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?

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/community/showthread.php?t=12787&highlight=cooling+ramp+cracks

Best of luck

Well, kinda...

vmirv8bldr said:

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.

Click to expand...

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"
KSBA

"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.

<<...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.

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

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?

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

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>

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

RV-8 exit ramp cracks

I too experienced exit ramp cracks on the ends of all stiffners. At around 80 hours I couldn't stand their progression even after stop drilling. I have had the turned down exaust from the very begining.
I built a stainless insert with flanges to pick up the sides just like yours (good minds think alike), and punched the holes for pop rivets in a position to pick up the existing stiffners, as well as the sides for support. As of 4/27/08 at 194.7 hours problem solved, also floor vibration is significantly less.

Finished ramp installed. In the end I inserted a glass-sealed foam wedge under the ramp, full width and about 4 inches wide. All the seams under the ramp were caulked with 3M Fire Barrier 2000 (intumescent silicone), then the block was caulked in place with the same. The panel is very, very "dead".

The bolted bracket is for cable suspension of the 4-1 tailpipe.

Warped minds think alike

Dan,
About 3 years ago, I did a modified version of what you have done. My original intent was to use the .020" thick 2024-T3 ramp as supplied by Vans. However, after reading about cracking problems experienced by other 8 and particularly 8A fliers, I wanted to improve the rigidity of the original Vans ramp design. (My 8A project is an old pre-punched, not match hole model) Van originally intended to make the exhaust ramp on the 8/8A models movable, sort of an adjustable cowl vent. They scrapped that idea but left the basic design. (Perhaps to allow an ambitious builder to make a movable ramp??) I decided to move the ramp doublers to the inner floor ribs on my 8A. I also bent up an angle to replace the hinge at the rear.

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The center section of the 3 piece cross braces gets riveted to the top side of the ramp. The center section of the cross braces sits below the stubs on the sides. Two #8 flush screws (one on each side) secures the 3 pieces of the cross brace together.

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The flat piece at the front between the inner floor ribs is a shim. This shim keeps the front of the ramp even. Without it, there would be two bulges at the edges, due to the ramp contacting the upper flanges of the inner floor ribs.

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I later decided to replace the original, aluminum ramp with a .016" thick ramp made of half hard stainless steel. I was concerned about possible exhaust failure or cracks allowing a flame to blast directly onto the aluminum ramp.
After I had riveted everything but the ramp into place, I decided to switch from riveting the ramp in, to using flush screws and dimpled nut plates. Vans mentions in the instructions that the area between the ramp and floor is a potentially high corrosion area, due to it's exposure to exhaust fumes. I had etched, Alodined, epoxy primed and even finish painted the area to prevent this. However, making the ramp removable allows me to inspect the high corrosion area during my condition inspections. I used the screws, nut plates, trim washers and NeverSeize (so I wouldn't scratch the paint) to create the dimples into the angles which were now firmly riveted to the inner floor ramps.
Those of you who might choose to do this now, will be able to simply dimple these parts prior to riveting them on! I also coated this area with thinned out ProSeal to keep the exhaust gases from working between the angles and the ribs.

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The photo above also shows one of the cross wise stub angles. These stub angles are actually riveted in place. The #8 flush screw is actually for retaining the stainless steel ramp. If I had decided to use nut plates and screws from the beginning, I could have simplified my support angle design.
This system gives the ramp excellent support. I never posted this sooner, because I didn't figure out how to insert photos till 2 weeks ago. I apologize for the grainy top 3 photos. They were taken with a disposable camera. That was before I broke down and purchased a digital model.
Charlie Kuss

More info please

DanH said:

Finished ramp installed. In the end I inserted a glass-sealed foam wedge under the ramp, full width and about 4 inches wide. snipped

Click to expand...

Dan,
How about a photo of that foam wedge? How about details on what it's made from, who makes it and where to buy it?
Charlie Kuss
PS I don't want much, do I?

vmirv8bldr said:

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/community/showthread.php?t=12787&highlight=cooling+ramp+cracks

Best of luck

Click to expand...

Bart,
On the 8A, there is a LOT of turbulent air caused by the nose gear leg. Adjusting the exhaust won't cure the problem for us.
Charlie Kuss

Dan,
How about a photo of that foam wedge? How about details on what it's made from, who makes it and where to buy it?

Click to expand...

It was so mundane I didn't take a picture. Lined the area under the ramp with some plastic sheet, mixed some two-part urethane foam, dropped a blob on the sheet, tossed another plastic sheet on top of that and fastened down the ramp. The foam expands to fill the space and cures hard in 15 minutes. Popped it apart, took out the foam block, sawed the edges square, and covered it with one wet ply of glass fabric/epoxy to ensure the foam would never trap moisture, acids, or bad karma.

Ramp Cracking

The cracking I have witnessed on my 8A other 8's is on the flat skin just aft of the ramp. The cracking starts near the aft most internal stiffener rivets. The internal stiffeners appear to be weak and the skin has a great deal of flex. On the QB and all completed aircraft there is no internal access and it will require an external doubler. I have not personally witnessed any cracking in the ramp area.

Pat

RV8A
J3Cub

Here's What We Did...

....before reading all of the good ideas above! Darn!

On a related note

Here is my new Aerospace Welding 4 into 1 collector. This is now the standard configuration. As soon as I round up some thin stainless, I'll start on a "winged" ramp.