ORIGINAL: rustywallace5934
I've heard about these ''issues'' with the older Comp-ARF designs needing the fuse crutch. My work takes up most of my time, so I rarely have the time to sit in front of the computer for hours looking for info. Do you know where I can find this info about why and how to install the fuse crutch? I appreciate the help, guys. That's one thing about pattern fliers, most are always willing to help out a fellow competitor.
Kevin
Kevin,
Some (very few) Impact fuses had a construction flaw in them where, under certain conditions, the fuse would buckle under flying loads. The buckling almost always would occur either just behind the wing, or just in front of the stab. Some models crashed but not all. I don't recall if the Rev Pro had the same problem although construction was the same.
The crutch is a piece of 1/4" depron that is inserted into the aft part of the fuse, from the TE of the wing to the LE of the stab. It is glued in horizontally making sure that the rudder cables would not interfere. Some people built a ladder from balsa which worked the same. These things are very lightweight, on the order of less than 1 ounce installed (includes the glue). The "fix" worked fine.
The aft part of the fuse is voluminous and the composite skin not quite strong enough for the load. Turned out as I recall that the herex material used to construct the fuse was too light and too thin which means the glass layers were too close to one another. To make these types of composites light enough for the application, light glass (2 oz, 3/4 oz) is used on outside and inside res. They must be separated enough to make the composite structure work. Had the herex been twice the thickness or only moderately heavier (maybe 4 lb per cu ft, like soft balsa, rather than 1 or 2 lb), it would have worked better. Guess what....light balsa is used now to make many of the pattern models.