Tail lift at first seems obvious, but on closer look it is actually quite interesting. When a forward command is initiated, you’ll recall from my forward flight section on Coaxial Quirks that the tail rotor creates lift on the tail, right? Well, when the main rotors are spinning fast enough to enable a hover above ground, this slight lift from the small tail rotor blade is negated by the huge drop in upward lift caused by less of the overall main rotor lift going in that direction.
When the coaxial is near the ground however, specifically on the ground but with the main rotors turning, this lift is enough to raise the overall height of the heli, as can be seen in the picture to the side. With the tail propeller off, this heli would be on the ground level, but the lift combined with the skids pushing on the ground enables the heli to move forward even though pushing it on the ground may not enable this. The tail propeller in effect supplements the lift and forward thrust of the main rotors.