low voltage igniters

[War Bird]

I'm trying to airstart a couple of Aerotech F-20's. The problem is e-matches are too large to fit in the nozzles. So I made some igniters from 30 guage wire soldered to a short piece of nicrome wire then dipped in pyrogen. They tested fine but my last flight yielded one only burning half the pyrogen and the other not any. I'm using a perfect flight mini timer 3 with a nicad rechargable 9 volt.

I'm also thinking about front-end e-matches for these single use motors. Has anyone tried drilling a hole in the foward end of a single use, inserting a pyrogen dipped e-match, then epoxying the forward end to seal it? Since these will be air-started the ejection charge will not be needed.

Thanks guys

Kevin Trueblood

 

[KenParker]

I'll throw out some ideas and suggestions from my own experimentation and research.

Welllll.... first of all, I'm pretty sure that the modifications you are talking about making to single-use motors (drilling through the top) are illegal under both TRA and NAR guidelines. I'm 99% sure it's illegal under NAR, and pretty darn sure it's illegal under TRA as well. I COULD BE WRONG ON THIS. Someone who is intimately familiar with TRA and NAR regs please jump in here.

IF..... the mods you are planning are illegal under TRA and NAR, then you could not use motors so modified at a sanctioned launch.

Mark Brown and I have been delving into the EX world, and we have kind of divided up our research. Mark has been concentrating on EX propellant formulations and manufacture, and I have been concentrating on igniters.

First off, 30 gauge nichrome might be a *tad* heavy for low current igniters. I would try to find some 36 gauge, or even 40 gauge (I'm pretty sure that both gauges are available from Aerocon - great place to do business). The next thing I would do is make up a batch of igniters, and then test each one with an ohm meter. Try to find 2 (you did say a "couple," of motors, right?) that are as close to the same ohms reading as possible. Then, TEST THEM WITH THE ACTUAL DEVICE that you intend to use for the real flight. Wire them up to the device, do whatever you have to do to trick the device (vacuum bottle, etc) into thinking it is time to fire the igniters, and see if they both ignite as they should - simultaneously and vigorously.

Then, if it were me, I would match two more igniters and run the test again. If I got the same results, at that point I would feel safe in using them for an actual flight.

By the way, on the igniters that I am making, I don't solder the nichrome to the lead wires, I just wire wrap it. Quicker, easier, cheaper, and it has been working great for me. However, there is certainly nothing wrong with soldering it if you want to go that way.

Just my thoughts on the matter. Hope it is of some help.

 

[n3tjm]

Those mods are not leagle, and most likely would fail. The problem is sealing the forward bulkhead once you drill a hole through it.

Here is one thing I do: You can buy low current pyrogen from firefox (www.firefox-fx.com). Take some thin wire, strip the ends, dip a little of this pyrogen on the end. Then once dry... dip in Magnelite Pyrogen. The igniters work great, but only have a short shelf life, even when dipped in a sealent.

 

[aksarben10]

Could be your pyrogen and or you wire. High current ignitors are easy to make, low current is more challenging.

What pyrogen mix are you using? There are many good mixes on the market right now, the ones I know of are Magnalite, Firefox, Ignitorman and Jim Ball has a mix as well.

I would check out the low current line of primer and pyrogen from Firefox. They also sell presoldered chips for low current ignitors and nichrome wire of many sizes.

I agree that the 30 gauge wire may be too big and that you should try a smaller gauge. I use wire wrap instead of soldering but that gets hard with the smaller gauges of wire, like 40 gauge.

Make sure that you test the matches with an ohm meter for consistancy as mentioned alreay and verify that you battery is fully charged and test it as well.

Scott Pearson

 

[War Bird]

Thanks for the ideas guys. I am using Firefox pyrogen. Their pre-soldered chips are too large to fit in the nozzle of the smaller single use motors. Even when I grinded them narrower. I think I'll give the 40 guage wire wrapped around nicrome a try. Can anyone give me the procedure for testing with an ohm meter? My ohm meter has selections for x1K, x100, and x10. I'll admit to being a multi meter dummie!

How do the Gates Brothers get away with front-end igniters in M motors if it's against the rules?

Thanks again guys

Kevin Trueblood

 

[rstaff3]

I suspect the Gates Bros use the head-end igniters at EX launches. One of the left-coast members will probably be able to confirm or deny this.

Oh, are they investors in AT now? Could be they get by the rules as manufacturer demos? Or do demos have to be at EX launches too? I forget.

MDRA lets you fly what you brung at all launches so I lose track.

 

[KenParker]

mikeyd - you probably already know this - the 24mm E18 works great as a substitute for the E15-PW SU. Just leave out the ejection charge BP. I have used a *lot* of E18s in my SR-71.

OT: I'm on my way to an Information Systems Disaster Recovery test that my company conducts twice a year. Our data center is in Greensboro NC and we conduct the DR test in Sterling Forest NY. I'm currently on a bus *somewhere* in northern MD using a cellular network card to connect to the internet.

Ain't technology great? This is a pimpin' bus too. It is usually used to transport touring rock bands.

Time to delve back into that "adult beverage" cooler.....

 

[marvSRG]

I believe the Gates Brothers only tried head end igniters once, and that was with limitied success....the ends of the closures weren't sealed well enough and the two sets of M1315W's they airstarted had forward end leakage. Tore the rocket up! I think it was Athos II...since then they may have tried other methods, but I'm not sure. And as for legality, head end igniters on big stuff like that is often just overlooked.

https://www.gbrocketry.com/athos_ii.htm

Check that link...the first flight. There's vids in the gallery.