# Drag Coefficient

Discussion in 'Recovery' started by Magin, Mar 16, 2019.

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1. Mar 16, 2019

### Magin

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what depends on the drag coefficient number?

2. Mar 16, 2019

### Steve Shannon

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Everything moving through a medium.

3. Mar 16, 2019

### jsdemar

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Depends on the meaning of your question: (A) what factors of the rocket design affect the drag coefficient? Or, (B) given a drag coefficient value, what does it affect on the flight characteristics of the rocket?

The shape, size, finish, and dynamic angle of attack will affect the drag coefficient. Larger rockets of the same design will have a lower drag coefficient due to the larger Reynolds number.

The drag coefficient will be lower during powered flight due to the reduced base drag from the propellant gasses.

At transonic speed (Mach 0.8+), there is an increase in drag coefficient.

Regarding question (B), a higher drag coefficient will change the dynamic stability of the rocket. Increased forces from drag will dampen the motion of the rocket. The heating on the surface will also increase with a higher drag coefficient.

https://www.grc.nasa.gov/WWW/K-12/airplane/dragco.html

http://www.interactiveinstruments.com/pdfs/28.pdf

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4. Mar 16, 2019

### Magin

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İf it's so comlex how can ı calculate my parachute diameter?

5. Mar 16, 2019

### Steve Shannon

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The easiest is to ask the parachute manufacturer what weight the parachute is suited for. Most will have some kind of table. Or ask the manufacturer for the Cd of the chute.
The equation, once you know the Cd, is pretty straightforward.

6. Mar 16, 2019

### Magin

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Actually we are trying to make ouw own parachute. We had huge paragliding chutes. we are trying to reshape it as a rocket chutes.

7. Mar 17, 2019

### dhbarr

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This is like the fifth time your team has asked the same question but provided no additional information.

Make it as large as possible, then if it's too slow coming down on the test flight reef up the shrouds. If it's WAY off you'll drift everything.

8. Mar 17, 2019

### Magin

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I know it's the fifth time but ı still dont know how to calculate it. Is drag coefficient depends on the shape of chute and the metarial?

9. Mar 17, 2019

### Handeman

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Download the Parachute Recovery System Design Manual from the Defense Technical Information Center. Just click on the Full Text link to get the .pdf version. Section 5.2 should give you all the answers you need, although I would recommend you read all the applicable sections. There is a lot of great info in there.

10. Mar 17, 2019

### jsdemar

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For a 200# rocket, buy a surplus military man-rated T10D parachute. It is 36ft, with an effective inflated canopy diameter of 25ft and Cd of 1.4. It weighs about 25lb without the harness and bag.

If you are building a large rocket, you must be familiar with OpenRocket or RasAero2. Both are free. You can simulate the descent with your drogue and main parachute guesses, and tweak from there.

11. Mar 19, 2019

### dhbarr

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The 200# number is my fault, I was asking if their bird was within an order of magnitude of the chute they already have.

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