RPM issue.

[Lood]

Over the past year or so, I've quite often experienced not getting max rpm during take off. I was confident that I could definitely feel the lack of full power, but always made it off as the rpm indicator being faulty. After installing the EDM900 however, my suspicions were confirmed.

During some take off's, I don't even get 2600rpm, but then on the next take off, I would get the full 2700rpm. My CSU was overhauled two years ago and the prop was overhauled 5 months ago. Seeing that the problem is not consistent, it can't be a setting on the CSU.

I tend to suspect that the problem is more evident when it is cold and whenever it does happen, the rpm will eventually go to 2700rpm during the climb, after about 5 minutes or so.

 

Anybody have any ideas on this one?

[carusoam]

I would be guessing.....

The two fly weights on the governor may be mis-behaving.

They have a tendency to wear and possibly be sticky.

Other things related to the governor... Like the valve sticking partially closed

Probably not...

Seals, these things release oil pressure in the system that would move the prop towards high rpm.

Gear pump, if it does nothing, low oil pressure would send rpm to max.

Sounds like your local mechanic could verify what is working or not working.

To verify the actual rpm, there is an app for that....

Does your body sense the difference? Sounds and feel of acceleration?

In a Long Body Mooney 200 rpm is the difference (2500 - 2700rpm) between 1200' and 800' ground roll caused by a 10% difference in HP...

Small difference in rpm = large difference in T/O run...high altitude departure won't help any either...

Good luck,

-a-

[Guest]

The engine should turn up to 2700 RPM on static run up. Both the prop and the governor are adjustable, your digital tachometer is more accurate than the old mechanical one.

The delayed reaction from the prop could be a faulty prop governor cable not allowing the actuating arm to hit the stop, and a long shot of a shipping plug or rag left in the crankshaft bore when the prop was installed.

Clarence

[Mooneymite]

>>>>a faulty prop governor cable....<<<<<

 

I agree.  This sounds like inconsistent linkage position to me.

 

Let us know what you find.

[Andy95W]

>>>>a faulty prop governor cable....<<<<<

 

I agree.  This sounds like inconsistent linkage position to me.

 

Let us know what you find.

+1

Cold weather can gum up an otherwise healthy prop cable. After a little vibration and a little heat, it finally goes to full forward, even though the cockpit control was at full forward the whole time.

[Lood]

Thanks guys.

Just to clarify: Both my old rpm indicator, as well as the EDM900 agree on the rpm readout and I was actually quite surprised at how accurate the old one was. This then rules out indication error.

I can certainly feel the lack of power during acceleration and especially during climbout.

 

Seeing that both the governer and prop have been overhauled recently, I'll certainly have them checked out, but I'd like to go with the prop cable that might have had it. I'll keep you posted once we've found the problem.

[John Pleisse]

Lood....just OH'ed my prop....same thing. I was only getting a static RPM of 2600. Simple adjustment.

[takair]

I had a governor do this. It would change with oil viscosity. Tried adjusting the prop governor, even the prop stops. Then I would start getting overspeeds. Sent out the governor and they said no fault found (same shop "repaired" it previously). Went through another 6 months of troubleshooting, even considered the engine as a culprit. Finally sent the governor to another shop (pm me for the name) and they found the problem. It was, in fact, the pump portion of the governor. The teeth on the pump had grooves in them as if something had gone through it. No evidence in the oil filter, oil analysis or any other problems, but the pump was shot. Basically, as the oil became more fluid, the pump could not keep up the pressure. So, hot, thin oil would result in less regulation. In my case, the pump could not be rebuilt, but an overhauled pump solved the problem.

The ideas above are all valid, but I'm leaning toward a governor issue.

[Lood]

Well, just for interest sake, a friend and myself took an hour and a half flight this morning to attend a meeting. On the way to our final destination, I landed to drop off my daughter and then continued.

When selecting pitch fully fine on final approach, I felt something give in the pitch control. Nothing strange resulted and we landed safely. Before take off this afternoon, I removed the cowling to take a look see and found that the last part of the governer control cable, which is a solid 4" metal tube outer, through which the cable runs, detached from the rest. Not a big issue, except that it might result in maximum rpm not being possible, as the inner cable would now be able to develop some slack.

I pushed it back into the part where it came out from and slid the rubber cover back over, but whenever I would push the control all the way in, this tube would agaian push out. Since I've bought my Mooney, the control could never move all the way forward and it seems that the inner cable is actually a bit too long to suite the outer sheath.

I'll have it fixed or just replace the complete rpm control with a new one. However, even with the end tube detached, the governer does reach both stops. So, I doubt whether this is a cable problem. I'm a bit concerned that it might be the governer itself. During the first take off this morning, I got a maximum rpm of 2580rpm during take off and it increased after about 5 minutes. During the second take off, after dropping off my daughter and only having been shut down for 15 minutes, I got full rpm and twice during the take off run, the rpm would very briefly reach 2710rpm.