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  #1  
Old 11-17-2017, 05:05 PM
jwilbur jwilbur is offline
 
Join Date: Dec 2010
Location: Culpeper, VA
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Default remove baffle material

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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Last edited by jwilbur : 11-18-2017 at 09:19 AM.
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  #2  
Old 11-18-2017, 09:14 AM
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Phil Phil is offline
 
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Location: Waco, Texas
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Default

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?
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  #3  
Old 11-18-2017, 09:18 AM
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rzbill rzbill is offline
 
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Location: Asheville, NC
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Quote:
Originally Posted by Phil View Post
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???
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  #4  
Old 11-18-2017, 09:29 AM
jwilbur jwilbur is offline
 
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Location: Culpeper, VA
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Default

Quote:
Originally Posted by Phil View Post
Assuming 4000 is meant to be 2400?
Yep. That was a typo that I've now corrected.

Quote:
Originally Posted by Phil View Post
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.

Quote:
Originally Posted by rzbill View Post
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)?
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  #5  
Old 11-18-2017, 10:23 AM
rocketman1988 rocketman1988 is offline
 
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Location: Sunman, IN
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Default 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...
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  #6  
Old 11-18-2017, 10:40 AM
jwilbur jwilbur is offline
 
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Location: Culpeper, VA
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Quote:
Originally Posted by rocketman1988 View Post
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.

Quote:
Originally Posted by rocketman1988 View Post
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.
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  #7  
Old 11-18-2017, 11:06 AM
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Phil Phil is offline
 
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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.
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  #8  
Old 11-18-2017, 11:08 AM
BobTurner BobTurner is offline
 
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Location: Livermore, CA
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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.
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  #9  
Old 11-18-2017, 11:11 AM
jwilbur jwilbur is offline
 
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Location: Culpeper, VA
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Quote:
Originally Posted by Phil View Post
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.
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Phase II - 11/2017
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RV-10 Build Log
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  #10  
Old 11-18-2017, 11:17 AM
BobTurner BobTurner is offline
 
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Quote:
Originally Posted by jwilbur View Post
It's good to know mine isn't the only one like this. But I don't think it should behave this way.
I trimmed 1/8” off, vibration went away.
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