Propeller governor

[N6387P]

Hi,
I am completing the restoration of my Comanche 250 and when I ran the( Remanufactured) engine recently during a ground run, I noticed that the propeller would not feather until about 2000 rpm. Is this normal? At what engine rpm should the prop start to feather. It is the correct Hartzell 2 blade ( newly overhauled)with a Woodward prop governor.
Thanks,
Neil B.

[Ben Ayalon]

Neil
First, your prop will never feather, only twins do feather, your prop moves towards coarse pitch but that's all.

In my opinion 2000rpm is too how, your CSU should response at 1500rpm.

Happy New Year

Ben

[N6387P]

Thanks Ben,
Since the pitch change does not respond until about 2000, what would be the reason? Is there an adjustment to be made to the governor? Also the propeller is freshly overhauled. Thanks,
Neil

[Ben Ayalon]

Although the prop is the last item that was touched and my first thought is "if it was ok before it must be the prop" I would say that the problem is with the CSU, start with a simple adjustment on the CSU, this might sort it. If not see if you can borrow another working CSU and try on your aircraft, if the problem remain it is the prop.

In any case wait and see what other say, more than one opinion usually help.

Ben

[Zach Grant L1011jock]

Neil,
Lets start with how the system works. The prop maintains a fine pitch(high RPM) until it is acted upon by oil pressure regulated by the governor. The governor gets its oil from the crank case oil supply. On the 540 series it gets it from the forward gallery and then acts as a high pressure pump/regulator before pressurizing the forward crank and then acting on the prop piston that controls the blade pitch through linkages. When you move the prop lever, all you are doing is reindexing the governor to regulate the oil pressure to maintain a different rpm as determined by the governor flyweights.

I say all of this to help explain the next part. There are two basic areas of operation of an engine with a constant speed prop installed. One area is governing range, and the other is non governing range. The non governing range is anytime you are operating on a prop pitch stop, unaffected by the governer. An example of this is when ever you are taxiing the aircraft, on runup, on takeoff until the engine reaches redline RPM, and low power settings such as found when manuvering in the pattern. Basically, anytime throttle movement causes an RPM change, you are operating in the non governing range, and the prop is on the low pitch stop. The governing range of the engine is limited to the range of rpm that the prop control can get the governor to set an RPM.

If your aircraft is set up properly, you should be able to check governor performance during the runup by running the engine up to a set RPM ungoverned, and then pulling the prop lever out causing the governor to set an RPM lower than the one you set with the throttle ungoverned. If you are not able to get the governing range below 2000 rpm, I would first look at the linkage and make sure that your prop control cable is attached to the governor correctly, and that the governor arm is indexed correctly. The movement should not be limited by the cable bottoming out on either end. If that checks good, then I would run the engine again and run it up to an RPM that you can get some response. Pull the prop all the way out, and let the rpm stabilize. Return prop control to max rpm. Repeat 3-4 times (cycling prop to stabilize at min rpm) and then leave the prop back and reduce the throttle to idle. Return the prop forward and then try cycling at a normal run up rpm. You may have air trapped in the system, and this should purge it, and you should get good checks after this proceedure. If you do not, then run the engine momentarily up to red line rpm with the throttle only, and then see if the governor controls the rpm as you carefully add more power. The prop should not continue to increase rpm, but the MP should climb. If that test is good, reduce power. There is probably a setup issue with the governor, either internal, or external. Ireally cannot go further in the diagnosis without further info or seeing the installation first hand.

-Zach

[N6387P]

[Zach Grant L1011jock]

[N6387P]