Engine Vibration

SixPapaCharlie

SixPapaCharlie

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I am chasing a vibration issue and am looking for some input.

Lycoming 540 / 3 Blade Hartzell prop
I have been experiencing a vibration in my engine that tends to increase when I increase the prop pitch. I don't notice the vibration on the ground.

1. Prop out of balance? - I had the prop balanced a couple months ago and got it down from a 0.48 to a 0.06
2. Bad engine mounts? - Next, I had the engine mounts replaced with new Lord mounts.
3. Induction Leak? - Then, I have all the intake gaskets replaced.

The behavior as best I can tell
On the ground it runs like butter.
There are times when it isn't there at all best pattern I can pick up on is really cold days, climbing out, low.

This is something fairly new as the first year I had the plane, I never noticed it. I went back and reviewed some videos from when I got it and I don't see visors / ipad shaking at all.
Now it is a pretty constant thing. I am not seeing any performance issues and at annual in July, the compressions were all very good.

Any thoughts on what things can lead to vibration that haven't been addressed and how to test for them?

Thanks,



Screenshot 2023-12-31 095040.png
 
SixPapaCharlie said:
I am chasing a vibration issue and am looking for some input.
...
Any thoughts on what things can lead to vibration that haven't been addressed and how to test for them?
Click to expand...
Knowing the frequency of the vibrations can tell you a lot about potential sources. An integer multiple of RPM points to engine/prop (3x says prop), some other value points to other things like (e.g.) resonant vibration of a skin, control surface freeplay. Worth noting that these can also be excited by RPM, so RPM-related alone does not conclusively mean engine related, but it's a strong indicator.

Nauga,
and Lionel Hampton
 
SixPapaCharlie said:
Any thoughts on what things can lead to vibration that haven't been addressed and how to test for them?
Click to expand...
Are you sure its the blades and not some other "loose" item(s)?

Once you have performed a thorough tactile check of the entire aircraft, there are some things to look at. The blades could be going out of track as you change pitch, ie, the load increases on the blades. Or its possible one of the blades has a different CG which can affect the balance. The only way I know how to check for this outside of going to a prop shop to check feather movement, etc. is to reinstall the prop balance gear and go fly, checking the balance at different flight attitudes and power settings. Unfortunately not all balance providers will fly with their gear installed.
 
As mentioned, knowing more about the vibration and its frequency can narrow down the potential sources to look at. If you have someone that can help you determine that, it is where I’d start.

But another thing to think about is what changed from the time that there was no vibration to now. Was any major airframe, engine, or propeller work performed that may have induced a problem?
 
nauga said:
Knowing the frequency of the vibrations can tell you a lot about potential sources. An integer multiple of RPM points to engine/prop (3x says prop), some other value points to other things like (e.g.) resonant vibration of a skin, control surface freeplay. Worth noting that these can also be excited by RPM, so RPM-related alone does not conclusively mean engine related, but it's a strong indicator.

Nauga,
and Lionel Hampton
Click to expand...
Will you come flying with me

Bryan,
I am not the smartest one in the room
 
There are certain things you can look at on your own.

Is there any oil on the blades, and is it pink when wiped with a white paper towel? How about the wind screen?

Can you wiggle any of the blades fore-aft? Twist?

Turn a prop blade to 6 o’clock. Place a block of wood right behind the blade just barely not touching it. Then turn the prop and see if the next blade is exactly the same distance from the block.

This should give you some prop based knowledge to follow-up or rule out while your A&P is on vacation.
 
mondtster said:
As mentioned, knowing more about the vibration and its frequency can narrow down the potential sources to look at. If you have someone that can help you determine that, it is where I’d start.

But another thing to think about is what changed from the time that there was no vibration to now. Was any major airframe, engine, or propeller work performed that may have induced a problem?
Click to expand...

No changes.
I mean, I had hinges replaced on my cowl because 4 were worn pretty good.
I added a new seal to the cargo door as the prior was rotten.

In my most amature way to confirm it was the engine, I pulled power to idle and dove to build up some speed and see if I get the same vibration but did not. This was my attempt to determine if it was an airframe thing.

I am thinking of putting a gopro on the belly to look for anomalies (gear door fluttering or something) It really "feels" like engine or propeller but I don't know what satbilator trim jiggle or some other loose part would feel like.
 
455 Bravo Uniform said:
There are certain things you can look at on your own.

Is there any oil on the blades, and is it pink when wiped with a white paper towel? How about the wind screen?
No
Can you wiggle any of the blades fore-aft? Twist?
I will try this
Turn a prop blade to 6 o’clock. Place a block of wood right behind the blade just barely not touching it. Then turn the prop and see if the next blade is exactly the same distance from the block.
I will try this
This should give you some prop based knowledge to follow-up or rule out.
Click to expand...
Thanks.
 
It's probably nothing, but I'm new to flying behind a 540. One of the things I saw in the Lycoming operating instructions was to be very deliberate and slow with throttle inputs.

I doubt this is an issue for you, but something to keep in mind.

OPERATING IN FLIGHT.
a. Subject engines are equipped with a dynamic counterweight system and must be operated accordingly. Use a smooth, steady movement (avoid rapid opening and closing) of the throttle.
 
Bryan:

when you write, “when I increase the prop pitch,” do you mean “increase rpm“ (which means decreasing the prop pitch)?
 
SCCutler said:
Bryan:

when you write, “when I increase the prop pitch,” do you mean “increase rpm“ (which means decreasing the prop pitch)?
Click to expand...

When I rotate the blue knob out to reduce my RPMs.

When it's flatter and faster I don't get the vibration as much. Climbing out it's either not there or barely noticeable It's when I adjust for cruise. And if I go below 2400 RPM it just gets more pronounced
 
Dave Theisen said:
Signature line not necessary. :)
Click to expand...
dayum.gif
 
Total stab in the dark, but in a car high load low rpm is when ignition problems like misfire show. If other things don’t help maybe look at mags/wires/plugs???
 
Not an A&P (as I assume you know), so take this with a grain of salt - but issues with counterweights can cause vibration to the point that the crank can break (happened to one of the old man's Navions). Ask your A&P about it.
 
You can check the stabilator bearings for wear by simply grabbing the end of the stab and lifting it up and down. You should feel no play, zero. You can do the same thing with the trim tab, hold the stab down with the palm of your hand and try to move the trim tab up and down, again, there should be zero play. If those are good, the vibration isn't coming from the tail feathers.

If recall, you have wing root fairings, correct?
 
Chip Sylverne said:
You can check the stabilator bearings for wear by simply grabbing the end of the stab and lifting it up and down. You should feel no play, zero. You can do the same thing with the trim tab, hold the stab down with the palm of your hand and try to move the trim tab up and down, again, there should be zero play. If those are good, the vibration isn't coming from the tail feathers.

If recall, you have wing root fairings, correct?
Click to expand...
Yes
 
I'm assuming it's not a good, good, good, good vibration?
 
SixPapaCharlie said:
I mean, it tickles but I don't think it's supposed to
Click to expand...

You say you changed the lord mounts, did you have the mount itself inspected? A crack developing there might contribute to an itinerant vibration.
 
Certain engine/prop combinations are prone to harmonic vibrations at certain RPM. My Decathlon with AEIO-360 and Hartzell CS prop is placarded to avoid operation at 2000-2300 RPM due to excessive vibration.

Before you get too deep in troubleshooting, do some controlled experiments to see how the vibration is related to operating conditions and power settings such as RPM, MP, mixture, etc.
 
giphy.gif



Sent from my iPhone using Tapatalk
 
When the tail horn inspection was done, were the trim drum bushings inspected for wear? Again, this is an item where no play is allowed. Unlikely the cause of your problem since you would first feel the vibrations in the flight controls, but since you brought it up...
 
1. Don’t ignore this. If it feels like something is different it probably is. Once you get to a certain point of familiarity in your plane, the little clues shouldn’t be brushed aside.

2. It does sound more engine related to me, but hard to tell without hearing or feeling it.

3. I’d mainly see if others who own Commanches have more input. A bunch of non-Commanche pilots aren’t the knowledge base you need for this, IMO. Maybe similar engine/prop setups as well.
 
Went up with an A&P who flies a 260 yesterday.
He said the vibration is noticeable but he wouldn't lose sleep over it. We did an in air mag check and no difference.
He noted that my aileron control end bearings had more play than he likes. He said there was a touch of play in the trim so he replaced a worn bushing and tightened that up.

He asked me to confirm the counterweights were installed with the prop which I believe I looked up once before but am about to confirm.
His take was it is prop / engine / harmonic and not any sort of flutter or control surface issue. We pulled the engine to idle and dove to gain speed and didn't notice the vibration.

It definitely gets more pronounced when the prop pitch in increased down to 2200 - 2300 RPM
We went through all the books and there are a lot of notes about not running it from 2250-2275 due to harmonic issues.
We found many others with this engine prop combo chasing the same issue.

He wants to reclock the prop and see if that helps but it doesn't answer why it hasn't always been there.

I had the thought maybe I never noticed it early on because "new to me plane" and not focuses on little nuances.
I went through videos and the camera doesn't pick it up so new flights look like old flights on a little GoPro.

For grins, I am going to put a camera on the belly just to make sure something like a gear door isn't hanging down and flapping in the wind.

I can't prove it but I do believe I started to notice this about a year ago. March 5th 2023 is when I had the prop balanced which was the first step toward chasing this.
 
We did a poor mans "blade alignment test" made sure when each blade was vertical the distance to the tip trailing edge was the same for all 3 blades. This isn't a precise way to do it but ballparking it nothing was more than 1/8 difference but the margin of error using a yardstick and a level is likely that or more. but nothing obvious with respect to blade position.

Not able to twist any of them by hand either.
 
SixPapaCharlie said:
His take was it is prop / engine / harmonic and not any sort of flutter or control surface issue. We pulled the engine to idle and dove to gain speed and didn't notice the vibration.
Click to expand...
Hitting the same airspeed at a different RPM with no vibration might tell you it's not related to dynamic pressure but it doesn't rule out something in the structure that's excited by the engine. As long as you have the luxury of time looking at the gear doors is a good idea before trying to fix it by fixing something that someone else had a problem with on a different airplane.

Are you certain it wasn't there before you balanced the prop but masked by worse vibes the balance addressed? I think you already covered this.

Nauga,
with Johnny Kidd and the Pirates
 
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SixPapaCharlie said:
It definitely gets more pronounced when the prop pitch in increased down to 2200 - 2300 RPM
We went through all the books and there are a lot of notes about not running it from 2250-2275 due to harmonic issues.
Click to expand...

Not at all unusual. Here's my factory tach. Note the red arc from 2000 to 2250.
PXL_20231229_225955832~2.jpg

Reminds me of the joke about the guy who goes to his doctor about shoulder pain. He twists his arm above his head and says "doc, it hurts when I do this". The doctor replies, "well, don't do that!"
 
SixPapaCharlie said:
I can't prove it but I do believe I started to notice this about a year ago. March 5th 2023 is when I had the prop balanced which was the first step toward chasing this.
Click to expand...
Here's proof

www.pilotsofamerica.com

Engine vibration

Over the last few months, I have noticed a vibration that I don't recall being there before. No changes have been made to anything. I am scheduled for a prop balance next week but the MX said "3 blade prop on the Lycoming 540 sometimes vibrates and you might not be able to get rid of it."...
www.pilotsofamerica.com www.pilotsofamerica.com
 
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Ed Haywood said:
Not at all unusual. Here's my factory tach. Note the red arc from 2000 to 2250.
View attachment 123875

Reminds me of the joke about the guy who goes to his doctor about shoulder pain. He twists his arm above his head and says "doc, it hurts when I do this". The doctor replies, "well, don't do that!"
Click to expand...
Christmas colors (red & green). How festive. But how are you supposed to go from idle to 2400 without being in the red?

Grumman Tigers have a yellow in that region.
 
Have you changed anything else? Pulled the carpet, maybe the seats, replaced a battery? I'm wondering if something is tight that wasn't before, or something is loose that was tight before, or something is resting against something it was either hard against or completely separated from before. My RV-6 has a noticeable change in interior noise/resonance if the passenger moves his/her feet. Startled me several times (WHAT's THAT NOISE?!!) before I/we identified the cause.
 
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