When the terminal velocity is reached, it requires F=0

So (1/2) CpAv[sup]2[/sup]=mg sin? - ? mg cos? =mg (sin? - ? cos? )

v[sup]2[/sup]=2 mg (sin? - ? cos? )/ (CpA)

For ?=0.1 and 20 degree (?=0.349), (sin? - ? cos? )=0.248, air density p=1.2 kg/m[sup]3[/sup]

which give us v[sup]2[/sup]=4.05 * m/(C A)

The drag coefficient C for a skier is between 1.0-1.1 (http://en.wikipedia.org/wiki/Drag_coefficient)

The area is estimated to be A=0.5*1.7*cos(?)=0.8 then we will have v[sup]2[/sup]=5.06*m

For a skier with mass (80kg) it will give us v=20.1m/s=72.5 km/h.

It is very close to your value 80 km/h.

I will add this drag force to the simulation and update it soon!

C*A=0.11 for an upright body, minimum frontal area

C*A=0.84 for a horizontal body,maximum frontal area

C*A=0.46 for a body in tuck position