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Shock cord mount...

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sbaryenbruch

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I just started building a Fliskits richter recker tonight and was wondering about alternatives to the folded paper shcok cord mount. What other methods can be used to mount the shock cord on a rocket such as this (no centering rings) that would be stronger and more "sophisticated"...or is the folded paper method really good enough?
Thanks,
SAB
 

TheRadiator

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You could use the "LOC" method. Get a nice length of 100 pound test kevlar thread and tie an over hand knot in each end. Form the thread into a "U" shape with the ends of the thread pointing down the BT. Hold the ends down with a small piece of masking tape and absolutely smother the thread ends and masking tape with 30 minute epoxy. Just be sure to not get any epoxy too close to where the nose cone shoulder or the BT coupler should be.
 

astrowolf67

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Here is a pic of the LOC style shock cord mount. This particular one is in my Deuce. As stated, you can use kevlar thread, or you can use nylon cord, which this one is made of. On my mid power rockets, I use the same method, but I ad a piece of light weight fiberglass across the ends (probably overkill, but it adds no weight, and makes me feel better :) )
 

jflis

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I've seen that method a few times before and always wondered about it. Good to hear some feedback on it.

Another option (if you haven't already assembled the kit) would be to run a length of kevlar down to the motor mount and secure it there.

I *will* point out that the folded paper mount will work fine for the Richter Recker, even for its large size, because the top and bottom section come down separately on their own chutes. Because of this there is no nose cone mass on the lower section or on the shock cord making the stress on this point much lower than it would be normally.

jim
 

rbeckey

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If I do not run my shock cord to the motor mount with a kevlar leader, I lay the kevlar straight down the length of the tube and use polyurethane glue to attach about 6 inches of the kevlar to the tube. As previously mentioned, do not forget to leave a space at the top of the tube for the coupler or NC to slide in.
This also works when an Estes type rocket damages its shock cord. After several ejection charges the inside of the tube is sooty and dirty, and most adhesives don't bond well to it. I clean the inside of the tube with a paper towel or rag moistened with alcohol, let in dry, and rub a sponge moistened with water on the tube where I want the shock cord mount to be. Run a bead of polyurethane down that area and use a scrap of balsa or soda straw to push the kevlar cord into the glue, and make sure it is really soaked. Lay on its side and wait overnight and the cord will be secure, even in the nastiest tube.
 

rabidsheeep

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dunno what its called but ive seen it before... if you have a strong body tube you can cut a hole in the side of it, thread the tube throught and make a not so it cant come back through the hole... then take a nosecose, cut it alittle in half, slim it down so its really small, and put it over the not so it doesn't screw up the aerodynamics too much... ill put up a pict of a rocket i have that uses it... its basically the same thing you would do if you had a side mounted camera...
 

Stones

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All of my smaller Estes kits get 1/4" elastic, 3 times the length of the rocket. Making sure there's enough room for the shoulder of the NC, I simply glue with a drop of yellow glue, then end of the elastic in the BT. After it dries, I'll put a dime sized puddle of epoxy over it and call 'er good.
 

shockwaveriderz

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I immediately replace my estes shock cords with kevlar cord from Pratt Hobbies....I just wrap/wind some of the kevlar around the engine , use apiece of tape to hold it in place and then insert the engine....the combination of the tape and the friction fit keeps the kevlar shock cord wrapped around the engine in its engine mount....simple....

a variation of this method is called the lariat loop, where again you use kevlar cord, and create a small loop to lasso the engine......add a piece of tape to hold it in place and increase the friction fit of the engine....

http://www.troop7.org/Knots/Lariat.html

using either of the above methods, the shock cord can be inside or external...

These are ways competition modelers use kevlar shock cords in their models....

http://www.apogeerockets.com/education/downloads/newsletter95.pdf
 

powderburner

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I have always had an aversion to using the Estes folded-n-glued paper anchors, or anything else that blocks the inside of the body tube. This is probably just a left-over preference from my early days of flying lots of streamer and parachute duration rockets---you don’t want ANYTHING to get in the way of deployment. I still try to build with no internal obstructions or features where the guts can get snagged and stopped. Then again, I am usually just a bit conservative in my approach to design and reliability.

First off, I like to use nylon cord for a tether, but I coat mine with glue for the part that will be inside the BT. Some of these TRF guys don’t like using anything less than Kevlar, but I have not had problems with burn-through on my cords. Whatever you decide on, I recommend making the primary attachment at the back of the recovery compartment, and running the continuous tether out the front of the BT. (I put my elastic bungee chords between the tether and the nose cone.) I pull and hold the tether taught as I insert wadding and recovery items, and pack the excess tether last (just be sure it is bundled loosely and is free to pull out). The ejected materials slide over the cord and have nothing on which to get snagged before they pass out the front of the BT.

If I want an internal attachment for my tether line, I tie to the thrust ring, or outer edge of the centering ring, and coat that sucker with glue or epoxy at the attachment. If you are doing a minimum-diameter rocket and only have a thrust ring to work with, you may have to put a notch in it to make room for the tether. I pull the string tightly out the front of the BT so that the tether material runs straight along the inside wall of the BT, and glue it in place for several inches in front of the motor (much like what astrowolf has posted above).

Other options: Attach your tether externally at one of the fin roots or launch lugs, and ‘secure’ it underneath a layer of fillet material. This leaves a string on the outside of your rocket that runs all the way up to the NC; some people don’t like to do things that way. Or, use a small external attachment at the front of the BT, just behind the front edge, and run the tether around the corner and under the NC for minimal exposure.

If you must put your anchor inside the front, Stones has already posted a very good approach (and an Excellent illustration!). Looks to me like if you put a small puddle of epoxy over the attach point (and keep your fingers out of it) you will get a smooth bump that should not cause any snags.
 

rabidsheeep

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ive never had a problem with mount burn problems... you could always wrap your cords that might get burnt in alittle recovery wadding...
 

Quasar

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I'm experimenting with 1" wide kevlar tape. Glue one end where the paper mount would normally go and leave about 1 or 2 inches sticking out of the body tube. Glue the shock cord to the end sticking out and you have a anti-zipper, fire-proof mount.
 

Fore Check

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I've found all kinds of great uses for the fix-it epoxy clay I got from Apogee. One of which is to use the tri fold, but then smear epoxy clay all over it and feather it out so it goes about 1/4 to 1/2 inch all the way around the paper 'fold. After a few launches, I'm very confident that the sucker ain't coming out and it ain't getting burnt through, either.
 
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