- Joined
- Jan 6, 2015
- Messages
- 478
- Reaction score
- 180
Hello Pitts folks,
Ive just installed a new prop (MTV-9-B-C/C200-25) and governor (PCU5000X) on my experimental Pitts. RPM control is generally excellent throughout all power settings and airspeed. I do have two problems, though:
1) Max RPM is only 2500 (should be 2700) at any power setting and airspeed, EXCEPT
2) Max RPM will sometimes surge up to 2650 at high airspeed (175 mph) when I reduce power from 25 inches manifold pressure down to say 20 inches.
I had similar behavior on my old metal Hartzel 2-blade prop and Woodward governor, so Im thinking there is something odd about the engine that causes this. Perhaps some kind of strange behavior on the crank case pressure. The last condition inspection lists two of the six cylinders at 69/80 on compression test. Perhaps Im getting blow by on these two cylinders that is adding pressure to the case and somehow influencing the operation of the governor? I dont imagine that crank case pressure would influence oil pressure into the governor but perhaps it does something to the oil return from the governor to the sump? Like when I reduce power the crank case pressure drops and allows more oil to flow out from the exit of the governor?
I do not believe the engine case ventilation is blocked. I do get the typical oil dripping out the exit tube back by the tailwheel after acro, and I think that would confirm proper operation of the vent and air-oil separator. I dont know what pressure is typically built up inside the case but if it is just vented to atmosphere then my pressurized crankcase theory may not hold.
Appreciate any thoughts on this. Ive done some simple acro and with max throttle and prop full forward I get 25 inches manifold and 2500 RPM and it holds very steady. Id like to adjust the governor stop to get more RPM but if I set 2700 RPM Im afraid of surge past 2700 RPM when I pull power back at high airspeed.
Thanks,
Paul Klusman
Ive just installed a new prop (MTV-9-B-C/C200-25) and governor (PCU5000X) on my experimental Pitts. RPM control is generally excellent throughout all power settings and airspeed. I do have two problems, though:
1) Max RPM is only 2500 (should be 2700) at any power setting and airspeed, EXCEPT
2) Max RPM will sometimes surge up to 2650 at high airspeed (175 mph) when I reduce power from 25 inches manifold pressure down to say 20 inches.
I had similar behavior on my old metal Hartzel 2-blade prop and Woodward governor, so Im thinking there is something odd about the engine that causes this. Perhaps some kind of strange behavior on the crank case pressure. The last condition inspection lists two of the six cylinders at 69/80 on compression test. Perhaps Im getting blow by on these two cylinders that is adding pressure to the case and somehow influencing the operation of the governor? I dont imagine that crank case pressure would influence oil pressure into the governor but perhaps it does something to the oil return from the governor to the sump? Like when I reduce power the crank case pressure drops and allows more oil to flow out from the exit of the governor?
I do not believe the engine case ventilation is blocked. I do get the typical oil dripping out the exit tube back by the tailwheel after acro, and I think that would confirm proper operation of the vent and air-oil separator. I dont know what pressure is typically built up inside the case but if it is just vented to atmosphere then my pressurized crankcase theory may not hold.
Appreciate any thoughts on this. Ive done some simple acro and with max throttle and prop full forward I get 25 inches manifold and 2500 RPM and it holds very steady. Id like to adjust the governor stop to get more RPM but if I set 2700 RPM Im afraid of surge past 2700 RPM when I pull power back at high airspeed.
Thanks,
Paul Klusman
