Manuscripts/Mixed Material Beinn Bhreagh Recorder by Alexander Graham Bell, from July 24, 1909 to October 19, 1909
Suppose we wish to steer to starboard, and put the helm in the proper position. Let the machine turn in a wide curve and completely reverse its path. Then the center of the machine, and every portion of the machine for that matter has described a semi-circle in the air.
Now the semi-circle described by a point on the starboard wing is necessarily of smaller diameter than the semi-circle described by the corresponding point on the port wing, and both paths have been traversed in the same time. Hence the velocity of translation of the starboard wing is less than that of the port wing while making the turn; and the supporting power of the starboard wing during the turn is therefore less than that of the port wing.
Now, so long as the machine remains horizontal the vertical rudder at the rear is vertical; but when the machine tips down on the starboard side while making the turn, the rudder at the rear is no longer vertical but is tilted obliquely to starboard. There is then a vertical component in its steering action: It steers downwards as well as to one side.
This diving tendency, induced during a turn, seems to me to be one of the principal causes involved in making the manipulation of a machine difficult during a turn. At the very moment when the starboard wing loses some of its supporting power the head of the machine is steered downwards