This is a great overview, Hal. Really interesting to see a 331 under the skin and how it operates. I would never have imagined it being so 'ye-olde-worlde'.
I just bought an airplane with a TPE 331-6 and I am having issues with developing full speed. I am suppose to get close to 320Kts but I am one getting 240kts right now. We suspect it has something to do with the prop perhaps not developing enough pitch. Anyway, I don't have anyone local here in ABQ to help me, wondering if there is something I can take a quick look at to determine if I am correct, a setting I can measure or something like that. My pilot has had trouble getting the prop to go on the stops during shut down, don't know if that could be related.
If the propeller governor is able to maintain RPM at higher power settings. What we normally call Alpha. It is quite likely that there’s nothing wrong with the propeller. However, if the torque system is not a calibration, the engine just may not be getting enough power even though it’s indicating it is, I would do a torque calibration check. If the start latches are not catching on shut down, they may need to be cleaned and lubricated. These engines do need to be put into reverse thrust a little bit during shut down. Otherwise the latches will be missed. The latches are at 0° properly angle.
