Protecting the shock cord when using Nomex parachute protector

[overklock]

Hey RF, quick question.

I'm rebuilding my Mega Der Red Max, and purchased a Nomex chute protector for the first time. I'm still using an elastic shock cord. Ideally, I don't want to have to use dog barf or recovery wadding.

How would one go about protecting the shock cord in this scenario? Is the nomex chute protector also enough to protect the shock cord?

 

[waltr]

If the chute is wrapped in the Nomex Burrito style then no cord protection.

You could add a Nomex cord sleeve or Kevlar from anchor to just out of BT with another piece of Nomex as wadding.
I use the second method if BT has enough space.

 

[ThirstyBarbarian]

You can use a nomex cord protector sleeve, like the ones at the bottom of this page: http://topflightrecoveryllc.homestead.com/page3.html

Lots of sources for those kinds of things, so check around.

Realistically though, that elastic cord is not going to last, even with protection. Ideally, you’d find a way to replace it with a nylon or kevlar one. You can protect a nylon cord with the nomex sleeve I mentioned before, and it will last a long time.

And BTW, a lot of people still use a bit of dog barf even with protective blankets and sleeves. Nothing wrong with using both.

 

[sriegel]

And BTW, a lot of people still use a bit of dog barf even with protective blankets and sleeves. Nothing wrong with using both.

Second this! A hot ejection charge can burn through the wrap. Using some dog barf to soften that hit greatly extends the life of the blanket.

Think of it as using both seat belt and airbag in a car.

 

[overklock]

You can use a nomex cord protector sleeve, like the ones at the bottom of this page: http://topflightrecoveryllc.homestead.com/page3.html

Lots of sources for those kinds of things, so check around.

Realistically though, that elastic cord is not going to last, even with protection. Ideally, you’d find a way to replace it with a nylon or kevlar one. You can protect a nylon cord with the nomex sleeve I mentioned before, and it will last a long time.

And BTW, a lot of people still use a bit of dog barf even with protective blankets and sleeves. Nothing wrong with using both.

Any worry about a half inch nylon bridle zippering a cardboard tube?

 

[ThirstyBarbarian]

Second this! A hot ejection charge can burn through the wrap. Using some dog barf to soften that hit greatly extends the life of the blanket.

Think of it as using both seat belt and airbag in a car.

Yep. The blanket helps, but they are susceptible to blast just blowing holes right through them. The really hefty kevlar ones aren’t as susceptible, but a handful of dog barf does the trick too.

When my old blankets get a bit tattered, I give them a second life as a kind of primary blast protector. I cut them down to about the airframe diameter and poke a hole in them so the hole will fit down over the eyebolt I use as the chord anchor. Then I attach my cord in its sleeve to the eyebolt. When it’s time to fly, I position that blast protector piece of nomex over the bulk plate in the chute compartment so it covers the motor tube hole where the ejection charge blast will come from. Then I toss in a handful of dog barf on top of that. Next I z-fold the cord and set that in on top of the dog barf, followed by the chute burrito in its blanket. On top of that is the cord leader to the nosecone.

The first blanket and the dog barf on top provide a nice protection for everything above it.

 

[ThirstyBarbarian]

Any worry about a half inch nylon bridle zippering a cardboard tube?

Nope. I’ve never had it happen. I’d be concerned about a small diameter kevlar cord, but not 1/2” nylon. Of course it the delay is way off, anything can happen, but within reason, the nylon should be fine.

 

[overklock]

Nope. I’ve never had it happen. I’d be concerned about a small diameter kevlar cord, but not 1/2” nylon. Of course it the delay is way off, anything can happen, but within reason, the nylon should be fine.

Thanks! I think I may replace my elastic with Nylon. Luckily I paid attention this time and used a quick link. The Mega Der Red Max instructions have you permanently mounting the shock cord through the forward centering ring which i've come to realize is a huge no-go.

 

[waltr]

Only tube zipper I've had with 1/2 nylon happened when pulling the rocket out of a tree. We did snap the nylon cord at one point in the retrieval and left 1/4 of the chute in the tree. There were three of us hanging on the 40 foot lineman's pole.
We also had a Zephre in a tree (an L1 cert flight) with 1/2" nylon and zipped tube all to way to the motor mount pulling it down.

Other wise I braid the nylon cord so that when pulling apart the braid a lot of energy is absorbed.
Same rocket had a delay go way too long. Came in ballistic from 600 feet and ejected about 100 feet from the ground. Perfect deployment with no damage of any kind.

I do not believe in many of the 'zipper prevention' methods that have been posted.
I believe in controlling and dissipating the energy of deployment to prevent SHOCK to the recovery system.

 

[ThirstyBarbarian]

Thanks! I think I may replace my elastic with Nylon. Luckily I paid attention this time and used a quick link. The Mega Der Red Max instructions have you permanently mounting the shock cord through the forward centering ring which i've come to realize is a huge no-go.

Perfect. If you have an eyebolt and quick link setup, then I’d definitely upgrade to nylon. Here’s the super-deluxe nylon harness I have on my modified Mega Der Red Max. I kind of splurged because it was my L1 cert rocket, so it’s a bit of overkill. But it comes with the cord, sewn loops, a kevlar sleeve, and a nice quick link, all included and assembled together very nicely. If you get all the parts separately, it might add up to something similar. I’ve had mine for around 8 years. Plus Teddy AKA @Onebadhawk is one of the nicest people in rocketry, and makes great products.

9/16" Tubular Nylon w/ Kevlar Sleeve- 2 Loop

High Power Rocketry Recovery Harness / Shock Cord with 2 sewn Loops. These are made from 9/16" Military Spec. Tubular Nylon. This material is listed as having a 1500 lb minimum breaking strength....

onebadhawk.com

 

[ThirstyBarbarian]

Only tube zipper I've had with 1/2 nylon happened when pulling the rocket out of a tree. We did snap the nylon cord at one point in the retrieval and left 1/4 of the chute in the tree. There were three of us hanging on the 40 foot lineman's pole.
We also had a Zephre in a tree (an L1 cert flight) with 1/2" nylon and zipped tube all to way to the motor mount pulling it down.

Other wise I braid the nylon cord so that when pulling apart the braid a lot of energy is absorbed.
Same rocket had a delay go way too long. Came in ballistic from 600 feet and ejected about 100 feet from the ground. Perfect deployment with no damage of any kind.

I do not believe in many of the 'zipper prevention' methods that have been posted.
I believe in controlling and dissipating the energy of deployment to prevent SHOCK to the recovery system.

My shock absorption strategy is to z-fold the nylon cord, and wrap a loop of masking tape around each folded handful. Typically you get 3-4 bunches, each with a single wrap of tape — not too much tape! The shock breaks each piece of tape, dissipating energy.

 

[overklock]

Only tube zipper I've had with 1/2 nylon happened when pulling the rocket out of a tree. We did snap the nylon cord at one point in the retrieval and left 1/4 of the chute in the tree. There were three of us hanging on the 40 foot lineman's pole.
We also had a Zephre in a tree (an L1 cert flight) with 1/2" nylon and zipped tube all to way to the motor mount pulling it down.

Other wise I braid the nylon cord so that when pulling apart the braid a lot of energy is absorbed.
Same rocket had a delay go way too long. Came in ballistic from 600 feet and ejected about 100 feet from the ground. Perfect deployment with no damage of any kind.

I do not believe in many of the 'zipper prevention' methods that have been posted.
I believe in controlling and dissipating the energy of deployment to prevent SHOCK to the recovery system.

Yeah I generally braid/crochet even my smallest rockets. Elastic shock cord or not

 

[overklock]

My shock absorption strategy is to z-fold the nylon cord, and wrap a loop of masking tape around each folded handful. Typically you get 3-4 bunches, each with a single wrap of tape — not too much tape! The shock breaks each piece of tape, dissipating energy.

Sounds quite a bit like rig packing when skydiving. I like it

 

[teepot]

I make my own shock cord protectors and blankets. I sew some of the Kevlar cloth into a sleeve and slid it down the cord. I made several and move them from rocket to rocket. I get the Kevlar aramid cloth from Amazon. I use only Kevlar shock cords. Get the delay right and no zippers. Here is how I load a tube in order from the bottom. Dog Barf, Z folded shock cord, chute burrito with Z folded chute, the rest of the shock cord.. That is whether it's LPR, MPR or HPR.

 

[waltr]

My shock absorption strategy is to z-fold the nylon cord, and wrap a loop of masking tape around each folded handful. Typically you get 3-4 bunches, each with a single wrap of tape — not too much tape! The shock breaks each piece of tape, dissipating energy.

Yes, that method also works well and is good in smaller BTs as the cord packs in less space than the braided cord.

 

[jahall4]

Unless weight is an upmost concern, the best/simple solution is always going to be, use the longest Kevlar harness you can. Kevlar for all practical purposes will not fail in a given launch due to the ejection charge (but should always be inspected). The length mitigates zippers. The saying… “If you have any room left in the airframe the harness is not long enough.”

This rocket has nearly 100 feet of harness:

 

[overklock]

Unless weight is an upmost concern, the best/simple solution is always going to be, use the longest Kevlar harness you can. Kevlar for all practical purposes will not fail in a given launch due to the ejection charge (but should always be inspected). The length mitigates zippers. The saying… “If you have any room left in the airframe the harness is not long enough.”

This rocket has nearly 100 feet of harness:

100 feet? That’s a bit extreme, no? Keep in mind the projected altitude of my current mega der red max is like, 600 feet

 

[jahall4]

100 feet? That’s a bit extreme, no? Keep in mind the projected altitude of my current mega der red max is like, 600 feet

Nope. Not for the rocket you see being tested. Deployment energy that needs to bleed off could be extreme. The point is use Kevlar, as much as you can. Harness length is the "great redeemer".

At the very least what is the tallest tree in your launch area?

 

[overklock]

Nope. Not for the rocket you see being tested. Deployment energy that needs to bleed off could be extreme. The point is use Kevlar, as much as you can. Harness length is the "great redeemer".

At the very least what is the tallest tree in your launch area?

About zero feet, as there are none over at Lucerne dry lake.

 

[jahall4]

About zero feet, as there are none over at Lucerne dry lake.

Then you are blessed. Might I suggest you fly higher than 600' In my region its difficult enough to find launch sites, much less w/o trees close by. The closest I've come is Argonia and even that site had a few small trees.

 

[overklock]

Then you are blessed. Might I suggest you fly higher than 600' In my region its difficult enough to find launch sites, much less w/o trees close by. The closest I've come is Argonia and even that site had a few small trees.

It's a double edged sword, actually getting there is quite the adventure to say the least and can be quite expensive.

Working on my Level 1 now