Sanded too much off of my cowling

[BGordon]

Good morning everyone,
working on fitting my cowling halves and have sanded a bit too much off. I wanted a gap of 3/32 and in a few spots it noticeably enlarges to about 1/16. Any suggestions on how to fill the gaps so that I can re-sand. The shim in the picture is .032

thanks
Brandon

 

[agent4573]

I did the same thing. To fix it I scarfed on 2 plies to the inside of the cowl, sanded them to the correct gap, then filled the surfaces with micro to make everything look pretty. There's a few posts on here about scarfing on flanges,

 

[penguin]

Good morning everyone,
working on fitting my cowling halves and have sanded a bit too much off. I wanted a gap of 3/32 and in a few spots it noticeably enlarges to about 1/16. Any suggestions on how to fill the gaps so that I can re-sand. The shim in the picture is .032

thanks
Brandon

Yes, the only way to have a strong edge is to scarfe and layup new glass. To get a good finish you need a mould, alumin(i)um sheet held on with double sided tape makes a good mould but will introduce a step the thickness of the dst. A scarfe length of 15 or 20:1 should be adequate (structural glass = 30:1). 3 layers of light glass (6 or 7 oz) or 2 layers of medium (10 oz) will add around 0.030", so a 1/2" scarfe would be OK. working with a 1" strip of glass is not the easiest. It is difficult to glue on a small amount so build the edge out 1/2" and cut or sand back. Its also easy to get a step along the edge, use some thick resin at the edge. It is a lot of bother to replace what is only a small amount but using filler, or similar, with no reinforcement will result in a weak edge that will damage easily. Or just accept a slightly wide gap ...

 

[BGordon]

Thank you for the responses. Scarfing fiberglass is exactly what I was thinking.

 

[Skysailor]

Look in the Sticky section of this section for the "Tip: Fiberglass Fabrication" by DanH. It is an excellent guide on exactly this problem. I built a fiberglass airplane so I'm familiar with fiberglass work and Dan gives a great (as always) description on the correct process.

 

[DanH]

Good morning everyone,
working on fitting my cowling halves and have sanded a bit too much off. I wanted a gap of 3/32 and in a few spots it noticeably enlarges to about 1/16. Any suggestions on how to fill the gaps so that I can re-sand. The shim in the picture is .032

Brandon, the raw gap will be reduced in the paint and paint prep process. Builders often create lovely tight gaps and then suffer paint chipping and edge rubbing in service. Fasteners and hinges wear over time, so nothing retains perfect alignment forever. If you have some 3/32 gaps, your best bet is to simply make them consistent all around. In terms of finished appearance, wide gaps look fine and stay that way. The trick is making them all the same.

 

[bjdecker]

Echoing DanH comments -- 3/32" gap is too tight. You'll want a 1/16" minimum gap, and consistency is more important than the absolute distance.

 

[[email protected]]

Echoing DanH comments -- 3/32" gap is too tight. You'll want a 1/16" minimum gap, and consistency is more important than the absolute distance.

I second the gap being a bit wider. My RV-6A has about 1/8" or ??? gaps now. Seems to widen as it ages. Hinge wear or what ever. You can't see it flying anyway. Not very many planes that "fly" are perfect. Ya I know shoot for the best and settle for what happens.
That said I have some cracking in my cowl that someday I will get around to fixing and will probably address the massively over sized gaps. Have to do a repaint so that will be the time. Probably get it to tight and get some chipping on the edges then.
My luck varies FIXIT

 

[CTCole]

Faced the same situation and had to extend the aft edge about 3/32". A layer of fiberglass on the inside of the cowl makes the addition to the edge robust. Here's some pictures of the repair, inside and out, then after trimming & sanding but before painting the cowl.