How do I calculate how many parachutes I need?

[SiliconPyro]

Up until now, I've either spitballed or just kept things as simple as possible, but I got such a feeling of satisfaction at having learned to calculate my rocket's DeltaV that I'd like to do the same for parachutes. I know there is at least one online calculator, but how does the math actually work in KSP?

Edited September 8, 2014 by norcalairman

[Geschosskopf]

If you're using stock chutes, there's this:

http://ksp.freeiz.com/

If you're using RealChute mod, it comes with its own calculator.

EDIT: Whoops, didn't read closely enough. You want to calculate manually.

In that case, can't help you. There are way too many variables involved for my small brain, and you can't do anything with them uniless you have some understanding of how the weird stock or kluged mod (FAR/NEAR) atmospheres work.

Edited September 8, 2014 by Geschosskopf

[Red Iron Crown]

It's just a drag calculation. You can see the workings here.

[Pecan]

I have a simple pair of simultaneous equations for powered landings on Kerbin:

Drogue Parachutes = 2

deltaV = 100m/s

(seriously; if I've got an engine with 100m/s deltaV, and >1 TWR, I've only ever found a need for two drogues. They slow the ship to 20-40m/s, leaving very little for the engine to do).

[Laie]

Looking at http://forum.kerbalspaceprogram.com/threads/31405-Parachute-guidelines, I suspect that it might simply be (drag/mass)*pressure.

[SiliconPyro]

Thanks for those resources. Looks like I've got some math to do.