Good operating practices
Successful operation of the 9 series engines depends on understanding its differences and treating it accordingly.
The basic difference is that this is a geared engine that is designed to run at 5500rpm. The other conventional aircraft engines are direct drive and run at about 2500 RPM.
Gearbox: anytime you have a propeller and pistons connected you can have problems, huge forces are at work and the gearbox is able to handle them but the operator must treat the engine properly in order to maximize the longevity and reliability.
�� This is not a snowmobile or chainsaw, do not use rapid throttle movements as this causes undue wear on the gearbox. Smooth and steady is the mark of an expert.
�� Avoid low idle speeds; at idle the piston pulses are more pronounced and the gearbox has to deal with a lot of pulsing. This is worse when compounded with a heavy prop. (Rotax has a limit for the propeller “moment of inertia”)
�� Do not take off or cruise at low engine speeds. The engine was designed to take off at 5800rpm and run its whole life at 5500 rpm; the ignition, carburetion and valve timing are all designed to be at their best at this rpm. Don't run the engine in the 4600 to 4900 rpm range for any length of time because of induced harmonics.
o Low piston speeds actually contribute to piston wear as the “rocking motion” duration is increased.
o High prop loading at low rpm increases stress throughout the drivetrain.
o More combustion byproducts (carbon and lead) build up in the cylinder head with low engine speeds.
�� Avoid excessive carb heat; this is not a C-150, this engine is not prone to carb ice so the teachings of the average C-150 pilot are not relevant. If safe and sensible a quick check for a normal rpm drop when carb heat is applied is all that is needed.