Wadding with electronic deployment

[billdz]

Just did my first ground test with electronic deployment. Worked fine, but afterwards noticed some discoloration on the shock cord. Is that because there needs to be some wadding or nomex between the charge and the recovery system? I've never seen this mentioned but it seems to make sense.

 

[tim cubbedge]

Some people do use wadding, some don't. You are still going to damage your shock cord over time. One solution is to use kevlar cord instead of nylon. Kevlard doesn't stretch as much so I usually make my kevlar cords slightly longer (10-20%) than if I were using nylon. Not sure what size you are using but there are a few manufactures who make kevlar sleeves that goes over nylon, usually about 3 ft. in length. They still are not 100% impermeable to BP chages and also need to be replaced over time.

https://topflightrecoveryllc.homestead.com/page3.html

 

[Banzai88]

I use nylon cord a lot, but I always cover it with a nomex sleeve. Recently I've also been using plenty of dog barf. Since then, no scorching of the nylon and much less mess inside the tubes.

 

[rharshberger]

I use nylon cord a lot, but I always cover it with a nomex sleeve. Recently I've also been using plenty of dog barf. Since then, no scorching of the nylon and much less mess inside the tubes.

+1, I use dog barf along with my chute protectors. The dog barf does a good job of protecting the shock cords too. As others have stated eventually the shock cords will be damaged and have to be replaced whether nylon or kevlar.

 

[thomas]

Unprotected Nylon can already break at the first contact with a BP flame. I have seen an booster on a L2 flight dropping without a chute because of that.

I either use a strap of kevlar connected to the nylon shock cord or nomex sleeves.
You can also get a Nylon harness complete with a kevlar sleeve:
#https://onebadhawk.com/nylon-w-kevlar-sleeve.html

I would avoid using only kevlar since it has almost no stretch and the shock loads get unnecessary large.

And I do not use BP for ejection charges with electronic deployment, since it will create a lot of hot particles which you do not need.
NC wool/ flakes are better suited (not smokeless gunpowder), since they create more gas per heat and almost no solid residue.

 

[watheyak]

Disclaimer: the following is my opinion!

I would avoid using only kevlar since it has almost no stretch and the shock loads get unnecessary large.

This is a myth. If you're worried about the shock loads due to the difference in stretch between tubular nylon and Kevlar, you have other problems. And one thing that gets overlooked is that braided Kevlar, which most harnesses are made of, stretch even more than tubular nylon.

A recovery harness made entirely of Kevlar will last much longer and have less failure points than one made from a combination of TN and Kevlar. The other issue is that many times one doesn't realize it's time to replace the nylon harness until a booster is coming in ballistic. Most of the damage is hidden deep inside the airframe and/or by a nomex sleeve.

 

[Tim51]

And I do not use BP for ejection charges with electronic deployment, since it will create a lot of hot particles which you do not need.
NC wool/ flakes are better suited (not smokeless gunpowder), since they create more gas per heat and almost no solid residue.

Thomas - I've not heard of 'NC wool' - can you please clarify what it is, and where it is available? (I currently use FFFF BP)

 

[blackjack2564]

Wrap masking tape around the first 15-20 inches , keep rest of shock cord behind chute nomex.
Only that small "tail" is exposed to blast.

See Here read 4 or 5 posts:https://www.rocketryforum.com/showt...x-quot-build-starts-now!!&p=455638#post455638

 

[rharshberger]

Thomas - I've not heard of 'NC wool' - can you please clarify what it is, and where it is available? (I currently use FFFF BP)

NC wool is also known as flash cotton. Its more expensive than BP and it is shipped wet iirc as its extremely easy to ignite,its commonly used to perform magic tricks. It does however burn very cleanly.

 

[Tim51]

NC wool is also known as flash cotton. Its more expensive than BP and it is shipped wet iirc as its extremely easy to ignite,its commonly used to perform magic tricks. It does however burn very cleanly.

Aha - yes, I know the stuff. I know some flyers have experimented with it here in England. Thanks Rich.

 

[rharshberger]

Aha - yes, I know the stuff. I know some flyers have experimented with it here in England. Thanks Rich.

Evidently its easier got get in England and Europe than BP without permits or something.

 

[cbrarick]

Save the nylon for your undies, use kevlar. Never a problem. I tend to run my cords long enough to reach the ground from the largest tree, so shock loads are negligible. On the real big projects, I use some rubber bands after I fan fold the kevlar.

 

[amarillo_rocket]

I use both kevlar and nylon to save a little cost and have not had any issues. I use a length of kevlar that is long enough to allow me to attach my chute. The remainder of the shockcord is kevlar. I use bowline knots to secure the kevlar to the nylon. I pack the kevlar first near the deployment charge, then the chute and nylon sits on top the chute. The larger the rocket the more cost effective.

 

[o1d_dude]

Kevlar y-harnesses and nomex sleeve over nylon from OneBadHawk are working for me. Topped off with dog barf and a circular nomex blanket from Giant Leap to protect the chute in a Fruity Chutes liner.

 

[Tim51]

Evidently its easier got get in England and Europe than BP without permits or something.

There may be a bit of mythologizing going on there - I certainly didn't know what the wool stuff was or how to find it, whereas applying for either a 'Use only' or a 'Acquire & Keep' explosives license via the police and the Health & Safety Executive sounds daunting but is actually very straight forward here. If you want to store BP then you apply for the A&K and they check you have the facilities to do so. In my experience it was easier to find a rocketry vendor selling BP and a local police station than a magician's supplies shop.:wink: But Thomas's points about temperature interested me in terms of avoiding singed chutes. Anyway, apologies enough hijacking about UK explosives laws - on with the thread!

 

[rharshberger]

@Tim51, hopefully you understood that I was implying that I really don't know whats involved in purchasing either product outside the USA only that several foreign members have stated its more difficult for them to acquire BP.

 

[Tim51]

@Tim51, hopefully you understood that I was implying that I really don't know whats involved in purchasing either product outside the USA only that several foreign members have stated its more difficult for them to acquire BP.

Yes of course - I wasn't suggesting you were mythologising Rich - my apologies if my reply came across that way. I was merely trying to say some people (including some on this side of the pond) seem to have the idea that using BP it's too complicated legally or availability wise to bother with. If you have the license, you can get it from a vendor.

 

[OverTheTop]

I use tubular nylon exclusively (due to increased elasticity compared to Kevlar), treating the end bits in particular as consumables. It is sleeved with a Nomex protector that covers the harness, quicklink (if used), and eyebolt. The protector also helps prevent any windmilling damaging the harness.

Details on my 1/2 scale Nike Smoke here, along with how the harnessing was set up and the rationale for it:
https://forum.ausrocketry.com/viewtopic.php?f=6&t=4612&start=78

 

[Handeman]

Just did my first ground test with electronic deployment. Worked fine, but afterwards noticed some discoloration on the shock cord. Is that because there needs to be some wadding or nomex between the charge and the recovery system? I've never seen this mentioned but it seems to make sense.

I have a rocket with 40+ flights that has a nylon cord. It has a 36" nomex cord protector and I wrapped the first 6" of cord and protector in masking tape. When the tape gets burned, brittle, etc, I just wrap some more tape on it. That keeps the nylon cord protected.

I also use dog barf. I have chute protectors, but after finding burn holes in my chutes that match the burn hole in the chute protector, I went back to adding dog barf. It's worked great. Dog barf is CHEAP! You can buy a whole bale for the cost of one 12" x 12" nomex chute protector and it will last longer.

 

[soopirV]

I have a rocket with 40+ flights that has a nylon cord. It has a 36" nomex cord protector and I wrapped the first 6" of cord and protector in masking tape. When the tape gets burned, brittle, etc, I just wrap some more tape on it. That keeps the nylon cord protected.

I also use dog barf. I have chute protectors, but after finding burn holes in my chutes that match the burn hole in the chute protector, I went back to adding dog barf. It's worked great. Dog barf is CHEAP! You can buy a whole bale for the cost of one 12" x 12" nomex chute protector and it will last longer.

do you double up then, or do you use solely dog barf now?

 

[billdz]

Thanks for all the interesting replies to my post. For extra safety, I'm going to be using both motor deployment and electronic deployment, so my rocket will be safe even if one or the other malfunctions. So I'll need to put wadding, barf, or nomex on both sides of the chute and shock cord. In all the articles I read about electronic deployment, don't think I ever saw a mention of the need to protect the recovery materials, perhaps self-evident but I had not thought of it.

 

[Steve Shannon]

I use tubular nylon exclusively (due to increased elasticity compared to Kevlar), treating the end bits in particular as consumables. It is sleeved with a Nomex protector that covers the harness, quicklink (if used), and eyebolt. The protector also helps prevent any windmilling damaging the harness.

Details on my 1/2 scale Nike Smoke here, along with how the harnessing was set up and the rationale for it:
https://forum.ausrocketry.com/viewtopic.php?f=6&t=4612&start=78
View attachment 320564

I also use primarily tubular nylon. Nylon stretches up to 30% of its length. Kevlar, no more than about 5%. Yes, a person can use longer Kevlar, but you still don't get the distribution of load over time that stretching nylon provides. The only strap I've ever broken was a Kevlar one. It broke very unexpectedly. If I do use Kevlar I'll use wide strap, not thin braid. There's a place for each.


Steve Shannon