Flight Stability of Rigid Wing Airborne Wind Energy Systems

The flight mechanics of rigid wing Airborne Wind Energy Systems (AWESs) is fundamentally different from the one of conventional aircrafts. The presence of the tether largely impacts the system dynamics, making the flying craft to experience forces which can be an order of magnitude larger than those experienced by conventional aircrafts. Moreover, an AWES needs to deal with a sustained yet unpredictable wind, and the ensuing requirements for flight maneuvers in order to achieve prescribed control and power production goals. A way to maximize energy capture while facing disturbances without requiring an excessive contribution from active control is that of suitably designing the AWES craft to feature good flight dynamics characteristics. In this study, a baseline circular flight path is considered, and a steady state condition is defined by modeling all fluctuating dynamic terms over the flight loop as disturbances. In-flight stability is studied by linearizing the equations of motion on this baseline trajectory. In populating a linearized dynamic model, analytical derivatives of external forces are computed by applying well-known aerodynamic theories, allowing for a fast formulation of the linearized problem and for a quantitative understanding of how design parameters influence stability. A complete eigenanalysis of an example tethered system is carried out, showing that a stable-by-design AWES can be obtained and how. With the help of the example, it is shown how conventional aircraft eigenmodes are modified for an AWES and new eigenmodes, typical of AWESs, are introduced and explained. The modeling approach presented in the paper sets the basis for a holistic design of AWES that will follow this work.

Design of sliding mode flight control system for a flexible aircraft

The evolution of large transport aircraft is characterized by longer fuselages and larger wingspans, while efforts to decrease the structural weight reduce the structural stiffness. Both effects lead to more flexible aircraft structures with significant aeroelastic coupling between flight mechanics and structural dynamics, especially at high speed, high altitude cruise. The lesser frequency separation between rigid body and flexible modes of flexible aircraft results in a stronger interaction between the flight control system and its structural modes, with higher flexibility effects on aircraft dynamics. Therefore, the design of a flight control law based on the assumption that the aircraft dynamics are rigid is no longer valid for the flexible aircraft. This paper focuses on the design of a flight control system for flexible aircraft described in terms of a rigid body mode and four flexible body modes and whose parameters are assumed to be varying. In this paper, a conditional integral based sliding mode control (SMC) is used for robust tracking control of the pitch angle of the flexible aircraft. The performance of the proposed nonlinear flight control system has been shown through the numerical simulations of the flexible aircraft. Good transient and steady-state performance of a control system are also ensured without suffering from the drawback of control chattering in SMC.

Colin James Pennycuick. 11 June 1933—9 December 2019

Colin Pennycuick was almost single-handedly responsible for the successful, and continuing, merger of the engineering and mathematical sciences of aerodynamics and flight mechanics with ornithology, ecology and bird flight behaviour. He developed a mathematical/ aerodynamical/ecological model of bird flight that could explain and predict bird body and wing shapes and sizes, and hence flight behaviour over a broad range of length- and time-scales, for real birds. He sought to bring rigorous quantitative methods to the people, and insisted that no matter how complex and sophisticated a theoretical model may be, unless it showed some improvement and advance in its practical utility, then it was of questionable value. He similarly insisted that model predictions be testable, and that results be openly and quantifiably given. His approach was marked by two distinct characteristics: first he pioneered the use of small aircraft and powered and unpowered gliders to follow soaring and migrating birds in their natural environment, exploiting his top-level pilot skills; second, he invented, designed and built novel instrumentation for making hitherto unheard-of laboratory and field measurements. The most well-known were his tilting wind tunnels, in which birds and bats could be trained to perform steady gliding flight. His intellectually and geographically-broad range of interests and contacts led to his being a giant influence in theoretical and practical bird flight mechanics and behaviour, one that is likely to stay with us for many decades.

Improving a real-time helicopter simulator model with linear input filters

For a broad range of applications, flight mechanics simulator models have to accurately predict the aircraft dynamics. However, the development and improvement of such models is a difficult and time consuming process. This is especially true for helicopters. In this paper, two rapidly applicable and implementable methods to derive linear input filters that improve the simulator model are presented. The first method is based on model inversion, the second on feedback control. Both methods are evaluated in the time domain, compared to recorded helicopter flight test data, and assessed based on root mean square errors and the Qualification Test Guide bounds. The best results were achieved when using the first method.

Expert System for Aerial Vehicle Deployment System Selection

An expert system is a programmable device developed to provide automation for engineering problem solving. It is composed of artificial intelligence modules, subroutine functions, and databases. Under this framework, a design process is proposed to assist the conceptual design of aerial vehicles' deployment systems. The problem is first defined by a set of design requirements for take-off, landing, and cruise. The values are then translated to a set of performance parameters needed for the design process via a newly developed parametric search algorithm. Such parameters are categorised by a fuzzy inference module to determine the most suitable deployment-propulsion system, for conventional and V/STOL vehicles. Through the use of linear and neural network regression, a number of aerodynamic terms are estimated to support flight mechanics analyses, where the optimal take-off and landing thrust vectors are determined. Engine specifications are deduced in terms of unit thrust, weight, bypass ratio and dimension. The design process demonstrates effectiveness in sizing engines for V/STOL operations.

Expert System for Aerial Vehicle Deployment System Selection

An expert system is a programmable device developed to provide automation for engineering problem solving. It is composed of artificial intelligence modules, subroutine functions, and databases. Under this framework, a design process is proposed to assist the conceptual design of aerial vehicles' deployment systems. The problem is first defined by a set of design requirements for take-off, landing, and cruise. The values are then translated to a set of performance parameters needed for the design process via a newly developed parametric search algorithm. Such parameters are categorised by a fuzzy inference module to determine the most suitable deployment-propulsion system, for conventional and V/STOL vehicles. Through the use of linear and neural network regression, a number of aerodynamic terms are estimated to support flight mechanics analyses, where the optimal take-off and landing thrust vectors are determined. Engine specifications are deduced in terms of unit thrust, weight, bypass ratio and dimension. The design process demonstrates effectiveness in sizing engines for V/STOL operations.