Early Developments in Stability and Control

While scientists and mathematicians in the United States and Europe built the foundations of future advances by developing fundamental aeronautical theory, practical aeronautical designers invented and improved the airplane empirically. As recognized by the Wright brothers, solutions to the stability and control problem had to be found. This chapter presents the largely empirical development of airplane stability and control from the precursors of the Wrights through the end of the first World War. It was only then that aeronautical theory started to have an impact on practical airplane design.

1.1 Inherent Stability and the Early Machines

Pioneer airplane and glider builders who came before the Wright brothers recog­nized the importance of airplane stability. They had discovered that some degree of inherent stability in flight could be obtained with an appropriate combination of aft-mounted tail surfaces (Cayley and Penaud), wing dihedral angle or lateral area distribution (Langley and Lanchester), and center of gravity location (Lilienthal).

However, very little thought had been given to the problem of control except for the provision of horizontal and vertical rudders (Langley et al.). It was commonly held that an airplane should hold its course in the air while the pilot decided what to do next. Then the pilot would deflect the rudder to steer it, more or less in the manner of a boat. Only the Wrights recognized that (1) an airplane has to be banked to turn in a horizontal plane; (2) an interaction exists between the banking or roll control and the yawing motion of an airplane; (3) excessive dihedral effects hinder pilot control unless sideslip is suppressed and makes the machine unduly sensitive to atmospheric turbulence; (4) wings can be stalled, leading to loss in control; and (5) control can be regained after stalling by reducing the angle of attack.

After the Wright brothers, Bleriot and Levavasseur, the constructor and designer of the Bleriot and Antoinette machines, respectively, pioneered in developing tractor monoplanes with normal tail surfaces and wing dihedral angles (Figure 1.1). These two airplanes had a fair amount of inherent stability, unlike the Wright biplanes. They had superior speed, which helped establish the aft tail as the normal arrangement. In fact, the Bleriot and Antoinette machines were the transitional forms that led from the Wright brothers’ biplanes to the famous pursuit airplanes of World War I.