Low Engine RPM after Propellor Overhaul

[jonhop]

MooneySpacers,

I just had my propellor overhauled after an annual inspection because it was throwing grease from the hub. I got two used blades because mine were no longer serviceable. After install, my engine tops out at 2550 RPMs. We looked at the governor and noticed that it was adjusted to its stop of high RPM. I had the governor flushed and tested by two shops and they both confirmed that the governor was good. I had it overhauled anyways because I cant tell when it was last done. Put it in and got the same 2550 with the governor adjusted to where it should be or adjusted out to the high rpm stop. I took the plane for a lap around the field and saw 2700 rpm on climb out and around 2685 on downwind. We had a prop strobe tach with us and it coincided with the tach in the plane. I'm having my A&P check the fuel pressure and fuel flow today. We also measured the blade angles and and they were within specs of the TCDS...

Any advice on what I can check next would be great fully appreciated.

Thanks much,

Jon

[MB65E]

Hi Jon! 2700 on take off sounds acceptable to me. I guess I'm not understanding te question. I can't remember if I can get 2700 static in the chalks or not. Any time something is adjusted or changed it sure seems like it changes 3 other things. Make sure your prop cable has a bit of cushion at the panel, and make sure the actuator arm is hitting the stop. Sounds like you are adjusting the right things and you are on the correct track. 

-Matt

[jonhop]

Thanks Matt.. I was under the impression that 2700 could be reached in a stationary max power run up. Mine tops out at 2550 even on a high speed taxi and my A&P and a Mooney C pilot thinks it should hit 2700. The propellor and governor shops think the same. The propellor shop said it must be due to a weak engine but I'm not buying it. There is 1/4" between the prop cable and the panel. Will double check the cable. I have never monitored the exact rpm on takeoff as I'm glancing at all of the guages for good indications while flying the plane...

Edited October 7, 2016 by jonhop

[N201MKTurbo]

It should make full RPM at about 20 in of manifold pressure on the ground. You might check the rigging of the prop cable to make sure the wheel on the governor can make it to the stop screw.

It is curious that it goes to 2700 on climb. Was that with the stop screw all the way out? It should go to about 2900-3000 with the screw all the way out.

[Oldguy]

It would be too easy, but do you have an engine monitor recording everything? If so you can check data from pre and post o/h.  If not, Christmas list item?

[jonhop]

48 minutes ago, N201MKTurbo said:

It should make full RPM at about 20 in of manifold pressure on the ground. You might check the rigging of the prop cable to make sure the wheel on the governor can make it to the stop screw.

It is curious that it goes to 2700 on climb. Was that with the stop screw all the way out? It should go to about 2900-3000 with the screw all the way out.

Will check the cable and yes, it is strange that it speeds up to 2700 in flight. That had the governor and prop overhaul shop stumped as well... I didn't get a chance to fly it more than once around the pattern. I may take it out and high to see if the prop overspeeds in a shallow dive with 20".

[jonhop]

6 minutes ago, Oldguy said:

It would be too easy, but do you have an engine monitor recording everything? If so you can check data from pre and post o/h.  If not, Christmas list item?

That's 3rd on my list after a Flight Stream 510 and ADS-B compliance... the prop overhaul was a big hit to my budget for the year, so they have to wait until after Christmas.

[MB65E]

What rpm will it cycle at? What does 22in give for rpm? 

Does sounds like something lazy is going on. Almost sounds like there could be a blockage in the Gov. Is the gasket on correctly?

I once had an MT that came back from the prop shop with the spinner bulkhead indexed one screw hole off. The prop would only make 1400rpm. I even pulled the prop to check for a rag in the crank ( I don't use rags), also overhauled the Govoner. All to find out the the Counter weights were hitting the bulkhead. The bulkhead was installed and safety wired at the factory...

Start back tracking. Same s/n gov as was sent out. Same pitch change shaft, it all needs to be lined out. 

Ive also had the wrong shafts installed in props that should have been different P/n...

Could be an intermittent mag. 

-Matt

[Guest]

The prop should make 2650 static according to the manual.  See the note at the bottom of the page.

Clarence

[wishboneash]

2 hours ago, jonhop said:

Will check the cable and yes, it is strange that it speeds up to 2700 in flight. That had the governor and prop overhaul shop stumped as well... I didn't get a chance to fly it more than once around the pattern. I may take it out and high to see if the prop overspeeds in a shallow dive with 20".

If I understand aerodynamics, static max RPM will be less than when the aircraft is moving forward since the airflow resistance has now decreased. Also the MP probably increases due to increased impact pressure as plane moves forward.  I usually have to dial back from ~2730 down to 2600 or whatever I need for that take off.

[Cody Stallings]

Screw the low pitch stop out on the propeller.

That will flatten the prop out a bit taking some of the load off of the engine, hints increased RPM.

1/2 revolution to start.

[Cody Stallings]

4 hours ago, jonhop said:

Will check the cable and yes, it is strange that it speeds up to 2700 in flight. That had the governor and prop overhaul shop stumped as well... I didn't get a chance to fly it more than once around the pattern. I may take it out and high to see if the prop overspeeds in a shallow dive with 20".

The reason the prop makes 2700 in flight is because the prop has unloaded. It's not having to make it's own air anymore, in cruise it's corkscrewing through the air.

[jonhop]

Thanks for all the replies.... now I need to find the missing 100 rpm. My mechanic found the rpms jumping up about 200 rpms during the mag check, so he's going to check the ignition switch. He thinks that maybe the switch or rpm gauge may be robbing engine power from the p leads...

[Guest]

Just now, Cody Stallings said:

Screw the low pitch stop out on the propeller.

That will flatten the prop out a bit taking some of the load off of the engine, hints increased RPM.

1/2 revolution to start.

Isn't that for a Hartzell, if his is stock it's a McCauley.

Clarence

[Guest]

Just now, jonhop said:

Thanks for all the replies.... now I need to find the missing 100 rpm. My mechanic found the rpms jumping up about 200 rpms during the mag check, so he's going to check the ignition switch. He thinks that maybe the switch or rpm gauge may be robbing engine power from the p leads...

The "P" leads provide grounding to the magnetos, I don't understand how they could rob power?

Clarence

[jonhop]

Clarence it's a McCauley C214....

[Cody Stallings]

Just now, M20Doc said:

Isn't that for a Hartzell, if his is stock it's a McCauley.

Clarence

You are correct Doc.

Thought I was still on the vintage page. No 200 Series McCauleys on those ol birds.

 

The Cylinder will have to come off of his prop to adjust the low pitch setting.

Bummer.

[Guest]

Just now, Cody Stallings said:

You are correct Doc.

Thought I was still on the vintage page. No 200 Series McCauleys on those ol birds.

 

The Cylinder will have to come off of his prop to adjust the low pitch setting.

Bummer.

Not really field adjustable as I've discovered before  Bummer for most, work for you.

Clarence

[jonhop]

We measured the low blade angle at 14 degrees which is within the TCDS spec...

[jonhop]

Just now, M20Doc said:

The "P" leads provide grounding to the magnetos, I don't understand how they could rob power?

Clarence

I probably mis quoted him on that... 

[Guest]

The blade angle may well be correct, but for what ever reason the engine is either not making enough power to turn it to rated RPM.  

If the engine is healthy, minor adjustment of the fine pitch stops are an accepted correction, just not field adjustable for your McCauley.

Clarence

 

[nels]

I'm not really qualified but I assume your new blades are not longer than stock? Or maybe your old prop was leaking bad enough it couldn't hold the blades in the course position?

[Lionudakis]

I also learned a while back that the slightly lower static rpm as Cody mentioned is normal, but also your only real indication that your engine is making full power. Unlike a fixed pitch, the controllable prop can hide reduced performance if it was able to make 100% or more rpm while sitting static and the governor was governing the max rpm. I believe my Hartzell book says the low pitch stops are set to around 50 rpm UNDER max rpm for this reason. If static rpm is low, its because the engine power is low, and not covered up by the prop unloading and letting it make rated rpm.  Once moving the last little bit of rpm increases and the governor will start its job and keep it at max rpm.

 

[jonhop]

I flew today and recorded the some indications:

Static runup, propeller control full in, achieved 2600 on the tach and 2680 on the strobe tach. During takeoff and climb-out i observed about 27" of manifold pressure and 2600 indicating on the tach; Strobe tach had about 2680-85 indicating. Once at 1000ft, pulled back to 25" of MP and RPM's did not change on either gauge. Weight was approximately 2300lbs and the plane climbed at 1000fpm at 100kts. This was at 90°F, so I don't think the engine is too weak to reach 2700 rpm.

Leveled off at 4500ft and RPMs did not change and the plane accelerated to 150kts indicated airspeed--on par with what it did with the old prop that would turn at 2700rpm. Performed a 500fpm descent with 25" of MP in and the RPM's stayed at 2600 on the plane tach and 2685 on the strobe tach. I would think this is telling me that the governor is working by not allowing the prop to over speed and that the engine is producing enough power to hit 2600/2685. The plane accelerated to 185kts so that surely unloaded the prop...

I then climbed up to 5500ft and slowed down. At 22" of MP the following tachometer readings were observed. There was no observable propeller rpm change until about 2550 while twisting the prop lever out. I observed a + or - 10 rpm change on the strobe tach during climbs and descents at this power setting. The Mooney's tach did not change.

Mooney Tach              Strobe Tach

2700                            2680

2600                            2680

2500                            2580

2400                            2465-75

2300                            2365

2200                            2260

2100                            2170

2000                            2075

At this point I don't know if there is anything else I can check, other than slop in the prop cable. I find it weird that the gauges won't/can't get to 2700 rpm at high power and then read 60 to 80 rpm high as compared to the strobe tach on the lower power settings.

[Lionudakis]

I did notice on the lower left side of the AMM page uploaded, It states max rpm is 2700, and the static rpm may be 50 rpm less, that confirms the same info my hartzell book says. You stated in a shallow dive it is limiting to 2680. It sounds like in flight the governor is doing its job. Is the adjusting screw backed out or have you just verified that the control arm is touching the limit screw?