What is the relationship between the Drag force and the position function?

[ShadowElite]

I am trying to find the relationship between the position function and the drag force. So far I have D=1/2kv^2 in which k=something*y(t). I am just to find the relationship. I meant to say height.

Edited May 24, 2015 by ShadowElite

[Gaarst]

There is no direct relationship between drag and position but one can be established related to height in idealised atmospheric models.

For low speeds, drag depends on speed, fluid density and other constants as follows:

D = 1/2 * p * A *C_x* V²

A is the area exposed to airflow and C_x is the drag coefficient which depend on the ship itself and its orientation. It is very hard to determine precisely in KSP.

V is the velocity relative to the fluid you're travelling into.

p (rho actually) is the density of the air. It is related to height in static atmosphere as follows:

p = P₀ * e^-z/H / (R_spec * T)

P₀ is the pressure asl (1013.25 hPa for Kerbin and Earth);

z is the height above sea level;

H is the pressure scale height which varies with temperature and therefore altitude but according to the wiki, for Kerbin: H = 5600 m;

R_spec is the specific gas constant (287 J.kg^-1.K^-1 for Kerbin and Earth);

T is the tempeature of air.

TL;DR

D(V,h) = A * V² * e^-h/B with A and B approximately constants

[ShadowElite]

When I said position, i meant height (should have rephrased it). Should be enough to separate from a constant to actual values. thanks

A * V² * e^-h/B

[OhioBob]

p = P₀ * e^-z/H / (R_spec * T)

P₀ is the pressure asl (1013.25 hPa for Kerbin and Earth);

z is the height above sea level;

H is the pressure scale height which varies with temperature and therefore altitude but according to the wiki, for Kerbin: H = 5600 m;

R_spec is the specific gas constant (287 J.kg^-1.K^-1 for Kerbin and Earth);

T is the tempeature of air.

FYI, scale height does not have a constant value as it did in pre-1.0. H = 5600 m was derived as an approximation. Using it does not yield a reliable value of the pressure at a given altitude.