That appeared on its first flight and of course gets worse each flight. This one is on my EPM-010:
This one showed up as a crease after its first flight on a B6-4, and this photo is what it looks like after only two flights. I'm afraid to fly it again. Are they not making BT-50s like they used to or have they always been fragile? I thought with my Photon Disruptor that it was because it was a bit heavy, but the EPM-010 was built light and weighs less than Estes' estimated weight.
My responses:
I've had BT-50 tubes fail also.
They aren't making tubes like they used to. If the inside spiral seam has any space between the wraps, you'll get crimps.
Before I lost my Midget this last Saturday, the BT-50 tube got crimped when I was packing the wadding and streamer.
There were always crimps when friction fitting an engine in a thin BT-20 tube.
I remember my Andromeda (long coupled BT-20 tubes) bent in two spots during boost and pinwheeled.
That's why I've pretty much switched over to the Centuri style ST tubes for scratch builds.
They have thicker walls than the Estes.
BT-5 and ST-5 tubes are the same.
The ST-7 is thicker walled than a BT-20 and the ST10 is thicker than a BT-50.
After that and all larger tubes, the ST-13 and BT-55 have the same wall thickness.
See the tubes page on the Semroc website and you can check the wall thicknesses.
If you haven't used the ST tubes before, the nose cones and mounts are not compatible with the Estes parts.
All those (kit supplied) blue and yellow engine mount tubes get replaced with ST-7 tubing.
Looking at both the pictures,
The bends are right above the leading edge of the fins.
That leads me to believe the crimp happens when the fins hit the ground first at recovery.
Maybe add some long coupler (3" or so) inside the tube above the engine mount centering rings.
BMS sells the long coupler material in 34" lengths. That would be enough for quite a few model reinforcements.
I think you meant ST-9 is comparable to BT-50. (ST-9 ID=0.950 OD=0.976, BT-50 ID=0.950 OD=0.998). If you use ST-7 to replace the kit motor mount tubes, are you able to still use the stock centering rings.
ReplyDeleteHi Eero,
ReplyDeleteThe ST-9 is comparable to the BT-50 but is thicker walled.
Many use the ST-9 as a replacement for the 50 tube in engine mounts.
BMS does sell a heavy walled BT-50 style tube, same inside diameter as the Estes 50, but thicker walls.
The 50 size nose cones will fit it, but sometimes the shoulder "step" on the nose cone will be smaller than the tube.
If using the ST-7 instead of the BT-20s, you do have to widen the inside holes on centering rings. It's not hard to do, sometimes a few hits of 220 grit around your fingertip will do it.