Multi-Axis Inputs for Identification of a Reconfigurable Fixed-Wing UAV

Piotr Lichota

doi:10.3390/aerospace7080113

Abstract

Designing a reconfiguration system for an aircraft requires a good mathematical model of the object. An accurate model describing the aircraft dynamics can be obtained from system identification. In this case, special maneuvers for parameter estimation must be designed, as the reconfiguration algorithm may require to use flight controls separately, even if they usually work in pairs. The simultaneous multi-axis multi-step input design for reconfigurable fixed-wing aircraft system identification is presented in this paper. D-optimality criterion and genetic algorithm were used to design the flight controls deflections. The aircraft model was excited with those inputs and its outputs were recorded. These data were used to estimate stability and control derivatives by using the maximum likelihood principle. Visual match between registered and identified outputs as well as relative standard deviations were used to validate the outcomes. The system was also excited with simultaneous multisine inputs and its stability and control derivatives were estimated with the same approach as earlier in order to assess the multi-step design.

Highlights

It is no doubt that flight safety is an issue of great importance in modern aviation and each risk should be reduced if possible
The flight controls are separately deflected to provide that sufficient amount of diverse information about the object dynamics is stored in the measured flight data. It raises the cost of the experiments, in particular, when the object has multiple flight controls, so, e.g., in the case of an aircraft that uses multiple flight surfaces for reconfiguration, even if the controls are exciting the motion with respect to the same primary axis
The multi-step inputs design was assessed by selecting other type of system identification excitations that allows for simultaneous flight control deflections and comparing the accuracy of the estimates [27]

Summary

Introduction

It is no doubt that flight safety is an issue of great importance in modern aviation and each risk should be reduced if possible. It raises the cost of the experiments, in particular, when the object has multiple flight controls, so, e.g., in the case of an aircraft that uses multiple flight surfaces for reconfiguration, even if the controls are exciting the motion with respect to the same primary axis To solve this issue, it is possible to design special manoeuvres that allow for simultaneous excitations by using multi-step [26] and multisine inputs [21,27], and this is preferable over exciting single surface separately. The linear aircraft model allows for accurately capturing dynamic properties and shortening the optimization time in simultaneous multi-step excitations design This assumption is typically valid in major part of the flight envelope as can be seen e.g., in [25] and it is reflected by the aeronautical standards referring to flight dynamics and control [30,31].

Multi-Step Inputs

Multisine Inputs

System Identification

Results

Conclusions