Help me fix my cowling issue

RBD · #1 02-23-2010, 07:50 PM

A little background: I didn't build this plane (or any others) and I'm not real familiar with airplane construction. I have attended the RV SportAir workshop, and should be able to drill a few holes and squeeze a decent rivet - I'm not completely helpless.

Problem: There are two screws in each of my cowl inlets that help hold the top and bottom halves of the cowling together. I think the edge distance must be too close and/or the aluminum backing plate is too thin, as the screws are elongating the holes in the top half of the cowl (the nutplates are attached to the bottom half.) In this picture, you can see the worst hole, which has nearly worn through.

And here is a picture of the other inlet, looking at the fiberglass side. You can see that the fiberglass is beginning to bow out from the constant stress and vibration.

And to complete the mental picture, here is a shot of where the screws meet the nutplate holes on the lower cowl.

Solution: This is where you guys chime in.

So what is the best fix for this? Do I need to drill out all of the rivets attaching the aluminum backing plate to the fiberglass and fab a new backing plate? If I need to replace it, would using a harder metal (like stainless) be acceptable? Or should I just go with thicker aluminum?

Buying these things already built sure gets one in the air quicker, but leaves a massive knowledge/skills gap when it comes to maintaining them.

Thanks in advance!

frazitl · #2 02-23-2010, 08:18 PM

it does look like the lower cowl holes with nutplates are too low (pretty close to the edge for the upper cowl). this results in the other (upper?) half with holes too close to the edge. I'd either rebuild the lower aluminum flange with holes a little higher (at least 3/8" edge distance on the mating part) or build a fiberglass flange attached to the lower cowl with similar spacing for the upper cowl edge clearance. My 7A is all glass in that area and is working fine at 80 hours...

Geico266 · #3 02-23-2010, 08:28 PM

How many hours on this cowl set up?

Kyle Boatright · #4 02-23-2010, 09:30 PM

Quote:

Originally Posted by RBD

So what is the best fix for this? Do I need to drill out all of the rivets attaching the aluminum backing plate to the fiberglass and fab a new backing plate? If I need to replace it, would using a harder metal (like stainless) be acceptable? Or should I just go with thicker aluminum?

Thanks in advance!

With those edge distances, I would suggest a steel backing plate. So, yes, I would remove the existing plate and replace it with a steel plate of the same thickness. Often, reinforcements in that area are bonded and riveted, so you may want to go that route.

sf3543 · #5 02-24-2010, 02:22 AM

When the hinge in that location failed on my RV6, here's what I did:
Remove the existing hardware.
Clean up the area and patch with epoxy and cloth. (Add a layer of cloth on inside for additional strength since this is a high stress area.)
Make a rectangular plate out of .062, cleco it on to the cowling, with the cowling on the plane, and drill for four #10 flush screws. (You will need to bend the plate some for a good fit sit this is a curved area. Make sure you allow correct spacing for the larger screws, two on top and two on the bottom. #8 screws would probably be OK, I just used #10's for the larger head area.)
Put nut plates on the back of the metal plates and screw the plate on.
When you remove the cowling, just take out the top two screws and leave the bottom ones in place.
The biggest pain is touching up the paint!
This fix lasted for over 600 hours till I sold the plane. I wouldn't use steel here, since I would rather allow the aluminum piece to fail rather than break the fiberglass cowl. It is easier to make a new metal backing piece.
Good luck.

L.Adamson · #6 02-24-2010, 08:27 AM

Quote:

Originally Posted by Kyle Boatright

With those edge distances, I would suggest a steel backing plate. So, yes, I would remove the existing plate and replace it with a steel plate of the same thickness. Often, reinforcements in that area are bonded and riveted, so you may want to go that route.

I used steel also. It was cut from some spare parts that I ended up with from building the elevators twice.

L.Adamson --- RV6A

RBD · #7 02-24-2010, 06:49 PM

Quote:

Originally Posted by Geico266

How many hours on this cowl set up?

Approximately 850.

Thanks for all of the replies. Looks like I've got my first real project ahead - one that involves metal, fiberglass, and paint. Fortunately for me, there are a few local RV guys that I don't mind pestering for a little oversight.

Geico266 · #8 02-24-2010, 07:06 PM

Quote:

Originally Posted by RBD

Approximately 850.

Thanks for all of the replies. Looks like I've got my first real project ahead - one that involves metal, fiberglass, and paint. Fortunately for me, there are a few local RV guys that I don't mind pestering for a little oversight.

If the first attempt lasted 850 hours stick with it, maybe a tad thicker material. Just replace the metal and move on. Don't over think it. 850 hrs is a lot of flying time.

JMHO.