Parachute Opening Force and Inflation Time Calculations

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Well-Known Member
Feb 5, 2012
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Hello again TRF,

Right now I'm working on quantifying some of the parameters surrounding the recovery system on our collegiate sounding rocket team and was hoping to find some insight from some of the experienced members.

I have being trying to use the infinite mass method for analyzing the opening force of the annular parachute but it seems to be very sensitive to certain coefficients that I don't have a lot of reliable data to calculate, including the opening force coefficient c_x and also the force reduction factor (x_1). Here is the simplest form of the equation for those who are wanting to follow along.

F_Opening = c_D * S * q * c_x * x_1

Does anyone have any information on how to calculate the opening force coefficient and force reduction coefficient besides extrapolating graphs?

Maybe I should ask first, does anybody know of a better way to go about finding the force exerted on the rocket by the inflation of the main parachute? I can also use the inflation time to find the max opening force if anyone has any documented method to find this parameter. I appreciate the help everyone.

I'm sure others will have better ideas, but it sounds like an interesting problem. So, here are my two cents ....

You could try dropping the 'chute with a weight and recording altimeter attached. I'm not sure how to do it, but I bet you could calculate the values from knowing the weight and the altimeter's acceleration data.

Making a video of the opening of the 'chute might also help.

-- Roger
Do a search on DTIC there is a "Parachute Recovery Systems Design Manual" from 1991 that may give you some data.
What I want to know is why wasn't there a sounding rocket team when I got my aerospace engineering degree from A&M in the 90's?!? We made some hybrid rocket motors, but never got to launch anything. Grrr.

(Awesome that there's a team now!)
All I know is when you use the personal round laundry - wham! But I hear it is better than the alternative.