Parachutes Recovery Technology - NARCON 2013
| Published: Mar 01, 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 close to 2000 chutes and shipped all over the US as well as internationally to over 30 countries and counting. During this time and after helping so many hobbyists, universities and corporations with their projects, we've learned quite a bit!
Subjects of the talk included:
- Types of Parachutes – I compare the most popular chutes used by Rocketry and UAV recovery
- Packing Density – Predicting packing volume using chute weight
- Deployment & Packing Methodology – Compare the various types of recovery technologies and packing methods out there
Here a link to the 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/in^3 of weight. Dividing this factor into the weight measured as oz gives you the volume in in^3.
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 by different research groups. One such study found that a density of 30 lb/ft^3 (.28 oz/in^3) can be achived by compressing the parachute at an equivalient force of 15 psi. Compressing at 100 psi yields a density of about 45 lb. However at this pressure, you start to damage the nylon. The Peregrine IDS uses this exact technique to get the small packing volumes featured by that product. We use 15 psi as an ideal 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 our How to Pack a Parachute tutorial for instructions). We have found that a typical density with this method is about 0.13 oz/in^3.
Let's look at packing the IFC-60 parachute with a weight of 10.9 oz. The volume is calculated as:
10.9 oz / 0.13 oz/in^3" = 84 in^3
To convert that to length in your airframe you use the formula:
L = (V * 4) / (pi * D^2) = V / (D^2 * .7854)
If we have a 3.9 inch inner diameter airframe we get:
L = 84 / (3.9^2 * .7854) = 7 inch length
If you use a deployment bag, you can achieve a higher density of about 0.18 oz/in^3 or maybe even higher depending on how hard you push. The Peregrine IDS has the highest packing density at 0.28 oz/in^3 by pressing the chute into the canister at 15 lb/in^2. For the 6 inch Peregrine IDS, 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 using different packing techniques:
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 have a lot of practice packing my parachutes! However if you want to be conservative, these are good numbers to start with when making these calculations.
Tip: To convert from imperial units for packing density (given as oz/in^3) to metric (g/cc), multiply by 1.73.
Download the PDF – Here is a detailed writeup of my talk at NARCON 2013 about Parachute Recovery Technology for Sport Rocketry: NARCON 2013 - Rocketry Recovery Technology.