Math for testing chutes or anything else??

[Gurthang99]

Earlier, I had posted about testing a parachute. Thru a lot of trial and error, I finally got the contract done.

Now I would like to know if there is math that I can use to reduce trial and error.

Addons or mods are welcome, too, but I am mostly interested in the math.

Here is the original post, if you are curious:

http://forum.kerbalspaceprogram.com/threads/97037-Test-Mk16-Parachute-in-flight-over-Kerbin

Edited October 21, 2014 by Gurthang99

[Axelord FTW]

The requirements float a lot and ships are too diverse to make a tool just for that (can be done, too many options, too tedious, less efforts than just testing).

Personally, for parachute tests, I use airplanes. I strap the parachute to a structural pylon and set the stage so it decouples at the same time as the parachute go off so it's doesn't rip the plane in half. I don't even lose the cost of the part because of Debrefunds.

Try it out. Get to the altitude, reach the speed, stage, go land.

In fact, most of my in-atmosphere testing is done this way unless it the testing of a very big engine or something likewise heavy or cumbersome.

Here's my latest semi-working in-flight testbed.

Edited October 18, 2014 by Axelord FTW
clarification

[capi3101]

I'm not sure about the underlying mathematics of it, but for chutes there's always the KSP Parachute Calculator - http://ksp.freeiz.com/

I'm reasonably certain the guy who created the site can explain the principles on which it's based.

As for other parts tests, as a rule it's pretty much trial and error. For engines, you can stick them on the sides of your ship with - if nothing else - a Modular Girder Segment, and set the thrust limiter to zero; you don't have to fuel the thing. It becomes payload dead mass at that point - handled easily through use of the Rocket Equation.

[Sirrobert]

Just bring enough fuel to control you speed by flying sideways

[el_coyoto]

I'm not sure about the underlying mathematics of it, but for chutes there's always the KSP Parachute Calculator - http://ksp.freeiz.com/

I'm reasonably certain the guy who created the site can explain the principles on which it's based.

As for other parts tests, as a rule it's pretty much trial and error. For engines, you can stick them on the sides of your ship with - if nothing else - a Modular Girder Segment, and set the thrust limiter to zero; you don't have to fuel the thing. It becomes payload dead mass at that point - handled easily through use of the Rocket Equation.

As an avid user of the awesome KSP Parachute Calculator, I highly approve this post!

<nerd>I even pulled the formulas into an excel file to generate nice graphs...</nerd>

If you plan to land on Kerbin though, you can forego the calculator and do this in your head with a small trick : a small 0.1 t mk16 parachute lands a 0.8 mk1 capsule just fine, which gives us a 1/8 ratio parachute mass to rest of the ship mass. I.e. take your ship mass, divide it by 8 and this gives the mass of parachutes (not drogues) required to soft land on Kerbin.

If you punch these numbers in KSP Parachute Calculator, you'll find a 6 m/s landing speed @ sea level, which is fine and comfy as long as it's Jeb in the capsule, rather than me...

The calculator also works for all the planets and moons with an atmosphere in the Kerbol system.

The thing to note is that the "braking power" (and thus touchdown speed) of a parachute depends on its mass x drag coefficient and atmospheric density, which itself is linked to landing elevation and the atmosphere of planet/moon you're landing on. Drogue chutes also work, but have less drag coefficient, so their use is more specialized...

Fly safe!

EDIT : not remembering the maths by heart, but the idea is computing the craft terminal velocity at a given height (landing elevation) with the chute(s) in deployed state, which increases the parachute drag coefficient A LOT (0.22 -> 1) and dramatically increase the overall drag coefficient.

Edited October 20, 2014 by el_coyoto

[Gurthang99]

KSP Parachute Calculator, very nice! Thanks for help, as always.