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Tricks for perfect cowl to fuse gap

sblack

Well Known Member
I am fitting the cowl on my -4. I know I need a non zero gap between the fibreglass and the aluminum. I am using skybolt fasteners on the top and sides and piano hinges where the bottom attaches to the firewall. I suspect on the bare glass I need 1/32" or so to provide room for primer and paint. I was going to find some sheet styrene or similar to put in that gap and the spread some flox up to the edge. Are there any other tricks out there that people use to get the fit just right? It is one of those real noticeable things that sets a nice
Y built airplane apart so I would like to get it right.
 
I used hinges on the cowl to firewall interface (on the sides). It's been a while, but I recall just block sanding the cowl and marking with sharpies until I had the abutment fit that I wanted. Then held the cowl tight and strethed out the hinge as I drilled the holes. I then block sanded a bit more after it was fully fitted to the the gap I wanted.

I am surprised you are using hinges on the bottom. It was my understanding that this gap gets the greatest loads and most with hinges down there get damage to the eyelets.

Larry
 
I fit the cowl to the plane and then just create a thin gap between the skin and cowl as good as i can.
Then I take an old credit card or something and stick on sand paper on one side
Use the sandpaper side against the cowl and you can create a perfect gap. Use something thicker if you want a wider gap.
You can also sand on the aluminum if it isn?t perfectly straight and needs to be trued up. Just wrap the sand paper on both sides.
I also use this method wherever I need a nice gap, such as the wheel pant halves, but I usually used a piece of hacksaw blade to get the gap started and then wrap sandpaper around the blade to final sand.
The gap is just right to accept the paint.
 
Gap

Realize that there will be paint on both sides of that gap. Also realize that there WILL be vibration and relative movement between the cowl and fuselage. Too small a gap will guarantee paint removal...
 
I fit the cowl to the plane and then just create a thin gap between the skin and cowl as good as i can.
Then I take an old credit card or something and stick on sand paper on one side
Use the sandpaper side against the cowl and you can create a perfect gap. Use something thicker if you want a wider gap.
You can also sand on the aluminum if it isn?t perfectly straight and needs to be trued up. Just wrap the sand paper on both sides.
I also use this method wherever I need a nice gap, such as the wheel pant halves, but I usually used a piece of hacksaw blade to get the gap started and then wrap sandpaper around the blade to final sand.
The gap is just right to accept the paint.

Thanks Steve
 
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