Need to rebuild/replace the firewall to my H9 Corsair. What kind of wood or ply should I use and what thickness?

thanks,,,

If I have to replace a firewall, I usually use 1/4" marine or aircraft plywood. this would have 5 or more ply laminations, rather than the three laminations reqular plywood has. 1/4" ply easily holds engines up to 75-80 cc. You may get away with 3/16" aircraft ply, but these planes usually tend to be tail-heavy, so the stronger, heavier wood couldn't hurt.

Good luck with you repairs.

Mike Boyd

1/4 in plywood (5 ply aircraft) would be plenty for your H9 60 sized corsair. HOwever, I would never hang an engine over 50 CC on a firewall of that thickness. That's just me, though.

I had to add to the firewall in my H-9 P-47 so that I could mount the engine inverted (completely) I use 3/16 aircraft ply and epoxied & pinned it to the existing firewall. Very substantial. (especially when you consider the original thickness of the firewall.

1/4" aircraft grade ply should do it if you plan to use an engine up to a 1.50 four stroke.

What about 100cc... what's the concensus?

100 CC, or 1.00 CI? There is a big difference. For 100 CC, I'd go with a bare minimum 3/8, but more like 1/2 or even 5/8 inch ply--6 or 7 ply if possible. For 1.00 CI, The 1/4 is fine. I think my Giant Stik, which is designed for a max 38 CC engine, has a firewall of 3/8 or 1/2. I didn't measure it, but it's thicker than 1/4 for sure!

Ohh, sorry, should have said what size engine. I had a Magnum .91RFS on there which I'll be reinstalling.

thanks for the suggestions..

3/16 should do fine. Have you ever noticed how thin the ARF firewalls are?

I'm going to quote you on this. Many H9 Mustangs and Corsairs have had their firewall cracked or broken due to the cheap 3/16" thick firewall. Other ARF manufacturers, such as Kyosho, WM, VQ, CMP, and KMP to name a few, use high quality 1/4" firewall.

On my H-9 P-47, the firewall is/was very thin. In fact, it was only doubled where the original mount holes were. (the rest was cut away to lighten the structre) Since I was not going to use a Saito 4-stroke, but am using an OS .91 Surpass which is physically larger, and since I did not want to have to, "Butcher" the cowl, I laminated in a piece of 3/16 real aircraft ply. I installed this using the tried and proven method of drilling both firewall parts, and epoxying the sandwich, and epoxying dowells through the drilled holes. Works (and has worked well for years) The engine is now truly inverted, and the cowl needed no additional hole for the rocker box to protrude through. I suppose you are correct, in that now my firewall is truly 3/8" thick. Not having any experience with ARF's other than this one, I suppose that what you have said is true. I do know that I would never trust 3/16 alone to support a high output engine. I was under the impression that he was adding to his existing firewall, and not using it as a stand alone part. Sorry about the misunderstanding.