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View Full Version : Thoughts on where to break this dual deploy rocket



dmjung
29th July 2010, 01:23 AM
I'm on the final stretch of getting my PML BBX ready for an L2 cert flight at NARAM. I started this rocket a long time ago (think years and years) and it sat about 3/4's finished until earlier this year.

I'm thinking through where I want to make the breaks at this point based on how the construction was started. In the picture below, option "B" was my original thinking, but I'm starting to wonder if the 68" airframe section in the middle might be a problem since the attachment points are both buried deep at both ends. So I came up with option "A" where I leave a section of the tube with the fin can. (Lengths may look funky due to couplers being exposed/hidden between the options.)

The electronics are in the middle where the little fins are. Anticipated altitude according to Rocksim is about 1543' on a J350W.

Maybe it doesn't matter...any thoughts?

--David

http://i133.photobucket.com/albums/q41/dmjung/DualDeploy.jpg

WillMarchant
29th July 2010, 01:31 AM
I did a rocket as "B" once and that "apogee tube" kept getting beat up as it landed...

Handeman
29th July 2010, 01:36 AM
I did a "B" in dual deploy. I wouldn't bother doing a zipperless fin can on a DD rocket again. The electronics are so dependable that you don't need it.

If you do a "B" design, put the drogue close to the center/upper section. Keep that section above the fin can on the way down. When the main deploys, fin can will already be below the main and the shock on the recovery harness will be much less and there will be no chance of the fin can fouling the main.

G2Rockets
29th July 2010, 01:47 AM
IMO,
I would do B. I like zipperless. I agree that electronics are very reliable, but It gives a sense of security.

That being said, I didn't do a dual deploy for my level 2. I was going to, but the TAP talked me out of it. He feels that a person is under enough pressure just doing a level 2, so you don't need the added pressure of DD. If you have done DD several times before I would disregard what I just said and go with plan B.

Which ever you choose, I wish you the best of luck.

John

Handeman
29th July 2010, 01:56 AM
IMO,
I would do B. I like zipperless. I agree that electronics are very reliable, but It gives a sense of security.
John

I agree with the sense of security. That is why I build mine zipperless.

After 8 flights, I've found it to be more trouble then it's worth. I wouldn't bother with the zipperless on a DD again, but that's just me.

troj
29th July 2010, 02:03 AM
Personally, I don't think "zipperless" is really what it claims to be. I've seen those zipper, too. Besides, zippers are typically a problem of either A) the wrong delay, or B) a poorly packed recovery system. I've gotten enough from B over the years....

Now, that said, I like B because you can easily put the charges under the parachute. I wouldn't make that tube 3/4 the length of the rocket, though. If it's not too late, I'd adjust the break point and where that bottom bulkhead is.

-Kevin

G2Rockets
29th July 2010, 02:33 AM
Personally, I don't think "zipperless" is really what it claims to be. I've seen those zipper, too. Besides, zippers are typically a problem of either A) the wrong delay, or B) a poorly packed recovery system. I've gotten enough from B over the years....


-Kevin
Or no delay.
We have all seen the motors that for some reason have no delay and pop! out comes the shoot. I think that is the biggest positive it has. Personally I like the DD that Nate uses. He showed me that before he took the core sample, but I don't think it was because of his DD was it?
I knew you weren't big on Zipperless. I think you told me that once. I think you said Greg is an advocate of the zipperless system. Have you ever debated it with him?

John

Rocketman248
29th July 2010, 02:38 AM
I would go with A. That's the way I've done all my dual deployment flights. One tip, attach your drogue as close to the top section as possible. Attach it directly to the e-bay if possible. This way, it keeps the nose cone pointing in the ideal direction for main deployment. Also, put a small pilot chute on the nose. When the nose pops, the pilot chute will pull everything right out.

With option B, your nose cone will most likely be pointing straight down, and you have a much bigger chance of having the main get tangled up with everything.

troj
29th July 2010, 02:49 AM
Or no delay.
We have all seen the motors that for some reason have no delay and pop! out comes the shoot. I think that is the biggest positive it has. Personally I like the DD that Nate uses. He showed me that before he took the core sample, but I don't think it was because of his DD was it?

Yah, short or bonus delays are a problem.

Nate's recovery system was built such that it didn't leave much room for issues. I think he plans to tweak it a bit, to allow for more "error" of things not quite coming all the way out of the tube.


I knew you weren't big on Zipperless. I think you told me that once. I think you said Greg is an advocate of the zipperless system. Have you ever debated it with him?

We've had a few discussions about it, but that's it. Greg and I have differing philosophies.

-Kevin

dmjung
29th July 2010, 04:17 AM
At this point (and with the time I have available) rebuilding the rear section isn't really an option so it's basically A or B. Or single deploy I guess...1500' isn't that high and there's lots of room--depending on the wind I might go that route. My inclination is to stay with B rather than over-think it at the last minute.

It does seem to be the consensus to have the drogue closer to the airframe than the fin can though. Drogue is 18".

Thanks!

--David

brianc
29th July 2010, 04:24 AM
Go with option A. The longer aft tube length will give you
the chance to fly in the future with longer motor tubes, yet
still fit the drogue and recovery harness inside...

This assumes of course, the U-bolt in your drawing is in
a centering ring, not a bulkhead.

dmjung
29th July 2010, 04:51 AM
It's a bulkhead so a longer motor isn't an option without a bunch of surgery. However fatter motors are possible with the kwikswitch so 54mm is doable in the future.

I guess since I'm using rivets, it would be possible to try both A and B over time.

In any event, it's essentially done building-wise other than the rivets, rail buttons, and drilling vent/shear-pin holes. Electronics need some minor cleanup of the wiring and testing. Finalize hookup of the harness/chutes. Hopefully all done tomorrow night and we're not leaving town until Saturday morning. Will be about 13 lb's at launch...heavier than I wanted. I'm targeting a flight on Monday--assuming I pass the test Sunday night :D and the weather is OK...looks like rain all next week.

http://i133.photobucket.com/albums/q41/dmjung/P1010005.jpg

--David