According to the formula from
, the air drag force is equal to Cd*Ap*[b]rho[/b]*V[sup]2[/sup]/2.
You forgot the air density term which is 1.2

I used g=10 m/s[sup]2[/sup] in the previous version. It will be changed to 9.8 m/s[sup]2[/sup]

Another smaller difference was due to I added another cos? in the air drag force:

I am going to remove the cos? and change it to

From the formula:
sqrt(60*9.8*(sin(c)-cos(c)*0.1)*2/0.84/1.2)*3.6=61.24 km/h
From the latest version : the simulation give 61.2 km/h

P.S. I am still working on another case, however, there are so many adjustable parameters that I have not found a good way to model the  new case.