What Drag Coefficient For a Nylon Chute.

[lakeroadster]

What should I be using in Open Rocket as the drag coefficient (cd) for a 18" ripstop nylon parachute? The default is 0.80.

 

[Kelly]

The material used (nylon vs plastic, etc.) doesn't really come into play - it's the shape. If it's 18" I'm guessing its probably just a round sheet (parasheet)? In that case, 0.8 or 0.75 is probably about right. For more efficient shapes - like an ellipsoidal - higher numbers are possible.

 

[teepot]

The parachute decent calculators I've seen use .75 cd for round chutes. Rocketman has chutes with .97 cd and 2.2 cd. Not sure about others. I asked Top Flight what the CD of their Cross Fire chutes were and they couldn't tell me because the person I talked to didn't know. I don't think anyone has a CD higher than 2.2. I could be wrong. I've been wrong before.

 

[Joe Rocket 97]

Top Flight has the decent rate on the web site

 

[jmasterj]

Top flight x-type chutes I think are listed at .5.

 

[Handeman]

I wouldn't bother with it too much. Use what you want in the simulation. When it comes time to actually buy a chute for the rocket, use the manufacture's decent rate estimates to select your chute size.

You can always go back into the simulation and adjust the cd so it matches the manufactures estimates.

 

[teepot]

Yes the X forms have a lower CD than regular chutes. There selling point is a straighter decent. They are bulkier too.

 

[Kelly]

I think the word we are looking for here is "descent":

descent: an action of moving downward, dropping, or falling.
decent: conforming with generally accepted standards of respectable or moral behavior.

Although I'm sure there are some pretty decent chutes out there!

 

[sriegel]

For flat sheets, I use 0.75. For ellipsoid (elliptical) canopies, I use 1.5. Both are based on the constructed diameter (what it's supposed to be before any gathering in as it inflates).