As a result of inability to carry out completely rational design of the man-machine combination, it is customary for the government agencies that are responsible for the procurement of military airplanes, or for licensing civil airplanes, to specify compliance with certain handling qualities require­ments (e. g. refs. 12.26 to 12.28).

These requirements have been developed from extensive and continuing flight research. In the final analysis they are based on the opinions of research test pilots, substantiated by careful instrumentation. They vary from country to country and from agency to agency, and, of course, are different for different types of aircraft. They are subject to continuous study and modifi­cation in order to keep them abreast of the latest research and design infor­mation.

The purpose of these regulations is to ensure the safety of operation of new aircraft. If the rules are too lenient or incomplete the result can be degraded performance, poor flight safety, and perhaps an inability to complete the intended mission. On the other hand, if the rules are too stringent the penalties can be degraded performance, added complexity, and reduced economic efficiency. When a new aircraft is designed with novel features and per­formance characteristics, the old regulations are not always sufficient to cover the situation, and subsequent prolonged vehicle flight testing is then required before it can be certified. In the past, regulations have merely specified minima for the various aspects of handling qualities. It is anticipated that ongoing research in this field will lead to the specification of optimum values for the various handling qualities parameters and the definition of acceptable ranges for these parameters.

The following is intended to show the nature, not the detail, of typical handling qualities requirements. Most of the specific requirements can be classified under one of the following headings.