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James Pierson
06-10-2007, 07:22 PM
I finally got around to fixing the Plutonic Avenger's upper body tube. I would like to attach a Kevlar shock cord this go around but, this design is a minimum diameter with no CR to attach to. How do I attach the Kevlar cord to the upper body tube? :confused:

Any ideas and help is greatly apperciated.
Thanks in advance, JP

James Pierson
NAR# 77907

Solomoriah
06-10-2007, 07:50 PM
Quest and Semroc minimum diameter kits have the thrust ring notched slightly and the Kevlar tied to it.

CPMcGraw
06-10-2007, 08:23 PM
I finally got around to fixing the Plutonic Avenger's upper body tube. I would like to attach a Kevlar shock cord this go around but, this design is a minimum diameter with no CR to attach to. How do I attach the Kevlar cord to the upper body tube? :confused:

Any ideas and help is greatly apperciated.
Thanks in advance, JP

James Pierson
NAR# 77907

Study the attached images...

(They're not in sequence, due to the forum uploading in file-size order instead of numeric order...)

A Fish Named Wallyum
06-10-2007, 09:18 PM
Study the attached images...

(They're not in sequence, due to the forum uploading in file-size order instead of numeric order...)

Try 4,5,1,2,3

James Pierson
06-10-2007, 09:47 PM
Thanks Guys, you're great. Should be an easy enough fix. Thanks, JP

James Pierson
NAR# 77907

barone
06-10-2007, 09:52 PM
Another option for minimum diameter.....and the thinner kevlar......is to feed the kevlar through the forward section of BT, tie a loop in it, and slip fit it to a motor....tape in place. Works every time for me and when it wears out, it's easy to replace.... ;)

Ltvscout
06-10-2007, 10:15 PM
Try 4,5,1,2,3
Whoa! Remind me to never let you be an LCO at a launch! :D :p

A Fish Named Wallyum
06-10-2007, 10:23 PM
Whoa! Remind me to never let you be an LCO at a launch! :D :p

Thou shalt not let me throw the Holy Hand Grenade of Antioch either. :cool:

Chas Russell
06-11-2007, 09:17 AM
Bill said:


"Thou shalt not let me throw the Holy Hand Grenade of Antioch either. "

Three, Sir!

Solomoriah
06-11-2007, 10:04 AM
Study the attached images...
Okay, now that's cool. I assume that's a piece of BT-5 stuffed through a couple of CR-5-20's (or equivalent components for larger engines). I never thought of doing it that way...

Nuke Rocketeer
06-11-2007, 11:04 AM
You could also drill a small hole in one of the fins and attach the kevlar thread to it. A drop of glue on the hole will really secure it. I have used this method many times, especially for field repairs.

CPMcGraw
06-11-2007, 11:26 AM
Okay, now that's cool. I assume that's a piece of BT-5 stuffed through a couple of CR-5-20's (or equivalent components for larger engines). I never thought of doing it that way...

BT-5 or ST-5, whichever you have on-hand. The length is only about 3/8", and the gap between the rings should only be about 1/16" to 3/32" -- just enough for one loop of Kevlar thread and the knot.

EchoVictor
06-11-2007, 01:51 PM
When my US TOG was almost complete I came upon the instructions calling for the kevlar to be externally-mounted. Not liking this method, I decided to attach a piece of kevlar to a CR-2050 with a notch on the outside for the thickness of the thread.

http://i73.photobucket.com/albums/i204/EchoVictor/Rocket%20Stuff/100_0455.jpg

If you look closely, I just have the knot rotated so that it's on the ID of the ring. To attach it, I just smeared some glue ahead of the thrust ring, set up the thread mount at the front end of the tube, and then pushed it down with a section of launch rod until it bottomed out on the thrust ring. Worked great!

Later,
EV

A Fish Named Wallyum
06-11-2007, 03:19 PM
When my US TOG was almost complete I came upon the instructions calling for the kevlar to be externally-mounted. Not liking this method, I decided to attach a piece of kevlar to a CR-2050 with a notch on the outside for the thickness of the thread.

http://i73.photobucket.com/albums/i204/EchoVictor/Rocket%20Stuff/100_0455.jpg

If you look closely, I just have the knot rotated so that it's on the ID of the ring. To attach it, I just smeared some glue ahead of the thrust ring, set up the thread mount at the front end of the tube, and then pushed it down with a section of launch rod until it bottomed out on the thrust ring. Worked great!

Later,
EV

I did it this way after my Satellite Interceptor upscale puked its internals a few years back. So far it has held up fine, and these days I use heavier Kevlar. :rolleyes:

James Pierson
06-11-2007, 08:52 PM
Are you folks also using a section of elastic shock cord after the Kevlar for shock purposes or just Kevlar alone?

Also what about the kevlar cutting into the Bt after deployment?

I had an idea to use some small surgical tubing about 3 inches long tied to the Kevlar at the point when it exits the BT. I could only use this on ST-13 or large size tubes for fear of it getting stuck. The surgical tubing might prevent the BT from getting cut. What do you folks think?

Thanks in advance, JP

James Pierson
NAR# 77907

A Fish Named Wallyum
06-11-2007, 09:44 PM
Are you folks also using a section of elastic shock cord after the Kevlar for shock purposes or just Kevlar alone?

Also what about the kevlar cutting into the Bt after deployment?

I had an idea to use some small surgical tubing about 3 inches long tied to the Kevlar at the point when it exits the BT. I could only use this on ST-13 or large size tubes for fear of it getting stuck. The surgical tubing might prevent the BT from getting cut. What do you folks think?

Thanks in advance, JP

James Pierson
NAR# 77907

I've only had one instance of Kevlar cutting a body tube, and that was on an Estes E9-4 in my Centuri Thunder Roc. (It was more like an Estes E9-1.5 :mad: ) I've got a Qmodeling Rogue that uses nothing but Kevlar and it works great. Just use plenty.

CPMcGraw
06-11-2007, 09:59 PM
Are you folks also using a section of elastic shock cord after the Kevlar for shock purposes or just Kevlar alone?

Also what about the kevlar cutting into the Bt after deployment?

I had an idea to use some small surgical tubing about 3 inches long tied to the Kevlar at the point when it exits the BT. I could only use this on ST-13 or large size tubes for fear of it getting stuck. The surgical tubing might prevent the BT from getting cut. What do you folks think?

Thanks in advance, JP

James Pierson
NAR# 77907

This is the second biggest reason for trying to get the lowest Dv number you can at deployment. With a high Dv, if the parachute doesn't shred itself the Kevlar can zipper the tube. Make sure you use a motor with the best delay to get the lowest number, preferably below 20, better still below 10, soft as a feather below 5.

A Fish Named Wallyum
06-11-2007, 10:47 PM
This is the second biggest reason for trying to get the lowest Dv number you can at deployment. With a high Dv, if the parachute doesn't shred itself the Kevlar can zipper the tube. Make sure you use a motor with the best delay to get the lowest number, preferably below 20, better still below 10, soft as a feather below 5.

What does an E9-1.5 in a Centuri Thunder Roc give me? :eek: I'm thinking that it's somewhere in the GICK! range. (Gick being the sound you make when being clotheslined. Been there. Done that. Got the scar. Real clothesline, too. :rolleyes: )

severenz
06-12-2007, 05:22 PM
I finally got around to launching my new rockets that had the kevlar shock cord. Surprisingly, on one rocket, the ejection shot so hard that it broke the nose cone off at the plastic ring where the shock cord was attached. I guess a bit of elastic can come in handy. Both rocket and nose cone were recovered. :)

Nuke Rocketeer
06-13-2007, 07:17 AM
Are you folks also using a section of elastic shock cord after the Kevlar for shock purposes or just Kevlar alone?



Yes, and no problem as long as the delay is not too long or too short and the Kevlar string is nice and long.

snaquin
06-13-2007, 07:47 PM
Are you folks also using a section of elastic shock cord after the Kevlar for shock purposes or just Kevlar alone?

James,

I use both the methods you referenced in my scratch built models with good results. As Bill and Joe mentioned earlier, Kevlar alone works fine if you use plenty to make up a nice long length. Since I attach most of my Kevlar to either the motor mount or a baffle, I figure how much Kevlar would be needed to reach just before the edge of the airframe with a small loop tied in it and secured with a drop of CA or Epoxy. I use either a snap swivel or tie off my elastic cord to the loop. The loop in the Kevlar also makes it easy to move the entire recovery system from one rocket to another in the field and only the elastic shock cord extends past the edge of the airframe when I use this set up.


Also what about the kevlar cutting into the Bt after deployment?

Thanks in advance, JP

James Pierson
NAR# 77907

With many of my high altitude models it would be impossible to get a proper DV without the use of electronics due to limited delay selections and I frequently deploy at high speeds. When I use elastic I use as much as I can comfortably fit in the body tube and still have room for the chute or streamer. With an all Kevlar cord set up in model rockets & hpr rockets, I use at least 3 - 4 times the length of the model and I have found this to work well. Last flight with my scratch built Lasor-134 with a G10-10W showed an estimated 57.32 Feet/Sec DV with RockSim and was recovered without a scratch on it. I used about 4 yards x 1/4" of polyester elastic from Wal-Mart in that model (half the package). The longest cord I can fit is what I generally use for any application.

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