A rather quiet and fuel sipping engine especially during idle. The 3-cylinder radial design offers a balanced geometry while keeping the number of valves requiring regular maintenance to a minimum.
This model airplane initially had a twin-cylinder 2 stroke engine. When mounted on a test stand, the engine would idle beautifully down to about 1500 RPM but when mounted onto the airplane, the fuselage would get into a resonance with the engine whenever the shaft revolution was lower than 3000 RPM.
This radial engine offers a solution to the resonant problem as it has 1.5 power pulses per shaft revolution. So with this radial engine installed, the idling RPM can comfortably be lowered to 2000 RPM without the fuselage going into a resonance. The radial engine itself with the 14" propeller can idle down to 1400 RPM (but of course on the air frame this will cause the resonant issue to return).
The video also shows that when the engine is switched off, the propeller typically "sits" in between the end of a power stroke and the start of a compression stroke. Thus, although it has only a minimal number of cylinders for a radial engine, there is already virtually no "loose" region experienced by the propeller.
[ Some further info ]
Effective engine cc per shaft revolution: 9.6 cc
Propeller: Master Airscrew, K series 14 x 6
RPM at wide open throttle: 9850 RPM
Factory default timing: ~ 48 deg bTDC
Corrected timing: ~ 28 deg bTDC
Fuel: Isopropanol (A.R. grade)
Fuel rate at idle: 0.023 ml/s
5 сен 2024
