Considering MP easy install beneficial flying engine life remark able people hesitate use it just takes someone show Big John really lays out. ABC John Kilsdonk IT WAS week before Christmas Bill Winter called asked would write how-to article muffler pressure seems old man careful John out flying week two before having some fuel draw problems RC models Some suggested try muffler pressure after little deliberation did presto problems went away says cant teach old dog new tricks Actually could relate very well Bills problem continually witness similar situations time go clubs Michigan Signal Seekers flying field Having interested engines first model airplanes close second life disturbs great deal see other modelers continually abuse engines out ignorance what about poor engine runs Usually four culprits cause needle valve setting dirt fuel system type fuel fuel-draw article about fuel-draw Better stated about ability supply consistent pressure resultant flow fuel powerplant spite certain physical limitations model natural obstaclegravity Although pressurized fuel systems models have used form another least 30 years seemingly competition crowd Typical modern tuned muffler system installed ST-X60 again note pressure tap Four sources tank pressure left right Perry pump crankcase pressure Robart pump muffler pressure examples common denominator always concerned fuel drawand consider thatthere may 5 6 inch variation fuel head typical fair-sized model changes horizontal flight path vertical OS-4OFSR left right Tuned muffler note pressure tap location MACs flow-through muffler close front stock OS muffler install muffler pres sure nothing required install muffler tap connect tubing tank vent Sport fliers avoided because too complicated Perhaps ear liest form pressure ram-pressure derived directing tank vents air stream Along way came Jim Walkers balloonregulator tanks pen bladders crankcase pressure now anti-pollution movement enforcing muf flers flying fields have new source mysterious muffler pressure perhaps easiest reliable use especially throttled en gines Following discovery now also have sophisticated sources coming along like Perry Pump various micro pumps Robart latter units offer some advantage pressure somewhat regulated constant pressure Both driven crank case pressure Perry built engine backplate Robart external goes fuel line Before get two-step how-to lets examine engines fuel flow require ments Without tank pressure source engine must supply its own fuel through suction process venturi some sort spray bar supplies fuel may adequate under some conditions dependent venturi size position spray bar tank location total fuel draw elevation risk engine does go over-lean slows down suction reduced making leaner yet eventually situation can snow-ball seizing engine causing premature engine failure constant positive pressure source would course ultimate solve problem however would require some sort external motor-driven pump generally practical could however settle predic table fuel pressure infinite number throttle settings idle full throttle match carburetor interest simplicity cost model engine carburetors have two-posi tion adjustment idle full throttle mixture control combined fixed taper throttle barrel everything between So dont have ideal have something can make work Since main needle valve idle needle valve mixture control equipJune1979 19 ped essentially fixed orifices need fuel pressure source proportional throttle angle virtually instantaneous response Old fashioned crankcase pres sure alone doesnt provide tank pressure cannot relieved fast enough However muffler exhaust system pressure does approach its asking first step preparation article determine what pressure levels various mufflers generated So spent next three weeks running different systems could find come up representative cross-section run some crankcase pressure measurements 15 years ago seems 05 psi range So borrowed pressure gauge work calibrated inches water 060 feeling would adequate Really wanted water mano meter since temperature hover ing between 0100F plan out water would freeze used gauge compile data Fig No 1 Due low pressure levels fact gauge calibrated 700F wont attest accuracy claims rather trust relative levels differences reference did bench-test engine Perry Pump shown did measure Robart couldnt find set-up convenient time Characteristically full throttle back muffler pressure varies about inch water column about eight inches water dependent particular muffler engine used Although pressure relatively low inch water lbs/sq psi enough help us out especially have muffler giving least five inches pressure Idle pressures essentially zero Generally speaking original equip ment mufflers provide backpressure replacement types although some performance loss engines increased backpressure Also point interest compiling data shown observed rather subjectively backpressure lower noise leveltuned mufflers excepted Now what will magic pressure First lets consider tank installations Ideally always want vertically align centerline tank centerline needle valve isnt too difficult side-mounted engines because tank can aligned engine crank shaft However model designs upright engines tank usually ends up 1/2 2 inch below needle causes richening fuel mixture inverted flight during rolling maneuvers due variations static fuel head Also tank sufficiently below needle valve engine will able draw fuel Next consider average 12 oz tank 2-1/2 high Therefore tank full needle valve set 11/4 positive fuel head near Tuned muffler installation Quickie 500 Pylon racer fuel tubing connection between the tank muffler tan may clearly seen 2-line system filling throuah line bottom tank 1-1/4 negative head 2-1/2 head change during flight noticeable taking off rich side going progressively leaner through flight Refer Fig No 2 vertical maneuvers becomes evident pressure head changes since now have 5 6 head change Refer Fig No 3 may have noticed usual needle setting can loop well beginning flight later fuel level goes down engine loses power going overlean So unless head changes compensated initial needle setting results over-lean engine may scrap after 20 such flights increasing tank static pressure variations wont go away can significantly reduced Without getting too technical can proven mathemati cally basic flow equation iv KAVP K tant P sure Tank-full versus tank-empty pressure differences reduced depen dent static pressure head change along needle setting havent tested either Perry Robart regulated systems model should better however competition crowd generally expensive what required sport flying except possibly some unique cases Tuned mufflers have become increasing popular late well touch enough say generally respond similar standard muffler respect pressure characteristics provided pressure tap up-stream divergent cone section distinct advantage high performance spite reduced noise hook up muffler pressure favorite machine requires two very simple steps first install pressure tap muffler other connect fuel tubing tank vent Most modem engines come both mufflers pressure taps cases location tap already threaded muffler case just screw pressure tap youre ready Other mufflers come undrilled bosses will have drill tap yourself cases use crankcase pressure fitting Super tigre Fox KB-Veco tap muffler whatever thread size fitting requires thing check pressure tap has least 1/16 diameter hole tank pressure may bleed down fast enough consistent transition idle muffler has neither above locate suitable area ahead con verging end cone drill tap have found tap location isnt very critical generally put can run shortest fuel line tank pressure tap run good quality fuel line latex silicone neoprenenot plastic vent line tank making sure except fuel line needle valve other lines plugged rest fuel system airtight completego fly start engine youll notice yoi will have turn needle valve leaner turn compensate increased pressure Set engine basically same have first flight fuselage pointed up slight angle 15 degrees engine should set slightly rich usually peak-out engine back needle off point itjust barely goes back four-cycle gurgle-gurgle Try Slight adjustments may necessary subsequent flights dependent results should notice immediate improvement degree depends bad pressure amount pressure generated system two types conventional mufflersflow-through closed front flow-through has opening front generally increases engine performance however provide minimal pressure shown Fig No 1 Generally original equipment mufflers closed-front except certain Super tigres have flow-through muffler such MACs Semco still want pressure switch closed-front muffler MACs sells separate plug install front Semco must purchase different model muffler Closing front will generally give pressure less noise hope article has inspired either unknowledgeable hesitant try muffler pressure will turn make hobby fun less frustratingHappy Flying June1979 21 typical sport muffler pressure system stock muffler ideal tank/engine combination muffler pressure will improve run since needle setting less compromise batteries chief cause crashes engine failures must close sec ond Jerry Bugni left checks needle setting scale Piper Cherokee
Edition: Model Aviation - 1979/06
Page Numbers: 18, 19, 20, 21
Considering MP easy install beneficial flying engine life remark able people hesitate use it just takes someone show Big John really lays out. ABC John Kilsdonk IT WAS week before Christmas Bill Winter called asked would write how-to article muffler pressure seems old man careful John out flying week two before having some fuel draw problems RC models Some suggested try muffler pressure after little deliberation did presto problems went away says cant teach old dog new tricks Actually could relate very well Bills problem continually witness similar situations time go clubs Michigan Signal Seekers flying field Having interested engines first model airplanes close second life disturbs great deal see other modelers continually abuse engines out ignorance what about poor engine runs Usually four culprits cause needle valve setting dirt fuel system type fuel fuel-draw article about fuel-draw Better stated about ability supply consistent pressure resultant flow fuel powerplant spite certain physical limitations model natural obstaclegravity Although pressurized fuel systems models have used form another least 30 years seemingly competition crowd Typical modern tuned muffler system installed ST-X60 again note pressure tap Four sources tank pressure left right Perry pump crankcase pressure Robart pump muffler pressure examples common denominator always concerned fuel drawand consider thatthere may 5 6 inch variation fuel head typical fair-sized model changes horizontal flight path vertical OS-4OFSR left right Tuned muffler note pressure tap location MACs flow-through muffler close front stock OS muffler install muffler pres sure nothing required install muffler tap connect tubing tank vent Sport fliers avoided because too complicated Perhaps ear liest form pressure ram-pressure derived directing tank vents air stream Along way came Jim Walkers balloonregulator tanks pen bladders crankcase pressure now anti-pollution movement enforcing muf flers flying fields have new source mysterious muffler pressure perhaps easiest reliable use especially throttled en gines Following discovery now also have sophisticated sources coming along like Perry Pump various micro pumps Robart latter units offer some advantage pressure somewhat regulated constant pressure Both driven crank case pressure Perry built engine backplate Robart external goes fuel line Before get two-step how-to lets examine engines fuel flow require ments Without tank pressure source engine must supply its own fuel through suction process venturi some sort spray bar supplies fuel may adequate under some conditions dependent venturi size position spray bar tank location total fuel draw elevation risk engine does go over-lean slows down suction reduced making leaner yet eventually situation can snow-ball seizing engine causing premature engine failure constant positive pressure source would course ultimate solve problem however would require some sort external motor-driven pump generally practical could however settle predic table fuel pressure infinite number throttle settings idle full throttle match carburetor interest simplicity cost model engine carburetors have two-posi tion adjustment idle full throttle mixture control combined fixed taper throttle barrel everything between So dont have ideal have something can make work Since main needle valve idle needle valve mixture control equipJune1979 19 ped essentially fixed orifices need fuel pressure source proportional throttle angle virtually instantaneous response Old fashioned crankcase pres sure alone doesnt provide tank pressure cannot relieved fast enough However muffler exhaust system pressure does approach its asking first step preparation article determine what pressure levels various mufflers generated So spent next three weeks running different systems could find come up representative cross-section run some crankcase pressure measurements 15 years ago seems 05 psi range So borrowed pressure gauge work calibrated inches water 060 feeling would adequate Really wanted water mano meter since temperature hover ing between 0100F plan out water would freeze used gauge compile data Fig No 1 Due low pressure levels fact gauge calibrated 700F wont attest accuracy claims rather trust relative levels differences reference did bench-test engine Perry Pump shown did measure Robart couldnt find set-up convenient time Characteristically full throttle back muffler pressure varies about inch water column about eight inches water dependent particular muffler engine used Although pressure relatively low inch water lbs/sq psi enough help us out especially have muffler giving least five inches pressure Idle pressures essentially zero Generally speaking original equip ment mufflers provide backpressure replacement types although some performance loss engines increased backpressure Also point interest compiling data shown observed rather subjectively backpressure lower noise leveltuned mufflers excepted Now what will magic pressure First lets consider tank installations Ideally always want vertically align centerline tank centerline needle valve isnt too difficult side-mounted engines because tank can aligned engine crank shaft However model designs upright engines tank usually ends up 1/2 2 inch below needle causes richening fuel mixture inverted flight during rolling maneuvers due variations static fuel head Also tank sufficiently below needle valve engine will able draw fuel Next consider average 12 oz tank 2-1/2 high Therefore tank full needle valve set 11/4 positive fuel head near Tuned muffler installation Quickie 500 Pylon racer fuel tubing connection between the tank muffler tan may clearly seen 2-line system filling throuah line bottom tank 1-1/4 negative head 2-1/2 head change during flight noticeable taking off rich side going progressively leaner through flight Refer Fig No 2 vertical maneuvers becomes evident pressure head changes since now have 5 6 head change Refer Fig No 3 may have noticed usual needle setting can loop well beginning flight later fuel level goes down engine loses power going overlean So unless head changes compensated initial needle setting results over-lean engine may scrap after 20 such flights increasing tank static pressure variations wont go away can significantly reduced Without getting too technical can proven mathemati cally basic flow equation iv KAVP K tant P sure Tank-full versus tank-empty pressure differences reduced depen dent static pressure head change along needle setting havent tested either Perry Robart regulated systems model should better however competition crowd generally expensive what required sport flying except possibly some unique cases Tuned mufflers have become increasing popular late well touch enough say generally respond similar standard muffler respect pressure characteristics provided pressure tap up-stream divergent cone section distinct advantage high performance spite reduced noise hook up muffler pressure favorite machine requires two very simple steps first install pressure tap muffler other connect fuel tubing tank vent Most modem engines come both mufflers pressure taps cases location tap already threaded muffler case just screw pressure tap youre ready Other mufflers come undrilled bosses will have drill tap yourself cases use crankcase pressure fitting Super tigre Fox KB-Veco tap muffler whatever thread size fitting requires thing check pressure tap has least 1/16 diameter hole tank pressure may bleed down fast enough consistent transition idle muffler has neither above locate suitable area ahead con verging end cone drill tap have found tap location isnt very critical generally put can run shortest fuel line tank pressure tap run good quality fuel line latex silicone neoprenenot plastic vent line tank making sure except fuel line needle valve other lines plugged rest fuel system airtight completego fly start engine youll notice yoi will have turn needle valve leaner turn compensate increased pressure Set engine basically same have first flight fuselage pointed up slight angle 15 degrees engine should set slightly rich usually peak-out engine back needle off point itjust barely goes back four-cycle gurgle-gurgle Try Slight adjustments may necessary subsequent flights dependent results should notice immediate improvement degree depends bad pressure amount pressure generated system two types conventional mufflersflow-through closed front flow-through has opening front generally increases engine performance however provide minimal pressure shown Fig No 1 Generally original equipment mufflers closed-front except certain Super tigres have flow-through muffler such MACs Semco still want pressure switch closed-front muffler MACs sells separate plug install front Semco must purchase different model muffler Closing front will generally give pressure less noise hope article has inspired either unknowledgeable hesitant try muffler pressure will turn make hobby fun less frustratingHappy Flying June1979 21 typical sport muffler pressure system stock muffler ideal tank/engine combination muffler pressure will improve run since needle setting less compromise batteries chief cause crashes engine failures must close sec ond Jerry Bugni left checks needle setting scale Piper Cherokee
Edition: Model Aviation - 1979/06
Page Numbers: 18, 19, 20, 21
Considering MP easy install beneficial flying engine life remark able people hesitate use it just takes someone show Big John really lays out. ABC John Kilsdonk IT WAS week before Christmas Bill Winter called asked would write how-to article muffler pressure seems old man careful John out flying week two before having some fuel draw problems RC models Some suggested try muffler pressure after little deliberation did presto problems went away says cant teach old dog new tricks Actually could relate very well Bills problem continually witness similar situations time go clubs Michigan Signal Seekers flying field Having interested engines first model airplanes close second life disturbs great deal see other modelers continually abuse engines out ignorance what about poor engine runs Usually four culprits cause needle valve setting dirt fuel system type fuel fuel-draw article about fuel-draw Better stated about ability supply consistent pressure resultant flow fuel powerplant spite certain physical limitations model natural obstaclegravity Although pressurized fuel systems models have used form another least 30 years seemingly competition crowd Typical modern tuned muffler system installed ST-X60 again note pressure tap Four sources tank pressure left right Perry pump crankcase pressure Robart pump muffler pressure examples common denominator always concerned fuel drawand consider thatthere may 5 6 inch variation fuel head typical fair-sized model changes horizontal flight path vertical OS-4OFSR left right Tuned muffler note pressure tap location MACs flow-through muffler close front stock OS muffler install muffler pres sure nothing required install muffler tap connect tubing tank vent Sport fliers avoided because too complicated Perhaps ear liest form pressure ram-pressure derived directing tank vents air stream Along way came Jim Walkers balloonregulator tanks pen bladders crankcase pressure now anti-pollution movement enforcing muf flers flying fields have new source mysterious muffler pressure perhaps easiest reliable use especially throttled en gines Following discovery now also have sophisticated sources coming along like Perry Pump various micro pumps Robart latter units offer some advantage pressure somewhat regulated constant pressure Both driven crank case pressure Perry built engine backplate Robart external goes fuel line Before get two-step how-to lets examine engines fuel flow require ments Without tank pressure source engine must supply its own fuel through suction process venturi some sort spray bar supplies fuel may adequate under some conditions dependent venturi size position spray bar tank location total fuel draw elevation risk engine does go over-lean slows down suction reduced making leaner yet eventually situation can snow-ball seizing engine causing premature engine failure constant positive pressure source would course ultimate solve problem however would require some sort external motor-driven pump generally practical could however settle predic table fuel pressure infinite number throttle settings idle full throttle match carburetor interest simplicity cost model engine carburetors have two-posi tion adjustment idle full throttle mixture control combined fixed taper throttle barrel everything between So dont have ideal have something can make work Since main needle valve idle needle valve mixture control equipJune1979 19 ped essentially fixed orifices need fuel pressure source proportional throttle angle virtually instantaneous response Old fashioned crankcase pres sure alone doesnt provide tank pressure cannot relieved fast enough However muffler exhaust system pressure does approach its asking first step preparation article determine what pressure levels various mufflers generated So spent next three weeks running different systems could find come up representative cross-section run some crankcase pressure measurements 15 years ago seems 05 psi range So borrowed pressure gauge work calibrated inches water 060 feeling would adequate Really wanted water mano meter since temperature hover ing between 0100F plan out water would freeze used gauge compile data Fig No 1 Due low pressure levels fact gauge calibrated 700F wont attest accuracy claims rather trust relative levels differences reference did bench-test engine Perry Pump shown did measure Robart couldnt find set-up convenient time Characteristically full throttle back muffler pressure varies about inch water column about eight inches water dependent particular muffler engine used Although pressure relatively low inch water lbs/sq psi enough help us out especially have muffler giving least five inches pressure Idle pressures essentially zero Generally speaking original equip ment mufflers provide backpressure replacement types although some performance loss engines increased backpressure Also point interest compiling data shown observed rather subjectively backpressure lower noise leveltuned mufflers excepted Now what will magic pressure First lets consider tank installations Ideally always want vertically align centerline tank centerline needle valve isnt too difficult side-mounted engines because tank can aligned engine crank shaft However model designs upright engines tank usually ends up 1/2 2 inch below needle causes richening fuel mixture inverted flight during rolling maneuvers due variations static fuel head Also tank sufficiently below needle valve engine will able draw fuel Next consider average 12 oz tank 2-1/2 high Therefore tank full needle valve set 11/4 positive fuel head near Tuned muffler installation Quickie 500 Pylon racer fuel tubing connection between the tank muffler tan may clearly seen 2-line system filling throuah line bottom tank 1-1/4 negative head 2-1/2 head change during flight noticeable taking off rich side going progressively leaner through flight Refer Fig No 2 vertical maneuvers becomes evident pressure head changes since now have 5 6 head change Refer Fig No 3 may have noticed usual needle setting can loop well beginning flight later fuel level goes down engine loses power going overlean So unless head changes compensated initial needle setting results over-lean engine may scrap after 20 such flights increasing tank static pressure variations wont go away can significantly reduced Without getting too technical can proven mathemati cally basic flow equation iv KAVP K tant P sure Tank-full versus tank-empty pressure differences reduced depen dent static pressure head change along needle setting havent tested either Perry Robart regulated systems model should better however competition crowd generally expensive what required sport flying except possibly some unique cases Tuned mufflers have become increasing popular late well touch enough say generally respond similar standard muffler respect pressure characteristics provided pressure tap up-stream divergent cone section distinct advantage high performance spite reduced noise hook up muffler pressure favorite machine requires two very simple steps first install pressure tap muffler other connect fuel tubing tank vent Most modem engines come both mufflers pressure taps cases location tap already threaded muffler case just screw pressure tap youre ready Other mufflers come undrilled bosses will have drill tap yourself cases use crankcase pressure fitting Super tigre Fox KB-Veco tap muffler whatever thread size fitting requires thing check pressure tap has least 1/16 diameter hole tank pressure may bleed down fast enough consistent transition idle muffler has neither above locate suitable area ahead con verging end cone drill tap have found tap location isnt very critical generally put can run shortest fuel line tank pressure tap run good quality fuel line latex silicone neoprenenot plastic vent line tank making sure except fuel line needle valve other lines plugged rest fuel system airtight completego fly start engine youll notice yoi will have turn needle valve leaner turn compensate increased pressure Set engine basically same have first flight fuselage pointed up slight angle 15 degrees engine should set slightly rich usually peak-out engine back needle off point itjust barely goes back four-cycle gurgle-gurgle Try Slight adjustments may necessary subsequent flights dependent results should notice immediate improvement degree depends bad pressure amount pressure generated system two types conventional mufflersflow-through closed front flow-through has opening front generally increases engine performance however provide minimal pressure shown Fig No 1 Generally original equipment mufflers closed-front except certain Super tigres have flow-through muffler such MACs Semco still want pressure switch closed-front muffler MACs sells separate plug install front Semco must purchase different model muffler Closing front will generally give pressure less noise hope article has inspired either unknowledgeable hesitant try muffler pressure will turn make hobby fun less frustratingHappy Flying June1979 21 typical sport muffler pressure system stock muffler ideal tank/engine combination muffler pressure will improve run since needle setting less compromise batteries chief cause crashes engine failures must close sec ond Jerry Bugni left checks needle setting scale Piper Cherokee
Edition: Model Aviation - 1979/06
Page Numbers: 18, 19, 20, 21
Considering MP easy install beneficial flying engine life remark able people hesitate use it just takes someone show Big John really lays out. ABC John Kilsdonk IT WAS week before Christmas Bill Winter called asked would write how-to article muffler pressure seems old man careful John out flying week two before having some fuel draw problems RC models Some suggested try muffler pressure after little deliberation did presto problems went away says cant teach old dog new tricks Actually could relate very well Bills problem continually witness similar situations time go clubs Michigan Signal Seekers flying field Having interested engines first model airplanes close second life disturbs great deal see other modelers continually abuse engines out ignorance what about poor engine runs Usually four culprits cause needle valve setting dirt fuel system type fuel fuel-draw article about fuel-draw Better stated about ability supply consistent pressure resultant flow fuel powerplant spite certain physical limitations model natural obstaclegravity Although pressurized fuel systems models have used form another least 30 years seemingly competition crowd Typical modern tuned muffler system installed ST-X60 again note pressure tap Four sources tank pressure left right Perry pump crankcase pressure Robart pump muffler pressure examples common denominator always concerned fuel drawand consider thatthere may 5 6 inch variation fuel head typical fair-sized model changes horizontal flight path vertical OS-4OFSR left right Tuned muffler note pressure tap location MACs flow-through muffler close front stock OS muffler install muffler pres sure nothing required install muffler tap connect tubing tank vent Sport fliers avoided because too complicated Perhaps ear liest form pressure ram-pressure derived directing tank vents air stream Along way came Jim Walkers balloonregulator tanks pen bladders crankcase pressure now anti-pollution movement enforcing muf flers flying fields have new source mysterious muffler pressure perhaps easiest reliable use especially throttled en gines Following discovery now also have sophisticated sources coming along like Perry Pump various micro pumps Robart latter units offer some advantage pressure somewhat regulated constant pressure Both driven crank case pressure Perry built engine backplate Robart external goes fuel line Before get two-step how-to lets examine engines fuel flow require ments Without tank pressure source engine must supply its own fuel through suction process venturi some sort spray bar supplies fuel may adequate under some conditions dependent venturi size position spray bar tank location total fuel draw elevation risk engine does go over-lean slows down suction reduced making leaner yet eventually situation can snow-ball seizing engine causing premature engine failure constant positive pressure source would course ultimate solve problem however would require some sort external motor-driven pump generally practical could however settle predic table fuel pressure infinite number throttle settings idle full throttle match carburetor interest simplicity cost model engine carburetors have two-posi tion adjustment idle full throttle mixture control combined fixed taper throttle barrel everything between So dont have ideal have something can make work Since main needle valve idle needle valve mixture control equipJune1979 19 ped essentially fixed orifices need fuel pressure source proportional throttle angle virtually instantaneous response Old fashioned crankcase pres sure alone doesnt provide tank pressure cannot relieved fast enough However muffler exhaust system pressure does approach its asking first step preparation article determine what pressure levels various mufflers generated So spent next three weeks running different systems could find come up representative cross-section run some crankcase pressure measurements 15 years ago seems 05 psi range So borrowed pressure gauge work calibrated inches water 060 feeling would adequate Really wanted water mano meter since temperature hover ing between 0100F plan out water would freeze used gauge compile data Fig No 1 Due low pressure levels fact gauge calibrated 700F wont attest accuracy claims rather trust relative levels differences reference did bench-test engine Perry Pump shown did measure Robart couldnt find set-up convenient time Characteristically full throttle back muffler pressure varies about inch water column about eight inches water dependent particular muffler engine used Although pressure relatively low inch water lbs/sq psi enough help us out especially have muffler giving least five inches pressure Idle pressures essentially zero Generally speaking original equip ment mufflers provide backpressure replacement types although some performance loss engines increased backpressure Also point interest compiling data shown observed rather subjectively backpressure lower noise leveltuned mufflers excepted Now what will magic pressure First lets consider tank installations Ideally always want vertically align centerline tank centerline needle valve isnt too difficult side-mounted engines because tank can aligned engine crank shaft However model designs upright engines tank usually ends up 1/2 2 inch below needle causes richening fuel mixture inverted flight during rolling maneuvers due variations static fuel head Also tank sufficiently below needle valve engine will able draw fuel Next consider average 12 oz tank 2-1/2 high Therefore tank full needle valve set 11/4 positive fuel head near Tuned muffler installation Quickie 500 Pylon racer fuel tubing connection between the tank muffler tan may clearly seen 2-line system filling throuah line bottom tank 1-1/4 negative head 2-1/2 head change during flight noticeable taking off rich side going progressively leaner through flight Refer Fig No 2 vertical maneuvers becomes evident pressure head changes since now have 5 6 head change Refer Fig No 3 may have noticed usual needle setting can loop well beginning flight later fuel level goes down engine loses power going overlean So unless head changes compensated initial needle setting results over-lean engine may scrap after 20 such flights increasing tank static pressure variations wont go away can significantly reduced Without getting too technical can proven mathemati cally basic flow equation iv KAVP K tant P sure Tank-full versus tank-empty pressure differences reduced depen dent static pressure head change along needle setting havent tested either Perry Robart regulated systems model should better however competition crowd generally expensive what required sport flying except possibly some unique cases Tuned mufflers have become increasing popular late well touch enough say generally respond similar standard muffler respect pressure characteristics provided pressure tap up-stream divergent cone section distinct advantage high performance spite reduced noise hook up muffler pressure favorite machine requires two very simple steps first install pressure tap muffler other connect fuel tubing tank vent Most modem engines come both mufflers pressure taps cases location tap already threaded muffler case just screw pressure tap youre ready Other mufflers come undrilled bosses will have drill tap yourself cases use crankcase pressure fitting Super tigre Fox KB-Veco tap muffler whatever thread size fitting requires thing check pressure tap has least 1/16 diameter hole tank pressure may bleed down fast enough consistent transition idle muffler has neither above locate suitable area ahead con verging end cone drill tap have found tap location isnt very critical generally put can run shortest fuel line tank pressure tap run good quality fuel line latex silicone neoprenenot plastic vent line tank making sure except fuel line needle valve other lines plugged rest fuel system airtight completego fly start engine youll notice yoi will have turn needle valve leaner turn compensate increased pressure Set engine basically same have first flight fuselage pointed up slight angle 15 degrees engine should set slightly rich usually peak-out engine back needle off point itjust barely goes back four-cycle gurgle-gurgle Try Slight adjustments may necessary subsequent flights dependent results should notice immediate improvement degree depends bad pressure amount pressure generated system two types conventional mufflersflow-through closed front flow-through has opening front generally increases engine performance however provide minimal pressure shown Fig No 1 Generally original equipment mufflers closed-front except certain Super tigres have flow-through muffler such MACs Semco still want pressure switch closed-front muffler MACs sells separate plug install front Semco must purchase different model muffler Closing front will generally give pressure less noise hope article has inspired either unknowledgeable hesitant try muffler pressure will turn make hobby fun less frustratingHappy Flying June1979 21 typical sport muffler pressure system stock muffler ideal tank/engine combination muffler pressure will improve run since needle setting less compromise batteries chief cause crashes engine failures must close sec ond Jerry Bugni left checks needle setting scale Piper Cherokee