An Innovative Experimental Approach to Lateral-Directional Flying Quality Investigation for Tailless Aircraft

Bowen Nie,Zhitao Liu,Hongxu Ma,Fei Cen,Duoneng Liu,Olivier Sename

doi:10.1109/access.2020.3001913

Abstract

Tailless aircraft suffers from limited yaw control power and poor directional stability inherently. To address these issues in the early design process of a tailless configuration with low costs and risks, this paper presents an innovative experimental approach to control law validation and quantitative flying quality evaluation with a dynamically scaled model mounted on a three degree-of-freedom rig in the wind tunnel. The motion equations of the tailless demonstrator on the rig are derived, and then the comparisons of the lateral-directional flight dynamics between the rig constrained model and the free flight model are carried out. Construction of the control augmentation system for yaw and roll motion is accomplished according to the scale modified criteria of flying qualities. Effectiveness of the designed control law is demonstrated with steady pilot-in-the-loop flights at different airspeeds and angles of attack. The achieved closed-loop flying qualities are evaluated by applying multistep maneuvers for low order equivalent system identification. Whereas severe instability is observed in yaw for the open-loop case, the closed-loop flying quality of the Dutch-roll mode can be improved to level 1 at low angle of attack.

Highlights

Tailless aircraft has regained much research interest over the last decades
This paper aims at exploring the aforementioned dynamic rig to deal with lateral-directional control law validation of the tailless configurations with a particular focus on quantitative evaluation of flying qualities according to the scale modified criteria
An important aspect of modeling is the establishment of an aerodynamic model with data from static and dynamic wind tunnel tests, which reveals challenging yaw stability and control

Summary

INTRODUCTION

Tailless aircraft has regained much research interest over the last decades. A significant reduction of radar signature and fuel consumption makes the tailless configuration one of the most promising candidates for future generation military and civil aircraft [1], [2]. The novelty of this work lies in the first combination of a 3-DOF dynamic rig and dynamically scaled tailless demonstrator in a pilot-in-the-loop (PIL) setup for control law validation and flying quality evaluation in the wind tunnel. A pilot-in-the-loop (PIL) experimental setup is figured out via the integration of wind tunnel, aircraft model, dynamic rig, flight control system and pilot, which can be applied to validate and evaluate the control laws. To the real-time controller, which locates outside the test section and performs control law operation, data acquisition and command allocation at a frequency of 100 Hz. During the tests, the aircraft model is driven by the airflow and surface deflections to perform semi-free flights, namely rotate freely with respect to the center of the spherical joint, while the translational motions are eliminated by the rig. The subscript a, cg, f denotes aerodynamic actions, misalignment of the CG with respect to the center of the spherical joint, and rig friction, respectively

AERODYNAMIC MODELING The aerodynamic moments are generally given by

FLIGHT DYNAMICS ANALYSIS AND COMPARISON

CONTROL LAW DESIGN

EXPERIMENTAL VALIDATION AND EVALUATION

CONCLUSION