RE: Repairing my Alpha .40
Hi,
Good for you wanting to make the repairs yourself. Depending on you skill level this could take a little while or a few hours but it sounds like something you should be able to handle.
If you could take a few pictures of the damage that would help everyone.
If the firewall cracked or separated from the side of the fuselage then you would take some glue(yellow carpenters glue or 15-30min epoxy) and brush the glue between the joint and move it back in place and clamp it till it dries. Then go behind (backside of the firewall)and reinforce the edges where the firewall meets the fuselage with some 3/8 or 1/2 inch triangle stock balsa and glue those in place on each side for additional support.
If the firewall is cracked through the main part ,it really depends how bad and where the crack is.
If the crack is on the rear of the firewall,it could be reinforced from the rear by cutting a piece of thin plywood the size of the firewall and gluing it directly to the back and then re-drill the holes through for the engine mount.
If it's cracked on the front it could be repaired in a similar fashion but it depends where the crack is located. It may be better to carefully cut out the firewall from the fuselage sides and bottom using a thin saw blade(a hacksaw blade works good for this)and make a new firewall. You can take a piece of heavy paper and make a template of the firewall before removing to mark the mounting holes or depending how well you cut out the existing one you could use it. Then glue the replacement back in and reinforce from the rear with triangle stock.
Depending how you make the repairs,when you have finished, take some epoxy glue and thin it down to the consistency of paint and brush it onto all of the new/bare wood you replaced or added on the rear and/or front . This will help keep the fuel or any other liquid from soaking into the wood.