Caveat: I am not the pyro expert. (Personally, I usually just use an e-match and pyrodex.) Also, I wasn't actually at this launch, so I don't know the details, but I'll give you the recipe that Jim (our pyro guy) relayed:
In 2012 we used igniters that were dipped in a slurry of Boron/KNO3 and > then put inside a plastic bag of copper thermite. The thermite gives the > "instant-on" but the plastic bag is kind of fragile. I think we did have to > remove the nozzle to install the igniter on the sustainer > This year I used the BKNO3 with no thermite and coated the igniters with > ABS cement. The ABS cement made them much more durable. He's right about 2012: I remember that the thermite bags wouldn't fit through the "Medusa" nozzle on our sustainer, so they had to be assembled inside the motor, which was a pain and not as safe as we'd like. We dropped the thermite this time to avoid that. Casey On Wed, Jul 1, 2015 at 2:59 PM Kurt <[email protected]> wrote: > Ok, > > I've done a lot of testing of different igniter schemes. Were they > ematches like Double-ended E-match-Initiated with Dual-End Burn > Shown here when you scroll down: ttp://www.berfield.com/igniters.html > > Or was it a variation of a standard nichrome igniter? If a variation of > say a "first fire" type igniter, one has to have enough current > and I would have suspected the project team would have ground tested these > igniter with the electronics that > was going to be used to start them in flight. Is that what you mean by > "he tested 6"? Did he use the altimeter that was going to fly to test > them or just a plain battery? > > I doubt the theory of "thin pyrogen". If the nichrome is too fine, it may > heat up unevenly and more intensely > in some spots as opposed to others. The overlying pyrogen can react > locally in a violent fashion and "pop" > off the wire. In the process of "popping" off it fractures the wire and > since there is no more current flowing > there is no longer any heat flux, the rest of the igniter remains unburned. > > Three ways around this: 1. Use a thicker gauge nichrome wire. Only > problem there is it requires more battery current to heat up > and might not be able to be > supplied by the staging electronics. > 2. Experiment like crazy and try > to find the optimum (smallest) nichrome gauge that will reliably > work so you can get away > with smaller and lighter battery capacity > 3. Use a little trick I learned > when a batch of my igniters seemingly turned into "poppers". It's very > simple. > I take my fingers, small > hemostat or needle nosed pliers and gently crack the igniter head along its > length. I do it very gently > because I just want to introduce some transverse cracks along the length > of the pyrogen head in > several spots tip to base. I don't want the pyrogen to fall off but crack > it just a > "little bit". > What I think now happens is the cracked pyrogen allows any rapid buildup > of gases to safely "vent" and allow just a fraction more time > for the pyrogen to catch. It seems that the igniter might start from the > "cracks". Once the head is burning the tough part is over. > > I've had "bad" batches of homemade igniters that would work nicely after I > started cracking them. In fact, I just routing "crack" all my > homemade igniters now out of habit 'cause I hate walking back to the pad. > > Yeah, I know for staging it's a different story but if using a nichrome > wire as opposed to a ematch augmented the theory should be the same > as I expressed above. > > Kurt > > > > -------------------------------------------- > On Tue, 6/30/15, Casey Barker <[email protected]> wrote: > > Subject: Re: [altusmetrum] Update and Questions about TeleMega on 100K > Attempt > To: "Altus Metrum" <[email protected]> > Date: Tuesday, June 30, 2015, 1:48 PM > > Our pyro > guy dissected it and determined that the pyrogen was too > thin in one spot, so it didn't ignite all of it. Out of > his batch of 10, he tested 6, flew his own rockets on 2, and > lit the booster with 1. Figures the sustainer would be the > one that failed. > Casey > On Tue, Jun > 30, 2015 at 11:13 AM Kurt <[email protected]> > wrote: > Homemade > igniter? If so it might have popped and fractured the > nichrome wire. > > Was it ematch/pyrodex or a dipped ematch augmented pyrogen > or did you have > > sufficient battery juice to use a standard nichrome dipped > pyrogen igniter. > > Kurt > > > _______________________________________________ > altusmetrum mailing list > [email protected] > http://lists.gag.com/mailman/listinfo/altusmetrum >
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