Tuesday, March 12, 2013

BT-50 Crimp Reinforcement Part 1

I should have made a resolution to install a length of coupler above the engine mount on all BT-5, BT-20 and BT-50 tube models. I've been through this tube crimping too many times in the past.
You can get longer couplers from many vendors. The standard 1" long coupler would be too short to reinforce the tube. You can even get 34" long coupler tubing from BMS. Cut it to the length you need. 

Here's how my Custom Solar Explorer body tube looked like after the first flight!
I'm not blaming the Custom Rockets company - it's just that BT-5, BT-20 and BT-50s are thin tubes. All three will crimp and buckle especially right above the internal motor mount.
One hard landing and you'll see wrinkles.
Pull a friction fit engine that's too tight and you'll crimp the tube.

I had to pick a location to cut the body tube to insert a long coupler.
The coupler won't get rid of the wrinkle in the tube, it'll just strengthen the area above the engine mount where crimps occur.


To hide the separation line I decided to cut right along the base edge of the stick on decal.
With any luck, when the tubes are re-joined the seam won't be that noticeable.

I used a new, sharp razor blade. It was difficult to cut around the leading edges of the fins.



Here's the tube after being cut.

I had to untie the Kevlar from the elastic, coil it and store it in the mount for the next step.

Both ends of the cut tube were sanded square with 400 grit on a block.

The coupler will butt-up against the forward centering ring of the engine mount.
It will need to be long enough to extend past the crimped area of the upper tube.

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