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  #11  
Old 01-29-2008, 08:09 PM
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lluciani lluciani is offline
 
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Location: Tomball, TX
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Default

My floor vibrated a lot for first few flights. I moved the exhaust pipes around and found that with them angled down and out almost touching the bottom outside corners of the center part of the cowl, the vibration went away.

Luis Luciani
RV8 N188LC - Phase 1
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  #12  
Old 02-13-2008, 01:35 PM
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Andy Hill Andy Hill is offline
 
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As Lusi says, our RV-8 experienced Test Pilot observed some vibration on our floor. His advice was to lower the pipes as far as possible, which we did, which has largely if not completely removed the vibration ....

Andy & Ellie Hill
RV-8 G-HILZ
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  #13  
Old 02-14-2008, 06:10 AM
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atreff atreff is offline
 
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Default Raise the Fn with Stiffeners

I too wanted to minimize any floor vibration in the ramp area, so I did what I could to raise the resonant or natural frequency (Fn) of the metal in that area.
I ruled out any material that could absorb moisture, fuel or oil. Instead, I riveted three stiffeners to the backside of the ramp and to further dampen it, I spread a layer of ProSeal on the backside of the skin.

To top it off, I riveted the trailing edge of the ramp, and eliminated the pivot point, the hinge. IT ain't easy, ,but it's permanent. And, since the ramp was now permanent, I prosealed the edges where they meet the other floor skins.

I"m flying now, (hi compression pistons Angle Valve and 2" crossover exhaust) and i have no floor vibration under my feet.

Art Treff
N666AT "Lil Snorkey'
RV-8 Fastback
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  #14  
Old 05-21-2009, 08:50 AM
Wild Blue Wild Blue is offline
 
Join Date: Nov 2006
Location: St. Petersburg
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"Secondly, after only 50 hrs. I noticed cracking at the rivets at each end of the F-867-D stiffener at the center of the ramp."

I have the same issue on my 8A. Vibrations are most notable at approach speeds/RPM.

Looking for a solution

N717WB
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  #15  
Old 05-21-2009, 10:55 AM
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RVG8tor RVG8tor is offline
 
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Location: McKinney, TX
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Default Proseal

Wild Blue,

I am at the stage on my QB, riveting on the exhaust ramp. The plans call for using proseal along the siffeners to help prevent cracking. My kit is a fairly new one only 1.5 years since I picked it up. I was wondering if you used proseal when yours was built and do you think using it would help if you did not. Thanks.

Cheers
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  #16  
Old 05-21-2009, 03:09 PM
chaskuss chaskuss is offline
 
Join Date: Mar 2005
Location: SE Florida
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Default Another thread

Quote:
Originally Posted by RVG8tor View Post
Wild Blue,

I am at the stage on my QB, riveting on the exhaust ramp. The plans call for using Proseal along the stiffeners to help prevent cracking. My kit is a fairly new one only 1.5 years since I picked it up. I was wondering if you used Proseal when yours was built and do you think using it would help if you did not. Thanks.

Cheers
Mike
Yes, I used ProSeal in this area. Vans recommends it due to the corrosive nature of the exhaust gases which will accumulate between the floor skin and the ramp. I used a very thin bead of it, because I made my ramp removable, to check for corrosion and to ease replacement, if it should crack. I would suggest you check out the thread below

http://www.vansairforce.com/communit...t=exhaust+ramp

Charlie Kuss
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  #17  
Old 05-21-2009, 07:19 PM
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Vern Vern is offline
 
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Location: Peachtree City, Ga
Posts: 1,040
Default Floor vibration

It's not just the 8's that have this phenom. The side by sides do also. Typically some 3/4" black foam sound prof from Spruce with a thin carpet over it takes care of the problem.
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  #18  
Old 05-21-2009, 08:46 PM
chaskuss chaskuss is offline
 
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Location: SE Florida
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Default Won't work

Quote:
Originally Posted by Vern View Post
It's not just the 8's that have this phenom. The side by sides do also. Typically some 3/4" black foam sound prof from Spruce with a thin carpet over it takes care of the problem.
Vern,
You offer great advice. However, it does not carry over to our 8s and 8As. We have a floor skin ABOVE the belly skin. These two skins are separated by a set of floor ribs.



This is a view of the forward cockpit sitting upside down in the jig [canoe stage]. The area with the gray finish paint is the forward cockpit floor [viewed from the bottom]. The yellow primer area is the forward belly skin. The parts connected via silver Clecos to the belly skin are the inboard floor support ribs for this area. There are also a pair of outer floor support ribs.
This floor above the belly setup, continues all the way back to the rear baggage compartment.

Charlie

Last edited by chaskuss : 12-11-2012 at 07:01 AM. Reason: Added photo and explanation
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  #19  
Old 05-21-2009, 09:11 PM
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AlexPeterson AlexPeterson is offline
 
Join Date: Sep 2005
Location: Maple Grove, MN
Posts: 2,334
Default Prop pulses vs exhaust pulses?

Caveat - I have a 6A and not an 8. In any case, how does one determine if the pulses are related to exhaust or if they are related to prop pulses? I know in my 6A, at slower speeds, I can feel the prop pulses in the elevator if it is being pulled aft a bit, such as during rotation. Indeed, many earlier RV's with the .016" rudder and elevator skins exhibited cracks at the forward ends of the stiffeners, mine included. Yes, this is a weak area, but it clearly is not exhaust pulses doing this. I can also feel pulses in the side walls at various speeds/rpms.

Just something to think about. I seem to recall several years ago that a certain exhaust manufacturer ran the pipes all the way to the spar, just to see how much of the floor vibration was due to exhaust. Didn't make any appreciable difference, so his conclusion was that it was primarily the prop pulses.

I also have watched video of a tufted cooling exit area. Not a real pretty site, with yarns flopping every which way. And, this is in front of the exhaust pipes.
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