If it suddenly "took off like a bat out of you know where ", then it had to have lit from the nozzle end. If it lit from the ejection end and burnt backwards, only a bit of thrust would have come out the nozzle as the fuel grain burned thru. Also, the order of events would have been:

motor 1 burns
motor 1 ejects
motor 2 ejects
motor 2 burns

Did the second thrust burn occur after the laundry was out? Or before?

I hear lots of guys talk about guarding against ignition of unlit motors during ejection, and it makes sense. I haven't used that, and haven't needed it, knock wood, but probably should use it. Frankly, I haven't thought about it. As far as technique, a bit of wadding in the end of the motor should do the trick.

That said, what I don't see enough talk of is getting them all lit. I always scrape all the nozzles, use ignitors with longer leads (and no clip whips), and a relayer or beefy controller with 12V battery. If you get them all lit at launch, it becomes a moot point

BTW, sorry about your rocket.

Doug

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YORF member #11

That's what I think too just by the way that thing took off for the ground. But read the answer below to your second question...


That depends on who you talk to. It seems like different people saw different things. Here is what I do know. The main BT tube was burried six inches into the ground right up to the chute compartment spacer. The nose cone was laying beside the tube on the ground.


I forgot to mention the wadding in the end of the motor method. Some of the people at the launch mentioned that also.


Since you focus on getting them all lit in the first place you will get a kick out of "the rest of the story".

The guy who the rocket tried to take out just happend to be one of the best cluster guys in these parts, Boris Katan. He was sitting there minding his own business wiring up his Scratch Toginator Upscale. You can see a review here: http://www.rocketreviews.com/review...toginator.shtml

Anyway after the crash he and I talked a bit. Boris told me that he uses pyrogen dipped igniters on his clusters to ensure ignition. I can't argue with his success rate but that does get a bit expensive.

Oh, his Toginator is a 26 engine cluster and yes all of them lit and the flight was great. The Toginator did crash, but only after a great flight. The crash was due to a chute problem and I belive he is rebuilding. I got a great video of the flight. Man that thing looked great going up.

Here's TLP's site:

http://www.the-launch-pad.com/

FWIW, I do this on all my cluster flights (unless the motor tubes are plugged), using a small piece of masking tape to hold the wadding in. Also, if the engine *had* lit from the top, the inside of the rocket above the motor mount would have been burnt to a crisp.

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Paul
If we weren't all crazy, we would go insane - Jimmy Buffett
NAR #87246 www.wooshrocketry.org

I can confirm that the inside of the rocket looks great. Nothing more than the typical grey residue.

What are clip whips and why do you avoid them? Is that a group of clips hanging off wires all going to a common connection point?

Yes, clip whips are pairs of wire bundles - eg, a red bundle and a black bundle - wherein the 3 (or 4 or more) wires in each bundle are joined at one end for connecting to the launch controller, and at the other end have alligator clips on each lead.

In use, several bad things can - and often do - happen. With 6 or 8 or 10 clips, the likelihood of one falling off goes way up, so getting all the motors lit is unlikely. And it gets crowded with all those clips clustered together, so the likelihood of a short is way up, too. And, depending on the quality of each clip's connection - ie, how much resistive crud and/or lack of spring grip - the resistance will vary thus causing some motors to light later than the others - or not at all should the rocket pull away first.

Basically, it only took me a few attempts before moving on to lead extensions. They're much more consistent and reliable.

Usually, clusters will still fly OK with one motor out, but in some cases, it can be catastrophic. Here's a pic showing a rocket with only two of three lit. OUCH! It was going horizontal when the (2/3) sustainers lit. It ended up doing a combo power-prang / landshark. But I salvaged it to fly again Doug



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YORF member #11

Thank you, Doug. But one thing leads to another. .. What are lead extensions? Is there a web resource where I can read up on this, in the event that you tire of typing out explanations?

Soldered wire extensions to the ignitors.

Tim answered it best - soldered wires. I use phone wire. It's 26 guage IIRC, and strips quite easily. Twisting would work, but the bridge wires are easily broken, so soldering is less likely to damage the ignitor. A wrap of masking tape over the joints will prevent shorting and maintain the spacing of the ignitor leads.

Like prepping for staging, it's time consuming and a PITA, but it's still easier than rebuilding wrecked rockets Here's a pic of one I recently made. Doug.



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YORF member #11