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Full-Envelope Flight Control for Compound Vertical Takeoff and Landing Aircraft

Jean-Marie Kai

TL;DR

This work develops a unified nonlinear geometric control framework for compound VTOL aircraft that remains valid across the full flight envelope, eliminating the need for switching between distinct controllers. The approach couples outer translation/velocity guidance with inner attitude and rate control, and employs a high-level transition strategy implemented as a sequence of setpoints to reconfigure from hover to cruise and back. The control laws incorporate a bounded aerodynamic-force model, a blended thrust-vector/torque allocation, and a robust estimation scheme, all validated through Hardware-In-The-Loop simulations and real-flight experiments on a commercially available compound VTOL. The results demonstrate stable, near-ideal tracking and smooth transitions within narrow flight corridors, with proofs of convergence and stability provided in the appendices. This has practical implications for autonomous operation of hybrid VTOLs in UAM contexts and other mission profiles requiring seamless mode transitions.

Abstract

This paper presents a flight control design for compound Vertical Takeoff and Landing (VTOL) vehicles. With their multitude of degrees of controllability as well as the significant variations in their flight characteristics, VTOL vehicles present challenges when it comes to designing their flight control system, especially for the transition phase where the vehicle transitions between near-hovering and high-speed wing-borne flights. This work extends previous research on the design of unified and generic control laws that can be applied to a broad class of vehicles such as hovering vehicles and fixed-wing aircraft. This paper exploits this unifying property and presents an extension for the case of compound VTOL vehicles. The proposed control approach consists of nonlinear geometric control laws that are continuously applicable over the entire flight envelope, excluding the use of switching policies between different control algorithms. A transition strategy consisting of a sequence of high-level setpoints is associated with the flight control laws, it is defined with respect to flight envelope limitations and is applied in this work to a commercially available compound unmanned aerial vehicle. The control algorithms are implemented on a Pixhawk controller, they are evaluated via Hardware-In-the-Loop simulations and finally validated in a flight experiment.

Full-Envelope Flight Control for Compound Vertical Takeoff and Landing Aircraft

TL;DR

This work develops a unified nonlinear geometric control framework for compound VTOL aircraft that remains valid across the full flight envelope, eliminating the need for switching between distinct controllers. The approach couples outer translation/velocity guidance with inner attitude and rate control, and employs a high-level transition strategy implemented as a sequence of setpoints to reconfigure from hover to cruise and back. The control laws incorporate a bounded aerodynamic-force model, a blended thrust-vector/torque allocation, and a robust estimation scheme, all validated through Hardware-In-The-Loop simulations and real-flight experiments on a commercially available compound VTOL. The results demonstrate stable, near-ideal tracking and smooth transitions within narrow flight corridors, with proofs of convergence and stability provided in the appendices. This has practical implications for autonomous operation of hybrid VTOLs in UAM contexts and other mission profiles requiring seamless mode transitions.

Abstract

This paper presents a flight control design for compound Vertical Takeoff and Landing (VTOL) vehicles. With their multitude of degrees of controllability as well as the significant variations in their flight characteristics, VTOL vehicles present challenges when it comes to designing their flight control system, especially for the transition phase where the vehicle transitions between near-hovering and high-speed wing-borne flights. This work extends previous research on the design of unified and generic control laws that can be applied to a broad class of vehicles such as hovering vehicles and fixed-wing aircraft. This paper exploits this unifying property and presents an extension for the case of compound VTOL vehicles. The proposed control approach consists of nonlinear geometric control laws that are continuously applicable over the entire flight envelope, excluding the use of switching policies between different control algorithms. A transition strategy consisting of a sequence of high-level setpoints is associated with the flight control laws, it is defined with respect to flight envelope limitations and is applied in this work to a commercially available compound unmanned aerial vehicle. The control algorithms are implemented on a Pixhawk controller, they are evaluated via Hardware-In-the-Loop simulations and finally validated in a flight experiment.
Paper Structure (32 sections, 1 theorem, 50 equations, 27 figures, 3 tables)

This paper contains 32 sections, 1 theorem, 50 equations, 27 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Control Model
  3. Thrust force
  4. Aerodynamic forces
  5. Torque modeling
  6. Control laws design
  7. Position Control
  8. Altitude Control
  9. Guidance: Trajectory Tracking
  10. Guidance: Path Following
  11. Speed Vector Control
  12. Vertical speed Control
  13. Horizontal speed Control: Velocity Tracking
  14. Horizontal speed Control: Heading Tracking and Speed Regulation
  15. Thrust Vector and Attitude Setpoints Computation
  16. ...and 17 more sections

Key Result

Theorem 1

Consider a vehicle whose translation dynamics is governed by Eq. eq:trans-dyn, where the applied thrust and aerodynamic forces are modeled accoding to Eqs. eq:trans-dyn and eq:fa-2 respectively. Given a desired acceleration vector $\bm a_r$, define the desired body-fixed frame ${\mathcal{B}_r}=\{G,

Figures (27)

  • Figure 1: Inertial frame and body-fixed frame axis.
  • Figure 2: Thrust vectoring representation.
  • Figure 3: Modified body-axis.
  • Figure 4: Acturators configuration for a compound VTOL.
  • Figure 5: Control Architecture.
  • ...and 22 more figures

Theorems & Definitions (1)

  • Theorem 1