Placement of BP Charge for deployment

[edwardw]

Okay, I have a question here. I have a rocket that I plan to recover in two separate pieces - the motor/fin section and then parachute bay. I will be using a perfectflite MAWD altimeter. Before I have had success with what I would call a rearward 'gun' deployment. In the nose cone I put the charge as far forward, some wadding, then the parachutes. When the charge goes off it 'fires' the chutes out and they open. I have had success with this, but at the cost of having to use a lot of powder and loading up on the wadding as not to flame fry my chute.

I just recently tested what I call a rearward deployment with separation charge. For this I jam the small chute all the way into the forward section, the other chute right behind it, and then I have some room left where the two sections of the rocket couple together. I put a much smaller BP charge there( about 1/10) the size. When it goes off it just separates the sections and aerodynamic forces pull out the chutes.

Has anyone else used this method, any suggestions? It seems to work fine for me, but are there any things I should be looking out for?

Thanks!

Edward
www.stlrocketry.com

 

[firemanup]

Pictures or a sketch... sorry i'm not following it but i'm interested in what you're trying to do...

 

[powderburner]

but I think that what edwardw is describing is something like:

The ejection charge (in the mid-body) separates the two body tube sections. The inertia of the front section tends (briefly) to carry it on forwards, until the chute (tethered to the rear section) is pulled out.

Sounds OK in theory, but I have no experience with high-power stuff. I don't know how consistent/reliable this would be, as opposed to 'blowing' the laundry out the nose via a conventional ejection setup. Might work just fine (as edwardw points out, it already has).

 

[edwardw]

You have it exactly - much better description than I have. That is what I am trying to explain. Does anyone know how well this will work if I scale it up?

 

[wyldbill]

The thing to remember is that the charge will blow the chute back into the other section, potentially packing it tighter. I try to push 'chutes OUT or have them dragged out by a pilot or drouge. Just relying on them to be dragged out by the "other" section seems a little iffy to me.

YMMV,
-bill

 

[powderburner]

Maybe you could avoid having the ejection charge force the recovery system farther into the fwd BT by keeping the ejection gas contained in a stuffer tube that extends past your parachute and vents into the nose (the ejection gas tube would be attached to the rear BT, and would be left 'hanging out' when your rocket lands).
That way, the force of the ejection still separates the two parts of the BT, the hot gases might go completely past your laundry without damaging it, and your 'chute would not get packed into the nose.
Your model would have to be large enough, however, to have room left between the gas tube and the outer body tube to still be able to pack in a parachute.

 

[edwardw]

The tube diameter I am using is 3" ABS black pipe. The parachutes I'm using are about 2.75 OD when packed so they rattle around quite a bit in the tube.