HyperTEK questions for the experts out there

I'm working on my L3 cert rocket, and am planning to use my HyperTEK Armageddon M for propulsion. First flight will use a single motor.
However, I have a love of clusters, and of airstarts, and of hybrid motors, in general.
So, for my *second* flight, I'm planning to airstart two additional motors. For sheer coolness factor, and to be the first who has done it, I'm planning on making the two airstarted motors be 54mm *HyperTEK* hybrid motors, probably in the K240 configuration.
I've already worked out how to carry an oxygen source on-board, and am working on the electronics needed to do a sequenced O2 solenoid and ignition trigger. It'll add a few pounds, and require some space, but it's a 10 foot tall 10.5" diameter rocket lifting on an Armageddon M, and I'm not too worried about minor issues like that....
What I *am* worried about is dropping stainless steel fill tube "stingers" from altitude. Has anyone ever tried filling and firing a HyperTEK 54mm motor using nylon and/or acrylic tubing to make the fill stem assembly?
Also, to reduce complexity slightly, I'm wondering if anyone has ignited these same motors using standard electric matches instead of the high voltage speaker-wire sparkers. I'm concerned that the match heads might partially block or damage the nozzles as they are expelled after ignition....
Any suggestions or advice will be appreciated.
Thanks!
- Rick "Creative complexity" Dickinson
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Rick Dickinson - snipped-for-privacy@notesguy.com
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Rick Dickinson wrote:

Interesting goal. I'd suggest contacting Cesaroni directly for ideas on this.

There's no way to hold it in place without modifying the motor which makes it non-usable at commercial launches.

I don't think it will burn long enough to do the job.
-Kevin
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On Thu, 28 Jul 2005 16:49:17 -0500, Kevin Trojanowski

Good idea. I'll email Anthony and see what he says.

Rigid acrylic tubing could be held in place in exactly the same way that the stainless tubing is held, currently -- via nylon tie-wraps looped through the slots next to the nozzle, and around a clamp of some sort attached to the tube outside the motor. I can't think of any obvious reason that a small block of Lexan or other plastic couldn't be drilled through, and glued to the OD of a plastic fill stem assembly....
Thinking out loud, here, I'm visualizing a small Lexan block with three intersecting holes drilled in it, plus a couple of non-intersecting holes to run the tie-wraps through. Ignoring the tie-wrap holes for the moment, the remaining holes would almost form a "T" as follows:
+---------+ +---------+ | | C | | | | +---------+ | | B | \ +---------+ | \ / | | | D | | +----------+ | | A | | +----------+ / | | \_/ | | | +-------------------------+
Hole "A" would be threaded to accept a check valve for the nitrous supply. Hole "B" would be sized to accept a tube (either glued-in or threaded) from my on-board oxygen supply. The plastic "stinger" assembly would fit in hole "CD", with the outer rigid acrylic GOX tube stopping at point "C", and the inner high-pressure nylon or acrylic nitrous tubing stopping at point "D".

What makes e-match wire so much less flammable than speaker wire in a pure oxygen environment? I'm not talking about getting rid of the GOX supply; I'm talking about using an e-match instead of a sparker to get things going in the *same* oxygen-rich environment.
- Rick "Thanks for the feedback, however!" Dickinson
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Rick Dickinson wrote:

Um, how is dropping acrylic from altitude any better than dropping stainless steel? Either one is a Bad Idea.

Okay, I was thinking you meant in place of. I don't think the ematch would provide any real benefit, and may prove to be problematic in the high oxygen environment. You'd certainly want to test it. It may also blow itself out, plus the insulation on an electric match lead is MUCH thinner than the insulation on speaker wire, and the speaker wire is what helps get things going.
-Kevin
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On Thu, 28 Jul 2005 21:25:54 -0500, Kevin Trojanowski

I was thinking that, in the initial GOX-fed portion of the burn, the feed tubes that make up the stinger would be at least partially consumed by the flames, and what wasn't consumed entirely would probably be at least partially melted (and seriously deformed) when dropped.
Thus, it would not present the same clean aerodynamic cross-section to the air as a metal spike, and would present a much smaller hazard to people on the ground, due to a combination of the slower terminal velocity, and the lower mass. After all, kinetic energy equals mass times velocity squared -- if I can make the stinger half the weight, and cut its terminal velocity in half, that's an eight-fold reduction in kinetic energy right there.
Plus, stainless steel and brass are much more expensive than plastic for a throw-away part....

Well, the benefit of using an e-match to ignite each air-started motor would be the elimnation of two on-board HV sparker units, along with their associated weight and the added complexity (and failure points) of the additional components.
For reliability, things should always be made as simple as possible, but no simpler.
- Rick "Complexity where fun, however" Dickinson
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Rick Dickinson wrote:

I still think dropping a solid object like that balistically is a BAD idea. Perhaps some way to retain it via lightweight cables, or have it pull out a small recovery system so it doesn't free fall?

The question is whether or not it is more reliable. The motors are known to work with the stock ignition system; e-matches are a different ballgame. CTI or Korey Kline are the ones who can answer that.
Regardless, you're creating an interesting puzzle. It should be able to be solved.
-Kevin
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Yes, Davey fire 28B's. (No steel or wire wool, or pyrogen dipping were used: Just the daveyfires) In the presence of 90 psi of GOX indicated at the regulator. It was an experimental procedure but ignition was precise and sharp.
It was succesfully tested four times on the ground and for one flight.
I can't report on repeated reliability of the method; only this small sample.
I would suggest, most humbly, that you could test this method for reliability on the ground using an expired grain and your proposed on board GOX supply. Until satisifed that the method works with your on board supply of GOX.

I would suggest the risk is far less than a lump of pre-heater grain blocking the nozzle as per conventional monotube methods of hybrid ignition. Not that we are allowed this privaledge here in the UK :(
Damian
p.s. You might want to consider the hybrid mailing list of Doug Pratts. A higher concentration of hybrid expertise can be found there.
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On Fri, 29 Jul 2005 01:50:12 +0100, "Uncle Bob" <www.unclebobsrocketshop .com> wrote:

Definitely a good idea (ground testing). I'm glad to hear that at least one other rocketeer has tried it, and had success with it.

Darn good point. Although, the "chip" that the e-matches are built on is essentially a small piece of G10 circuit board. It's a bit less "soft" than the thin cardboard and cast HTPB or PBAN-based APCP pre-heater grain used in monotube hybrids. It may be small enough to not worry about, but, I'm used to trying to envision failure modes and plan for them.

I asked on the hybridmotors mailing list *first*, and got a grand total of zero responses. So, I came here next, looking for a wider audience.
- Rick "Looking for technical assistance on RMR?" Dickinson
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