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Red Tail 6A Fixes

LouFly

Well Known Member
After about 4 years of flying I decided it was time to take a bigger hammer to some of the chronic issues with the 6A this year. Like an old house, starting one project often gets you into other ones. I've learned a lot from VAF and though I am a bit stuck on a couple of issues, have had a number of successes. Since I like to fly off of grass occasionally I wanted to add some of the Anti-Splat upgrades. I found Allan to be a super guy. Started out by getting the brace as well as the sealed for life better bearing and the tire balance. We keep the tire at 50 PSI now, which according to Allen helps make sure that the tire won't squeeze out and grab the pant. I learned this can be an issue on concrete. While I was at it made peace with being able to test the nosegear preload so I bought Allan's wrench and fish scale.
 

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One of the next items was to replace the beat up nose fairing and work to get a better fit than we had in the past. Van's parts are not cheap but their prices sure beat certified parts. Also in general compared to others, you can expect to get a fairly complete assembly.
 

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One of the first things I ran into was that the new Vans nose fairing interfered with my existing FAB. So now I dive into learning about fiberglass fabrication, thanks to Dan H and others. Notched and repaired the FAB. Note for the non-builder, the FAB does not sit symmetrical to the engine and fuel injection centerline..I did a lot of head scratching over that before making peace with that fact..If I did it again, would have made a bigger notch but after flying clearance seems fine. Mistake - riveted some too-thick silicone to the FAB/cowl interface - it will need to come off and replaced with the more flexible black. We had the classic shrunk K&N filter; I kept the shrunk one for reference. Maybe we'll replace every 5 years or so. Makes me really appreciate not to over-prime, that fuel has to go somewhere.
 

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Next item is to address the exhaust. My 6A has nice metalwork as built by an aviation sheet metal mechanic. But the custom exhaust mount was a problem. It allowed the port side pipe to touch and damage the fuselage. Clint of Vetterman to the rescue. We installed his standard hose and ss pipe method and it seems to be working well. We sent him the exhaust to repair the small hole and look it all over. Also added a patch to the bottom fuselage.
 

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OK cowl was next. The inside was a mess. I tried some of the recommended cleaners but in the end MEK and rags with thick rubber gloves seemed to help the best. After cleaning off the cowl could see the port side burn marks better. They were pretty shallow so sanding took most of them off pretty easily. Decided on 2 fixes for this. The first was recommended by Clint / Vetterman -- add a 2nd heat muff in series with the first, also will improve cabin heat. The downside of this is more ducting, but we made it work.
 

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The original bottom cowl was two piece. The aft was warped and had chronically pulled out the nutplates. Also studying the seam, it looked like going back to one piece would help create another 1/2 clearance to the exhaust. I always take the bottom cowl off to change the oil anyway, so I didn't feel we'd be losing any functionality.
 

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I ground down to raw fiberglass and then "glued" the removable cowl down with flox & epoxy feathered the edges and laid 3 plies of bidi about 2" wide at the seam. I cut out the really warped pieces on the aft side, shaping expandable foam, and then guesstimated a 12:1 scarf ratio. More voids in the expandable foam than I would have liked. I decided to leave in the bottom cowl piano hinge and work around it as best as possible. Also replaced the warped piece on the bottom cowl center. The whole thing seemed pretty strong.
 

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Working on the inside of the cowl. Tried a thin layer of epoxy but decided to go ahead and paint. Brushed / rolled the Pettit boat primer/paint and self adhesive reflective stuff from ACS. Edges of insulation sealed with clear silicone. Pretty happy at this point, except I misjudged the insulation cuts and wasted a little. They can't take my engineering degree back though.
 

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Problem #1 - Filing w/ Micro

First problem. I filled the cowling with a mix of epoxy, micro and cabosil. Struggled to get a big enough batch. I used a Surform while in the "cheese grating" stage. and then when attempting to block sand, I noticed I didn't just have pinholes - craters would be more like it.

At this point I pretty much have it all sanded off while addressing the flying issues, then I'll come back to this filling. I'm wondering if a beginner should be using a dedicated filler like West 410 or some kind of resin for something like this?
 

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Problem #2 - Cowl Cracking

The immediate problem is that within a couple flights I started to get cracking at the trailing edge of the cowl where we'd bonded the scoop cowl on. (I know drilling out cracks in fg is not really practical but I had nothing to lose). Although I did the bonding off the airplane, I'm confident that the joint is not pre-loaded. It fits naturally on the plane.

I originally made the bond without removing the aluminum piano hinge. The flat area it rests on is a reference point for the hinge. I'm struggling with how to make this repair...modifying the flat reference point will mess up the geometry of the hinge to fuselage as will adding cloth on top. Cloth on the bottom will be proud of the fuselage.

So far the best idea I have is to dremel out a little space in the crack and add flox or cut fibers in the epoxy, like a thick glue - making sure I'm down to clean fiberglass wherever bonding. Then use the flox to make a fillet on each side of the ends.

I was also going to add one layer on the outside of the cowl and then some of the holes (the ones that are oversized a bit) with flox/micro where the piano hinge was riveted on, leaving at least a couple holes for a location guide. Really appreciate any of the fiberglass experts weighing in.
 

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<Edited by moderator to conform to VAF rules> Planning some crack repairs tomorrow. Current plan is to sand off the rest of the micro I left on there, bevel the cracks in x and y, and use flox in the joint and on the interior and flox with a little micro on the exterior. Still pondering.
 
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I had a similar situation. I cleaned it up, beveled the edges where I could and added layers of glass both sides of the lamination. Also, in some places added some rivets to help strengthen the area. Not flying yet but I think the rivets will help hold it together.
 
Plans Help

Looking for help from RV-6 builders...

Pretty pleased with fiberglass progress. Looking to do the job right --

Roger on bonding the piano hinge. Proseal, JB Weld. Probably use proseal as I think it will be more pliable.

Van's PDF from the CD, drawing 63 do:

1. 'Section R-R' calls out a .020 shim under the piano hinge. (I didn't remove one). It's logical that it would be used and might reduce stress. Strangely the note says "Only on side hinges"(?) Dont wanna think too hard but seems to be it would be used only on the *bottom* hinges. Maybe they meant "this side?"

2. There are notes with details "R1" and "R2" but those are blank in my PDF? My full set of plans from '99-94 don't seem to include this page; looks like it was a later update.
 
The shims under the hinges are to compensate for the different thicknesses of the stackup on the firewall (skin, firewall, <shim>) vs the thickness of the cowling. Use whatever shim is necessary to make an even transition from the cowl to the firewall.
 
Looking for help from RV-6 builders...

Pretty pleased with fiberglass progress. Looking to do the job right --

Roger on bonding the piano hinge. Proseal, JB Weld. Probably use proseal as I think it will be more pliable.

Van's PDF from the CD, drawing 63 do:

1. 'Section R-R' calls out a .020 shim under the piano hinge. (I didn't remove one). It's logical that it would be used and might reduce stress. Strangely the note says "Only on side hinges"(?) Dont wanna think too hard but seems to be it would be used only on the *bottom* hinges. Maybe they meant "this side?"

2. There are notes with details "R1" and "R2" but those are blank in my PDF? My full set of plans from '99-94 don't seem to include this page; looks like it was a later update.

I ditched the piano hinge on the bottom of the cowl a couple years ago. There seemed to be too much vibration and the piano hinge failed on both sides.
I removed the piano hinge from the cowl and the fuselage.
I cut 2 pieces of aluminum, .090" I believe, and riveted it to the fuselage where the hinge had been, shimming as needed.
I then drilled 3 locations through the cowl and the aluminum strips. I mounted nut plates for #8 screws on the aluminum plates. I installed #8 SS screws with machined washers from Skybolt.
I also added 2 screws to the plate that "traps" the bottom of the cowl around the nose gear.

I have not seen any cracking to date.
 
Thanks Skid and Kyle. The #8 screws are definite food for thought. I have been close to making peace with getting the bottom hinges in and out, threading around the exhaust pipes, on my back in hot, oily area. Every oil change, every time time I needed access.

But just close to it. Was not there yet.
 
I mounted nut plates for #8 screws on the aluminum plates. I installed #8 SS screws with machined washers from Skybolt.
I also added 2 screws to the plate that "traps" the bottom of the cowl around the nose gear.

I have not seen any cracking to date.

I did the same thing (sort of) from the get-go. I have 10 screws across the bottom of the cowl, attaching it to strips I riveted to the firewall. Four #6 screws plus one #8 screw (adjacent to the air exit) on each side.

No problems in 20 years.
 
one problem for a flying RV is that it looks like it will be really difficult to get a rivet squeezer between the lateral member of the engine mount and the flange at the bottom of the firewall. Stbd side is OK, but missing an eyelet on the port side. May use a single tab blind riveted for a #8 at the air exit and leave the hinge for now, unless there is a better way.
 

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My hinge didn’t go that far toward the center as there is nothing on the cowl to interface with. I have a narrow squeezer, but maybe not that narrow, remember the hinge "loops" will not be there. Can you get a small bucking bar in the space?
 
With help from VAF, Vetterman and others-- have made a lot of progress and helped also with my confidence in solving problems with the '6.

1. used the rubber hose / stainless tube exhaust mount. After 30 hr seems like it's a permanent fix.

2. replaced the bottom piano hinges with alum backing and 8 nutplates. Changed the oil today - night and day easier to get the cowl off.

3. Between the 2nd heat muff and the reflective materials, no more burning inside the cowl-- looks as nice as when I put it in.

4. Merged the warped bottom scoop into the lower cowl and learned a lot about composite fabrication

Thanks...
 

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Powder Coating

So once I got my rudder pedals upgraded, found a little powder coating outfit 5 min from the office. As usual I overdid it, and being tired of looking at the chipped and rusty-a$$ steel parts like the canopy and flap handle, towbars, aileron trim I had him do all of it. About $280 and once they get fresh hardware they'll be like new.
 

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