Nominal Flight Conditions Research Articles

Modelling and Simulation of a Fault-Tolerant Flight Control System

This paper describes the results of an attempt to develop a modelling and simulation environment for the closed-loop dynamics of the NASA Intelligent Flight Control System F-15 aircraft. Emphasis was placed on the modelling of fault tolerance capabilities for the aircraft flight control system. Failures of the primary control surfaces are simulated for the most common failure scenarios, which are actuator blockage with and without a missing portion of the control surface. The controller featured in the flight control system has an optimal “feedforward and feedback” architecture to provide desirable handling qualities at nominal flight conditions while retaining good performance at post-failure conditions. The parameters within the control laws are updated using an online real-time parameter identification scheme based on the Fourier Transform Regression method. The desirable performance and utility of the entire scheme are illustrated through numerical simulations in the event of stabilator failure.

Deployment of a flexible beam from an oscillating base

case when implemented judiciously. This example is an adaptive missile autopilot' where the controller measures the missile's acceleration normal to the flight path and seeks to make it follow a commanded acceleration by rotating the missile with tail-fin deflections (the control variable) to create body lift. Instead of being limited by established theory, the prior variances of the (two) unnormalized parameters, which are proportional to h and reflect variability in the flight conditions, were made as large as would empirically allow reasonable behavior at the nominal flight condition, which is Mach 2.0 at 6000 m altitude. The probing control term has little effect then but substantially improves the initial performance for the very different flight condition of Fig. 1 by causing the parameter estimates to converge more quickly to the corresponding nonzero values, which occurs because this control term reduces the uncertainties of these parameters more quickly.

Robust adaptive flight-path reconstruction technique for nonsteady longitudinal flight test maneuvers

Computational schemes are presented that allow accurate reconstruction of the flight path of the longitudinal aircraft motion in real time. The reconstruction of the flight path is formulated as a discrete, linear, time-variant state reconstruction problem that can be solved via Kalman filtering techniques. This imposes some conditions upon the flight test equipment. A reliable square-root covariance filter implementation is chosen and further developed in a fully adaptive flight-path reconstruction scheme. Therefore, the chosen Kalman filter implementation is modified to cope with several practical problems such as the automatic control of the convergence of the Kalman filter recursions, time-varying bias errors on the input signal of the system model used in the Kalman filter, variations in the wind, and the changing aircraft dynamics owing to a change in nominal flight condition. The developed solutions for these problems are all implemented in a numerically stable way, which guarantees the overall flight-path reconstruction scheme to be robust. Furthermore, some special features of the system model are exploited to make the algorithmic implementation very efficient. These different capabilities are highlighted in an experimental analysis using simulated flight test data.

An Auto-Pilot System Design Using Reduced Order Model Reference Adaptive Control

In this paper, the singularly-perturbed design of an auto-pilot system of a high speed fighter aircraft, for the same authors (1985), is modified. The previous suboptimal design based on singular perturbation technique was proper only for aircraft operation near its nominal flight conditions. The new proposed adaptive design would be adequate for all possible changes of aircraft dynamics. The plant with varying parameters, representing aircraft, is controlled to behave nearly similar to a chosen first order reference model. The proposed discrete model reference adaptive control design uses an adaptive algorithm of Suzuki and Takashima (1978), based on augmented error signal concept and Popov's hyperstability theorem. Computer simulation results are presented to demonstrate the usefulness of the proposed design.

The measurement of performance, stability and control characteristics of a high subsonic jet aircraft in non-steady flight conditions employing high accuracy instrumentation techniques

Aircraft lift and drag characteristics can be measured in flight by subtracting the components of engine net thrust along and perpendicular to airspeed from the corresponding components of the total aerodynamic force R.In steady straight flight the flight path angle can easily be measured and consequently the components of R when aircraft weight is known. Measurements in steady-straight conditions, however, are time consuming and furthermore the resulting accuracies are limited due to unavoidable deviations from the nominal straight flight condition.

Numerical Computation of Space Shuttle Laminar Heating and Surface Streamlines

Exact inviscid flowfield codes are used, together with a quasi-three-dimensional boundary-layer analysis, to provide estimates of the windward surface heating and streamline patterns of the shuttle orbiter vehicle under laminar flow conditions. The accuracy and limitations of the methods are established by comparison with available wind-tunnel experiments and with more exact numerical solutions for simple flows. Flight predictions are presented showing the effects of finite-rate (nonequilibrium) chemical reactions, and the effects of varying boundary-layer edge conditions due to the growth of the boundary layer into the inviscid flow (entropy-layer swallowing). Differences between flowfield predictions at wind-tunnel and nominal flight conditions are discussed.