_n dealing engine no FaCts Ilying -noise problems field its real have some familiarity fundamentals sound propagation measurement perceived human ear U George F Abbott ANYONE WHOS BEEN keeping up model press lately aware noise issue various ideas about limiting measuring sound produced models can no question about importance sound abatement Im sure noise far away signifi cant cause loss flying sites today reading reports discussions subject must have noticed use term dB decibel under stand actual significance some sound level standards have know what dB means Decibel means 10 bels Named af ter Alexander Graham Bell term bel measure comparative power As may know Bells experiments re sulted invention telephone orig inated studies human hearinghis wife deafand causes possible cures hearing impairment inventor discovered ears sensitivity sound intensity loudness linear twice much sound power isnt perceived twice loud rather just barely perceptible change Therefore appropriate unit measure compar ative sound power would have based exponential logarithmic relation ship Without going excessive detail Ill define explain dBand talk about practical implications dB defined dimensionless ex pression ratio power Specifically D og Pl/P2 dB P1 P2 two powers beTop Dick Pettit member Burlington NC Barks Club seen holding sound meter aimed authors Astro Hog powered OS FS9O four-cycle engine swinging Graupner 12 x 75 three-bladed prop Turning 8700 rpm noise levels measured 98 dBA 9 ft 92 dBA 18 ft airplane does seem noisy though air Note doubling distance turned out reduce sound level 6 dB lust theory predicts doesnt always come out close due variables encountered actual field condi tions Left Dick Pettit fires up OS 120 Gemini twin engine Aeronca C-3 engine turns 16 x 7 prop 7500 rpm producing 98 dBA 9 92 dBA 18 ft Right author Ace 4-40 powered Saito 45 four-cycle engine turning 12 x 6 Master Airscrew prop 8000 rpm recorded 93 dBA 9 ft 88 dBA 18 ft 5 dB difference doesnt quite agree theory still pretty close field measurement plane very quiet air though exceeds recommended AMA noise standard 3 dB 34 Model Aviation Table 1 Power Ratios Decimal Equivalents Power Ratio 1 1 2 1 4 1 5 1 lOto 1 100 1 1000 1 10000 1 Power Ratio 25 1 50 1 200 1 1000 dB 0 3 6 7 10 0 40 Product Power Ratios 51 x 51 51 x 101 1001 x 21 101 x 1001 ing compared Log means logarithm base 10that power 10 must raised equal particular value case value ratio P1/P2 example 10 third power 1000 thus log 1000 3 days pretechnological antiquity logarithms found log tables re member runic lists back algebra book Today scientific cal culators have log feature signifi cance logarithms found fact addition subtraction logarithms numbers equivalent multiplication division numbers themselves ex ample 100 times 1000 100000 log 100 2 log oft 000 3 log 100000 5 sum logs two smaller numbers Remember dB relative expres sion must base reference Whether previous paragraphs enlightening information follows should Because dB exponential expression because power ratios definition multiplication di vision can define changes power lev els simply adding subtracting dB As Table 1 shows doubling halving Power Ratio 1 1 1/2 1/4 1/5 1/10 1/100 1/1000 1/10000 0 3 -6 -7 -10 -20 -30 -40 power equals change plus minus 3 dB 10-to-one differ ence power l0-dB change fore have airplane mea sures 103 dB wish reduce must reduce noise output factor 2 l0-dB reduction 103 dB 93 dB would require reduc tion power factor 10 Doubling 10-dB reduction 20 dB 83 dB sound level represents whopping l00-to-l reduction sound power Its important remember because its easy kid self believing going 103 dB 93 dB just 10% changewhen reality its 1000% change Another important factor distance between listener measurer noise source general sound power will decrease square distance Thus twice distance get one-fourth power called inverse square law Since law inverse square also governs radio signal strength RC receiver function distance transmitter might worth take mo ment understand Figure 1 illustrates perceptible sound decreases ratio distance sourcein case model airplane will assume sound generated airplane radiates equally directions entirely true still reasonable sumption Consider l-ft-sq area 10 ft noise source sound meter distance will measure certain sound level However move away sound source distance 20 ft should clear sound impressed upon 1-ft square now impressed upon 2-ft square area square 2 ft side course 4 sq ft Figure 1 Decibel -6dB -6dB -12dB -95 dB -41 dB area 1-ft square 1 sq ft Since same amount sound im pressed upon 1 sq ft now spread over 4 sq ft sound level obviously reduced one-fourth what Thus compare sound levels two different distances source ratio sound levels will equal square ra tio distances few examples phenomenon presented Table 2 Table 2 shows six-dB reduc tion time distance doubled Sim ilarly distance 10 times greater sound drops 20 dB 10 squared 100 20 dB Therefore airplane measured 100 dB meter would mea sure 94 dB two meters 80 dB 10 ters about 33 ft 60 dB 100 meters about 330 ft Makes wonder peo ple complain since 60 dB approximately sound level conversation table also illuminates importance careful setup test site contest since 12% error measurement distance would make difference dB does affect modelers current AMA sound level recommenda tion flying sites needing noise abate ment 90 dB 9 ft FAt merly mandated level 100 dB ter RC Pattern competitions has consid erably relaxed requirement 98 dB three meters AMA FAI recom mendations call weighting specifies sound power reference level 0 db ubar refers air pressure changes caused sound fre quency response approximates human ear commonly ac cepted standard industrial hygiene some typical values decibel levels generated environmental sources indication human ear tol Con tinued page 146 4 sq ft \W 70k October 1989 35 Decibel Equivalent 7dB 14dB 7dB 20 dB B 10dB 3 dB 100 dB Radio Shack sound meter meter can purchased about 30 dollars isnt exactly laboratory quality cer tainly adequate model noise measurements covers 60 126 dB six ranges has weighting photo graph its showing 98dB 100dB scale PRECISION MODEL PRODUCTS uzZZ7Is# Made U S BARSTOCK ALUMINUM SPINNERS Pan No Size TT-150-B .. 1-1/2 TT-175-B . 1-3/4 TT-200-B 11-225-B .. 21/4 11-226-B .. 2-1/4 FAI . TT-250-B . 2-1/2 TT-251-B . 2-1/2 FAI .. TT-275-B 3/4 TT-276-8 .. 2-3/4 FAI .. 11-300-B 11-301-BPAl TT-325-B . 3-1/4 TT-350-B /2 TT-375-B .. 3-3/4 11-400-B 4 RetailApprox PriceWeight $1395058 02 149509502 159510002 169516002 189515002 189519002 209517002 229522002 249520002 269526002 289525002 369534002 499547002 599552002 699557002 3 Pieces Cone Back Plate Retainer Screw Note 3 4 Blade Spinners Available Sizes Add 5300 Per Spinner PROP NUT ADAPTORS Part No Size TT-140-A . 1/4-28 TT-147-A 4-28/7mm . TT-610-A 10mm TT-710-A 10mm TT-516-A '5/16-24 TT-518-A .. 5/16-24/8mm IT-BiD-A x 10mm TT-825-A . 8x 125mm TT-375-A3/8-24 TT-125-A x 125mm Retail Approx Price Weight $495 061 02 49506102 49506302 49508202 495 602 49507602 495076oz 495 .. 075 02 595 117 02 595 02 3 Pieces Nut Washer anti Machined Bushing Add S350 Shipping Handling Prices subject change notice ROMCO MFG INC OX 836 SOUTH HOUSTON TEXAS 77587 713 943-1867 other 357th alumnus Chuck Yeager alive well TV again again think single-seat Dornier-335 Air Space Museum Washington DCpossibly same wife Helen beginning push 70 pretty hard both still ac tive licensed pilots have dabbling RC several years am enclosing picture freehand scratch-builts little 50 Saito powered 514-pounderreferred Round big 13-lb 8footer named Mr Big Its powered Zenoah 23 Both fly very well Harvey Mace Ft Bragg CA Safety/Preston Continued page 22 letter stated story apparently first sur faced 1967 So happen prefer assem bling models components arc welding rather gluing also weareontact lenses dont alarmed saw warning National Newsletter Its just true Have another safe Fly Baby/Mathews Continued page 33 site Test range free surface movement deflections per plans engine carbure tor needle settings engine-on radio op eration Finally important make sure model balances slightly ward center-of-gravity shown plans Add ballast needed Dont fly model tail-heavy everything checks out OK Fly Baby ready big try field head wind add little right rudder advance throttle youre air borne 12 ft adding up elevator youre taking off downwind Remember climb rate func tion engine speed elevator Dont horse airplane around heavy-handedly gentle caresses thats needed Take model up bit throttle down dead slow Still isnt sinking much Find little thermal shut engine off Now isnt something kind flying too sedate taste try some slow-speed touch-andbumps Hows easy Did ever prettier Whatever style flying youll find Old-Timer will oblige Versatile brisk smooth responsive Fly Baby will exactly what want See yourself isnt up date Old-Timer could ask dB Facts/Abbott Continued page 35 erates Quiet whisper 20 dB Conversation 65 dB Loud orchestra 80 dB Start danger 90 dB Amplified rock band 110 dB Threshold pain 130 dB Federal agencies have established recom mended standards safe noise exposure eight hours per day 90 dB two hours per day 100 dB less one-quarter hour per day 115 dB Lets reexamine AMA FAI cri teria Current AMA90 dB 9 ft Old FAIl00 dB meter Current FAI98 dB three meters order compare recommenda tions need convert single distancein case 9 ft Thats easy enough involves converting meters feet meter ft applying inverse square law discussed above results Current AMA90 dB 9 ft Old FAI912 dB 9 ft Current FAI988 dB 9 ft As can see new FAI regulation considerably less stringent old 146 Model Aviation Matched Performance System TOP PERFORMANCE K&B ENGINES AirplaneManse K&B FUELS K&B Glow PLUGS 9 Blends4 Choices Free Flight Kits Supplies Rubber er Power Kits Scale Old Timer Too Co Electric Motors Rubber Tissue Cox Parts Rubber Accessories Winding Hooks Timers Nitrate Dope CATALOGUE $200 CAMPBELLS CUSTOM KITS PO BOX 5996 LAKE WORTH FL 33466-5996 Letters Editor Continued page 12 V difference 76 dB equates power ra tio 57that airplane permitted emit 57 times much sonic power permitted under old standard current AMA recommendation 88 dB tougher new FAI rule Thats power ratio 76 am surprised lack consistency between AMA FAI Because have sound meter know noise propagation 100 dB 9 ft very common flying field muf flers Ive also discovered fourcycle engines sound tolerably quiet ear measure 100 dB up range Obviously subjective evaluation noise can deceptive four-cycle en gine sounds less objectionable two cycle engine yet registers almost high big ignition engine too sounds tamer its high readings meter would suggest Additionally frequency spectrum af fects perception noise see arti cle Sound Related Flying Sites No vember 1987 MA fact deserves careful thought respect relations public doubt noise levels seeing todays muffled engines pose real threat hearing especially since time standing quite some dis tance models Thank heavens mufflers After 50 years listen ing model engines mostly unmuffled hearing quite impaired high fre quency end age might have something Finally since propeller sig nificantly increases sound output use larger slower props should help allay noise problem Noisehow produce mea sure itis becoming major issue hobby today Coping problem intelligent way demands some effort means familiarizing ourselves rele vant technical terminology educating ourselves about factors influence sound emission article written purpose mind Radio Technique/Myers Continued page 37 ceiver batteries will result presence DC-DC converter receiver batteries making contact low-voltage alarm LVA system also cluded receivers PCM computer battery voltage drops below 28 volts throttle servoand throttle servogoes preset position stays typographic error receiver continues func tion down 28 volts advertised thats LVA cuts may fine get ting everything possible out alkaline batteries its dangerously low Ni-Cds think Ive got Polks convinced move trip point up around 47 volts will enough charge left Ni-Cds land safely subject batteries Chal lenger 550 manual says Transmitter 96-108 VDC 8 9 Nicad tin batteries Mine came usual Polks nine-pencell Ni-Cd pack transmitter four-pencell Ni-Cd pack receiver Transmitter operating cur rent measured 120 mA predicts about four hours operating timebetter PCM transmitters Output power looks like about 550 milliwatts Receiver drain idle five servos measured 60 mA battery charge should last about four hours ordinary service Frequency agility plug-in module transmitter inexpensive receivers make easy field changes frequency within 72 MHz band make swap field should check ground range adequate fly time no modules Ham CB bands well does work Bob Aberle t did field test system performed very well type testing last discussed May 1988 column discussed length January 1986 column results testing follows M200 adjacent channels 20 kHz Gold FM old AM ilver AM 0 kHz Gold FM Gold AM ilver AM djacent-channel performance excellent 1989 environment Polks still working develop 'bulletproof receiver 1991 turns out job some folks expectedContinued page 148 October 1989 147
Edition: Model Aviation - 1989/10
Page Numbers: 34, 35, 146, 147
_n dealing engine no FaCts Ilying -noise problems field its real have some familiarity fundamentals sound propagation measurement perceived human ear U George F Abbott ANYONE WHOS BEEN keeping up model press lately aware noise issue various ideas about limiting measuring sound produced models can no question about importance sound abatement Im sure noise far away signifi cant cause loss flying sites today reading reports discussions subject must have noticed use term dB decibel under stand actual significance some sound level standards have know what dB means Decibel means 10 bels Named af ter Alexander Graham Bell term bel measure comparative power As may know Bells experiments re sulted invention telephone orig inated studies human hearinghis wife deafand causes possible cures hearing impairment inventor discovered ears sensitivity sound intensity loudness linear twice much sound power isnt perceived twice loud rather just barely perceptible change Therefore appropriate unit measure compar ative sound power would have based exponential logarithmic relation ship Without going excessive detail Ill define explain dBand talk about practical implications dB defined dimensionless ex pression ratio power Specifically D og Pl/P2 dB P1 P2 two powers beTop Dick Pettit member Burlington NC Barks Club seen holding sound meter aimed authors Astro Hog powered OS FS9O four-cycle engine swinging Graupner 12 x 75 three-bladed prop Turning 8700 rpm noise levels measured 98 dBA 9 ft 92 dBA 18 ft airplane does seem noisy though air Note doubling distance turned out reduce sound level 6 dB lust theory predicts doesnt always come out close due variables encountered actual field condi tions Left Dick Pettit fires up OS 120 Gemini twin engine Aeronca C-3 engine turns 16 x 7 prop 7500 rpm producing 98 dBA 9 92 dBA 18 ft Right author Ace 4-40 powered Saito 45 four-cycle engine turning 12 x 6 Master Airscrew prop 8000 rpm recorded 93 dBA 9 ft 88 dBA 18 ft 5 dB difference doesnt quite agree theory still pretty close field measurement plane very quiet air though exceeds recommended AMA noise standard 3 dB 34 Model Aviation Table 1 Power Ratios Decimal Equivalents Power Ratio 1 1 2 1 4 1 5 1 lOto 1 100 1 1000 1 10000 1 Power Ratio 25 1 50 1 200 1 1000 dB 0 3 6 7 10 0 40 Product Power Ratios 51 x 51 51 x 101 1001 x 21 101 x 1001 ing compared Log means logarithm base 10that power 10 must raised equal particular value case value ratio P1/P2 example 10 third power 1000 thus log 1000 3 days pretechnological antiquity logarithms found log tables re member runic lists back algebra book Today scientific cal culators have log feature signifi cance logarithms found fact addition subtraction logarithms numbers equivalent multiplication division numbers themselves ex ample 100 times 1000 100000 log 100 2 log oft 000 3 log 100000 5 sum logs two smaller numbers Remember dB relative expres sion must base reference Whether previous paragraphs enlightening information follows should Because dB exponential expression because power ratios definition multiplication di vision can define changes power lev els simply adding subtracting dB As Table 1 shows doubling halving Power Ratio 1 1 1/2 1/4 1/5 1/10 1/100 1/1000 1/10000 0 3 -6 -7 -10 -20 -30 -40 power equals change plus minus 3 dB 10-to-one differ ence power l0-dB change fore have airplane mea sures 103 dB wish reduce must reduce noise output factor 2 l0-dB reduction 103 dB 93 dB would require reduc tion power factor 10 Doubling 10-dB reduction 20 dB 83 dB sound level represents whopping l00-to-l reduction sound power Its important remember because its easy kid self believing going 103 dB 93 dB just 10% changewhen reality its 1000% change Another important factor distance between listener measurer noise source general sound power will decrease square distance Thus twice distance get one-fourth power called inverse square law Since law inverse square also governs radio signal strength RC receiver function distance transmitter might worth take mo ment understand Figure 1 illustrates perceptible sound decreases ratio distance sourcein case model airplane will assume sound generated airplane radiates equally directions entirely true still reasonable sumption Consider l-ft-sq area 10 ft noise source sound meter distance will measure certain sound level However move away sound source distance 20 ft should clear sound impressed upon 1-ft square now impressed upon 2-ft square area square 2 ft side course 4 sq ft Figure 1 Decibel -6dB -6dB -12dB -95 dB -41 dB area 1-ft square 1 sq ft Since same amount sound im pressed upon 1 sq ft now spread over 4 sq ft sound level obviously reduced one-fourth what Thus compare sound levels two different distances source ratio sound levels will equal square ra tio distances few examples phenomenon presented Table 2 Table 2 shows six-dB reduc tion time distance doubled Sim ilarly distance 10 times greater sound drops 20 dB 10 squared 100 20 dB Therefore airplane measured 100 dB meter would mea sure 94 dB two meters 80 dB 10 ters about 33 ft 60 dB 100 meters about 330 ft Makes wonder peo ple complain since 60 dB approximately sound level conversation table also illuminates importance careful setup test site contest since 12% error measurement distance would make difference dB does affect modelers current AMA sound level recommenda tion flying sites needing noise abate ment 90 dB 9 ft FAt merly mandated level 100 dB ter RC Pattern competitions has consid erably relaxed requirement 98 dB three meters AMA FAI recom mendations call weighting specifies sound power reference level 0 db ubar refers air pressure changes caused sound fre quency response approximates human ear commonly ac cepted standard industrial hygiene some typical values decibel levels generated environmental sources indication human ear tol Con tinued page 146 4 sq ft \W 70k October 1989 35 Decibel Equivalent 7dB 14dB 7dB 20 dB B 10dB 3 dB 100 dB Radio Shack sound meter meter can purchased about 30 dollars isnt exactly laboratory quality cer tainly adequate model noise measurements covers 60 126 dB six ranges has weighting photo graph its showing 98dB 100dB scale PRECISION MODEL PRODUCTS uzZZ7Is# Made U S BARSTOCK ALUMINUM SPINNERS Pan No Size TT-150-B .. 1-1/2 TT-175-B . 1-3/4 TT-200-B 11-225-B .. 21/4 11-226-B .. 2-1/4 FAI . TT-250-B . 2-1/2 TT-251-B . 2-1/2 FAI .. TT-275-B 3/4 TT-276-8 .. 2-3/4 FAI .. 11-300-B 11-301-BPAl TT-325-B . 3-1/4 TT-350-B /2 TT-375-B .. 3-3/4 11-400-B 4 RetailApprox PriceWeight $1395058 02 149509502 159510002 169516002 189515002 189519002 209517002 229522002 249520002 269526002 289525002 369534002 499547002 599552002 699557002 3 Pieces Cone Back Plate Retainer Screw Note 3 4 Blade Spinners Available Sizes Add 5300 Per Spinner PROP NUT ADAPTORS Part No Size TT-140-A . 1/4-28 TT-147-A 4-28/7mm . TT-610-A 10mm TT-710-A 10mm TT-516-A '5/16-24 TT-518-A .. 5/16-24/8mm IT-BiD-A x 10mm TT-825-A . 8x 125mm TT-375-A3/8-24 TT-125-A x 125mm Retail Approx Price Weight $495 061 02 49506102 49506302 49508202 495 602 49507602 495076oz 495 .. 075 02 595 117 02 595 02 3 Pieces Nut Washer anti Machined Bushing Add S350 Shipping Handling Prices subject change notice ROMCO MFG INC OX 836 SOUTH HOUSTON TEXAS 77587 713 943-1867 other 357th alumnus Chuck Yeager alive well TV again again think single-seat Dornier-335 Air Space Museum Washington DCpossibly same wife Helen beginning push 70 pretty hard both still ac tive licensed pilots have dabbling RC several years am enclosing picture freehand scratch-builts little 50 Saito powered 514-pounderreferred Round big 13-lb 8footer named Mr Big Its powered Zenoah 23 Both fly very well Harvey Mace Ft Bragg CA Safety/Preston Continued page 22 letter stated story apparently first sur faced 1967 So happen prefer assem bling models components arc welding rather gluing also weareontact lenses dont alarmed saw warning National Newsletter Its just true Have another safe Fly Baby/Mathews Continued page 33 site Test range free surface movement deflections per plans engine carbure tor needle settings engine-on radio op eration Finally important make sure model balances slightly ward center-of-gravity shown plans Add ballast needed Dont fly model tail-heavy everything checks out OK Fly Baby ready big try field head wind add little right rudder advance throttle youre air borne 12 ft adding up elevator youre taking off downwind Remember climb rate func tion engine speed elevator Dont horse airplane around heavy-handedly gentle caresses thats needed Take model up bit throttle down dead slow Still isnt sinking much Find little thermal shut engine off Now isnt something kind flying too sedate taste try some slow-speed touch-andbumps Hows easy Did ever prettier Whatever style flying youll find Old-Timer will oblige Versatile brisk smooth responsive Fly Baby will exactly what want See yourself isnt up date Old-Timer could ask dB Facts/Abbott Continued page 35 erates Quiet whisper 20 dB Conversation 65 dB Loud orchestra 80 dB Start danger 90 dB Amplified rock band 110 dB Threshold pain 130 dB Federal agencies have established recom mended standards safe noise exposure eight hours per day 90 dB two hours per day 100 dB less one-quarter hour per day 115 dB Lets reexamine AMA FAI cri teria Current AMA90 dB 9 ft Old FAIl00 dB meter Current FAI98 dB three meters order compare recommenda tions need convert single distancein case 9 ft Thats easy enough involves converting meters feet meter ft applying inverse square law discussed above results Current AMA90 dB 9 ft Old FAI912 dB 9 ft Current FAI988 dB 9 ft As can see new FAI regulation considerably less stringent old 146 Model Aviation Matched Performance System TOP PERFORMANCE K&B ENGINES AirplaneManse K&B FUELS K&B Glow PLUGS 9 Blends4 Choices Free Flight Kits Supplies Rubber er Power Kits Scale Old Timer Too Co Electric Motors Rubber Tissue Cox Parts Rubber Accessories Winding Hooks Timers Nitrate Dope CATALOGUE $200 CAMPBELLS CUSTOM KITS PO BOX 5996 LAKE WORTH FL 33466-5996 Letters Editor Continued page 12 V difference 76 dB equates power ra tio 57that airplane permitted emit 57 times much sonic power permitted under old standard current AMA recommendation 88 dB tougher new FAI rule Thats power ratio 76 am surprised lack consistency between AMA FAI Because have sound meter know noise propagation 100 dB 9 ft very common flying field muf flers Ive also discovered fourcycle engines sound tolerably quiet ear measure 100 dB up range Obviously subjective evaluation noise can deceptive four-cycle en gine sounds less objectionable two cycle engine yet registers almost high big ignition engine too sounds tamer its high readings meter would suggest Additionally frequency spectrum af fects perception noise see arti cle Sound Related Flying Sites No vember 1987 MA fact deserves careful thought respect relations public doubt noise levels seeing todays muffled engines pose real threat hearing especially since time standing quite some dis tance models Thank heavens mufflers After 50 years listen ing model engines mostly unmuffled hearing quite impaired high fre quency end age might have something Finally since propeller sig nificantly increases sound output use larger slower props should help allay noise problem Noisehow produce mea sure itis becoming major issue hobby today Coping problem intelligent way demands some effort means familiarizing ourselves rele vant technical terminology educating ourselves about factors influence sound emission article written purpose mind Radio Technique/Myers Continued page 37 ceiver batteries will result presence DC-DC converter receiver batteries making contact low-voltage alarm LVA system also cluded receivers PCM computer battery voltage drops below 28 volts throttle servoand throttle servogoes preset position stays typographic error receiver continues func tion down 28 volts advertised thats LVA cuts may fine get ting everything possible out alkaline batteries its dangerously low Ni-Cds think Ive got Polks convinced move trip point up around 47 volts will enough charge left Ni-Cds land safely subject batteries Chal lenger 550 manual says Transmitter 96-108 VDC 8 9 Nicad tin batteries Mine came usual Polks nine-pencell Ni-Cd pack transmitter four-pencell Ni-Cd pack receiver Transmitter operating cur rent measured 120 mA predicts about four hours operating timebetter PCM transmitters Output power looks like about 550 milliwatts Receiver drain idle five servos measured 60 mA battery charge should last about four hours ordinary service Frequency agility plug-in module transmitter inexpensive receivers make easy field changes frequency within 72 MHz band make swap field should check ground range adequate fly time no modules Ham CB bands well does work Bob Aberle t did field test system performed very well type testing last discussed May 1988 column discussed length January 1986 column results testing follows M200 adjacent channels 20 kHz Gold FM old AM ilver AM 0 kHz Gold FM Gold AM ilver AM djacent-channel performance excellent 1989 environment Polks still working develop 'bulletproof receiver 1991 turns out job some folks expectedContinued page 148 October 1989 147
Edition: Model Aviation - 1989/10
Page Numbers: 34, 35, 146, 147
_n dealing engine no FaCts Ilying -noise problems field its real have some familiarity fundamentals sound propagation measurement perceived human ear U George F Abbott ANYONE WHOS BEEN keeping up model press lately aware noise issue various ideas about limiting measuring sound produced models can no question about importance sound abatement Im sure noise far away signifi cant cause loss flying sites today reading reports discussions subject must have noticed use term dB decibel under stand actual significance some sound level standards have know what dB means Decibel means 10 bels Named af ter Alexander Graham Bell term bel measure comparative power As may know Bells experiments re sulted invention telephone orig inated studies human hearinghis wife deafand causes possible cures hearing impairment inventor discovered ears sensitivity sound intensity loudness linear twice much sound power isnt perceived twice loud rather just barely perceptible change Therefore appropriate unit measure compar ative sound power would have based exponential logarithmic relation ship Without going excessive detail Ill define explain dBand talk about practical implications dB defined dimensionless ex pression ratio power Specifically D og Pl/P2 dB P1 P2 two powers beTop Dick Pettit member Burlington NC Barks Club seen holding sound meter aimed authors Astro Hog powered OS FS9O four-cycle engine swinging Graupner 12 x 75 three-bladed prop Turning 8700 rpm noise levels measured 98 dBA 9 ft 92 dBA 18 ft airplane does seem noisy though air Note doubling distance turned out reduce sound level 6 dB lust theory predicts doesnt always come out close due variables encountered actual field condi tions Left Dick Pettit fires up OS 120 Gemini twin engine Aeronca C-3 engine turns 16 x 7 prop 7500 rpm producing 98 dBA 9 92 dBA 18 ft Right author Ace 4-40 powered Saito 45 four-cycle engine turning 12 x 6 Master Airscrew prop 8000 rpm recorded 93 dBA 9 ft 88 dBA 18 ft 5 dB difference doesnt quite agree theory still pretty close field measurement plane very quiet air though exceeds recommended AMA noise standard 3 dB 34 Model Aviation Table 1 Power Ratios Decimal Equivalents Power Ratio 1 1 2 1 4 1 5 1 lOto 1 100 1 1000 1 10000 1 Power Ratio 25 1 50 1 200 1 1000 dB 0 3 6 7 10 0 40 Product Power Ratios 51 x 51 51 x 101 1001 x 21 101 x 1001 ing compared Log means logarithm base 10that power 10 must raised equal particular value case value ratio P1/P2 example 10 third power 1000 thus log 1000 3 days pretechnological antiquity logarithms found log tables re member runic lists back algebra book Today scientific cal culators have log feature signifi cance logarithms found fact addition subtraction logarithms numbers equivalent multiplication division numbers themselves ex ample 100 times 1000 100000 log 100 2 log oft 000 3 log 100000 5 sum logs two smaller numbers Remember dB relative expres sion must base reference Whether previous paragraphs enlightening information follows should Because dB exponential expression because power ratios definition multiplication di vision can define changes power lev els simply adding subtracting dB As Table 1 shows doubling halving Power Ratio 1 1 1/2 1/4 1/5 1/10 1/100 1/1000 1/10000 0 3 -6 -7 -10 -20 -30 -40 power equals change plus minus 3 dB 10-to-one differ ence power l0-dB change fore have airplane mea sures 103 dB wish reduce must reduce noise output factor 2 l0-dB reduction 103 dB 93 dB would require reduc tion power factor 10 Doubling 10-dB reduction 20 dB 83 dB sound level represents whopping l00-to-l reduction sound power Its important remember because its easy kid self believing going 103 dB 93 dB just 10% changewhen reality its 1000% change Another important factor distance between listener measurer noise source general sound power will decrease square distance Thus twice distance get one-fourth power called inverse square law Since law inverse square also governs radio signal strength RC receiver function distance transmitter might worth take mo ment understand Figure 1 illustrates perceptible sound decreases ratio distance sourcein case model airplane will assume sound generated airplane radiates equally directions entirely true still reasonable sumption Consider l-ft-sq area 10 ft noise source sound meter distance will measure certain sound level However move away sound source distance 20 ft should clear sound impressed upon 1-ft square now impressed upon 2-ft square area square 2 ft side course 4 sq ft Figure 1 Decibel -6dB -6dB -12dB -95 dB -41 dB area 1-ft square 1 sq ft Since same amount sound im pressed upon 1 sq ft now spread over 4 sq ft sound level obviously reduced one-fourth what Thus compare sound levels two different distances source ratio sound levels will equal square ra tio distances few examples phenomenon presented Table 2 Table 2 shows six-dB reduc tion time distance doubled Sim ilarly distance 10 times greater sound drops 20 dB 10 squared 100 20 dB Therefore airplane measured 100 dB meter would mea sure 94 dB two meters 80 dB 10 ters about 33 ft 60 dB 100 meters about 330 ft Makes wonder peo ple complain since 60 dB approximately sound level conversation table also illuminates importance careful setup test site contest since 12% error measurement distance would make difference dB does affect modelers current AMA sound level recommenda tion flying sites needing noise abate ment 90 dB 9 ft FAt merly mandated level 100 dB ter RC Pattern competitions has consid erably relaxed requirement 98 dB three meters AMA FAI recom mendations call weighting specifies sound power reference level 0 db ubar refers air pressure changes caused sound fre quency response approximates human ear commonly ac cepted standard industrial hygiene some typical values decibel levels generated environmental sources indication human ear tol Con tinued page 146 4 sq ft \W 70k October 1989 35 Decibel Equivalent 7dB 14dB 7dB 20 dB B 10dB 3 dB 100 dB Radio Shack sound meter meter can purchased about 30 dollars isnt exactly laboratory quality cer tainly adequate model noise measurements covers 60 126 dB six ranges has weighting photo graph its showing 98dB 100dB scale PRECISION MODEL PRODUCTS uzZZ7Is# Made U S BARSTOCK ALUMINUM SPINNERS Pan No Size TT-150-B .. 1-1/2 TT-175-B . 1-3/4 TT-200-B 11-225-B .. 21/4 11-226-B .. 2-1/4 FAI . TT-250-B . 2-1/2 TT-251-B . 2-1/2 FAI .. TT-275-B 3/4 TT-276-8 .. 2-3/4 FAI .. 11-300-B 11-301-BPAl TT-325-B . 3-1/4 TT-350-B /2 TT-375-B .. 3-3/4 11-400-B 4 RetailApprox PriceWeight $1395058 02 149509502 159510002 169516002 189515002 189519002 209517002 229522002 249520002 269526002 289525002 369534002 499547002 599552002 699557002 3 Pieces Cone Back Plate Retainer Screw Note 3 4 Blade Spinners Available Sizes Add 5300 Per Spinner PROP NUT ADAPTORS Part No Size TT-140-A . 1/4-28 TT-147-A 4-28/7mm . TT-610-A 10mm TT-710-A 10mm TT-516-A '5/16-24 TT-518-A .. 5/16-24/8mm IT-BiD-A x 10mm TT-825-A . 8x 125mm TT-375-A3/8-24 TT-125-A x 125mm Retail Approx Price Weight $495 061 02 49506102 49506302 49508202 495 602 49507602 495076oz 495 .. 075 02 595 117 02 595 02 3 Pieces Nut Washer anti Machined Bushing Add S350 Shipping Handling Prices subject change notice ROMCO MFG INC OX 836 SOUTH HOUSTON TEXAS 77587 713 943-1867 other 357th alumnus Chuck Yeager alive well TV again again think single-seat Dornier-335 Air Space Museum Washington DCpossibly same wife Helen beginning push 70 pretty hard both still ac tive licensed pilots have dabbling RC several years am enclosing picture freehand scratch-builts little 50 Saito powered 514-pounderreferred Round big 13-lb 8footer named Mr Big Its powered Zenoah 23 Both fly very well Harvey Mace Ft Bragg CA Safety/Preston Continued page 22 letter stated story apparently first sur faced 1967 So happen prefer assem bling models components arc welding rather gluing also weareontact lenses dont alarmed saw warning National Newsletter Its just true Have another safe Fly Baby/Mathews Continued page 33 site Test range free surface movement deflections per plans engine carbure tor needle settings engine-on radio op eration Finally important make sure model balances slightly ward center-of-gravity shown plans Add ballast needed Dont fly model tail-heavy everything checks out OK Fly Baby ready big try field head wind add little right rudder advance throttle youre air borne 12 ft adding up elevator youre taking off downwind Remember climb rate func tion engine speed elevator Dont horse airplane around heavy-handedly gentle caresses thats needed Take model up bit throttle down dead slow Still isnt sinking much Find little thermal shut engine off Now isnt something kind flying too sedate taste try some slow-speed touch-andbumps Hows easy Did ever prettier Whatever style flying youll find Old-Timer will oblige Versatile brisk smooth responsive Fly Baby will exactly what want See yourself isnt up date Old-Timer could ask dB Facts/Abbott Continued page 35 erates Quiet whisper 20 dB Conversation 65 dB Loud orchestra 80 dB Start danger 90 dB Amplified rock band 110 dB Threshold pain 130 dB Federal agencies have established recom mended standards safe noise exposure eight hours per day 90 dB two hours per day 100 dB less one-quarter hour per day 115 dB Lets reexamine AMA FAI cri teria Current AMA90 dB 9 ft Old FAIl00 dB meter Current FAI98 dB three meters order compare recommenda tions need convert single distancein case 9 ft Thats easy enough involves converting meters feet meter ft applying inverse square law discussed above results Current AMA90 dB 9 ft Old FAI912 dB 9 ft Current FAI988 dB 9 ft As can see new FAI regulation considerably less stringent old 146 Model Aviation Matched Performance System TOP PERFORMANCE K&B ENGINES AirplaneManse K&B FUELS K&B Glow PLUGS 9 Blends4 Choices Free Flight Kits Supplies Rubber er Power Kits Scale Old Timer Too Co Electric Motors Rubber Tissue Cox Parts Rubber Accessories Winding Hooks Timers Nitrate Dope CATALOGUE $200 CAMPBELLS CUSTOM KITS PO BOX 5996 LAKE WORTH FL 33466-5996 Letters Editor Continued page 12 V difference 76 dB equates power ra tio 57that airplane permitted emit 57 times much sonic power permitted under old standard current AMA recommendation 88 dB tougher new FAI rule Thats power ratio 76 am surprised lack consistency between AMA FAI Because have sound meter know noise propagation 100 dB 9 ft very common flying field muf flers Ive also discovered fourcycle engines sound tolerably quiet ear measure 100 dB up range Obviously subjective evaluation noise can deceptive four-cycle en gine sounds less objectionable two cycle engine yet registers almost high big ignition engine too sounds tamer its high readings meter would suggest Additionally frequency spectrum af fects perception noise see arti cle Sound Related Flying Sites No vember 1987 MA fact deserves careful thought respect relations public doubt noise levels seeing todays muffled engines pose real threat hearing especially since time standing quite some dis tance models Thank heavens mufflers After 50 years listen ing model engines mostly unmuffled hearing quite impaired high fre quency end age might have something Finally since propeller sig nificantly increases sound output use larger slower props should help allay noise problem Noisehow produce mea sure itis becoming major issue hobby today Coping problem intelligent way demands some effort means familiarizing ourselves rele vant technical terminology educating ourselves about factors influence sound emission article written purpose mind Radio Technique/Myers Continued page 37 ceiver batteries will result presence DC-DC converter receiver batteries making contact low-voltage alarm LVA system also cluded receivers PCM computer battery voltage drops below 28 volts throttle servoand throttle servogoes preset position stays typographic error receiver continues func tion down 28 volts advertised thats LVA cuts may fine get ting everything possible out alkaline batteries its dangerously low Ni-Cds think Ive got Polks convinced move trip point up around 47 volts will enough charge left Ni-Cds land safely subject batteries Chal lenger 550 manual says Transmitter 96-108 VDC 8 9 Nicad tin batteries Mine came usual Polks nine-pencell Ni-Cd pack transmitter four-pencell Ni-Cd pack receiver Transmitter operating cur rent measured 120 mA predicts about four hours operating timebetter PCM transmitters Output power looks like about 550 milliwatts Receiver drain idle five servos measured 60 mA battery charge should last about four hours ordinary service Frequency agility plug-in module transmitter inexpensive receivers make easy field changes frequency within 72 MHz band make swap field should check ground range adequate fly time no modules Ham CB bands well does work Bob Aberle t did field test system performed very well type testing last discussed May 1988 column discussed length January 1986 column results testing follows M200 adjacent channels 20 kHz Gold FM old AM ilver AM 0 kHz Gold FM Gold AM ilver AM djacent-channel performance excellent 1989 environment Polks still working develop 'bulletproof receiver 1991 turns out job some folks expectedContinued page 148 October 1989 147
Edition: Model Aviation - 1989/10
Page Numbers: 34, 35, 146, 147
_n dealing engine no FaCts Ilying -noise problems field its real have some familiarity fundamentals sound propagation measurement perceived human ear U George F Abbott ANYONE WHOS BEEN keeping up model press lately aware noise issue various ideas about limiting measuring sound produced models can no question about importance sound abatement Im sure noise far away signifi cant cause loss flying sites today reading reports discussions subject must have noticed use term dB decibel under stand actual significance some sound level standards have know what dB means Decibel means 10 bels Named af ter Alexander Graham Bell term bel measure comparative power As may know Bells experiments re sulted invention telephone orig inated studies human hearinghis wife deafand causes possible cures hearing impairment inventor discovered ears sensitivity sound intensity loudness linear twice much sound power isnt perceived twice loud rather just barely perceptible change Therefore appropriate unit measure compar ative sound power would have based exponential logarithmic relation ship Without going excessive detail Ill define explain dBand talk about practical implications dB defined dimensionless ex pression ratio power Specifically D og Pl/P2 dB P1 P2 two powers beTop Dick Pettit member Burlington NC Barks Club seen holding sound meter aimed authors Astro Hog powered OS FS9O four-cycle engine swinging Graupner 12 x 75 three-bladed prop Turning 8700 rpm noise levels measured 98 dBA 9 ft 92 dBA 18 ft airplane does seem noisy though air Note doubling distance turned out reduce sound level 6 dB lust theory predicts doesnt always come out close due variables encountered actual field condi tions Left Dick Pettit fires up OS 120 Gemini twin engine Aeronca C-3 engine turns 16 x 7 prop 7500 rpm producing 98 dBA 9 92 dBA 18 ft Right author Ace 4-40 powered Saito 45 four-cycle engine turning 12 x 6 Master Airscrew prop 8000 rpm recorded 93 dBA 9 ft 88 dBA 18 ft 5 dB difference doesnt quite agree theory still pretty close field measurement plane very quiet air though exceeds recommended AMA noise standard 3 dB 34 Model Aviation Table 1 Power Ratios Decimal Equivalents Power Ratio 1 1 2 1 4 1 5 1 lOto 1 100 1 1000 1 10000 1 Power Ratio 25 1 50 1 200 1 1000 dB 0 3 6 7 10 0 40 Product Power Ratios 51 x 51 51 x 101 1001 x 21 101 x 1001 ing compared Log means logarithm base 10that power 10 must raised equal particular value case value ratio P1/P2 example 10 third power 1000 thus log 1000 3 days pretechnological antiquity logarithms found log tables re member runic lists back algebra book Today scientific cal culators have log feature signifi cance logarithms found fact addition subtraction logarithms numbers equivalent multiplication division numbers themselves ex ample 100 times 1000 100000 log 100 2 log oft 000 3 log 100000 5 sum logs two smaller numbers Remember dB relative expres sion must base reference Whether previous paragraphs enlightening information follows should Because dB exponential expression because power ratios definition multiplication di vision can define changes power lev els simply adding subtracting dB As Table 1 shows doubling halving Power Ratio 1 1 1/2 1/4 1/5 1/10 1/100 1/1000 1/10000 0 3 -6 -7 -10 -20 -30 -40 power equals change plus minus 3 dB 10-to-one differ ence power l0-dB change fore have airplane mea sures 103 dB wish reduce must reduce noise output factor 2 l0-dB reduction 103 dB 93 dB would require reduc tion power factor 10 Doubling 10-dB reduction 20 dB 83 dB sound level represents whopping l00-to-l reduction sound power Its important remember because its easy kid self believing going 103 dB 93 dB just 10% changewhen reality its 1000% change Another important factor distance between listener measurer noise source general sound power will decrease square distance Thus twice distance get one-fourth power called inverse square law Since law inverse square also governs radio signal strength RC receiver function distance transmitter might worth take mo ment understand Figure 1 illustrates perceptible sound decreases ratio distance sourcein case model airplane will assume sound generated airplane radiates equally directions entirely true still reasonable sumption Consider l-ft-sq area 10 ft noise source sound meter distance will measure certain sound level However move away sound source distance 20 ft should clear sound impressed upon 1-ft square now impressed upon 2-ft square area square 2 ft side course 4 sq ft Figure 1 Decibel -6dB -6dB -12dB -95 dB -41 dB area 1-ft square 1 sq ft Since same amount sound im pressed upon 1 sq ft now spread over 4 sq ft sound level obviously reduced one-fourth what Thus compare sound levels two different distances source ratio sound levels will equal square ra tio distances few examples phenomenon presented Table 2 Table 2 shows six-dB reduc tion time distance doubled Sim ilarly distance 10 times greater sound drops 20 dB 10 squared 100 20 dB Therefore airplane measured 100 dB meter would mea sure 94 dB two meters 80 dB 10 ters about 33 ft 60 dB 100 meters about 330 ft Makes wonder peo ple complain since 60 dB approximately sound level conversation table also illuminates importance careful setup test site contest since 12% error measurement distance would make difference dB does affect modelers current AMA sound level recommenda tion flying sites needing noise abate ment 90 dB 9 ft FAt merly mandated level 100 dB ter RC Pattern competitions has consid erably relaxed requirement 98 dB three meters AMA FAI recom mendations call weighting specifies sound power reference level 0 db ubar refers air pressure changes caused sound fre quency response approximates human ear commonly ac cepted standard industrial hygiene some typical values decibel levels generated environmental sources indication human ear tol Con tinued page 146 4 sq ft \W 70k October 1989 35 Decibel Equivalent 7dB 14dB 7dB 20 dB B 10dB 3 dB 100 dB Radio Shack sound meter meter can purchased about 30 dollars isnt exactly laboratory quality cer tainly adequate model noise measurements covers 60 126 dB six ranges has weighting photo graph its showing 98dB 100dB scale PRECISION MODEL PRODUCTS uzZZ7Is# Made U S BARSTOCK ALUMINUM SPINNERS Pan No Size TT-150-B .. 1-1/2 TT-175-B . 1-3/4 TT-200-B 11-225-B .. 21/4 11-226-B .. 2-1/4 FAI . TT-250-B . 2-1/2 TT-251-B . 2-1/2 FAI .. TT-275-B 3/4 TT-276-8 .. 2-3/4 FAI .. 11-300-B 11-301-BPAl TT-325-B . 3-1/4 TT-350-B /2 TT-375-B .. 3-3/4 11-400-B 4 RetailApprox PriceWeight $1395058 02 149509502 159510002 169516002 189515002 189519002 209517002 229522002 249520002 269526002 289525002 369534002 499547002 599552002 699557002 3 Pieces Cone Back Plate Retainer Screw Note 3 4 Blade Spinners Available Sizes Add 5300 Per Spinner PROP NUT ADAPTORS Part No Size TT-140-A . 1/4-28 TT-147-A 4-28/7mm . TT-610-A 10mm TT-710-A 10mm TT-516-A '5/16-24 TT-518-A .. 5/16-24/8mm IT-BiD-A x 10mm TT-825-A . 8x 125mm TT-375-A3/8-24 TT-125-A x 125mm Retail Approx Price Weight $495 061 02 49506102 49506302 49508202 495 602 49507602 495076oz 495 .. 075 02 595 117 02 595 02 3 Pieces Nut Washer anti Machined Bushing Add S350 Shipping Handling Prices subject change notice ROMCO MFG INC OX 836 SOUTH HOUSTON TEXAS 77587 713 943-1867 other 357th alumnus Chuck Yeager alive well TV again again think single-seat Dornier-335 Air Space Museum Washington DCpossibly same wife Helen beginning push 70 pretty hard both still ac tive licensed pilots have dabbling RC several years am enclosing picture freehand scratch-builts little 50 Saito powered 514-pounderreferred Round big 13-lb 8footer named Mr Big Its powered Zenoah 23 Both fly very well Harvey Mace Ft Bragg CA Safety/Preston Continued page 22 letter stated story apparently first sur faced 1967 So happen prefer assem bling models components arc welding rather gluing also weareontact lenses dont alarmed saw warning National Newsletter Its just true Have another safe Fly Baby/Mathews Continued page 33 site Test range free surface movement deflections per plans engine carbure tor needle settings engine-on radio op eration Finally important make sure model balances slightly ward center-of-gravity shown plans Add ballast needed Dont fly model tail-heavy everything checks out OK Fly Baby ready big try field head wind add little right rudder advance throttle youre air borne 12 ft adding up elevator youre taking off downwind Remember climb rate func tion engine speed elevator Dont horse airplane around heavy-handedly gentle caresses thats needed Take model up bit throttle down dead slow Still isnt sinking much Find little thermal shut engine off Now isnt something kind flying too sedate taste try some slow-speed touch-andbumps Hows easy Did ever prettier Whatever style flying youll find Old-Timer will oblige Versatile brisk smooth responsive Fly Baby will exactly what want See yourself isnt up date Old-Timer could ask dB Facts/Abbott Continued page 35 erates Quiet whisper 20 dB Conversation 65 dB Loud orchestra 80 dB Start danger 90 dB Amplified rock band 110 dB Threshold pain 130 dB Federal agencies have established recom mended standards safe noise exposure eight hours per day 90 dB two hours per day 100 dB less one-quarter hour per day 115 dB Lets reexamine AMA FAI cri teria Current AMA90 dB 9 ft Old FAIl00 dB meter Current FAI98 dB three meters order compare recommenda tions need convert single distancein case 9 ft Thats easy enough involves converting meters feet meter ft applying inverse square law discussed above results Current AMA90 dB 9 ft Old FAI912 dB 9 ft Current FAI988 dB 9 ft As can see new FAI regulation considerably less stringent old 146 Model Aviation Matched Performance System TOP PERFORMANCE K&B ENGINES AirplaneManse K&B FUELS K&B Glow PLUGS 9 Blends4 Choices Free Flight Kits Supplies Rubber er Power Kits Scale Old Timer Too Co Electric Motors Rubber Tissue Cox Parts Rubber Accessories Winding Hooks Timers Nitrate Dope CATALOGUE $200 CAMPBELLS CUSTOM KITS PO BOX 5996 LAKE WORTH FL 33466-5996 Letters Editor Continued page 12 V difference 76 dB equates power ra tio 57that airplane permitted emit 57 times much sonic power permitted under old standard current AMA recommendation 88 dB tougher new FAI rule Thats power ratio 76 am surprised lack consistency between AMA FAI Because have sound meter know noise propagation 100 dB 9 ft very common flying field muf flers Ive also discovered fourcycle engines sound tolerably quiet ear measure 100 dB up range Obviously subjective evaluation noise can deceptive four-cycle en gine sounds less objectionable two cycle engine yet registers almost high big ignition engine too sounds tamer its high readings meter would suggest Additionally frequency spectrum af fects perception noise see arti cle Sound Related Flying Sites No vember 1987 MA fact deserves careful thought respect relations public doubt noise levels seeing todays muffled engines pose real threat hearing especially since time standing quite some dis tance models Thank heavens mufflers After 50 years listen ing model engines mostly unmuffled hearing quite impaired high fre quency end age might have something Finally since propeller sig nificantly increases sound output use larger slower props should help allay noise problem Noisehow produce mea sure itis becoming major issue hobby today Coping problem intelligent way demands some effort means familiarizing ourselves rele vant technical terminology educating ourselves about factors influence sound emission article written purpose mind Radio Technique/Myers Continued page 37 ceiver batteries will result presence DC-DC converter receiver batteries making contact low-voltage alarm LVA system also cluded receivers PCM computer battery voltage drops below 28 volts throttle servoand throttle servogoes preset position stays typographic error receiver continues func tion down 28 volts advertised thats LVA cuts may fine get ting everything possible out alkaline batteries its dangerously low Ni-Cds think Ive got Polks convinced move trip point up around 47 volts will enough charge left Ni-Cds land safely subject batteries Chal lenger 550 manual says Transmitter 96-108 VDC 8 9 Nicad tin batteries Mine came usual Polks nine-pencell Ni-Cd pack transmitter four-pencell Ni-Cd pack receiver Transmitter operating cur rent measured 120 mA predicts about four hours operating timebetter PCM transmitters Output power looks like about 550 milliwatts Receiver drain idle five servos measured 60 mA battery charge should last about four hours ordinary service Frequency agility plug-in module transmitter inexpensive receivers make easy field changes frequency within 72 MHz band make swap field should check ground range adequate fly time no modules Ham CB bands well does work Bob Aberle t did field test system performed very well type testing last discussed May 1988 column discussed length January 1986 column results testing follows M200 adjacent channels 20 kHz Gold FM old AM ilver AM 0 kHz Gold FM Gold AM ilver AM djacent-channel performance excellent 1989 environment Polks still working develop 'bulletproof receiver 1991 turns out job some folks expectedContinued page 148 October 1989 147