Stains on Back of Prop Blade

[Jeff_S]

Hey all. Lately I have noticed what seem to be oil stains on the back of my propellor blades after a flight. It seems to only show up on 2 of the three, although I can't say for sure it's always the same two. The stains seem to start at the prop outside the spinner, and streak out toward the tips. And this is only on the backs of the blades.

This is the first constant speed prop I've ever had so I'm still learning the ins and outs, and what to be concerned about vs. what is normal. I've checked around the hub of each blade and there are visible leaks or residue there. And the prop cycles just fine at runup and in-flight. I'm wondering if it couldn't even be picking something up from the oil breather tube or something, but can't figure out why that would flow forward onto a prop, against the prop stream itself.

Anyway, photos attached from after my short flight today. Any ideas/thoughts are appreciated. I will of course consult my A/P as well, but thought I'd see if the group here has any wisdom to share. Thanks.

[jax88]

I was warned that oil on the prop blades was not good.  I'll be interested to see what the technical answer is.

[GeorgePerry]

Constant speed props use engine oil in the hub to maintain constant pitch.  If your getting blow by then you've probably got a seal or two going bad.  I'd recommned having an A&P take a look to confirm.

[Mooney_Allegro]

Fly it up to Sensenich Propellers, in Gainesville, GA, have Dan Landis look at it.  I just had my prop overhauled by them in January 2010, about 2 months ago, the prop started leaking oil, and they honored the warranty, and replaced the seals.  Good people there and you won't have to wait long to get in.  Very professional.  If you don't have time to fly it there, they will come to you. 

[richardheitzman]

Ditto, oil on the prop= prop seal leaking. Get it checked ASAP

 

[Jeff_S]

Thanks all. David,  I had Sensenich do a prop balance in the spring so I'll give them a call on Monday and talk to them.  I'm not sure what the potential dangers are of flying with the prop in this condition so I ended up driving to see my parents in Clemson today. Any guidelines about how much leakage becomes a non-airworthy condition?

[67M20F]

Thats a small amount of oil.

Take a quart or oil and drip it on a blad siting still and look how much of a mess it will make....

I'm not saying fly it and watch it but its no grounder if you know what I mean....

I am not an AP/ but I am a wrench turner....

[skyking]

i would like to hear the outcome of that also.

I have a brand new prop, hub, spinner etc and i see a little bit on the back of my prop every now and again too and was told it is perfectly normal.

Not as much as you have on yours though.

[Ned Gravel]

Maybe it is because I am not paying as much attention as I should, but I have never seen any oil on the back of my prop.  One of my walkaround items is to look inside the spinner to see if oil has pooled on the bottom (I always put my prop blades horizontal when I park the aircraft).  I have never seen any.

 

[carusoam]

Just for thought...

[1] A gear pump provides the pressure for oil to fill the pistons that open the blade angle when commanded by the prop speed govenor.

[2] The govenor gives this command based on position of the prop speed (blue) knob.

[3] There is a particular time when a large amount of pressure is required to make a significant adjustment to blade angle.  This occurs during the run-up exercise.  Testing the prop speed govenor at high rpm on the ground can put a fair amount of pressure on these seals.

Some people during the run-up make three large adjustments to this knob looking for rpm change, oil pressure drop, manifold pressure change.  This exercise also exchanges oil in the prop system with warm oil from the oil pan.

Recommendation:  Clean your prop.  Go do a run-up, test the govenor as indicated in the POH, Taxi back and take a look.  If it is leaking oil at the seals, it will stain the back of the prop. 

Other people, lightly make the test of the govenor.  They seem to know something about seal preservation.

My experience:  The failed govenor/system in my M20C failed in the high RPM mode.  Most Mooneys, on failure go to high rpm.  (Mooney Missiles go the other way).  Testing the govenor is good, if it fails, it will still allow safe take-off and landing.  "Over testing" the govenor / system may lead to seal leakage (This statement is up for debate and may not be factual).

Keep in mind, the oil that leaves the system is precious.  This is the oil that lubricates the engine.  If there is a significant leak, it could potentially drain the life-blood from your engine and put it all over your windshield.

Other issues for debate have been how to store the prop, either vertical or horizontal.  Seals have been suspected of drying out if you leave one vertical.  I am not so much a believer in this theory.  With a three bladed prop, one is going to be more vertical than the others.....When you store the prop horizontally, someone will walk into it during the pre-flight.

Just for thoughts,

-a-

[Kwixdraw]

Just my $.02, I have always been told to keep the prop blades as horizontal as possible to allow water to run off and not collect at the base of the blades. The idea being to avoid corrosion there.

[CoachTom]

With all the talk of prop cycling and seals being stressed, does anyone know of the caution of excessive prop cycling and the impact it has upon the counterweights on the crankshaft?  I will look through some notes, but I do remember as a part of engine break in to not cycle the prop as it induced severe instability in the counter weights.  I know it is ambiguous, but I cannot remember if it was in the Lycoming or Continental literature, but I will find it out so it can be referenced correctly.

let us know the result of all your investigation into the leak,

 

[Jeff_S]

So here's what I've learned so far. Talked to an MSC and a prop shop and got the same story. The seals are going bad, but this is just grease from the bearings that's splattering, not oil from the engine. Many of you may have known that already but it gives me a bit more security about flying it, although both said I shouldn't wait too long because if the all the grease gets out then it could be an additional $1000/blade to replace the bearings and races. Now it's just a logistical question of whether to leave my plane at the prop shop or have the prop removed at my home drome and have them pick it up.  I'll post a final report once I get it done. Thanks again to everyone for their thoughts and ideas.

[piperpainter]

Well one thing I'll add is if you have your prop off you might as well have them paint it....if it needs paint that is! When I had mine off I had them paint it, made sense at the time!

[Jeff_S]

The current thinking is something I borrow from The Bard: Much Ado About Nothing. I took it to the prop shop this afternoon and we pulled the spinner. There's no evidence of any grease leak or oil leak. What there was, was some residual grease around two of the zerk fittings, probably from when it was greased at annual. Since the two blades that showed stains were consistent with where this residual grease was, the theory is that once that blade starts spinning at 2500 RPMs the centrifugal force was atomizing the oil particles and shooting them out onto the blade. So they cleaned it all up, and I'm just going to watch it for the next 5-10 hours to see what happens. I did notice that after I got back, there were no additional stains.

So, it's always sumpin', eh?

[jax88]

Gotta love it when "problems" disappear like that.