Hung firing leads

[Last Ox]

I've (finally) finished editing video from a launch last September that included a higher performance camera. On a number of flights the firing leads did not separate cleanly, the rocket dragging them 10-20 feet into the air. The force of the lead pulled the rockets well off course, in a probably unpredictable direction. I've recorded hundreds of launches over the last year, but this is the first time I've noticed the issue (probably because the current videos are more clear).

Is this a thing? Has anyone else noticed leads pulling rockets off course? I'm not sure what the fix is, perhaps securing the lead within a foot or two of the igniter. I'm also haven't dug into whether the hang up is the clips, or the igniter coming free of the motor.

One example - the video includes 4x slow motion of the pad and 16x of the first few seconds of flight, at a lower resolution.

 

[burkefj]

Yes always secure the lead to the pad with a short allowance for movement/hookup

 

[kjhambrick]

Or when flying MPR / HPR with longer leads, wind the ignitor leads around the rail standoff a couple turns so it is pulled from the motor on liftoff.

An important suggestion that does not seem obvious to new fliers is to NOT put the clips under the nozzle -- set up the clips behind the rail instead.

Even E, F and G motors can destroy a set of clips PDQ.

-- kjh

 

[cls]

An important suggestion that does not seem obvious to new fliers is to NOT put the clips under the nozzle -- set up the clips behind the rail instead.

This can't be overstated! Suffered through a club launch last weekend, all the clips were burned. ARC teams and other newbies.

 

[bguffer]

yep. wrap launch wires around launch pad legs.

didn't wrap launch wires around launch pad legs in the following extreme example of what you are talking about:

 

[Azamiryou]

How does this happen? How can an igniter still be stuck in the nozzle of a burning motor? How can the motor work properly with something stuck in the nozzle?

 

[MarsLander]

How does this happen? How can an igniter still be stuck in the nozzle of a burning motor? How can the motor work properly with something stuck in the nozzle?

Because it do...

 

[teepot]

I had a rocket pull all the wire from the remote switch box back to the pad. Craziest thing I have seen rocket do. Just about everyone said what was that. The wiring from the switch is the size of an extension cord and is about 20' long. So anybody looking knew something just didn't look right.

 

[Handeman]

I've had a few motors come back with the plastic cap still on the outside of the motor with the bottom of it burned away from the exhaust.

I would guess if you don't thread your igniter threw the vent hole and instead, wrap it up along the outside of the nozzle and slide the cap over it, it would make the cap tighter and more likely to have the bottom melted with the remainder of the igniter still held to the side of the nozzle and flying away with the rocket.

What will make it worse is if you put the clip on the stripped igniter wire right close to the insulation and then wrap the rest of the stripped copper around the clip. If you do that, pulling on the igniter wire won't pull it loose from the clip because you are pulling on the part that is clipped and the rest of the wire is holding the clip closed. If you attach the clip at the very end of the igniter wire and then wrap the remainder around the clip, if you pull on the wire, it will unwind and easily pull the clipped part of the wire loose.

I don't know if these things are part of the cause or not, but I can see it happening. Especially the way the igniter is attached to the clip. If anything cause the igniter to stick on the rocket, catching on the retainer, etc. it will pull the whole clip wire up because the igniter just won't pull loose from the clip.

 

[Tractionengines]

If anything cause the igniter to stick on the rocket, catching on the retainer, etc. it will pull the whole clip wire up because the igniter just won't pull loose from the clip.

Yep. Had this happen at our night launch on a F27R in a 1.6" LOC IRIS. The air temp was cooling off and there was moisture forming on stuff. The rubber band used to hold the igniter in kept sliding off. SO...I put an extra wrap in the rubber band...

Rocket did a "brief pause" half way up the rod, and a BIG wiggle clearing the lauch rod. That really surprised us. After a relatively long walk to recover it; I put it in the car to clean up in the morning...
Video:

Here is what I found the next day. Kind of explains what happened.

 

[jmasterj]

Or when flying MPR / HPR with longer leads, wind the ignitor leads around the rail standoff a couple turns so it is pulled from the motor on liftoff.

An important suggestion that does not seem obvious to new fliers is to NOT put the clips under the nozzle -- set up the clips behind the rail instead.

This is the solution is use. I like to tape the wiring to the back or side of the blast deflector.