REDUCE EXHAUST NOiSE Rodney B Pharis YOU THINK its impossible have cake eat too Dont believe recently decided end retire ment resume active control-line stunt combat flying try RC Pattern started reading model airplane maga zines visiting hobby shops local contests happily noted new materials engines accessories available today shocked see ugly mufflers pro truding fuselages afterthought exactly what are. after-the-fact bandaid Can imagine muffler sticking out front fender car first reaction mufflers general negative after contemplating subject concluded logical inevitable However refused ac cept unsightly appearance aerody namic drag current commercially available side-mounted mufflers used otherwise fully-cowled installations able locate muffler inside fuse lage maintain minimum-width fuse lage cross section exhaust port must located rear engine course would best use engine originally designed feature front-intake engines currently pro duced rear exhaust port Taipan 15 STD R/C OPS 40 SPA/STD OPS 40 SPA/RCA engines equipped Schneurle porting crankshaft ball bearings appear out standing quality However Taipan too small CL stunt RC pattern planes typically used competition OPS engines weigh 106 ounces 116 ounces respectively Fox 35 Stunt Fox 40 weigh 6 11 ounces re spectively addition list price OPS 40 $10000 $10400 RC Fox 40 $3295 $4295 RC Because above bias Made America stamp decided experiment converting side-exhaust Fox rear-exhaust configuration dusted off trusty 1954 vintage Fox 35 called 35 Stunt days ended up few weeks later arrangement shown Fig ran series tests repeated several times under similar en vironmental conditions verify results averaged graphed data facilitate comparative analysis tested very used 1954 model Fox 35 modification 1975 model Fox 36 bushing crankshaft bearing model had few break-in runs before tests Fox 36 test ed both standard sidemounted Fox size B muffler .while improving performance appearance author contemplates finished rework Fox Stunt unsightly appearance aerodynamic drag conventional mufflers disturbed him Results d looked Conversion side-exhaust Fox 35 rear inside configuration shows encouraging promise tests run full available power using 10-6 Top Flight prop K&B Supersonic 500 fuel test engine mounted open test stand located outside remote vertical sound-reflecting surface mi crophone placed 3 feet en gine facing exhaust outlet Equipment used obtain analyze data included General Radio #1933 precision sound level meter/octave band analyzer tret condensor micro phone foam windscreen Sony Tapecorder #TC-8008 Honeywell j/SAI-52B real time spec trum analyzer/digital averager Hewlett-Packard #1220A oscillo scope Esterline Angus #241 ITB X-Y plotter Alnor Thermocon #4040 ther mocouple results tests compared Fig B Note temperatures shown represent highest temperatures detect ed engine exterior al ways exhaust stack area crank case results surprising Need less say excited pleased noise level standard Fox 36 dropped November1975 29 Reduce Exhaust Noise 10 dB peak sound level 3000 Hertz 90 dBA equals approximate ly all perceived level engine speed decreased 300 rpm dBA re fers -weighted frequency re sponse simulates human hearing charact ens tics given distance source general trend judge fre quencies up 1000 Hertz lower measured dB levelfrequencies 10006000 Hertz higher measured Db level frequencies 6000 Hertz upper audible limit approximately 14000 Hertz lower measured dB level corresponds l0-dB reduction 300- 400-rpm loss adver tised Fox literature magnitude noise reduction modified Fox 35 Stunt arrangement 92 dBA essen tially same Fox 36 standard muffler muffled peak sound level shifted 1500 Hertz lesscritical frequency 3500 Hertz Although shift perceptible 3 feet higher frequencies fall off much faster dis tance sound source increases Another surprising result increase 15 rpm after adding rear-facing manifold Although such small increase could support credible conclusion installing modified muffler mani fold resulted additional 240-rpm increase verified seemingly irrational effect inserting removing muffler several times during given engine run same results time ApparentFox 35 Stunt in/rear manifold wlo muffler 1134 dBA 9540 rpm 420F 110 Range sensitine human hearing Standard Fox 35 Stunt w/o muffler 1145 dBA 9525 rpm 300 F -77 Standard Fox 38 in/n mu e 1148 dBA 10200 rpm 305 F - 4----e] / 100 -J 0 z C N 0 C m 0 90 80 70 Standard Fox 36 wfstandard closed front fon muffler 11058 dBA 9900 rpm 390F{ Foe 35 Stunt in/rear manifold modfied Fox muffler 1053 dRA 97SOrpm440FII Foe 35 Stunt in/rear mandold modified Fox muffler packed steel wool 958 dBA 9750 rpm 455Fl Note Sound fecels approximarefy 2OdBA fosser measured 265 feet 8 meters engine II 2505001000 2000 4000800016000 Octane Band Center FrequencyHertz FIGURE B Exhaust Noise measured three feet engine ly rear-mounted muffler lesser extent rear manifold scavenge exhaust gases increasing power like tuned-pipe improving noise-reduction character istics same time Note stand ard muffler increased temperature hottest part exterior en gine exhaust stack 85eF rearfacing manifold increased 200F muffler combination rear manifold rear-mounted muffler raises l4OnF believe temperature crease result exposing crank case hot exhaust gases longer time gases deflected rearward manifold would occur exhaust port cylinder liner designed face rearward directly rear exhaust stack So far 4400F temperature has caused noticeable harm Cooling fins added side manifold would help dissipate some heat tuned-pipe efficiency also can utilized advantage achieving signifi cant reduction noise trading off some increased power depending upon magnitude additional muffling desired instance Fig B also shows results gained rear-mounted muffler 30 Model Aviation Fig Completed modification tuned pipe/muffler arrangement Tank located behind engine between mounts exhaust Air routed around engine muffler exits exhaust outlet Above Fig C Exhaust port mod exhaust deflector plate rear-exhaust prior welding operation Below Fig D rear exhaust slot made after deflector plate place packed Grade 2 coarse steel wool An additional 65 dBA reduction achieved retaining 225 255 rpm gain experienced prior using steel wool rear mounted-muffler also has other advantages Improved appearance mounting muffler inside fuselage having exhaust exit seldomseen bottom fuselage rather side Elimination muffler aerodynamic drag Additional noise reduction provided fuselage damping noise radiating off exterior muf fler housing Better weight distribution provided locating muffler between engine wing instead alongside engine Based test results believe arrangement offers inherent advan tages could successfully used other similar model-airplane engines Further development could optimize sound reduction engine performance minimize engine-temperature increases instance may possible maxi mize tuned-pipe power increase effect shifting sound-level peak higher frequency would significant ly less perceptible neighbors ear higher initial decibel levels modifications made Fox 35 tests evident photos some discussion may help First project us inexperienced unequipped welding high-silicon aluminum castings Aside major detail rest easy After completely disassembling en gine grind file off front half exhaust stack make exhaust-gas deflector plate 0032-thick 5086 5052 3003 aluminum sheet rearexhaust outlet tube 0625-OD X 0035-thick wall 5086 5052 3003 aluminum shown Fig C joints should fit closely gaps must surgically clean Use small fine file polish off oxide just before welding Welding crankcase muffler done Tungsten Inert Gas TIG method using 0062 diameter 5356 alumi num welding wire ground sharp point end prevent warpage dis integration aluminum-casting ma terial length weld should exceed Allow casting cool room temperature before proceed ing Cooling can accelerated placing airstream cooling fan welder unit Another way prevent heat damage submerge casting water almost up weld area welding however cool suddenly dipping water after welding could cause cracking casting weld zone Weld deflector plate place make 025- 066 slot rear continued page 73 November1975 31 Exhaust Noise/Pharis continued page 31 exhaust stack shown Fig D Weld outlet tube shown Fig E file away weld material pro tudes slot opening may also weld two three horizontal cooling fins outside deflector plate help minimize increased operating tempera ture caused exposing crankcase hot exhaust gases deflected rearward Carefully clean oil parts stall crankshaft wrist pin connecting rod piston Modify exhaust port cylinder liner follows Insert liner rotate required precisely align intake port fuel bypass crankcase baffle top piston Look rear exhaust outlet tube scribe vertical line onto liner locate left end exhaust outlet slot crankcase Remove liner scribe two parallel horizontal lines extending upper lower sides exhaust port vertical line Using small fine square file carefully lengthen rear liner exhaust port filing away scribed area Deburr inner side exhaust port area filed avoid scratching piston Clean reoil liner install Com plete engine assembly using new backp1 ate head gaskets muffler modified size B Fox silencer closed front style standard muffler shown disassembled Fig F Modify per Fig G follows Mill and/ file away front baffle inner part leaving three equally spaced vanes about 006 thick keep inner part centered outer part Cut off 012 normal side-exhaust inlet Using same type size aluminum tube used engine rear exhaust out let make flared muffler inlet tube curved outlet tube Use same thickness type aluminum sheet used make engine exhaust deflector plate make muffler mounting flange about 112 175 two 0125 diameter holes Weld curved outlet tube rear inner part oriented desired direc tion relative mounting flange ie downward sideways etc Seal open ing remaining portion normal side-exhaust inlet weld weld mounting flange flared inlet tube place outer part completed muffler modification shown Fig H inlet tube shown before welding expose exhaust-gas passage formed front modified baffle inner part mounting flange operat ing temperature 3000F recom mended thin piece asbestos used under flange protect fuse lage Use piece 0625 ID silicon rub ber hose 075 long join muffler engine-exhaust-outlet tube seems like lot trouble However well worth terms 46 Power 10- 19 $2695 SUPER ieose send illustrated coiolag 1of models accessories] enclose 25g INameI II Address II City State ______________________ Zip __________________ 1 JJJVT PRODUCTS CO StHobartIndiana 46342 providing reliable lightweight inexpen sive engine featuring muffler packaged within small streamlined fuselage better sound reduction greater power currently available side-mounted muffler Lets hope engines mufflers general configuration 35-61 size range UC Stunt RC Pattern use become commercially avail able soon WANTED ideas happenings hints/kinks howto sketches photos news etc Send colum nist category concernedat address shown column photo idea printed Model Aviation will pay $5 contributor G ollyG eeWhiz/R utherford continued page 34 tail-heavy almost impossible fly level worry about just move motor ahead 1/4 try plane once can always move engine back plane isnt responsive enough Pull wing off board turn over should now right side up pin down building board Mark inboard tip rib leadout position lay bellerank assembly posi tion Using best eye piece sharpened 1/4 brass tubing punch holes ribs leadouts Glue complete bellcrank assembly Thread leadouts through ribs notch TE pushrod Cut off front rib way bladder tube install bladder tube Check sure bellcrank working binds Add top sheeting want can glue tips leadout guides now usually wait until LE carved shape everything dry plane LE shape sand entire structure havent already done glue tips dont forget tip weight now ready cover plane cover planes tip rib tip rib FasCal cover tips MonoKote MonoKote does lot better job compound curves adds some color plane making easier see match cover FasCal can glue booms directly onto covering using other covering ma terial dont take chance Remove covering joint glue directly center section sheeting glue November1975 73 1-1g II UUIIOT SUDS weiaea rear inner part flange mounting welded remaining portion original side exhaust inlet outer part new exhaust inlet tube prior welding Note ex haust passage formed modification front baffle
Edition: Model Aviation - 1975/11
Page Numbers: 29, 30, 31, 73
REDUCE EXHAUST NOiSE Rodney B Pharis YOU THINK its impossible have cake eat too Dont believe recently decided end retire ment resume active control-line stunt combat flying try RC Pattern started reading model airplane maga zines visiting hobby shops local contests happily noted new materials engines accessories available today shocked see ugly mufflers pro truding fuselages afterthought exactly what are. after-the-fact bandaid Can imagine muffler sticking out front fender car first reaction mufflers general negative after contemplating subject concluded logical inevitable However refused ac cept unsightly appearance aerody namic drag current commercially available side-mounted mufflers used otherwise fully-cowled installations able locate muffler inside fuse lage maintain minimum-width fuse lage cross section exhaust port must located rear engine course would best use engine originally designed feature front-intake engines currently pro duced rear exhaust port Taipan 15 STD R/C OPS 40 SPA/STD OPS 40 SPA/RCA engines equipped Schneurle porting crankshaft ball bearings appear out standing quality However Taipan too small CL stunt RC pattern planes typically used competition OPS engines weigh 106 ounces 116 ounces respectively Fox 35 Stunt Fox 40 weigh 6 11 ounces re spectively addition list price OPS 40 $10000 $10400 RC Fox 40 $3295 $4295 RC Because above bias Made America stamp decided experiment converting side-exhaust Fox rear-exhaust configuration dusted off trusty 1954 vintage Fox 35 called 35 Stunt days ended up few weeks later arrangement shown Fig ran series tests repeated several times under similar en vironmental conditions verify results averaged graphed data facilitate comparative analysis tested very used 1954 model Fox 35 modification 1975 model Fox 36 bushing crankshaft bearing model had few break-in runs before tests Fox 36 test ed both standard sidemounted Fox size B muffler .while improving performance appearance author contemplates finished rework Fox Stunt unsightly appearance aerodynamic drag conventional mufflers disturbed him Results d looked Conversion side-exhaust Fox 35 rear inside configuration shows encouraging promise tests run full available power using 10-6 Top Flight prop K&B Supersonic 500 fuel test engine mounted open test stand located outside remote vertical sound-reflecting surface mi crophone placed 3 feet en gine facing exhaust outlet Equipment used obtain analyze data included General Radio #1933 precision sound level meter/octave band analyzer tret condensor micro phone foam windscreen Sony Tapecorder #TC-8008 Honeywell j/SAI-52B real time spec trum analyzer/digital averager Hewlett-Packard #1220A oscillo scope Esterline Angus #241 ITB X-Y plotter Alnor Thermocon #4040 ther mocouple results tests compared Fig B Note temperatures shown represent highest temperatures detect ed engine exterior al ways exhaust stack area crank case results surprising Need less say excited pleased noise level standard Fox 36 dropped November1975 29 Reduce Exhaust Noise 10 dB peak sound level 3000 Hertz 90 dBA equals approximate ly all perceived level engine speed decreased 300 rpm dBA re fers -weighted frequency re sponse simulates human hearing charact ens tics given distance source general trend judge fre quencies up 1000 Hertz lower measured dB levelfrequencies 10006000 Hertz higher measured Db level frequencies 6000 Hertz upper audible limit approximately 14000 Hertz lower measured dB level corresponds l0-dB reduction 300- 400-rpm loss adver tised Fox literature magnitude noise reduction modified Fox 35 Stunt arrangement 92 dBA essen tially same Fox 36 standard muffler muffled peak sound level shifted 1500 Hertz lesscritical frequency 3500 Hertz Although shift perceptible 3 feet higher frequencies fall off much faster dis tance sound source increases Another surprising result increase 15 rpm after adding rear-facing manifold Although such small increase could support credible conclusion installing modified muffler mani fold resulted additional 240-rpm increase verified seemingly irrational effect inserting removing muffler several times during given engine run same results time ApparentFox 35 Stunt in/rear manifold wlo muffler 1134 dBA 9540 rpm 420F 110 Range sensitine human hearing Standard Fox 35 Stunt w/o muffler 1145 dBA 9525 rpm 300 F -77 Standard Fox 38 in/n mu e 1148 dBA 10200 rpm 305 F - 4----e] / 100 -J 0 z C N 0 C m 0 90 80 70 Standard Fox 36 wfstandard closed front fon muffler 11058 dBA 9900 rpm 390F{ Foe 35 Stunt in/rear manifold modfied Fox muffler 1053 dRA 97SOrpm440FII Foe 35 Stunt in/rear mandold modified Fox muffler packed steel wool 958 dBA 9750 rpm 455Fl Note Sound fecels approximarefy 2OdBA fosser measured 265 feet 8 meters engine II 2505001000 2000 4000800016000 Octane Band Center FrequencyHertz FIGURE B Exhaust Noise measured three feet engine ly rear-mounted muffler lesser extent rear manifold scavenge exhaust gases increasing power like tuned-pipe improving noise-reduction character istics same time Note stand ard muffler increased temperature hottest part exterior en gine exhaust stack 85eF rearfacing manifold increased 200F muffler combination rear manifold rear-mounted muffler raises l4OnF believe temperature crease result exposing crank case hot exhaust gases longer time gases deflected rearward manifold would occur exhaust port cylinder liner designed face rearward directly rear exhaust stack So far 4400F temperature has caused noticeable harm Cooling fins added side manifold would help dissipate some heat tuned-pipe efficiency also can utilized advantage achieving signifi cant reduction noise trading off some increased power depending upon magnitude additional muffling desired instance Fig B also shows results gained rear-mounted muffler 30 Model Aviation Fig Completed modification tuned pipe/muffler arrangement Tank located behind engine between mounts exhaust Air routed around engine muffler exits exhaust outlet Above Fig C Exhaust port mod exhaust deflector plate rear-exhaust prior welding operation Below Fig D rear exhaust slot made after deflector plate place packed Grade 2 coarse steel wool An additional 65 dBA reduction achieved retaining 225 255 rpm gain experienced prior using steel wool rear mounted-muffler also has other advantages Improved appearance mounting muffler inside fuselage having exhaust exit seldomseen bottom fuselage rather side Elimination muffler aerodynamic drag Additional noise reduction provided fuselage damping noise radiating off exterior muf fler housing Better weight distribution provided locating muffler between engine wing instead alongside engine Based test results believe arrangement offers inherent advan tages could successfully used other similar model-airplane engines Further development could optimize sound reduction engine performance minimize engine-temperature increases instance may possible maxi mize tuned-pipe power increase effect shifting sound-level peak higher frequency would significant ly less perceptible neighbors ear higher initial decibel levels modifications made Fox 35 tests evident photos some discussion may help First project us inexperienced unequipped welding high-silicon aluminum castings Aside major detail rest easy After completely disassembling en gine grind file off front half exhaust stack make exhaust-gas deflector plate 0032-thick 5086 5052 3003 aluminum sheet rearexhaust outlet tube 0625-OD X 0035-thick wall 5086 5052 3003 aluminum shown Fig C joints should fit closely gaps must surgically clean Use small fine file polish off oxide just before welding Welding crankcase muffler done Tungsten Inert Gas TIG method using 0062 diameter 5356 alumi num welding wire ground sharp point end prevent warpage dis integration aluminum-casting ma terial length weld should exceed Allow casting cool room temperature before proceed ing Cooling can accelerated placing airstream cooling fan welder unit Another way prevent heat damage submerge casting water almost up weld area welding however cool suddenly dipping water after welding could cause cracking casting weld zone Weld deflector plate place make 025- 066 slot rear continued page 73 November1975 31 Exhaust Noise/Pharis continued page 31 exhaust stack shown Fig D Weld outlet tube shown Fig E file away weld material pro tudes slot opening may also weld two three horizontal cooling fins outside deflector plate help minimize increased operating tempera ture caused exposing crankcase hot exhaust gases deflected rearward Carefully clean oil parts stall crankshaft wrist pin connecting rod piston Modify exhaust port cylinder liner follows Insert liner rotate required precisely align intake port fuel bypass crankcase baffle top piston Look rear exhaust outlet tube scribe vertical line onto liner locate left end exhaust outlet slot crankcase Remove liner scribe two parallel horizontal lines extending upper lower sides exhaust port vertical line Using small fine square file carefully lengthen rear liner exhaust port filing away scribed area Deburr inner side exhaust port area filed avoid scratching piston Clean reoil liner install Com plete engine assembly using new backp1 ate head gaskets muffler modified size B Fox silencer closed front style standard muffler shown disassembled Fig F Modify per Fig G follows Mill and/ file away front baffle inner part leaving three equally spaced vanes about 006 thick keep inner part centered outer part Cut off 012 normal side-exhaust inlet Using same type size aluminum tube used engine rear exhaust out let make flared muffler inlet tube curved outlet tube Use same thickness type aluminum sheet used make engine exhaust deflector plate make muffler mounting flange about 112 175 two 0125 diameter holes Weld curved outlet tube rear inner part oriented desired direc tion relative mounting flange ie downward sideways etc Seal open ing remaining portion normal side-exhaust inlet weld weld mounting flange flared inlet tube place outer part completed muffler modification shown Fig H inlet tube shown before welding expose exhaust-gas passage formed front modified baffle inner part mounting flange operat ing temperature 3000F recom mended thin piece asbestos used under flange protect fuse lage Use piece 0625 ID silicon rub ber hose 075 long join muffler engine-exhaust-outlet tube seems like lot trouble However well worth terms 46 Power 10- 19 $2695 SUPER ieose send illustrated coiolag 1of models accessories] enclose 25g INameI II Address II City State ______________________ Zip __________________ 1 JJJVT PRODUCTS CO StHobartIndiana 46342 providing reliable lightweight inexpen sive engine featuring muffler packaged within small streamlined fuselage better sound reduction greater power currently available side-mounted muffler Lets hope engines mufflers general configuration 35-61 size range UC Stunt RC Pattern use become commercially avail able soon WANTED ideas happenings hints/kinks howto sketches photos news etc Send colum nist category concernedat address shown column photo idea printed Model Aviation will pay $5 contributor G ollyG eeWhiz/R utherford continued page 34 tail-heavy almost impossible fly level worry about just move motor ahead 1/4 try plane once can always move engine back plane isnt responsive enough Pull wing off board turn over should now right side up pin down building board Mark inboard tip rib leadout position lay bellerank assembly posi tion Using best eye piece sharpened 1/4 brass tubing punch holes ribs leadouts Glue complete bellcrank assembly Thread leadouts through ribs notch TE pushrod Cut off front rib way bladder tube install bladder tube Check sure bellcrank working binds Add top sheeting want can glue tips leadout guides now usually wait until LE carved shape everything dry plane LE shape sand entire structure havent already done glue tips dont forget tip weight now ready cover plane cover planes tip rib tip rib FasCal cover tips MonoKote MonoKote does lot better job compound curves adds some color plane making easier see match cover FasCal can glue booms directly onto covering using other covering ma terial dont take chance Remove covering joint glue directly center section sheeting glue November1975 73 1-1g II UUIIOT SUDS weiaea rear inner part flange mounting welded remaining portion original side exhaust inlet outer part new exhaust inlet tube prior welding Note ex haust passage formed modification front baffle
Edition: Model Aviation - 1975/11
Page Numbers: 29, 30, 31, 73
REDUCE EXHAUST NOiSE Rodney B Pharis YOU THINK its impossible have cake eat too Dont believe recently decided end retire ment resume active control-line stunt combat flying try RC Pattern started reading model airplane maga zines visiting hobby shops local contests happily noted new materials engines accessories available today shocked see ugly mufflers pro truding fuselages afterthought exactly what are. after-the-fact bandaid Can imagine muffler sticking out front fender car first reaction mufflers general negative after contemplating subject concluded logical inevitable However refused ac cept unsightly appearance aerody namic drag current commercially available side-mounted mufflers used otherwise fully-cowled installations able locate muffler inside fuse lage maintain minimum-width fuse lage cross section exhaust port must located rear engine course would best use engine originally designed feature front-intake engines currently pro duced rear exhaust port Taipan 15 STD R/C OPS 40 SPA/STD OPS 40 SPA/RCA engines equipped Schneurle porting crankshaft ball bearings appear out standing quality However Taipan too small CL stunt RC pattern planes typically used competition OPS engines weigh 106 ounces 116 ounces respectively Fox 35 Stunt Fox 40 weigh 6 11 ounces re spectively addition list price OPS 40 $10000 $10400 RC Fox 40 $3295 $4295 RC Because above bias Made America stamp decided experiment converting side-exhaust Fox rear-exhaust configuration dusted off trusty 1954 vintage Fox 35 called 35 Stunt days ended up few weeks later arrangement shown Fig ran series tests repeated several times under similar en vironmental conditions verify results averaged graphed data facilitate comparative analysis tested very used 1954 model Fox 35 modification 1975 model Fox 36 bushing crankshaft bearing model had few break-in runs before tests Fox 36 test ed both standard sidemounted Fox size B muffler .while improving performance appearance author contemplates finished rework Fox Stunt unsightly appearance aerodynamic drag conventional mufflers disturbed him Results d looked Conversion side-exhaust Fox 35 rear inside configuration shows encouraging promise tests run full available power using 10-6 Top Flight prop K&B Supersonic 500 fuel test engine mounted open test stand located outside remote vertical sound-reflecting surface mi crophone placed 3 feet en gine facing exhaust outlet Equipment used obtain analyze data included General Radio #1933 precision sound level meter/octave band analyzer tret condensor micro phone foam windscreen Sony Tapecorder #TC-8008 Honeywell j/SAI-52B real time spec trum analyzer/digital averager Hewlett-Packard #1220A oscillo scope Esterline Angus #241 ITB X-Y plotter Alnor Thermocon #4040 ther mocouple results tests compared Fig B Note temperatures shown represent highest temperatures detect ed engine exterior al ways exhaust stack area crank case results surprising Need less say excited pleased noise level standard Fox 36 dropped November1975 29 Reduce Exhaust Noise 10 dB peak sound level 3000 Hertz 90 dBA equals approximate ly all perceived level engine speed decreased 300 rpm dBA re fers -weighted frequency re sponse simulates human hearing charact ens tics given distance source general trend judge fre quencies up 1000 Hertz lower measured dB levelfrequencies 10006000 Hertz higher measured Db level frequencies 6000 Hertz upper audible limit approximately 14000 Hertz lower measured dB level corresponds l0-dB reduction 300- 400-rpm loss adver tised Fox literature magnitude noise reduction modified Fox 35 Stunt arrangement 92 dBA essen tially same Fox 36 standard muffler muffled peak sound level shifted 1500 Hertz lesscritical frequency 3500 Hertz Although shift perceptible 3 feet higher frequencies fall off much faster dis tance sound source increases Another surprising result increase 15 rpm after adding rear-facing manifold Although such small increase could support credible conclusion installing modified muffler mani fold resulted additional 240-rpm increase verified seemingly irrational effect inserting removing muffler several times during given engine run same results time ApparentFox 35 Stunt in/rear manifold wlo muffler 1134 dBA 9540 rpm 420F 110 Range sensitine human hearing Standard Fox 35 Stunt w/o muffler 1145 dBA 9525 rpm 300 F -77 Standard Fox 38 in/n mu e 1148 dBA 10200 rpm 305 F - 4----e] / 100 -J 0 z C N 0 C m 0 90 80 70 Standard Fox 36 wfstandard closed front fon muffler 11058 dBA 9900 rpm 390F{ Foe 35 Stunt in/rear manifold modfied Fox muffler 1053 dRA 97SOrpm440FII Foe 35 Stunt in/rear mandold modified Fox muffler packed steel wool 958 dBA 9750 rpm 455Fl Note Sound fecels approximarefy 2OdBA fosser measured 265 feet 8 meters engine II 2505001000 2000 4000800016000 Octane Band Center FrequencyHertz FIGURE B Exhaust Noise measured three feet engine ly rear-mounted muffler lesser extent rear manifold scavenge exhaust gases increasing power like tuned-pipe improving noise-reduction character istics same time Note stand ard muffler increased temperature hottest part exterior en gine exhaust stack 85eF rearfacing manifold increased 200F muffler combination rear manifold rear-mounted muffler raises l4OnF believe temperature crease result exposing crank case hot exhaust gases longer time gases deflected rearward manifold would occur exhaust port cylinder liner designed face rearward directly rear exhaust stack So far 4400F temperature has caused noticeable harm Cooling fins added side manifold would help dissipate some heat tuned-pipe efficiency also can utilized advantage achieving signifi cant reduction noise trading off some increased power depending upon magnitude additional muffling desired instance Fig B also shows results gained rear-mounted muffler 30 Model Aviation Fig Completed modification tuned pipe/muffler arrangement Tank located behind engine between mounts exhaust Air routed around engine muffler exits exhaust outlet Above Fig C Exhaust port mod exhaust deflector plate rear-exhaust prior welding operation Below Fig D rear exhaust slot made after deflector plate place packed Grade 2 coarse steel wool An additional 65 dBA reduction achieved retaining 225 255 rpm gain experienced prior using steel wool rear mounted-muffler also has other advantages Improved appearance mounting muffler inside fuselage having exhaust exit seldomseen bottom fuselage rather side Elimination muffler aerodynamic drag Additional noise reduction provided fuselage damping noise radiating off exterior muf fler housing Better weight distribution provided locating muffler between engine wing instead alongside engine Based test results believe arrangement offers inherent advan tages could successfully used other similar model-airplane engines Further development could optimize sound reduction engine performance minimize engine-temperature increases instance may possible maxi mize tuned-pipe power increase effect shifting sound-level peak higher frequency would significant ly less perceptible neighbors ear higher initial decibel levels modifications made Fox 35 tests evident photos some discussion may help First project us inexperienced unequipped welding high-silicon aluminum castings Aside major detail rest easy After completely disassembling en gine grind file off front half exhaust stack make exhaust-gas deflector plate 0032-thick 5086 5052 3003 aluminum sheet rearexhaust outlet tube 0625-OD X 0035-thick wall 5086 5052 3003 aluminum shown Fig C joints should fit closely gaps must surgically clean Use small fine file polish off oxide just before welding Welding crankcase muffler done Tungsten Inert Gas TIG method using 0062 diameter 5356 alumi num welding wire ground sharp point end prevent warpage dis integration aluminum-casting ma terial length weld should exceed Allow casting cool room temperature before proceed ing Cooling can accelerated placing airstream cooling fan welder unit Another way prevent heat damage submerge casting water almost up weld area welding however cool suddenly dipping water after welding could cause cracking casting weld zone Weld deflector plate place make 025- 066 slot rear continued page 73 November1975 31 Exhaust Noise/Pharis continued page 31 exhaust stack shown Fig D Weld outlet tube shown Fig E file away weld material pro tudes slot opening may also weld two three horizontal cooling fins outside deflector plate help minimize increased operating tempera ture caused exposing crankcase hot exhaust gases deflected rearward Carefully clean oil parts stall crankshaft wrist pin connecting rod piston Modify exhaust port cylinder liner follows Insert liner rotate required precisely align intake port fuel bypass crankcase baffle top piston Look rear exhaust outlet tube scribe vertical line onto liner locate left end exhaust outlet slot crankcase Remove liner scribe two parallel horizontal lines extending upper lower sides exhaust port vertical line Using small fine square file carefully lengthen rear liner exhaust port filing away scribed area Deburr inner side exhaust port area filed avoid scratching piston Clean reoil liner install Com plete engine assembly using new backp1 ate head gaskets muffler modified size B Fox silencer closed front style standard muffler shown disassembled Fig F Modify per Fig G follows Mill and/ file away front baffle inner part leaving three equally spaced vanes about 006 thick keep inner part centered outer part Cut off 012 normal side-exhaust inlet Using same type size aluminum tube used engine rear exhaust out let make flared muffler inlet tube curved outlet tube Use same thickness type aluminum sheet used make engine exhaust deflector plate make muffler mounting flange about 112 175 two 0125 diameter holes Weld curved outlet tube rear inner part oriented desired direc tion relative mounting flange ie downward sideways etc Seal open ing remaining portion normal side-exhaust inlet weld weld mounting flange flared inlet tube place outer part completed muffler modification shown Fig H inlet tube shown before welding expose exhaust-gas passage formed front modified baffle inner part mounting flange operat ing temperature 3000F recom mended thin piece asbestos used under flange protect fuse lage Use piece 0625 ID silicon rub ber hose 075 long join muffler engine-exhaust-outlet tube seems like lot trouble However well worth terms 46 Power 10- 19 $2695 SUPER ieose send illustrated coiolag 1of models accessories] enclose 25g INameI II Address II City State ______________________ Zip __________________ 1 JJJVT PRODUCTS CO StHobartIndiana 46342 providing reliable lightweight inexpen sive engine featuring muffler packaged within small streamlined fuselage better sound reduction greater power currently available side-mounted muffler Lets hope engines mufflers general configuration 35-61 size range UC Stunt RC Pattern use become commercially avail able soon WANTED ideas happenings hints/kinks howto sketches photos news etc Send colum nist category concernedat address shown column photo idea printed Model Aviation will pay $5 contributor G ollyG eeWhiz/R utherford continued page 34 tail-heavy almost impossible fly level worry about just move motor ahead 1/4 try plane once can always move engine back plane isnt responsive enough Pull wing off board turn over should now right side up pin down building board Mark inboard tip rib leadout position lay bellerank assembly posi tion Using best eye piece sharpened 1/4 brass tubing punch holes ribs leadouts Glue complete bellcrank assembly Thread leadouts through ribs notch TE pushrod Cut off front rib way bladder tube install bladder tube Check sure bellcrank working binds Add top sheeting want can glue tips leadout guides now usually wait until LE carved shape everything dry plane LE shape sand entire structure havent already done glue tips dont forget tip weight now ready cover plane cover planes tip rib tip rib FasCal cover tips MonoKote MonoKote does lot better job compound curves adds some color plane making easier see match cover FasCal can glue booms directly onto covering using other covering ma terial dont take chance Remove covering joint glue directly center section sheeting glue November1975 73 1-1g II UUIIOT SUDS weiaea rear inner part flange mounting welded remaining portion original side exhaust inlet outer part new exhaust inlet tube prior welding Note ex haust passage formed modification front baffle
Edition: Model Aviation - 1975/11
Page Numbers: 29, 30, 31, 73
REDUCE EXHAUST NOiSE Rodney B Pharis YOU THINK its impossible have cake eat too Dont believe recently decided end retire ment resume active control-line stunt combat flying try RC Pattern started reading model airplane maga zines visiting hobby shops local contests happily noted new materials engines accessories available today shocked see ugly mufflers pro truding fuselages afterthought exactly what are. after-the-fact bandaid Can imagine muffler sticking out front fender car first reaction mufflers general negative after contemplating subject concluded logical inevitable However refused ac cept unsightly appearance aerody namic drag current commercially available side-mounted mufflers used otherwise fully-cowled installations able locate muffler inside fuse lage maintain minimum-width fuse lage cross section exhaust port must located rear engine course would best use engine originally designed feature front-intake engines currently pro duced rear exhaust port Taipan 15 STD R/C OPS 40 SPA/STD OPS 40 SPA/RCA engines equipped Schneurle porting crankshaft ball bearings appear out standing quality However Taipan too small CL stunt RC pattern planes typically used competition OPS engines weigh 106 ounces 116 ounces respectively Fox 35 Stunt Fox 40 weigh 6 11 ounces re spectively addition list price OPS 40 $10000 $10400 RC Fox 40 $3295 $4295 RC Because above bias Made America stamp decided experiment converting side-exhaust Fox rear-exhaust configuration dusted off trusty 1954 vintage Fox 35 called 35 Stunt days ended up few weeks later arrangement shown Fig ran series tests repeated several times under similar en vironmental conditions verify results averaged graphed data facilitate comparative analysis tested very used 1954 model Fox 35 modification 1975 model Fox 36 bushing crankshaft bearing model had few break-in runs before tests Fox 36 test ed both standard sidemounted Fox size B muffler .while improving performance appearance author contemplates finished rework Fox Stunt unsightly appearance aerodynamic drag conventional mufflers disturbed him Results d looked Conversion side-exhaust Fox 35 rear inside configuration shows encouraging promise tests run full available power using 10-6 Top Flight prop K&B Supersonic 500 fuel test engine mounted open test stand located outside remote vertical sound-reflecting surface mi crophone placed 3 feet en gine facing exhaust outlet Equipment used obtain analyze data included General Radio #1933 precision sound level meter/octave band analyzer tret condensor micro phone foam windscreen Sony Tapecorder #TC-8008 Honeywell j/SAI-52B real time spec trum analyzer/digital averager Hewlett-Packard #1220A oscillo scope Esterline Angus #241 ITB X-Y plotter Alnor Thermocon #4040 ther mocouple results tests compared Fig B Note temperatures shown represent highest temperatures detect ed engine exterior al ways exhaust stack area crank case results surprising Need less say excited pleased noise level standard Fox 36 dropped November1975 29 Reduce Exhaust Noise 10 dB peak sound level 3000 Hertz 90 dBA equals approximate ly all perceived level engine speed decreased 300 rpm dBA re fers -weighted frequency re sponse simulates human hearing charact ens tics given distance source general trend judge fre quencies up 1000 Hertz lower measured dB levelfrequencies 10006000 Hertz higher measured Db level frequencies 6000 Hertz upper audible limit approximately 14000 Hertz lower measured dB level corresponds l0-dB reduction 300- 400-rpm loss adver tised Fox literature magnitude noise reduction modified Fox 35 Stunt arrangement 92 dBA essen tially same Fox 36 standard muffler muffled peak sound level shifted 1500 Hertz lesscritical frequency 3500 Hertz Although shift perceptible 3 feet higher frequencies fall off much faster dis tance sound source increases Another surprising result increase 15 rpm after adding rear-facing manifold Although such small increase could support credible conclusion installing modified muffler mani fold resulted additional 240-rpm increase verified seemingly irrational effect inserting removing muffler several times during given engine run same results time ApparentFox 35 Stunt in/rear manifold wlo muffler 1134 dBA 9540 rpm 420F 110 Range sensitine human hearing Standard Fox 35 Stunt w/o muffler 1145 dBA 9525 rpm 300 F -77 Standard Fox 38 in/n mu e 1148 dBA 10200 rpm 305 F - 4----e] / 100 -J 0 z C N 0 C m 0 90 80 70 Standard Fox 36 wfstandard closed front fon muffler 11058 dBA 9900 rpm 390F{ Foe 35 Stunt in/rear manifold modfied Fox muffler 1053 dRA 97SOrpm440FII Foe 35 Stunt in/rear mandold modified Fox muffler packed steel wool 958 dBA 9750 rpm 455Fl Note Sound fecels approximarefy 2OdBA fosser measured 265 feet 8 meters engine II 2505001000 2000 4000800016000 Octane Band Center FrequencyHertz FIGURE B Exhaust Noise measured three feet engine ly rear-mounted muffler lesser extent rear manifold scavenge exhaust gases increasing power like tuned-pipe improving noise-reduction character istics same time Note stand ard muffler increased temperature hottest part exterior en gine exhaust stack 85eF rearfacing manifold increased 200F muffler combination rear manifold rear-mounted muffler raises l4OnF believe temperature crease result exposing crank case hot exhaust gases longer time gases deflected rearward manifold would occur exhaust port cylinder liner designed face rearward directly rear exhaust stack So far 4400F temperature has caused noticeable harm Cooling fins added side manifold would help dissipate some heat tuned-pipe efficiency also can utilized advantage achieving signifi cant reduction noise trading off some increased power depending upon magnitude additional muffling desired instance Fig B also shows results gained rear-mounted muffler 30 Model Aviation Fig Completed modification tuned pipe/muffler arrangement Tank located behind engine between mounts exhaust Air routed around engine muffler exits exhaust outlet Above Fig C Exhaust port mod exhaust deflector plate rear-exhaust prior welding operation Below Fig D rear exhaust slot made after deflector plate place packed Grade 2 coarse steel wool An additional 65 dBA reduction achieved retaining 225 255 rpm gain experienced prior using steel wool rear mounted-muffler also has other advantages Improved appearance mounting muffler inside fuselage having exhaust exit seldomseen bottom fuselage rather side Elimination muffler aerodynamic drag Additional noise reduction provided fuselage damping noise radiating off exterior muf fler housing Better weight distribution provided locating muffler between engine wing instead alongside engine Based test results believe arrangement offers inherent advan tages could successfully used other similar model-airplane engines Further development could optimize sound reduction engine performance minimize engine-temperature increases instance may possible maxi mize tuned-pipe power increase effect shifting sound-level peak higher frequency would significant ly less perceptible neighbors ear higher initial decibel levels modifications made Fox 35 tests evident photos some discussion may help First project us inexperienced unequipped welding high-silicon aluminum castings Aside major detail rest easy After completely disassembling en gine grind file off front half exhaust stack make exhaust-gas deflector plate 0032-thick 5086 5052 3003 aluminum sheet rearexhaust outlet tube 0625-OD X 0035-thick wall 5086 5052 3003 aluminum shown Fig C joints should fit closely gaps must surgically clean Use small fine file polish off oxide just before welding Welding crankcase muffler done Tungsten Inert Gas TIG method using 0062 diameter 5356 alumi num welding wire ground sharp point end prevent warpage dis integration aluminum-casting ma terial length weld should exceed Allow casting cool room temperature before proceed ing Cooling can accelerated placing airstream cooling fan welder unit Another way prevent heat damage submerge casting water almost up weld area welding however cool suddenly dipping water after welding could cause cracking casting weld zone Weld deflector plate place make 025- 066 slot rear continued page 73 November1975 31 Exhaust Noise/Pharis continued page 31 exhaust stack shown Fig D Weld outlet tube shown Fig E file away weld material pro tudes slot opening may also weld two three horizontal cooling fins outside deflector plate help minimize increased operating tempera ture caused exposing crankcase hot exhaust gases deflected rearward Carefully clean oil parts stall crankshaft wrist pin connecting rod piston Modify exhaust port cylinder liner follows Insert liner rotate required precisely align intake port fuel bypass crankcase baffle top piston Look rear exhaust outlet tube scribe vertical line onto liner locate left end exhaust outlet slot crankcase Remove liner scribe two parallel horizontal lines extending upper lower sides exhaust port vertical line Using small fine square file carefully lengthen rear liner exhaust port filing away scribed area Deburr inner side exhaust port area filed avoid scratching piston Clean reoil liner install Com plete engine assembly using new backp1 ate head gaskets muffler modified size B Fox silencer closed front style standard muffler shown disassembled Fig F Modify per Fig G follows Mill and/ file away front baffle inner part leaving three equally spaced vanes about 006 thick keep inner part centered outer part Cut off 012 normal side-exhaust inlet Using same type size aluminum tube used engine rear exhaust out let make flared muffler inlet tube curved outlet tube Use same thickness type aluminum sheet used make engine exhaust deflector plate make muffler mounting flange about 112 175 two 0125 diameter holes Weld curved outlet tube rear inner part oriented desired direc tion relative mounting flange ie downward sideways etc Seal open ing remaining portion normal side-exhaust inlet weld weld mounting flange flared inlet tube place outer part completed muffler modification shown Fig H inlet tube shown before welding expose exhaust-gas passage formed front modified baffle inner part mounting flange operat ing temperature 3000F recom mended thin piece asbestos used under flange protect fuse lage Use piece 0625 ID silicon rub ber hose 075 long join muffler engine-exhaust-outlet tube seems like lot trouble However well worth terms 46 Power 10- 19 $2695 SUPER ieose send illustrated coiolag 1of models accessories] enclose 25g INameI II Address II City State ______________________ Zip __________________ 1 JJJVT PRODUCTS CO StHobartIndiana 46342 providing reliable lightweight inexpen sive engine featuring muffler packaged within small streamlined fuselage better sound reduction greater power currently available side-mounted muffler Lets hope engines mufflers general configuration 35-61 size range UC Stunt RC Pattern use become commercially avail able soon WANTED ideas happenings hints/kinks howto sketches photos news etc Send colum nist category concernedat address shown column photo idea printed Model Aviation will pay $5 contributor G ollyG eeWhiz/R utherford continued page 34 tail-heavy almost impossible fly level worry about just move motor ahead 1/4 try plane once can always move engine back plane isnt responsive enough Pull wing off board turn over should now right side up pin down building board Mark inboard tip rib leadout position lay bellerank assembly posi tion Using best eye piece sharpened 1/4 brass tubing punch holes ribs leadouts Glue complete bellcrank assembly Thread leadouts through ribs notch TE pushrod Cut off front rib way bladder tube install bladder tube Check sure bellcrank working binds Add top sheeting want can glue tips leadout guides now usually wait until LE carved shape everything dry plane LE shape sand entire structure havent already done glue tips dont forget tip weight now ready cover plane cover planes tip rib tip rib FasCal cover tips MonoKote MonoKote does lot better job compound curves adds some color plane making easier see match cover FasCal can glue booms directly onto covering using other covering ma terial dont take chance Remove covering joint glue directly center section sheeting glue November1975 73 1-1g II UUIIOT SUDS weiaea rear inner part flange mounting welded remaining portion original side exhaust inlet outer part new exhaust inlet tube prior welding Note ex haust passage formed modification front baffle