Continued page 30 der everything place range check equipmentand its time fly Flying has wide performance en velope compared Paskey Keytwo basically quite gentle flier Whether upright inverted stall shows abso lutely no tendency snap fact model balanced correctly its very diffi cult make snap snaps bag move center-of-gravity aft about /2 increase elevator throw rate /16 up down movement trailing edge aile rons about right comfortable flying Landings can made nose-high slow full aileron control way touch down problem knife-edge flight first airplane persistently climbed half-loop until learned nose stayed up just little rudder Once Id mastered technique knife-edge loops included Keytwos repertoire tricks what did Eddie Williams have say about latest re-creation see youve built another Paskey said unsung maestro drunken pilot routine Its about time Play again Eddie Radio Technique/Myers Continued page 34 Failsafe Flight System small 15 sq light less ounce inexpensive has very low operating current 70 mA works no doubt nine-volt transistor radio batteries expensive about $250 Duracells live will last long time some chance will get care less let run down some critical time unit meets its claims follow admonition use fresh batteries check servo speed during preflight inspection careless youll probably crash some other reason anyway Failsafe Flight System @ $3995 list T&D Flight Systems PO Box 1782 Staten Island NY 10314 additional information call Alex Kronfeld l-7t8/984-9121 Propeller Noise Continued page 42 cause poor community relations Much cure will depend upon education Modelers need understand nature problem order properly utilize solu tions article has introduced propel ler noise problem provided some neces sary background Subsequent articles will explain test results greater detail describe what modeler can achieve better aircraft performance less noise RC Soaring/Blakeslee Continued page 49 down hes hoping arrange factur ers demonstrations during meet would flying demos followed show-andtell sessions guys like Byron Bruce Combat Models Marty Silberstein Steve Peacock Cliff Hangar Models Brian Laird Paul Masura Slope Scale Models Other Id imagine itll much like fabulously suc cessful Richland Scale Slope Fun Flyie fly want long have pin Info available writing Charley SSN 2601 E 19th 51 #29 Signal Hill CA 90804 Better call him 1-213/494-3712 1990 Soaring contests Ray Hayes Vice Presi dent LSF wrote remind us now time plan next years big contests Spe cifically Ray talking about every-evenyear LSF Regionals annual NSS Soar-Ins put go-ahead clubs around coun try Theyre bit expensive Ray hoping Continue tradition awarding beautiful LSF plaques LSF Regionals Theyre worth winning Ray also hoping three super con tests NSS Masters LSF Nationals AMA Nats can spread around country 1990 contests West Coast 89 Ray afraid guys east Kansas beginning feel left out youd like info LSF Regionals check Ray 69598 Brookhill Dr Romeo MI 48065 phone 1-313/ 752-6163 NSS Soar-Ins have handled Marshall Long past few years assume youre 90 Marshall Marshalls address 824 Garden Meadow Universal City TX 78148 worry East Coasters hear Nats will Lawrenceville IL 90 RC Aerobatics/Van Putte Continued page 51 aerodynamic center segment wing Youll note root segment tip another segment Figure 4 shows geometric technique solu tion Remember aerodynamic center panel 25% point mean aerody namic chord panel Once youve determined aerodynamic cen ter panel must calculate area panel using Equation 2 measure distance convenient line aerody namic centers panels Figure 4 shows con venient reference line distance re spective aerodynamic centers distance back reference line aerodynamic center wing located determined Equation 3 mean aerodynamic chord complete wing calculated individual values shown Equation 4 looks just like equa tion determining distance wing aero dynamic center doesnt should since 156 Model Aviation
Edition: Model Aviation - 1989/12
Page Numbers: 36, 37, 38, 39, 40, 41, 42, 156
D Heathcoat R Nagel Model Propeller NOISEc first series articles describes in-depth research spon sored AMA conducted North Carolina State Univer sity severity sources reduction propeller noise findings some unprecedented could have ma jor impact model airplane_flying community ADVANCES model aviation over past decade have spurred tremendous growth hobby year thousands people across US becoming ac tive participants weekend sessions local flying field greatest influx newcomers sport naturally occurs near large cities population con centrated flying sites tend lo cated suburban areas allows easy access fliers also subjects uninterested neighbor characteris tic whine model aircraft surprisingly greatest activity model field occurs weekends weekday evenings just peo ple living nearby home expecting chance relax involved sport well aware bitter confrontation scenario sometimes provokes ten modelers lose battle begin search another suitable flying site Losing established flying site hav ing search new can frustrat ing costly experience Ultimately has negative effect organization continued growth sport Its clear continuously relocating flying fields farther farther away populated ar eas isnt answer rate rural de velopment flying site relocation will lit tle postpone inevitable return problem solution instead develop model aircraft operate lower sound levels quite evident commonly accepted model aircraft noise generated propulsion system casual observer obvious sources intake combustion exhaust noise generated power plantand airframe noise re sulting its characteristic vibration However propeller too impor tant source noiseone misunder stood consequently overlooked fact acoustic research full-scale aircraft indicates propeller noise dominates over other sources sound illustrated following quote Journal Aircraft has well known years propellerdriven aircraft propeller primary source noise observation may 36 Model Aviation gu hold true model aircraft well effort better understand model pro Di recti Ro tat peller noise establish guidelines ultimately will lead quieter model aircraft AMA sponsored research pro Table 1Selected Flight Test Data Prop Velocity RPM QASPI kmphdBA Group 1 11 x5180160001110 9x7519516400960 9x719016250934 Group 2 10x615013500878 11 x614312000990 Group 3 10x712011000840 9x7512011250810 10x612010800764 Group 4 11 x 5908500925 9 x 7908700830 gram conducted North Carolina State Uni versity principal investigators include Dr Robert T Nagel associate professor nearly 15 years research experience aeroacoustics Robert Vess aero space engineer six years experience coordinator NC State University aerospace laboratories 18 years activ ity Radio Control including Pattern Hel icopter fun fly competition David M Heathcoat received bachelors degree physics NC State University 1986 participated propeller noise research masters degree thesis article first series will describe tests performed explain results make recommendations toward reducing model aircraft noise Im proving noise problem means averting loss flying sites will depend largely having knowledgeable fliers Due technical nature mate rial will precede discussion test program details brief explanation basic propeller theory Introducing some important aspects propeller per formance section will lead better understanding both current study propellers general Since formulas scientific jargon tend limit interest type article effort has made avoid use Basic Propeller Theory order aircraft move through air propelling force must work propeller essentially small rotating wing produces required thrust speed aircraft level flight deter mined relating thrust available power plant total aircraft drag Note both forces vary signifi cantly airspeed depicted typi cal aircraft Figure 1 example moving left right along horizontal axis Figure 1 represents increasing airspeed notes aircraft drag increases eventually exceeds thrust Point 1 figure represents case air craft accelerating since thrust pro duced propeller much greater aircraft drag Conversely aircraft operating point 2 predominance drag over thrust causes decelerate cases airspeed will stabi lize point 3 thrust drag equal Since engine example full throttle point 3 represents maximum tainable airspeed aircraft/engine/ propeller combination level flight re duction power below full throttle ef fectively shifts thrust curve downward resulting reduction maximum airspeed see dashed curve Figure 1 Similarly anything can done pro duce thrust less drag will shift December 1989 37 Figu curves allowing greater flight speeds Figure 1 has shown thrust produced power plant actually decreases yond certain threshold airspeed phenomenon results changes air flow around propeller high airspeeds As propeller rotates flow approaches its leading edge speed depends rotational speed rpm engine However forward movement aircraft creates additional flow ap proaches propeller disc speed equal forces acting propeller best explained examining thin slice blade such shown cross section Figure 2 Once again explanation simplified differentiating effects due blade rotation caused forward speed Figure 3 depicts flow action sec tion typical propeller blade due its ro tation alone would case engine being run model re strained flow approaches prop angle dictated blade pitch Just wing produces lift drag certain gle attack propeller produces sim ilar forces depend engine rpm shape blade airfoil lift force example acts along axis rotation force axial direction termed thrust Similarly drag force acts plane rotation pro peller resists its rotation defined torque Figure 4 illustrates condition after aircraft released acquires addi tional flow field its forward move ment simple way graphically depict combination two flows use special arrows called vectors flow represented single vector relative speed flow given length its vector flow direction rep resented direction vec tor pointing two propeller flow vectors arranged nose-to-tail Fig ure 4 rotation forward flight other vector completes triangle represents flow field resulting combination Notice speed direction resultant vector can al tered changing length speed original vectors Therefore flow around propeller indeed does depend both engine rpm forward flight speed flow vectors combine shown Figure 4 forces acting propel ler diminish Hence blade airfoil angle attack Figure 4 decreased com pared Figure 3 addition since lift drag forces measured respect altered flow angle slanted away axis rotation propel ler Therefore net thrust decreased further since lift force acting pre cisely thrust direction misdirection lift also shown Figure 4 reality thrust lost due slanting lift force becomes ad ditional torque load engine must overcome effectively demonstrates propeller performance very different flight ground better understanding engine turns propeller under varying load conditions can gained referring Fig ure 5 Assume drag forces acting point blade propeller example added together sum found lso assume net drag force determined act ing through point 12 center crankshaft product lb 12-in distance represents 6 in-lb b torque load blade propeller Since two blades net torque load power plant must produce order turn blades constant rotational speed 12 38 Model Aviation 0 flight velocity Figure 2 illustrates relative directions simultaneous flows respect propeller ro tating counterclockwise in-lb 1 ft-lb engine capable producing torque under condi tions rotational speed will increase cant produce enough torque rotational speed will achieved power available engine simply rotational speed multiplied amount torque can applied propeller given rpm example engine can produce 33 ft-lb torque 10000 rpm 16667 rev/sec power rotational speed 550 ft lb/sec example chosen order put value power recogniz able units Since horsepower 1 hp equivalent 550 ft-lb/sec engine producing exactly horsepower under operating conditions Figure 6 illustrates way horsepower output torque typical model engine vary rotational speed Most engines available modelers have curves resemble example actual magnitude power torque rotational speed depends physi cal design particular engine As mentioned above power required turn propeller product torque rotational speed power produced propeller proportional product thrust forward speed ratio power produced propeller required turn known propeller efficiency An efficient propeller capable producing given amount thrust using less power inefficient Equivalently efficient propeller can produce greater thrust therefore greater ward speed using same engine power Rather being fixed value efficien cy depends physical design opera ting rpm flight speed specific pro peller therefore improper categori cally call prop efficient other unless advantage holds true rotational forward speeds Propeller ef ficiency plays major role increasing air craft performance reducing noise Basic Noise Definitions Sound waves simply minute pressure fluctuations propagate air characterized two parameters frequency amplitude Frequency refers number pressure pulses pres sure fluctuations occur sec ond perceived ear pitch Like higher notes piano keyboard higher frequencies actually sound higher pitched Pressure amplitude measure size acoustical disturbance corresponds loudness sound simple tone characterized single frequency single amplitude Complex sounds composed different fre quencies Pressure amplitude measured deci bels dB measured referred sound pressure level SPL Continued page 40 Order direct Add $1500 shipping Use VISA MC check money order COD GOLIDW AGE MODELS RO box 807 Ienn Vcilleq CA 95946 916 432-2928 B&P Associates Gives Total FlIgbt Line FREEDOM battery needs call write B&P Associates PO Box 22054 Waco TX 76702-2054 817662-5587 new electric starter battery pack cuts cord has always tied starter power panel Discover freedom being able start plane wherever added safety less wire get caught prop charge hefty 4 Amp/hour pack will take through weekend flying power enough spare dont stop have Ni-Cads virtually size imaginable cut experimenter free design whatever ii takes make yours best setup field December 1989 39 h C, qusrter scale com plete deluxe kit features exact scale outlines balsa plywo, onstruction light epoxy cowl wheel pants selected wood complete hardware flying wires full cockpit details 3-views photos decals extensive instruction manual 20 cu ne lighL upoxy glass uuiage cowl wheel pants complete hardware selected wood decals 3-views cu engliw epoxy glass fudy owl wheel pants light foam wing cores con test wood complete hardware decals Satisfaction Guaranteed1 EA~ HINELZ SH-710 Pkg 24-52 95 THE HIGH-TECH HINGE DESIGNED FOR THE CYANOACRYLATE AGE Easier install other hinge No gouging picking messy epoxies Simply cut single knife slot hinge slide hinges place apply few drops favorite CA glue youre donel SUPER FAST SUPER EASY SUPER STRONG SIG MFG CO INC401-7 So Front St.Montezuma IA 50171 23-5154 LANDER INDUST 1005 19TH ST CT HAVRE MONTANA 59501 406265-6529 PRICES INCLUDE FREIGHT CANADIAN ORDERS ADD 25% ViSA Pwtakeet SUpeJL Po4 PO4JIWkQ 40. FREE CATALOG Ti4ewaiwt I4otoluj eIdWIIAi*e 392SC SE 13th Court Scala FImna 32571 904 6943531 sound pressure level corresponds dis crete frequency range frequencies overall sound pressure level' OASPL also measured decibels measure sound obtained adding SPLs frequency spectrum decibel reflecting fact human ear perceives very wide range sound pressure based loga rithmic scale rather linear compresses sonic data ease inter pretation Still another measure noise sound power level PWL based quantity acoustical power pro duced given source rather pres sure amplitude given location Since sound power level also measured dB its important keep track whether mea surements given units PWLs SPLs Sounds certain frequency ranges perceived being louder sounds other frequencies Weighted sound level curves have developed take fact account weighted scale used almost industrial commu nity noise standards US Sound lev els measured according scale ex pressed units called dBA significance relative contribu tions various components noise cannot appreciated general understanding manner sound levels combined two equal sound pressure levels SPLs added together combined sound level will 6dB higher orig inal value Adding together two equal sound power levels PWLs produces level 3 dB higher phenome non result logarithmic nature dB scale means levels separated few dB fact very different ab solute values acoustic power level PWL expressed dB adding two powers differ 10 dB pro duces no significant increase power yond higher two Consider ex ample adding 80 dB 90 dB powers dB1 B dB2 B total dBtotai given follow ing formula dBtotai og[l0dB/o 2/1O] dB Sound pressure levels SPLs behave similar fashion two SPLs com bined variance between acoustic levels addition becomes insignificant about 20 dB adds SPLs 80 dB 100 dB result 1008 dB practical implications will become clear realizes model aircraft noise derives several sourcesthe engine airframe propellerand propeller noise itself blends several components Often reducing lesser noise source fails produce noticeably quieter aircraft Consider example aircraft 80 dB engine noise 90 dB propeller noise As have seen formula given above able completely elim inate engine noise lesser source resulting acoustic power would discernibly reduced hypothetical example subtracting 80 dB engine noise acoustical power 904 dB total noise power slightly lowers total output about 90 dBnot significant change achieve meaningful reduction model air craft sound necessary reduce dominant source noise Justification Propeller Noise Reduction fundamental objective research project has verify sound pro duced propeller fact domi nant noise mechanism model aviation project assumes reasonable offthe-shelf muffler used aircraft since absence such use use poor muffler engine sounds likely dominate noise signature Measure ments acquired during different phases research provide several pieces evi dence indicate propeller noise dominates over produced properly muffled engine Flight test data provides first bit ev idence An instrumented aircraft flown fixed height over microphone peak OASPL measured dBA flight speed rpm throttle setting also recorded data compared obtained same propellers driven electric motor wind tunnel laboratory thereby eliminating power plant significant source noise Although flight velocities precisely duplicated lab several cases offer reasonable basis compari son such case SPL bladepassing frequency lab 78 dB simulated flight velocity 100 kmph ki lometers per hour microphone dis tance corrected same distance used flight tests flight test 120 kmph resulted OASPL 764 dBA OASPL includes frequencies spectrum whereas lab data ob tained blade-passing frequency Since engine airframe noise absent lab data would have ex pected flight test noise louder results support inference engine airframe noise did reach significant level flight tests done would have tended dominate rais ing OASPL above SPL measured lab fact propeller noise alone approximately equal total noise mea sured flight Table 1 shows data selected tests operating conditions nearly identical Group 1 contains propel lers same manufacturer tal variation mean rpm less 1% total variation flight velocity approximately 5% Groups 2 3 in40 Model Aviation RIG SKY CRADLES FIELD BOX MODEL$1595 BENCH MODEL$1995 FLOOR MODEL$2395 CEILING HANGERS SMALL20-40 .$995 MEDIUM 40- 60 95 LARGE 50-BO. $1195 nvur HAIFt FITS ALL PICKUPS . 5 cluded propellers two different manu facturers Group 4 propellers sin gle manufacturer Since flight speed rpm nearly same group aircraft always level flight measure ment point thrust produced likewise nearly same data groups Table 1 Clearly engine airframe having almost identically groups can therefore inferred observed large variations OASPL between cases within group rather being caused engine airframe noise result dif ferences sound levels among propellers Further assuming situation en gine noise closely approximated level propeller noise completely eliminating engine noise would effect noise re duction 6 dBa value ex ceeded differences noted among props particular group final piece evidence yielded data obtained two different mufflers during flight tests stock muffler re placed high-quality state-of-the-art muf fler data recorded two different flight speeds using same propeller 120 kmph difference OASPL measured 02 dBA 90 kmph difference 03 dBA Such ex tremely small variance suggests given flight speed advanced muffler no effect total noise output ever full throttle engine performed better upgraded muffler ad ditional rpm permitted latter creased noise levels improved engine performance advanced muffler did significantly impact noise level long flight speed remained constant test results clearly establish pro peller dominant source model air craft noise remainder discus sion will assume case Propeller Noise Sources sound produced model propel ler compounded several elements important include noise due thrust torque noise thickness noise referred discrete fre quency noise sources because sound produced occurs bladepassing frequency its harmonics blade-passing frequency rate blade passes given point propel ler disc product number blades rotational speed rev/sec understand noise mecha nisms operate imagine fixed point rotational disc propeller time blade near point air pressure its ordinary value Air pres sure changes blade passes through pushes air aside amount dis placed air depending thickness blade noise produced periodic displacement air known thickness noise Continued page 42 VJO ds best Sel 09 Spak osen ByTan Odginds TItG Mfg ml AM Aircraft Saqiply its outstenhg ruimhity Comp e e s ng e cyl nder system nclud ng ho e couped spark advance kt spark gead25 p ug ba e y pack charger 900 sh elded Much kmger 1gm hIs Easy haid sterts-no kickback 1AUO-12000 RPM rubble ii 0% power few strokers oni nutubbmi mviii Lower pricad fuels no okra neededMqleeduul9Fphagcovw FormumyuapaesI0&p2ft4strokeslegieudtwlsctulrs Klotzaioahactsaviule Splc cub aperk ded ibm bed ft tbi*ag hits avabbis CAT NO 106 Proof Switch Retail S995 Add $125 shipping Send $150 catalog Michigan residents add 4% sales tax IMPROVE YOUR 1991 SWITCH OVER ej Proof Switch Positive Locking Prevents Arriving field dead batteries Accidental switching off before take-off Will vibrate apart causing loss radio Does require special mounts Works radios Ideal seaplanes completely water proof SEE YOUR LOCAL HOBBY DEALER unavailable locally send Bru Line Industries Inc 4.. PO Box 3786 Center Line MI 48015 WASHINGTON S AMA BASE. $ An50 1 per couple per night Check day Minimum stay 2 nights Free Parking Cars Free Full Breakfasts Free Merropass Sat Sun Free Harrington Hawk Cafeteria avA 11th & E Streets NW Washington DC 20004G9 0-424-8532 628 8140T70 omm December 1989 41 Em 0AMA MEMBER RATE Tax no included A Radio South Batteries 500 ma Pack 48V Futaba conn 800 ma Pack 48V Futaba conn 1200 ma Pack 48V Futaba conn TX batt Futaba G-Series PCM 1300 1550 2200 2475 2400 2700 2995 RADIO SOUTH __ AUTHORIZED SERVICE CENTER Call Tony Stiliman Ken Dudley custom work competition needs stock complete hobby line specializing competition accessoriesall discounted prices bS ______ __ FREQUENCY CONVERSIONS _______9jgCY~ Frequency Comnnuee Approved @0__ stock Futaba JR radios Featuring fast service byOAYS engines parts qualified people thePhHatori headers pipes latest equipment Including aGh$tIWe Repair Heli Sets Gyros SPECTRUM ANA YZER Al Orders COD VISA MC American Express OPEN 8-5 CST P rices subject change notice 9003 N Davis Hwy Pensacola FL 32514 904 478-6745 As propeller blade passes through given point disc also exerts thrust torque forces cause pressure fluc tuation As air pressure displacement pressure fluctuation propagates sound known thrust torque noise point propeller disc pres sure fluctuates time blade passes total pressure disturbance sum disturbances caused thrust torque thickness certain other effects disturbances vary strength travels its own preferred direction combined effect pressure fluc tuations perceived propeller noise pressure amplitudes of components propeller noise depen dent relative amounts thrust torque well propeller tip speed itself proportional product rotational speed propeller di ameter Thrust torque noise generally significant sources propeller sound should noted ever since thickness noise consider ably affected tip speed thrust torque noise its relative impor tance will increase increasing rota tional speed Any attempt make sense propel ler noise problem complicated overlapping often interdependent ef fects acoustic sources example Figure 4 shows propeller blade lift does point exactly thrust direc tion means blade lift contrib utes both thrust torque hence both thrust torque noise Additionally noise various sources radiates away propeller overlapping pat terns difficult distinguish reduce propeller noise must dis cover dominant noise mechanism work can directed toward lessening source cant done some knowledge intricate makeup pro peller noise Its important understand its interplay factors associ ated aircraft operationengine per formance aircraft drag flight speed rpm propeller diameter pitch etcwhich pro duces noise perceived human ear Conducting scientific study such truly complicated system ridden variables difficult structured building block approach being used North Carolina State University laboratory data correlated both flight test data classical mathematical propel ler theory Although quite time-consuming process does provide direct path final answers research findings suggest propel ler noise may dominant acoustic source model aircraft may deed possible diminish leading Continued page 156 TO ORDER CALL 1406 265-4828 IT-i TRANSMITTER TRAY * Recommended especially handicaps beginners.experienced pilots love also * Pays itself times over airplanes saved l With set Gimbal Extenders $350 Postage & Handling Make Flying Breeze~ BJ ENTERPRISES 1100 Center Havre Montana 59501 42 Model Aviation GATOR RIC PRODUCTS DELUX ALL BALSA KIT An new Tiger Tail 120 four strokes piped 60 two strokes beautiful performer competition just showing offI balsa kit machined wood parts complete lsardware package includes plug-in djustable stab parts new wing mounts Wing Span- 72 inWing Ara 860 sq Complete Delux KitSI 5995 TRANSMITTER CASE An inexpensive rugged molded case protect expensive transmitter both two stick single stick transmitters Black leather grain aluminum trim locking clasp SI 995 MV-I TYPHOON New F3A competition Big beautiful flyer balsa construction plug-in wings 120 four stroke 60 two stroke power Plans-two sheets S 1495 Fiberglass cowl Si 595 Clear butyrate canopy. 5 995 OTHER PLANS Tiger Tail 4S-two sheets 120 four strokesS 1495 TAR baby 120 four strokes51195 Alley Kat 40 size trainer sportS 895 Gator Flea 40 size sport5 895 Bobcat 40 size sportS 895 feather Ilte glass cloth 7 ozsq yd est weave Fastest Filling test Finished Weight Big 3 Sq Yard Pkg Oetailed Instructions- $895 Include $2 SOlItem UPS esidents Add 6% Sales Tax GATOR RIC PRODUCTS 3713 Pompano Dr acola FL 32514 4768639 Letters Editor Continued page 12 Ken opened hobby shop Burk & Company Department Store after World War II worked him full-time year until started college After worked part-time until completing college Milton H Fanning Nashville TN Safety/Preston Continued page 22 some MonoKote repairs moral tale wise keep small extinguisher field box As alter native may possible smother fire towel rag blanket Cub Yellow engine cowling first RC model powered Cox 09 began turn first orange brown able smother fire wrap ping rag around front model Have safe month Keytwo/Randoiph Continued page 30 der everything place range check equipmentand its time fly Flying has wide performance en velope compared Paskey Keytwo basically quite gentle flier Whether upright inverted stall shows abso lutely no tendency snap fact model balanced correctly its very diffi cult make snap snaps bag move center-of-gravity aft about /2 increase elevator throw rate /16 up down movement trailing edge aile rons about right comfortable flying Landings can made nose-high slow full aileron control way touch down problem knife-edge flight first airplane persistently climbed half-loop until learned nose stayed up just little rudder Once Id mastered technique knife-edge loops included Keytwos repertoire tricks what did Eddie Williams have say about latest re-creation see youve built another Paskey said unsung maestro drunken pilot routine Its about time Play again Eddie Radio Technique/Myers Continued page 34 Failsafe Flight System small 15 sq light less ounce inexpensive has very low operating current 70 mA works no doubt nine-volt transistor radio batteries expensive about $250 Duracells live will last long time some chance will get care less let run down some critical time unit meets its claims follow admonition use fresh batteries check servo speed during preflight inspection careless youll probably crash some other reason anyway Failsafe Flight System @ $3995 list T&D Flight Systems PO Box 1782 Staten Island NY 10314 additional information call Alex Kronfeld l-7t8/984-9121 Propeller Noise Continued page 42 cause poor community relations Much cure will depend upon education Modelers need understand nature problem order properly utilize solu tions article has introduced propel ler noise problem provided some neces sary background Subsequent articles will explain test results greater detail describe what modeler can achieve better aircraft performance less noise RC Soaring/Blakeslee Continued page 49 down hes hoping arrange factur ers demonstrations during meet would flying demos followed show-andtell sessions guys like Byron Bruce Combat Models Marty Silberstein Steve Peacock Cliff Hangar Models Brian Laird Paul Masura Slope Scale Models Other Id imagine itll much like fabulously suc cessful Richland Scale Slope Fun Flyie fly want long have pin Info available writing Charley SSN 2601 E 19th 51 #29 Signal Hill CA 90804 Better call him 1-213/494-3712 1990 Soaring contests Ray Hayes Vice Presi dent LSF wrote remind us now time plan next years big contests Spe cifically Ray talking about every-evenyear LSF Regionals annual NSS Soar-Ins put go-ahead clubs around coun try Theyre bit expensive Ray hoping Continue tradition awarding beautiful LSF plaques LSF Regionals Theyre worth winning Ray also hoping three super con tests NSS Masters LSF Nationals AMA Nats can spread around country 1990 contests West Coast 89 Ray afraid guys east Kansas beginning feel left out youd like info LSF Regionals check Ray 69598 Brookhill Dr Romeo MI 48065 phone 1-313/ 752-6163 NSS Soar-Ins have handled Marshall Long past few years assume youre 90 Marshall Marshalls address 824 Garden Meadow Universal City TX 78148 worry East Coasters hear Nats will Lawrenceville IL 90 RC Aerobatics/Van Putte Continued page 51 aerodynamic center segment wing Youll note root segment tip another segment Figure 4 shows geometric technique solu tion Remember aerodynamic center panel 25% point mean aerody namic chord panel Once youve determined aerodynamic cen ter panel must calculate area panel using Equation 2 measure distance convenient line aerody namic centers panels Figure 4 shows con venient reference line distance re spective aerodynamic centers distance back reference line aerodynamic center wing located determined Equation 3 mean aerodynamic chord complete wing calculated individual values shown Equation 4 looks just like equa tion determining distance wing aero dynamic center doesnt should since 156 Model Aviation
Edition: Model Aviation - 1989/12
Page Numbers: 36, 37, 38, 39, 40, 41, 42, 156
D Heathcoat R Nagel Model Propeller NOISEc first series articles describes in-depth research spon sored AMA conducted North Carolina State Univer sity severity sources reduction propeller noise findings some unprecedented could have ma jor impact model airplane_flying community ADVANCES model aviation over past decade have spurred tremendous growth hobby year thousands people across US becoming ac tive participants weekend sessions local flying field greatest influx newcomers sport naturally occurs near large cities population con centrated flying sites tend lo cated suburban areas allows easy access fliers also subjects uninterested neighbor characteris tic whine model aircraft surprisingly greatest activity model field occurs weekends weekday evenings just peo ple living nearby home expecting chance relax involved sport well aware bitter confrontation scenario sometimes provokes ten modelers lose battle begin search another suitable flying site Losing established flying site hav ing search new can frustrat ing costly experience Ultimately has negative effect organization continued growth sport Its clear continuously relocating flying fields farther farther away populated ar eas isnt answer rate rural de velopment flying site relocation will lit tle postpone inevitable return problem solution instead develop model aircraft operate lower sound levels quite evident commonly accepted model aircraft noise generated propulsion system casual observer obvious sources intake combustion exhaust noise generated power plantand airframe noise re sulting its characteristic vibration However propeller too impor tant source noiseone misunder stood consequently overlooked fact acoustic research full-scale aircraft indicates propeller noise dominates over other sources sound illustrated following quote Journal Aircraft has well known years propellerdriven aircraft propeller primary source noise observation may 36 Model Aviation gu hold true model aircraft well effort better understand model pro Di recti Ro tat peller noise establish guidelines ultimately will lead quieter model aircraft AMA sponsored research pro Table 1Selected Flight Test Data Prop Velocity RPM QASPI kmphdBA Group 1 11 x5180160001110 9x7519516400960 9x719016250934 Group 2 10x615013500878 11 x614312000990 Group 3 10x712011000840 9x7512011250810 10x612010800764 Group 4 11 x 5908500925 9 x 7908700830 gram conducted North Carolina State Uni versity principal investigators include Dr Robert T Nagel associate professor nearly 15 years research experience aeroacoustics Robert Vess aero space engineer six years experience coordinator NC State University aerospace laboratories 18 years activ ity Radio Control including Pattern Hel icopter fun fly competition David M Heathcoat received bachelors degree physics NC State University 1986 participated propeller noise research masters degree thesis article first series will describe tests performed explain results make recommendations toward reducing model aircraft noise Im proving noise problem means averting loss flying sites will depend largely having knowledgeable fliers Due technical nature mate rial will precede discussion test program details brief explanation basic propeller theory Introducing some important aspects propeller per formance section will lead better understanding both current study propellers general Since formulas scientific jargon tend limit interest type article effort has made avoid use Basic Propeller Theory order aircraft move through air propelling force must work propeller essentially small rotating wing produces required thrust speed aircraft level flight deter mined relating thrust available power plant total aircraft drag Note both forces vary signifi cantly airspeed depicted typi cal aircraft Figure 1 example moving left right along horizontal axis Figure 1 represents increasing airspeed notes aircraft drag increases eventually exceeds thrust Point 1 figure represents case air craft accelerating since thrust pro duced propeller much greater aircraft drag Conversely aircraft operating point 2 predominance drag over thrust causes decelerate cases airspeed will stabi lize point 3 thrust drag equal Since engine example full throttle point 3 represents maximum tainable airspeed aircraft/engine/ propeller combination level flight re duction power below full throttle ef fectively shifts thrust curve downward resulting reduction maximum airspeed see dashed curve Figure 1 Similarly anything can done pro duce thrust less drag will shift December 1989 37 Figu curves allowing greater flight speeds Figure 1 has shown thrust produced power plant actually decreases yond certain threshold airspeed phenomenon results changes air flow around propeller high airspeeds As propeller rotates flow approaches its leading edge speed depends rotational speed rpm engine However forward movement aircraft creates additional flow ap proaches propeller disc speed equal forces acting propeller best explained examining thin slice blade such shown cross section Figure 2 Once again explanation simplified differentiating effects due blade rotation caused forward speed Figure 3 depicts flow action sec tion typical propeller blade due its ro tation alone would case engine being run model re strained flow approaches prop angle dictated blade pitch Just wing produces lift drag certain gle attack propeller produces sim ilar forces depend engine rpm shape blade airfoil lift force example acts along axis rotation force axial direction termed thrust Similarly drag force acts plane rotation pro peller resists its rotation defined torque Figure 4 illustrates condition after aircraft released acquires addi tional flow field its forward move ment simple way graphically depict combination two flows use special arrows called vectors flow represented single vector relative speed flow given length its vector flow direction rep resented direction vec tor pointing two propeller flow vectors arranged nose-to-tail Fig ure 4 rotation forward flight other vector completes triangle represents flow field resulting combination Notice speed direction resultant vector can al tered changing length speed original vectors Therefore flow around propeller indeed does depend both engine rpm forward flight speed flow vectors combine shown Figure 4 forces acting propel ler diminish Hence blade airfoil angle attack Figure 4 decreased com pared Figure 3 addition since lift drag forces measured respect altered flow angle slanted away axis rotation propel ler Therefore net thrust decreased further since lift force acting pre cisely thrust direction misdirection lift also shown Figure 4 reality thrust lost due slanting lift force becomes ad ditional torque load engine must overcome effectively demonstrates propeller performance very different flight ground better understanding engine turns propeller under varying load conditions can gained referring Fig ure 5 Assume drag forces acting point blade propeller example added together sum found lso assume net drag force determined act ing through point 12 center crankshaft product lb 12-in distance represents 6 in-lb b torque load blade propeller Since two blades net torque load power plant must produce order turn blades constant rotational speed 12 38 Model Aviation 0 flight velocity Figure 2 illustrates relative directions simultaneous flows respect propeller ro tating counterclockwise in-lb 1 ft-lb engine capable producing torque under condi tions rotational speed will increase cant produce enough torque rotational speed will achieved power available engine simply rotational speed multiplied amount torque can applied propeller given rpm example engine can produce 33 ft-lb torque 10000 rpm 16667 rev/sec power rotational speed 550 ft lb/sec example chosen order put value power recogniz able units Since horsepower 1 hp equivalent 550 ft-lb/sec engine producing exactly horsepower under operating conditions Figure 6 illustrates way horsepower output torque typical model engine vary rotational speed Most engines available modelers have curves resemble example actual magnitude power torque rotational speed depends physi cal design particular engine As mentioned above power required turn propeller product torque rotational speed power produced propeller proportional product thrust forward speed ratio power produced propeller required turn known propeller efficiency An efficient propeller capable producing given amount thrust using less power inefficient Equivalently efficient propeller can produce greater thrust therefore greater ward speed using same engine power Rather being fixed value efficien cy depends physical design opera ting rpm flight speed specific pro peller therefore improper categori cally call prop efficient other unless advantage holds true rotational forward speeds Propeller ef ficiency plays major role increasing air craft performance reducing noise Basic Noise Definitions Sound waves simply minute pressure fluctuations propagate air characterized two parameters frequency amplitude Frequency refers number pressure pulses pres sure fluctuations occur sec ond perceived ear pitch Like higher notes piano keyboard higher frequencies actually sound higher pitched Pressure amplitude measure size acoustical disturbance corresponds loudness sound simple tone characterized single frequency single amplitude Complex sounds composed different fre quencies Pressure amplitude measured deci bels dB measured referred sound pressure level SPL Continued page 40 Order direct Add $1500 shipping Use VISA MC check money order COD GOLIDW AGE MODELS RO box 807 Ienn Vcilleq CA 95946 916 432-2928 B&P Associates Gives Total FlIgbt Line FREEDOM battery needs call write B&P Associates PO Box 22054 Waco TX 76702-2054 817662-5587 new electric starter battery pack cuts cord has always tied starter power panel Discover freedom being able start plane wherever added safety less wire get caught prop charge hefty 4 Amp/hour pack will take through weekend flying power enough spare dont stop have Ni-Cads virtually size imaginable cut experimenter free design whatever ii takes make yours best setup field December 1989 39 h C, qusrter scale com plete deluxe kit features exact scale outlines balsa plywo, onstruction light epoxy cowl wheel pants selected wood complete hardware flying wires full cockpit details 3-views photos decals extensive instruction manual 20 cu ne lighL upoxy glass uuiage cowl wheel pants complete hardware selected wood decals 3-views cu engliw epoxy glass fudy owl wheel pants light foam wing cores con test wood complete hardware decals Satisfaction Guaranteed1 EA~ HINELZ SH-710 Pkg 24-52 95 THE HIGH-TECH HINGE DESIGNED FOR THE CYANOACRYLATE AGE Easier install other hinge No gouging picking messy epoxies Simply cut single knife slot hinge slide hinges place apply few drops favorite CA glue youre donel SUPER FAST SUPER EASY SUPER STRONG SIG MFG CO INC401-7 So Front St.Montezuma IA 50171 23-5154 LANDER INDUST 1005 19TH ST CT HAVRE MONTANA 59501 406265-6529 PRICES INCLUDE FREIGHT CANADIAN ORDERS ADD 25% ViSA Pwtakeet SUpeJL Po4 PO4JIWkQ 40. FREE CATALOG Ti4ewaiwt I4otoluj eIdWIIAi*e 392SC SE 13th Court Scala FImna 32571 904 6943531 sound pressure level corresponds dis crete frequency range frequencies overall sound pressure level' OASPL also measured decibels measure sound obtained adding SPLs frequency spectrum decibel reflecting fact human ear perceives very wide range sound pressure based loga rithmic scale rather linear compresses sonic data ease inter pretation Still another measure noise sound power level PWL based quantity acoustical power pro duced given source rather pres sure amplitude given location Since sound power level also measured dB its important keep track whether mea surements given units PWLs SPLs Sounds certain frequency ranges perceived being louder sounds other frequencies Weighted sound level curves have developed take fact account weighted scale used almost industrial commu nity noise standards US Sound lev els measured according scale ex pressed units called dBA significance relative contribu tions various components noise cannot appreciated general understanding manner sound levels combined two equal sound pressure levels SPLs added together combined sound level will 6dB higher orig inal value Adding together two equal sound power levels PWLs produces level 3 dB higher phenome non result logarithmic nature dB scale means levels separated few dB fact very different ab solute values acoustic power level PWL expressed dB adding two powers differ 10 dB pro duces no significant increase power yond higher two Consider ex ample adding 80 dB 90 dB powers dB1 B dB2 B total dBtotai given follow ing formula dBtotai og[l0dB/o 2/1O] dB Sound pressure levels SPLs behave similar fashion two SPLs com bined variance between acoustic levels addition becomes insignificant about 20 dB adds SPLs 80 dB 100 dB result 1008 dB practical implications will become clear realizes model aircraft noise derives several sourcesthe engine airframe propellerand propeller noise itself blends several components Often reducing lesser noise source fails produce noticeably quieter aircraft Consider example aircraft 80 dB engine noise 90 dB propeller noise As have seen formula given above able completely elim inate engine noise lesser source resulting acoustic power would discernibly reduced hypothetical example subtracting 80 dB engine noise acoustical power 904 dB total noise power slightly lowers total output about 90 dBnot significant change achieve meaningful reduction model air craft sound necessary reduce dominant source noise Justification Propeller Noise Reduction fundamental objective research project has verify sound pro duced propeller fact domi nant noise mechanism model aviation project assumes reasonable offthe-shelf muffler used aircraft since absence such use use poor muffler engine sounds likely dominate noise signature Measure ments acquired during different phases research provide several pieces evi dence indicate propeller noise dominates over produced properly muffled engine Flight test data provides first bit ev idence An instrumented aircraft flown fixed height over microphone peak OASPL measured dBA flight speed rpm throttle setting also recorded data compared obtained same propellers driven electric motor wind tunnel laboratory thereby eliminating power plant significant source noise Although flight velocities precisely duplicated lab several cases offer reasonable basis compari son such case SPL bladepassing frequency lab 78 dB simulated flight velocity 100 kmph ki lometers per hour microphone dis tance corrected same distance used flight tests flight test 120 kmph resulted OASPL 764 dBA OASPL includes frequencies spectrum whereas lab data ob tained blade-passing frequency Since engine airframe noise absent lab data would have ex pected flight test noise louder results support inference engine airframe noise did reach significant level flight tests done would have tended dominate rais ing OASPL above SPL measured lab fact propeller noise alone approximately equal total noise mea sured flight Table 1 shows data selected tests operating conditions nearly identical Group 1 contains propel lers same manufacturer tal variation mean rpm less 1% total variation flight velocity approximately 5% Groups 2 3 in40 Model Aviation RIG SKY CRADLES FIELD BOX MODEL$1595 BENCH MODEL$1995 FLOOR MODEL$2395 CEILING HANGERS SMALL20-40 .$995 MEDIUM 40- 60 95 LARGE 50-BO. $1195 nvur HAIFt FITS ALL PICKUPS . 5 cluded propellers two different manu facturers Group 4 propellers sin gle manufacturer Since flight speed rpm nearly same group aircraft always level flight measure ment point thrust produced likewise nearly same data groups Table 1 Clearly engine airframe having almost identically groups can therefore inferred observed large variations OASPL between cases within group rather being caused engine airframe noise result dif ferences sound levels among propellers Further assuming situation en gine noise closely approximated level propeller noise completely eliminating engine noise would effect noise re duction 6 dBa value ex ceeded differences noted among props particular group final piece evidence yielded data obtained two different mufflers during flight tests stock muffler re placed high-quality state-of-the-art muf fler data recorded two different flight speeds using same propeller 120 kmph difference OASPL measured 02 dBA 90 kmph difference 03 dBA Such ex tremely small variance suggests given flight speed advanced muffler no effect total noise output ever full throttle engine performed better upgraded muffler ad ditional rpm permitted latter creased noise levels improved engine performance advanced muffler did significantly impact noise level long flight speed remained constant test results clearly establish pro peller dominant source model air craft noise remainder discus sion will assume case Propeller Noise Sources sound produced model propel ler compounded several elements important include noise due thrust torque noise thickness noise referred discrete fre quency noise sources because sound produced occurs bladepassing frequency its harmonics blade-passing frequency rate blade passes given point propel ler disc product number blades rotational speed rev/sec understand noise mecha nisms operate imagine fixed point rotational disc propeller time blade near point air pressure its ordinary value Air pres sure changes blade passes through pushes air aside amount dis placed air depending thickness blade noise produced periodic displacement air known thickness noise Continued page 42 VJO ds best Sel 09 Spak osen ByTan Odginds TItG Mfg ml AM Aircraft Saqiply its outstenhg ruimhity Comp e e s ng e cyl nder system nclud ng ho e couped spark advance kt spark gead25 p ug ba e y pack charger 900 sh elded Much kmger 1gm hIs Easy haid sterts-no kickback 1AUO-12000 RPM rubble ii 0% power few strokers oni nutubbmi mviii Lower pricad fuels no okra neededMqleeduul9Fphagcovw FormumyuapaesI0&p2ft4strokeslegieudtwlsctulrs Klotzaioahactsaviule Splc cub aperk ded ibm bed ft tbi*ag hits avabbis CAT NO 106 Proof Switch Retail S995 Add $125 shipping Send $150 catalog Michigan residents add 4% sales tax IMPROVE YOUR 1991 SWITCH OVER ej Proof Switch Positive Locking Prevents Arriving field dead batteries Accidental switching off before take-off Will vibrate apart causing loss radio Does require special mounts Works radios Ideal seaplanes completely water proof SEE YOUR LOCAL HOBBY DEALER unavailable locally send Bru Line Industries Inc 4.. PO Box 3786 Center Line MI 48015 WASHINGTON S AMA BASE. $ An50 1 per couple per night Check day Minimum stay 2 nights Free Parking Cars Free Full Breakfasts Free Merropass Sat Sun Free Harrington Hawk Cafeteria avA 11th & E Streets NW Washington DC 20004G9 0-424-8532 628 8140T70 omm December 1989 41 Em 0AMA MEMBER RATE Tax no included A Radio South Batteries 500 ma Pack 48V Futaba conn 800 ma Pack 48V Futaba conn 1200 ma Pack 48V Futaba conn TX batt Futaba G-Series PCM 1300 1550 2200 2475 2400 2700 2995 RADIO SOUTH __ AUTHORIZED SERVICE CENTER Call Tony Stiliman Ken Dudley custom work competition needs stock complete hobby line specializing competition accessoriesall discounted prices bS ______ __ FREQUENCY CONVERSIONS _______9jgCY~ Frequency Comnnuee Approved @0__ stock Futaba JR radios Featuring fast service byOAYS engines parts qualified people thePhHatori headers pipes latest equipment Including aGh$tIWe Repair Heli Sets Gyros SPECTRUM ANA YZER Al Orders COD VISA MC American Express OPEN 8-5 CST P rices subject change notice 9003 N Davis Hwy Pensacola FL 32514 904 478-6745 As propeller blade passes through given point disc also exerts thrust torque forces cause pressure fluc tuation As air pressure displacement pressure fluctuation propagates sound known thrust torque noise point propeller disc pres sure fluctuates time blade passes total pressure disturbance sum disturbances caused thrust torque thickness certain other effects disturbances vary strength travels its own preferred direction combined effect pressure fluc tuations perceived propeller noise pressure amplitudes of components propeller noise depen dent relative amounts thrust torque well propeller tip speed itself proportional product rotational speed propeller di ameter Thrust torque noise generally significant sources propeller sound should noted ever since thickness noise consider ably affected tip speed thrust torque noise its relative impor tance will increase increasing rota tional speed Any attempt make sense propel ler noise problem complicated overlapping often interdependent ef fects acoustic sources example Figure 4 shows propeller blade lift does point exactly thrust direc tion means blade lift contrib utes both thrust torque hence both thrust torque noise Additionally noise various sources radiates away propeller overlapping pat terns difficult distinguish reduce propeller noise must dis cover dominant noise mechanism work can directed toward lessening source cant done some knowledge intricate makeup pro peller noise Its important understand its interplay factors associ ated aircraft operationengine per formance aircraft drag flight speed rpm propeller diameter pitch etcwhich pro duces noise perceived human ear Conducting scientific study such truly complicated system ridden variables difficult structured building block approach being used North Carolina State University laboratory data correlated both flight test data classical mathematical propel ler theory Although quite time-consuming process does provide direct path final answers research findings suggest propel ler noise may dominant acoustic source model aircraft may deed possible diminish leading Continued page 156 TO ORDER CALL 1406 265-4828 IT-i TRANSMITTER TRAY * Recommended especially handicaps beginners.experienced pilots love also * Pays itself times over airplanes saved l With set Gimbal Extenders $350 Postage & Handling Make Flying Breeze~ BJ ENTERPRISES 1100 Center Havre Montana 59501 42 Model Aviation GATOR RIC PRODUCTS DELUX ALL BALSA KIT An new Tiger Tail 120 four strokes piped 60 two strokes beautiful performer competition just showing offI balsa kit machined wood parts complete lsardware package includes plug-in djustable stab parts new wing mounts Wing Span- 72 inWing Ara 860 sq Complete Delux KitSI 5995 TRANSMITTER CASE An inexpensive rugged molded case protect expensive transmitter both two stick single stick transmitters Black leather grain aluminum trim locking clasp SI 995 MV-I TYPHOON New F3A competition Big beautiful flyer balsa construction plug-in wings 120 four stroke 60 two stroke power Plans-two sheets S 1495 Fiberglass cowl Si 595 Clear butyrate canopy. 5 995 OTHER PLANS Tiger Tail 4S-two sheets 120 four strokesS 1495 TAR baby 120 four strokes51195 Alley Kat 40 size trainer sportS 895 Gator Flea 40 size sport5 895 Bobcat 40 size sportS 895 feather Ilte glass cloth 7 ozsq yd est weave Fastest Filling test Finished Weight Big 3 Sq Yard Pkg Oetailed Instructions- $895 Include $2 SOlItem UPS esidents Add 6% Sales Tax GATOR RIC PRODUCTS 3713 Pompano Dr acola FL 32514 4768639 Letters Editor Continued page 12 Ken opened hobby shop Burk & Company Department Store after World War II worked him full-time year until started college After worked part-time until completing college Milton H Fanning Nashville TN Safety/Preston Continued page 22 some MonoKote repairs moral tale wise keep small extinguisher field box As alter native may possible smother fire towel rag blanket Cub Yellow engine cowling first RC model powered Cox 09 began turn first orange brown able smother fire wrap ping rag around front model Have safe month Keytwo/Randoiph Continued page 30 der everything place range check equipmentand its time fly Flying has wide performance en velope compared Paskey Keytwo basically quite gentle flier Whether upright inverted stall shows abso lutely no tendency snap fact model balanced correctly its very diffi cult make snap snaps bag move center-of-gravity aft about /2 increase elevator throw rate /16 up down movement trailing edge aile rons about right comfortable flying Landings can made nose-high slow full aileron control way touch down problem knife-edge flight first airplane persistently climbed half-loop until learned nose stayed up just little rudder Once Id mastered technique knife-edge loops included Keytwos repertoire tricks what did Eddie Williams have say about latest re-creation see youve built another Paskey said unsung maestro drunken pilot routine Its about time Play again Eddie Radio Technique/Myers Continued page 34 Failsafe Flight System small 15 sq light less ounce inexpensive has very low operating current 70 mA works no doubt nine-volt transistor radio batteries expensive about $250 Duracells live will last long time some chance will get care less let run down some critical time unit meets its claims follow admonition use fresh batteries check servo speed during preflight inspection careless youll probably crash some other reason anyway Failsafe Flight System @ $3995 list T&D Flight Systems PO Box 1782 Staten Island NY 10314 additional information call Alex Kronfeld l-7t8/984-9121 Propeller Noise Continued page 42 cause poor community relations Much cure will depend upon education Modelers need understand nature problem order properly utilize solu tions article has introduced propel ler noise problem provided some neces sary background Subsequent articles will explain test results greater detail describe what modeler can achieve better aircraft performance less noise RC Soaring/Blakeslee Continued page 49 down hes hoping arrange factur ers demonstrations during meet would flying demos followed show-andtell sessions guys like Byron Bruce Combat Models Marty Silberstein Steve Peacock Cliff Hangar Models Brian Laird Paul Masura Slope Scale Models Other Id imagine itll much like fabulously suc cessful Richland Scale Slope Fun Flyie fly want long have pin Info available writing Charley SSN 2601 E 19th 51 #29 Signal Hill CA 90804 Better call him 1-213/494-3712 1990 Soaring contests Ray Hayes Vice Presi dent LSF wrote remind us now time plan next years big contests Spe cifically Ray talking about every-evenyear LSF Regionals annual NSS Soar-Ins put go-ahead clubs around coun try Theyre bit expensive Ray hoping Continue tradition awarding beautiful LSF plaques LSF Regionals Theyre worth winning Ray also hoping three super con tests NSS Masters LSF Nationals AMA Nats can spread around country 1990 contests West Coast 89 Ray afraid guys east Kansas beginning feel left out youd like info LSF Regionals check Ray 69598 Brookhill Dr Romeo MI 48065 phone 1-313/ 752-6163 NSS Soar-Ins have handled Marshall Long past few years assume youre 90 Marshall Marshalls address 824 Garden Meadow Universal City TX 78148 worry East Coasters hear Nats will Lawrenceville IL 90 RC Aerobatics/Van Putte Continued page 51 aerodynamic center segment wing Youll note root segment tip another segment Figure 4 shows geometric technique solu tion Remember aerodynamic center panel 25% point mean aerody namic chord panel Once youve determined aerodynamic cen ter panel must calculate area panel using Equation 2 measure distance convenient line aerody namic centers panels Figure 4 shows con venient reference line distance re spective aerodynamic centers distance back reference line aerodynamic center wing located determined Equation 3 mean aerodynamic chord complete wing calculated individual values shown Equation 4 looks just like equa tion determining distance wing aero dynamic center doesnt should since 156 Model Aviation
Edition: Model Aviation - 1989/12
Page Numbers: 36, 37, 38, 39, 40, 41, 42, 156
D Heathcoat R Nagel Model Propeller NOISEc first series articles describes in-depth research spon sored AMA conducted North Carolina State Univer sity severity sources reduction propeller noise findings some unprecedented could have ma jor impact model airplane_flying community ADVANCES model aviation over past decade have spurred tremendous growth hobby year thousands people across US becoming ac tive participants weekend sessions local flying field greatest influx newcomers sport naturally occurs near large cities population con centrated flying sites tend lo cated suburban areas allows easy access fliers also subjects uninterested neighbor characteris tic whine model aircraft surprisingly greatest activity model field occurs weekends weekday evenings just peo ple living nearby home expecting chance relax involved sport well aware bitter confrontation scenario sometimes provokes ten modelers lose battle begin search another suitable flying site Losing established flying site hav ing search new can frustrat ing costly experience Ultimately has negative effect organization continued growth sport Its clear continuously relocating flying fields farther farther away populated ar eas isnt answer rate rural de velopment flying site relocation will lit tle postpone inevitable return problem solution instead develop model aircraft operate lower sound levels quite evident commonly accepted model aircraft noise generated propulsion system casual observer obvious sources intake combustion exhaust noise generated power plantand airframe noise re sulting its characteristic vibration However propeller too impor tant source noiseone misunder stood consequently overlooked fact acoustic research full-scale aircraft indicates propeller noise dominates over other sources sound illustrated following quote Journal Aircraft has well known years propellerdriven aircraft propeller primary source noise observation may 36 Model Aviation gu hold true model aircraft well effort better understand model pro Di recti Ro tat peller noise establish guidelines ultimately will lead quieter model aircraft AMA sponsored research pro Table 1Selected Flight Test Data Prop Velocity RPM QASPI kmphdBA Group 1 11 x5180160001110 9x7519516400960 9x719016250934 Group 2 10x615013500878 11 x614312000990 Group 3 10x712011000840 9x7512011250810 10x612010800764 Group 4 11 x 5908500925 9 x 7908700830 gram conducted North Carolina State Uni versity principal investigators include Dr Robert T Nagel associate professor nearly 15 years research experience aeroacoustics Robert Vess aero space engineer six years experience coordinator NC State University aerospace laboratories 18 years activ ity Radio Control including Pattern Hel icopter fun fly competition David M Heathcoat received bachelors degree physics NC State University 1986 participated propeller noise research masters degree thesis article first series will describe tests performed explain results make recommendations toward reducing model aircraft noise Im proving noise problem means averting loss flying sites will depend largely having knowledgeable fliers Due technical nature mate rial will precede discussion test program details brief explanation basic propeller theory Introducing some important aspects propeller per formance section will lead better understanding both current study propellers general Since formulas scientific jargon tend limit interest type article effort has made avoid use Basic Propeller Theory order aircraft move through air propelling force must work propeller essentially small rotating wing produces required thrust speed aircraft level flight deter mined relating thrust available power plant total aircraft drag Note both forces vary signifi cantly airspeed depicted typi cal aircraft Figure 1 example moving left right along horizontal axis Figure 1 represents increasing airspeed notes aircraft drag increases eventually exceeds thrust Point 1 figure represents case air craft accelerating since thrust pro duced propeller much greater aircraft drag Conversely aircraft operating point 2 predominance drag over thrust causes decelerate cases airspeed will stabi lize point 3 thrust drag equal Since engine example full throttle point 3 represents maximum tainable airspeed aircraft/engine/ propeller combination level flight re duction power below full throttle ef fectively shifts thrust curve downward resulting reduction maximum airspeed see dashed curve Figure 1 Similarly anything can done pro duce thrust less drag will shift December 1989 37 Figu curves allowing greater flight speeds Figure 1 has shown thrust produced power plant actually decreases yond certain threshold airspeed phenomenon results changes air flow around propeller high airspeeds As propeller rotates flow approaches its leading edge speed depends rotational speed rpm engine However forward movement aircraft creates additional flow ap proaches propeller disc speed equal forces acting propeller best explained examining thin slice blade such shown cross section Figure 2 Once again explanation simplified differentiating effects due blade rotation caused forward speed Figure 3 depicts flow action sec tion typical propeller blade due its ro tation alone would case engine being run model re strained flow approaches prop angle dictated blade pitch Just wing produces lift drag certain gle attack propeller produces sim ilar forces depend engine rpm shape blade airfoil lift force example acts along axis rotation force axial direction termed thrust Similarly drag force acts plane rotation pro peller resists its rotation defined torque Figure 4 illustrates condition after aircraft released acquires addi tional flow field its forward move ment simple way graphically depict combination two flows use special arrows called vectors flow represented single vector relative speed flow given length its vector flow direction rep resented direction vec tor pointing two propeller flow vectors arranged nose-to-tail Fig ure 4 rotation forward flight other vector completes triangle represents flow field resulting combination Notice speed direction resultant vector can al tered changing length speed original vectors Therefore flow around propeller indeed does depend both engine rpm forward flight speed flow vectors combine shown Figure 4 forces acting propel ler diminish Hence blade airfoil angle attack Figure 4 decreased com pared Figure 3 addition since lift drag forces measured respect altered flow angle slanted away axis rotation propel ler Therefore net thrust decreased further since lift force acting pre cisely thrust direction misdirection lift also shown Figure 4 reality thrust lost due slanting lift force becomes ad ditional torque load engine must overcome effectively demonstrates propeller performance very different flight ground better understanding engine turns propeller under varying load conditions can gained referring Fig ure 5 Assume drag forces acting point blade propeller example added together sum found lso assume net drag force determined act ing through point 12 center crankshaft product lb 12-in distance represents 6 in-lb b torque load blade propeller Since two blades net torque load power plant must produce order turn blades constant rotational speed 12 38 Model Aviation 0 flight velocity Figure 2 illustrates relative directions simultaneous flows respect propeller ro tating counterclockwise in-lb 1 ft-lb engine capable producing torque under condi tions rotational speed will increase cant produce enough torque rotational speed will achieved power available engine simply rotational speed multiplied amount torque can applied propeller given rpm example engine can produce 33 ft-lb torque 10000 rpm 16667 rev/sec power rotational speed 550 ft lb/sec example chosen order put value power recogniz able units Since horsepower 1 hp equivalent 550 ft-lb/sec engine producing exactly horsepower under operating conditions Figure 6 illustrates way horsepower output torque typical model engine vary rotational speed Most engines available modelers have curves resemble example actual magnitude power torque rotational speed depends physi cal design particular engine As mentioned above power required turn propeller product torque rotational speed power produced propeller proportional product thrust forward speed ratio power produced propeller required turn known propeller efficiency An efficient propeller capable producing given amount thrust using less power inefficient Equivalently efficient propeller can produce greater thrust therefore greater ward speed using same engine power Rather being fixed value efficien cy depends physical design opera ting rpm flight speed specific pro peller therefore improper categori cally call prop efficient other unless advantage holds true rotational forward speeds Propeller ef ficiency plays major role increasing air craft performance reducing noise Basic Noise Definitions Sound waves simply minute pressure fluctuations propagate air characterized two parameters frequency amplitude Frequency refers number pressure pulses pres sure fluctuations occur sec ond perceived ear pitch Like higher notes piano keyboard higher frequencies actually sound higher pitched Pressure amplitude measure size acoustical disturbance corresponds loudness sound simple tone characterized single frequency single amplitude Complex sounds composed different fre quencies Pressure amplitude measured deci bels dB measured referred sound pressure level SPL Continued page 40 Order direct Add $1500 shipping Use VISA MC check money order COD GOLIDW AGE MODELS RO box 807 Ienn Vcilleq CA 95946 916 432-2928 B&P Associates Gives Total FlIgbt Line FREEDOM battery needs call write B&P Associates PO Box 22054 Waco TX 76702-2054 817662-5587 new electric starter battery pack cuts cord has always tied starter power panel Discover freedom being able start plane wherever added safety less wire get caught prop charge hefty 4 Amp/hour pack will take through weekend flying power enough spare dont stop have Ni-Cads virtually size imaginable cut experimenter free design whatever ii takes make yours best setup field December 1989 39 h C, qusrter scale com plete deluxe kit features exact scale outlines balsa plywo, onstruction light epoxy cowl wheel pants selected wood complete hardware flying wires full cockpit details 3-views photos decals extensive instruction manual 20 cu ne lighL upoxy glass uuiage cowl wheel pants complete hardware selected wood decals 3-views cu engliw epoxy glass fudy owl wheel pants light foam wing cores con test wood complete hardware decals Satisfaction Guaranteed1 EA~ HINELZ SH-710 Pkg 24-52 95 THE HIGH-TECH HINGE DESIGNED FOR THE CYANOACRYLATE AGE Easier install other hinge No gouging picking messy epoxies Simply cut single knife slot hinge slide hinges place apply few drops favorite CA glue youre donel SUPER FAST SUPER EASY SUPER STRONG SIG MFG CO INC401-7 So Front 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FREE CATALOG Ti4ewaiwt I4otoluj eIdWIIAi*e 392SC SE 13th Court Scala FImna 32571 904 6943531 sound pressure level corresponds dis crete frequency range frequencies overall sound pressure level' OASPL also measured decibels measure sound obtained adding SPLs frequency spectrum decibel reflecting fact human ear perceives very wide range sound pressure based loga rithmic scale rather linear compresses sonic data ease inter pretation Still another measure noise sound power level PWL based quantity acoustical power pro duced given source rather pres sure amplitude given location Since sound power level also measured dB its important keep track whether mea surements given units PWLs SPLs Sounds certain frequency ranges perceived being louder sounds other frequencies Weighted sound level curves have developed take fact account weighted scale used almost industrial commu nity noise standards US Sound lev els measured according scale ex pressed units called dBA significance relative contribu tions various components noise cannot appreciated general understanding manner sound levels combined two equal sound pressure levels SPLs added together combined sound level will 6dB higher orig inal value Adding together two equal sound power levels PWLs produces level 3 dB higher phenome non result logarithmic nature dB scale means levels separated few dB fact very different ab solute values acoustic power level PWL expressed dB adding two powers differ 10 dB pro duces no significant increase power yond higher two Consider ex ample adding 80 dB 90 dB powers dB1 B dB2 B total dBtotai given follow ing formula dBtotai og[l0dB/o 2/1O] dB Sound pressure levels SPLs behave similar fashion two SPLs com bined variance between acoustic levels addition becomes insignificant about 20 dB adds SPLs 80 dB 100 dB result 1008 dB practical implications will become clear realizes model aircraft noise derives several sourcesthe engine airframe propellerand propeller noise itself blends several components Often reducing lesser noise source fails produce noticeably quieter aircraft Consider example aircraft 80 dB engine noise 90 dB propeller noise As have seen formula given above able completely elim inate engine noise lesser source resulting acoustic power would discernibly reduced hypothetical example subtracting 80 dB engine noise acoustical power 904 dB total noise power slightly lowers total output about 90 dBnot significant change achieve meaningful reduction model air craft sound necessary reduce dominant source noise Justification Propeller Noise Reduction fundamental objective research project has verify sound pro duced propeller fact domi nant noise mechanism model aviation project assumes reasonable offthe-shelf muffler used aircraft since absence such use use poor muffler engine sounds likely dominate noise signature Measure ments acquired during different phases research provide several pieces evi dence indicate propeller noise dominates over produced properly muffled engine Flight test data provides first bit ev idence An instrumented aircraft flown fixed height over microphone peak OASPL measured dBA flight speed rpm throttle setting also recorded data compared obtained same propellers driven electric motor wind tunnel laboratory thereby eliminating power plant significant source noise Although flight velocities precisely duplicated lab several cases offer reasonable basis compari son such case SPL bladepassing frequency lab 78 dB simulated flight velocity 100 kmph ki lometers per hour microphone dis tance corrected same distance used flight tests flight test 120 kmph resulted OASPL 764 dBA OASPL includes frequencies spectrum whereas lab data ob tained blade-passing frequency Since engine airframe noise absent lab data would have ex pected flight test noise louder results support inference engine airframe noise did reach significant level flight tests done would have tended dominate rais ing OASPL above SPL measured lab fact propeller noise alone approximately equal total noise mea sured flight Table 1 shows data selected tests operating conditions nearly identical Group 1 contains propel lers same manufacturer tal variation mean rpm less 1% total variation flight velocity approximately 5% Groups 2 3 in40 Model Aviation RIG SKY CRADLES FIELD BOX MODEL$1595 BENCH MODEL$1995 FLOOR MODEL$2395 CEILING HANGERS SMALL20-40 .$995 MEDIUM 40- 60 95 LARGE 50-BO. $1195 nvur HAIFt FITS ALL PICKUPS . 5 cluded propellers two different manu facturers Group 4 propellers sin gle manufacturer Since flight speed rpm nearly same group aircraft always level flight measure ment point thrust produced likewise nearly same data groups Table 1 Clearly engine airframe having almost identically groups can therefore inferred observed large variations OASPL between cases within group rather being caused engine airframe noise result dif ferences sound levels among propellers Further assuming situation en gine noise closely approximated level propeller noise completely eliminating engine noise would effect noise re duction 6 dBa value ex ceeded differences noted among props particular group final piece evidence yielded data obtained two different mufflers during flight tests stock muffler re placed high-quality state-of-the-art muf fler data recorded two different flight speeds using same propeller 120 kmph difference OASPL measured 02 dBA 90 kmph difference 03 dBA Such ex tremely small variance suggests given flight speed advanced muffler no effect total noise output ever full throttle engine performed better upgraded muffler ad ditional rpm permitted latter creased noise levels improved engine performance advanced muffler did significantly impact noise level long flight speed remained constant test results clearly establish pro peller dominant source model air craft noise remainder discus sion will assume case Propeller Noise Sources sound produced model propel ler compounded several elements important include noise due thrust torque noise thickness noise referred discrete fre quency noise sources because sound produced occurs bladepassing frequency its harmonics blade-passing frequency rate blade passes given point propel ler disc product number blades rotational speed rev/sec understand noise mecha nisms operate imagine fixed point rotational disc propeller time blade near point air pressure its ordinary value Air pres sure changes blade passes through pushes air aside amount dis placed air depending thickness blade noise produced periodic displacement air known thickness noise Continued page 42 VJO ds best Sel 09 Spak osen ByTan Odginds TItG Mfg ml AM Aircraft Saqiply its outstenhg ruimhity Comp e e s ng e cyl nder system nclud ng ho e couped spark advance kt spark gead25 p ug ba e y pack charger 900 sh elded Much kmger 1gm hIs Easy haid sterts-no kickback 1AUO-12000 RPM rubble ii 0% power few strokers oni nutubbmi mviii Lower pricad fuels no okra neededMqleeduul9Fphagcovw 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Express OPEN 8-5 CST P rices subject change notice 9003 N Davis Hwy Pensacola FL 32514 904 478-6745 As propeller blade passes through given point disc also exerts thrust torque forces cause pressure fluc tuation As air pressure displacement pressure fluctuation propagates sound known thrust torque noise point propeller disc pres sure fluctuates time blade passes total pressure disturbance sum disturbances caused thrust torque thickness certain other effects disturbances vary strength travels its own preferred direction combined effect pressure fluc tuations perceived propeller noise pressure amplitudes of components propeller noise depen dent relative amounts thrust torque well propeller tip speed itself proportional product rotational speed propeller di ameter Thrust torque noise generally significant sources propeller sound should noted ever since thickness noise consider ably affected tip speed thrust torque noise its relative impor tance will increase increasing rota tional speed Any attempt make sense propel ler noise problem complicated overlapping often interdependent ef fects acoustic sources example Figure 4 shows propeller blade lift does point exactly thrust direc tion means blade lift contrib utes both thrust torque hence both thrust torque noise Additionally noise various sources radiates away propeller overlapping pat terns difficult distinguish reduce propeller noise must dis cover dominant noise mechanism work can directed toward lessening source cant done some knowledge intricate makeup pro peller noise Its important understand its interplay factors associ ated aircraft operationengine per formance aircraft drag flight speed rpm propeller diameter pitch etcwhich pro duces noise perceived human ear Conducting scientific study such truly complicated system ridden variables difficult structured building block approach being used North Carolina State University laboratory data correlated both flight test data classical mathematical propel ler theory Although quite time-consuming process does provide direct path final answers research findings suggest propel ler noise may dominant acoustic source model aircraft may deed possible diminish leading Continued page 156 TO ORDER CALL 1406 265-4828 IT-i TRANSMITTER TRAY * Recommended especially handicaps beginners.experienced pilots love also * Pays itself times over airplanes saved l With set Gimbal Extenders $350 Postage & Handling Make Flying Breeze~ BJ ENTERPRISES 1100 Center Havre Montana 59501 42 Model Aviation GATOR RIC PRODUCTS DELUX ALL BALSA KIT An new Tiger Tail 120 four strokes piped 60 two strokes beautiful performer competition just showing offI balsa kit machined wood parts complete lsardware package includes plug-in djustable stab parts new wing mounts Wing Span- 72 inWing Ara 860 sq Complete Delux KitSI 5995 TRANSMITTER CASE An inexpensive rugged molded case protect expensive transmitter both two stick single stick transmitters Black leather grain aluminum trim locking 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smother fire towel rag blanket Cub Yellow engine cowling first RC model powered Cox 09 began turn first orange brown able smother fire wrap ping rag around front model Have safe month Keytwo/Randoiph Continued page 30 der everything place range check equipmentand its time fly Flying has wide performance en velope compared Paskey Keytwo basically quite gentle flier Whether upright inverted stall shows abso lutely no tendency snap fact model balanced correctly its very diffi cult make snap snaps bag move center-of-gravity aft about /2 increase elevator throw rate /16 up down movement trailing edge aile rons about right comfortable flying Landings can made nose-high slow full aileron control way touch down problem knife-edge flight first airplane persistently climbed half-loop until learned nose stayed up just little rudder Once Id mastered technique knife-edge loops included Keytwos repertoire tricks what did Eddie Williams have say about latest re-creation see youve built another Paskey said unsung maestro drunken pilot routine Its about time Play again Eddie Radio Technique/Myers Continued page 34 Failsafe Flight System small 15 sq light less ounce inexpensive has very low operating current 70 mA works no doubt nine-volt transistor radio batteries expensive about $250 Duracells live will last long time some chance will get care less let run down some critical time unit meets its claims follow admonition use fresh batteries check servo speed during preflight inspection careless youll probably crash some other reason anyway Failsafe Flight System @ $3995 list T&D Flight Systems PO Box 1782 Staten Island NY 10314 additional information call Alex Kronfeld l-7t8/984-9121 Propeller Noise Continued page 42 cause poor community relations Much cure will depend upon education Modelers need understand nature problem order properly utilize solu tions article has introduced propel ler noise problem provided some neces sary background Subsequent articles will explain test results greater detail describe what modeler can achieve better aircraft performance less noise RC Soaring/Blakeslee Continued page 49 down hes hoping arrange factur ers demonstrations during meet would flying demos followed show-andtell sessions guys like Byron Bruce Combat Models Marty Silberstein Steve Peacock Cliff Hangar Models Brian Laird Paul Masura Slope Scale Models Other Id imagine itll much like fabulously suc cessful Richland Scale Slope Fun Flyie fly want long have pin Info available writing Charley SSN 2601 E 19th 51 #29 Signal Hill CA 90804 Better call him 1-213/494-3712 1990 Soaring contests Ray Hayes Vice Presi dent LSF wrote remind us now time plan next years big contests Spe cifically Ray talking about every-evenyear LSF Regionals annual NSS Soar-Ins put go-ahead clubs around coun try Theyre bit expensive Ray hoping Continue tradition awarding beautiful LSF plaques LSF Regionals Theyre worth winning Ray also hoping three super con tests NSS Masters LSF Nationals AMA Nats can spread around country 1990 contests West Coast 89 Ray afraid guys east Kansas beginning feel left out youd like info LSF Regionals check Ray 69598 Brookhill Dr Romeo MI 48065 phone 1-313/ 752-6163 NSS Soar-Ins have handled Marshall Long past few years assume youre 90 Marshall Marshalls address 824 Garden Meadow Universal City TX 78148 worry East Coasters hear Nats will Lawrenceville IL 90 RC Aerobatics/Van Putte Continued page 51 aerodynamic center segment wing Youll note root segment tip another segment Figure 4 shows geometric technique solu tion Remember aerodynamic center panel 25% point mean aerody namic chord panel Once youve determined aerodynamic cen ter panel must calculate area panel using Equation 2 measure distance convenient line aerody namic centers panels Figure 4 shows con venient reference line distance re spective aerodynamic centers distance back reference line aerodynamic center wing located determined Equation 3 mean aerodynamic chord complete wing calculated individual values shown Equation 4 looks just like equa tion determining distance wing aero dynamic center doesnt should since 156 Model Aviation