What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Engine/Prop vibration

Bill.Peyton

Well Known Member
Over the past 20 hours or so I have noticed that for the first 45 min to 1st hour of flight I have a slight vibration at most any RPM, which previously was not noticeable. Over a period of 45 min to hour of cruise flight, the vibration continuously gets less and less until it is not longer noticeable. This is not a lot of vibration, but enough that my wife noticed it. It's enough to notice in the glare shield, and on the stick. It is consistently repeatable and can be duplicated by letting the aircraft sit for several hours. Flying again for 45 minutes fixes the vibration. I can shut off each ignition in flight and not make any change to the vibration, so it's not an ignition issue.

Engine: IO540 D4A5 690 engine hours

Propeller: Standard RV-10 Hartzell Two blade blended airfoil HC-C2YR clocked in the standard position

I just concluded my annual inspection and did the following, with no change in the symptoms:

  • Reamed all 4 exhaust guides per Lycoming Service Instruction 1425
  • Removed left mag inspected, replaced points and cam, set e-gap etc. and re-timed
  • Verified timing of Electroaire electronic ignition
  • Serviced, gapped and measured resistance of all plugs
  • Measured resistance of all plug wires
When I review my Saavy data online it looks absolutely perfect, I can tell the engine is developing full HP in that my cruise speeds have not changed. My fuel flows and leaning have not changed. My CHT spreads are the same as prior spread a year ago as are the EGT spreads. I bore scoped the cylinders.

The only remaining idea that I have is that the prop grease seal has been compromised and grease is getting into the center of the hub and settling when the plane is sitting idle. When the prop starts spinning and the hub gets filled with warm oil, the grease redistributes itself and the vibration disappears.

So as I write this I am about to leave to drive Hartzell this morning to have them tear down the prop. and hoping that is the issue. Any other ideas from the VAF brain trust are appreciated.
 
Are you certain that the vibration is RPM-dependent, meaning coming from the prop or engine?

I had an interesting vibration chase on my 9A where I finally pinned it down to one of my gear fairings with a broken rivet that would fishtail a bit at cruise speed and cause the gear leg to resonate and transmit the vibration to the airframe. My "Ah-ha!" moment came when I started playing with the RPM and noticed the vibration did not change at all, in intensity or frequency, as I changed my engine RPM from 2700 down to 2000 as long as I maintained a decent airspeed.

Your 45 minutes to an hour timeframe could be caused by something similar, and only happens when the wings tanks are full of fuel and you get close to a resonant frequency. Once you burn off some fuel the resonant frequency gets away from the excitation frequency and it will stop resonating.

Just a thought...
 
Try applying your brakes. Might be a out of balance wheel.
Had a nose wheel that would start spinning if I exceeded 180mph. It was out of balance and caused a vibration. Asked my wingman to take a look. He saw the nose wheel spinning. Tightened up the axel bolt and balanced.Vibration gone.
 
Vibration Frequencies / Dampening

Before you spend the time and money on the prop disassembly, here are few ideas to possibly consider -

1. The (hot) oil in the typical Hartzell passes through a small tube in the center of the hub and feeds the oil to the prop dome, which imparts pressure on the piston inside it to vary pitch. The (hot) oil and grease are typically are not in direct thermal contact, so the grease doesn't typically "liquefy" too much and move around. Prop grease is designed to remain semi-solid through a wide temp range, not sure that linking prop vibes to grease propagation due to the effects of hot oil is probable. (but anything is possible)
2. The grease in the typical Hartzell prop is around 3" from the center of prop rotation and has fairly low mass, so its not likely that the mass of the grease at 3" can impart large mass moments / imbalance vibrations, provided the prop is greased properly. Typically, the standard Hartzell prop grease task is to pump equal amounts of grease into each blade grip. Once the engine is run, centrifugal force will compact the grease into the hub and blade bearings and it pretty much stays there. The only grease seal I have seen in the typical Hartzell prop is around the blade shank and it keeps the grease in the hub around the blade shank. Not sure if there are any grease seals internally that prevent grease propagation and becoming a cause of mass imbalance.
3. I have troubleshot many CS props for "inflight vibrations". A typical dynamic balance should take the "in-plane" dynamic balance down to 0.2 to 0.05 IPS. Note that dynamic CS prop balance can only measure the balance at the max RPM tested and whatever blade angle that provides. Balance can only be improved by making mass changes "in plane" to the prop rotation. The out of plane vibrations potentially caused by minor out of track blades or thrust imbalance or pulses cannot be altered with mass changes. Also, when the aircraft is on the ground, the airframe's interaction with the ground through the tires and landing gear can dampen resonant vibrations in the airframe. Once you are inflight, the prop pitch is going to be significantly difference than what is was on the ground (when you achieved perfect prop balance) and may cause resonant airframe vibrations from prop thrust impulses impinging on the airframe. Remember that most dynamic prop balance is done at fine RPM and max RPM, on the ground, which isn't what you get in flight. It is quite typical for airframes to have RPM specific resonant / natural vibration frequencies despite the prop being in perfect "in plane dynamic balance". The fix is to use vibration dampening materials in the cabin or operate outside the resonant natural frequency. Sometimes an inflight vibration is reported to come and go over time, think about the changes going during that time, burning fuel / mass dampening changes / temperature changes / speed / trim changes. They all have effects on vibration dampening and what you feel.

I fly an RV-9A that has significant resonant vibrations in he floor and dash at certain prop and power settings, yet its prop is balanced to 0.07 IPS. I put a case of bottled water on the co-pilots floor board and the vibration goes away...but its had to carry passengers then.
 
I fly an RV-9A that has significant resonant vibrations in he floor and dash at certain prop and power settings, yet its prop is balanced to 0.07 IPS. I put a case of bottled water on the co-pilots floor board and the vibration goes away...but its had to carry passengers then.

Thread drift - but try the turn-down tips on the exhaust pipes to route the blast downward away from the belly skin, worked for me.
 
Thanks for all the responses. Just a note, this vibration just started about 20 hours or so ago. Prior to this it was smooth as can be and had been dynamically balanced to .0233 IPS.
I just returned from the Hartzell facility. Not a bad drive from St. Louis. These guys are unbelievable to deal with. Talk about customer service!! They allowed me to witness the entire operation. I showed up at 7am and they promptly disassembled the prop. Matt, the tech support engineer looked at the grease that had leaked into the hub and thought that there was a good probability that this could be the issue. I'm not so convinced. The grease that is in the cavity where the #2 is written should not be there. What I am convinced of is that following the Hartzell prop servicing procedure of pumping in grease on the leading edge zerk fitting until it comes out of the trailing edge zerk fitting hole, with not more than 6 pumps, will yield an over lubed prop. In the photos below you can see the grease that has leaked by the inner o-ring seal and found it's way into the center section, which should normally be void of grease. This prop has been serviced 6 times in the 690 hours it has been on the RV using this method.
37245191314_09c57fd5b5_c.jpg
[/url]IMG_1337 by Bill Peyton, on Flickr[/IMG]
37245192174_5d2b25cb1c_c.jpg
[/url]IMG_1338 by Bill Peyton, on Flickr[/IMG]
37245193504_aaf9dfab99_c.jpg
[/url]IMG_1339 by Bill Peyton, on Flickr[/IMG]


In addition to re-sealing the hub, Hartzell checked the overall static balance, blade alignment, blade angles and leading edge blade alignment and all were well withing spec. Hopefully I will get to test this out this Saturday. If it is not the culprit, then on to another idea which Airguy posted. It reminded me of what happens when the nose wheel not have enough break out force, it will cant sideways in the prop wash. This might be causing some amount of vibration for a period of time could be another place to look. I have installed new engine mounts, so hard to imagine that's the issue. Ill be sure to post the results of the prop. reseal
 
Last edited:
Bill -

I think that the way you stated the Hartzell greasing protocal might be just a little misleading. You said "pump it in the leading edge until it comes out the rear, but no more than six pumps". That probably logically gets you to the same place as the actual recommendation, which is "put in six pumps - but stop if it comes out the rear fitting before you get to six". I have serviced three of these props for a dozen years now, and have never had grease come out the rear fitting with six pumps. There are many people who think that you are supposed to see grease coming out the rear - and this is just wrong .... it will definitely be overgreased, and you risk popping seals.

Like I said - I think that logically you get to the same place, but stating the "until it comes out the rear" first might empower those who think they should pump until the hub is "full".

Paul
 
Paul,
You are correct with your wording, which is better stated than mine.

I usually see grease exit the trailing edge fitting hole prior to achieving six pumps, except for the last service, which took the total six pumps. The service tech who re-assembled the prop suggested nor more than two pumps should really ever be needed unless grease has been leaking from around the seal. He also noted that they have seen a couple of props come in for overhaul with the entire inside cavity completely filled with grease.
Bill
 
Culprit or not for your vibration, this seems to be a service issue. I would expect you to be mindful of the procedures for prop lube, so what is the " proper" procedure that will prevent intrusion of grease in the center hub? Can you discuss the possible root cause and mitigation with the Hartzell guys?
 
The Hartzell technician that assembled the prop suggested that unless you see leakage around the prop hub, any more that a couple of pumps of grease does not due anything other than over pressurize the bearing chamber. He also suggested that prior to putting anything in the leading edge port that you run a piece of safety wire into the trailing edge port to make sure the grease has not hardened and blocked the witness hole. As an additional data point, it took 44 pumps to fill each side dry chamber after final assy. I'm going to follow his advice for future service.
 
I installed the prop. and was able to get a short flight in today. Ceilings were not to conducive to getting a good long test flight.
Preliminarily I can say with 99% certainty, the vibration is gone! I am planning on a long test flight tomorrow, and if anything changes I will post it here, but for now, I believe the problem has been resolved. Thanks everyone for all the suggestions.
 
Great news!

I installed the prop. and was able to get a short flight in today. Ceilings were not to conducive to getting a good long test flight.
Preliminarily I can say with 99% certainty, the vibration is gone! I am planning on a long test flight tomorrow, and if anything changes I will post it here, but for now, I believe the problem has been resolved. Thanks everyone for all the suggestions.
It's threads like this that really add a lot of value to this site - I'll bet that almost everyone that's read it has learned something new. I know that I have! Thanks for sharing this.
 
It's threads like this that really add a lot of value to this site - I'll bet that almost everyone that's read it has learned something new. I know that I have! Thanks for sharing this.

I'd love to see more hub disassembly photos. Who has some?

Anyone have a compact Hartzell which has been rendered un-airworthy? I'd be happy to dissect it.

BTW, we've talked about leaking zerk fittings in past threads. Apparently it is now an approved procedure to replace the outlet zerk (the one we remove for greasing) with a plug:

http://hartzellprop.com/wp-content/uploads/HC-SL-61-354-R00-W.pdf
 
I wish I had taken more photos of the assembly and disassembly Dan. Those are all the photos I took unfortunately. My prop was reassembled with zerk on the leading edge and a plug on the trailing edge.
 
....so what is the " proper" procedure that will prevent intrusion of grease in the center hub?

Random stuff.

One of the Hartzell SBs says...

(2) Propellers that are improperly lubricated, or leak grease, leave greaseless areas in the bearing. These greaseless areas can accumulate moisture and lead to corrosion.

...which suggests the bearing cavity should be full. Obviously that's not entirely desirable or we would be instructed to pump until grease exits the other hole, every time.

I'm in the group that doesn't understand the annual or 100 hr grease requirement. Assuming I have a totally dry prop (no sign of throwing anything), where does the old grease go?

Somebody must have drawings or pictures. Where is the seal that supposedly keeps grease out of the fork chamber? I'm guessing on the inside of the cup surrounding the blade butt (in the photo, to the right of the "2", with the big slot for the blade pin). That cup kinda looks like it's clamped in the hub. Without sealant, grease may pump in the fork chamber around it's OD.

WAG...temperature when greased could be a factor, as could oil content.

Both Aeroshell 5 and 6 are mineral oil based, with the same thickener. However, many have noticed that the oil tends to leak out of Aeroshell 6 while the grease gun is sitting on the shelf. It can be so bad that it won't pump a year later, at the next annual, not to mention making a mess in the shop.

The optional grease is Aeroshell 5, the proviso being it can't be used at minus 40F. It does not seem to lose much oil in gun storage. If you look at the spec sheets, the reason seems obvious. The oil used in Aeroshell 6 has a 104F viscosity of 35, vs 500~525 for Aeroshell 5.

The given worked and unworked penetration specs (essentially a viscosity rating for grease) are similar at the rated temperature (35C), so I would think they would pump about the same. What the specs don't tell us is the change in penetration spec with change in temperature. The #6 is slightly less viscous (higher penetration number) at 35C (95F), and may be a a lot less viscous at some typical "Hey, it winter, let's do the annual!" shop temperature. The upshot is #5 may be less prone to squeeze through seals.

http://www.shell.com/business-custo...66f2004ed372bbef1/aeroshell-book-5greases.pdf
 
Yeah Dan, where does the grease go? It appears there is no perimeter seal to the inner chamber. I was thinking maybe the issue is hydraulic lock with 100% filled bearing voids, and a little seal displacement, (like a disc brake caliper) then if (and only if) this pressure has pushed the prop inward (it is a stepped bore), then the centrifugal force of the prop can pressurize the grease, and combined with thermal expansion, it either burps externally, or it pushes back inward. Likely, a little of both. Displacing some grease from under the exit plug makes sense to help, but is that enough?

Does anyone know if the retention bearing has any play or is it preloaded? Are there shims in there to adjust preload? If it has play, then over filling with an inward radially displaced prop might make sense.
 
If we are only to do 2 or 3 pumps per side, are these calibrated strokes, what if you did only a 3/4 stroke, possible imbalance? I have a newly rebuild Hartzel CS with a new non AD hub, the first condition inspection I did the pump until it came out the other zerk hole method, and it actually took quite a bit of grease, upon reaching this point I did notice that the grease coming out was proportional to the amount being pumped in, hard to imagine it going somewhere else. I did notice that after this service cycling the prop during run up, the prop feathered sooner and easier than before and no leakage.
 
Bret,
The current Hartzell procedure calls for removing the trailing edge zerk fitting. Inserting a piece of safety wire to make sure the hole is free of coagulated grease. Pump up to 1 oz. or approximately 6 strokes or until grease emerges from the trailing edge hole. Use the same amount for both side to prevent prop imbalance. This is called out in the manual under maintenance practices 61-00-15.

This is exactly how I serviced my prop., yet still ended up with grease in the center of the hub.

Also from the manual
?Over lubricating an all aluminum hub propeller may cause th grease to enter the hub cavity, leading to excessive vibration and/or sluggish operation. The propeller must be disassembled to remove th grease.?
 
Yeah Dan, where does the grease go? It appears there is no perimeter seal to the inner chamber. I was thinking maybe the issue is hydraulic lock with 100% filled bearing voids, and a little seal displacement, (like a disc brake caliper) then if (and only if) this pressure has pushed the prop inward (it is a stepped bore), then the centrifugal force of the prop can pressurize the grease, and combined with thermal expansion, it either burps externally, or it pushes back inward. Likely, a little of both. Displacing some grease from under the exit plug makes sense to help, but is that enough?

Does anyone know if the retention bearing has any play or is it preloaded? Are there shims in there to adjust preload? If it has play, then over filling with an inward radially displaced prop might make sense.

The prop blade has two o-rings. In between is the cavity that the bearing race rides in. The bearings are separated with a with plastic bearing holder. The outer seal keeps the grease out of the prop blade and glare shield. The inner o ring should prevent grease from entering the center of the hub. It is obvious from the photo with the “2” that th grease has easily migrated outside of the inside o-ring. There are no shims when the prop is assembled.
I’m going to try to get an exploded view of this assembly from my contact at Hartzell.
 
Temperature is also something to keep in mind, I won't lube a prop unless it's at least 60F but preferably warmer, and pump slowly to allow the grease to work its way around the hub.
 
Bret,
The current Hartzell procedure calls for removing the trailing edge zerk fitting. Inserting a piece of safety wire to make sure the hole is free of coagulated grease. Pump up to 1 oz. or approximately 6 strokes or until grease emerges from the trailing edge hole. Use the same amount for both side to prevent prop imbalance. This is called out in the manual under maintenance practices 61-00-15.

This is exactly how I serviced my prop., yet still ended up with grease in the center of the hub.

Also from the manual
?Over lubricating an all aluminum hub propeller may cause th grease to enter the hub cavity, leading to excessive vibration and/or sluggish operation. The propeller must be disassembled to remove th grease.?

or, or? mine was after the last or, until grease comes out the trailing edge zerk hole :rolleyes: I have read that the first service after a rebuild would take a lot of grease, mine did. the two O rings per blade mentioned above makes sense.
 
or, or? mine was after the last or, until grease comes out the trailing edge zerk hole :rolleyes: I have read that the first service after a rebuild would take a lot of grease, mine did. the two O rings per blade mentioned above makes sense.

I was questioning your procedure in the same way Bill probably was.
You wrote "upon reaching this point I did notice that the grease coming out was proportional to the amount being pumped in"

This would imply you didn't follow the written procedure....
You are supposed to stop pumping as soon as grease begins to exit the opposite hole.
If grease coming out is proportional to what you are pumping in, then you must have kept on pumping. Correct?
 
I was questioning your procedure in the same way Bill probably was.
You wrote "upon reaching this point I did notice that the grease coming out was proportional to the amount being pumped in"

This would imply you didn't follow the written procedure....
You are supposed to stop pumping as soon as grease begins to exit the opposite hole.
If grease coming out is proportional to what you are pumping in, then you must have kept on pumping. Correct?

No, I just kept pumping and pumping and grabbed another tube and.......:rolleyes: really? the first 1/4" of grease coming out was followed by a little air burp, and so one more half stroke after that to confirm no more air was in there, then cleaned out the threads to prevent hydraulic pressure upon re installation of the zerk.
 
WOW!!

Almost as many parts as engine itself.

Good work Bill.

I still dream about upgrading to CS from FP, what a kick in butt that would be with the 8!

dd
 
Back
Top