Thread: Discussion Dynam grand cruiser
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Old Nov 12, 2010, 10:25 AM
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Sedona, Arizona
Joined Nov 2006
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Structural Mods

This is a beautiful plane, no doubt. But, it has some structural issues I thought I'd pass along. Maiden flight was a little hairy because it needed a lot of down trim to get it to cruise level (watch Nitro video takeoff). I had the CG set at the forward dimension of 55mm, so this puzzled me. Perhaps some down thrust is in order? I fly at 4,000 feet altitude, so it needed almost full throttle for even a minimum cruise speed. But wait, there's more!

Once I got it trimmed out and flying hands off, I decided to do a touch and go. It had a slight bounce to the "touch" part, so I gave it full throttle for the "go" part. Unbeknownst to me, the right motor mount had come unglued (out of line of sight), and when I hit the throttle, the motor flew back over the wing, cutting up the wing and fuselage. Of course, with just the left motor operating, it did a wingover from about two feet. The wing broke in three pieces!

What I found was 1) they use hot glue on the motor mounts just like they did on the elevator joiner, and 2) there is no continuous spar through the center connecting the left and right sides of the wing. The are just a couple of little plastic strips embedded in the foam that stop short of the fuselage. One side of the wing broke through the retract wheel well. When I looked at the cross section of the wing, I realize how truly weak it is through that area.

I think even without the motor coming mount unglued, the wing is still a disaster waiting to happen. It's ready to fly again, but I made some mods I'd like to pass along. I removed the other motor mount and used epoxy to glue them both back in. I cut a groove along the rear of the front plastic strip and inserted some 1/8" lite ply to create a spar. I joined the two halves together in the center with a 3rd piece. It took very little time, weighs 14 grams, and is strong as a 2x4 now!

Good luck to all. I would like to hear your impressions once you fellas get yours into the air!

John
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