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  #1  
Old 04-28-2008, 09:34 AM
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DanH DanH is offline
 
Join Date: Oct 2005
Location: 08A
Posts: 10,943
Default Cooling Ramp

We've been kicking around cures for the cracking cooling ramp as well as floor vibration (RV-8). I has originally cast a pour-in-place foam filler block to deaden the panel (previous thread), but I had an idea the other day and decided to chase it a little.

The stock ramp is an aluminum panel with some poor stiffeners riveted to the backside. It has no support along the sides where it meets the fuselage belly panels except for the stiffeners. All support is at the fore and aft ends, and the stiffeners don't reach that far.

So, why not make a new panel with integral bent side flanges? The bend adds stiffness, and a few pop rivets along those flanges means the panel is attached and supported along all four sides.

I made this one from 0.018 stainless (exactly 1 lb penalty) and polished it, but the same idea should work in aluminum. Thoughts?

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Last edited by DanH : 04-28-2008 at 09:36 AM.
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  #2  
Old 04-28-2008, 10:08 PM
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vmirv8bldr vmirv8bldr is offline
 
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Location: Eastvale, CA
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Default Bend the exhaust

I believe I read on here somewhere that one of our cohorts had the tips of his exhaust bent downward ever so slightly (10-15 degrees maybe), aiming the pulsing exhaust to the ground instead of onto the colling ramp. He reported the plane got quieter, the vibrations went away, and the cracks stopped.

I think it was the end of this thread, but memory tells me there were pictures too......
http://www.vansairforce.com/communit...ng+ramp+cracks

Best of luck
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  #3  
Old 04-28-2008, 11:25 PM
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John Clark John Clark is offline
 
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Location: Santa Barbara, CA
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Default Well, kinda...

Quote:
Originally Posted by vmirv8bldr View Post
I believe I read on here somewhere that one of our cohorts had the tips of his exhaust bent downward ever so slightly (10-15 degrees maybe), aiming the pulsing exhaust to the ground instead of onto the colling ramp. He reported the plane got quieter, the vibrations went away, and the cracks stopped.
The ends of the exhausts on my '8' are turned down enough to eliminate the major noise/vibration issues but, there is still quite a bit of motion in the ramp. the way it is designed it will move and rub slightly on the sides. You can hear it on the ground, I suspect because of the pulses from the prop. I am interested in how Dan's design works out. Besides, the stainless looks very cool.

John Clark
RV8 N18U "Sunshine"
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  #4  
Old 04-29-2008, 05:49 AM
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RV8RIVETER RV8RIVETER is offline
 
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Default "Purty"

Dan

Your stainless ramp looks really nice. I wish I had thought of that when I was at that stage.

I wish I would have also dispensed with the hinge at the back, it is totally pointless, blindly following the plans I guess. At least I added more stiffeners and prosealed the thing together. Due to my exhaust/cooling exit design I will be adding a stainless plate on top, the sandwhich should be pretty darn stiff, but your idea of stainless to begin with is much better.
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  #5  
Old 04-29-2008, 08:02 AM
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DanH DanH is offline
 
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Default

<<...tips of his exhaust bent downward ever so slightly ...>>

That's a new AWS 4 into 1 bent-tip tailpipe in the photo background. I recall a report of cracking in belly panels further aft with a straight tip on the 4 into 1. The vibrating cooling ramp appears to be an issue with a variety of exhaust systems if the tips are not turned downward.

I'm leaning toward a simple z-bend web across the center of the panel, under the ramp, full depth to the underside of the floor. Perhaps no rivets; bond it in with a fat bead of silicone or proseal on each flange. Should make the ramp and floor pretty "dead" and not trap exhaust by-products/moisture like a filler block.
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  #6  
Old 04-29-2008, 10:18 AM
Tom Martin Tom Martin is offline
 
Join Date: Jan 2005
Location: Ontario, Canada
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Default

Dan
Consider adding stiffeners lengthways to the bottom/exterior of the ramp. I made a ramp such as you have for my Rocket


This has worked well and on the other side it gave me a good place to attach my crankcase breather tube
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  #7  
Old 04-29-2008, 11:08 AM
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DanH DanH is offline
 
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Default

Set material choice aside for a moment. The point was to add real support at the sides of the ramp with a bent flange, eliminating the need for the ineffective (no end support) stiffener angles on the underside. I may add some support in the middle of the panel too. With it I think the idea would work just fine in aluminum.

I was curious about stainless mostly for fire-hardening the ramp area under the floor. "Curious" means "weighs how much more?" Answer is 1 lb, which is about what I figured. Not the first time I've built a part just to see how it turns out. I think I'll keep it. Personal choice.

No doubt the exhaust pressure waves are the root cause, and some degree of turndown is desirable. The AWS turndown on their 4-1 is probably more than necessary.

I'm on record as saying I doubt a 4-1 makes significantly more power (and please, no, I'm not interested in debating the point with 4-1 fans). Mostly what I like about a 4-1 is the lack of crossovers radiating heat at everything under the engine. The entire forward fuel servo area is open and relatively cool. I have a lot of respect for Larry Vetterman. What doesn't he like about 4 into-1's?
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  #8  
Old 04-29-2008, 01:27 PM
Transporter Transporter is offline
 
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Location: Lee's Summit, MO
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Default Got Plans?

Dan,
I'm about to start on my fuselage and it's great to know there are craftsman like you working on improvements like this.

I don't know if you made a template/pattern you can share, but I'd be interested in one if it's available.

Thanks,
Mike
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  #9  
Old 04-29-2008, 04:56 PM
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DanH DanH is offline
 
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Default

Mike, you already have a template; the stock ramp panel. Add an extra 3/4" at the rear so you can pop rivet and skip the hinge deal. Add 2" or so extra width for "wings" on each side, then bend them 90 degrees. Drop it in the fuselage and mark a line on each wing flush with the belly skins. Cut off the excess about an 1/8" shy of the line to drop the edge below the radius on the belly skins. I'll post a picture later with the ramp on the airplane if that detail isn't clear.

Oh yeah, wear gloves. Working 0.018 stainless can leave you with lots of little cuts on your fingers. Saturday night I had to ask my wife to squeeze the lime juice into my gin and tonic <g>
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Last edited by DanH : 04-29-2008 at 05:36 PM.
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  #10  
Old 04-29-2008, 09:11 PM
Transporter Transporter is offline
 
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Default Thanks!

Gotta love the lime juice in a cut

Thanks for the tip-I'll give it shot when I get that part of the fuselage assembled.

Mike
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