Floor Vibration F-867

I am researching ideas to eleminate noise and vibration transferred through the cooling ramp and 822 floor plate. I have an idea and have played around with it a little already but would like to know what the general population thought of it before I make it a go in my head.

I have some 1" thick Refactory ceramic fiber which looks like tight fiberglass weave. This stuff is to contain heat when melting metal in the casting process. This stuff is inches away from 2700 degree molten metal and you only get a little shrink out of it. That's it! Someone mentioned this stuff possibly breaking down over time.
My approch to this was to cut this material to size. Use contact spray(3M) to adhere it to the ramp and spray a little coaton the material itself to seal the fibers on the blanket then proseal the ramp in with rivets. Proseal sealing out any liquids.

Let me know what you think and if all this is even worth the trouble.

Bruce Gray
RV8 Fuse

Ideas

Hello

I would think the best material to use would be high density foam or vibration dampening material.

I plan the inject high density expanding foam into the are, I also will have a stainless sheet riveted to the bottom of the ramp, but I don't think this area is going to get too awfully hot anyway. The stainless is there for my future speed mod tinkering.

Another good material is ISODAMP. It is lead foam that does an incredible job at reducing vibration, and comes in very light sheets and is not terribly expensive. I bought 2 sheets for the cockpit area and 1 sheet of the firewall application material . Unfortuately, I didn't think about using it under the cooling ramp until after I already put it together.

Good luck

Vibration from, I presume exhaust pulses drumming on the ramp, is indeed an issue with RV-8's. I built my 8-A exactly as shown in the plans and have noted two problems. First, there is a very significant noise/vibration coming from the floor at cruise. This can be dampened significantly by judicious placement of your foot - in my plane in the center of the floor just aft of the rudder pedals. Works, but annoying and tedious. 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 suppose there are lots of ways to avoid this if you haven't installed the ramp yet. My first inclination would be to make up your own ramp out of heavier material and/or extend the F-867-D stiffener to tie into the F-867-B stiffeners on each side.

But what do you do if the thing is already installed, painted and flying?

Have any of you experienced and solved this problem? One idea I've seen suggested drilling a hole in the floor and squirting foam into the space between the floor and the ramp. I'm hesitant to do this because of concern about trapping moisture leading to corrosion and about long term deterioration of the foam from the heat and vibration in this area.

Other ideas anyone?

Thanks,

John Miller

noise & vibration

Wicks Aircraft Supply sells insulation-soundproofing material , it's sold by the foot 48" wide. I picked up mine at an aircraft uphoulstery shop (pay cash,lot cheaper that way) 54" wide.

RV-9 builder
G.P.

injection

I agree moisture must ne considered. Luckily I had heard about cracking problems and the entire ramp floor area I prosealed with the rivets. I would think a closed cell foam would be best, since it will not absorb moisture.

I believe you could also inject RTV, but not sure how much of that it would take.

Gary Bricker

Has anyone found a prop balancer at a good price. Our chapter is looking to buy one that maybe a a & p could use or a good experenced builder.

Reviving an old thread with a follow up.

I have no doubt that exhaust pulses are the primary cause of floor vibration and cracking of the F867 ramp. Pipes that turn down away from the ramp seem like a good idea. In addition there were several proposals to reinforce or damp the F867 assembly. One proposal was to fill the space between the floor and the F867 with expandable urethane foam. Someone mentioned the possibility of corrosion, either chemical or because the foam might trap moisture. Here's what I decided to do.

First I lined the cavity with some cheap, thin dropcloth plastic so the foam could not stick to the aluminum. I did several small pours, fastening down the "lid" while each expanded and cured (only about 15 minutes). In the end I had a 4lb density urethane foam block molded to fit the cavity.

I trimmed it a little and laid a single ply of light glass cloth on each side. Tomorrow I'll also seal the edges with some painted-on epoxy. The idea is to reinforce the block as well as seal out any way it can absorb moisture.

By the middle of the week I should be ready to install the glassed foam block for good. I'll run beads of proseal (or maybe just silicone) on the top and bottom surfaces to bond it to the F867 and the underside of the floor.

Just the foam block alone in the cavity makes the F867 and floor quite "dead". I think when bonded in with an elastic adhesive those panels will not vibrate much at all.

reviving thread

Dan,

I am reviving the thread to see how your plan to deaden the noise and vibration on the cooling ramp worked out.

Anybody else have any recent input on the topic?

Sorry Tony, not flying yet so nothing new to report. As I stand now, the molded foam is sealed in glass and will be installed with a few beads of electronics grade silicone.

thanks

Dan,

Thanks for your response. I am ready to install my cooling ramp now. I know that I need to do something about the vibration issue, I am just not sure what

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

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

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

"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

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

Another thread

RVG8tor said:

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

Click to expand...

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/community/showthread.php?t=29475&highlight=exhaust+ramp

Charlie Kuss

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.

Won't work

Vern said:

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.

Click to expand...

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

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.