Knots etc...

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Rocketman35

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New to the board :)

Born again Rocketman here. Starting back on small stuff like estes and quest rockets.

Was making my own chutes the other day for the first time and wondered what was the best way to attach the shroud lines to the chute. Just a regular square knot or two? Some kind of slip knot?
Now how about the shock cords? I read that a lot of people were placing super glue on the elastic shock cord knots...everytime i have done this the elastic breaks right at the point where it was glued (more brittle at that point?) Same would go for the kevlar and elastic joining point.
So to sum it up

1- What kind of knot(s) are used at chute/shroud line join.
2- What kind of Knot(s) are used at Shock Cord join:
A) Kevlar/elastic join
B) Elastic/Nose cone join
3- Use super glue at knots? Yes or No



Im sure i'll have more question but i'll leave it here for now.
Big hello to all! and TIA

Chuck
 
Here are the answers (as best as I know).


1)For the Estes stuff I don't use a knot, just loop the shroud under a tape disc.

2)If there is a loop in the nose, attach the shock cord to it using a standard knot, and if you have the Estes and Quest style of attaching shroud lines (no loose ends) put the cords thru the loop, and bunch all the cords together and put the chute through it. I don't use kevlar in most of my rockets, when it is used I just use a standard knot.


3) CA weakens elastic shock cords.Don't use it to attach them. There are several other ways to attach them, including motor mount attachment, and a paper "shock lock". I don't have a pic, but one can be found in the Handbook of Model Rocketry.


BN
 
I use a square knot to attach shrouds to chutes. I use a notebook hole reinforcement on BOTH sides of the chute first.
With Estes chutes, I pull the three loops through the ring on a snap swivel, and push the swivel up through the loops, then pull tight. This way I can pull the swivel off fairly easily to untangle and untwist the shrouds. They invariably become messy after a few launches.

I use a kevlar leader to mount shock cords to the body. To tie them together, I lay them beside each other and tie a simple overhand knot, and pull tight. I then super glue the free ends together, making certain that I get no glue on the knot or the part of the shock cord that will be stretching.

I never attach a shock cord directly to the nose cone. I put a small metal split ring on the NC's plastic anchor, and attach the chute to that with a snap swivel at the time of launch prep. I permanently attach the shock cord to the ring with a square knot, and put a tiny drop of glue on a part of the knot that is not directly touching the part of the cord that will stretch. The idea of the metal split ring is that the plastic anchor of the nose cone bears no stress except the weight of the cone, and not the additional stress of the weight of the body or the shock of the chute deploying. It is also generally easier to attach the snap swivel to the ring than the plastic NC anchor.

I have found that ball bearing swivels work somewhat better than barrel swivels and preventing twisted recovery components. They can be found at WalMart and KMart for model rockets.
 
Finished. Easy to pull out, in case of tangles, but the more weight on it the tighter it gets.
 
For low power, I have always had good luck with simple square knot kinds of attachments. I usually reinforce the knot (to prevent unraveling) with a couple drops of Elmer's white glue, rubbed into the elastic.

To attach shroud lines to parachutes, I tie a knot or two in the very tip of the shroud line and tape it to the plastic with a small square of scotch tape. I position my anti-pull-through knot in the middle of the tape square, or toward the top edge.

For mid- and high-power, you better pay closer attention to the knots. Maybe you should use a "figure 8" knot like climbers use; it is supposed to give the best strength.
 
I am an old climber and spent many hours on the rocks trusting my life to rope, webbing and knots.

Some things to know about knots. Any knot or bend in a rope/webbing will cut its strength in half, at the point of the bend. You do not want to add bends unnecessarily and keep this in mind while purchasing cord/webbing as the weight ratings are done without knots. Heat will deteriorate any rope or cord so protect them as much as possible and inspect them each time before use. Glues and adhesives can eat away or weaken the rope/webbing material. This depends greatly on the rope and the adhesive used, but a well tied knot is always better as it is stronger and can be undone. A well tied knot looks good it should have a clean look to it and messy knot is not tied correctly. With knots the strength is determine on what it would take to pull the knot until it unties it self. This does not usually happen the cord or webbing fails first in most cases. When knots do fail it usually caused by the knot not being tied correctly or the tail being to short. If the tail is to short the knot will untie, all knots are a friction device the stronger you pull the tighter it grips and all knots will have slip before it grips and a bit of slip while it is being pulled if the tail is too short it can be pulled through and the knot will untie. Just make sure you have a good 3-4 inches of tail on your knots and you will be fine.

Two or three knots are all you will ever need in rocketry. You will need one to join rope/cord and one to join webbing. You will also need one for loops on the end of a rope.

Webbing is best joined by the water knot. The water knot is one of the easiest knots to do and does not lose as much strength as some others. The water knot can be used to join two pieces of webbing or too add a loop on the end of a long piece of webbing. You can use a double fisherman's knot to join webbing but the water knot is easier and can be untied easier.

For rope or cord you want a double fisherman's knot to join them and a figure eight or overhand on a bight to make a loop on the end. The double fisherman's knot takes some practice to get it down but it is a wonderful knot, climbers us it to join two ropes together to rappel of a climb, very reliable. The water knot can be used to join cord but it is not as strong with cord as it is with webbing.
To make a loop in the end of a cord the figure eight makes the strongest but takes more cord then overhand in most cases the overhand on a bight will serve you well as it is quick to make and uses less cord. I only use the figure eight for extremes, climbers use the figure eight to tie into the rope the knot that counts the most.

Here are a link that show these knots. You can also search the internet for the knots to find some better guides on how to tie them as this is not the best but shows them all.

https://www.climbgeorgia.com/train/knots1.html

With the right cord/webbing you can trust you life with these knots.


Scott
 
Good post. Thanks for the attachment pics rbeckey! Where can I buy those split rings?
Jeff
 
Originally posted by aksarben10
I am an old climber . . .


For anyone out there who does not climb, that means he is a very CAREFUL climber



Any knot or bend in a rope/webbing will cut its strength in half


I thought the figure 8 was supposed to be good for something like 80% (or more?) of basic line strength?
 
Originally posted by powderburner
For anyone out there who does not climb, that means he is a very CAREFUL climber






I thought the figure 8 was supposed to be good for something like 80% (or more?) of basic line strength?


Its a basic rule of thumb to 'live by' all knots have a different rating as to how much strength they take away. It may be that figure 8's are better, I dont remember. They most likely are better, as I said they are the knot of choice to tie in with. Bowline are also used but not by are many climbers. Climbers have knot discussions like rocketeer's have glue discussions.


And yes I was a very careful climber, I tried to stay within my limits.

Scott
 
Those particular split rings were scarfed from the local humane society, where they were given away to attach a license to a dog collar. I asked the lady if I could have some for a "special project" and she gave me about thirty! :cool: They are aluminum and will not rust.
I have seen small split rings sold where keys are made and certain old fashioned hardware stores. They are also sold for making jewelry, I believe. I know that one local craft store had some in that isle.
 
1- I use two half hitches for attaching parachute shroud lines to the canopy. For larger 'chutes I use a taught line so I can adjust the final loop of shroud line trough the canopy. These knots get pulled tighter with use.
2.A- For Kevlar to elastic I use a sheet bend and lock it with an over hand knot in the elastic and Kevlar.
2.B- To attach the shock cord to the nosecone I use a bowline.
3- I no longer fix the knots with glue as this makes a brittle spot in the elastic or Kevlar and provides nice place for the cord to break or get caught on something.

Bruce S. Levison, NAR # 69055
 
Kermie,

Yep, that's very similar to what I do. It looks remarkably like what a we fishermen use for various monofiliment knots for securing hooks, lures, etc. That's where I get all of my knots for rocketry, from my fishing...
 
Looks like that might work for elastic low & mid power too. Have to try it.

I keep all glues off the stretchy part of the cord, just like the diagram suggests. I believe this locks the knot and does not weaken the cord any more than tying already has.
 
Another way to secure the short loose ends of a knot in nylon webbing is to use a couple of stitches.

This is what some climbers use to help make their webbing knots more secure. All it takes is some heavy thread (our lighter-weight kevlar threads would be ideal). A needle can be pushed through most nylon webbing very easily. It doesn't take a lot of stitches, they are not for 'structural' purposes, the stitches are just a way to make a quick visual inspection to make sure the tail of the knot has not loosened up and allowed the knot to unravel.

For those of you with heavily loaded mid- and high-power rockets, this check stitch would allow you to build without any glue on the knot anywhere. And it is more removable if you need to disassemble your rocket later, for any reason.
 
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