Autonomous landing control of highly flexible aircraft based on Lidar preview in the presence of wind turbulence

This paper investigates preview-based autonomous landing control of a highly flexible flying wing model using short range Lidar wind measurements in the presence of wind turbulence. The preview control system is developed based on a reduced-order linear aeroelastic model and employs a two-loop control scheme. The outer loop employs the LADRC (linear active disturbance rejection control) and PI algorithms to track the reference landing trajectory and vertical speed, respectively, and to generate the attitude angle command. This is then used by the inner-loop using H∞ preview control to compute the control inputs to the actuators (control flaps and thrust). A landing trajectory navigation system is designed to generate real-time reference commands for the landing control system. A Lidar (light detection and ranging) simulator is developed to measure the wind disturbances at a distance in front of the aircraft, which are provided to the inner-loop H∞ preview controller as prior knowledge to improve control performance. Simulation results based on the full-order nonlinear flexible aircraft dynamic model show that the preview-based landing control system is able to land the flying wing effectively and safely, showing better control performance than the baseline landing control system (without preview) with respect to landing effectiveness and disturbance rejection. The control system’s robustness to measurement error in the Lidar system is also demonstrated

Probabilistic Robustness Analysis with Aerospace Applications

This thesis develops theoretical and computational methods for the robustness analysis of uncertain systems. The considered systems are linearized and depend rationally on random parameters with an associated probability distribution. The uncertainty is tackled by applying a polynomial chaos expansion (PCE), a series expansion for random variables similar to the well-known Fourier series for periodic time signals. We consider the linear perturbations around a system's operating point, i.e., reference trajectory, both from a probabilistic and worst-case point of view. A chief contribution is the polynomial chaos series expansion of uncertain linear systems in linear fractional representation (LFR). This leads to significant computational benefits when analyzing the probabilistic perturbations around a system's reference trajectory. The series expansion of uncertain interconnections in LFR further delivers important theoretical insights. For instance, it is shown that the PCE of rational parameter-dependent linear systems in LFR is equivalent to applying Gaussian quadrature for numerical integration. We further approximate the worst-case performance of uncertain linear systems with respect to quadratic performance metrics. This is achieved by approximately solving the underlying parametric Riccati differential equation after applying a polynomial chaos series expansion. The utility of the proposed probabilistic robustness analysis is demonstrated on the example of an industry-sized autolanding system for an Airbus A330 aircraft. Mean and standard deviation of the stochastic perturbations are quantified efficiently by applying a PCE to a linearization of the system along the nominal approach trajectory. Random uncertainty in the aerodynamic coefficients and mass parameters are considered, as well as atmospheric turbulence and static wind shear. The approximate worst-case analysis is compared with Monte Carlo simulations of the complete nonlinear model. The methods proposed throughout the thesis rapidly provide analysis results in good agreement with the Monte Carlo benchmark, at reduced computational cost

The Validation and Application of CFD-generated Aircraft Carrier Airwakes for Flight Simulation

This thesis describes an extensive experimental and computational study of the air flow over the UK Royal Navy's Queen Elizabeth Class (QEC) aircraft carriers, including how the air flow will affect aircraft flying operations, particularly rotorcraft. Maritime fixed- and rotary-wing aircraft routinely perform launch and recovery manoeuvres to and from ships at sea, often in challenging environmental conditions. Pilots performing such manoeuvres must contend with ship motion, sea spray, and an unsteady airwake generated by the air flow shedding off the ship’s superstructure. The main aim of the research was to investigate the use of modelling and simulation to improve understanding of the flying environment over the flight deck of the QEC. The unsteady air flow over the QEC was created using Computational Fluid Dynamics (CFD) and incorporated into flight simulators at the University of Liverpool (UoL) and at BAE Systems, Warton. Experimental data to confirm the validity of the computed air flow was obtained from a small-scale experiment in which a 1.4 m long (1:200) scale model of the QEC was submerged in a water channel and Acoustic Doppler Velocimetry (ADV) was used to measure the unsteady flow around the ship. The results show generally very good agreement between the model-scale experiment and CFD. Piloted flight simulation trials were conducted using the UoL’s HELIFLIGHT-R full-motion flight simulator in which a test pilot conducted simulated deck landings of a representative Sikorsky SH-60B Seahawk helicopter to the flight deck of the QEC under a range of wind conditions. Results for aircraft performance and pilot workload are presented. These trials demonstrated how flight simulation could be used to support flight trials and helicopter clearance activities, but also notes that real-world trials data are needed to compare with the simulations before the techniques can be beneficially deployed. A non-piloted simulation technique was also deployed in which the unsteady forces and moments imposed by the air flow onto the helicopter fuselage were quantified; the results were correlated with the pilot workload ratings from the piloted simulation trials. The results have demonstrated how modelling and simulation can be effectively used to inform real-world flight trials. The simulations reaffirmed how important it is that helicopter flight models respond to the very different velocity components that are imposed on different parts of the aircraft by the highly unsteady three-dimensional air flow. Fixed-wing flight models, however, are not typically designed to capture the unsteady moments created during hover in a highly turbulent flow at low speeds. A new aerodynamic model of a fixed-wing aircraft has been developed which uses strip theory to create the overall forces and moments acting on the aircraft when hovering in a ship airwake. The results show the effect of the QEC airwakes on a hovering fixed-wing aircraft and provide recommendations for the number of strips required to accurately capture the effect of the flow

Experimental Investigation of Shrouded Rotor Micro Air Vehicle in Hover and in Edgewise Gusts

Due to the hover capability of rotary wing Micro Air Vehicles (MAVs), it is of interest to improve their aerodynamic performance, and hence hover endurance (or payload capability). In this research, a shrouded rotor conguration is studied and implemented, that has the potential to oer two key operational benets: enhanced system thrust for a given input power, and improved structural rigidity and crashworthiness of an MAV platform. The main challenges involved in realising such a system for a lightweight craft are: design of a lightweight and stiff shroud, and increased sensitivity to external flow disturbances that can affect flight stability. These key aspects are addressed and studied in order to assess the capability of the shrouded rotor as a platform of choice for MAV applications. A fully functional shrouded rotor vehicle (disk loading 60 N/m2) was designed and constructed with key shroud design variables derived from previous studies on micro shrouded rotors. The vehicle weighed about 280 g (244 mm rotor diameter). The shrouded rotor had a 30% increase in power loading in hover compared to an unshrouded rotor. Due to the stiff, lightweight shroud construction, a net payload benefit of 20-30 g was achieved. The different components such as the rotor, stabilizer bar, yaw control vanes and the shroud were systematically studied for system efficiency and overall aerodynamic improvements. Analysis of the data showed that the chosen shroud dimensions was close to optimum for a design payload of 250 g. Risk reduction prototypes were built to sequentially arrive at the nal conguration. In order to prevent periodic oscillations in flight, a hingeless rotor was incorporated in the shroud. The vehicle was successfully flight tested in hover with a proportional-integral-derivative feedback controller. A flybarless rotor was incorporated for efficiency and control moment improvements. Time domain system identification of the attitude dynamics of the flybar and flybarless rotor vehicle was conducted about hover. Controllability metrics were extracted based on controllability gramian treatment for the flybar and flybarless rotor. In edgewise gusts, the shrouded rotor generated up to 3 times greater pitching moment and 80% greater drag than an equivalent unshrouded rotor. In order to improve gust tolerance and control moments, rotor design optimizations were made by varying solidity, collective, operating RPM and planform. A rectangular planform rotor at a collective of 18 deg was seen to offer the highest control moments. The shrouded rotor produced 100% higher control moments due to pressure asymmetry arising from cyclic control of the rotor. It was seen that the control margin of the shrouded rotor increased as the disk loading increased, which is however deleterious in terms of hover performance. This is an important trade-off that needs to be considered. The flight performance of the vehicle in terms of edgewise gust disturbance rejection was tested in a series of bench top and free flight tests. A standard table fan and an open jet wind tunnel setup was used for bench top setup. The shrouded rotor had an edgewise gust tolerance of about 3 m/s while the unshrouded rotor could tolerate edgewise gusts greater than 5 m/s. Free flight tests on the vehicle, using VICON for position feedback control, indicated the capability of the vehicle to recover from gust impulse inputs from a pedestal fan at low gust values (up to 3 m/s)

Identification of a small-scale helicopter dynamic model

The aim of this thesis is to develop a model for flight simulation of a radio controlled aerobatic helicopter, available in the Industrial and Civil Department of the University of Pisa. The purpose of the project is to make the small scale helicopter capable to complete a planned mission in autonomous flight, with automatic take-off and landing and sense and avoid capabilities. In the first part of this work, a non-linear open-loop analytic model of the rotor-craft is developed, with the discussion of hypothesis and possible simplifications. The second part focuses on the identification of the helicopter model parameters, based on a trust region reflective algorithm, in order to evaluate the inertial, aerodynamic and elastic variables introduced in the foregoing section. The accuracy of the developed model is verified by the comparison between responses from the model and flight measurements. In the last part, a simplified model is evaluated in order to define the transfer functions needed for the synthesis of autopilot control laws

Feature Papers of Drones - Volume I

[EN] The present book is divided into two volumes (Volume I: articles 1–23, and Volume II: articles 24–54) which compile the articles and communications submitted to the Topical Collection ”Feature Papers of Drones” during the years 2020 to 2022 describing novel or new cutting-edge designs, developments, and/or applications of unmanned vehicles (drones). Articles 1–8 are devoted to the developments of drone design, where new concepts and modeling strategies as well as effective designs that improve drone stability and autonomy are introduced. Articles 9–16 focus on the communication aspects of drones as effective strategies for smooth deployment and efficient functioning are required. Therefore, several developments that aim to optimize performance and security are presented. In this regard, one of the most directly related topics is drone swarms, not only in terms of communication but also human-swarm interaction and their applications for science missions, surveillance, and disaster rescue operations. To conclude with the volume I related to drone improvements, articles 17–23 discusses the advancements associated with autonomous navigation, obstacle avoidance, and enhanced flight plannin

Aeronautical engineering: A continuing bibliography with indexes (supplement 237)

This bibliography lists 572 reports, articles, and other documents introduced into the NASA scientific and technical information system in February, 1989. Subject coverage includes: design, construction and testing of aircraft and aircraft engines; aircraft components, equipment and systems; ground support systems; and theoretical and applied aspects of aerodynamics and general fluid dynamics