Need some ideas concerning how to fix a cowl

MrNomad · #1 11-03-2009, 04:59 PM

A friend of mine with a 7A has a cowl that needs some help. Unlike the cowl in this picture that mates properly along the horizontal hinge, my friend's cowl does NOT look good. The line is irregular and in some areas, the hinge is exposed.

Structurally, the 7A cowl works OK but he'd like me to make the edges straight with a uniform gap.

Essentially, I'm looking for ideas how others would solve this. Yes, we're good with glass but would like to learn from the experiences of others.

Thanks.

Scott Hersha · #2 11-03-2009, 05:07 PM

How are you at drilling out rivets? I think the best way to make it right is to remove the offending hinge, mix some epoxy/flox to fill the holes, lay a layer of 9 OZ cloth on the inside to make it smooth again, and start over. Whole job should take no more than 2 hours (plus overnight cure) to get back to the start over part.

Scott

terrykohler · #3 11-03-2009, 06:16 PM

If the "open" areas are minor, you should be able to repair with flox and filler. To get a uniform seam, you can take a hacksaw blade and slowly work it fore and aft from the front of the cowl to the back. If done properly, you'll end up with a seam the width of the blade. Take your time. Without a seam,i.e. with upper cowl butted against the lower, it's almost impossible to get the hinge pin to fit. In addition, too close of a fit will result in the paint chipping when the two pieces come in contact. The important thing is to take your time and proceed slowly. Good luck.
Terry, CFI
RV-9A N323TP

Erik Westlund · #4 11-03-2009, 06:44 PM

I wouldn't try to fix it with just filler. you have to think about the fact that you have a very thin edge to bond to. I fear that it will just pop right off over time. if you are wanting to go that route then i would put a light layer of glass over the top of it to hold it in place. we use a style 120 glass that would do the trick or even like a 4 oz. then fair it in with the rest of the cowl.
I think the best bet would be to replace the hinge like Scott said.
good luck
Erik

MrNomad · #5 11-04-2009, 02:40 AM

The reason I didn't want to remove the hinge is because I don't have access to the plane during the glass work. If I kept the original hinge in place, fitting it to the plane wouldn't change.

Replacing the hinge makes the most sense but that could alter how the cowl fits onto the airplane. Without access to the airplane, the chances of it fitting properly are slim to none.

I think I will pass unless I have access to the plane.

Thanks.

thinkn9a · #6 11-04-2009, 03:39 AM

if it is just gap,.. then sanding blocks etc will help get it more uniform.

I had a problem with the partial built kit I bought, with the hinge pin "(very) hard to install". Closer inspection revealed that the joint had been "forced" and it actually was pinching the cowl (front to back) to make it fit. (you could actually see a inward dip in the cowl below the hinge) I ended up having to remove some of the aft end of the cowl to allow it to properly fit. That along with some reset to the joining line, with a sanding block.

minor in or out alignment can be made with bend of hinge "fingers" ... but you can chase that for a while and end up with it finding it's own favorite place

I really don't know how you can "fix" the problem without having the plane there to check fit and alignment.

For info, you can buy some "premade" epoxy for fairing and joint work from 'System Three"

N208ET · #7 11-04-2009, 07:13 AM

I have never seen this before but do a layup on the top cowl so it comes down over the outside of the bottom, leaving enough space between the overlap and bottom cowl for a piece of felt on the inside of the overlap, then you wouldn't see a gap of any kind. I spent a lot of time trying to get my spacing just right and finally gave up, but after you get some paint on it, things will look good.

Randy

Jim F · #8 11-05-2009, 01:28 PM

If the fit with the spinner will allow, taking off the hinge and smoothing the gap would be the best way to go. I built a tool for this by bolting wallboard sanding screen between two thick pieces of Alum. sheet (approx 4" X 20 ") so that about an inch of the sanding screen stuck out beyond the alum. sheets. I was able to work this tool back and forth in the cowl seam to get a smoothe fit. In fact it was so close I had to shave a little more off before paint! If you are dealing with gaps of an eight of an inch or less this might work without dramatically changing the fit of the cowl.

Jim F
RV-9A
ready for inspection!