View Full Version : Metal for boot cowl and engine cowl

Jim Miller
12-15-2009, 11:06 AM
What alloy and thickness is recommended for boot cowl and engine cowl?
My engine cowl will be open J3 style.

Jim Miller

12-15-2009, 01:03 PM
I used .025 2024-T3 for my boot cowl. I didn't build a engine cowl so can't help you there.


bob turner
12-15-2009, 01:11 PM
I made my engine cowl out of 7075-O .032 in 1964. Only cracks after thousands of hours of service are where the Brackett filter touched my beautiful rolled edges - which cleared the stock air filter. The dash O rolled just like the original.

The original was soft .025. It lasted about 2000 hours, then fell apart. I repair the boot cowl as needed, using flat head rivets and bondo to preserve the original look. You cannot tell . . .

12-15-2009, 01:20 PM

Flat or slightly curved you want 2024, for other things that have extreme curves you should plan on 3003 since it is softer and forms easier.


mike mcs repair
12-15-2009, 05:35 PM
2024 t3 for all.... cowl doors, top and bottom cowl, and top of boot cowl are all .032

bottom of boot cowl .025 or .020.... if on skis(attaching check cables allot use .025 to keep from denting bottom corners/edges)

always double up rivets at ends of stifeners...like if they are 2" make last 3 at 1"

12-15-2009, 08:50 PM
Along the same lines,

What metal is used for the engine cooling baffles?



Steve Pierce
12-15-2009, 09:14 PM
I use .025" 2024T3 on the cowl and boot cowl. .032" on the cowl doors. Nose cowl on a J3 type might need to be softer stuff. It is a lot stronger than the 3003 that Piper used. 5052 on the baffles.

12-15-2009, 09:48 PM
Steve why do you use 5052 on the baffles insted of 2024?

Steve Pierce
12-15-2009, 09:50 PM
Not as hard and brittle and likely to crack, yet strong.

12-15-2009, 10:01 PM
Jason and I are covering the fuselage Monday :onfire:

Steve Pierce
12-15-2009, 10:07 PM

12-16-2009, 08:54 AM
I Have made many J-3 baffles using 3003 .032, Never seen a crack yet, First set made was over 10 years ago. Not saying it is the Only choice or Best but It is easy to work and Make a very nice finished part. I always made mine as the originals (Other than improved rivet spacing and Proper rivets) so they were nice and compact with plenty of support. Easy to roll the wires into and a pleasure to work.

Steve Pierce
12-16-2009, 09:19 PM
I made some 90 hp Super Cub baffles out of 3003 and some of them cracked. It works well on the baffles that bend 180 degrees.

12-17-2009, 12:09 AM
what about 6061 T-6?

12-17-2009, 12:11 AM
works just fine for cowl doors... I'm with Steve on 5052 for baffles though.

don d
12-17-2009, 11:03 AM
I like 6061 T6X .032 for cowling.


12-17-2009, 12:27 PM
OK everyone, step back from the keyboard and re-read what the original poster posted: J3 style cowling. It is hemmed or hemmed with wire on virtually all edges. Some of those harder alloys mentioned won't take to hemming very well.

For the cowling (less the nosebowl halves) .025 3003 is appropriate.

For the boot cowl - if the firewall is attached like Piper did it you want .025 3003 due to the floding for firewall attachment. IF modifying by attaching a flange to the rear of the firewall, 2024 can be used.

John Scott

Jim Miller
12-17-2009, 12:49 PM
I did add a flange to back of firewall by making some thin 1 inch by 1 inch
stainless steel angle then cutting wedges out of one side so it would bend around the firewall shape and riveted to firewall with 1/8 hard alum rivets.
I have decided from info offered to use 2024 T3 (.032 top and .025 sides and bottom) for boot cowl. The engine cowl will definitely need some soft alum and the nose piece will be difficult due to using a 0235 with starter and ring gear. In looking at my Colt nosebowl I think if I duplicate the middle third (with mods) it will approximate a J3 nose in appearance.
I will do this in fiberglass by making a female mold using medical bone cast material or roll gauze strips and plaster.

05-12-2015, 06:54 PM
Just double checking: I'm about to order metal for my pa-12 boot cowl, one piece and using the Cub Doctor's bottom stainless tunnel. Is 2024 t-3 0.025 correct.

How about for metal cockpit interior panels lining if I don't go with Kydex?

Steve Pierce
05-13-2015, 07:58 AM
I use .020".

05-13-2015, 08:57 AM
I use .020".

for which?

Steve Pierce
05-13-2015, 09:32 AM

mike mcs repair
05-13-2015, 11:30 AM
i use .020 boot cowl sides and .025 or .032 top

cowl doors are .032, the crosswinds? pa-12 conversion calls out .025, but i like .032 (and roll them to shape in slip rolls)

I used thicker on sides of boot cowl if putting doors to storage areas in the sides(-12 has ton of room up there, and if you lower/use flat floor you need storage..