Cycling the Prop Governor on Run-up

[LevelWing]

I've been having some issues with my prop governor lately. I wasn't able to get the RPMs to drop when cycling the prop. The mechanic messed with it and it seemed to work until last week when it didn't work again. The mechanic checked it out again and wasn't able to replicate the problem. I tested it again today and it seemed to work fine. The POH says that upon seeing a 100 RPM drop to put the prop full forward. Are the RPMs supposed to drop beyond the 100? If so, mine doesn't. This is at 1900 RPM. At 2000 RPM it drops about 250 RPM.

 

Is this normal or am I just looking too much into it? This is a '68 C.

[jrwilson]

Mine drops quite a bit more than that, not really sure what it would go down to, because I bring the rpm forward pretty quick. I'd say something is wrong.

[Lood]

It is supposed to drop more than 100rpm, but it's not good for your engine to let it drop excessively, hence the "caution " to go full forward once a 100rpm drop was observed.

[Marauder]

What RPM does your POH say to do the prop cycle? Also how cold is it where you are at? On really cold days, it takes my plane a little time before the oil is warm enough to do a proper cycle.

[MooneyBob]

I have 3 blade prop and drops definitely more than 300 RPM before I bring it quickly up. If I hold it longer back I would see probably 500 RPM drop.

[carusoam]

Exercising the magnetos...

Right, both, left both (looking for the 100 rpm drop)

Exercising the prop...

Are you guys pulling it all the way out to see what it drops too?

The idea is to get oil to flush through the system, and test it's functionality. Maintain control when pulling out the knob.

One day it might not drop rpm. This is a sign of internal oil leak, a $5 seal in a 1 AMU place...

Now I'm going back to reading the procedure....

Good morning,

-a-

[Hank]

Level,

 

When cycling my [3 blade] prop during runup, at 1700 RPM, I pull the lever all the way back. On cold mornings, or if I haven't flown in a while, it may take 2-3 seconds for anything to happen. As soon as the RPM starts to drop, I push it back all the way forward, giving me ~100 RPM drop. If it was slow to move, I'll keep cycling it until it responds immediately.

 

The reason it is slow is due to cold, thick oil. Cycling the prop forces warm oil from the engine through the mechanism, but the cold oil doesn't push out easily.

 

The key is to get the cold oil out and warm oil in. Flying home on a burger run, the RPM drop is immediate, sometimes I don't even get the lever to the stop before I'm pushing it forward again. When it's below freezing, I've sat up to about 5 seconds with nothing at all happening--those days get at least three cyclings, until it responds smoothly like when warm.

[MooneyBob]

My exact procedure is:

After magnetos check I lower the RPM by 200 and wait a little.

I increase the MP a little to see if the RPM stay stable and the oil pressure doesn't drop drastically. That would be indication on massive oil leak from the governor.

Then I cycle the prop 3 times all the way back slow enough to get around 300 RPM.

Before all that I make sure my oil is warm enough to move the needle.

Again, I am new to my Mooney and I was told to do that this way by my instructor / Mooney owner.

[Gone]

One of the things I have learned on Mooneyspace is that the governor needs to be cycled only once per flying day.

Sent from my iPad

[orionflt]

I cycle my prop 3 times looking for 100 rpm drop, when it's cold it will be slow to cycle initially until the warmer oil has been pushed to the prop. When it's warm the prop responds immediately. I'm not sure where I learned to cycle the prop three times but I do it to ensure the oil is flowing properly to the prop and any air that may have accumulated in the lines from sitting has been purged.

Brian

Sent from my iPad using Tapatalk

[carusoam]

Classic training is the three cycles. Looking for different things on each. (oilT, oilP, ?)

The system drains a lot of oil back to the sump when the engine is off. Cold oil is slow and has a long way to go on the first cycle.

The O3 checklist (because I have this CL on my IPad) set engine to 2000 rpm, cycle the prop. (Once)

It is somewhat stressful to cause the engine rpm to drop while power is being applied... Definitely different stress level than turning off a single mag, one at a time.

Best regards,

-a-

[orionflt]

Classic training is the three cycles. Looking for different things on each. (oilT, oilP, ?)

oil pressure drop

RPM drop 

Manifold pressure rise

[LevelWing]

I have a 2 blade prop and the RPMs never drop more than 250 RPM. 100 RPM at 1900 and 250 RPM at 2000. I can pull the prop full aft and it will only drop a max of 250 RPM depending on the RPM setting. This is why I'm wondering if something is wrong. I cycle it at least 3 times.

[orionflt]

I have to admit you should be able to get more of a drop even though you do not want to load down the engine so much, it almost sounds like you have an internal leak.

to get a better answer we would need more info like what your pressures (oil and manifold) are doing during the ground check and how well your prop maintains RPM inflight. does it wander and surge? does the RPM's increase when descending or do the remain constant? do you have any indications of external leaks? when the engine is up to operating temp and you change your RPM settings is the change immediate or is it sluggish?

 

Brian

[Oscar Avalle]

I run up the engine to 1800 and then cycle it the prop after the Mag check. As soon as I see a 100 RPM drop (and hear it) I put it back and repeat the excercise.

[carusoam]

LW,

Have you mentioned the plane or engine you may be using?

Some people put it a couple details with their avatar...?

When the governor isn't working, the prop flattens out to max RPM (unless you have a missile).

When it is wearing out it tends to not hold rpm or oscillate.

If it is not going to the extremes, it can be measured / set on the ground.

Seek a mechanic for help on this...

Best regards,

-a-

[Hank]

Anthony--

 

He has a 68 C, last line in his post.

 

I'm curious what his book says. My 1970 C says to run up at 1700.

[carusoam]

There is some newer discussion on how fast one needs or should do the run up.

My paper POH is at the plane and my memory is still a bit fuzzy...today?

1,700 vs 2,000 rpm for magnetos and or governor.

Above, I quoted from an O3 POH. Unfortunately I don't know the validity of the source...

Best regards,

-a-

[BigTex]

My 1965 C model owners manual states to cycle the prop between 1800 and 2000 RPM. Then after seeing a drop of at least 100 RPM, to push it full forward.

[aaronk25]

I cycle the prop once maybe twice if it takes a couple seconds to respond and never check it on remaining flights.

In fact if it's 2nd, 3rd flight of the day I skip the run up all together. I do flip though the mags at idle on subsequent flights but run ups throw sand on the cowl and chip paint so I minimize them.

If launching into soup on subsequent flights I'll go though the whole run a sequence.

[Bob_Belville]

The "owner's manual" for my '66E calls for mag check @ 1700 rpm (max drop 125 rpm) and prop exercised @ 1800-2000 rpm by pulling prop full out until 100 rpm drop then push full forward.

 

Interestingly this old manual has this procedure to clear rough running on one mag: With mags on "both" reduce to 800 rpm for 1 minute then slowly increase power to 2200 rpm and recheck the mags. "This operation will usually clear fouled plugs." This is to be done with mixture full rich and boost pump on!

[LevelWing]

I have to admit you should be able to get more of a drop even though you do not want to load down the engine so much, it almost sounds like you have an internal leak.

to get a better answer we would need more info like what your pressures (oil and manifold) are doing during the ground check and how well your prop maintains RPM inflight. does it wander and surge? does the RPM's increase when descending or do the remain constant? do you have any indications of external leaks? when the engine is up to operating temp and you change your RPM settings is the change immediate or is it sluggish?

 

Brian

The plane just came out of annual in January so I would hope there's no internal leak that the mechanic wouldn't have caught. I'll have to get a more definitive answer the next time I run the plane in regards to the oil and manifold pressures however yesterday when I ran the plane (didn't fly it) the pressures looked fine. No indications of external leaks. The last time I flew the plane when I adjusted the prop it was an immediate change and didn't appear sluggish.

 

LW,

Have you mentioned the plane or engine you may be using?

Some people put it a couple details with their avatar...?

When the governor isn't working, the prop flattens out to max RPM (unless you have a missile).

When it is wearing out it tends to not hold rpm or oscillate.

If it is not going to the extremes, it can be measured / set on the ground.

Seek a mechanic for help on this...

Best regards,

-a-

The engine is a Lycoming O-360-A1D.

 

Anthony--

 

He has a 68 C, last line in his post.

 

I'm curious what his book says. My 1970 C says to run up at 1700.

The POH says to cycle the prop at 1700 RPM however an A&P wrote a note in there stating that a new prop governor had been installed and to cycle the prop during run-up at 1900 RPM. The mag check is done at 1700 RPM.

[Gone]

Classic training is the three cycles. Looking for different things on each. (oilT, oilP, ?)

oil pressure drop

RPM drop

Manifold pressure rise

+1

Sent from my iPad

[carusoam]

The advantage of exercising it to 100 rpm drop, is to get oil flowing and verify that the control is working.

The disadvantage of higher rpm drop, is the possibility of pre-ignition.

The timing is set to (20 or 25) degrees BTDC, slowing the engine down gives more time for the flame front to burn and possibly cause engine stoppage and possible damage. Worst case would be flames escaping out the intake valves before they close? Speculation, but defines back firing...

There is no additional advantage of slowing it further, but the risk starts to increase.

If the oil leaks internally, you can pull the control all the way back and nothing changes.

My '65 C blew the front internal drive shaft seal (aluminum disk in the shaft). The gear pump delivers oil to the front of the shaft to actuate the prop blades. Leaky seal = no oil pressure to the prop = no change in RPM.

It received a governor OH while putting the seal back in.

So, I vote....

Follow your POH for initial rpm,

look for the drop, 100 rpm works, more rpm drop adds risk with no additional advantage.

There is no spec for a lower limit (is there?)

I'm only a pilot, not a mechanic or flight instructor...

Best regards,

-a-

Notes on my thought process...

The engine oil P drops because there is another place for oil to flow, less oil is being pushed, momentarily, through the engine. Oil pressure in the shaft is not measured.

Rpm drops because the load on the shaft has increased.

MP increases because there is less rpm, and less air being drawn away by the cylinders.

[jetdriven]

The -A1D isn't effected by counterweight detuning but the -A3B6 and -A3B6D engines can be. A large drop in RPM on the governor check causes the counterweights to go to the limit on the bushing and stick there. They won't free up again until the next shutdown cycle. So the counterweights are locked at the edge of their travel on the pin and don't provide damping for that run.