RE: What Mods/renforcement needs to be done on Hangar 9 Corsair ARF for it to fly safe?
The fuselage/ firewall mod has already been covered in this thread, altho I don't think you need to add a half of a pound of 'glass and epoxy to fix it, I think it could be done with much less. Just my opinion.
Next is the wing failures which have been reported and photographed by several RCU members. After I examined those pictures, and then examined my own Hanger 9 wings, I can see the the problem: The main spar for the most part does not pass thru the retract bay ribs. Rather, it is butted up to the rib and glued (hot melt?), which translates to a retract bay which can rather easily be seperated from the spar and inner wing section. This is INBOARD of the retracts, thus landing loads are imposed on this joint.
My cure was performed on my electric one (Saito .91 powered one remains un-modified), and again: covering must be removed to do it right. The picture shows my primered wing (ready for paint). What I did before priming was round the edges of the inner retract bay ribs towards the center of the wings, then added a total of 3 layers of 1/2 oz 'glass cloth over these rounded edges with a generous overlap. You could use fewer layers of heavier cloth, but it is difficult to 'bend' heavier cloth around those rounded edges. This mod allows the wing sheeting to 'grip' the retract bay ribs, and thereby adds a lot of additional strength.
This is another case that altho I have never personally seen a wing failure, I have seen the evidence that it should be modified to prevent such a failure.