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RPM overspeed on takeoff

WingnutWick

WingnutWick

Well Known Member
Hello,

New to the C/S world for the most part with our new RV-10. Initially I had to adjust the governor as I couldn't get 2700 in flight. That worked well and at full forward it is right at 2700. In flight the governor manages RPM seemingly fine and there is no seeking. However on takeoff the RPM will spike above 2700 (2760 or so) during the first half of roll.

Curious if this is normal and nothing to worry about or what.

Thanks!

Charles
 
Can't speak to the RV-10 (yet), but in both my Arrow and the C182 I fly I find that if you add throttle too quickly on the takeoff roll, you can overrun the governor on takeoff and exceed red line. Typically you can hear the governor "catch up" as the throttle advances. I generally advance fairly quickly to half throttle or above 2k rpm, and then slow to let things settle as I advance the rest of the way.
 
1. As noted above, you may get a momentary over-shoot if you advance either the prop control or the throttle too rapidly. Smooth operation is what you want. However, recovery by the governor should be prompt - not half the runway.
2. At the start of the takeoff roll, you should never get an overshoot (unless there’s a strong headwind), because you have (haven’t you?) adjusted the fine pitch hard stop in the prop to not allow it.
 
I adjusted the hard stop on the governor by setting 2700 in flight then landing and adjusting the hard stop to where the prop lever was at, which has worked in flight. The prop will correct within a couple seconds or so and I do advance slowly but I am pretty sure I can exceed 2700 at the start of the roll if I just blast the throttle forward. Not sure if I am missing something or if this is all just normal.

BobTurner said:
1. As noted above, you may get a momentary over-shoot if you advance either the prop control or the throttle too rapidly. Smooth operation is what you want. However, recovery by the governor should be prompt - not half the runway.
2. At the start of the takeoff roll, you should never get an overshoot (unless there’s a strong headwind), because you have (haven’t you?) adjusted the fine pitch hard stop in the prop to not allow it.
Click to expand...
 
In my comment (2) I said and meant the hard stop inside the prop (hub), not the governor’s stop. As long as the governor works this internal stop is unimportant. But if the governor fails (or you run out of oil!) you will be glad you adjusted it properly.
Yes, if you ‘blast the throttle’ forward, it will overshoot. But should recover in 1, maybe 2 seconds.
 
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You should adjust the low pitch stop on the prop. Remove the spinner and turn the hex screw in 1 full turn and check it next time you TO.

I hear this surge all the time being right next to the runway, bugs the **** out of me.

See fig 5-3 in the Hartzell owner manual for limits.
 
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Walt said:
You definitely need to adjust the low pitch stop on the prop. Remove the spinner and turn the hex screw in 1 full turn and check it next time you TO.
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I am only seeing 2650 or so on take off, would backing the hex screw out help or should I adjust the gov.?
 
Mike S said:
I am only seeing 2650 or so on take off, would backing the hex screw out help or should I adjust the gov.?
Click to expand...

If you see 2650 (prop control full in) in cruise, too, then it’s the governor stop. If you see 2650 at rest on the ground, but 2700 in cruise, then it’s the hard stop (fine pitch) in the prop hub. Assuming it’s the prop stop, it’s up to you if you want to change it. Personally mine is at 2680 or so, but goes to 2700 in cruise. I like knowing that the stop is set correctly. And if the governor fails, I can get a tiny bit more power without overspeeding the engine/prop.
 
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Mike S said:
I am only seeing 2650 or so on take off, would backing the hex screw out help or should I adjust the gov.?
Click to expand...

Rapidly advancing the throttle will usually cause an overshoot to the low pitch stop setting while the gov tries to catch up (surge).

So, you can either try a rapid advance and see what happens or adjust the low pitch stop out a turn and see if gives you a rise in RPM.
If it makes no difference then it's back to gov. adjustment.

The only way you really know where the low pitch stop is set is to keep turning it in until you get a drop in max RPM, then back off from there. I personally like to see around 2725 setting on low stop adjustment and a solid 2700-2720 on TO.

Sometimes you have to go back and forth between the gov and stop to get it set.
 
Might be worth mentioning that in the case of counterweighted crankshaft engines like my IO-540 C4B5, Lycoming recommends slow advancement of throttle to avoid throwing the pendulum counterweights out of proper position with rapid throttle opening. Since I adhere to this advice religiously, I've never had the governor overspeed on takeoff issue discussed here, but I do have my gov set for 2800 max cruise and can get to 2760 on the takeoff roll.

My electronic ignition will take care of any excursions above 2800 on its own...
 
std adj

This A&P has used the following procedure which I think is consistent with most CS prop manufacturers instructions and should be mentioned here.

With this routine you can easily set numbers similar to those posted by Walt, Boyd and other in this thread.

1 Back off the propeller low pitch stop toward a higher RPM setting so it is not a factor for governor setting.

2 Set governor adjustment to the desired max RPM - 2700 or ? at or near full throttle static.

3 Adjust the propeller low pitch stop to pull the static RPM down 20 -50 RPM or so at full throttle from the governor setting.

4 Done.

This will assure no over-speed on takeoff and reduce likely over-speed on a go-around. Further, you get a free dyno check that all is well by a glance at the tach at the beginning of the take-off roll. (since the governor can not fudge for an ignition problem or whatever)

Oh, and you will be less likely to annoy Walt (or anyone else who knows how to set up a prop).

Ron
 
Walt said:
Rapidly advancing the throttle will usually cause an overshoot to the low pitch stop setting while the gov tries to catch up (surge).

So, you can either try a rapid advance and see what happens or adjust the low pitch stop out a turn and see if gives you a rise in RPM.
If it makes no difference then it's back to gov. adjustment.

The only way you really know where the low pitch stop is set is to keep turning it in until you get a drop in max RPM, then back off from there. I personally like to see around 2725 setting on low stop adjustment and a solid 2700-2720 on TO.

Sometimes you have to go back and forth between the gov and stop to get it set.
Click to expand...

Got that Walt, thanks. Hoping it is the adjustment under the spinner as the gov is virtually impossible to reach.
 
Bill Boyd said:
Might be worth mentioning that in the case of counterweighted crankshaft engines like my IO-540 C4B5, Lycoming recommends slow advancement of throttle to avoid throwing the pendulum counterweights out of proper position with rapid throttle opening. Since I adhere to this advice religiously, I've never had the governor overspeed on takeoff issue discussed here, but I do have my gov set for 2800 max cruise and can get to 2760 on the takeoff roll.

My electronic ignition will take care of any excursions above 2800 on its own...
Click to expand...

Totally agree it hard on the Eng/prop to just slam the throttle forward, going slow on the throttle also makes it much easier to deal with’P’ factor.
Also good to close the throttle gradually.

2800 is pretty high, without looking at the Hartzell manual I think that would fall into the 5 minute limitation range (required inspection).
 
Some certified aircraft are setup such that the low stop only allows about 2650 at static. The theory is that this will allow the pilot to assure the engine is making power. As the plane accelerates down the runway the prop should come off the stop and hit 2700.

I'm not particularly sure I like this idea (I want the holeshot) but it does have some merit.
 
Rallylancer122 said:
Some certified aircraft are setup such that the low stop only allows about 2650 at static. The theory is that this will allow the pilot to assure the engine is making power. .
Click to expand...

I don’t understand how 2650 vs 2700 ‘assures the engine is making power’. My guess is it allows the plane to fly at 70 knots without exceeding 2700 rpm, following a governor failure.
 
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