Momentary Prop Over-Speed on Takeoff

[twcroy]

All,

I was wondering if you ever had much problem with the prop governor? It surges sometimes, just for a second or two. The last several flights it has been over-speeding momentarily before the governor grabs it and brings it back into range (<2700RPM) during takeoff. My A&P has adjusted the high RPM stop down twice, and it appears to have limited the over-speed range down to 2740-2800 before the governor brings it back to 2640 during take off. It was spitting a little grease at me too on the windshield, but now that it tops out at 2800, it doesn't do that.

I was wondering if you had any thoughts on it. My A&P plans to adjust it down further a third time to see if it will not momentarily surge above 2700RPM.

Thanks,
Tim

p.s. I had it bench-tested two annuals ago, and the tester said it checked out fine. Maybe it's worn since then?

[Mike S]

What prop, what gov, and how warm do you get the oil prior to runup and prop cycle??

[Brantel]

If it is a typical Hartzell, your adjusting the wrong thing.

Adjusting the low pitch stop is the key here....The Hartzell manual details this procedure. That is if it is a Hartzell...

[paul330]

Originally Posted by Brantel

If it is a typical Hartzell, your adjusting the wrong thing.

Adjusting the low pitch stop is the key here....The Hartzell manual details this procedure. That is if it is a Hartzell...

I believe this is correct. I have a MT prop and governor and haven't actually started the engine yet.......... However, my reading and research indicates the following:

- full power static run should be limited by the prop fine pitch stop to something less than 2700rpm. In other words, the governor has not yet started to control the RPM. If the RPM is over 2700 then the physical fine pitch stop needs to be adjusted.

- as the aircraft accelerates and the RPM increases due to the windmill effect, the governor starts to bring the prop off the fine stop and coarsen the blades. If the RPM settles above 2700, then the prop control should be brought back to 2675 and left for the rest of the flight. After landing, the governor high RPM screw should be adjusted against its stop.

So, at the start of the TO run, the governor should be doing nothing and the blades should be at full fine against the prop stop. It appears that this is set too fine so the prop initially overspeeds until the governor can coarsen the blades and bring it back under control. Sounds like the governor is working exactly how it should and it's the prop fine pitch stop that needs adjusting.

[Andy Hill]

As above, it is the static RPM wrongly (or just not) set on the prop.

My suggestions:

1. Set Governor (what your A&P is adjusting) to ~2680-2690 RPM
2. Set Static RPM to 2600-2650 RPM
3. Unless you are brave, I would not advise setting these in a "static" scenario i.e. aircraft tied down. You have the info now to incrementally tweak the settings - the static RPM needs to come down by ~150RPM and the governor +50RPM.
4. The manual(s) will give guides as to how many turns adjust by what RPM. I'd use about 1/2 - 3/4 of what they advise, then fly again i.e. anticipate taking 2-3 adjustments to get it just right

[Low Pass]

I would first recommend you re examine your procedures. The only time my prop ever surged in 13.5 years was when I failed to cycle the propeller properly during run up (removing air from the system). The other question I would ask is how fast are you advancing the throttle at takeoff? Have you changed your procedures? I sometimes hear people slamming the throttle forward so fast that there's no way the propeller control for the first couple of seconds. (Probably the same kind of people who start their Bonanzas and Cirruses up at 2200 rpm, but that's another discussion.)

Just rule out a simple procedural change before you start taking your plane apart.

[Jesse]

I'd also recommend you check the actual rpm with an optical tach. If you fly up to X35, we have an optical tach as part of our Dynamic Balancer (which we just got trained on and are having a blast balancing props with!).

[twcroy]

Thanks for the help on this. I'll discuss it with my A&P and move ahead. The original owner thinks I should have it overhauled, but I'm not sure this is necessary at this point.

Tim

[kiwipete]

Tom

On the 3 hartzell prop's I have setup they all needed about 1 1/2 turns on the fine pitch stop. This was with a 180 hp IO-360

Cheers

Peter

[AlexPeterson]

Originally Posted by Low Pass

I would first recommend you re examine your procedures. The only time my prop ever surged in 13.5 years was when I failed to cycle the propeller properly during run up (removing air from the system). The other question I would ask is how fast are you advancing the throttle at takeoff? Have you changed your procedures? I sometimes hear people slamming the throttle forward so fast that there's no way the propeller control for the first couple of seconds. (Probably the same kind of people who start their Bonanzas and Cirruses up at 2200 rpm, but that's another discussion.)

Just rule out a simple procedural change before you start taking your plane apart.

This is right on the mark. Exactly where in the takeoff roll is the overspeed happening? Any C/S prop can only react so quickly.

Another point - static RPM tests need to have the plane securely anchored - see other threads on this subject. A light RV will not sit still on its own at full power.

One could make the argument that static RPM is almost not relevant, since as the plane picks up speed, the governor starts controlling. More important is if you are getting full rpm on rotation and climb, and that is a function of the governor limits, not the prop's hard adjustments.

I too constantly hear idle to full throttle takeoff power changes in less than a second, and it almost always is accompanied by a momentary overspeed. And yes, it does seem to be the above mentioned airplane brands...