Others will have other thoughts, but effectively, with any fixed pitch propeller, its maximum rpm at full throttle will follow airspeed. If you left the prop in low pitch and leveled off and let the bird accelerate without reducing throttle, the rpm would readily exceed maximum redline rpm. Similarly, with the propeller in cruise pitch, its rpm will also follow airspeed. Slowing from cruise airspeed to thermalling speed will also reduce rpm. At the extreme, if these propeller had much more pitch or bite, rpm at climb could be significantly less that what you are seeing. Think of a bicycle kept in the wrong gear. But extreme pitch would be unusable in anything other than level flight. Does it matter that your rpm drops to 2200? I see that frequently at reduced airspeeds especially at high altitudes where the engine produces less power. After 16 years, I would say it is not a factor, and it is improbable that you will harm the engine. If you could fly at an airspeed significantly less than stall speed, maximum rpm with cruise pitch would be even less. You might do a static runup before your next takeoff with the pitch in cruise position to discover the minimum/maximum anticipated full throttle rpm. If you ever inadvertenly try a takeoff with the prop in cruise pitch position, you will likely see rpm of 2000-2200 as you accelerate to liftoff speed.
On Tue, Oct 16, 2018 at 2:20 PM Jarek Steliga <[email protected]> wrote: > > > Hello, > > When trying to thermal with engine running and propeller in cruise > position, I noticed that the recommended RPMs of ca 2400, drop with > airspeed even as low as 2200. Is this harmful to the engine and should be > avoided? > > > Best regards > Jarek > > >
