I am considering a parachute on a 7Kg (15lb) UAV.

I have found various formulas on the web, but the question is what parameters to use.

What rate of descent should I choose so that, after a parachute landing, a well built but not overweight UAV will be able to fly again after straightening the undercarriage and minimal repairs?

My guess would be 3 metres per second (10ft/s) but I have no real experience. My calculations indicate such a hemispherical parachute would need to be 5 metres (16ft) in diameter, which would need 40 square metres (430 squ ft) of material - which is huge, and does not seem right.

I would appreciate any useful information. Jack.

## Replies

"a big rubber band" is basically what we used on our rockets. it did just that. took up the shock. the slider also helps. and on my reserve chute, where it has to open in a hurry, i have a spring loaded deployment bag. its always under tension. when the cord for that pulls, either by aad or my own doing, it releases, springs to clear air in a hurry, and then opens up pulling off the diaper and allowing the chute (that also has a slider) to open just as weve talked about already. i suck at software. joined this site a while ago with a buddy of mine who could do the software. so youre on your own there. however, if youre looking for mechanical ideas, im happy to offer my assistance.

The equations on that page work out to:

V = Sqrt(13.63M/D^2)

D = Sqrt(13.63M/V^2)

in kg, m/s, and m

Or 3.25m for your specifications.

Traditional human chutes apparently aim for about 5.5m/s descent speed, which would give you 1.78m diameter.

It would appear that hardening the UAV a bit to shocks (spring steel skids, etc) might pay off, but ripstop nylon is a very light material in the first place.

This, for example: http://www.fabrics-n-stuff.co.uk/product_info.php?products_id=983&a...

is 38g/m^2

Fabric for a 3.25m chute for 3m/s would weigh about 315g without any lines or deployment mechanism

This might help:

http://my.execpc.com/~culp/rockets/descent.html