Rick Lind

Lyapunov-Based Exponential Tracking Control of a Hypersonic Aircraft with Aerothermoelastic Effects

Hypersonic flightconditionsproducetemperaturevariationsthatcanalterboththestructuraldynamicsand flight dynamics. These aerothermoelastic effects are modeled bya nonlinear, temperature-dependent, parameter-varying state-space representation. The model includes an uncertain parameter-varying state matrix, an uncertain parameter-varying nonsquare (column-deficient) input matrix, and a nonlinear additive bounded disturbance. A Lyapunov-based continuous robust controller is developed that yields exponential tracking of a reference model, despite the presence of bounded nonvanishing disturbances. Simulation results for a hypersonic aircraft are provided to demonstrate the robustness and efficacy of the proposed controller.

Flight Characteristics of Shaping the Membrane Wing of a Micro Air Vehicle

Biologically inspired concepts are rapidly expanding the range of aircraft technology. Consideration is given to merging two biologically-inspired concepts, morphing and micro air vehicles, and the resulting flight characteristics are investigated. Specifically, wing shaping is used to morph the membrane wings of a micro air vehicle. The micro air vehicle has poor lateral control because hinges, and consequently ailerons, are difficult to install on a membrane wing. Instead, a set of torque rods, aligned along the wings, are used to twist the membrane and shape the wing. The resulting morphing is shown to provide significant control authority for lateral dynamics. A set of flight tests are undertaken to determine the flight characteristics by commanding pulses and doublets to the control actuation. The vehicle demonstrates excellent roll performance in response to wing shaping. Futhermore, the vehicle demonstrates several types of spin behavior related to combinations of elevator deflection and the wing shaping.

Vision-Based State Estimation for Autonomous Micro Air Vehicles

plane. This paper explores both of these robustness issues using results from a micro air vehicle simulation model developed at the NASA Langley Research Center. In particular, a hierarchy of dynamic models, ranging from a random walk model to a high-fidelity nonlinear micro air vehicle model, is employed in the Kalman filter for a simulated micro air vehicle trajectory with varying levels of measurement noise. It is demonstrated that the visionbased measurement updates in the filter are capable of compensating for significant modeling errors and filter initialization errors. As would be expected, superior overall results are achieved using higher-fidelity dynamic modelsintheKalman filter.Theworkpresentedinthispaperrepresentsthe firststeptowardtheultimateobjectiveof incorporating vision-based state estimation into the design of autonomous flight control systems for micro air vehicles operating in urban environments.

ROLL CONTROL FOR A MICRO AIR VEHICLE USING ACTIVE WING MORPHING

A micro air vehicle is a ight system being designed for operation within urban environments. Such vehicles are small and highly agile but often have limited control authority. This paper investigates the use of morphing as an effector to provide control authority. Simple mechanisms for morphing are designed to twist the wings of a 24 in vehicle and to curl the wings of a 12 in vehicle. Flight tests show the morphing is an excellent strategy to command roll maneuvers. The resulting vehicles are relatively easy to y and consequently are suitable for autopilot design and mission deployment.

Match-Point Solutions for Robust Flutter Analysis

The computation of robust e utter speeds presents a signie cant advancement over traditional types of e utter analysis. In particular, π-method analysis is able to generate robust e utter speeds that represent worst-case e ight conditions with respect to potential modeling errors. Robust e utter speeds may be computed using a model formulation that has been previously presented; however, that formulation has limitations in its ability to generate a match-point solution. A model formulation is introduced for which π-method analysis is guaranteed to compute a match-point solution. The match-point solution is immediately realized by analyzing a single model so the computation time is reduced from the previous approach that required iterations. Also, the solution is able to consider parametric uncertainty in any element, whereas the previous formulation did not consider mass uncertainty. The match-point formulation is derived by properly treating the nonlinear perturbations and uncertainties that affect theequation of motion. TheAerostructures Test Wing isused to demonstrate thatthe π-method analysis computes match-point e utter speeds using this new formulation.

Flutterometer: An On-Line Tool to Predict Robust Flutter Margins

Robust eutter margins can be computed for an aeroelastic model with respect to an associated uncertainty descriptionthatdescribes modelingerrors. Anon-lineimplementationtocomputetheserobustmarginsisconsidered. The on-line approach generates uncertainty descriptions at test points and can account for time-varying errors in themodel.A eutterometer isintroduced as an on-linetool toindicateameasure ofdistancetoe utterduringaeight e utter test. Suchatool is formulated based on robust euttermargin analysis. A e ight test of an F/A-18 is simulated todemonstrate theperformance ofthee utterometer.Thistool isclearly more informativethantraditional tracking of dampingtrends and provides accurate information about the true eutter margin throughout the e ight test. The simulation demonstrates characteristics of the eutterometer that could improve eight test efe ciency by increasing safety and reducing eight time for envelope expansion.

Flight Testing and Response Characteristics of a Variable Gull-Wing Morphing Aircraft

Contemporary morphing designs are focused towards enabling a vehicle to transition from one distinct flight regime to another. Such a change often requires highly complex morphing that is designed to address both aerodynamic performance and handling criteria. The University of Florida has developed a morphing demonstrator to investigate the effect of a biologically-i nspired gull-wing morphing on the flight characteristics of a small aircraft. The vehicle, equipped with sensors and data logging devices, is flight tested using a variety of maneuvers and techniques. The flight data from several mor phing conditions is analyzed to determine the extent of the change in the dynamic properties. Modeling of the lateral-directional dynamics indicates that gull-wing morphing has a considerable effect on the handling qualities and stability.

Flight Dynamics of a Morphing Aircraft Utilizing Independent Multiple-Joint Wing Sweep:

Morphing, which changes the shape and configuration of an aircraft, is being adopted to expand mission capabilities of aircraft. The introduction of biologically-inspired morphing is particularly attractive in that highly-agile birds present examples of aerodynamically-effective shapes. This paper introduces an aircraft with a multiple-joint design that allows variations in sweep to mimic some shapes observed in birds. These variations are independent on the left and right wings along with on the inboard and outboard sections. The aircraft is designed and analyzed to demonstrate the range of flight dynamics which result from the morphing. In particular, the vehicle is shown to have enhanced turning capabilities and crosswind rejection which are certainly critical metrics for the urban environments in which these aircraft are anticipated to operate.

Investigation of Membrane Actuation for Roll Control of a Micro Air Vehicle

A class of micro air vehicles uses a flexible membrane wing for weight savings and passive shape adaptation. Such a wing is not amenable to conventional aileron mechanisms for roll control, due to a lack of internal wing structure. Therefore, morphing (in the form of asymmetric twisting) is implemented through the use of a torque-actuated wing structure with thousands of discrete design permutations. A static aeroelastic model of the micro air vehicle is developed and validated to optimize the performance of the torque-actuated wing structure. Objective functions include the steady-state roll rate and the lift-to-drag ratio incurred during such a maneuver. An optimized design is obtained through the use of a genetic algorithm presenting significant improvements in both performance metrics compared with the baseline design.

Nonlinear Aeroelastic/Aeroservoelastic Modeling by Block-Oriented Identification

The investigation of aeroelastic/aeroservoelastic stability through flight testing is an essential part of aircraft certification. The stability boundary prediction is especially difficult when the instability is associated with nonlinearities in the dynamics. An approach is presented for the characterization of the nonlinear dynamics by noniterative identification algorithms. Two different block-oriented nonlinear models are considered to augment existing linear models with nonlinear operators derived by analyzing experimental data. Specifically, focuse is placed on the identification of Hammerstein or Wiener block-oriented models from a N-point data record {¯k, ¯ yk} N = 1 of observed input‐output measurements from an aeroelastic/aeroservoelastic system. Central in the identification of block-oriented models is the use of an a priori set of orthonormal bases tuned with the dynamics of the aeroelastic/aeroservoelastic system. In both cases, a method is proposed to generate the orthonormal bases that is based on the cascade of input-normal balanced state-space realizations of all-pass filters. Case studies with a simulated structurally nonlinear prototypical two-dimensional wing section and actual F/A-18 active aeroelastic wing ground vibration test data are presented.