RPM increases with Airspeed

[Gary Baldwin]

Prop Gov Problem: My 1960 250 with woodward prop gov and 2 bladed hartzell prop has a weird problem. On take off roll the best rpm I get is about 2450 but has the airspeed picks up in flight, 110 kts plus, the rpm slowly increases too the limit of 2575. The problem began when I had the gov overhauled and the hartzell prop AD done about two yrs ago. The gov (model A210185/sn 529063 w) has been off twice since then for re-inspection and the prop has been rechecked by the prop shop...everything is in spec. The gov cable has been checked for proper adjustment and the tach has been checked for accuracy. Its as if the gov isn't generating enough oil pressure to bring the rpm the limit without the aid of the slip stream..much like a fixed pitch prop.
Anyone heard of this issue before?

[md11flyer]

Gary, not familiar with the single's peculiarities regarding prop/gov problems, but you can rule out oil pressure.
The single engine crowd except a few aerobatic installations use oil pressure to decrease rpm so if you had an oil pressure problem the reverse would be evident
and you would have a prop that would overspeed at full throttle at cruise. Now this is a guess and it may be way off base, but if your engine is not making full power and the
prop governor has set your prop to its pitch limits, then thats all you will get. Because you had the shop check the prop over, the pitch stops are probably set correctly....assuming they have....
How is the health of the engine otherwise?

Gary

[Gary Baldwin]

Hi Gary

The engine is a factory overhaul with about 900 hrs and burns little oil, runs strong and has good compression. I can dial up full rpm in flight (2575) very easily if needed. But like I said it can't do it on the take off roll. Oddly enough I can get max RPM or close to it on take off roll if its a cold day. I use Philips 20w50 oil. Even though I only see 2450 to 2500 on take off roll the airplane accelerates nicely and I don't see a safety issue at this point.

[Kristin Winter]

I am guessing that the low pitch stop may need to be adjusted. Shops don't always get it right. The procedure is in the SM. You will need a propeller protractor.

[Gary Baldwin]

Hi Kristin

Thanks for the idea on the prop. The AD was complied with at Santa Monica...so I'll give them a call.

Gary