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Spinner/Cowl clearance issue

AviatorJ

Well Known Member
When I fit my cowling I had the spinner mounted and was extremely diligent in maintaining the plans stated 1/8" space between spinner bulkhead and cowling. However it's now apparent that I probably should have had the spinner actually installed because the shiny spinner from Hartzell actually comes back maybe another 1/16" or so. Put that I mounted my cowl a bit lower to accommodate engine drop and it's apparent I have a clearance issue.

The solution is going to be to sand about 1/8" off the front of the cowl to accommodate extra spacing. I'm going to shoot for 1/4" clearance between the spinner and front face of the cowling. I would imagine taking 1/8" of material off the front will either eat up all the material in places or at least severely weaken it. My thought is to buildup the inside and about 1/4" up the inside radius's with cloth and resin.

What is the best cloth type to build thickness but not lose strength? Is E glass still fine or do I need to use S glass, or something else?

Thanks,
 
Spinner

Justin, I'm guessing you just had the backplate on for cowl fitting. The spinners do come back about 1/16" further. Have you talked to hartzell about removing the 1/16" overhang off the back of the spinner? May be an option.
 
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Just add washers to move the spinner back plate and front plate forward. The Hartzell manual gives you some option to do this.

You can also add a washer under the engine mounts to move the engine forward a 1/16?. Between the two you can get your extra 1/8? gap.

Carl
 
I did just have the backplate on, would rather not sand up the pretty spinner. But I did think about it.

Carl you are correct that you can add up to two washers for spacing (3 washers total). Problem is I was concerned about having the gap too big when I sized everything up so I had the two washers already in there, with the idea I could remove some to make up the gap. Didn't work out that way though...

I don't mind doing the sandback/build up stuff. I've grown accustomed to the pain and misery that is fiberglass. Just want to make sure what I lay up is strong enough to last.
 
Just add washers to move the spinner back plate and front plate forward. The Hartzell manual gives you some option to do this.

You can also add a washer under the engine mounts to move the engine forward a 1/16?. Between the two you can get your extra 1/8? gap.

Carl

+1 .
 
I know a guy here that had a similar problem on his RV and filled the back side of the forward flange with West System epoxy/fiberglass cloth, then sanded down to his desired dimension. If I did it that way I would sand the area, clean it up with acetone, squeegee on a flox/resin mixture to fill voids, then lay about 4-5 layers of 9 oz bidirectional cloth - all at the same time. Use a tool to make the cloth lay down smoothly over the flox mixture with no voids. Sand to your desired depth and if that gets you into the flox layer, you can fill it with epoxy/fairing filler on the front side. If the flange is too thin at that point, you can add additional layers to the inside if you need to. Using peel ply on the first step would aid in that event. I think washers under the engine mount - firewall attach would work too.
 
Thanks Scott. 9 ounce it is!

It's nice to know you can adjust with washers on the engine mount ect. I may use that in the future but for now it seems easier to mess with some fiberglass.
 
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Thanks Scott. 9 ounce it is!

. . . . but for now it seems easier to mess with some fiberglass.

Now, THAT is funny!!

Maybe if you take some expanding foam in a can and fill the back side of the cowl ring, then sand it down to the desired gap plus .060", then 4 layers over that. (Sanding^4) This method may take the fun out though.:D
 
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