This paper proposes a soft switching mode for electric vertical takeoff and landing (eVTOL) compound-wing unmanned aerial vehicles (UAVs) to achieve a smooth transition between modes. The proposed mode pre-compensates the lift loss with the rotary wing during the deceleration stage before UAV landing. The control law adopted in this paper consists of implicit nonlinear dynamic inversion (NDI) and incremental nonlinear dynamic inversion (INDI). The outer loop (attitude angle loop) control law is based on implicit NDI, while the inner loop (attitude angle rate loop) controller is based on INDI. An extended state observer (ESO) is employed to estimate the angular acceleration. This paper innovates by proposing a soft switching strategy that improves the robustness, safety, and smoothness of the transition for the compound-wing UAV, and applying advanced control law to mode transition design. For the future application of eVTOL aircraft in UAM scenarios, this paper evaluates the smoothness of transition and passenger comfort using normal overload as a physical quantity. The Monte Carlo (MC) simulation results demonstrate that the proposed mode can reduce the peak normal overload by about 89%.

Large-slenderness-ratio (LSR) aircraft exhibit more severe lateral–directional coupling compared with other aircraft, which poses a significant challenge to their flight safety, especially during high-speed maneuvers. Reliable attitude decoupling control is, therefore, essential for LSR aircraft. In this study, a novel control framework that combines incremental nonlinear dynamic inversion (INDI) and extended state observer (ESO) is proposed for supersonic roll maneuver control of LSR aircraft. The ESO is used to estimate the angular acceleration on the basis of an onboard mathematical model. The acceleration estimator based on ESO achieves superior noise reduction compared with the complementary filter (CF) and reduces the onboard model requirement without significantly sacrificing estimation accuracy. Monte Carlo (MC) simulations and frequency–domain analysis demonstrate the effectiveness and robustness of the proposed controller. The sensitivity of parameter uncertainties is also investigated, revealing that the natural frequency of the actuator is the most critical parameter affecting robustness. Finally, flight tests validate the effectiveness of the proposed control structure.

This work provides a feasible solution to the shipborne short landing problem for thrust-vectoring V/STOL vehicles. The short takeoff and shipborne rolling vertical landing strategy was designed in this work. First, the strategy design reference was established by flying performance and mission requirements, including the short takeoff and landing performance, deceleration performance, trajectory stability, velocity stability, and conversion corridor, using attainable equilibrium set methods based on the six dimensions of freedom model of the study object. Then, a piecewise short takeoff landing strategy was designed based on the references, together with a nonlinear dynamic inverse-based control designed frame for strategy execution. Finally, the hardware-in-loop Monte-Carlo simulation was implemented for the strategy feasibility verification. The proposed short takeoff and landing strategy satisfies the shipborne short takeoff and landing mission requirements. The short takeoff shortens the taxiing distance by 40% compared to a normal takeoff. With a 20% perturbance on all model parameters, the touchdown speed can be controlled to 14 ± 1 m/s, and the landing point position can be constrained inside a 5 m radius circle with almost zero lateral displacements.

Large-slenderness-ratio aircraft in which a large portion of the aircraft’s mass is concentrated along its centreline face the problem of severe lateral-directional coupling. Previous research has not fully considered the inertia product when conducting stability analyses of such aircraft. However, neglecting the inertia product may threaten the safety of the aircraft during high-speed flight. This paper investigates the effect of the inertia product on the lateral–directional stability. Two methods, one based on eigenstructure assignment (EA) and the other based on an extended state observer (ESO), are developed for the lateral–directional decoupling of a research large-slenderness-ratio aircraft. Simulation results show that both methods can realize decoupling control. The EA-based control achieves better decoupling performance, whereas the ESO-based control has an advantage in terms of disturbance rejection. Finally, the ESO-based attitude controller is validated through a high subsonic flight test. The decoupling and tracking performance of the attitude control demonstrate the effectiveness and practicality of the ESO-based controller.

The task of achieving a safe and short landing for a flying-wing unmanned aircraft with a three-bearing-swivel thrust vector is highly challenging. The process is further complicated due to the need to switch between multiple control modes, while also ensuring the protection of the flight boundaries from environmental disturbances and model uncertainties to ensure flight safety. To address this challenge, this paper proposes a short-landing strategy that employs mixed control using lift fans, thrust vectors, and aerodynamic control surfaces. The extended state observer (ESO) is integrated into the inner angular rate control and outer sink rate control to account for environmental disturbances and model uncertainties. To ensure flight safety, the attainable linear and angular acceleration is calculated through a trim analysis to determine the command value of velocity and angle of attack during a short landing. Additionally, a flight boundary protection method is employed which includes an additional command value of the angle of attack, resulting in a higher probability of a successful landing. This paper provides a detailed description of the short-landing strategy, including the control objectives for each phase. Finally, a Monte Carlo simulation is conducted to evaluate the effectiveness and robustness of the short-landing strategy, and the landing accuracy is assessed using the circular error probability metric.

At cryogenic temperatures, gases exhibit significant deviations from ideal behaviour, and the commonly employed gas model may inadequately represent the thermodynamic properties of cryogenic gases, subsequently impacting numerical simulations using various thermodynamic and transport models at cryogenic temperatures. The findings of this study reveal that the relative errors in aerodynamic characteristics obtained through different isentropic relations are noteworthy, with the maximum relative error in the drag coefficient reaching 16%. The impact of the equation of state, viscosity model, and thermal conductivity model is relatively minor, with relative errors in the pressure drag coefficient and viscous drag coefficient remaining well below 1%. Nevertheless, the relative error in the skin friction coefficient cannot be ignored due to transonic shock wave/boundary layer interactions. Consequently, when conducting numerical simulations of cryogenic flow, it is imperative to select appropriate gas models to attain precise results.