One black art that exists in rocketry is deciding on the proper descent rate for your rocket. There are plenty of ways to compute your rocket’s descent rate if you know the rocket’s weight and the parachute dimensions. The question then becomes, what is a good descent rate for my rocket?
The speed at which the rocket impacts the ground determines the forces that the rocket must endure to land without damage. I’ve assembled the following table to give rocketeers an easy way to imagine what forces will be at work. You could even use this table to test your rocket, to see if it would survive impacting the ground at 15 fps.
The first column has velocities, the second column has height. If a dense body is dropped from a height in column 2, then the body will be traveling at the velocity in column 1 when it hits the ground.
Example, you have a chute that will give your rocket a 16 fps descent rate under the chute. Look at column 1, find 16 fps in column 1. In column 2, you will see the height listed as 4’. Descending at 16 fps is roughly the same as being dropped from 4’ in the air. If you believe you could safely drop your rocket 4’ without damage, then 16 fps is fine.
| Velocity | Distance |
|---|---|
| 5 fps | 0’ 5” |
| 6 fps | 0’ 7” |
| 7 fps | 0’ 9” |
| 8 fps | 1’ 0” |
| 9 fps | 1’ 3” |
| 10 fps | 1’ 7” |
| 11 fps | 1’ 11” |
| 12 fps | 2’ 3” |
| 13 fps | 2’ 8” |
| 14 fps | 3’ 1” |
| 15 fps | 3’ 6” |
| 16 fps | 4’ 0” |
| 17 fps | 4’ 6” |
| 18 fps | 5’ 1” |
| 19 fps | 5’ 8” |
| 20 fps | 6’ 3” |
| 21 fps | 6’ 11” |
| 22 fps | 7’ 7” |
| 23 fps | 8’ 3” |
| 24 fps | 9’ 0” |
| 25 fps | 9’ 9” |
| 26 fps | 10’ 7” |
| 27 fps | 11’ 5” |
| 28 fps | 12’ 3” |
| 29 fps | 13’ 2” |
| 30 fps | 14’ 1” |
Submitted by: David Urbanek