be equally applicable to a standard rear fuselage each tail boom 4 has mounted thereon a vertical fin 5 and a tailplane 6 extending outwardly of the aircraft in a conventional aircraft the positions of the fins and tailplane would be fixed as part of the design and would be subject to the disadvantages mentioned above the fin 5 would be generally vertical and the tailplane 6 substantially horizontal including the possibility of the tailplane being fixed at a slight dihedral in the present invention however the tailplane 6 is pivotally mounted on the fuselage so that it may move between vertical and horizontal positions this is illustrated in fig2 with a possible mechanism being shown in fig3 and 4 referring to fig2 there is shown a section through a tail boom 4 the tail boom has a relatively angular section and the tailplane 6 is mounted to the boom in the region of a lower corner of the section the tailplane 6 is fitted to the boom 4 by means of a spigot 7 rotatably mounted in a pair of bearings 8 9 to allow the tailplane to be rotated about an axis 10 extending along the span of the tailplane to provide necessary aerodynamic control rotation of the tailplane 6 is effected by an actuator 11 acting upon a lever 12 fitted to the end of the spigot 7 to enable.