Quantcast

Limits on scaling chute sizes?

The Rocketry Forum

Help Support The Rocketry Forum:

boatgeek

Well-Known Member
Joined
Dec 27, 2014
Messages
3,152
Reaction score
1,613
I'm planning one or two x-form chutes for my next project. Coincidentally, the SLI team I'm helping used an x-form drogue on their launch, so I have some really nice descent data*. That is great for my drogue, but I'm not sure if I can scale up as big as my main would need to be. Assuming that Force = constant * A * V^2, where the constant covers both the drag coefficient and air density, I get that my main needs to be about 10 times the area of the drogue, or about 3 times the edge length. That seems like a really big scaling factor. Does that seem reasonable for assuming that the drag coefficient is going to be fairly constant?

Thanks!

* For figuring out the drag force, I was going to assume that the drogue just carried the entire upper airframe weight, since the upper airframe was hanging straight down from the drogue and the fin can was falling fairly flat. Comments appreciated.
 

Bat-mite

Rocketeer in MD
Joined
Dec 5, 2013
Messages
10,986
Reaction score
1,736
Location
Maryland
I'm planning one or two x-form chutes for my next project. Coincidentally, the SLI team I'm helping used an x-form drogue on their launch, so I have some really nice descent data*. That is great for my drogue, but I'm not sure if I can scale up as big as my main would need to be. Assuming that Force = constant * A * V^2, where the constant covers both the drag coefficient and air density, I get that my main needs to be about 10 times the area of the drogue, or about 3 times the edge length. That seems like a really big scaling factor. Does that seem reasonable for assuming that the drag coefficient is going to be fairly constant?

Thanks!

* For figuring out the drag force, I was going to assume that the drogue just carried the entire upper airframe weight, since the upper airframe was hanging straight down from the drogue and the fin can was falling fairly flat. Comments appreciated.
Are you making your chutes? Otherwise, just use the mfg.'s data for the weight of your rocket. I'm probably missing something....
 

boatgeek

Well-Known Member
Joined
Dec 27, 2014
Messages
3,152
Reaction score
1,613
Are you making your chutes? Otherwise, just use the mfg.'s data for the weight of your rocket. I'm probably missing something....
Yes, both chutes will be scratch built. I already have the ripstop, in white, fluorescent orange, and olive green. Not sure what color pattern to use yet, but it'll be visible!
 

Handeman

Well-Known Member
TRF Supporter
Joined
Jan 18, 2009
Messages
7,766
Reaction score
363
Location
Stafford, VA
I think your assumption on the weight when falling is probably pretty good. The spinning/flying fin can doesn't contribute much to the decent rate.

The Cd of a chute is a function of it's shape so it should scale pretty well.
 

Rex R

LV2
Joined
Apr 21, 2010
Messages
6,101
Reaction score
143
I use OR to find the proper size (standard)chute, then divide by 0.8 to get the appropriate size X-form chute.
Rex
 

Bat-mite

Rocketeer in MD
Joined
Dec 5, 2013
Messages
10,986
Reaction score
1,736
Location
Maryland
For kicks, once you have your calculation, you could compare it with TFR's X-form chute Cd and see how it compares.
 

Latest posts

Top