Cowl Fit

[lr172]

I posted on another thread about my cowl fitting. I noticed a problem with the slope in the forward face of the cowl. It seems to want to be higher in the front or lower in the back, which isn't really possible. Have others seen this? Any ideas for correcting it?

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I should mention that the aft end is still sitting on top of the skin prior to the trim cut. However, I don't seem like dropping .050" is going to solve this.
I appreciate any assistance that can be offered here.

Larry

[BillL]

I am not totally sure what the picture shows, but assume it is the nose behind the spinner. If you have not fitted to the firewall then, do that first. Paying attention to keeping it straight (mark a line) and a little close to the spinner for the first cut on the back. A tendency is to clamp all together with a strap. That is ok, but I think you will want the cowling to assume its shape rather than forcing it, so you might not want to proceed too far using that method. Tape can pull halves together nicely and eventually clean off with mineral spirits. Cut it long for the first cut to allow block sanding for even clearance. Tight at first is ok, as you can trim off the paint clearance amount at the later stages.

I fit my SJ cowl in the last month. I concluded the fiberglass is not a precision part. I did not worry about the spinner clearance parallelism (for a different reason) and focused on the general alignment of left/right and over the top with the spinner contour. There are a lot of gyrations of fitting the halves together around the nose so take it step by step keeping the big alignments in mind and then adjust the final .030 stuff at the end.

Although I have to extend my nose behind the spinner, after the other fitting steps it settled in pretty parallel to the back of the spinner.

Oh - what prop and fastening system (cam locks, sky bolt, hinges?) are you using for the cowl?

[lr172]

Originally Posted by BillL

Although I have to extend my nose behind the spinner, after the other fitting steps it settled in pretty parallel to the back of the spinner.

Oh - what prop and fastening system (cam locks, sky bolt, hinges?) are you using for the cowl?

Thanks for your help here. How did you extend the nose? Filler / Epoxy?

I have a Catto 2 blade prop and intend to use #8 Screws (3" spacing) on the top and bottom and hinges on the sides (horizon & Vert.)

[DanH]

Originally Posted by lr172

I noticed a problem with the slope in the forward face of the cowl.

Routine stuff. Shorten the cowl (move it rearward) to get an appropriate clearance between the cowl and spinner at the tightest point, then add fill (dry micro is fine) and block sand to make the clearance equal all around.

[BillL]

Originally Posted by lr172

Thanks for your help here. How did you extend the nose? Filler / Epoxy?

I have a Catto 2 blade prop and intend to use #8 Screws (3" spacing) on the top and bottom and hinges on the sides (horizon & Vert.)

This should provide strong cowl connection. Yes, I will use a microballoon/epoxy filler to extend the flange behind the spinner. Will James suggested this as the best method. He also said to take some #8 nuts and bond them to the back of that ring, then make some screws with pointed ends. A piece of aluminum or plexiglass will be inserted behind the spinner and adjust the pointed screws until they touch the spaced plate. Then remove the cowl, sit nose up, and build a dam around the ring to be cast. Using a piece of waxed glass, press down until the screws touch the glass. Fill the ring with micro/epoxy mix then sit the well waxed glass on top to make a perfectly flat surface. The inside and outside will be sanded and final finished after the main ring is cast. I will have to work the details of the split line in the process. Either cast half at a time or cut with a fine blade. I am thinking half at a time.

Your gap should be relatively small, so bond the nuts inside the cowl. Hobby shop modeling clay is what I use. Put 5 coats of wax on the glass, lightly polishing off each application. This should provide you a perfect, parallel surface behind the spinner. Waiting until the prop and spinner is fully fitted would be best.

Good luck on your fitting.

edit - I see DanH is engaged - do what HE says, not me

[lr172]

Thanks for chiming with your experience here guys; I appreciate it. I will press on and fill it over the winter. My current goal is to get the cowl attachment done, pull the engine, flip her over and paint the bottom half. I didn't like the idea of painting on my back.

Larry

[RViter]

Originally Posted by lr172

I posted on another thread about my cowl fitting. I noticed a problem with the slope in the forward face of the cowl. It seems to want to be higher in the front or lower in the back, which isn't really possible. Have others seen this? Any ideas for correcting it?

I should mention that the aft end is still sitting on top of the skin prior to the trim cut. However, I don't seem like dropping .050" is going to solve this.
I appreciate any assistance that can be offered here.

Larry

Two observations; 1) You have the front/top of the cowl ring aligned with the alum backing plate and not the actual spinner and 2) Dropping the aft end will probably make enough difference to re-evaluate.

You might be happy with the front/top of the ring being slightly higher than the spinner. Personal preferences, etc, seem to be the norm. In a perfect world there would be a perfect fit however I found that the width of the ring side-to-side and the top-to-bottom distance dictated that there is some ring BEYOND the edges of the spinner in order to keep the RING ROUND. DON'T CUT TOO MUCH off the sides of the cowl on the aft edge, raise the nose enough to judge the aft cut better and reduce the spinner to cowl gap for the first cut or you WILL cut the aft end too much. (Ask me how I know) Small cuts = small regrets.

gary