Igniting AP Motors in the Upper Atmospher

Quest MicroMax motors are black powder.

Bill Spadafora

I would try "gluing" the igniter directly to the propellant using a small amount of pyrogen. I would thin out some Magnelite pyrogen. Dip the very tip of the igniter in it and quickly put it in the motor. The physical contact may help with ignition.

Doc

Your right. I was a little fast in posting. Typeing on a Treo 600 while eating lucnh does not for complete posts make. I had first tested the Quest motors to different altitudes. With the results listed. After I had done that I packed them with AP propellant and did the test over again. Except this time there was no ejection charge. I plugged the ejection end and ran the tests again. The casings were the same as were the ignitors. The AP would not burn past 30 30,000'. I then tried AP chunks with the ignitor buried inside and still no go after 30'000'. I then tried hotter ignitors with the same results, so I suspect that I will need to cap the end with some type of rubber to give the AP time to catch before the hot gas burns through the rubber.

I really have to stop doing email on a Treo 600. I leave too much out. The tests are to find out how to ignite an AP motor in low pressure. The motor that will be used will be an N or O equivalent. The rocket is going to be launched off a balloon at 80,000' about 180 miles off the coast very early in the morning when their are no planes in the air.

Arnold

That may make it easier to light. Place a certified burst disc over the aft grain (just fwd of the nozzle) to allow pressure to build up. A deeply dipped igniter should build pressure in the core and ignite the AP. Once the AP is lit, the burst disc will "give" and the motor will sustain itself.

If the burst disc is sealed, you will have 14 (& some change) PSI in the core at altitude.

The only problem I can see is access for the igniter. You may have to modify a plugged fwd closure and light it from the fwd end.

Doc

Iz re-posted an e-mail from John Wickman some time back about BP and APCP burning in a near vacuum:

We got around the problem by clamping a rubber gasket made from rubber roof material around the end of the nozzle. When we ignited the motor at a pressure equivalent to 80,000', the motor ignited and then after two seconds burned through the rubber.

Arnold