Lessons Learned:
Don't Hotwire Your Rocket Motor!

The rebuilt TRFKAB (The Rocket Formerly Known As Black) flew on an Aerotech K695 motor on Saturday, June 12 2004. Beautiful, straight flight atop a brilliant, crimson red flame. The altimeter read 5900 feet, although I doubt that reading is correct. But I wouldn't know, because I really didn't see it.

Why, you ask?

My launch controller battery died, so we borrowed another system. The owner was kind enough to hook up the leads - which, unfortunately, were HOT! The igniter popped as soon as he touched the leads. We cleared out as fast as we could, but were only six or eight feet away when the rocket roared off the pad. From my vantage point, all I saw was an ascending ball of flame at the end of a tunnel of smoke.

Everyone escaped unhurt, but it was a heart-pounder. No photos of the rocket until it was under chute.

Since that day I've been thinking that it would be a good idea to carry a multimeter to the pad and test the clips before I hook them up. Some (see below) suggest that it is advisable to touch the leads together to see if the spark -- but I'd be a bit concerned that I may not detect a spark when testing the leads in the Arizona sun. So after some consideration, I plan to mount a 12 volt siren to the underside of my launch pad. I'll make it part of my protocol to hook the clips up to the siren leads while I install the igniter. That should do it.

Burl Finkelstien added this:

Publishing a story about it may make touching the clips a way of life for many fliers. A similar story did it for me.

Several years ago almost the same thing happened at Orangeburg S.C. The flyer had his rocket ready to go with a 54mm motor, put in the igniter, then crouched down to hook up the clips. As he hooked up the last clip he saw a little spark and heard a pop inside the motor. Without a second thought he rolled over backwards to see his rocket blast off the pad.

These launch clips had no juice.

This happened with a major club's multichannel launch controller with key interlocks, not an individuals. An investigation showed that the system, although in the safe mode had a stuck set of contacts in a relay. It was surmised that the last LCO had held the button to long and the shorted igniter leads overheated the contacts fusing them. After that, the controllers were all modified to have dual relays on the firing circuits, (the common leg had its own relay).

This event was fresh in my mind as we watched a couple M motor flights go up. When I thought of witnessing couple feet wide fireball from a M1939 and the dirt it threw up at ground zero I was a believer. I flew an M motor later that day, and from that day on I always touched the clips together on any HP motor before hooking it up.

Here are three more options for an individuals controller:

1. Place an inline junction box in the lead about 8 feet from the clips. Put a low current pizeo buzzer in the box parallel to the line. If it is buzzing, don't hook.
2. Have the clips on a 6 foot pigtail that unplugs with a 1/4 phone plug. But a jack with a LED to show power. Hook up the pigtail to the igniter, plug in if not lit. This also give you the option of replacing the pigtails in the field if they get toasted.
3. Splice a jack or a plug socket inline with the leads. Insert a shorting plug before hooking up.
4. Or, just make certain the battery is out of the circuit when down range!

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