Hi Aperiera

I haven't flown mine yet but I have spent a fair amount of time over the months reading the very long thread on the Composite arf Impact build alng with two or three others that are in the RCU pattern section. It is my understanding that some of the parts that were "developed" during the course of these threads are now included in the "kit." What I think I have learned (the proof is in the flying and longevity of the plane) is that in addition to the short horizontal stab brace that ties into a vertical piece, another vertical rib/bulkhead/ also should go in to stiffen the fin. I ran a ("hollowed out" lite ply for lightness) bulkhead from the bottom of the fuselage to the top of the fin. It touches the top of the fin at about the point where the top becomes horizontal. I felt that even with the stab brace and vertical piece there was a possibility of flexing at the point where the fuselage curves in along the sides and then kicks up to become fin (even with the rudder post). This aft piece has solidified that.

Another thing to consider is some kind of horizontal bracing as rgreen shows in his picture. It was my understanding that Comp. Arf was going to include a piece of Depron foam to accomplish this. I used the foam (ordered my own and cut it to fit and integrated it with the DEPS elevator pushrod system. I made the DEPS system first with the long 1/4" sticks and the tubes and a couple of spacers setup to work in my fuselage and then glued the aft ends of the sticks and then Depron crutch to the sticks, the sides of the fuse, and the vertical stab brace all at the same time (well -- sticks in first then the crutch right after). Be sure the servo end of the pushrods is finished and the servo real close to where it will live -- this will provide front end support (another set of hands) during the gluing (the exit slots aft will hold the other end in place while putting the foam crutch in place). I also put the foam piece on top of the DEPS sticks -- it puts the foam closer to the vertical middle of the fuselage where it will do the most good.

At the front of the crutch, tie into a vertical or slanted bulkhead that goes right behind the canopy opening. There are several good photos of this in the big thread. Continue this stiffening forward not necessarily in the same plane as the Depron but close for max help. This more forward piece can be used as a rudder servo mount. Use the middle of the rudder for the aft ends of the pull cables instead of the bottom as the factory advises.

Whatever system used for stiffening it is very important to tie (touching and glued) all the sections together -- vertical stab brace to crutch -- crutch far enough forward to prevent flexing right behind the wing -- etc.... The forces that will break anything, know how to find the weakest point and breaks in the continuity become soft points.

One piece of advice that I would give is that because of a few failures I have heard of behind the wing, I would reinforce the belly of the fuse in the area where the muffler will exit and where there will be vent exit slots/holes -- reinforce from the inside. These vent/exit holes take away some of the eggshell that gives the structure it's strength. It is much easier to reinforce now when the fuselage is empty than after the floor is in (don't ask...). Rough it up and add a layer of glass cloth that will make the stresses go around the cutouts instead of through them -- through them means breakage...

Holler if you have any questions,
Tom