This modified Goldberg Eaglet Its Screamin Eaglet printed August 1984 Model Aviation powered 0S Max 25 FSR Silencer modules can added required obtain desired level sound three modules engine very quiet _ THE MODERN four-cycle model aircraft engine has heralded salvation sport rightly engines pro duce soft whirring sound banshee scream typical two-cycle engine objectionable sound causing problems flying field neigh bors across country goes against grain mod eler what required silence two-cycle engine appropriate level environment flying area can done Surprisingly result careful si lencing can power unit still much powerful per unit weight equivalent four-cycle engine power per unit weight ratio still bottom line aircraft engine design basic problem two-cycle en gines model aircraft sizes seem develop maximum power rpm produces sound frequency near middle C 16000 rpm approximately frequency human ear days ever behooves us keep flying quiet unobjectionable flying field neighbors two ideas worth trying John Hunton hears best four-stroker other hand may develop maximum power 10000 rpm generates sound pulse oth er stroke thus lowering sound frequen cy equivalent 5000 rpm sound pulses octave lower two-stroker tone range ear hears much less efficiently Compare sounds Harley David son motorcycle new Kawasaki Harley straight pipe makes less objectionable sound Kawasaki tuned pipe possible divide exhaust sounds two-stroker lower frequency see May 1979 MA Heavenly Sound However mechanism complex path toward effective silencing has two branches reduce rpm reduce ex haust energy reduce engine rpm use larger pro peller Use diameter blades etc Remember will probably have less horsepower lower rpm must compromise get less noise reduce exhaust energy try modu lar silencer add-on silencer sys 72 Model Aviation tern can tailor amount sound pro duced model appropriate levels may able drive 100 miles find field can fly open exhaust might drive 10 miles fly RC field stock silencer required Perhaps could fly school yard next door model silent enougheven some degraded perform ance concept typical muffling system provide chamber gases expand lose some energy efficient silencer expansion chambers typical three-pass muffler family car has three chambers very effective modular silencer can screw expansion chambers like need Additional silencing will result some changes operation instance tapping stock silencer tank pressure additional modules will increase pressure thus require mixture ad justment addition module will result some power loss surpris ingly small Increased back pressure actual ly will result better fuel economy bad proper balancing rpm silenc ing modules can make two-cycle engine quiet likeand still have power equivalent four-stroke engine SAFE FLYING IS NO ACCIDENT April 1988 73 / four-bladed propeller shown symbolic reducing rpm corresponds reduc ing objectionable sounds larger prop diameter wider blades can also reduce engine rpm Caution urged modification two-blade props Without adequate structural engineering approach safety hazard may presented photos Bernie Stuecker Finished parts silencer module built per sketch top expansion chamber beneath plywood mounting support flexible coupler sili cone preferred though rubber works fine
Edition: Model Aviation - 1988/04
Page Numbers: 72, 73
This modified Goldberg Eaglet Its Screamin Eaglet printed August 1984 Model Aviation powered 0S Max 25 FSR Silencer modules can added required obtain desired level sound three modules engine very quiet _ THE MODERN four-cycle model aircraft engine has heralded salvation sport rightly engines pro duce soft whirring sound banshee scream typical two-cycle engine objectionable sound causing problems flying field neigh bors across country goes against grain mod eler what required silence two-cycle engine appropriate level environment flying area can done Surprisingly result careful si lencing can power unit still much powerful per unit weight equivalent four-cycle engine power per unit weight ratio still bottom line aircraft engine design basic problem two-cycle en gines model aircraft sizes seem develop maximum power rpm produces sound frequency near middle C 16000 rpm approximately frequency human ear days ever behooves us keep flying quiet unobjectionable flying field neighbors two ideas worth trying John Hunton hears best four-stroker other hand may develop maximum power 10000 rpm generates sound pulse oth er stroke thus lowering sound frequen cy equivalent 5000 rpm sound pulses octave lower two-stroker tone range ear hears much less efficiently Compare sounds Harley David son motorcycle new Kawasaki Harley straight pipe makes less objectionable sound Kawasaki tuned pipe possible divide exhaust sounds two-stroker lower frequency see May 1979 MA Heavenly Sound However mechanism complex path toward effective silencing has two branches reduce rpm reduce ex haust energy reduce engine rpm use larger pro peller Use diameter blades etc Remember will probably have less horsepower lower rpm must compromise get less noise reduce exhaust energy try modu lar silencer add-on silencer sys 72 Model Aviation tern can tailor amount sound pro duced model appropriate levels may able drive 100 miles find field can fly open exhaust might drive 10 miles fly RC field stock silencer required Perhaps could fly school yard next door model silent enougheven some degraded perform ance concept typical muffling system provide chamber gases expand lose some energy efficient silencer expansion chambers typical three-pass muffler family car has three chambers very effective modular silencer can screw expansion chambers like need Additional silencing will result some changes operation instance tapping stock silencer tank pressure additional modules will increase pressure thus require mixture ad justment addition module will result some power loss surpris ingly small Increased back pressure actual ly will result better fuel economy bad proper balancing rpm silenc ing modules can make two-cycle engine quiet likeand still have power equivalent four-stroke engine SAFE FLYING IS NO ACCIDENT April 1988 73 / four-bladed propeller shown symbolic reducing rpm corresponds reduc ing objectionable sounds larger prop diameter wider blades can also reduce engine rpm Caution urged modification two-blade props Without adequate structural engineering approach safety hazard may presented photos Bernie Stuecker Finished parts silencer module built per sketch top expansion chamber beneath plywood mounting support flexible coupler sili cone preferred though rubber works fine