Posted by
J.W. French
on
03/16/10 - 00:45:49
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There is indeed a major flaw in the original design on the first side bay of the fuselage truss. The bottom rear corner of the first bay has only a corner steel plate gusset to carry the load imposed by the landing gear on the bottom chord of the truss. This puts a significant bending moment on the bottom chord. A redundant diagonal needs to be added from the bottom chord just ahead of the landing gear to the top front corner of the first side bay of the fuselage truss. The whole concept of a truss is that all members must be in either direct tension or compression with no bending stresses. I bought N31524 when it only had 60 hours on it. At approximately 200 hours the bottom truss member had a catastrophic failure, it broke completely through on a normal greased on three point landing. I can't speak for the first 60 hours but I was acurrent taiwheel pilot with over 1500 hours of tail wheel time at the time and I didn't make any hard landings in the plane. Of course when the fuselage member broke the gear geometry went out the window and the plane did a violent ground loop that included scraping one wing tip and pulling the valve stem out of the tire on the other side. The next day after I had put a new tire and tube on I noticed that the plane still had a ruptured duck stance and discovered the real damage. It took a major effort to rebuild the plane. Removed the wing, sheet metal and fabric on the sides back to the rear of the front cockpit. Then I built a gantry to support it at the wing attach points on the center section. Next was dropping reference points to the hangar floor and some subtle romancing of the fuselage frame with a hydraulic port-a-power and other delicate instuments till every thing was lined up properly. When we did the repair on the bottom member that broke in two we noticed that only about 1/4 of the circumference of the break was bright metal, indicating that the break had progressed over a long period of time til complete failure. We added redundant truss members on both sides as I described. It is my understanding that the current plans have corrected the deficiency in the original design. If you have an older Deuce check to make certain this problem doesn't exist in your plane. It is not a question of whether it will fail, but when it will fail. I was lucky in that mine failed at my home field. It could have happened on the Sam Burgess Memorial Junket in 2005 in any of the 38 states over 9494 miles I flew that summer. J.W. French, PE |
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