protecting a tubular nylon harness

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I'm in the planning stages for my next build: a 2.2" fiberglass Adventurer I got at the Madcow Black Friday sale.

The stock kit comes with tubular nylon. Up until this point, I've always used kevlar for my harnesses but my current plan is to use the supplied material for this build.

I recently picked up a few yards of nomex cloth that I can sew up as a harness protector, but I need a little help understanding the principal behind this. If the first foot or two is protected, what about the rest of the harness? Isn't that going to get just as cooked folded up inside the body tube? Is there some kind of residual heat/burn after eject that suggests the need for extra protection for what's still inside the tube? Or is it simply that the part closest to/connected to the motor mount is literally on top of the charge and that extreme proximity is all it takes to accelerate/cause failure?

For attachment, my plan is to use a Giant Leap hardpoint anchor that I'll tap and screw in to the body tube itself just above where the longest motor I'll likely use will end. It will allow me to remove the anchor at a later date to inspect and change the harness. Any thoughts on this plan? Will three countersunk screws be strong enough? Not even sure I can countesink in thin-wall fg? Typically these are epoxied into the end of the motor mount tbe, but the suppled mount is way too short for the CTI 5 grain case I plan to use. I wanted to avoid the expense of ordering a new, longer motor mount tube plus a third centering ring.
 
I prefer Tubular Nylon over Kevlar as it has more stretch. It does need a bit more protection, so I use a Nomex harness protector and Nomex chute protectors where needed.

Here is a bit of an indication of what I do:
https://forum.ausrocketry.com/viewtopic.php?f=6&t=4612&start=78

I won't exclude other types of harnesses on a religious basis, but each rocket will be considered as an individual build and the appropriate choice made. TN is the usual result. YMMV.

You do need to treat the TN as a consumable and cut off any damaged pieces when necessary.

FYI, Kevlar will stretch only 6-8% before failure, but it is strong.
 
Thanks OTT for your quick reply - great link and awesome looking rocket! You mention in your link the same phrase I keep hearing as it relates to a sleeve over the end of the harness: "to protect from hot ejection gasses". I still pose the same question: what about the rest of it? Still trying to wrap my head around why the rest of the harness it's less vulnerable to said hot ejection gasses than the part that's wrapped.
 
Hey Rob. To clarify somewhat: The protected end is closest to the charge wells. Following that is a square of Nomex chute protector, fixed to the harness with a cable tie. Anything else that matters is above that or in a Nomex deployment bag. If you do double-ended dual deploy, like I usually do, the harness and risers then get folded up and another Nomex blanket over the top, with the harness protector continuing to the NC eyebolt (near the charge wells.

Anything in there needs a blanket or protector between it and the charges.

Just think it through, whatever you choose. Charge is hot, chute and harness should be kept cool. Put protectors where they are needed :)

Really consider using deployment bags as they seem to make the packing easier and deployment more reliable. My opinion anyway!
 
I fly a protector on my TN. It is placed at the beginning of the cord where it attaches to the rocket. The nylon after that is loaded above or in the burrito, thereby protecting it. Not a perfect process, but it seems to do the trick.
 
I double up on protection ;-0

I put heat shrink on the first 6-8 inches of the TN harness where it meets the EBay.
This provides great protection with the tradeoff of being stiffer.

The stiffness drives the length of TN you cover.
You need enough length to cover the TN that is outside the BURRITO cover of Nomex.
You really don't need the whole length of the harness left in the chute bay treated with heat shrink, but just enough to cover that tail that connects the burrito bundle to the EBay.
 
I sew up a pocket on the drogue side:
020-1.jpg


Everything below the pocket fits in the pocket, and the top part is protected with a Nomex sleeve.

3M green masking tape protects the hot spots, and is extra sticky. Sometimes I just wrap the end nearest the avbay with green tape, and skip the Nomex sleeve, it's that good.
 
Great suggestions and answers here - thanks to you all. So I guess the bottom line is: protect it all. My challenge is going to be doing so within a fairly small diameter airframe. I think a combination of nomex sleeve (and maybe a little heat shrink which I do regularly use) for the attachment point and perhaps extending to just outside the body tube (I like the idea of protecting also against tube edge abrasion) and either a nomex burrito or a Wayco pocket (an idea which I LOVE) for the rest of the harness in addition to my usual nomex burrito chute protection is going to be the way to go. I will experiment as I start putting it together.

I can see now why folks like using kevlar for everything, but in this case I'd like the slight stretch TN affords. My plan to have a removable harness attachment above the motor (assuming this is sound) should give me plenty of options.

This will probably be motor eject for my first flight but after that single deploy and a chute release with motor eject as backup. Once I feel comfortable with electronic deployment, I'll move up to full dual deploy.
 
I protect my cords with ductape. :D

Until the cords get really wide, a single strip just folds over and encases it perfectly.

Sounds like you're taking a similar approach as I while preparing for full dual deployment.

Good luck!
 
Sometimes I use 2 nomex blankets - one for the exposed tubular nylon, one for the chute.

Honestly, the tubular nylon is probably just fine even with no protection at all. It might get a little crispy near the MMT, but it will last a while. Since you are planning on a removable anchor, you can easily replace it if needed.

I bought the same kit. My concern with the tubular nylon is the bulk, especially for dual deploy with the chute in the payload tube. Not much room in there. I will likely go all kevlar for this reason.

This rocket is pretty heavy with just 54mm diameter space, so packing an adequate chute can be a challenge. What are you using for chute? I am going to try a Spherachute 42" (measured across top of canopy), but it might be a tad undersized.
 
Honestly, the tubular nylon is probably just fine even with no protection at all.

Not if it is directly in line with the charge well when it goes off. I normally coil it so that isn't the case, but once it moved to that location during a flight and the protector saved the day.
 
I bought the same kit. My concern with the tubular nylon is the bulk, especially for dual deploy with the chute in the payload tube. Not much room in there. I will likely go all kevlar for this reason.

This rocket is pretty heavy with just 54mm diameter space, so packing an adequate chute can be a challenge. What are you using for chute? I am going to try a Spherachute 42" (measured across top of canopy), but it might be a tad undersized.

I haven't started contemplating chutes yet. I've always used flat chutes - typically the thin mill ones from Top Flight - so this is a new area for me to get schooled on. I'll run sims of course, but I guess ideally the biggest drag coefficient for the size right? Have you ever used a military surplus flare parachute? I hear they are often good options. Would it make any sense to have the drogue in the payload bay and the main in the main airframe to give us more room to pack a bigger chute?
 
Picked up one of these too, was thinking of ditching the nose cone bulkhead and putting an attachment point in the tip which would give a bit more packing room for the main. Especially as I was thinking of getting rid of the band and having the coupler epoxied into payload bay so would lose another ~20mm from that.
 
I haven't started contemplating chutes yet. I've always used flat chutes - typically the thin mill ones from Top Flight - so this is a new area for me to get schooled on. I'll run sims of course, but I guess ideally the biggest drag coefficient for the size right? Have you ever used a military surplus flare parachute? I hear they are often good options. Would it make any sense to have the drogue in the payload bay and the main in the main airframe to give us more room to pack a bigger chute?

I think thin-mil from TopFlight will be fine, also. Never used the flare chute. I guess I'd like to keep the option open for motor backup, so I will keep the drogue in the booster airframe.
 
Picked up one of these too, was thinking of ditching the nose cone bulkhead and putting an attachment point in the tip which would give a bit more packing room for the main. Especially as I was thinking of getting rid of the band and having the coupler epoxied into payload bay so would lose another ~20mm from that.

Yep. I recessed the nose cone bulkhead deep in the coupler. Also replaced eyebolt for kevlar loop.
 
I've got 45 flights on my 9/16" TN cord. The drogue side has a protector and I use blue masking tape over the knot on the quick link. I think I've changed or added to the tape twice. Because it's on the drogue side, the thrust pushes everything down the tube away from the charge on the av-bay. I keep the unprotected TN opposite of the burrito and only let the protected part exposed to the charge. I also use dog barf. The protected TN on the main side is pulled tight and dog barf dropped in. That protects the rest of the TN and only the part connected to the av-bay is really exposed. Dog barf is cheap, easy, and adds that extra protection since most of my chute protectors have small burn holes in them now and need a little help.

The only damage to the TN in 9 years and 45 flights is where the drogue side is sewn back together after the linemen cut it to get the rocket off the power lines. YMMV
 
As several others have posted, I protect the nylon at the drogue charge and the rest in or above the ‘burrito wrap’. One variation I use is ‘cheap’ one inch tubular nylon over my good quality 9/16 tubular nylon instead of a nomex protector. I have been very frustrated recently with crappy sewing on the seams of my purchased nomex protectors. Have had a few recently coming apart after only a couple uses. A local surplus store has lower quality 1” tubular nylon in various colors. I pick a bright color so it is easy to see the black powder wear from the deployment charges. When it gets a little crispy I swap it out for a new 2-3 foot piece. So far I have not had any wear on the nylon harness below, even at the areas where the upper layer is most scorched. Biggest downside is more bulk if you have a tight packing situation.
 
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