Helicopter update from Maik:

Helicopter update from Maik:
 More realistic calculation of vortices at the blades and therefore
 real airfoil parameters can be used now (not to be mixed up with the
 vortex ring state which is still not simulated), ground effect is now
 continuous e. g. at buildings, calculating of the rotor in more than 4
 directions, better documentation of the airfoil parameters.