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remove baffle material

jwilbur

Well Known Member
I've got an annoying vibration. When I set high power and lower the RPM below 2350 it becomes noticeable. Lower the RPM and it gets worse. By 2200, it's really bad where I can feel it in my feet. I won't go lower. Raise the RPM to 2400 and you can't feel it at all - even at takeoff power. At lower power levels, no apparent vibration.

I think it may be the baffle material just behind the prop governor. It's not hard up against the cowl and I can flop it when I reach my hand into the air inlet. I think the prop blast is smacking it around more and more as the prop pitch increases.

I'm thinking about running a little experiment and just remove that piece of aluminum and fabric baffle material. That segment of aluminum is fairly easy to remove. But I'm concerned about unintended consequences. Weather is cool enough that I don't think I'll have CHT issues - especially on a short flight. But can anybody think of any other issues removing this piece of aluminum might cause?
 
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Assuming 4000 is meant to be 2400?

What’s your Manifold pressure? There’s a good chance you are going way over square and that’s what you’re experiencing.

There’s technique in flying a CS prop and going well over square isn’t a good practice and can aause damage.

Curious what your MP is while reducing the RPM’s?
 
Assuming 4000 is meant to be 2400?

What?s your Manifold pressure? There?s a good chance you are going way over square and that?s what you?re experiencing.

There?s technique in flying a CS prop and going well over square isn?t a good practice and can aause damage.

Curious what your MP is while reducing the RPM?s?

Really?? Remind me how turbocharged engines make extra power???
 
Assuming 4000 is meant to be 2400?
Yep. That was a typo that I've now corrected.

There’s technique in flying a CS prop and going well over square isn’t a good practice and can cause damage.

Curious what your MP is while reducing the RPM’s?
I do fly over-square.

Really?? Remind me how turbocharged engines make extra power???

I also believe the whole over-square thing is a myth. But please let's not get into a debate about that. My question is simple. If I remove the portion of baffling aluminun just behind the prop governor and prop, will I cause some other bad problem that I'm not thinking of? Or will a short flight with this removed be a non issue in these fall temperatures (surface OAT in the 40s)?
 
Baffle

If you remove that piece of baffle, you will most likely reduce the differential pressure between the upper and lower portions of the cowl reducing your cooling capability. How much remains to be seen.

Could you look at conversely and possibly use a piece of duct tape to ensure the baffle material seals, instead? Then fly it and check for the issue?

Just thinking out loud...
 
If you remove that piece of baffle, you will most likely reduce the differential pressure between the upper and lower portions of the cowl reducing your cooling capability. How much remains to be seen.

Someone else privately warned me of the same thing.

Could you look at conversely and possibly use a piece of duct tape to ensure the baffle material seals, instead? Then fly it and check for the issue?

Just thinking out loud...

I suppose I should just fix it. Whether or not it's the primary source of my vibration it needs to be fixed. It seems to be a tough spot to get "right". The way the baffling material has to bend, I can't quite visualize how to lay it so it seals tightly.

I read that some people have had success fixing or reducing an RV10 vibration by re-clocking the prop. I'm really hoping that I don't need to do that.
 
My 540 behaves similarly when it's deeply over square. If I'm running 2400 and 27", then it's fine. But when you start slowing the prop down it will start barking and letting you know by shaking. Going all the way down to 2200 really shakes it.

It seems like, as long as the prop is turning higher RPM's and the produced energy has a place to go, it wants to run fine. But when that prop gets slow it sure doesn't like it when it has a hard time expending the energy.

YMMV, but mine behaves very similarly.
 
I had something similar - vibration at lower rpm. IIRC I tracked it down to a metal part of the ramp baffle being a fraction to big - it was touching the cowling instead of the flexible material.
 
My 540 behaves similarly when it's deeply over square. If I'm running 2400 and 27", then it's fine. But when you start slowing the prop down it will start barking and letting you know by shaking. Going all the way down to 2200 really shakes it.

It seems like, as long as the prop is turning higher RPM's and the produced energy has a place to go, it wants to run fine. But when that prop gets slow it sure doesn't like it when it has a hard time expending the energy.

YMMV, but mine behaves very similarly.

It's good to know mine isn't the only one like this. But I don't think it should behave this way.
 
I had something similar - vibration at lower rpm. IIRC I tracked it down to a metal part of the ramp baffle being a fraction to big - it was touching the cowling instead of the flexible material.

This is actually interesting that you had a problem here. I happen to know that I have a spot where the ramp baffle is too close. My last few flights have been without the rubber material on the lower inlets at all. The metal part actually cut the material on one side so I temporarily removed it! (Seems to have no impact on my CHTs, by the way.) In addition, where the baffle metal curls up on the side, I know it's touching the top cowl in one spot. Just didn't click with me it was a problem until you wrote this. I'll be surprised if this isn't the actual source of my vibration.

Thank you!!
 
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I had something similar - vibration at lower rpm. IIRC I tracked it down to a metal part of the ramp baffle being a fraction to big - it was touching the cowling instead of the flexible material.

Bob,

This was it. I trimmed the ramps (including the vertical portions) and went for a flight today. Vibration gone. Dialed it all the way down to 2100 and it was smooth running all the way. What a relief. That vibration has been dogging me since the start.

I must have had the cowl on and off a few dozen times since first flight. And each time I installed, I fought getting the cowl around those inner vertical baffle pieces. Amazing what doesn't compute when you're expecting a problem to be somewhere else. Not only is the vibration gone, but installing the cowl is a lot easier.

Thank you again for taking the time to post.
 
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