cowling fit

What to do here?, looks like 2 to 3 degrees between flange and spinner. Will the engine sag that much? I saw somewhere that a guy with another model had the same problem and cut the whole flange off and reglassed it, is that recommended here? If I do that will the bottom need to be cut as well?
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I wouldn't do anything as my engine sagged at least enough to end up parallel once it "settled in. But my plane isn 't a prize winner so take that for what it is worth.

The bigger question is how did it end up that way? Did you put a spacer ring behind the spinner mount when you cut the cowling to fit. At this stage you could retrim the rear and get it parallel with the spinner mount. You' probably have to drill some more holes in the mounting hinge at the rear but you will have plenty of chances to fill the extras when you finish it.

No need to modify the flange - it the rear trim that is the issue here.

BTW - I just repainted my cowl after repair some damage and improved the fit at the front as well. After both halves are mounted and all hinges mounted I joined the halves together off the airplane and added 3/4 layers of glass to the back side of the front outlet edges essentially gluing the front pieces together. After cured I used a small cutoff wheel in a dremel tool to cut them apart on a straight line after using dry micro to get a perfect fit and shape to the inlet. Then you end up with a perfect match in this difficult area.

I have not trimmed anything yet, just laid it on top so it is overlapping the top of the fuse, shimmed the front up to line up with the spinner and saw the alignment issue.

not following you - confused

Are you referring to the narrow gap on top, and wider distance between cowl and prop flange at the bottom? Top to bottom? That is the way mine is, and all the others I've seen. Mine also was wider on one side than the other, so I thinned down one side, and built up the other. I had to add glass/epoxy layups to the back on the thinned down side; both top and bottom. The wider gap at the bottom makes it easier to remove the lower cowl; less paint damage over time. For removal, the top cowl can be lifted straight up, but the bottom must be pulled slightly forward.

Otherwise, my engine cowl parts were well made, and fit pretty well; no complaints.

Airplane Bondo!

I would just:

1. Mix up some epoxy and microballoons

2. Pile it on the flange to fill in the gap between it and the spinner

3. Wait for it to cure and sand to contour

3. Add a layer of thin glass over the top

3. Be done in a couple of hours

Thanks, Bob K.

Too soon to tell.

If you have only laid the top half in place I don't think you should be cutting off anything or using bondo yet. Fitting that thing is exasperating. When you get the the two halves together, tacked in place as best you can and have done some of the required cutting to get it close, you may have a better fit or at least a more rigid and fixed cowling that you can then modify if required.

Cowl gap

Exactly what Brian said. The fit will get a little better when the cowl is aligned with the fuse skin, but this is normal.

I would strongly suggest you bondo a spacer on the front face and off the top of the top cowl to use as spacer guides to the spinner back plate. It's the best way to reproduce the cowl position as you take it off and on MANY times during the trimming process.

Cowl fits

Welcome to the ?fit the cowl club.? Mine was very similar to your situation. He is what I did.

First fit and trim the cowl so that it is attached to the firewall and the two cowl halves are attached. Leave ~1/4-3/8? clearance between the back of the spinner and the nose of the cowl. The greater the clearance the easier it will be to remove the lower cowl. I set the spinner proud by about 3/16? for engine sag. My engine was on the mounts for ~2 months prior to fitting the cowl. After 4 years (2.5 flying) my sag was a total of ~1/4?. So now the spinner is no longer above the cowl but below by ~1/8?.

The nose of the cowl sloped away for the spinner and I had to build up ~1/4? on the bottom cowl tapering up to the top cowl. I bonded some balsa wood to the front face of the cowl. ?? in some areas, less in others. I then glued some sand paper to a flat piece of wood to make a flat sanding plate. I sanded the balsa wood until I got the nose of the cowl proper. I intentionally sanded back an additional 1/16? so when I glassed over the balsa wood it would be at the final gap with spinner.

Contrary to a few posts you should have several layers of glass over the nose.

I didn?t have the prop on when I fit the cowl, I used a spacer adapter to simulate the prop hub. Having the prop on may make things a bit more challenging.

FYI I have a Hartzell BA prop.

I drilled and clecoed some aluminum angles on the top of my cowling to lay on top of the spinner backplate to hold the front vertical position. I glued some Popsicle sticks to the front for my 3/8 gap. When I fit the rest of the cowling to the fuse my gap behind the spacer was uneven like your pic shows. I was going to buildup the front face of the cowling with west systems micro light, but I didn't want all the sanding and a huge glob of filler.
Instead i Installed the cowling, and used a die grinder to cut the cowling about an inch back from the lip. I left part of the lip attatched to the cowling that had the proper spacing. Then I clampd the lip to the spinner backplate with the proper spacing of Popsicle sticks and installed a couple of fiberglass strips to hold things in place. Removed the cowling and glassed/filled the gap that I had cut. I put most of the fiberglass on the inside of the cowling so it didn't have to be as smooth.
Sorry no pics, it was intimidating to cut into my cowl like that but I think it was much easier in the end to have the spacing behind the spinner set and just fill 1/4 cut on the cowling.

old style cowl

my old style cowl (no pink) was the same. I used fiberglass layers to build it up, up to 1/4 inch in some areas. it was a real effort sanding to final dimension but it's solid. covering with softer material and covering with glass may be a easier method.

scottw said:

I have not trimmed anything yet, just laid it on top so it is overlapping the top of the fuse, shimmed the front up to line up with the spinner and saw the alignment issue.

Click to expand...

Starting with that statement, it's premature to be very concerned about the parallel surfaces of the flange behind the spinner. When the aft end of the top cowl is trimmed sufficiently to drop down in the proper alignment (in front of the FW edge) then the surfaces on the flange will be more parallel. (ask me how I know).

I found that allowing the flange/spinner 'gap' to be smaller during this fitting step, allows room to be long on the aft edge and avoid over aggressive trimming there. Drop the aft end in, and then trim slowly to 'retreat' from the spinner and get the gap you desire while slowly improving aft edge alignment.

IMHO --
gary

I had a ugly spinner to cowl gap when I was finished fitting the cowl.

I decided to cut off the front flange of the cowl and re-glass it.
Put some blobs of epoxy to hold it in place where i wanted it and added 3
layers of glass inside and one layer outside.