I received my Astrobee kit about the same time Randy Thomas’s article, appeared on ROL. I liked what Randy did and decided to “go for it”.
I sewed up a 6’ x-form chute as the article described but my rocket ended up not quite as heavy as Randy’s and the decent rate was a little slow for windy days (12.7 ft./sec.). So I looked at the formula and started to do some “what if’s”. Well, after a time or two of crunching numbers by hand I decided to plug it into Excel and let it do the work. I needed to be able to change chute size and rocket weight. I use the 3:1 (length/width) arm ratio but wanted the ability to play with this as well so I added this in while I was at it. The formula Randy gave for the area is:
Where:
This is the calculations being done in the first part of the form.
The next part is to figure the actual decent rate. The formula used for this is:
Where:
These figures got me close enough for what I wanted even though they were at sea level. I didn’t feel the need to be able to calculate rho for elevation and temperature, this would be nice though.
Submitted by: Steve Gerber