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Cooling Air Ramp Cracked

Gash

Gash

Well Known Member
While giving my RV-8 a belly rub this morning (she likes that), I noticed some serious cracking along the front rivets of my cooling air ramp. It's time for a little repair.

I would like to modify the replacement parts as necessary to avoid the same cracks later. I searched on the topic here and found a couple of threads referencing stainless steel as well as a foam insert. I'm mainly interested in the foam insert. Dan Horton wrote a few years ago about his foam mod, but the photos are no longer in his posts.

Dan, do you have photos that you could re-post? Also, if anybody else has photos or experiences related to their repair, I would like to learn from you before I fix my plane. Thanks very much!
 
Cooling ramp

Gash,

I used Dynamat on the inside of the cooling ramp. It is a sound deadening, vibration dampening material that can be purchased at Best Buy and other like stores. It is a "peel and stick" material. 2 years and no cracks. My take is this reduces vibration which is the genesis of the cracking. Good luck

Doug
 
Learn something everyday here!

Doug94 said:
Gash,

I used Dynamat on the inside of the cooling ramp. It is a sound deadening, vibration dampening material that can be purchased at Best Buy and other like stores. It is a "peel and stick" material. 2 years and no cracks. My take is this reduces vibration which is the genesis of the cracking. Good luck

Doug
Click to expand...

Good to know, thanks ;)
 
Gash, that was a block of 4 lb density pour-in-place urethane foam in one ply of glass. Next time I would use a cut/shaped block of pink foam wrapped in glass. Either bonds in place with a few stripes of silicone sealant.
 
Thanks guys. I may try a combination of Dynamat and glass-wrapped pink foam. Dynamat is a good idea--I didn't think of that. Although I would love to play with some expanding 4 lb. urethane (the stuff always appeals to my inner kid), I think just cutting foam sheet will be less messy.
 
I used Dynamat on the inside of the cooling ramp.
Click to expand...

By the way Doug, which side did you put the Dynamat on? Did you stick it to the cockpit floor panel (F822-1) or the cooling ramp (F867A-1)? I'm wondering which side would work better.
 
Bummer, I didn't take any pictures. What I did was replace the cooling ramp with a new part and added two more stiffeners that went across left to right evenly spaced. I made all three stiffeners a little longer and put a joggle on the ends and tied them (riveted) to the angles that run along the sides and thru the ramp. My crack occurred early on and my plane now has over 900 hours. I think the original problem as designed was there was too much flexibility in the center with the stresses concentrated at the ends of the stiffeners without a proper path for the loads similar to horizontal spar SB.

Jerry Esquenazi
RV-8 N84JE
 
P.S. Also, work the curved bend so there is as little preload as possible on those leading edge rivets.

Jerry
 
One piece stainless ramp. No transverse stiffeners, and note folded sides. Just flatten out the original aluminum panel as a pattern, add the sides, fold, mark them with a trial fit, and trim an 1/8 or so short of the belly skin:

2uzfin8.jpg


The point of the silicone sealant is to bond the ramp, glassed block, and forward floor into one inflexible part...no flex, so the two panels can't vibrate like drum heads. You won't need the dynamat. While you're there, seal all the seams under the ramp, and then seal all the edges of the ramp itself before you rivet. You'll never have oil and exhaust inside the fuselage.

65xqix.jpg
 
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Dan, one more thing. What was your reason for encasing the urethane foam in a single ply of glass? Was it for flame resistance? It seems to me like I'll get much better vibration dampening by having just urethane sandwiched tightly between the cooling air ramp and the cockpit floor.
 
Gash said:
Dan, one more thing. What was your reason for encasing the urethane foam in a single ply of glass? Was it for flame resistance? It seems to me like I'll get much better vibration dampening by having just urethane sandwiched tightly between the cooling air ramp and the cockpit floor.
Click to expand...

The foam panel is much tougher with glass skin, and adhesives stick to the surface better.
 
DanH said:
One piece stainless ramp. No transverse stiffeners, and note folded sides. Just flatten out the original aluminum panel as a pattern, add the sides, fold, mark them with a trial fit, and trim an 1/8 or so short of the belly skin:

2uzfin8.jpg


The point of the silicone sealant is to bond the ramp, glassed block, and forward floor into one inflexible part...no flex, so the two panels can't vibrate like drum heads. You won't need the dynamat. While you're there, seal all the seams under the ramp, and then seal all the edges of the ramp itself before you rivet. You'll never have oil and exhaust inside the fuselage.

65xqix.jpg
Click to expand...

All I have to say;
Work of art

One day I will fly to your neck of the wood just to check out your plane and shop as I am envious
 
Gash,

You may want to reconsider using Dynamat.

I know it would be great as a damper but may also be flammable at a fairly low temp. I know it would be outside the cockpit but could still be a problem.

I used a layer of Fiberfrax between my fuse and the cooling ramp when I did this to my -4 several years ago.

YMMV,

Glenn Wilkinson
 
Bavafa said:
All I have to say;
Work of art

One day I will fly to your neck of the wood just to check out your plane and shop as I am envious
Click to expand...

Just be prepared when you belly up to his work bench. You'll probably feel like you just wondered into Oz, for this is where a giant must work :).
As we already know, Dan is a true craftsman. He doesn't have a whole warehouse full of expensive exotic tools. He uses the one between his ears well. Don't fool yourself, he is still holding back some secrets that we can milk out of him over time.

Dan, thanks for sharing so much with those of us that aspire to be hot on your heels!
 
Glenn, I tried Googling for the Dynamat MSDS but couldn't find anything. Has anybody else seen a Dynamat MSDS and/or flammability ratings?

I already have some ordered, so I suppose I'll take my blow torch to a piece of it and see what happens (which of course will appeal to my inner child). My plan is to use both Dynamat (assuming favorable flame resistant quality) and urethane foam.

Fiberfrax is a good idea too.
 
Cooling ramp

Gash,

I attached the dynamite to the cooling ramp. I got the idea for this product from other rv8 builders who have used this. I know three others - working great for all.

Doug
 
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