copperhead questions

[DJ Delorie]

Ok, two questions:

1. Why is it important to allow air to get in to the core? The instructions talk about poking a hole in the tape to let air in.

2. Why can't you just use a wad or two of ejection wadding in the nozzle to hold the igniter in place? You wouldn't have to bend the copper at all that way.

Bonus question: why can't they just make the myler film wider than the copper to avoid shorts?

 

[Omega_D]

1. Why is it important to allow air to get in to the core? The instructions talk about poking a hole in the tape to let air in.

Well, lessee... in order to have fire you need a fuel source, an ignition source and oxygen. The fuel source is the motor, the ignition source is the igniter and the nozzle is the source for oxygen. If you block the nozzle, the igniter could burn all of the oxygen from inside the motor, and not light the motor. Or the motor could chuff and blow itself out. You have to remember that the igniter and motor burn very fast and quickly uses up any oxygen inside the motor itself. You have to give it all of the air it can possibly take, in this case the nozzle hole.

2. Why can't you just use a wad or two of ejection wadding in the nozzle to hold the igniter in place? You wouldn't have to bend the copper at all that way.

See above.

Bonus question: why can't they just make the myler film wider than the copper to avoid shorts?

As far as I've seen, the crapperhead has been replaced with a dipped igniter with all new motors.

Make sense?

 

[DJ Delorie]

The fuel source is the motor, the ignition source is the igniter and the nozzle is the source for oxygen.

Oxygen for the igniter itself? There's no way oxygen is getting in that nozzle once the engine is thrusting (oxidizer is part of the propellent mix).

 

[RocketboyG80]

DJ, you are correct that composite motors do not require oxygen to function. I believe the reason for the hole is to prevent rapid depressurization of the motor. As in, the motor is beginning to light, when it builds up enough pressure so that it pushes the unvented igniter holder off, and the pressure changes so rapidly from the hot air in the motor escaping that it snuffs the motor out.

 

[Justin Horne]

Yeah, what RBG80 said is just about it. APCP burns better under pressure. As the igniter lights the propellent, it starts to build pressure. If the cap was on w/o a hole, it would blow off, and the motor would have a harder time pressurizing. The little hole keeps that cap on and most pressure in.


As for B, the copperhead is a great mass production device. Copper, insulator, copper, cut, crimp and then dip. Quick and easy for them. If it was thicker it would be hard to bend and may actually crack more readily. One thing I do is take a hobby knife and run it down the side of the igniter to get rid of any copper that jumps the insulator. Doing this with the idea of heating the insulator and melting it by a lighter ( I have never done this, alot recommend it) and you should be fine. I get about 95% success rate with them.

Justin

 

[Justin Horne]

Also, the good igniter (First Fire) is only standard on the bigger motors. The smallest I have gotten one was in a G75. I get copper's in my G64 loads...

 

[DJ Delorie]

If it was thicker it would be hard to bend

Not thicker, wider. I assume they make them from sheets of copper and insulator, then cut them into strips. If instead they were made of spools of copper and insulator ribbons, the copper could be narrower and thus kept away from the edge.

 

[Justin Horne]

Oh, gotcha. Maybe it has to do with the amount of pyrogen on the end? I guess it would only be on small motors, so not too much concern there.. They are all c grains, so... Huh. Maybe they are designed to be the biggest they can to fit the smallest nozzle, and not have to deal with many kinds of coppers. Really though, I don't know.
Although really, it's a good idea. Probably hard to make though...
Also, most of the time, with copperheads I just use tape to hold it in, the place where the igniter comes out is the right size hole to let is lose a little pressure. Works for me...

 

[Omega_D]

I don't know, it made sense as I was writing that reply...

Let's just say I've been enlightened with the other responses. I've even lit igniters under water, I should know better than to write that crap.

Sorry folks, just a bout of temporary insanity. That's my story and I'm sticking to it.

I'd have to go with the sudden depressurization story, that makes the most sense. It seems to me I've heard that from someone before... Give me a minute though, I might come up with something crazier than the first reply.

Too much work, not enough sleep, no time to build rockets, missing LDRS, OH THE HUMANITY! MAKE THE VOICES STOP!!!

I now return you to your regularly scheduled program... I'm okay, no really...