Anti-zipper idea

[Sooner Boomer]

I've never had a rocket zipper (yet...). An idea came to me about a way that might help eliminate them. It seems like a good idea, so someone has probably already thought of it, but here goesThe idea is to have a thick, perforated disk attached to the recovery harness in a way that the disk can go down inside the body tube, but the attachment point on the harness keeps the disk from going past about an inch or so inside the body tube. This assumes the harness is attached to the motor mount, or somewhere to the aft of where the parachute sits in flight. When the ejection charge goes off, everything is pushed out the top of the rocket, but the disk comes up short. It keeps the recovery harness centered in the body tube. The diameter (just under body tube diameter) and thickness help spread out the force on the harness when the parachute opens. The harness should never touch the top lip of the body tube (when it's under tension). For lack of a better term I call this a snubber

An example of what the disk (snubber) could look like


Cross section in flight


On deployment of parachute


The openings in the disk should be as big as possible, and could be a varity of shapes or numbers. It could be easily 3D printed.

 

[GlenP]

A disc might rotate and get tangled and stuck in the tube, maybe a slightly longer type of vented “piston” would work? But a clever idea!

 

[tim cubbedge]

Giant Leap makes the Fireball zipper stopper.
https://giantleaprocketry.com/products/components_recovery.aspx#Fireball

 

[dhbarr]

You know those squishy foam grip things that come on cheap mechanical pencils?

 

[Nathan]

Your disk looks similar to the baffle in my Frenzy XXL. But the purpose of that was to keep the chute at the top of the 5 foot payload tube.
https://www.rocketryforum.com/threa...d-8-upscale-frenzy.139390/page-4#post-1697758

 

[shawn_rocket]

Your disk looks similar to the baffle in my Frenzy XXL. But the purpose of that was to keep the chute at the top of the 5 foot payload tube.
https://www.rocketryforum.com/threa...d-8-upscale-frenzy.139390/page-4#post-1697758

Nathan - Just read that build thread. Just awesome. Frenzy XL is on my wish list; but that XXL is amazing!

 

[BABAR]

I think I’ve got it.

Instead of a disk Alone,put a disc on the end of a cylinder to act as a piston to keep it aligned and from twisting inside the body tube.

have holes along the outside of the cylinder.

Deployment the cylinder extends almost but not COMPLETELY out of the body tube.

The side holes allow venting of the ejection gases around the sides once the forward end of the piston is outside the Rocket body.

 

[Bat-mite]

Just buy the Fireball that Tim referenced.

 

[burkefj]

Or just do anti-zipper construction of course....if the design will work with that. Or do external attachment, I use that with thin kevlar on almost all of my low power stuff so that it also comes down horizontally, comes down slower a win/win, nothing is attached inside the model, easy replacement.

 

[bschultz32]

Just buy the Fireball that Tim referenced.

 

[Banzai88]

Just buy the Fireball that Tim referenced.

View attachment 443791

Just a foam nerf ball with a kevlar sock.

How long does that thing last?

 

[bschultz32]

I flew a Fireball five times in my LOC/Precision EZI-65 with no apparent degradation. Got a little dirty-looking from the black powder blast, but cleaned up okay with a soapy-wet cloth. (Rocket was eaten by a very large corn harvester machine after getting lost in a corn field on its sixth flight.) In the photo above, a brand-new Fireball is shown in a 7.5"-diameter LOC Mega-Magg. That provides enough room to attach it to two hard-point U-bolts in the forward centering ring with quick links, and it's possible to get one's hand down in there to disconnect and remove if things get too gnarly. When that happens, next stop will be my wife's next batch of laundry.
The moral of the story is that while large-diameter rockets require pushing a lot of air out of the way to get to altitude, they DO have their advantages!
Bob Schultz

 

[David Schwantz]

Wiffle ball, already has holes to pass shock cord through. I have used the little golf ball size ones before.

 

[BrendanH69]

For narrow, non-flat shock chords and especially steel wire, like on this 3inch PML Intellicone, I like to use a blob of Loctite Kintsuglue. Did that after the first deployment of this nose cone where cone retainer wire zippered the nose cone shoulder a little. Seems to work a treat and doesn't take up much space.

 

[Titan II]

Pipe insulation wrapped with Nomex. Smaller versions are 1/4 foam wrapped around the shock cord and covered with electrical or duct tape.

 

[Ronz Rocketz]

I've never had a rocket zipper (yet...). An idea came to me about a way that might help eliminate them. It seems like a good idea, so someone has probably already thought of it, but here goesThe idea is to have a thick, perforated disk attached to the recovery harness in a way that the disk can go down inside the body tube, but the attachment point on the harness keeps the disk from going past about an inch or so inside the body tube. This assumes the harness is attached to the motor mount, or somewhere to the aft of where the parachute sits in flight. When the ejection charge goes off, everything is pushed out the top of the rocket, but the disk comes up short. It keeps the recovery harness centered in the body tube. The diameter (just under body tube diameter) and thickness help spread out the force on the harness when the parachute opens. The harness should never touch the top lip of the body tube (when it's under tension). For lack of a better term I call this a snubber

An example of what the disk (snubber) could look like
View attachment 443649

Cross section in flight
View attachment 443650

On deployment of parachute
View attachment 443651

The openings in the disk should be as big as possible, and could be a varity of shapes or numbers. It could be easily 3D printed.

I look forward to your test videos.

 

[prfesser]

Someone please correct me if I'm wrong, but my understanding is that the piston-type harness attachment can tend to jam after a few flights, if one is not careful to remove BP residue. Would the proposed idea have this potential problem too?

 

[Ronz Rocketz]

Someone please correct me if I'm wrong, but my understanding is that the piston-type harness attachment can tend to jam after a few flights, if one is not careful to remove BP residue. Would the proposed idea have this potential problem too?

I think if there was enough room. All it has to do is reach close to the edge to avoid zippering. The Fireball and pipe insulation would do just the same.

 

[MetricRocketeer]

Hi TRF colleagues,

On Saturday (10 July 2021), at the Maryland Delaware Rocketry Association’s launch, my wife flew her 10.2 cm LOC/Precision V2 rocket on a G115 using the small Fireball (zipper protection) that she bought from Giant Leap Rocketry.

It worked beautifully! No zippering whatsoever. The aft end of the Fireball did get a little singed, so she will figure out a way to repair that. But it worked fine, and she flew her rocket with peace of mind regarding zippering.

As long as you have room for it in the rocket’s airframe, I highly recommend this piece of equipment.

Stanley

 

[bschultz32]

Yup. Don't overthink this long-ago-solved problem. Just buy Giant Leap's Fireball, don't worry, be happy.
Bob

 

[MidOH]

With a fiberglass rocket, you could glue your disk in place, it can then become your shock cord mount.

Paper, the fireball trick looks better. We've run the shock cord through baffles before, it just tears them up.

 

[Funkworks]

I sure would like to see a video of zippering fiberglass tube.

 

[Banzai88]

I sure would like to see a video of zippering fiberglass tube.

There are a few photos of zippered tubes based on motor issues or electronics issues......but if you're trying to 'anti zipper' a fiberglass tubed rocket as a matter of course, your design and flight profile probably has bigger problems that should never allow it past the RSO.

 

[lakeroadster]

The Piston Song

 

[MidOH]

I don't know the proper term, but my fiberglass ''antizipper-ish'' woes are more about saving the shock cord, not the tube. Related similar issue, but not the same. Usually, on LPR or MPR, I just motor mount the cord and use aluminum tape on the shock cord where it contacts the tube edge.

If there is no terminology for that, then I vote for: ''The Tube Strikes Back''.

My point kinda was, if your paper tube is strong enough, putting the shock cord on a reinforced baffle or bulkhead could work. I don't want a floating disk rolling around. I haven't had much luck with that, so prefer carbon or glass for larger rockets for now. But I haven't played with monster sized paper rockets that may have giant baffles designed in, with a cord mount.

 

[MetricRocketeer]

Hi TRF colleagues,

And now I have discovered another, I think even better, anti-zipper idea. The Giant Leap Rocketry Fireball does work, and I do recommend it. I realize, however, that setting it up takes a little bit of work -- all doable and not extremely time-consuming, but not completely insignificant either. But the main problem occurs if you do not have a lot of room in your body tube.

An alternative method is the Shock Cord Bumper, which Dino Chutes manufactures and which Apogee Components sells. With great success, I used the large-size Shock Cord Bumper, which is Apogee's model #29354. You wrap it around the shock cord. It takes up less room than does the GLR Fireball and the installation is quicker. The small-size Shock Cord Bumper may also work, but I have not used it.

Here is a not-great photograph of it installed in my Minie-Magg, and my wife is holding the body tube. The shock cord still needs to be extended, and I have a water bottle also installed in the body tube as I was preparing to do a waterloft at NARAM-62.

Stanley

 

[Rob Campbell]

The LOC-Loop shock cord mount works very well, if set up correctly. I've used them on my 4 inch and smaller rockets with a 100% success rate.

 

[MetricRocketeer]

Hi @Rob Campbell,

Thank you for the post. Could you kindly provide a link to the exact item to which you are referring. I would like to examine that, please.

Stanley