Streamers and OpenRocket

[KzJ]

Hi all, I've got a mockup of a minimum diameter (29mm inner) rocket flying a G75. Using a streamer for recovery, OpenRocket predicts a ground hit of 36 m/s (way too fast). I'm aware from the documentation that OpenRocket treats descending rockets as essentially having no drag coefficient except for that of the recovery device. Based on this, I'm just wondering if from anyone's experience they can tell me if this number is somewhat accurate. If it is, I may have to opt for dual-deploy (not ideal) or delaying the opening of a chute somehow. I've attached the ork file.

 

[MarsLander]

Multiply tube length by outside diameter. Multiply by 4. Divide that by pi. Take the square root.

Make a round parachute in Open Rocket with a diameter = the number you got above. Use a Cd of .75 for that chute. Make the chute 0 mass and deploy at ejection.

That will get you in the ball park...

See page 6, step 3:

https://www.apogeerockets.com/education/downloads/Newsletter361.pdf

 

[waltr]

Here is an Apogee Newsletter about Streamer size.
https://www.apogeerockets.com/education/downloads/Newsletter244.pdf
I did try your .ork file and it seems that the Cd of the streamer is not high enough in the sim.
As Tim states in the news latter, Cd of streamers are not well known.

 

[JoePfeiffer]

I spent some time trying to make sense of the various NAR TR's regarding streamers, and the wind tunnel data in the OR technical documentation, and gave up.

1. You need a much bigger streamer than you would ever guess. At least, much bigger than I would have guessed. The people who have done drop tests of weights with streamers reported them coming in pretty hot.
2. Putting pleats in your streamer makes a *huge* difference. Outweighs all the different material choices I've seen people use. OR doesn't have a way to enter this directly. If you've got a guess about how it affects the streamer Cd you can adjust that, but it's your guess...
3. And the one that made me give up: if the rocket sort of "hangs" by the streamer, OR's estimate that only the streamer's drag matters is pretty good. If it ends up with the body tube "hanging out" horizontally, it adds a lot of extra drag. Guessing which is going to happen seems to be impossible; some of the streamer competitors I talked to told me a particular rocket/streamer combination may do both on successive flights on the same day. This is one that I could add to the streamer model pretty easily, but haven't yet...