MT prop governor surging

I now have 12.1 hours on my airplane. At about 10 hours the propeller started surging at takeoff power. I've read gobs of information here, but I wonder if there is an update. The propeller governor is a MT P-860-4. It calms down once airborne and set to 2450 RPMs and acts fine until the next takeoff. There's always a problem to solve, I guess.

David Watson
49FD

Hey Dave, you rekon it is the oil temp?

On another subject, how are your oil temps now?

Check the revision level - some of those, not all, below revision F has the surging issue. This is a known issue that MT acknowledges and they will take care of you if that's the case.

Bob

Yes, I think it might be. It doesn't do it on the first flight of the day.....only after the engine is heat soaked. What is the cure? Temperature is now running about 207. Switching the oil cooler lines is all that I've done so far. You were right!!!!!

I'll be up to visit sooner or later. I'm looking forward to meeting you.

David

David

As Bob pointed out check the serial number of the unit. If it ends in a letter less than f then you'll need to return the unit to MT to be updated.
Once I sorted mine out it's been fine.
Another thing to check is the fine pitch stops on the prop, as per the hartzell manual. So when you open the throttle quickly the prop won't overspeed before the governor has time to work.

Peter

David...

Worth ensuring the MT governor is a modifed one. But it is not the whole story... It is a fairly common problem, and usually "caused" by the builder not setting up the static RPM of the Prop (Fine Pitch Stop).

If a Hartzell, you'll know if you've done this by taking off the spinner, and adjusting the Hex screw/bolt on the front of the hub. Many (including us!) forgot / did not realise we had to do this. The Hartzell manual has you do this via a tie down and full power runs... this is quite dramatic IMHO. An alternative approach which I prefer, is on every takeoff during the test phase, establish both the static RPM (maybe initially via an aborted takeoff i.e. full power, note max RPM achieved, idle, coast to a halt) v Headwind, and then governed RPM in the early climb.

Setting the static RPM too low e.g. 2600RPM will only cost you 5%? 10%? thrust/power for the very early takeoff roll - by 20K-30K it will have increased to ~2700RPM i.e. the governor setting.

The surging is caused by the governor's inability to limit the RPM to 2700 as you smartly set takeoff power - you set the static RPM to initially do that like a FP prop, and then as IAS increases, the governor can cope with slowly altering the blades to maintain 2700RPM.

My suggestion would be to set static RPM to 2600-2650, and governor RPM to 2670-2700. The latter - refine the governor RPM and your EFIS "overspeed death is upon you warning lights / bells / whistles" far enough apart you do not routinely trigger them

Andy
RV-8 G-HILZ
RV-8tors

Prop surge

Andy,

I have a Hartzell blended airfoil propeller that I bought from Vans. The prop governor is a MT and the part # is P-860-4. The serial number is 07G044-D. I've never seen the RPM exceed 2650 static. It will rev up to about 2760 when it surges on takeoff when the oil temperature is up.

What needs to be done? Does the governor need to come off and sent back to MT for inspection. I'll check the fine pitch stops on the propeller tonight and make sure that's not the problem. I checked them when I installed the propeller but I'll check it again.

As Alton said, it only does the surging when the oil is hot.....never on the first takeoff of the day. When the oil teperature is hot though, it will surge back and forth until I do something about it. I have been decreasing the throttle setting and pulling the prop governor back to make it quit.

Thoughts....

Hi David...

I've never seen the RPM exceed 2650 static

Click to expand...

Sitting on the runway, pointing into wind, brakes off, smartly select full power and watch for absolute Max RPM before, say, 20K... is that your judge of Max RPM? If so, then it seems right. However, since it is relatively quick/easy, I'd back that off to nearer 2600RPM and see if it helps.

We got our Governor in ~2007, as a B. As per advice here we sent it back, and it came back as an -E, and it did surge a bit on touch and go's, overshoots etc. Reducing the Static RPM cured it. The advice in 2007 was that the -B were the problem, and that a -C or -D would solve it. That advice now seems to be you need a -F ! (Our -E is fine).

Overall - have a play with Static RPM, unless you operate out of a 300' strip, setting it a bit too low won't be a safety issue. If it solves it great, if not, maybe look at modifying/changing the governor, but that will take sometime...

I've test flown a few C/S RVs, and the RPM governing is often a bit suspect, but lowering the static RPM seems to help, even when logic says it should not

What engine have you got? And have you ever setup the static RPM? I find invariably they are supplied too fine for 180HP...

HTH?
Andy

DEWATSON said:

Andy,

I have a Hartzell blended airfoil propeller that I bought from Vans. The prop governor is a MT and the part # is P-860-4. The serial number is 07G044-D. I've never seen the RPM exceed 2650 static. It will rev up to about 2760 when it surges on takeoff when the oil temperature is up.

What needs to be done? Does the governor need to come off and sent back to MT for inspection. I'll check the fine pitch stops on the propeller tonight and make sure that's not the problem. I checked them when I installed the propeller but I'll check it again.

As Alton said, it only does the surging when the oil is hot.....never on the first takeoff of the day. When the oil teperature is hot though, it will surge back and forth until I do something about it. I have been decreasing the throttle setting and pulling the prop governor back to make it quit.

Thoughts....

Click to expand...

I have the same prop and governor combo and had similar problems. Adjusting the low pitch stop to a higher angle fixed it. Here is how I adjusted mine.

Run up at full power and note the static rpm (should be 2700 rpm or so depending on your engine specs). Shut down. Take off your spinner and adjust the stop to a coarser angle then run up at full power again. If the RPM is the same then keep increasing the low pitch stop (I think this is turning the stop clockwise, it says in the prop manual) until the static RPM is slightly less than redline (50-100 rpm).

Goodluck

Andy and Drew,

I set the propeller stop (checked it) when I was doing the first engine runs. It turns static at about 2650 (tied to a tractor....not moving down the runway). For the first 10 hours, I had no problem with the prop wandering up and down. It will now, and will exceed 2700 and then come back to 2560, etc. It has started doing this in the last two hours. The engine has 192 horsepower according to Americas Aircraft engines. It is an IO 360 paralell valve engine.

I'll reset the stop to 2600 RPM. I have plenty of power and this won't be unsafe at all.....I operate out of a 2000' strip. If this doesn't correct the problem, I guess I need to contact MT and see what they suggest?????

David

Hi David...

I set the propeller stop (checked it) when I was doing the first engine runs

Click to expand...

Sounds like you did better than most of us!

For the first 10 hours, I had no problem with the prop wandering up and down. It will now, and will exceed 2700 and then come back to 2560, etc

Click to expand...

It might be that as the engine wore in, it is now producing more HP?

I think your plan sounds ideal. Up to you whether you reset it with the tractor, or just observations on takeoff.

ATB
Andy

I know David has it, but just for clarification to others, make sure the governor is backed out of the way when setting the pitch stop. You want to see what the prop is turning all by itself without aid of the governor. The Hartzel manual wants 50 RPM below max.

I have never thought of it, but it makes sense that the engine could be producing more power as it breaks in. I am probably going to check my static RPM next time out (no tractor, I have to use my truck).

David, glad to hear the oil temps have come down. They still sound a little warm, but 207 seems good. I would think it will continue to come down as you get more time on the engine. The real test will come in about 6 months. I sure hope this winter does not drag out like the last one. I am headed to the paint shop Feb 1. I just know I am going to pick up another 10 knots .

Alton,

Claim 10 more knots...we're all pulling for you.

David

Alton and Drew,

Just FYI. I flew the airplane at lunch and the outside air temperature was 51 degrees F. After allowing the engine oil temperature to reach 100 degrees F, I watched the tachometer (digital) on take off and all the way to 1000 feet. It was rock solid on 2700 RPMs the entire time. It did not budge; not 10 higher, not 10 lower. This was with the throttle wide open. After reaching 1000 feet, I set the RPMs at 2450 and the manifold pressure at 24.5 and it remained there for 30 minutes with no hiccups. I did not have time to make a second takeoff, but at least I do know that the propeller's maximum RPM is set at 2700. Should I reduce this to 2600 or leave it alone? I think you both recommended about 2600 maximum. I don't want to start "messing" with stuff if I can isolate the problem.

David

David...

Should I reduce this to 2600 or leave it alone? I think you both recommended about 2600 maximum. I don't want to start "messing" with stuff if I can isolate the problem.

Click to expand...

No - not what I'm saying... This is the "governed" RPM, which you want at, or maybe 10-20RPM less than 2700.

What we are suggesting is adjusting the static RPM via the FPS of the blades. The only way you can see this value is:

1. Increase Governor RPM to well above 2700RPM, then do static runs or
2. "Slam" the throttle open whilst (initially) stationary (brakes off) and watch Max RPM achieved until the governor brings it back to 2700RPM

I tend to do the second way. There is no value in doing this airborne, or tied to a tractor and looking for a stable setting unless you alter the governor as well.

Summary: Slam the throttle open and RPM will rise to the static RPM, and then get pulled back by the governor. What you are trying to achieve is where the static RPM is less than the governed, so this "pull back" does not occur, which manifests itself as a "surge"...

Make sense?
Andy

David

If your serial number ends in a D then you really need to contact MT and get it updated. Then this should solve all your problems.

Peter

Andy,

Got it........I'll try it after work today. When set properly, I should be able to slam the throttle open on takeoff and not see the RPM go over 2600. If it doesn't, then the staic setting will be at 2600. Correct? Thanks so much for your patience and help.

David

David...

Yes - think you're getting the idea "Slamming" is a crude way of doing it, but saves tie down / altering the (correct) governor setup. In essence you are looking for the RPM to stabilise well <2700 due to the blades on the Fine Pitch Stop, then RPM increase with IAS until the governor then acts to limit at 2700.

If you get that, and still surges, then try the MT governor route.

Andy

Andy,

I just finished the test the way you said to do it. The tachometer went to 2860. I'll go back out to the hangar shortly and make the adjustments to limit it to 2600 (I thought I had done this properly when I installed the prop). I think I'm finally understanding what you are saying. If I can limit the quick RPM response to 2600 and the prop still surges while making the second takeoff of the day (heat soaked oil), I'll contact MT and see what needs to be done.

I owe you a steak.

I believe that those who have said to just send the governer back to MT if it is not an F revision are correct. I had the same problem on around the 5th flight. Called MT and they new exactly what they had to do to fix it. Fortunately I live just a few miles from MT in Deland, FL. I drove it over and picked it up the next day. It is a minor adjustment for them but essential for the prop/aircraft combination. The same prop gov may work fine on a different aircraft but not an RV-8/Hartzell. MT can turn it around quickly and save alll the adjustments that are unlikely to fix to the problem --- and for free.

I have a surge in my F1 Rocket with new MT prop and old MT governor. Contacted MT about the surge and they said sure, they could fix it. But since the governor is 6 years old, it needs overhauled for $550 and they'll throw in the "upgrade" to correct the surge.

DEWATSON said:

Andy,

I just finished the test the way you said to do it. The tachometer went to 2860. I'll go back out to the hangar shortly and make the adjustments to limit it to 2600 (I thought I had done this properly when I installed the prop). I think I'm finally understanding what you are saying. If I can limit the quick RPM response to 2600 and the prop still surges while making the second takeoff of the day (heat soaked oil), I'll contact MT and see what needs to be done.

I owe you a steak.

Click to expand...

Sounds like you may have it licked. If the RPM is going to 2860 on the ground, static, with a full throttle "slam", then your low pitch stop needs to be set to a more coarse setting. I hope it works

prop surge

I have reset the pitch stops to limit the propeller RPM to 2650 when I slam the throttle open. After the oil is warmed up, the propeller still surges on takeoff. I contacted MT yesterday afternoon and they said to take the governor off and ship it to them for a free upgrade. It will cost me the shipping only. Good service as far as I'm concerned. Hopefully I can put this problem to bed shortly.

David Watson
49FD

Sounds like a good deal to me too.