[roc-chat] Re: Tube type pros and cons?
- From: Jeff Gortatowsky <indanapt@xxxxxxxxx>
- To: "roc-chat@xxxxxxxxxxxxx" <roc-chat@xxxxxxxxxxxxx>
- Date: Tue, 25 Dec 2012 17:22:04 -0800 (PST)
Like all engineering choices, everything is a compromise.
Glassing is a PITA (IMO). Especially filling it. By the time you sather over it
and sand it out, you may have cut through some of the weave. And the more
glass, the more to sand. And of course you can use fine weave over coarse, and
that is even more work. That said, I've done it. And I did it without all the
fancy shamcy peel-n-pluck (or whatever its called), BBQ spits, and curing
ovens, power sanders, and junk. I was just really really stingy on a epoxy
(which is probably why I had a lot of weave to fill).
I've had several PML QT machines. One with piston, one without. Both are
working spectacularly for up to J motors. Never flew anything on a K (yet). I
sanded the pi$$ out of the piston and keep the tube clean and even in 39 degree
weather, it's not gotten stuck. Call me a QT fan-boy for what it is.
Paper and phenolic. If you fly to crash, its a bad choice. And in normal use
the motor end tends to get frayed and dented. There are ways to prevent that as
well.
Many materials I chose were to suit my flying. I only recently started flying a
lot of dual deploy. So my historical choices were, keep the rocket low with a
big chute, or only launch in calm conditions, still with a big chute. That
keeps landing damage to a minimum. Now that I am flying more DD, I am even more
comfortable flying paper and phenolic. I am focusing strictly on landing damage
because I tend not to fly anything that is going to stress the rocket on the
way up (and I've planted my fair share). I don't fly for speed or altitude. I
fly for fun. I like see the rocket. So YMMV. I have a hypothesis that most (not
ALL!) problems going up are fin and fin flutter related, not buckling tube
related. But I can not back that up. So take it FWIW.
That all said, my next three HPR rockets all use 4 and 5 inch fiberglass
tubing. Go figure... :)
Merry Solstice.
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