>I am worried about the durability of 4 layers of 1/8" birch
>ply, though. I remember Bob Bearden selling fast combat kits
>(his Viper, which looked like a Voodoo) where the mounts
>were 4 or 5 layers of 1/8" birch ply. After a while, they'd
>crush. And in a bad crash, break right off. The more usual
>3/8" x 3/4" maple bearers most people used were far stronger
>and more durable. True, no one used metal mounting plates,
>but Combat planes aren't supposed to last as long as Stunt
>planes, not by a long shot, and the crushing problem still
>manifested itself.
The crutch only transmits forces to the side walls of the fuselage. In this manner it is different than a combat plane crutch, which stands on its own.
I have done several planes with the plywood crutch. All of these planes were for the Saito 72. I have never experienced crushing, but have experienced broken aluminum pads, which apparently means there was certain amount of flex, but given the nature of the Saito 72 and its brutish vibration, the nose construction would need to be substantially upgraded in many areas to be truly bulletproof.
In the case of the RO Jett and PA engines, the nose construction is almost an aside. The vibration is so low and the torque transmition so benign that construction can be a little lighter than say with a ST 60 or Saito 72. If you will notice in the picture, the crutch is relieved to a thickness of 1/4" after F1. I would never do this if I were concerned about forces from the engine.
All of crutches up until the Solace were two layer of 1/4" ply. In the latest cases, I decided to go to 4 layers of 1/8" ply. The crutch does seem to be stiffer and should be much more "dense" with the greater number of plys. The Solace has .2 oz CF mat between each layer of ply, I should think this would suffice for any engine. On the Zone 2 I felt this was simply not necessary and adds needless weight.
Considering that the standard nose construction method has not changed since the Nobler, except for the addition of plywood, I felt that someone should be trying alternatives. I feel that plywood can be stronger than hardwood if sone correctly. I know that laminates are superior in terms of st
I have considered rigging a stress test for laminate members over hardwood, just to compare the true strength, but I have been busy painting the house!!!
