Flight dynamics analysis and trajectory optimization of some gliding phases
Creators: name:  SEBASTIEN KOLB 
Publisher: name: Proceedings of the Aerospace Europe Conference - EUCASS - CEAS - 2023
Year: 2023
Subjects: PIO
OPTIMAL CONTROL
NONLINEAR ANALYSIS
SAILPLANE
SPACE SHUTTLE

description: As far as the gliding phases are concerned, the specificities of the aircraft flight dynamics and the surrounding aerology must be taken into account seriously, especially since no propulsion is at disposal to cope with possible problems. In this study, several issues are examined. On the one side, pilot induced oscillations of the space shuttle command channel are expertized and on the other side, a performance (range, mean velocity, altitude loss) is maximized for a sailplane in an environment with a given repartition of thermals ( or wind). Even if the study is more applied mathematics oriented, the results are interesting for engineers and pilots since it helps to take in-flight decisions and to make pre-flight preparations. The analysis of some issues coming from nonlinear flight dynamics is accomplished here by means of the bifurcation theory and continuation algorithms. Some nonlinear features are actually due to couplings with pilot reaction here and may imply unexpected events and it is then important to evaluate whether there are dangerous or not. The main topic of this part concerns pilot-aircraft couplings for a configuration with forced oscillations as inputs.4 The application concerns the space shuttle which meets some issues in its gliding phase.11 The analysis of the command channel with a rate-limited actuator reveals the presence of jumps (flying qualities cliffs), indeed a little variation of the input pulsation may imply large variation (of amplitude and phase). According to the describing function method (DFM), a continuation algorithm allows to predict the amplitude (and the phase shift) at the entry of the actuator thanks to the resolution of an harmonic balance equation (HEE) which involves the transfer functions of the different parts and the describing function of the nonlinearity (saturation or rate limiting). Besides another topic is the flight trajectory optimization of a sailplane. When (the mean velocity is) calculated in a stationary environment with only one vertical thermal, it is associated to the so-called MacCready speed, whereas configurations with several thermals raise some questions such as the optimal speeds and the best strategy to adopt (which speed to take or which thermals to target, in which order, etc). Another strategy might be to realize a dolphin-style gliding and keep on flying (in thermals). In this case, optimal control can furnish the best speeds (and altitudes) to follow during a longitudinal flight (in the vertical plane) depending the magnitude distribution of the vertical wind. Finally for such studies, one hope is surely to help pilots to make wise in-flight decisions and to prepare as well as possible the gliding phases taking into consideration the amount of data and their level of precision at disposal but also to compare different scenarios and to avoid unscheduled off-field landing and more generally to diminish soaring risks. The mathematical analysis, optimization and underlying physics are explained in theoretical and practical terms in order to be valuable for mathematicians and aerospace specialists. Introduction Gliding phases are specific in the sense that it is not possible to use thrust. It implies a necessity of carefull handling of the other controls and an obligation to take seriously into account the aerology (and aerodynamics). In this study, two themes are dealt with, the types of aircraft are not the same and the mathematical tools employed neither but all of them present interesting features. Copyright 2023 by S. Kolb. Posted on line by the EU CASS association with permission.