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  #1  
Old 11-28-2008, 01:18 PM
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DanH DanH is offline
 
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Default Cowling Side Flanges

Fitting a cowl, no hinges, so a flange is needed along the side for 1/4 turn fasteners or screws/nutplates. The usual method is a riveted and bonded aluminum strip. The problem is that such a strip is flat, while the cowl is rounded, in particular as you near the front. I suspect this to be the cause of some misalignment reports after fastener installation. So, an alternate method for your amusement. I elected to lay up some glass flanges; quite easy to do.

Get the cowl fittted and trimmed to your satisfaction. Sand (40 grit) the inner surface of the lower cowl for good bonding. Paint two coats of PVA on the upper cowl inner surface. Jig the cowl (by whatever means necessary) so the outer surfaces of the two parts are flush and the parts can't shift fore and aft in relation to each other. I used scrap aluminum and clecos plus some shims and tape here and there. The cleco holes are a non-issue; plenty of surface filling in the future anyway.



The flange layup is 5 plies of tape, pre-impregnated in plastic and dropped in place whole over a light epoxy "surface prime" wipe. Stipple or roll to eliminate air bubbles.



When cured, pop it apart and trim/sand the new flange 1" wide.



The finished product precisely matches the upper cowl curvature.

After installing all the fasteners, I'll probably go back in and add more flange all across the front around the cooling inlets, just to eliminate any visual gap between the cowl sections.

BTW, with an angle valve 360 or 390 there is not much clearance down the left side (1/2" or so max). I may ditch the planned Skybolts here and use screws/nutplates instead.
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Last edited by DanH : 10-30-2018 at 12:58 PM.
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  #2  
Old 11-28-2008, 01:59 PM
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chrispratt chrispratt is offline
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Dan:

Looks good.

I suggest doing the same to the forward section by the air inlets to give the area some added strength and provide a spot for a screw/nutplate to secure this area tightly. I did this on my -8 cowling (see pics below). I used the conventional piano hinge method for the cowl but thought the forward area could use some extra strengthening/tightness due to its being literally at the pointy end of the stick and taking all the airflow abuse.

Fiberglass buildup before trimming.




And after trimming and adding a platenut. It seems to work well.




Chris
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  #3  
Old 11-28-2008, 02:43 PM
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Hi Chris,
That's the flange I'm installing later, but I hadn't thought about a nutplate there. Hmmmm, thanks!
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  #4  
Old 11-28-2008, 09:08 PM
RatMan RatMan is offline
 
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Wish you guys had made these post about 9 months ago. Awesome work!
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  #5  
Old 04-30-2009, 07:09 PM
Lars Lars is offline
 
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Dan, did you ever get around to installing the fasteners in those fiberglass flanges? If so, I'd be interested in seeing a photo. I'm sitting here looking at the piece of 2024-T3 I was going to use; after seeing your photos, I think I'm going to use glass instead- they look great. Thanks for posting this!
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  #6  
Old 04-30-2009, 09:51 PM
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Lars,
I used #8 nutplates. You know what they look like <g>
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  #7  
Old 04-30-2009, 10:13 PM
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Default Nice work

Hey Dan,

Nice work. Did you know Skybolt has some low profile fasteners? I got a couple of them for "close" places. I'm doing a 390 in the new project so step on all the land mines for me!!!!
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  #8  
Old 05-01-2009, 07:15 AM
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Quote:
Originally Posted by RV7Guy View Post
Hey Dan,

Nice work. Did you know Skybolt has some low profile fasteners? I got a couple of them for "close" places. I'm doing a 390 in the new project so step on all the land mines for me!!!!
Thank you, no I didn't know that, and no land mines yet. You doing an 8? The 390 has the same "problem" as the other angle valve installs; clearance to the cowl is very tight on the port side. The really tight spot isn't the split line, although fasteners need to be low profile there. It's up near the 1/4-20 screw ears on the heads, in particular at the most forward and rearward corners.
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  #9  
Old 05-01-2009, 12:23 PM
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Quote:
Originally Posted by DanH View Post
Lars,
I used #8 nutplates. You know what they look like <g>
All too well...

Mine will get Milspec fasteners, since I happen to have the kit on hand.
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  #10  
Old 07-20-2009, 05:14 AM
Oldgeezer Oldgeezer is offline
 
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Default fiberglas flange

Dan
How wide is the fiberglas tape you used to make up the cowl side flange?
Also when you preimpregnate the cloth tape, do you lay it up over wax paper on a flat surface and then just lay it upside down within the cowl and peel of the wax paper or lay each of the 5 tapes individually, stippling out the air bubbles as you go?

Thanks
Oldgeezer
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