X-HALE: A Very Flexible UAV for Nonlinear Aeroelastic Tests

Abstract

The University of Michigan has designed and is currently building an unmanned aerial vehicle, denoted X-HALE, which is aeroelastically representative of very flexible aircraft. The objective of this test bed is to collect unique data of the geometrically nonlinear aeroelastic response coupled with the flight dynamics to be used for future code validation. The aircraft will present specific aeroelastic features (e.g., coupled rigid/elastic body instability, large wing deflection during gust, etc.) that can be measured in flight. Moreover, the airframe construction choice is such that the elastic, inertial and geometric properties can be well characterized. These are requirements driven by the need of the collected data to be used to support validation of coupled nonlinear aeroelastic/flight dynamics codes.

Model-Predictive Gust Load Alleviation Controller for a Highly Flexible Aircraft

“…25 and L g =0.5, are presented in Figs. [17][18][19][20][21][22]. Note that in the absence of GLA the aircraft experienced control surface saturation, and the controller failed to stabilize the plant when it was flying through a discrete gust with L g =0.5.…”

“…The main challenge for a feed-forward controller is the availability of a reliable gust-induced angle of attack measurement. Recently, Dillsaver et al [17] designed a GLA controller for the highly flexible flying wing X-HALE [18]. A linear quadratic Gaussian (LQG) controller was designed and applied to the linear reduced-order model representing the aircraft dynamics.…”

Modeling for Control of Very Flexible Aircraft

“…In order to validate the modeling approach presented by the authors in [11] the same authors have built an unmanned very flexible UAV called X-HALE with flight tests coming in the future. 12,13 For a more comprehensive literature review see Ref. [14].…”

Gust Load Alleviation Control for Very Flexible Aircraft

“…The aircraft's design airspeed was eventually exceeded, causing it to break apart and fall into the Pacific Ocean. 3 The nonlinearities and coupling between aerodynamics and structural modes lead to difficulties in the modeling, simulation and control of HALE aircraft. In fact, one of the recommendations from the Helios accident report was to "develop more advanced, multi-disciplinary (structures, aeroelastic, aerodynamics, atmospheric, materials, propulsion, controls, etc.)…”