A "zipperless" question

[Marc_G]

Hi folks,

I'm going to do a build with a baffle in the lower section, sticking out, with the parachute fitting into the upper part that slips over the extended baffle section. I understand this is essentially the zipperless design.

My question is (within the bounds of LPR and small MPR), what prevents the shock cord from zippering the upper tube that goes flying off at ejection? Is it just less prone to such, being (generally) lighter?

Perhaps I'm missing something basic. I've read a few of the informative articles I've found by googling, but am missing this basic point.

Thanks in advance!

Marc

[Wayco]

I think you are right Marc, less mass and momentum with the lighter N/C section and since you should attach the chute near the coupler, the upper section will still be heading away with a straight pull back to the chute. No shock cord folded over the body tube.

[qquake2k]

I've built and flown a lot of mid and high power zipperless designs. So far, I have yet to have a zipper. My thoughts are that the upper section is relatively light, and because of the design, the shock cord doesn't tend to fold over the edge of the body tube. My shock cords have been everything from tubular nylon, nylon rope, paracord, and even 5/32" braided poly cord. Also, because of the design, I think the upper section tends to blow straight away from the lower section at ejection, so it gives even less chance for a zipper. You can see what I mean in the videos. And in the video of the Ion Disruptor, you can see that it was a way early ejection, but it still didn't zipper.


http://www.youtube.com/watch?v=7Wh3jKMwmwg


http://www.youtube.com/watch?v=j5MHkfOs-mk


http://www.youtube.com/watch?v=dCK8_dq-Yu4

[astroimgur]

Got a question for you qquake regarding zipperless shock cords. I know the typical shock chord length for most rockets is usually 3x the BT length, but does this apply to the main chord for the zipperless design as well? What about the short chord for the payload section?