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## Terminal velocity calculation

I've been using Openrocket to try to figure out what speed some rockets would attain if they just came in ballistic without any recovery deployment and they don't seem right. I'm trying to see if a dual deployment scheme could work with the first event long after apogee but I need to know what kinds of speeds I will be dealing with. Does anybody have a different method of figuring out terminal velocity?

2. Terminal velocity is reached when the drag equals the object's weight. Figure out the speed at which the drag on the rocket is equal to the rocket's weight.

The Drag equation is given at:

http://en.wikipedia.org/wiki/Drag_equation

Substitute the weight of the rocket for the result (Fd) in the equation then solve for v (the speed).

-- Roger

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Terminal velocity is reached when the drag equals the object's weight. Figure out the speed at which the drag on the rocket is equal to the rocket's weight.

The Drag equation is given at:

http://en.wikipedia.org/wiki/Drag_equation

Substitute the weight of the rocket for the result (Fd) in the equation then solve for v (the speed).

-- Roger
Right, thanks. I should have been more clear. I was looking for where I could find the various components using openrocket, but I've found them.

4. Originally Posted by k-rad du0d
Right, thanks. I should have been more clear. I was looking for where I could find the various components using openrocket, but I've found them.
To bad you're limiting yourself to openrocket, you could have played with this http://www.grc.nasa.gov/WWW/k-12/airplane/termv.html on the NASA page. It has all the formulas, explains them and has a cool tool for calculating terminal velocity on any planet in the solar system.

5. Open rocket should give you results that are about as accurate as you can get for the rocket speed after apogee, if you set it up so that the deployments happen after apogee like you're thinking. RASAero will do that, too. Either of these sims should be more accurate than a hand calculation, which would have to rely on guesswork for the rocket Cd which will change as a function of velocity.

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Originally Posted by Handeman
To bad you're limiting yourself to openrocket, you could have played with this http://www.grc.nasa.gov/WWW/k-12/airplane/termv.html on the NASA page. It has all the formulas, explains them and has a cool tool for calculating terminal velocity on any planet in the solar system.
I'm definitely not limiting myself to openrocket, which is why I am asking for other methods. Thanks for the link.

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Open rocket should give you results that are about as accurate as you can get for the rocket speed after apogee, if you set it up so that the deployments happen after apogee like you're thinking. RASAero will do that, too. Either of these sims should be more accurate than a hand calculation, which would have to rely on guesswork for the rocket Cd which will change as a function of velocity.
I was more looking for a way to double check. The speeds that openrocket is giving me seem way too slow - like 30-40 mph at ground impact.

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Have you configured the parachute to never deploy? I just tried it, and got an impact velocity in the neighborhood of 180 mph with OpenRocket.

Reinhard

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Originally Posted by Reinhard
Have you configured the parachute to never deploy? I just tried it, and got an impact velocity in the neighborhood of 180 mph with OpenRocket.

Reinhard
I set the delay to 1000 seconds. Is there something else I need to do?

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I set the delay to 1000 seconds. Is there something else I need to do?
This should work - it works for me - or you can set the parachute to deploy never. Is this a rocket with multiple parachutes?

If you want, you can upload the file and I will take a look at it.

Reinhard

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