Zipperless...

Would anyone have a decent pic or drawing of a typical "zipperless" designed rocket? From what I can gather so far, it appears that most designs of this type come apart somewhere in the middle of the length of the rocket, rather than at the nosecone.

ROL's InfoCentral has a good description with a diagram:Anti-Zipper Design You will need to search for 'Zipper'

Tnx much...
Stumbled across that very site after posting this thread.

After becoming familiar with the "zipperless" design theories, I thought I may give 'er a try. The bird I have in mind is the Estes Executioner. Now, I'm sure I can probably get away with the standard NC seperation stock design but, being I plan on flying it on F's, I thought this would be a good one to start with. Especially being a fairly long expanse from the stock shockcord mounting area to the top end of the tube. Plus, it just plain makes so much sense to go zipperless and cure some of the recovery "problem areas".
The part of this plan I'm not sure about is, is the bodytube(BT-80 /.012 wall ) to thinned wall for this type of recovery to be feasable? I guess I'm concerned that the ejection charge my damage the tube when pressurising it.
Opinions appreciated.

I personally don't think the Estes wall tubes will be too thin. It shouldn't be much harder on them than a regular nose ejection, PROVIDED you put plenty of vent holes in the baffle to allow the gases to escape. My level 1 bird was "zipperless" and has deployed flawlessly so far (probably would have had problems if I had done it normally--it's a Murphy's law kinda thing for me). The Sentinel (see the thread in the High Powered Rocketry forum) is also anti-zipper. I'll let you know tomorrow evening how that flies.

Tnx for the response Kermie...
Yea, I like that Sentinel. The Packers motiff is nice. I'm just 60 miles or so down the road from Lambeau.

Ya think 1/8 basswood is enuff for the baffle? Tryin to keep 'er light but, don't want it blowin out on it's maiden flight. Also, I would imagine I should put a slight angle on the baffle holes to redirect the gasses a bit?

I have used zipperless construction on low, mid and high power rockets. On the mid and high-power I used the 'Bob Kaplow' baffle: motor tube abuts the bulkhead, holes drilled on side of motor tube and around edge of bulkhead (you can search TRF for this approach, it's well documented somewhere herein). On my Estes Mean Machine I used 1/8" ply, but uses a baffle made from a coupler and two offset half-circles.

IMHO the thickness of the bulkhead in the Kaplow approach is not a factor in containing the ejection as much as it is to provide a secure mount for the shock tether. For a low power or most mid-power models, 1/8 ply should be fine. Make sure it is recessed a bit into the coupler and provide a good filet around the edge. Note that the rear end of a rocket in this method is lighter than it would be with the full BT attached.

Yeah. What Dick said. On both of my rockets that are zipperless, the distance from the motor to the baffle makes it unnecessary for me to redirect the gases.

60 miles from Lambeau? Which direction? I'm about 60 miles south of Lambeau myself. Oshkosh to be precise.

Originally posted by KermieD
60 miles from Lambeau? Which direction? I'm about 60 miles south of Lambeau myself. Oshkosh to be precise.

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Well...it is a small world now isn't it....wow. What's the chances on that...Oshkosh it is Kermie...

We usually launch over by county park on the weekends by the southend soccer fields. Wanted to go this weekend but, as you know, little too much wind.
Do you go down to Bong for your HPR launches? Went there for the 1st time this year in August. I just got back into rocketry this year after stumbling across some sites that show the hobby as it is now. I got out back in the 70's when D's were just starting to make their appearance. It appears that the sky is the limit when dropping $$ on it nowadays.

As far as the zipperless, I plan on using the stock coupler with an 1/8 in. basswood bulkhead. Put 1/2 a dozen holes in it with an eyescrew or u-bolt in the center. The motor tube is 12 in. long and ends about 3 in. from the bottom of said bulkhead. I'll put about 1/2 to 3/4 of an in. of coupler in the lower BT and the rest of the 2 1/2 in. of coupler will support the upper BT.

One other thought on the thin tubing and zipperless construction. I have only flown my baffled Mean Machine on BP motors. I had used E15's before the baffle. The composites have a habit of delay burn-thru after the ejection has gone off. This can wreak havoc on Estes tubes.

Anyone else ever have this problem?

It might be a good idea to pain the inside of the tubes with epoxy of you are going to try composites. I've also heard yellow shellac will help, but I hardly even know what that stuff is.

Originally posted by rstaff3
The composites have a habit of delay burn-thru after the ejection has gone off. This can wreak havoc on Estes tubes.
It might be a good idea to pain the inside of the tubes with epoxy of you are going to try composites...

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I did paint the inside of the MMT with epoxy, inside of the BT's with sanding sealer. I take it you mean that the composite "burn thru" is residual delay that continiues to burn inside your MMT?
Meaning that in a stock ejection, it is pushed out with the chute and wadding? Hmmm...
Sounds like I could end up with a baffle coupler on fire or after awhile, it will become loaded up with ejection particals. Which I would assume could be shaken out through the baffle plate holes.
This brings me to another question(always another question)...does the NC get affixed to the upper BT in a zipperless design, meaning permanently glued in place, or do you leave it so it can be removed in case of a needed shockcord replacement?
Sry for all the questions...'tis a live and learn kinda thing for me right now.

No problem, questions are good.

I doubt if the delay material gets blown forward by the ejection since it is behind the charge. I think it isn't totally burned out though, and small amount of flame continued to emanate through the hole that separates the ejection well from the combustion chamber.

I've never seen this cause a fire, but I've had it char a body tube on BT-50 rocket fired on a D21. The tube almost looked melted. I've also seen deteriorated motor mount tubes after performing an autopsy on a damaged rocket.

In all cases where I've used zipperless construction, the recovery harness is attached to the nose cone or an eye bolt on a bulkhead. On some I've attached the cone permanetly, on others its removable. If you use the properly sized Kevlar cord, it will outlast the rest of the rocket.

I've got about 12 in. or so of upper BT from the top of the baffle. What would be a good length of shockcord to use? And also, where abouts should one put the chute attachment point on said shockcord? Let me know when I start to bore you guys with this stuff... ;-)
Really though, tnx much for all the help that is offered here. Most appreciated.

The total *exposed* length should be 2 - 3 times the length of the rocket. Longer doesn't hurt. As I remember I placed the chute about 1/3 of the way up from the lower attachment point. On the bigger (heavier) rockets (i.e. all but my Mean Machine), I also made sure the cord was long enough so that I could hang the 2 pieces from the chute attachment point and not have them bang into one another. I haven't used any elastic for these designs, just Kevlar and tubular nylon. I have no problem with elastic as long as it is sized for the job, is long enough, and is protected from the ejection gasses.

Would like some input on this design...
What interests me most is the distance from the top of the MMT to the bottom of the 1st baffle plate. Is this distance too short? The baffle plates are someones design I found from one of the threads here. I made them from 1/8 basswood.
Just want to be fairly sure the baffles will hold up. I'll be using Econo's (F21's to be exact) for the 1st flight.

I think your design will be fine with the basswood so long as it's secured well. In fact, it looks to me as if that third plate is redundant. I don't think there's anything wrong with the length at all.

I personally use an eye bolt screwed into the cone, cut out part of the shoulder and put a nut and washer inside the cone. Then, I put a well of epoxy in there to make sure that nothing will ever go anywhere. I then secure the cone permanently to the upper BT (personal preference). As Dick mentioned, if you use nylon or Kevlar, the shock cord won't be the first thing to fail.

Originally posted by KermieD
I think your design will be fine with the basswood so long as it's secured well. In fact, it looks to me as if that third plate is redundant...

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Hi Kermie...
The reason I thought to go with the third plate is the designer of them stated that he never gets any chute damage when using three plates and no ejection residue gets past the 2nd plate when using this design. A little more weight(about 4 grams per plate with epoxy coating, both sides) but, sounds like better protection.
I've thought about just building it stock(no zipperless-use the baffle) and use stock recovery(seperation at the NC). It's just the idea of the building technique that interests me. Guess there's only one way to find out.

Btw...
I'm thinking that at launch exceleration, there's more than likely quite a bit of force on the edge of the upper BT.Would it be a good idea to add a 1/2 in. wide coupler in the upper BT as a positive stop against the baffle coupler?
Questions....questions...

I don't think a stop for the coupler would be necessary. The only thing I might add is a little bit more length to the aft part of the coupler you have shown. From the diagram it looks like you only have the coupler about 1/2" into the aft body tube and on BT-80, I personally would want at least an inch if not an inch and a half.