Rocket Doctor,
During a much anticipated launch, I was unable to get the engine I was using to properly fire. It was my first try with a composite engine (Aerotech F25W-6) and the copperhead igniter system. I'm fairly certain I correctly inserted the copperhead igniter, I placed it about 3 inches in, where I hit the delay grain. When I connected the igniter and fired it there was about 1 second in which the engine "sizzled"- it didn't burn the propellent grain- and then the ejection charge fired. Any ideas on what I could have happened or what I could have done wrong would be greatly appreciated. Thanks in advance for any help or ideas,
Joe.

Unfortunately, composite engines aren't my cup of tea. I'm sure there is someone out here who has more experience with composites..

Have you contacted Aerotech? One possible cause, did you have enough battery power? What was the condition of the ignitor?

RD

I have not yet contacted Aerotech, but I may try tommorow. The battery I used was a car battery which was fully charged. It's possible igniter condition could have played a role, I've just read elsewhere that its probably a good idea to scratch the surface off the igniter to get it to the right temperature which I did not do. Also I read composites are peculiar about the pressure, unlike black powder motors, so the wind there was on the launch field could have possibly effected it. Thanks for your help,
Joe.

That's quite odd, if there was only 1 second between the time you pressed the button and the ejection charge went off.

If for some reason the delay grain started burning without the propellant burning (i think almost an impossibility), the delay grain should have burned for at least 15-20 seconds before igniting the ejection charge. The delay grain depends on the operating chamber pressure to do most of its burning, then slows down to about 1/32" per second after burnout.

What did the motor look like after ejection?

__________________
Roy
nar12605

If the igniter burned it is not igniter or battery related. If this were a reload I'd say it was a missing or misplaced O-ring (had something similar happen to one of my TARC teams with a reload last week). Now since the single use also have O-rings installed in the factory, I think you got an improperly assembled one from the factory - contact AT and pass this on.

__________________
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Dale Greene

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" Speaking the Truth in times of universal deceit is a revolutionary act. " George Orwell

This is a single use motor.

http://www.aerotech-rocketry.com/cu...su_in_21004.pdf

This is very odd as others have indiciated, the delay usually needs pressure to burn and part of it will burn fast while the propellant is burning and then the remainder will burn slower after the propellant is all consumed. With no propellant burning it should have burned for a very long time. Contact Aerotech. Could be a defective motor or batch.

__________________
-Fred Shecter NAR 20117 (L2)
Southern California Rocket Association, NAR Section 430

yep, I think Dale's right. A missing, or misplaced, o-ring must've let the gasses reach around the delay insulation to the ejection charge well and set it off, while the propellant chuffed itself out.

__________________
Roy
nar12605

Yea, thanks for the help, I'll probably try to contact AT tomorrow. Just for further detail the motor seemed to more or less 'explode' after the charge went off. The plastic casing was broken and the propellent part of the motor was still intact, unburned. Also, the delay grain burned for no longer than 2 seconds before the ejection charge fired based on the video we have a of the launch. Thanks again for the help. -Joe

The ejection charge could not have possibly broken the casing to bits. Only a propellant overpressure can do this and is caused by either:

1) Defective casing unable to remain intact under normal operating pressure.
2) Clogged nozzle - usually when an igniter does not spit out and lodges in the nozzle.
3) Propellant with voids (bubbles) or a defective liner allowing more burning surface area than designed resulting in way more pressure than the casing was designed to withstand.

Is the delay grain intact and completely unbunt, partially unburn of completly burned with nothing but the ash of the delay paper liner remaining in the delay housing?

__________________
-Fred Shecter NAR 20117 (L2)
Southern California Rocket Association, NAR Section 430

Honestly, I don't remember looking significantly at it, but I do remember that it was not completely burned, so either it was unburned or only partially burned. The propellent looked fairly intact, as in the propellent seemed to all be contained in the cardboard shell that had broken out of the plastic shell.