bkuns

Mike

I'm assuming you read my first post in this thread. I used Futaba 9202's at 6V, 98in.oz of torque. As I explained in the post, the grain of the spars ran diagonally across the spars over a length of about 1 - 1.2in. My spars failed on the inboard side of the aluminum tube breaking along the grain. In my first post I talked about the engineering shortcomings of the wings. Perhaps poor quality control of the materials would be more appropriate. I also mentioned that I have only seen two other F90s. Both had wing failure on the first flight, and they had the same problem with the spars as mine. If I had not used large nylon hinges and sealed the hinge gaps, my contention is that the weak spar material would allow flexing in the wings which would set up oscillations that would cause the ailerons to flutter. I believe this is what has been happening to many people.
From my 10 years as a kit manufacturer, I certainly learned that if one is going to build a light airframe, quality of materials is extremly important. Also in my first post I said that the spar material was totally inadequate. Again, let me restate that by saying that the quality of the spar material was totally inadequate. If the spars on my F90 had straight grain I doubt I would have had a problem.
I have unsucessfully tried to post a picture showing where my spars broke, I will try again.

Bob