FLIGHT DYNAMICS AND MODEL BASED CONTROL FOR FIXED WING UAV DEMONSTRATOR
Creators: name:  V. PENEV 
Publisher: name: Proceedings of  the 9th European Conference for Aerospace Sciences. Lille, France, 27 June - 1 July, 2022
Year: 2022
Subjects: FLIGH DYNAMICS
GNC
AVIONICS

description: Flight control for reentry vehicle is extremely challenging and inspiring due to the combination of nonlinear dynamics, parametric uncertainty and complex constraints. Flight testing of hypersonic vehicles is an expensive effort and it is quite effective to verify such technologies through small-scale flight tests in practical subsonic-speed environments, prior to installation to large-scale vehicles. Thus the scaled-down subsonic flight experiment vehicle was developed in the environment of Simulink. Part of the common problems of flight control system of hypersonic vehicle is usual to specific platforms with subsonic and supersonic velocities. The low cost requirement to test bed limits the following parameters: Size of simulated aircraft wing span, tail span etc. Air speed developed by thrust propeller, lift and drag respectively. Angle of attack and side slip angle. Roll and pitch ranges In spite of low cost requirement the following well known problematic features of hypersonic flight with reasonable average level of fidelity (higher than low cost-low fidelity) will be reproduced: Uncertainty of stability and control derivatives Flexible Aircraft Model Vibrational Model Non-minimum phase behavior of flight path angle dynamics of the system Pulsed roll angle bank maneuver for a hypersonic glider The relationship between the problematic feature (set of aerodynamics parameters) of hypersonic flight and related platform response is determined with one purpose to replace the feature with artificially created response. Usage of that artificially created response will allow using subsonic flight and scaled down vehicle to investigate flight control problems of hypersonic vehicle. There are 3 core elements in the design of flight control system are: Secondary control surfaces position, orientation, dimensions and shape. Those parameters depend on the test bed airframe aerodynamics and requirements for response of system. Primary FLCS (pFLCS) Secondary FLCS (sFLCS) The problematic features could be observed not only in hypersonic flights. It is assumed at very high degree of confidence, that with those restrictions the test bed will not be able to reproduce the required flight conditions with only one pFLCS and primary control surfaces. Because of that it is proposed to use sFLCS and secondary control surfaces which will be able to reproduce the required response. The response generated by secondary control surfaces is called modified open loop system response. The role of pFLCS or tested flight control system is to shape modified open loop system response to desired closed system loop. The proposed sFLCS will be able to reproduce the following well known problematic features of hypersonic flight using following control laws: Adaptive Model based control Inverse dynamics control Gain scheduled Three loop structure Sliding mode control The aim of this research is to build a simulation model of flight mechanics, primary and secondary control systems of fixed wing UAV in Simulink according to the following requirements: Turns with 15 roll angles Flight-path trajectory with -8 and 17 m/s Steady and Leveled flight, Descending and ascending flights at steep and with less inclination trajectories Total weight up to 15 kg Wing span 1.5 to 2.2 m Relevant geometry model was developed in the environment of Tornado VLM. The demonstrator of atmospheric entry vehicles presumes that flight path profile is often determined a priori. That could require massive real-time calculation and precise knowledge of flight dynamics. Instead intuitive and robust MB control is used. Proposed MB approach could be used for: azimuth, bank or pitch control. The concept of Model based control includes two basic steps: design the reference trajectory or response and design the model following controller. The model based control concept works well with proposed approach of using sFLCS and pFLCS. If the primary aerodynamics is minimum phase (or zero dynamics for nonlinear), it could be converted to non-minimum phase response adding non-minimum phase response to sFLCS, wich will be generated by secondary control surface directly. The second option is to use reference model with non-minimum phase response as reference model. That will be again implemented to sFLCS and secondary control surfaces generate appropriate output. During the simulation azimuth demand is changed from 0 to 10 . The advantages of proposed algorithm are: 1. Two-loops autopilot angular position and angular velocity 2. Off-line procedure for tuning the parameters of control complete search for optimal solution 3. Robust control to the changes of flight parameters and environment