Gust Load Alleviation for Highly Flexible Aircraft

Student : Matt Dillsaver

Sponsor : United States Air Force


Summary:

High Altitude, Long Endurance (HALE) aircraft have become popular for dull, dirty, and dangerous missions. Long on-station times require high L/D ratios, high aspect ratios, high fuel fractions, and low structural weight – which all lead to increased flexibility. This increase in flexibility leads to an increase in loads due to gust encounter and also the possibility of entering in a divergent flight condition due to the gust. This work focuses on characterizing the response of a HALE aircraft to a gust disturbance and then designing a control system to track a desired trajectory, while rejecting a gust disturbance.

  • Develop gust response Linear Quadratic Gaussian (LQG) controller which minimized aircraft root curvature and therefore effectively controlled aircraft deformed shape.

  • Modify Dynamic Inversion (DI) control scheme first proposed by Shearer for trajectory control of Very Flexible Aircraft for use on flying wing aircraft model in presence of gust.

  • Develop Reference Governor (RG) control scheme using closed loop linearized aircraft model with DI controller in the loop to constrain wing curvature during aircraft maneuvering and in the presence of a gust disturbance.

  • Complete studies to characterize the sensitivity of the open and closed loop response to gust disturbances while varying aircraft stiffness properties.

Gust profile from UM/NAST
AeroVironment/NASA Helios experiencing high dihedral due to gust
Source: NASA