Tank size for a Fox .35

Thanks Ken,

I was planning on making a new outboard doubler 1" longer than stock so the stress from the fox isn't isolated in a small area. Do you think I would be safe using 1/8" ply for the new doubler and going with the stock doubler inboard backed up a 1/4" hard balsa tripler?

Jim

Ken's right, it needs good stiff doublers, and a hard balsa cheek block on the inboard side is a good idea too. Make the cheek thick enough so the backplate bolt won't protrude through it. I also learned from Ken to make a big thick laminated center rib to capture and distribute the Fox vibrations. If it's too late for that, don't sweat it.

Use good hard aluminum mounting bearer plates on both sides, plus nylon offset wedges, and be sure to trim the edges of the ones under the engine tabs do they all fit flush and don't jam against the crankcase. Check the tightness of the mounting bolts on every preflight inspection.
Rusty

The Fox is a funny one. Your engine condition is critical. If you don't know the history or the engine is new, it could be problematic. Getting it out of it's vibration zone is critical to a good run. The Sterling Ringmaster has engine bearers about 2" long and they don't extend back and it works fine. The Ring defies the standard principles.  I've snapped dozens of Ring noses off and 5 min epoxied them back on and the darn thing never vibrated. However, I had a few that would shake the balsa to pieces. My suggestion into the doubler size was mainly due to avoid issues like vibrations. I feel 1/8" will certainly add a lot of unnecessary weight to the plane that generally builds nose heavy. I use 3/32" but not the 3 ply varieties nor lite ply. I certainly would recommend running the doubler back to the high point of the wing. My concerns of adding a tripler would be that you might be rubbing the grain in terms of the rules. In New Jersey, I find it hard that they wouldn't let you fly, but adding a tripler wasn't a part of the kit in terms of design and I can see someone contesting it. Your club would certainly understand and know what would be allowed.  It would be said that your giving the airframe a unfair advantage against say a similar opponent who was flying the same design without one due to encapsulating vibration. The outline of the plane is being changed by the additional piece therefore your not in compliance as well. If your not flying in a contest, I would say go for it.

My suggestion to Rusty in regards to a solid 1/2" center rib on the Yak which is the same plane essentially as the Mustang was due to the way the fuse connects to the wing. The glue area is very limited to sheeting only due to the fuse sitting on top of the wing. The Brodak designs look the same but aren't the same in terms of construction. They're built lighter and not as strong as the originals. This really benefits the modern engine, but the Fox and the older engines were really staple to those designs and when used, certain precautionary measures should be followed. Ken