Control strategies for flight in extreme turbulence

The spatial and temporal variations in wind velocity which cause atmospheric turbulence are exacerbated by the topographic and temperature gradients often present at low altitudes. Such gradients exist within the atmospheric boundary layer, which is the region proximate to the ground in which the wind speed varies from near-zero at ground level to the nominal wind speed around 300 m above the ground. With few exceptions for aircraft such as medical evacuation helicopters and crop dusters, low altitude turbulence is a transient problem for manned aircraft in the brief ight phases of take-o and landing. For small unmanned aircraft, however, the entirety of the ight typically exists within an altitude band characterized by high turbulence intensity. Small xed-wing aircraft operating at slow airspeeds are particularly sensitive to turbulence which can generate large disturbances that a ect attitude and ight path stability. UAV control laws are often developed in the absence of signi cant turbulence, since ight tests are often conducted at remote test ranges and on days with benign atmospheric conditions. The environment in which these control laws are developed does not necessarily re ect the expected operating conditions. For new aircraft designs, airworthiness safety review boards may permit ight only in test areas away from structures and population centers. Flight test engineers usually schedule tests for days with calm winds to improve the quality of the aerodynamic and dynamic data measurements. The result of both the expansiveness of typical UAV test sites with the quiescence of the wind conditions is ight at low turbulence intensity which fails to provide sucient excitation to evaluate the disturbance rejection capability of control systems. The objective of the current research is to study how the design of control law parameters a ects the attitude stability and ight path tracking accuracy of xed wing aircraft operating in extreme turbulence. Turbulence is rep