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**Robert Lees** · 10-09-2009, 16:32

Re: Saggy Cowl

Just my initial thoughts, Josh:

Part of the problem may be the lower cowl itself. I don't know about your 1940 model, but my previous 1941 and my current 1946 models both have compound curve lower cowls. Yours looks like a single curve (flat sheet bent over, if you will).

It's difficult to show it in a photo because the compound curve is so slight...this is the best I have:

This might raise the front lip when compared with yours, so raising the aperture for the crankshaft. I did use a mandrel to locate the prop flange:

Even then, under gravity, it still dropped a bit (maybe by 1/16"). If I were to do it agin, I'd bias the mandrel up a bit by that 1/16th to allow for the cowl weight.

I'm not sure that in your case it would raise the top cowl to fit the plugs that you want.

Bearing in mind that it's a monocoque cowl mounted from the firewall, are the mounting holes for the whole cowl assembly a bit loose with age? Could these be causing the droop?

**bashibazouk** · 10-09-2009, 17:03

Re: Saggy Cowl

Thanks, Robert.

The pictures are great. I see what you mean by the compound curves. My original was not original apparently and that helps explain the stress cracking at the air intake opening. I think I'll go back to the drawing board and try again with the mandrel you suggest.

Josh

**Hank Jarrett** · 10-09-2009, 17:22

Re: Saggy Cowl

You don't need to make a new cowl, you just need to finish that one.
If you can get access to an English Wheel your cowl needs to be bowled out on the bottom, which will make it longer, and that will cause you to need to shrink the front edge so the fasteners will fit the bowl again. The net effect of these operations will move the bowl up.
English Wheels are a lot of fun, but need to be treated with a lot of respect. As you roll the cowl the wheels can crush your fingers as flat as a sheet of paper. It is a real pinching machine and will grab the edge of your finger or hands so quick it's scarry. Not trying to put you off because it really is a blast to watch a piece of flat aluminum become a smooth curved cowl.
Find someone who has one to show you the ropes on a wheel and you won't regret it.
Hank
By the way, there is a pretty good chance you will end up making that second cowl anyway. I have screwed up some aluminum pretty bad, but I haven't smashed a digit yet. Just got to be careful.
I HAVE cut myself a couple of times on the edge of the metal, but if you do metal work you will do that no mater HOW careful you are. It's worth it.

**Ray36048** · 10-09-2009, 18:28

Re: Saggy Cowl

I am not sure the shape of the cowl being compund or flat would make a difference in the location of the bowl. I think you just need to make a fixture to locate the bowl and work from it.

Where some of the laterT-crafts built with "flat" bottom cowls?

I am also making a cowl. I made a fixture to do what Robert did to locate the nose bowl. I went to a local heating contractor and bought steel sheetmetal. This is much cheaper and easier to get than aluminum. I have made 2 so far, I am very happy with the second one and plan to use it as a template to make the final cowl from aluminum.

My process was to make the first template from stiff cardboard. From that I made the first one from the steel sheetmetal. I then layed out all of the demension lines so I could take some measurements. The mesaurements showed the template was not symetrical. From this information, I layed out the second cowl to make the hole locations symetrical and fine tuned the hole locations by careful measuremnets of the bowl and booth cowls.

This is a slow process, but I think I am zeroing in on a workable part.

**bashibazouk** · 10-09-2009, 18:33

Re: Saggy Cowl

Hank and Ray,

You're right, I'll be making a new one anyway! I went nuts and made the one that's on there out of 2024T3 and that's not very workable stuff. I'll have to go a little softer and borrow my neighbor's wheel. Another neighbor's got a shrinker so between all of us, I should get a cowl out of the deal.

Templates are definitely the way to go. It makes perfect sense now that the bottom cowl should be dished. I couldn't figure out why the edge of the nosebowl was at such a wacky angle relative to the bowl. It mated fine once I smooshed it together, but it was/is definitely under stress.

Thanks for the input, guys!

Josh

**N96337** · 10-10-2009, 11:50

Re: Saggy Cowl

Just a little hint... a 3# coffee can is about the right size for the opening on the nosebowl... just a little foam (such as thick weatherstripping) around the middle of it and it'll fit nicely. I took one and then punched the holes in it to fit over the prop shaft, with the ability to fasten it to the flange, to keep it from moving....works great!
Josh, you can anneal that aluminum with a flame of pure acetylene... just let it get all black with the flame and it'll amaze you how much nicer it will be to work. (wipe off the carbon to keep the mess down) Not having an english wheel shouldn't stop ya...just use some sandbags and a slapper and if you're gentle and patient, you'll get your curve....been there, done that...but a wheel is much faster!
JH

**astjp2** · 10-13-2009, 11:04

Re: Saggy Cowl

Use 3003 H-14 .063 or .050 for the bottom cowl, Its easy to work and is the correct material, 2024 is not correct for the older aircraft. Tim

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