Help please - floor vibration

hevansrv7a · #1 11-12-2006, 04:19 PM

I finally got my wife to take her first ride in N17HH. After a couple of minutes I looked over and saw she had her knees up to her chin and her heels on the spar box cover. She complaned that the floor vibration was like a dentist's drill. I knew from riding in my CFI's -6 that it is just the exhaust causing it.

OK, it's normal. What's the best way of damping it without using fire-inappropriate materials?

Please and thanks, gang!

AlexPeterson · #2 11-12-2006, 04:37 PM

It is conventional wisdom that the floor vibrations come from the exhaust. However, here is some contrary data: Larry V. extended the pipes all the way to the main spar on a -6 or -7, and the vibration did not go away. His conclusion is that a lot of it is from prop pulses. No doubt others have had different experiences.

gmcjetpilot · #3 11-12-2006, 05:22 PM

Quote:

Originally Posted by AlexPeterson

It is conventional wisdom that the floor vibrations come from the exhaust. However, here is some contrary data: Larry V. extended the pipes all the way to the main spar on a -6 or -7, and the vibration did not go away. His conclusion is that a lot of it is from prop pulses. No doubt others have had different experiences.

That is interesting and believe it, prop wash and aerodynamics cause vibrations.

One thing you might try is vibration/sound deadening mat. Unfortunately the more effective the mat is the absorb vibration/noise, the heavier it is, but it will dampen the vibrations. There are a lot of good products out there. Here is one I saw today:

http://powerblocktv.com/sites/redire...t_hushmat.html direct http://hushmat.com

Here's another: http://www.soundproofing.org/index.html prices: http://www.soundproofing.org/sales/prices.html

I know what you are talking about. The RV-6/7/9 has a large wide expanse of floor real estate to vibrate. I personally did not think it was super disagreeable in the side by's I flew. I did not insulate my first RV, a dash 4. Did you put all the rivets in your RV-7?

Congrats, fly safe. G

PS Weight counts, the vibration damping mat must have mass to change the floors response to vibration, since it is a fairly low frequency vibration.

L.Adamson · #4 11-12-2006, 05:37 PM

I know of a "6" that didn't have two floor stiffiners attached to the main spar with the angle pieces. It did a nice job of vibrating untill installed. I'm just mentioning this is case, as I have no idea of the inner workings of the "7".

Bryan Wood · #5 11-12-2006, 05:46 PM

How long is your exhaust? I cut mine in an attempt to pick up some speed and for the most part all I got was a floor constantly working under our feet. I added the length back and the vibration went away. Did you shorten yours?

Best,

Harvey L. Sorensen · #6 11-12-2006, 05:59 PM

Aircraft Spruce sells a black foam rubber sound deadner insulation. I placed that in between the ribs in the floor. 3/4" thick as that is what the ribs are. Over that I have 1/4" ply wood for the floor and I have no floor vibration at all. I also run exhausts with dual mufflers. These are the pipes that are made by the company that makes the exhaust pipes for the RV-10. I know most people think Veterman makes the RV-10 pipes but when I bought these pipes this company had just recieves a large order for -10 pipes from Vans.

Bob Axsom · #7 11-12-2006, 06:16 PM

I bought the black foam sound proofing material from and some red carpet from GBI Sales (George and Becki Orndorff). I put in the gussets from the floor stringers to the spar bolts in my RV-6A, cut and glued the black foam between the floor stringers with 3M Super 77. Then I cut and glued the carpet on top of the foam with 3M Super 77 spray adhesive. I have never felt a thing from the floor.

Bob Axsom

hevansrv7a · #8 11-12-2006, 06:36 PM

For those questions, I built a QB and used Van's FW-FWD kit exhaust unmodified. I am pretty sure it's just the normal vibration. It doesn't bother me, but my wife is often sensitive to things I don't notice.

Your suggestions seem very practical and effective. THANKS.

penguin · #9 11-12-2006, 09:45 PM

Make sure the tail pipes make at least a 25 degree angle with the fuselage floor, also if there is any exhaust staining on the fuselage the angle is not large enough. You could also try using Barry or Lord engine mounts (from someone like skygeek) rather than the ones Van's supplies.

Pete

RV7Guy · #10 11-12-2006, 09:50 PM

If it is buzz type vibration, it could be several things. Have you had the prop dynamically balanced? Check the spinner mounting and backplate. Anything loose could cause a high freq vibration.

I'd rule out these things first as they could lead to more problems down the road. My vibration was minimal but improved when I had the prop done.

Finally, the flooring foam from Flightline interiors took care of the rest. I also used some of the black stuff from Spruce in the fuselage aft to dampen the noise.