Explosive Bolts....

[awseiger]

Hello all...

I was dozing off in class today thinking about rockets (figures), and I realized that explosive bolts may not be as hard to make as one would think...

My plan is to have a glider attached Parasitically to a HPR rocket that ejects the glider at a given altitude. This removes the reliance on drag, removes the possibility of a tangle with the recovery system, etc. The same thing would work for strap-on boosters, but I like gliders more, and engines are expensive. If these can be made small, MPR Parasitic gliders could be done this way as well.

My idea is to hollow out 1/4in nylon bolts and throw a teeny bit of Pyrodex in there with an E-match, then fill the hole back up with epoxy. Spacers on the glider and inside of it ensure that the Pyrodex-filled part is exposed outside the rocket, while the use of metal nuts ensures that the airframe will not be damaged by the exploding bolt. The use of Pyrodex is due to the high-compression characteristics, where a little bit goes a LONG way when in a tight container.

I know that there are a few places online that have done this, but it seems as if they are using a container filled with BP held together with a weak nylon bolt. The BP igniting pushes the container open, putting so much tension on the bolt it breaks. This seems great, but I do not have access to a machine shop to make the little containers.

Anyone ever successfully used Explosive bolts? Are there any rules that say we can't use them? Post your experiences! I probably won't get around to messing with these until December or so, but it seems like something worth developing.

 

[troj]

Anyone ever successfully used Explosive bolts? Are there any rules that say we can't use them? Post your experiences! I probably won't get around to messing with these until December or so, but it seems like something worth developing.

We've used a lot of them -- that's how we hold the sections together on our big projects.

A couple things....

1) When you hollow out the bolt, do it through the head
2) Drill it out with a drill press; if you do it on a lathe with a boring bar, you need to run a tap into the hole, afterwards -- you want the hole rough, or the epoxy just pops out
3) Put a little bit of filler in the epoxy, or the plug just shatters
4) Test, test, test, test, test. Plan on consuming at least a half dozen bolts, if not more, to make sure you have your charge size correct, and your bolts are working. We've literally blown up two dozen bolts in ground testing. We've also used 30 bolts in 5 flights, and haven't had a bolt fail, yet.

-Kevin

 

[ClayD]

There was someone on here that posted about droping gliders with nylon bolts, just like you and Troj are talking about. I can't find the thread. it was complete with " PICTURES"

Me thinks that quest Q2G2 ignitors, and some "SMALL" nylon bolts would be perfect for a small MPR project... i think i could get it to work down to a #10 bolt.

 

[fyrwrxz]

FWIW- you can dip a q2g2 in 'nail hardener' sold by the fingernail polish and they will pop rather than ignite. Chemistry is our friend.....

 

[G_T]

This seems to me to be an application where aluminum may be a better bolt material. It is more brittle than nylon, so it should fragment more cleanly I would think. Has aluminum been tried?

Gerald

 

[luke strawwalker]

This seems to me to be an application where aluminum may be a better bolt material. It is more brittle than nylon, so it should fragment more cleanly I would think. Has aluminum been tried?

Gerald

Compare the tensile strengths... need a lot more bang for aluminum...

later! OL JR

 

[troj]

This seems to me to be an application where aluminum may be a better bolt material. It is more brittle than nylon, so it should fragment more cleanly I would think. Has aluminum been tried?

Overkill.

Nylon works, and it doesn't take much of a charge to make them shatter.

-Kevin

 

[cwbullet]

Overkill.
Nylon works, and it doesn't take much of a charge to make them shatter.

And it is less likely to create Shrapnel.

 

[jimzcatz]

Guys, I kinda thought this would be forbidden in our hobby. I dont care one way or the other, but really? Just wanting to keep the alphabet guys away.

 

[troj]

Guys, I kinda thought this would be forbidden in our hobby. I dont care one way or the other, but really? Just wanting to keep the alphabet guys away.

Why would it be forbidden? How is it any different from using ejection charges? Rather than being contained in a tube, they're inside a plastic (nylon) bolt.

-Kevin

 

[MaxQ]

Wasn't this kinda like an explosive bolt?
I mean for a different reason but kinda like one.

https://www.defyg.com/tether.html

 

[awseiger]

Guys, I kinda thought this would be forbidden in our hobby. I dont care one way or the other, but really? Just wanting to keep the alphabet guys away.

I was afraid of the same thing, but it seems as if they are totally acceptable.

I actually thought of an interesting alternative to actually blowing up the bolt using two pipe caps that fit inside each-other held together with a shear pin. No shrapnel! I'll post a poorly drawn GIF at some point. If I can find the proper bits at the hardware store it may be a very good option.

 

[Barry]

We've used a lot of them -- that's how we hold the sections together on our big projects.

A couple things....

1) When you hollow out the bolt, do it through the head
2) Drill it out with a drill press; if you do it on a lathe with a boring bar, you need to run a tap into the hole, afterwards -- you want the hole rough, or the epoxy just pops out
3) Put a little bit of filler in the epoxy, or the plug just shatters
4) Test, test, test, test, test. Plan on consuming at least a half dozen bolts, if not more, to make sure you have your charge size correct, and your bolts are working. We've literally blown up two dozen bolts in ground testing. We've also used 30 bolts in 5 flights, and haven't had a bolt fail, yet.

-Kevin

Do you have an image of how you connect your sections together without breaking any confidentiality?
barry

 

[troj]

Do you have an image of how you connect your sections together without breaking any confidentiality?

As the guy who designed the rockets we used them in, confidentiality isn't an issue. I don't have pictures of that, but I can explain it. Keep in mind, these are large airframes - 16" - 24" in diameter.

Put a 3/4" bulkhead at the end of each airframe section you want to join. In the middle of the lower section is a 7.5" hold with a piece of (you guessed it) 7.5" airframe. That 7.5" is where the parachute goes - we have it in a deployment bag specifically sized to fit that size tube.

No coupler is used - the two sections of airframe butt up against one another, flat plate to flat plate. Around the perimeter is a series of holes, sized for the nylon bolts. We cut access holes in the side of the airframe, allowing someone to reach inside to attach them. Put the airframe sections together, reach in and install the bolts.

The bagged main parachute has a spring-loaded pilot chute from man-rated reserve parachutes. When the two sections are put together, the spring is compressed, and the pilot chute sits at the very top of the parachute tube. When the bolts fire, the spring pushes the sections apart.

-Kevin

 

[Ez2cDave]

Guys, I kinda thought this would be forbidden in our hobby. I dont care one way or the other, but really? Just wanting to keep the alphabet guys away.

Jim,

I share your concerns . . . https://en.wikipedia.org/wiki/Pyrotechnic_fastener

Dave F.