Parachutes

Misc Info
	Altimeters Altimeter Port Sizing Altitude Charts CAD Drawing Software Centering Rings Metal Plates Delay Time Charts Ejection Charge Sizing Epoxy Igniters Launch Pads Parachutes (etc) Rocket Finding

Links
	General Information Clubs & Organizations Rocketry Vendors Kits and Components Rocket Motors Fun & Useful Sites Electronics Construction Supplies Software Tools Rocketry Magazines Photographers NASA

I use Rocketman parachutes. The recommended weight for each size of parachute is shown in the table below. (This table is a copy of the table in the Rocketman catalog.)

Scorpion on an R12C

Parachute Model	Weight Range
R3C	1.5 - 2.5 lbs
R4C	2.0 - 3.5 lbs
R7C	3.5 - 8.0 lbs
R9C	6 - 12 lbs
R12C	12.5 - 20 lbs
R14C	20 - 35 lbs
R18C	45 - 65 lbs

Quick Links

I use stainless steel delta shaped quick links to connect the recovery harness to the parachute and to the U-bolts on my rockets. Three sizes are shown here as compared to a US quarter. These are available from McMaster-Carr. The one on the left is a 1/8" stock diameter (part number 3709T31). It has a working load limit of 330 lbs. (Failure point is way above that!) The part in the middle is a 3/16" diameter (part number 3709T32). It is rated for a working load limit of 716 lbs. The one on the right side is the 1/4" diameter (part number 3709T33) with a working load limit of 990 lbs. All three are made from 316 stainless steel. McMaster-Carr also offers them in zinc plated steel. Those are about half the cost but only about half as strong.

Three sizes of delta shaped threaded links.

The delta links shown here are the 1/8", 3/16" and 1/4" sizes.

McMaster-Carr also offers a square shaped link that works great for making connections between two harness straps. This one is the 3/16" size. It is part number 33785T64 and has a rated working load limit of 715 lbs but it will take a lot more than that to get it to fail.

Tubular Kevlar and Tubular Nylon

I use tubular nylon webbing for the main part of the recovery harness and tubular Kevlar for the part that gets exposed to the hot blast of the ejection charge. Shown below are two convenient sizes of each. The Kevlar is in yellow and the nylon is in red.

I get the tubular nylon from my local REI store. The 9/16" webbing is part number 472-315 and is $0.22/ft, weighs 0.20 oz/ft and is rated at 1500 lbs. The 1" wide webbing is part number 472-006 and is $0.30/ft, weighs 0.41 oz/ft and is rated at 4000 lbs.

Another good source for tubular nylon is at Para-Gear. They supply anything and everything that has to do with skydiving. They have 1/2", 9/16", 5/8", 3/4" and 1" tubular nylon. Part number W9530 is 1/2" tubular nylon and part number W9610 is 1".

I have purchased the tubular Kevlar from several different rocketry vendors and it tends to go for about $1.00/foot for the 1/2" wide, and about $0.66/ft for the 3/8" wide.

Tubular Kevlar and Tubular Nylon webbing

3/8" and 1/2" tubular Kevlar webbing (yellow).

9/16" and 1" tubular Nylon webbing (red).

I used to sew loops into the ends of the nylon webbing using Kevlar thread. However, lately I have just been using a simple knot that is very easy to tie yet will not pull itself loose. Start by folding a generous length of webbing back on itself.

Loop the end around and over itself.

Now pull the end up and through the loop.

Continue to pull the end until the loop comes tight.

Pull the knot tight as you make sure the flat webbing is neatly layered. I tend to secure the loose end with a few stitches just to make sure it can't possibly be pulled back through the knot, but as far as I have seen, this is not really necessary. Especially since the knots always get checked before every flight anyway!

I use this same knot on the tubular Kevlar.

I tend to use about 30-40 feet of tubular nylon for the recovery harness on my larger 5.5" diameter rockets. For one thing I want to absolutely minimize the risk that the two pieces at each end of the harness will clang into each other. Particularly if the ejection event is "off nominal" and is more energetic than normal. The longer length of nylon also allows a little more stretch for absorbing the shock when it all comes tight the first time.

Flame Shields

I use 8 oz Kevlar cloth to protect my parachutes. This is done in two ways. A circular piece much larger in diameter than the body tube is cut for use as a flame shield between the ejection charge and the recovery harness. Another piece of Kevlar is then cut into a larger rectangular shape that is used to cover the parachute itself. This piece is folded shut and completely encloses the parachute much the same way a traditional "chute bag" would. However, unlike a traditional chute bag, there is no problem with pulling the parachute from it since it is just a flat rectangular piece of cloth. (See pictures below.)

I got the Kevlar cloth from Thermostatic Industries, Inc. It is the lightest weight cloth they sell. (They sell lots of really heavy duty textiles for heat and fire protection.) Their part number for it is 8K-60 which I think means it is 8 oz/sqyd and 60 inches wide. I bought 3 yards x 60 inches (45 sq ft) for $100 plus $4 shipping. This comes out to $2.31 per square foot and is cheaper and much more heavy duty than any flame shields I have found from the regular rocketry vendors. This Kevlar cloth is 0.026" thick. Many other material properties and specifications for it are available right here.

One slight draw back is that the Kevlar is pretty difficult (but not impossible) to cut. One advantage is it is heavy duty and holds up really well to heavy use.

I sew the outer edges of the cloth with a Kevlar thread just to keep it from fraying and unraveling. I also sew a button hole into one edge of it so that the recovery harness can pass through the button hole to keep the cloth attached.

I got my Kevlar thread from McMaster-Carr. The part number was 8800K81. It is trade size 69, 0.014" diameter, 375 yard/spool for $13.50.

Parachute Preparation

Rocketman R14 Parachute about to be folded and wrapped.

This is a Rocketman R14 parachute laying on a 20" x 24" rectangular piece of Kevlar cloth.

Wrapping the parachute in a Kevlar heat shield.

Fold the parachute and then roll it up in the Kevlar cloth. Leave enough Kevlar on each end to fold the ends closed too.

This is what I call a "Burrito Style" parachute protector.

Also notice how the red nylon webbing goes through a button hole in the Kevlar cloth.

Continuing to wrap the parachute in the Kevlar cloth.

Continue wrapping the Kevlar around the parachute.

Fully wrapped and the bottom end is folded shut too.

Fold the bottom closed. Ideally the top would be closed too, but this is not absolutely necessary.

24" Nomex heat shield with two Kevlar anchor straps.

This is a 24" diameter piece of Nomex cloth that is used as a heat shield in a 5.5" diameter rocket like Wildfire. It is large enough to enclose and protect the 30-40 feet of nylon webbing in the recovery harness.

There are two Kevlar anchor straps that pass through the middle of the Nomex cloth. Only one is actually needed, but two are used as redundancy backups for each other. This is because these anchor straps are subjected to the hot ejection charge gasses and must tolerate a great deal of "wear and tear". If one should happen to fail, the other will still hold. (Of course these also get inspected prior to every flight.)