Development of pilot-in-the-loop analysis.

PILOTED aircraft, to be effectively used, have always required a satisfactory match of the aircraft characteristics (including vehicle dynamics, control manipulator, stability augmentors, displays, etc.) with the controller properties of the human pilot. An agreeable marriage is not intrinsically achieved in the design process, so the provision of proper aircraft flying qualities has often posed serious problems which the designer must solve. Until fairly recently these solutions relied very heavily on intuitive cutand-try procedures. Over the years this approach fostered many of the adventures and uncertainties of flight testing. The desire to handle aircraft stability and control problems in a more analytical fashion was recognized long ago. For example, before World War II Koppen stated: Since the controlled motion of an airplane is a combination of airplane and pilot characteristics, it is necessary to know something about both airplane and pilot characteristics before a satisfactory job of airplane design can be done. But the central difficulty in accomplishing a pilot/vehicle analysis was recognized earlier still. For example, W. Crowley and Sylvia Skan remarked in a 1930 Aeronautical Research Committee report: A mathematical investigation of the controlled motion is rendered almost impossible on account of the adaptability of the pilot. Thus if it is found that the pilot operates the controls of a certain machine according to certain laws, and so obtains the best performance, it cannot be assumed that the same pilot would apply the same laws to another machine. He would subconsciously, if not intentionally, change his methods to suite the new conditions, and the various laws possible to a pilot are too numerous for a general analysis. Actually, matters are even worse than Crowley and Skan recognized; for while much of the pilot's dynamic behavior is governed by the aircraft dynamics, many additional factors also affect his properties.