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floridawing

Well Known Member
Hello, I have a RV6 with a o-320. I do not have any carpet on the floor or sidewalls. It has about 200 hours total. The floor vibrates really bad in flight and I am starting to see some of the rivets attaching the floor starting to smoke! Most of the RV6 I see have carpet and side panels. Will adding carpet help stop the vibration and stop the smoking rivets.If carpet will not help I would like to keep the basic look. I do not want to replace these rivets. I have read some post on checking the exhaust which I will do. Thanks for your help.
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Aren't those the rivets along the main spar carrythrough bulkhead?

Can you confirm that the braces that tie the center section to the floor pan are installed? On one end, they attach to the fore/aft stringers on the cockpit floor and on the other end, they are bolted to the spar.

I always thought the drawings representing those braces would be easy to miss or mis-interpret.
 
Vibration

You should probably have your prop balanced and see what that does for the vibration.
 
Kyle Boatright said:
Aren't those the rivets along the main spar carrythrough bulkhead?

Can you confirm that the braces that tie the center section to the floor pan are installed? On one end, they attach to the fore/aft stringers on the cockpit floor and on the other end, they are bolted to the spar.

I always thought the drawings representing those braces would be easy to miss or mis-interpret.
Click to expand...

I've seen those left out, and it certainly vibrates. I have carpet in my 6A now, but it wasn't bad vibration wise, before the carpet was installed.

L.Adamson --- RV6A
 
However...

floridawing said:
Thanks everyone for your help.I will look for the braces. I bought this already built.
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...the braces are inboard on the fore-aft angles on the floor boards.

I would think no braces would smoke inboard rivets, not the outboard ones you picture.

Does it look like the rivets may have been initially under-driven?
 
what kind of prop do you have? Metal or wood? How many blades? Constant speed or fixed? Are you using auto gas? The back side of the wing drain looks like auto gas stains... More info.
 
Four attachments

Gil didn't mention this but, in addition to the two small F-699 brackets, the floor also attaches to the spar via the fuel selector assembly legs. The legs are bolted to the spar and riveted(or bolted) to the inner floor ribs. The 699s attach the outer rib on each side.

That way each of the 4 floor ribs is attached to the spar. It would be easy to forget the inner rib attachments as well.

I looked long and hard for the description of the 699s; it is in a small corner on DWG 46.

Dave A.
6A build
 
No matter what might be missing, you will have to remove and replace those rivets. You might even have to go to a 1/8 rivet. Find a local builder, he (or she) will have everything you'll need to get it done right.
 
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az_gila said:
...Does it look like the rivets may have been initially under-driven?
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Sometimes the plans call out rivet lengths that may in fact, be a bit too short. When it comes to smoking rivets, the first thing I immediately examine is the quality of the rivet shop heads. In your case, are the rivets bucked properly so the shop heads are acceptable per spec? Have you checked the rivet shop heads with a rivet gauge? Is the stackup of all the parts (if applicable) the smoking rivets tie into such as the skin, stiffener, rib, bracket etc. nice and tight? Finally, can you provide us with a good detail photograph of the rivet shop heads?
 
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Brake fluid

I spilled some brake fluid while bleeding that made it between the floorboards and the belly before I could clean it up. Looked like smoking rivets but it was just the oil. It attracked exhaust and made it look that much worse. Worse on one side like yours because of uneven ground where hangered. Just something to check before you get too excited.
 
Exhaust pipes!

Are your exhaust pipes straight, or are they bent down on the exit? If they are straight the exhaust pulses can create quite a bit of vibration on the floor. My RV4 made smoking rivets on the belly skin only.

Steve Barnes "The Builders Coach"
 
If your pipes are almost straight back, you can make the noise pulses bend down and away from the end of the pipe by slicing the end of the pipe at an angle of 30* to 45*. (BTW, Mel, I tried the ALT 0176 and it didn't work for me) It works by refraction based on Snell's law from the difference in sound velocity in the pipes vs in the air.
 
Couple questions...are those rivets Countersunk or Dimpled? Are they #3 or #4 rivets?

This phenomenon was very, very common and has been discussed at length over the last 15 years or so....just to let you know you're not alone and not the first.

Go over to the matronics list and do a search, you'll find literally hundreds of posts on the subject along with the discussed fixes. Some replaced with button heads, some upsized them to 4's if they had 3's, some just added another row, etc..

Anyway, like I said nothing it's new on the older 4's and 6's.

Cheers,
Stein
 
Thanks for the help, I will do a search. I am out of town but when I get back home I will take a closer look at the rivits. Everyone on the board is a great help. Thanks.
 
Stein, I believe the main location...

SteinAir said:
Couple questions...are those rivets Countersunk or Dimpled? Are they #3 or #4 rivets?

This phenomenon was very, very common and has been discussed at length over the last 15 years or so....just to let you know you're not alone and not the first.

Go over to the matronics list and do a search, you'll find literally hundreds of posts on the subject along with the discussed fixes. Some replaced with button heads, some upsized them to 4's if they had 3's, some just added another row, etc..

Anyway, like I said nothing it's new on the older 4's and 6's.

Cheers,
Stein
Click to expand...

...for smoking rivets was actually at the lower firewall, not the spar bulkhead.

However, the stack up on the front row of rivets shown is

0.040 floor skin
0.025 skin under seats
0.063 F-604

In this case, the -5 rivet length is actually a good callout.

If the floor skin was dimpled, the thickness could cause problems for a stacking fit, but I think most folks countersunk.
If countersunk, then a slight cutting too deep could certainly cause loose rivets.

Since this is quite a structural joint, the best fix might be a switch to 1/8 countersunk rivets. You could even add the extra rivets at half the original spacing, leaving in the "loose" rivets, and not violate the minimum rivet pitch.

If those rivets are truly smoking, I'd say to replace them.
 
az_gila said:
...for smoking rivets was actually at the lower firewall, not the spar bulkhead.

If those rivets are truly smoking, I'd say to replace them.
Click to expand...

That's partly true, but not entirely. We've fixed more than one of these with the same problem so I'm not making it up...as I said, been there done that! Anyway, I'd have to see it in person before I recommended a fix and I'd probably talk to Van's first. As I said before, this isn't the first time and it isn't altogether unheard of either. We've had a lot of RV's through my shop/hangar over the years & decades and I'm not too surprised by seeing this. There isn't always one specific cause nor one specific fix that is a catch all. Depends a lot on the builder, components, installation, etc.. Gill is one the right track though, something should be done.

My 2 cents as usual.

Cheers,
Stein
 
elippse said:
If your pipes are almost straight back, you can make the noise pulses bend down and away from the end of the pipe by slicing the end of the pipe at an angle of 30* to 45*. (BTW, Mel, I tried the ALT 0176 and it didn't work for me) It works by refraction based on Snell's law from the difference in sound velocity in the pipes vs in the air.
Click to expand...

30? to 45?. Did you try holding down ALT while keying in 0-1-7-6, then releasing ALT, using the numeric keypad digits?
 
Exhaust Angle

Sorry to be late on this discussion, but my floor also vibrated badly when I bought my airplane - as Paul & Steve suggested it was due to the angle the exhaust made with the floor. Larry Vetterman recommended that the angle should be at least 25°, and also that there should be no exhaust staining on the fuselage. Larry re-built my pipes at a very reasonable price - vibration was much improved.

Pete

PS Thanks for the ALT0176 hint!!
 
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Hey! Look at this: 30?! Thanks to you, Jonathan, and to Mel. I had previously used the numeral keys on the main keyboard.
 
Thanks for the help. When I can get out to the hanger I will begin to look at the items that the board members have suggested. Lots of great information. I appreciate it.
 
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