No description available.

Wind-shear is a spatial or temporal gradient in wind speed and/or direction, and is generally associated with the presence of cold and warm fronts and thunderstorm cells. It is a serious hazard in the terminal stages of flight for all aircraft but for light aircraft in particular. The research work presented in this dissertation concerns the design of a wind-shear detection system which involved the application of estimation theory and digital simulation techniques. The wind-shear detection system was designed after a careful study of the results obtained from a digital simulation of an aircraft landing phase, including the effects of wind-shear.

No description available.

No description available.

The following work is directed towards an evaluation of aircraft that undergo structural shape change for the purpose of optimized flight and maneuvering control authority. Dynamical equations are derived for a morphing aircraft based on two primary representations; a general non-rigid model and a multi-rigid-body. A simplified model is then proposed by considering the altering structural portions to be composed of a small number of mass particles. The equations are then extended to consider atmospheric flight representations where the longitudinal and lateral equations are derived. Two aspects of morphing control are considered. The first is a regulation problem in which it is desired to maintain stability in the presence of large changes in both aerodynamic and inertial properties. From a baseline aircraft model various wing planform designs were constructed using Datcom to determine the required aerodynamic contributions. Based on nonlinear numerical evaluations adequate stabilization control was demonstrated using a robust linear control design. In maneuvering, divergent characteristics were observed at high structural transition rates. The second aspect considered is the use of structural changes for improved flight performance. A variable span aircraft is then considered in which asymmetric wing extension is used to effect the rolling moment. An evaluation of the variable span aircraft is performed in the context of bank-to-turn guidance in which an input-output control law is implemented. / Ph. D.

Control Allocation as it pertains to aerospace vehicles, describes the way in which control surfaces on the outside of an aircraft are deflected when the pilot moves the control stick inside the cockpit. Previously, control allocation was performed by a series of cables and push rods, which connected the 3 classical control surfaces (ailerons, elevators, and rudder), to the 3 cockpit controls (longitudinal stick, lateral stick, and rudder pedals). In modern tactical aircraft however, it is not uncommon to find as many as 10 or more control surfaces which, instead of being moved by mechanical linkages, are connected together by complex electrical and/or hydraulic circuits. Because of the large number of effectors, there can no longer be a one-to-one correspondence between surface deflections on the outside of the cockpit to pilot controls on the inside. In addition, these exterior control surfaces have limits which restrict the distance that they can move as well as the speed at at which they can move. The purpose of Constrained Control Allocation is to deflect the numerous control surfaces in response to pilot commands in the most efficient combinations, while keeping in mind that they can only move so far and so fast. The implementation issues of Constrained Control Allocation techniques are discussed, and an aerodynamic model of a highly modified F-15 aircraft is used to demonstrate the various aspects of Constrained Control Allocation. This work was conducted under NASA research grant NAG-1-1449 supervised by John Foster of the NASA Langley Research Center / Master of Science

Traditional flight control design is based on linearization of the equations of motion around a set of trim points and scheduling gains of linear (optimal) controllers around each of these points to meet performance specifications. For high angle of attack maneuvers and other aggressive flight regimes (required for fighter aircraft for example), the dynamic nonlinearities are dependent not only on the states of the system, but also on the control inputs. Hence, the conventional linearization-based logic cannot be straightforwardly extended to these flight regimes, and non-conventional approaches are required to extend the flight envelope beyond the one achievable by gain-scheduled controllers. Due to the nonlinear-in-control nature of the dynamical system in aggressive flight maneuvers, well-known dynamic inversion methods cannot be applied to determine the explicit form of the control law. Additionally, the aerodynamic uncertainties, typical for such regimes, are poorly modelled, and therefore there is a great need for adaptive control methods to compensate for dynamic instabilities. In this thesis, we present an adaptive control design method for both short-period and lateral/directional control of a fighter aircraft. The approach uses a specialized set of radial basis function approximators and Lyapunov-based adaptive laws to estimate the unknown nonlinearities. The adaptive controller is defined as a solution of fast dynamics, which verifies the assumptions of Tikhonov's theorem from singular perturbations theory. Simulations illustrate the theoretical findings. / Master of Science

Aerospace systems such as aircraft or missiles are subject to environmental and dynamical uncertainties. These uncertainties can alter the performance and stability of these systems. Adaptive control offers a useful means for controlling systems in the presence of uncertainties. However, very often adaptive controllers require more control effort than the actuator limits allow. In this thesis the original work of others on single input single output adaptive control in the presence of actuator amplitude limits is extended to multi-input systems. The Lyapunov based stability analysis is presented. Finally, the resultant technique is applied to aircraft and missile longitudinal motion. Simulation results show satisfactory tracking of the states of modified reference system. / Master of Science

Reduced order modelling has been extensively used in the solution of problems in flight mechanics. In particular the lowest-order attractive due to its simplicity, energy model is but because of the assumptions made (γ = 0.0) is of little use for realtime guidance. The method of matched asymptotic expansions can be used to generate corrections by the use of boundary layer fairings, but this technique is too complex for an onboard-setting. A method suitable for an onboard guidance system is presented which makes use of some of the same ideas, i.e. that the energy determines the optimal altitude and pathangle, and trajectories which do not initially lie on the optimal schedule rapidly fair into it. (The optimal schedule is an Euler solution to the twopoint- -boundary-value-problem, found by a multiple shooting technique) . This transition which occurs instantaneously in the energy model, is approximated by the use of a feedback control law. The gains are determined by numerical differentiation about the nominal optimal path. Once the nominal path and the feedback gains have been found as functions of energy, they are represented using cubic splines for real-time implementation, requiring minimal onboard computaional and storage capabilities. The problem which was studied was to maximise range in symmetric flight with fuel open. Some computational results are presented comparing the paths generated by the feedback law to Euler solutions from the same point. / Doctor of Philosophy

International Telemetering Conference Proceedings / October 25-28, 1999 / Riviera Hotel and Convention Center, Las Vegas, Nevada / To meet challenging constraints on telemetry system weight and volume, a custom Light-Weight Instrumentation System was developed to collect vehicle environment and dynamics on a short-duration exo-atmospheric flight test vehicle. The total telemetry system, including electronics, sensors, batteries, and a 1 watt transmitter weighs about 1 kg. Over 80 channels of measurement, housekeeping, and telemetry system diagnostic data are transmitted at 128 kbps. The microcontroller-based design uses the automotive industry standard Controller Area Network to interface with and support in-flight control functions. Operational parameters are downloaded via a standard asynchronous serial communications interface. The basic design philosophy and functionality is described here.