question regarding dual parachutes

I searched this, but didn't really find what I'm looking for. If I wanted to use dual parachutes from a single rocket body (as opposed to two sections connected by long cord), do I have to do anything special to minimize risk of entanglement? Obviously,I could simply use one 'chute, but the design I'm playing with (I call it Binary Star) would seem a logical candidate for dual 'chutes:


I'd like to put an 18" chute in both tubes, which based on my RockSim model, ought to give it a fairly easy rate of decent, but are large enough to not be totally without merit if one fails. Thoughts?

One thought. It will go wrong. The odds of a good deployment where (1) you get simultaneous release so that one nosecone doesn't center punch the other chute (2) where the chutes open beside each other instead of one inside the other (3) where the chutes pull apart upon opening in time to avoid twistup - just seems the odds are against it working.

If you must do it, I'd suggest substantially different length lead lines to the chutes and release the longest one first (to handle issue 1 and 3). Use strong enough line for the first chute so that a tangle on deploy of the second at ejection velocity doesn't rip the line out or apart. Size the chutes so that it is safe just from the first chute being deployed. That way if a tangle occurs which puts the second chute out of order then the recovery is still nominal. Stagger deployment of the chutes by a few seconds because essentially you won't get it sumultaneous enough anyway so better to go safe the other direction.

You could make the two nosecones be a single cone joined at the base. Use a single deployment charge (with redundancy perferrably) to push the cones off. Etc. I still don't like it though.

YMMV, and it is your rocket, not mine!

One can make dual deployment of chutes fairly reliable but I think that is easier with larger rockets, deployment bag(s), tether arrangement, etc. I did an arrangement with tethered drogue which was also dbag pilot, and nosecone and body mains deployed from the one bag. Deployment was very predictable and reliable. But a lot of thought and preparation goes into making it so. It is several times more work and is intrinsically intolerant of packing errors. Working from two tubes I think you are making the job several times more complex.

Gerald

I assume this is a motor eject, 2X 24mm model?

How about putting, in the left tube lets say, a 12" parachute attached to a 6ft long cord, with the motor set to deploy right at apogee, or as close as you can get. Then, in the other (right) tube, put an 18" or 24" chute attached to a 3ft. cord with the motor set to deploy well after apogee (maybe even the longest possible delay.) So, you have the first parachute deploying, and dropping it quickly for a while, staying out of the way, and then you have the second, larger parachute deploying at a lower altitude, much like standard dual deploy ( drogue [small] parachute at apogee, and larger parachute at preset altitude) without the possibility of it tangling into the larger parachute. You can use whatever chute size you like, but the smaller at apogee will help reduce drift.

Nate

There is an easier way to get near simultaneous deployment: cross connect the tubes.

I would use the top 4" of the two tubes as lower extensions of the nose cones. Glue the nose cones to the tubes and glue the tubes together so you have a single unit as a nose cone. You'll need some coupler tube and some bulkhead to make the single nose cone unit. Then make sure you have a large port from one BT to the other so which ever motor fires it's ejection charge first, that is the one that will blow off the single nosecone unit and deploy the two chutes.

That's the only way, short of a single electronic controller, I can think of that will allow you to ensure both tubes open up and both chutes deploy at the same time, which is what you need if you don't want all the deployment problems that G_T described and then some.

Good luck and let us know how it turns out.

Point taken, G_T. That sort of sums up my concerns. Nute, your suggestion was what my original intent was, but once I started modeling it, I realized that it would require long delays to get to apogee, and anything much earlier would occur while the rocket was still moving pretty fast. I might get away with 2-seconds between ejections (assuming there's no bonus on the first one), but that doesn't really allow the rocket to drop very far on the first chute. I decided that it really wasn't worth the effort.

Instead, I think I'll put a single chute in the alpha tube and port the two together. I'll place a bulkhead into the top of the beta tube and use that side for small payloads. It'd be a good place for an altimeter.