Matching Parachute Size to Weight

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Alby

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Does anybody have calculations on how big of a parachute you should
use based on the weight of the rocket?

For example, what would be the acceptable chute size for a 2.5/lbs rocket?
 
According to my calcs, a rocket with a recovery mass of 1134 g (~2.5 pounds) will need a parachute of 60 inch size to get a safe descent rate of 11.95 f/s (3.643 m/s).

YMMV.

Greg
 
There are numerous charts available to determine proper chute sizing.

Check out FruityChutes or K&S Rockets for examples of these charts.

The Cd of the chute is a significant factor in the calculation of these charts. The higher the drag of the chute, the smaller the chute needed to achieve the standard 15 fps descent speed.

Flat parachutes (parasheets) have less drag than cupped chutes.
 
30" semi hemispherical chute at 2.5# will give you a decent rate of 16.5 fps and a 36" semi hemispherical chute will give you 14.5 fps. This is based on our chutes and the data we collected during testing.
 
Thanks. When I punched a 60" chute into OpenRocket, I got a descent
rate of 3.97 m/s. With the 42" I currently have installed, my descent
rate was 5.81 m/s.
 
Could one argue that a descent rate above 5 m/s is bad and one below
4 m/s is Good? I'm just trying to determine what is the typical target
that most people try to achieve.
 
With modern construction, a lot of folks will go as high as 20 fps descent.

I fly tube fins (no TTW there!) and try to stay at or below 15 fps.
 
One factor to keep in mind is the typical ground surface the rocket will come down on. If you are pretty certain to be landing on grass, you can go with a faster descent rate (and enjoy the smaller packing size, lighter weight, lower cost, etc.). But if you are often landing on harder ground (like I am), then you want to really slow things down.

Where I usually launch the ground is hard sun baked dirt or dry lake beds. Too many times I have wished I'd chosen a larger, slower chute when the rocket hits that ground. Lately I pretty much always take the size that RockSim says to use for a "slow" descent, and then go with the next size larger. It means a longer walk sometimes, but I'm doing a lot less repairs.

my two pesos, s6
 
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