Posted: 11/16/2009 17:36:59
I'm building a wood airplane, an 85% scale version of a Supercub. It's time to start on the aluminum cowl, and I don't have a clue what thickness tjhe panels should be. The Supercub side panels bulge out at the rear to form gills and I don't want them to be flimsy, but I don't know what's flimsy and what is too heavy. I would certainly like to hear from someone with some expertise in this area. Can you help ? Thanks, Ken
Posted: 11/18/2009 21:45:39
You're asking a complex question that depends on design factors. For example, the Thorp T-18 uses 2024 for panels that permit simple bending, but .050 6061 for portions that need forming. You don't say what engine you're using, but I anticipate you'll want a pressure cowl.
Does your design allow a prop extension? What's your lift-off speed and best L/D speed? Can you exhaust along the sides or only out the bottom? What approach are you taking for baffles??
If you provide more detail, the better answers you'll recieve.
TC # 5436
Posted: 11/18/2009 23:10:47
I've recently had the pleasure to help two members, one w/ a J 4 boot cowl that needed replacement of the top section, and one w/ a 47 Funk nose bowl that needed to be reformed, w/ several deep dents/ tears... The boot cowl from the factory used .025" 2024 T3, or T6,(hard to tell after 50 years). The Funk nose bowl appeared to be .040" 6061- 0 (0 condition ), it will harden up as you work it. Keep in mind I have an English wheel, Planising hammer, and a large assortment of metal working hammers, dolly's, beater bags, sheet metal roller, torch set, and the like. See if one of your local collages has an evening Adult Education course in metal working, if you don't have a local mentor. You'll also need to learn some basic pattern making.. Hope this helps, and don't give up!
Bob Quick (ex Pres. EAA 486)
Posted: 11/19/2009 06:14:00
Bob, I'm using a stock glass nosebowl and all the panels are straight with no forming required. If Piper used .025 for the boot cowl on the Cub that sounds like a good way to go. At least I can use that for the top and bottom pieces. The sides bulge out at the rear, and maybe something a little heavier will be needed for them but by then I should have a bit of a feel for what I need. Thanks for the info, I know there are a lot of variables for something like this, but I'm just going to have to dive in ! Thanks a lot, Ken
Posted: 11/19/2009 06:34:47
Marc, I'm using a stock glass nosebowl and the 4 panels , top, bottom and 2 sides run from that to the firewall with no bending or forming. I'm trying to duplicate a Supercub cowl. I'm using a 65 hp Hirth mounted inverted which will not require any real baffling, just some short aluminum ducting to get the air from the cowl vents directed down at the cylinders. air will exit out the 2 gills formed by the rear of the side panels bulging out as well as a cutout in the rear of the lower panel. I've just received a reply saying the Cub boot cowl is .025 stock, and I guess that's as good a place to start as any. Thanks a lot for responding. Aluminum sheet isn't cheap and I didn't want to order something only to find that it wasn't much better than tin foil, or, that it was so heavy I was going to have a CG problem ! Thanks, Ken
Posted: 11/28/2009 20:35:03
I built my cowling sides on my wag aero back in 1992 with .025 6161 with no problems with hundreds of hours.
Posted: 11/29/2009 05:50:30
Thanks Creighton, That's encouraging. The cowl I'm building should look just about like your picture ! Thanks, Ken
Posted: 12/5/2009 11:11:30
You mention that the metal will work harden. Did you anneal it before starting (the 6061 used on the nose bowl) or did you just work it until done?
Did you anneal it when the bowl was complete or leave it in the work hardened state?
Also, what grade of Al would you recommend for a nose bowl if starting from scratch? (I'm building a Zenith 801 and plan on an all Al nosebowl. Using the english wheel and hammering when needed. but learning as I go.)
Any tips greatly appreciated!
Posted: 12/20/2009 18:35:28
I started w/ .040" 6061 - 0 aluminum. That's 0 condition, dead soft, for the nose bowl. It will work harden as you form it, depending on how much curvature, and the tightness of the radius you're trying to put into it. It takes some experience to know when to reaneal the work piece, before it beguins to crack, while working it. You would want to leave the finished piece in the hardest state possible, to resist dents and dings, w/o it being so hard, as to easily crack... It's a bit of a ballet..Sorry for the delay in replying, but I'm trying to come up w/ a better intake system for a 2180 VW, installed in my Sonerai 2L..