Reduced static lateral stability in airplanes

Abstract

Recent flight test experience and simulator studies have shown that the traditional test for static lateral stability, the steady heading sideslip, in some cases may be overly conservative and place unnecessary restrictions on the aircraft operation or design. In addition, effective dihedral need not be positive in all areas of the flight envelope to provide acceptable handling qualities. Positive static lateral stability is desired so that the aircraft will be safe and that the airplane handling characteristics will be "pleasant." The safety requirement stems from a desire for redundancy in the primary control system. However, safety analysis of modern aircraft often show this redundancy without effective dihedral through other means such as aileron trim, roll spoilers, etc. In terms of handling characteristics, positive static lateral stability usually provides for a more favorable rating of flying qualities by pilots. However, tests have shown that acceptable handling qualities are obtained in most areas of the flight envelope even with negative effective dihedral. Development flight testing on recent business jet aircraft have shown that the aircraft can be operated safely without use of the primary roll control system, even though the basic aircraft did not pass the traditional steady heading sideslip test in all configurations. Furthermore, the handling qualities of the aircraft were considered excellent. (Abstract shortened by UMI.)