Head-end ignition through a smoke grain?

[vahpr]

Anyone try this with either success or failure?

I machined a fwd bulkhead with a hole and counterbore to pot the lead, the question is how to deal with the igniter lead through the smoke grain which consists of propellant, smoke and a bulkplate?

 

[Brent]

Cast the igniter wire in the smoke grain.

 

[jimzcatz]

Absolutely what Brent said!

 

[patelldp]

Don't use a smoke grain, add more propellant!

 

[vahpr]

The grain is cast, I'd like to drill it and seal the igniter lead, however I've not done this before - has anyone?

And Dan, yea, I might just do that

 

[blackjack2564]

The grain is cast, I'd like to drill it and seal the igniter lead, however I've not done this before - has anyone?

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.



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!



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

 

[ksaves2]

Oh Geez, So the double flame front of the smoke grain causes failure of the forward closure? Kurt

 

[FredA]

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.

 

[vahpr]

Well Fred, you'll be happy to know that this the same project which is using your "pins in a groove" design on the carrier so if this doesn't work we'll be having some words

Seriously though, thanks for the words of experience!

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.

 

[vahpr]

I like that design, great idea. Thanks for sharing the pics too,
Jerry

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.

View attachment 325753 View attachment 325754

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!

View attachment 325755

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

 

[pondman]

Jerry, reach out to Bill Good; I believe he does this on his two-stage projects.

 

[vahpr]

Thanks Gary, just emailed him, Jerry

 

[Binder Design]

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.

 

[vahpr]

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?

 

[patelldp]

Can you possibly carve a channel in the top of the grain, down the OD, then across the web of the bottom of the grain to accept the wire? Then pot the whole thing in R45, Curative, and Lampblack. I agree that you want to keep the grain intact, but in rockets like what you're flying a smoke grain is just a loss in mass fraction.

 

[FredA]

OK -- I'll agree that a "D" shape might be an improvement.
But really, it's all about backfilling the wire-access with something basically non-flammable and strong that fills without voids.

For how I cross the bulkhead - I just use a 1/4-20 bolt that is center-drilled with a step
I've done it both ways with the bolt-head inside and out. Clearly, make sure you put the step so that it necks DOWN on exit.
And sometimes I don't drill directly in the center of the forward closure.

And cool that "the same project which is using your "pins in a groove" design on the carrier".
Hope you found it easy to make and I'll in watching for the results to be posted!

 

[Binder Design]

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.

 

[FredA]

Is this a Balls project?

 

[vahpr]

Yes Fred, it's an 88mm sustainer, 42" tpl, boosting on a 17k ns 98.

Is this a Balls project?

 

[vahpr]

Cool, I like it. Gonna mix up another, longer, 88 today, maybe I'll try this.... Thanks.

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.

 

[FredA]

Yes Fred, it's an 88mm sustainer, 42" tpl, boosting on a 17k ns 98.

Excellent - look forward to seeing it.

 

[Cl(VII)]

Sorry for the necromancy, but I have a question on the HEI topic.

Assuming you are using a normal, open Aerotech forward closure. Could you purchase the appropriate size delay insulator from RCS (example: https://www.rocketmotorparts.com/Delay_Insulator,_2938mm/p1577809_7824126.aspx), and then cast your ematch wires in an epoxy plug filling the insulator as the delay grain normally would?

Assuming you strip the wires for say 1/2 the length of the plug facing the "internal/aft" side would there be any reason to expect the plug to leak in flight assuming the motor is built with the normal forward o-rings?

Yes, I know this makes it research.

Also, CJ, what is the black material in your closure pic?

 

[Andrew_ASC]

I just know filling an inert CTI delay grain with rocketpoxy after drilling a hole into it and inserting an ignitor for top fuel grain was the worst way to do HEI on a CTI H Skidmark, for a 29mm MD. Totaled a sustainer tube this year at SEDS. What did you expect a bunch of no nothings complete noobs to do? We read about HEI. We never did it or had any experience before with HEI... We didn't have a Crazy Jim or a mentor around to ask and we accidently figured out a way to instantly explode a motor. It failed at epoxy plug in our case. Never could find that sustainer tube...

 

[blackjack2564]

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.

 

[Viperfixr]

Wasn't Aerotech showing some HEI closures a while back? Is EXP motors the only option for HEI?

 

[Titan II]

You can modify a commercial motor for HEI. It then becomes a research motor.

 

[ksaves2]

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.

It looks to me like there's two pieces of G10. One larger circular piece that abuts against an internal lip in the closure and a second one that's shown externally?
Am trying to picture how the eyebolt is secured but it might just be acting as a handle and isn't used with a recovery harness? Did you bake the closure after you
injected the 800F epoxy as most off that high temp stuff requires? Is that machined aluminum ring part of the assembly too?

Ahhhhhhhh, 40ga. wire. The magic wire that made my home made ematches work consistently. 36ga. and 50ga. blanks were "blankety-blank" worthless and
until I turned, soldered and sheared my own blanks I could never approach 99.99%. Kinda fun to do but tedious and totally needless now with the current resources available. But........ If the environment had turned out different I would have been able to keep flying electronics albeit in a very tedious fashion. Kurt

 

[Steve Shannon]

Wasn't Aerotech showing some HEI closures a while back? Is EXP motors the only option for HEI?

You’re 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.

 

[Andrew_ASC]

That would be awesome to have HEI as a non research option someday and instructions similar to their reloads. My opinion is HEI is only more dangerous when the procedures, techniques, and proper closures aren't used. Right now I'm okay with it being a research option until standardized closures are field tested and approved. In some cases it was dangerous to slot and wire externally a MD airframe to meet existing rules because it comprises the airframe integrity at the slot on complex multistages.

 

[ksaves2]

You’re 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.

That would be the kicker. Having a safe means of applying power to a circuit (electronic device) that has an upper stage igniter attached to it. Me thinks one way (sans shunts mind you) would be to have an external switch (keyed or otherwise) hard wired on the battery to a wireless deployment device along the lines of an EggTimer Quantum. Once the switch is turned on to supply power to the Quantum (which defaults to off anyways) the flier would have to then activate it from their wireless device and they could elect to do it at a distance.

I guess the Quantum is supposed to get a staging firmware if it's not already out there. Barring using a Quantum, a wireless switch could be used which again has an external switch hard wired to the battery. Turn it on to activate the wireless switch which of course defaults to the off position and then wirelessly activate the deployment/staging device (like a Tele-Mega, Easy-Mega, Raven or whatever is being used). Again, only one person would be involved in upper stage arming and the entire setup could be mocked up and tested on the ground to ensure of it's feasibility and safety. Heck I take new altimeters and bench test them with contained ematches and flick on/off switches rapidly to see what happens. So far I've seen nothing adverse.

The weak point is the hard wired switch to the battery but I think the increase in safety is workable by using a very high quality G resistant switch. Or if you crazies fly Wildcat, twist and tuck or tape (Arrrrrgh!) if you please but not on TRA or NAR's dime. (I mean in the context of complex staged rockets here and realize some do this reliably in single staged rockets at venues where it's allowed.)

Dr. Paranoid still doesn't like shunts "unless" the shunt has been proven to be "failsafe" for the given installation. I don't care how much "math" anyone does, it's unproven unless tested in a controlled failure situation. Kurt