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Parachutes Recovery Technology - NARCON 2013

NARCON 2013 was February 2013. I gave a talk about Parachute Recovery Technology and some of the cool stuff I've learned over the years.

Parachutes Recovery Technology - NARCON 2013

NARCON 2013 was held February 22 2013 in Santa Clara. It was my chance to get up and talk about some of the cool stuff I've learned over the years. As of this date we have made over 1700 chutes and shipped all over the US, and internationally to over 30 countries, and growing. During this time, and after helping so many folks, Universities, and Corporations with their projects I guess I've learned quite a bit!

 The Subjects of the talk were:

  • Types of Parachutes - I compare the most popular chutes used by Rocketry and UAV recovery
     
  • Packing Density – predicting packing volume using chute weight - simple
     
  • Deployment & Packing Methodology - Compare the various type of recovery technologies out there

Here a link to the power point presentation - Rocketry Recovery Technology.

About Packing Density - One of the more interesting parts of the talk is the discussion about packing density, and calculation of packing volume by simply knowing the weight and dividing that by the density. In this case the packing density is measured as oz / cu" of weight. Dividing this factor into the weight measured as oz gives you the volume in cu".

A key fact is that packing density is not dependent on the chute design, as long as we're taking about nylon! This has been verified by a number of studies done be different research groups. They found that a density of 30lb / cu' (.28 oz / cu") can be achived by compressing the parachute at an equivalient force of 15psi. Compressing at 100psi yields a density of about 45lbs. But at this pressure you start to damage the nylon. The Peregrine IDS uses this exact technique to get the small packing volums featured by that product. We use 15psi as a more resonable pressure.

As a typical example that rocket folks can relate to let's look at the packing density and volume you can achive when you fold and wrap your chute (see how to pack a parachute for instructions). We have found that a typical density with this methos is about 0.13 oz / cu". Lets look at packing the IFC-60 stock chute with a weight of 10.9oz. The volume is calculated as:

10.9 oz / 0.13 oz per cu" = 84 cu"

To convert that to length in your airframe you use the formula: 

L = (V * 4) / (pi * D^2) = V / (D^2 * .7854)

In this example if we have a 3.9" ID airframe we get:

L = 84 / (3.9^2 * .7854) = 7"L

If you use a deployment bag you can achieve a higher density of about 0.18 oz/cu" or maybe even higher depending on how hard you push. The Peregrine IDS has the highest packing density at 0.28 oz / cu" by pressing the chute into the canister at 15lb / sq". For the 6" PIDS this means we use a pnumatic press that applies about 450 lb of force!

Packing density factors - Below is a table of packing densities you can use to calculate your packing volume and length uwing different packing techniques:

 
Type
Oz/cu"
gram/cc
Description
 
Fold and Wrap
0.13 - 0.14
0.22 - 0.24
Traditional fold, roll and wrap chute
 
D-Bag
0.16 - 0.2
0.28 - 0.35
Hand pack into deployment bag
 
Jam
0.22
0.38
Jam into section of airframe with hand pressure
 
Pressure Pack
0.26 - 0.28
0.45 - 0.48
Pressure Pack into PIDS Canister

Feel free to fudge these numbers as you see fit. For instance I know I get a better packing density on my fold and wrap as I've has a lot of practice with my chutes! But if you want to be conservative these are good numbers to start with when making these calculations.
TIP: To convery from english unit packing density given as oz / cu iin to metric g / cc multiply by 1.73.

About Author

Name: Gene Engelgau

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