Rocket Knots

[edwardw]

Okay, fess up everyone, what kind of knots do you all use on various parts of your rockets?

I have "The Ashley Book of Knots" and have been looking through it for some good ones...but wanted some real life input.

Edward

 

[powderburner]

I have never had problems with knots or lines (other than the occasional burn-through due to ejection charge), but for the past few years I have been using the 'figure 8' knot that rock climbers use. It is supposed to be one of the strongest knots available (rated at approx 80 percent of basic line strength) and has held up fine so far.

I usually soak the knots with white glue to make sure they don't unravel.

 

[cls]

hey, this is a great topic!


I find granny knots are best on LPR parachute shrouds. years of sailing has taught me to always tie square knots. but square knots will too easily pop in to a pair of hitches, which then tighten up and cut the chute. bowlines are too hard to tie with fat fingers and little bitty carpet thread.


hard to be a doubled figure 8 for strength and reliability under shock loads, so that's a natural for putting a loop in tubular nylon or elastic.


tying knots in kevlar or other synthetic line is an art form because the line is so slippery. double figure 8s seems to work best.


for stopper knots (like the one at the end of the kevlar at the MMT ring in the Quest system) I use "fisherman's knot". this is like tying a figure-8 except you go around a bunch of times before you go back through the loop. this makes a big ball and won't slip.


for tying elastic to nose cones I generally go with a pair of half hitches. no chance of it popping back in to a square knot and it won't slop and it can be undone.

 

[Elapid]

the most useful knots are the figure 8 and the square knot.
water knots and barrel knots could have a place too...

 

[edwardw]

I like the butterfly loop - kind of hard to explain, but the lines come out straight and you get a nice loop to tie stuff to. Also the daisy chain is nice for putting into a TN harness to it takes up less space but still uncoils. I also like the bowline because it forms a loop that doesn't move at all.

Edward

 

[aksarben10]

Here is a link to a past knot thread. Many good tips in this one, lots of pictures and a few links to some site with how-to guides for knot tying.

Seems, to me at least, that people fall into one of two knot tying schools. One crowd that goes for the "good old tried and true" Fishing knots and the other would be the "I would trust my life to this knot" Climbers knot crowd.

I think that both work its really depends on your materials, function and past experiance leads you to.

http://www.rocketryforum.com/showthread.php?s=&threadid=4468


Scott

 

[shockwaveriderz]

animated knots:


http://www.mistral.co.uk/42brghtn/knots/42ktmenu.html

 

[teflonrocketry1]

I use a Bowline or Taught line to attach the nose cone to the shock cord. If I need a loop at the end of the shockcord then I go with the Bowline. I typically use two half hitches for shroud lines through the parachute canopy. I leave a pencil diameter loop at the canopy end of the shroud lines since I use a pencil as a form to tie the two half hitches around. I use a clove hitch to secure the leads from the launch controller to a leg of the launch pad. I use a simple slip knot to make a harness around my rocket that I can side along the airframe to find its balance point or CG.

Bruce S. Levison, NAR #69055

 

[SecretSquirrel]

A knot is like a mile, only more expensive

 

[Hospital_Rocket]

Ae rhe risk of being burned at the lauch rod as a heretic, I don't use knots that often. For anything with a shock cord larger than a 1/4", I sweet talk my wife into sewing the end into a loop. The junction is usually as long as the width of the material and then I use a quick-link or snap swivel to connect the assembly. I use the same technique for mid-line loops.

For amall stuff I still use knots.

For end loops I use a bowline

http://131.230.57.1/knots/bowline.htm

For mid loops I use a butterfly

http://home.comcast.net/~djs461/knots/butterfly.htm

 

[Micromeister]

Model and LMR rocket Knots:
Every knot has a specific purpose. I cringe everytime I hear folks talking about using square knots or even surgeon's knots on shock lines or anything other than line to line knots of identical diameter.

By adding glue to your knots you are decreasing the strenght of the line and knot by more then half! Please do not add glue to your Knots, If you feel the knot your tying requires glue to remain tied your using the wrong knot.
If you must, apply glue only to the very ends of the knotted line outsde the knot. One last warning.. Do not CA knots in kevlar, If you are imbedding a kevlar loop in a balsa nosecone or such it's better to tack the loop with a drop of CA but imbed in epoxy. this still weakens the line but not as badly as in pure CA.

My preferred Knots:
Shock cord to eye or nosecone: Two half hitches
Shock line or cord to motor mount or motor block: Bowline or Two half hitches, depending on line dia.

Inline (shockline) attachment loop: Butterfly knot.

Kevlar to elastic: Simple overhand, Bowline on a Bight or Figure 8 Double (which is I hope the figure 8 knot powderburner mentioned as a simple figure 8 is a stopper knot only.)

Streamer attachment Line to swivel: Improved clinch Knot

Chute knots: Figure 8 in shroud end with half bend under tape disc.
Two half hitches shroud to canopy through reinforced holes.
Overhand loop bundle shrouds through eye of swivel forming a Lark's head.

Freestanding flag poles: Clove hitch around pole, Taught-line Hitch (locking adjustable hitch) around adjustment lines to stakes.

Bundle controller leads: Clove hitch bundle to the table leg and Chain hitch down the bundle to the ground.

 

[Micromeister]

Though you guys might like to see some of the Knots were talking about

 

[rstaff3]

I am knot challenged but there are two good links.

http://www.killroys.com/knots/surgeon.htm


http://brmrg.med.virginia.edu/knots/water.html

You can navigate around and find other types.

 

[wyldbill]

I'm firmly in the climber camp, they've saved my life, I trust 'em for rockets.

If you're using 1/4" kelvar see this

More general info here

-bill

 

[wwattles]

I'm a firm believer in Surgeon's End Loops. When building my rockets, I attach kevlar leaders to the motor mounts and put a surgeons loop on the end of it, to attach elastic shock cords, nose cones, chutes, streamers, beepers, whatever I need.

A buddy has a wife who's into sewing, and has a heavy-duty sewing machine, and he stitches the loops into his tubular nylon cords. He lays it flat, folds it over to make the loop, and stitches down a 1.5" section using a very heavy thread. Since knots weaken a line/rope/cord, this prevents that weakening.

WW

 

[Micromeister]

He lays it flat, folds it over to make the loop, and stitches down a 1.5" section using a very heavy thread. Since knots weaken a line/rope/cord, this prevents that weakening.

WW [/B][/QUOTE]
WW:
I believe the thread question was What knots do we use in rocketry...
While sewing flat tubular kevlar and other flat woven materials is the way lifting slings and other flat webbing type materials are commonly joined. Machine stitching does indeed have a weakening effect on this stock.. the needle is beaking, nicking, shearing and splitting webbing fibres. Is this weakening as bad as knots, I doubt it but would depend on the material size,stitch and stitch method as well as other factors.
Actually the act of bending line/rope/cord OR webbing weakens the materials. That loop we make in our lines about halves the strength of whatever material your using. compress the bend in a metal Eye creates even more stress on the center fibres,( the reason D rings were invented). Which rope or webbing is stronger? It's a matter of choice, just don't believe sewing "prevents weakening" in flat woven materials.
Just to get as much info out there as possible