I am getting ready to mount the cowl on my Sig Kadet MK II with an O.S. 35 AX. I want to get the gap between the spinner & the cowl as close as practical but do not want any interference or fouling. To me, too big a gap just looks bad. In my attempt to achieve the best compromise here is what I have so far. I cut a shim piece to establish a consistent 1/16" gap out of 1/16" balsa, it actually measures .062" with my dial calipers. Here is what it looks like:


Is this about right? Or am I being too picky thinking it's a bit too big? I have a piece of 1/32" balsa that actually measures .042" which is actually closer to 3/64" with which I could make a shim of and it would definitely look better, but would it be enough of a gap? I would rather go with the .042" for looks but I am unsure if it would be adequate as I do not know how much movement the front of the engine will experience.
Thoughts and opinions please!

It kind of depends on how stiff the cowl is. When the nose of the plane is to be covered in monokote I usually use 1/16 plywood glued to the spinner backplate as a spacer. For a fiberglass cowl I use 1/32 or1/64 ply. If the cowl can flex you need a little more space. I glue the ply on with rubber cement so I can easily remove it from the backplate.

Exactly! You want the gap to be as small as possible without hitting the cowl. If the cowl can move and hit the spinner, then you need more gap. A 1/16" gap is very commonly-used, since 1/16" ply is readily available for making shims. If smaller works, then go smaller. Whatever appeals to your eye.

If the spinner hits the cowl it diffenetly won't look good. I have no idea how much things will move in flight I'd leave a gap

Hi!
I strive for a 0,5-1mm gap.

Its a trainer and not a Quarter forty pylon ship. Do yourself a favor DBD, give yourself a whole bunch more breathing room or go to a spinner nut, honest.

John

Getting that spinner perfectly aligned and with minimal gap is fine until the engine thrust needs adjusting then it's back to square one.
I wouldn't even mount the cowl until the plane is trimmed for flight. Just my .02


Tom

To my eye, it looks like DBD1 has a nicely trimed and fitted cowl. To alter it's location at this point would be a shame. I would fly as is.

In the future, I would suggest that the gap be set first, and then make the cutouts for the needle valve, etc.

Hi!
For a newbi a spinner is no good!
A much better way is to use a spinner nut

DBD what you have is perfectly acceptable. I think some guys here are over thinking it. Being the type of airplane it is I seriously doubt there will be any thrust adjustments made. Hell I see that on at least 50% of the aerobatic airplanes I see have never had a thrust angle adjustment and these guys want to anticipate one on a trainer. Lol. The only thing I would add is that if it is too close you could have some interference should the engine mounting screws work loose or you loose an engine bearing. In the end anything more then 1/32 would work just fine for your particular set up. Looks to be fantastic workmanship on the build from what I can see. Trimming a cowl causes some guys lots of greif, yours looks great.

Jaka, awesome looking Proud Bird, makes me want to go out and get one. I would of course have to bash it into a Rivets though. I hear those EF1 airplanes are great conversions with a good .32

Thanks for the compliment Shawn, it has been a long time since someone has told me I think too much....

Scott

LOL Scott, I didn't have you in mind when I wrote that but isn't it nice to know that someone thinks your a deep thinker? I actually liked what you had to say on the matter. Nothing wrong with keeping it simple.