The grain is cast, I'd like to drill it and seal the igniter lead, however I've not done this before - has anyone?
I've done dozens of HEI motors with nothing but raw shooters wire epoxied into place and NEVER have seen the mythical "burn up the wires" problem.
Everything burnt to a crisp in the inward side of the JB Weld plug and nary a sign of anything on the outer side....even with 14s burntime motors.
So I chalk that up to "questionable tribal knowledge."
The few times I've done HEI with smoke, I've used a smaller smoke grain potted in the proper casting tube with a layer of R45 insulator around the sides and in front.
The HEI igniter was dressed sideways once inside the motor and then turning rearwards to penetrate the R45 insulator ring outside the smoke grain proper.
The hole made to clear the wire back filled with JB Weld.
This worked fine the few times I did it.
Twice with 14s burn time moon burners with 30 seconds of smoke, so I know it will take some abuse.
I would suspect that you could center drill your smoke grain and install the igniter and you'll be fine if you backfill the hole WELL with JB Weld.
Your chance of working is slim. Build a proper H.E.I. closure. Separate channels for each wire with no way a flame front can get through. This is 54mm. We have 75 & 98 also. They work.
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Running wire through smoke, can result in wire accelerating pre-heat & flame front following........this is what happens. This was a test of exactly what you are proposing, unfortunate end to a Nike just last month. Fire coming out both ends about 3-4 seconds into burn. I did warn him not to try it!
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Edit: I have never seen it work, though some may have a "magic" way of making it so. Therefore I can" never say never"....lol
Going through the grain center is the wrong idea. You cut the delay grain like a D, slide the wire past it and fill the cavity with red silicone. Your wire gets potted in a brass plug fitting drilled for the wire and filled with JB weld. That's what I designed for Rob Lamb's two stagers. I drill and tap though the side of a "top hat" forward bulkhead for the fitting. You could do a c-slot in the grain, but I think that would be harder to fill without getting an air pocket in there.
Thanks Mike. You wouldn't happen to have a picture?
Sorry, I didn't take one but it's pretty simple. You buy the brass plug that has the base hollowed out (not solid) and just drill a hole bigger than the wire to pass through, then pot the hollowed out base in JB Weld. Then when it's cured, put teflon tape on the threads and thread into the tapped bulkhead. Then install your D-grain delay with the gap towards the wire so that your wired goes past it. Then fill the open part of the D with red silicone. You want to get it completely full with no voids because it is not only protecting the JB Weld on the fitting from direct heat, but it is also inhibiting the side of the grain. Secondary benefit of doing it this way is that you can put your tapped port off center and leave your tapped hardpoint for recovery.
Also, CJ, what is the black material in your closure pic?
Just a black G-10 disc,[top & bottom] holds the 2 rods perfectly centered in their holes. One rod is wrapped in teflon plumbers tape, then covered with shrink wrap tube to insulate the rod from metal part of closure electrically. Also provides a nice flat surface for nuts to bind against when tightened.
Hole in center is then injected with high temp epoxy [800] to fill the closure cavity. [3/4 in. deep epoxy. Disc gets charred but one with 20+ firings is still fine.
Just finished casting some BKNO3 pellets directly to ignition wire. Used 40 ga nichrome for bridge wire. [same as E-match bridge wire]. Pre tested with 9v battery and lit just fine.
Wasn't Aerotech showing some HEI closures a while back? Is EXP motors the only option for HEI?
Youre right; they have a pretty slick setup for head end ignition. Tripoli has asked that it be tested at research launches and feedback provided to me. If it works well and if people can develop procedures around it that adhere to the rules that require the ignition devices be installed at the pad or a special prep area, we would consider asking TMT to certify it for use at HPR launches.
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