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Basic Training - Zipper Prevention
#1
This is really a dual deploy related question as well, in a way.  I have a Fireball (http://www.giantleaprocketry.com/Product...p#fireball) that I originally planned to use in my LOC Fantom using motor ejection.  I have since moved on to a dual deploy design, but have only one fireball.  I still plan to use it at apogee to protect the boost section of the rocket from the dreaded zipper as it would be the hardest to repair.  If the 'payload' section containing the main chute zippered I could replace that much more easily.  I'm curious, though, where the most stress is in a dual deploy situation.  Is there more of a jolt at main deployment or at apogee?  I would think main deployment, but have no experience to base that on.  Should I be more concerned with the 'payload' zipper?  I would think the lighter weight of the AV bay would ease some of the stress, but that would be a guess.  What do you think?

Dale
Dale Stoyer - L3
NAR #91256
TRA #13499
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#2
Dale.

Here is my 2 cents.

I do believe that we have all had zippers at one time or another.  A zipper is usually caused by deployment that takes place too early or too late, or your shock cord is to short.  If you pack your chute properly, have a long enough shock cord (longer the better), your BP charges not over sized, then having a zipper is reduced dramatically.  Unfortunately there is no 100% way to prevent a zipper but if you follow the basic guidelines, you should be successful. Another trick is to soak the inside of your airframe in a denatured alcohol and epoxy mixture.  Coat the inside a few times and will strengthen the airframe.  You can also use CA glue for this purpose.  Then sand your couplers to ensure they fit properly.

Jim
Jim Goggins NAR  L3
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#3
Jim is right, eventually you will get a zipper because the randomness of deployment is so large. The vast majority of my zippers seem to occur during apogee deployment. A non-vertical flight will be the most hazardous as the velocity at apogee can still be significant with a parabolic flight.  A Geneseo this will be an increased hazard because straight up flights will only happen now by accident.  However with good practice the zippers can be modest (less than 1"). 

Dave R has a trick where he puts one of those rubber cat toy things on the shock cord right at the opening.

Another construction technique is to put a wrap of fiberglass or kevlar (harder to work with) at the tube opening for extra toughness.

John Derimiggio
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#4
I should know better than to comment on this, But here it is. If I'm correct, Dale, you are looking to get your L1, right? The August launch is coming quick. If that LOC Fantom is done, put a Aerotech H123 in it with the SHORT delay, and just do it. Skip the dual deploy for now. Skip the bells and whistles for now. Do like the Nike commercial, just do it! I got my L1 last year with my LOC IV, motor ejection, and an AT H73 with the short delay. The LOC IV is real close to the Fantom in size and weight. I bet it'll be a great flight, and you'll have an L1 and a smile.
David Haas
NAR #13780
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#5

That's good advice, David.  I'm actually contemplating doing just that.  Problem is I LIKE the bells and whistles.  Heck, I was just at the American Whistle Corporation (http://www.americanwhistle.com/) in Columbus last week.  Wink  I'm just planning ahead.   
You said once:
(06-17-2010, 05:34 PM)David Haas link Wrote: If I knew last year what I know today, I could have done L1 and L2 with the same rocket.
Just planning for that - and practicing for L3 all at the same time.  It's my own warped version of multi-tasking. ;D

Dale
Dale Stoyer - L3
NAR #91256
TRA #13499
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#6
Dave and Dale,

The key phrase here is the KISS program, (Keep It Simple Stupid), The more bells and whistles you use in the rocket for your cert flight, the more things that have to work correctly to get your cert level. Worry about the bells and whistles after you get the cert level you want. Even a L2 cert doesn't require electronics, but a L3 does. Practice with those after the L2 so you feel experienced enough to do your L3 if that is the route you plan to go for.
I just wanna fly ROCKETS!!

Dutch
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#7
(08-12-2010, 11:56 AM)Mike Dutch link Wrote: The key phrase here is the KISS program, (Keep It Simple Stupid), The more bells and whistles you use in the rocket for your cert flight, the more things that have to work correctly to get your cert level. Worry about the bells and whistles after you get the cert level you want. Even a L2 cert doesn't require electronics, but a L3 does. Practice with those after the L2 so you feel experienced enough to do your L3 if that is the route you plan to go for.

On the other hand (playing the Devil's advocate).....

There is nothing special about a cert flight, its just another flight.

There is no practical difference with failed flights AFTER certification than during certification, other than having MORE personal certification flights which is always more exciting and entertaining!

John Derimiggio
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#8
Right you are, John.  I may only get one HP launch in this year, so I am going to get my money's worth and fly a dual deploy system with an onboard camera.  Just happens to be my L1 cert flight. ;D

Dale 
Dale Stoyer - L3
NAR #91256
TRA #13499
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#9
Cat toy info available upon request:

The cat toys I use are available at Wegman's and I use them on my mod rocs and up. You can put a direct flame on them (lighter) and they do not burn (they get a bit black if you keep doing that though). It is made of some kind of multi-color foam / rubber stuff. If you go to the cat toy area at Wegman's they are in a pack of four for about $3.00. You can use whole ones for the larger models or chunks of them (they cut nicely with an Xacto) for your mod rocs (I generally quarter them).

All you do then (for mod rocs) is thread your Kevlar line through the the ball (use a large needle such as those used for leather) and secure in place with a bit of glue or a knot. Just position it so when the shock cord / kevlar / nylon is at full extension, the ball / chunk of ball is positioned half way on the lip of your tube. It works the same as the fireball (where I got the idea) and can be made small enough for any mod roc or larger model.

Note the ball is about 1 1/2" diameter, so if you have a really large rocket, you might have to find something similar as its effectiveness of distributing the load drops as a percentage of size of the rocket tube ( ie: real large tube will need a bigger ball)

David
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#10
Very cool.  I'll check it out as it may come in handy.  The Fantom kit I am basing my rocket on is a 4" airframe so it might not be ideal.  Of course - it may be better than nothing

Dale
Dale Stoyer - L3
NAR #91256
TRA #13499
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