A simple means of improving the yaw authority of an intermeshing helicopter.

 Design the fuselage so that it is aerodynamically in balance about its vertical axis. By doing this, a wind from any direction will not yaw the craft. This will be achieved by giving the vertical stabilizer a small chord. This will result in the yaw control (by opposed longitudinal cyclic or differential collective) requiring less rotor authority.

Forward flight requires more directional stability. The trailing edge of the vertical stabilizer has a slat, similar to a rudder but this slat only slide forward and aft. It does not pivot. As the craft's forward velocity increases, this trailing edge extends back. This increases the vertical stabilizer's chord and reduces unwanted yaw. During rearward flight the chord decreased.

The extension of the trailing edge tab might be done by the pressure of the forward velocity and thereby be completely automatic.

A superficial review of US patents and Goggle search reveals nothing on this idea.

1/ The extension of the trailing edge tab might be done by the pressure of the forward velocity. and thereby be completely automatic.

Hinge the tab at its top or bottom. This hinge will have a lateral axis. Have the other end, bottom or top, on a for-aft guide. A bladder will run the full vertical length of the tab and will be located inside the vertical fin. A form of enlarged Pitot tube will provide air pressure, via a restriction in the tube, to the bladder. The large contact area between the bladder and the leading surface of the tab will provide a relatively large force for a small amount of air pressure.

The restriction in the tube is to restrict the speed at which the tab extends and retracts of the tab.

On a T-tail, such as the UniCopter's, this Pitot tube might be located at the juncture of the vertical and horizontal stabilizers. Here it is in the clean air and any small drag that it causes might be beneficial for stability.

2/ Consider two small flaps that are located on each side of the vertical stabilizer. In forward flight, the air pressure causes them to fold back so that their trailing edges touch. Both flaps cannot fold back more than 90º. This will increase the area of the vertical stabilizer. A wind from the rear will cause one or both to swing forward, to not increase the drag.

When the fold back they might also, through appropriate linkages, cause an trailing edge extension to come out of the vertical stabilizer.