I'll try to be briefwhile alerting modelers to the dangers of improper use of giant scale Dubro control horns, catalog #913.
I believe my application of this product was one of the two known causes of the crash, on first flight, of my 1/4 scale Brisigella Steen Skybolt. Pictures included. Dubro's control horn is designed with two "ball joint" washers so that the assembly can be tightened against non-parallel surfaces such as would be found on a thick aileron. My mistake was using the same hardware on a thin, slab elevator. The integrity of #913 DEPENDS on the screw engaging a LONG, close fit hole thru a THICK surface. The long hole prevents the screw from pivoting on the double ball joint washers. If used on a thin slab elevator, the horn will slip under load, causing a loss of surface travel.
The second cause was the loss of a hinge pin. See the picture belowthe elevator is shown as it was pulled out of the woods. About halfway thru the first flight, I had to adjust more up trim unexpectedly. Then, in the final moment before the crash, I experienced a more severe and fatal loss of "up" elevator. The plane arc'ed into the forest. Here's a link to the fatal flight. http://www.youtube.com/watch?v=dat2mjpOjkM
I don't know if the Dubro slipped first, or the hinge pin was the first event. But the combination of the two proved too much to overcome. I rebult the Skybolt, using the same hardware on the elevator. But I turned the ball joint washers around and let the "ball" dig into the balsa surface. The standoff and washer, both of which contain a concave mate to the ball, now mated to a flat surface. Problem solved. Note that Dubro does not show this hardware installed on a flat surface at all. That was my doing. But they don't say NOT to do that either. Maybe they should. There's a picture of their installation diagram below, too.
The provide pictures show the missing hinge pin, the crash site, partial rebuild, the completed rebuild, and Dubro's diagram. And here's a link to the sucessful 2nd flight, after the rebuild. http://www.youtube.com/watch?v=Kyq_hZul-4Q
That took about 6 weeks. Power is a CRRC Pro 50cc with a 22x6 laminated XOAR prop. Please don't give me c**p about the bouncy first landing attempt!
Plane gain about 3/4 lb in epoxy, glass, paint, an extra elevator servo, and some metal aileron tabs. Total weight is 19.5lbs.