Constant speed prop not maintaining constant speed

[7DeltaLima]

Group:
Help.... IO360A1B6, MT 3 Blade Prop, MT prop governor-P420-3...all three have about 575 hours.

Last couple flights the prop will not maintain constant rpm on either descents not aggressive climbs. RPM's act like a fixed pitch prop. (Boy, makes me appreciate the braking action of the constant speed prop. You really do float a long time and have to manage speed much more effectively without the braking of cs prop.)

The prop will cycle at pre-takeoff checks. It does get 2700 rpms on takeoff. Oil temp & pressure are good-same as they've been the last 3 years. After an hours flight and after landing last night, I tried cycleing the prop with the oil hot and it worked as expected. But on the landing, the rpm's dropped in coorelation with pulling the throttle. Acted just like a fixed pitch prop. 50 feet agl, you could hear and feel the prop going to coarse as it should have 3 minutes beforehand.

My typical landing sequence is to turn the prop back up to around 2400 - 2450 on downwind (or when getting to IAF on instrument approach). This seems to have been a great compromise between full coarse for go-arounds, noise and braking action.

No oil leaks. Changed oil, no change. Replaced the prop cable as it felt it had some play so thought it might be hanging.... all nojoy.

Where do I start next?

Thanks,
Doug

[DickDe]

Doug...

A friend of mine has had problems with his MT governor and MT made good on it due to a design problem. You may want to check with them. Others on this list may also know more on this issue as I have a Hartzell with a MaCaully Governor so I am not a good source on this.

Dick DeCramer
N500DD RV6
Northfield, MN

[RVjim]

Hi Doug,

2600 RPM is recommended, instead of 2400 to 2450 RPM, for a constant speed propeller in the pattern and particularly on short final for a potential go around.

I'll call you after I have talked to MT Propeller in Germany. They are just getting back from their two week company holiday.

Regards,
Jim Ayers

[brianwallis]

Apparently there is a test you can do by pulling the gov and putting a plate on the port and doing a pressure test. This will tell you if you have any internal leaks at the bearings.... not sure it applies in this case but call the manuf... Best of Luck!
Brian