No Prop Drop

[bucko]

Coming back from trip, noticed prop RPM was slowly increasing. With Prop control pulled all the way back, I ended up needing to pull about 0.5 to 1 inch of MP (power) to keep prop at 2,500. 

On ground with run up to 1,700, pulling the Prop control back full resulted in minimal RPM decrease. Usually, pulling the prop causes an immediate 200 RPM decrease and prop control must be advanced quickly to avoid too much of a drop.

Have called mechanic, so investigation starting.  Looking for thoughts.

Need to get into logbook, but Prop has not been overhauled for a long time (not since engine overhaul). 

Mechanical linkage seems intact. All engine instruments seem normal. Oil pressure and temp were normal. 

Thanks,
Bucko

M20-E   (1965)
 

[mike_elliott]

I am  no expert here, but we do have one, Bucko @Cody Stallings might chime in. If you need a new governor, consider just replacing yours with a PCU5000 unit

http://www.pcu5000.com/  

[1964-M20E]

sounds like it may be your governor.    The prop defaulting to low pitch high RPM.

 

 

[Jerry Pressley]

Mine was the result of the freeze plug becoming dislodged in the crankshaft.  that allowed oil to leak back into internal of engine.

[FloridaMan]

Sounds like someone has a runaway prop, which I understand to be a major airworthiness issue that should be resolved before attempting to fly again. Good luck!

[Mooneymite]

Start out with the simple things....check the prop control cable.

[RobertGary1]

8 hours ago, Antares said:

Sounds like someone has a runaway prop, which I understand to be a major airworthiness issue that should be resolved before attempting to fly again. Good luck!

Probably not. He only needed to pull an inch of MP out. A runway prop would require substantial amount of power reduction. 

-Robert 

[carusoam]

Redline is 2700rpm?

With the prop knob all in, Does the gov control the rpm at 2700rpm, or does it exceed?

If it exceeds, expect that the gov is no longer in control. 

The reason for the loss of control can be a leak of gov oil pressure. Plumbing, plugs, or the internal shaft seal...

or the gov’s gear pump is no longer generating oil pressure, or the control valve in the gov is not operating properly...

Pulling back on the prop control is a request for the gov’s gear pump to supply oil pressure through a control valve to the prop.  There is a set of rpm dependent flyweights that operate the valve.

If the oil pressure from the gov isn't getting to the prop... this is a set-up to exceed rpm redline easily.  Start looking up engine OH costs  before doing that...

1) check on hours on the gov.

2) Check on pressure applied to the gov plumbing to see if the prop is operating properly.  Procedure to be followed.

3) Basically, oil engine pressure is needed, to supply prop’s oil pressure... with no oil pressure, the prop returns to full flat, mechanical limit.  Prop oil pressure is not the same as engine oil P...

4) worn fly weights are an easy fix, part of an OH kit...

5) New gov’s Probably cost less than OHs, with better results...

My C lost its aluminum disc shaft seal. It fell out after landing. Replacing the seal required prop removal and a hammer.... press the disc back in place properly.

When if failed, it gave no hint something was wrong... just couldn’t do a run-up.

no run-up, no flight... lesson learned in the pre MS days....

 

PP thoughts only, not a mechanic...

Best regards,

-a-

[Cody Stallings]

I think I would start at the Gov too.

Sound like you have oil pressure bypassing allowing the Propeller to migrate towards High Rpm(Fine pitch).

PCU 5000 an McCauley 290D’s are good Govs to look at

Edited February 11, 2018 by Cody Stallings