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Cowl attach hinges and fluted flange problem

PaulvS

PaulvS

Well Known Member
I'm hoping somebody may have previously solved this problem.
My 'classic' -6A kit has a firewall with the main part being stainless and the curved out side cheeks are aluminum. I fluted the cheek flanges in the normal way to eliminate the manufacturing bow in the flat part of the stamped parts. The attached pic shows the flutes on one side, though the photo is rotated 90* for some reason that eludes me.

Now the piano hinge for the cowl needs to be riveted on the inside of the flange, but there is a problem because the hinge won't sit flush against the flange because of the flutes.

I guess I could cut small .032 shims to go in between every flute, or use liquid shim (epoxy with micro) to make a flat surface for attaching the piano hinge. Is this viable, or did you solve the problem another way?

Thanks
Paul.
 

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Check F-602B part

I don't see any replies to this, did you come up with a solution yet? For me this was something like 23 years ago but I believe (and a quick look at my firewall seems to confirm it) the part came pre-curved and shouldn't need flutes. Looks like your part is .040 or less? F-601B on my plans and kit are .062, not something you'd be able to flute easily. Check your kit for F-601B and plans for the correct thickness part.

Bear in mind mine is a -6 not -6A and has the old hand-drawn plans so maybe something is is different or changed there but that's my take.
 

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F-601B

Hi Randall,
Thanks for the reply, I don't yet have a solution. It's also about 23 or 24 years since I made the firewall. The two side pieces F-601B are .062 and I expect I fluted them because the 90 degree curved bend for the flange would have put a bow in the flat part, and so I straightened it.

The jig uprights are a bit in the way at the moment so access to that area is a bit awkward but I may be able to reduce the depth of the flutes without throwing out the line of rivet holes. Otherwise I think I will need to bed the hinge in epoxy because the flutes are too close together to cut individual shims.

I think I inadvertently made more work for myself 20+ years ago! :(

The new firewalls are all 1 piece of stainless steel so mine is definitely now a minority.
 
PaulvS said:
I'm hoping somebody may have previously solved this problem.
My 'classic' -6A kit has a firewall with the main part being stainless and the curved out side cheeks are aluminum. I fluted the cheek flanges in the normal way to eliminate the manufacturing bow in the flat part of the stamped parts. The attached pic shows the flutes on one side, though the photo is rotated 90* for some reason that eludes me.

Now the piano hinge for the cowl needs to be riveted on the inside of the flange, but there is a problem because the hinge won't sit flush against the flange because of the flutes.

I guess I could cut small .032 shims to go in between every flute, or use liquid shim (epoxy with micro) to make a flat surface for attaching the piano hinge. Is this viable, or did you solve the problem another way?

Thanks
Paul.
Click to expand...

Funny enough I have one of those in my garage... :)

I just checked and I've not used any shims in that zone (on the sides) but shims are definitely used over the top and along the bottom. I recall many others using shims too... partly to get around flutes but also to align the cowling with the skins. The old polyester cowling was quite thick along that edge sometimes.

Hope that helps.
 
Appears that the aluminum angles haven't been riveted yet.

Have you considered simply shrinking the flutes flat, by hand, the same way they form the SS firewall flanges without fluting?

If you are unfamiliar with the technique, search this forum (?) or try YouTube searching on Tuck Shrinking.
 
Thanks all for the suggestions.
I've measured the thickness of the engine cowl and it is 0.060. I think it must be the newer epoxy honeycomb style cowl, versus polyester, it came with the finishing kit in 2000. The fwd side skin is .032 and the firewall side flanges are .062 where the attach hinges go on, so the fuselage side is already thicker than the cowl, notwithstanding the flutes that make it even thicker!
I researched Tuck Shrinking but I'm not sure that I'm game to try and learn the skill on the RV firewall.
There's enough other jobs to keep me busy while trying to come up with a solution, I don't want to make it any worse.:eek:
 
I just looked at 2 RV-6s in my hangar. Appears that both builders did a bit of shrinking on the aluminum flanges with no spacers visible. The hinge installation came out in both cases with a flush outside fit between the cowl & side fuselage. (honeycomb cowls on both)
 
Ralph Inkster said:
I just looked at 2 RV-6s in my hangar. Appears that both builders did a bit of shrinking on the aluminum flanges with no spacers visible. The hinge installation came out in both cases with a flush outside fit between the cowl & side fuselage. (honeycomb cowls on both)
Click to expand...

Thank you Ralph for checking, maybe I am over-thinking this and it will work out OK without any further modification!
 
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