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Old 06-03-2019, 08:26 PM
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timorley timorley is offline
That 70's Rocketeer
 
Join Date: Jan 2007
Location: Bright, Indiana
Posts: 397
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To Engine Mount or Not to Engine Mount? That is the question.

I have a dilemma. An 18mm BT-20 engine mount will not fit in the space left from the BT-4 tank tubes. The math doesn't work and I tried anyway, it is so frustratingly close. I was planning on cutting out a small strip down the length of each BT-4 to accommodate the engine mount. However, the diameter remaining within the BT-4s happens to be almost exactly, the interior diameter of the BT-20, this means an 18mm rocket motor fits snug as a bug nestled within the BT-4s. So, I could use the BT-4s as the engine mount. I can still glue an engine block in, it would only have 8 touch pints for glue, versus the entire circumference, I could even put in a longer engine block for more glue surface. I plan on using epoxy to fill triangular gaps to prevent ejection gases from flowing backwards anyway, so that will further strengthen the engine block attachment. I am capping off the BT-4 ends with a BT-60 to BT-20 centering ring for the same reason. I can also still have an engine retaining hook, by placing it inside one of the BT-4s , it would still be pushed through a slit in the BT-4 at the engine block. It would further be secured with a piece of BT-4 pushed up inside the BT-4 tube and glued to keep the retaining hook in place. All the BT-4s would be glued together as well. I am sure this will work, it just feels odd to not have a traditional engine mount. I'm including a picture where I mocked it up with the previous too short BT-4s. Obviously the easy way out, but I still may go the hard way.

Anybody have any options one way or another?
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Tim

"You know, it, uh, won't fly unless somebody pushes the button." From the movie October Sky.

I am SAM # 0167
NAR 98303 Southwestern Ohio Rocketry Association (SORA) #624
https://www.rocketryohio.com
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