Blaine's Kevlar Anti-Zipper using Foam Ear Plug

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BlaineS

Blaine Seaboalt
Joined
Aug 3, 2017
Messages
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Location
Ennis, TX
Hello all,

In the "totally over engineered LPR department"...

I just wanted to share my Kevlar Anti-Zipper using a Foam Ear Plug.

Producing motorsports television, I have an over abundance of foam ear plugs so, to put them to good use... please see description below pictures...

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1. I poke a hole through a new & clean (LOL) ear plug with an awl

2. Insert a plastic "bar straw and stir stick" using the inserted awl

3. Cut away excess straw

4. Thread kevlar shock cord through straw with the "big end" of the ear plug orientated to the top of the body tube

5. Use plastic cement to glue ear plug in place on shock cord at the top of body tube

Have a great day and thank you all for sharing your great ideas!
Blaine
 
Thank you K'Tesh... that means a lot!

Also, some types of glue and kevlar don't stick well together, in that case, another option is to...

1. Tie a knot in the kevlar below the ear plug

2. Remove the straw (or leave it in)

3. Tie a knot in the kevlar about the ear plug

...and your plug is secure at the top of the body tube!
 
Why not just use the straw as a mandrel to get the Kevlar through the plug, then slide the plug off the straw onto some dries-flexible glue like E6000 once it's in its final position? Would work well for thicker Kevlar. For 100-lb, you can probably just use a heavy sewing needle to pull it through the plug.
 
I just purchased a few rubber grommets as "bumpers'. This is a WAY much better idea.
To quote the video "Closet Cases of the Nerd Kind": You'll laugh. You'll Cry. You'll kiss 3 buck goodbye.

Thanks for the tip.
Chas
 
That's a great idea!

Can I suggest one 'improvement'?

Instead of a coffee stirrer try the plastic tube from a Q tip. It has a lot smaller ID and will be more likely to stay put!
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Well , if you use a plastic Q-Tip, initially cut with a steep bevel, you can skip the awl and just poke the hole with the Q-tip.

Mind your fingers, it is pretty sharp.
 
Looks like this will help as long as the delay isn't too long. I stopped building 4 inch diameter cardboard rockets due to this issue. Yeah, I'd fiberglass some of the 4 inch tubes but a late delay can lead to a zipper no matter what using motor delay that's mismatched. Much easier to use heavier fiberglass tubing. Heck, in the Midwest can't fly that high anyways! For small projects as shown, I think this technique will work quite well though and will consider adding it to some of my small projects. The deal is, is how much mass is in the nosecone or if there is one, a payload bay on the end of the harness? More mass, more damage on a late deployment. That's just physics for you.
I have a tendency to sim like crazy with Rocksim and Open Rocket to chose a delay grain (or drill it) if I need a shorter delay. I've had to order extra "long delay" grains from Aerotech or my local dealer and drill them to what I needed for a delay time based on the simulations with the larger impulse motors. Always gave me a good apogee deployment at minimal velocity (ideal) on apogee only rockets.
It's a moot point with electronics 'cause when the rocket tips over at apogee, "pop goes the main parachute or drogue". I "sorta" switched to electronics to relieve the stress of getting motor deploy "just right" on high powered rockets. Modrocs not so critical. I still like a challenge and have a few rockets I need to do preflight calculations on with sims using motor only deployment. Shoot, can have the motor deploy at apogee and no zippers.
I had some rockets that flew with the Robert Galejs magnetic anomaly detector for apogee deployment: https://aeroconsystems.com/cart/flight-avionics/magnetic-apogee-detector/ which is out of production now and added a Jolly Logic chute release later on when it became available. I now had dual deploy in my MAD originally apogee only rockets! I later bought a Zeptomag device: https://www.tindie.com/products/ZeptoBit/zeptomag/ but it seems both are out of production now. It has more safety to it as if armed for launch, if one has to replace the igniter for a misfire, one can turn it over without turning it off and not have it go off. A G-Switch fully arms the device just after launch in flight. I always turned it off when I rarely had to take a rocket off the pad. The Galejs device, one had to turn it off and gingerly remove the nosecone upright and unplug one leg of the ematch wire from the terminal to avoid a ground fire of the deployment charge.
I'm surprised there isn't a small MAD unit for smaller rockets now. When the Rocket Logic Chute Deploy came out, I got dual deploy on my smaller MAD apogee only rockets. Because of this, I'd launch with bigger motors with the longest smoke delay I could get. Many times the rocket would be way out of sight but I could see a descending smoke trail for awhile after the unseen apogee and knew the chute bag deployed. The chute release would unfurl the main at the selected lower altitude and at least I had a direction to start at as I saw the smoke trail of the descending rocket up high.
When the smaller dual deploy altimeters came out, this combo MAD and JLR chute release sort of became a moot point (unless one wanted to save on ematches!) but it's in a few of my flyable rockets and I'll continue to use it as I have the experience to make it work every time. A single deploy, apogee only altimeter and a JL chute release is viable too as long as the body tube diameter is enough to contain the JLCR. Kurt
 
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Alternative to glue

Easier way to place.

Place needle through.

Place second q-tip tube.

Pass the Kevlar through both and tie a knot.
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