Trajector shock cord upgrade?

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neil_w

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I am building a Trajector which is to be wrapped in Accur8 skins. It occurred to me that I'm not sure what the best shock cord upgrade would be for these E2X PSII models. When building LPR I do the standard Kevlar loop around the motor mount, tied to elastic just below the top of the BT. Then I looked at the plastic centering rings and realized that I haven't actually seen if folks do the same thing with these, or if there is a different technique called for.

Also, the Kevlar I have on-hand is about 130 lb, I'm guessing you'd normally use a bit heavier on these? I was thinking of just doubling it rather than buying new just for this one rocket.

For what its worth, I expect to fly this mainly on Estes BP E and F motors.

Any input here appreciated.
 

dhbarr

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I just used a pin vise to drill two holes in the forward CR of a Mammoth, then connected them with a #11 blade resulting in an ovalish passthrough.

Standard Madcow braided Kevlar, then a knot. Was fine on a baby H.
 

Sabrina

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If you are flying on the Estes E and F motors, there really is no reason why you must upgrade the stock shock cord. Another bonus is easy replacement if/when you need to. Just go to the local fabric store for more elastic.

Kevlar is usually a good upgrade, but the zippers you'll get from Kevlar - that's not so much fun.

Don't get me wrong... Kevlar is popular, but not always necessary.

Right now I'm building an upgraded Leviathan "XL" with an extended airframe, a baffle, a payload bay to hold a tracker, and 25 feet of Wildman brand 1/4" braided Kevlar.

This is intended to fly on H and I motors for my next attempt at Jr L-1. :)

2017-09-05 20.45.31.jpg
 

neil_w

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If you are flying on the Estes E and F motors, there really is no reason why you must upgrade the stock shock cord. Another bonus is easy replacement if/when you need to. Just go to the local fabric store for more elastic.

Kevlar is usually a good upgrade, but the zippers you'll get from Kevlar - that's not so much fun.
I would not expect to experience a zipper with the Kevlar terminated below the end of the BT. Fabric store elastic still handles the load from the end of the Kevlar to the nose cone.

Keeping the stock shock cord (or the mount at least) is certainly an option, although it would make this the first rocket in a looooooooong time where I used the stock shock cord mount. Maybe I'll do it just for kicks.

Don't get me wrong... Kevlar is popular, but not always necessary.
Quite true, although it brings me comfort and joy. :)

Thanks for the input!
 

RickGr4

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I have all five of the Pro Series E2X rockets and have flown all of them with either E16's or F15's. I don't see the supplied shock cord as being a weak point in any way. It seems really strong to me.
 

Rex R

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depends on what your projected weight of the rocket will be. rule of thumb for me is to take the weight of the rocket and multiply by 50. running it backward if the rocket weighs less than 2.6 pounds then 140 lb. test will work nicely(except for zippers).
Rex
 

dhbarr

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I don't do Kevlar for weight or strength, just to add some length and resist ejection gases.
 

Nytrunner

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I put ductape on the elastic and just make stronger attachment points.

This has worked fine for the heavier PSII builders with aftermarket items adding to the weight and electronic deployments.


Wait a sec, is Neil building a Mid-power E2X? Did I wake up in the wrong timeline?
 

neil_w

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Wait a sec, is Neil building a Mid-power E2X? Did I wake up in the wrong timeline?
Guess you haven't been reading my sig. ;)

It's my "practice rocket" for applying Accur8 skins, with a bonus I get my first proper MPR out of it. Then I move onto the Ragnarok Orbital Interceptor, which is quite a bit more challenging.
 

Scott_650

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I have built a couple of the E2X Pro Series II kits using the included shock cord mount and it has worked well. I also have a Mammoth in-work with a reworked Kevlar and elastic shock cord attached to the motor mount - no specific reason, just wanted to try something different. So I guess it all depends on what you prefer since I think both methods work.
 

mccordmw

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I've flown my Trajector with the stock elastic shock cord almost 30 times. While it was starting to look a bit dried out, the shock cord still performed just fine. I usually stay away from that dental floss Kevlar; too zippery.

I recently lost my Trajector to a rocket-hungry tree. I'm building my replacement Trajector now, and I plan to again use the stock shock cord.
 

dhbarr

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I just don't like the glued in plastic teabag. It's merely a personal preference. My kevlar doesn't hang out the nose, so no increased zipper potential.
 

AndrewW

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I have a trio of PSII rockets that include an Argent, a Partizon and a Ventris. They have all been built essentially stock including the elastic shock cord and paper "tea bag" mount. I have nearly 20 flights logged between the three with more than half of them on H motors up to 2800'. I usually use a JLCR and have never had a single issue with the provided shock cord. It didn't even fail when the Ventris was caught in a tree which required a somewhat abusive recovery effort.
 

Nytrunner

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Lol.....Somewhat Abusive Recovery. Had one of those with my Leviathan earlier this year.

Personally, I like the epoxied in plastic rigging point better than the paper trifold.
 

KarlS

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If you want to upgrade the elastic, use the same size braided nylon elastic from the fabric store. It is much stronger than regular elastic.
 

Nantucketdink

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Neil-the way you have been doing it really does get the best of both worlds. I would agree that 130 Kevlar sounds awfully skinny, but would probably be just fine. This build gives you an excuse to get a spool of 300# or 500# for bigger projects.
 

rocketron1948

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The shock cord mount and shock cord provided are more than adequate to handle flights using E16 or F15 engines. I see no reason why they would not be adequate for flights with composite E, F or G flights as well. I have never had one fail in my Pro Series II rockets.

Rocketron
 

BlaineS

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Hey neil_w,

Since I failed miserably last time to help you with your fin painting question, please let me try again to help! LOL!


I have not posted pics of it yet on my site but, on my Trajector, I drilled a hole between the fin slots in the rear and forward CRs and epoxied a “tunnel” of clear plastic tubing between the CRs. I “lassoed" a 36” kevlar shock cord around the bottom of the motor mount and passed the cord through the “tunnel" and out the top of the BT. I then tied it to the stock elastic shock cord. If I ever need to replace the kevlar cord, I can simply cut the lasso, pull it out, "re-lasso" the bottom of the motor mount with a new cord and tread it through the “tunnel” and back out the BT.


I will post the pics of this part of the build as soon as my schedule allows.


Hope this helps!
 

burkefj

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I simply installed 2" coupler piece and a 1/8" ply baffle plate and mounted a 1/8" kevlar cord to the ply plate that is long enough to allow me to attach the elastic to a loop at the top, so that the elastic is going over the edge of the tube.

Frank
 
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