I have a pa-18 with a 180 in it. This weekend I flew it and I noticed a slapping sound at certain RPM's (between 1600 and 1800). The sound is similar to a prop that is really digging in, but much more embelished. It is hard to explain. At these RPM's the plane really vibrates also. I have a borer prop on it and there is no range where I am not supposed to run it. I first noticed it on runup, but also later. It runs very smoothly at 2400 and 2500 cruising RPM's. Can anyone tell me what they think might be the problem? Engine or prop?
Thanks,
Sean
Thanks,
Sean