Spinner/cowling fit

I'm curious how many of you out there went the extra mile to build up the lower cowling with foam/balsa & fiberglass to be flush with the spinner.

I'm not building a show plane, but I do want it to look nice!

I'm assuming you're trying to have the cowling match a perfect gap behind the spinner of 1/4 inch or so?

I'm no expert but I found instead of filling the gap with filler/balsa/fiberglass etc I found it easier to cut 2 or 3 inches behind the spinner on the cowling, clamp it in place and temporarily glass it.

Sorry no pics, I installed the cowling on the airplane and cut semi circles several inches back on the cowling around the spinner area that I wanted to fix. I was able to leave the pieces attached to the cowling, but the cuts let me manipulate the cowling behind the spinner where I wanted it. Using a spacer I clamped everything in place to the back of the spinner and used little fiberglass strips on the outside of the cowl to "hold" everything in place. When my fiberglass strips cured I removed the cowling, filled the cut/gap with flox and filler and topped with fiberglass on the inside of the cowl. I sanded down the fiberglass strips on the outside and fared it out with filler. I hope my description makes sense.

I almost piled on a lot of filler on the outside to match the rear of the spinner, I'm glad I didn't. Too hard to get it right and too many iterations of cowl on again and off again.

It was really hard to take the die grinder and make the big cuts, but very little work to make a perfect spinner to cowling gap.

Thanks, Crabandy. I'm not sure I completely understand how you did it, but your approach gave me some ideas on how to proceed.

The bigger gap at the bottom makes it much easier to remove the lower cowl. Be careful that you don't create a long term problem if you close that gap...

When my cowl and spinner was on the plane I measured 3/16" or 1/4" (cant remember now) for the gap. The wider the gap, the easier it is to get the cowl on and off later without scratching up the paint. Then I used tongue depressors cleko'd to the cowl to hold the correct distance. The holes can easily be filled later. I then applied a dry microballoon and epoxy mixture.



I then used a piece of waxed formica counter top I had laying in my scrap lumber pile. I pressed the piece down till it contacted the popsicle sticks.



Removed the counter top piece next day.



Still had a lot of filling left to do but it gave me the perfect gap to work with.

rightrudder said:

I'm curious how many of you out there went the extra mile to build up the lower cowling with foam/balsa & fiberglass to be flush with the spinner. I'm not building a show plane, but I do want it to look nice!

Click to expand...

Everyone who wanted it to look nice.

MikeyDale said:

I used tongue depressors cleko'd to the cowl to hold the correct distance....I then applied a dry microballoon and epoxy mixture.... I then used a piece of waxed formica counter top I had laying in my scrap lumber pile. I pressed the piece down till it contacted the popsicle sticks.

Click to expand...

Very clever!

I found it easier to cut 2 or 3 inches behind the spinner on the cowling, clamp it in place and temporarily glass it.

Click to expand...

See Mike's method above.

MikeyDale said:

When my cowl and spinner was on the plane I measured 3/16" or 1/4" (cant remember now) for the gap. The wider the gap, the easier it is to get the cowl on and off later without scratching up the paint. Then I used tongue depressors cleko'd to the cowl to hold the correct distance. The holes can easily be filled later. I then applied a dry microballoon and epoxy mixture.


I then used a piece of waxed formica counter top I had laying in my scrap lumber pile. I pressed the piece down till it contacted the popsicle sticks.

Removed the counter top piece next day.

Still had a lot of filling left to do but it gave me the perfect gap to work with.

Click to expand...

Nice! Will James recommended something similar, with clay on the perimeters for a dam, and a piece of window pane glass for the surface. Waxed of course!

It makes a perfectly flat surface like this! I am not there yet

Mike, that looks like a great method, one my pea brain can process.

After filling and shaping the micro, did you fiberglass over it, or can you just prime and paint?

I just filled several times, 3 epoxy skim coats, then primed several times. Hope it dont all fall off but I have read lots of other people did not lay cloth. The thickest part was probably only 3/16. The part doesn't require any strength.

I had a lot of similar filling on my old white cowl.

With the cowl upper and lower attached to each other I contact cemented two whole sheets of sandpaper to a piece of plywood and used that to keep the surface reasonably flat during finishing.

Thanks, guys. I think I'm sold on adding some micro here. In the grand scheme of cowl fitting, it's not much extra time/effort.