Vertical Take-off And Landing Aircraft Research Articles

Controllability Evaluation for VTOL Aircraft in Velocity Envelope: A Distance-Based Metric

This paper introduces an approach for evaluating and quantifying the controllability of vertical takeoff and landing (VTOL) aircraft across various flight states. By employing the controllability theory for linear systems subject to bounded control, this study derives sufficient conditions for the local controllability of the nonlinear VTOL system. These conditions are cohesively integrated with the trimmability condition directly derived from nonlinear dynamics, establishing a comprehensive criterion that facilitates the assessment of both trimmability and controllability of VTOL aircraft. This unified criterion elucidates the relation between desired and achievable specific forces and moments with clear implications for flight mechanics. Building upon this criterion, a distance-based metric is proposed to quantify the controllability, with an optimization-based algorithm developed for its calculation. Focusing on an exemplary lift plus cruise VTOL aircraft, this study investigates controllability variations within the aircraft’s velocity envelope and assesses the impact of rotor failures on controllability. These applications demonstrate the proposed method’s effectiveness in quantifying the controllability of VTOL aircraft in various flight conditions.

Urban Air Mobility Profitability and Operational Sensitivity to Battery and Charging Technology

Designs for electric vertical takeoff and landing (VTOL) aircraft deviate from traditional aircraft designs and include a wide variety of different configurations. Significant uncertainty also exists regarding the status of future battery technology, including energy density and charge rates. This paper presents a simple analytic model to estimate the profitability of an urban air mobility electric VTOL aircraft for a variety of vehicle configurations, battery technology parameters, and economic factors. Five main elements are considered by the framework: aircraft performance, battery technology, mission profile, mission economics, and electrical grid parameters. A sensitivity analysis is provided, comparing the operational performance and profitability of three electric VTOL concepts (lift plus cruise, quadcopter, and side by side), with respect to electrical grid and battery technology factors. The takeoff weight to maximize the number of completed routes or the overall profitability is also examined. Interestingly, results show that these two values do not coincide across the entire design space due to the nonlinearity of the battery life cycle with respect to the depth of discharge, which strongly affects battery replacement cost.

Optimization-Based Control for a Large-Scale Electrical Vertical Take-Off and Landing during an Aircraft’s Vertical Take-Off and Landing Phase with Variable-Pitch Propellers

The UAV industry has witnessed an unprecedented boom in recent years. Among various kinds of UAV platforms, the vertical take-off and landing (VTOL) aircraft with fixed-wing configurations has received more and more attention due to its flexibility and long-distance flying abilities. However, due to the fact that the advance ratio of regular propeller systems during the cruise phase is significantly higher than that during the VTOL phase, a variable-pitch propeller system is proposed and designed which can be applied without additional propulsion mechanisms during both flying stages. Thus, a VTOL aircraft platform is proposed based on the propulsion system constructed of variable-pitch propellers, and appropriate control manners are precisely analyzed, especially during its VTOL phase. As a basic propulsion system, a nonlinear model for variable-pitch propellers is constructed, and an optimization-based control allocation module is developed because of its multi-solution and high-order characteristics. Finally, the objective function is designed according to the stability and energy consumption requirements. Simulation experiments demonstrate that the proposed controller is able to lower energy consumption and maintain the stability of the aircraft while tracking aggressive trajectories for large-scale VTOLs with noises at the same time.

Online Adaptive Dynamic Programming for Optimal Self-Learning Control of VTOL Aircraft Systems With Disturbances

In this paper, a novel online adaptive dynamic programming control algorithm is developed to solve optimal control problems for Vertical Take Off and Landing (VTOL) aircraft systems. Considering the input disturbances of the VTOL systems and adding perturbation interference term to the value function, a robust policy iteration-based ADP method will be introduced to obtain the optimal controller with an approximate optimal control approach. The convergence property is developed to ensure the value function converges to a finite neighborhood of the optimal one. The uniform ultimate boundedness (UUB) of the iterative errors will be strictly proved by Lyapunov stability theory. Finally, we will give mathematical simulation results with the developed method. Compared with sliding mode control (SMC) and linear quadratic regulator (LQR) methods, the simulation results illustrate better overall performance of the novel method. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Note to Practitioners</i> —As an effective tool to solve the optimal control problem of complex nonlinear systems, adaptive dynamic programming (ADP) can effectively overcome the computational problems caused by “curse of dimensionality”. VTOL aircraft system is a typical strongly coupled, underactuate, non-minimum phase system, and the sudden random disturbances will make the control task more challenging. Aiming at the particularity of VTOL system, a new online policy iteration-based ADP algorithm is developed to obtain optimal control with an approximate optimal control strategy in this paper. Decoupling and disturbances can be effectively avoided. convergence will be analyzed to make sure the value function converge to a finite neighborhood of the optimal value function. The UUB property of the system will be proved by the Lyapunov approach.

Design of Bionic Landing Gear with Multi-Link Mechanism for UAVs in Desert Terrain

The terrain in desert areas is rugged and uneven, lacking suitable landing points for unmanned aerial vehicles (UAVs). In addition, sand and dust in the desert can easily damage the internal circuits of propellers through vortexes. To address the high demands for hardness and smoothness of landing sites for vertical takeoff and landing (VTOL) aircraft, as well as the low level of intelligence of traditional landing gear, an optimized biomimetic leg-type terrain-adaptive landing gear based on a multi-link hybrid mechanism was developed for landing in desert areas. First, the design configuration of a single leg was optimized, and the length of each link was calculated accordingly, followed by motion simulations. Secondly, the overall design was developed, and slope landing simulations were conducted on the four-leg mechanism. Research results showed that the optimized multi-link hybrid mechanism terrain-adaptive landing gear was better suited for adapting to desert terrain and could land on sand dune slopes, effectively improving the adaptability of VTOL aircraft in desert areas.

Vertical takeoff and landing aircraft: Categories, applications, and technology

A Vertical Take-Off and Landing (VTOL) aircraft is an aircraft with the ability to take off and land vertically. The ability of removing the need for a runway allows VTOL aircraft to be used for applications that standard aircraft cannot be used for. These applications include military, firefighting, and transportation applications. For the purposes of this paper, helicopters will be considered to be VTOL aircraft, as they fit the general criteria and are among the first to be widely used. VTOL aircraft can be split into several categories, including hybrid VTOL aircraft, VTOL Unmanned Aerial Vehicles, and electric VTOL aircraft. These categories of VTOL aircraft are compared. Famous VTOL aircrafts like Osprey and Harrier are introduced. The technology behind VTOL aircraft is explained, and the ways in which VTOL aircraft can be made useful are reviewed. In addition, the prospect of VTOL aircraft has been made. This paper may offer a reference for the future works about VTOL.

Large Eddy Simulation for Empirical Modeling of the Wake of Three Urban Air Mobility Vehicles

Recent advances in urban air mobility have driven the development of many new vertical take-off and landing (VTOL) concepts. These vehicles often feature original designs departing from the conventional helicopter configuration. Due to their novelty, the characteristics of the supervortices forming in the wake of such aircraft are unknown. However, these vortices may endanger any other vehicle evolving in their close proximity, owing to potentially large induced velocities. Therefore, improved knowledge about the wakes of VTOL vehicles is needed to guarantee safe urban air mobility operations. In this work, we study the wake of three VTOL aircraft in cruise by means of large eddy simulation. We present a two-stage numerical procedure that enables the simulation of long wake ages at a limited computational cost. Our simulations reveal that the wakes of rotary vehicles (quadcopter and side-by-side helicopter) feature larger wake vortex cores than an isolated wing. Their decay is also accelerated due to self-induced turbulence generated during the wake roll-up. A tilt-wing wake, on the other hand, is moderately turbulent and has smaller vortex cores than the wing. Finally, we introduce an empirical model of the vortex circulation distribution that enables fast prediction of wake-induced velocities, within a 2% error of the simulation results on average.

Position and Attitude Tracking Finite-Time Adaptive Control for a VTOL Aircraft using Global Fast Terminal Sliding Mode Control

In this work, the position and attitude tracking finite-time adaptive control problem of a type of vertical take-off and landing (VTOL) aircraft system is studied. Here, the dynamic of the VTOL aircraft is subjected to external disturbances and unknown nonlinearities. Firstly, radial basis function neural networks are introduced to approximate these unknown nonlinearities, and adaptive weight update laws are proposed to replace unknown ideal weights. Secondly, for the errors generated in the approximation process and the external disturbances of the aircraft system, adaptive parameter update laws are presented. After that, based on the designed global fast terminal sliding mode control functions and adaptive update laws, we present the position tracking control laws and the roll angle control law. Then, based on this, the adaptive global fast terminal sliding control laws for the given aircraft system are finally obtained. Meanwhile, the stability of the aircraft control system is proven by using Lyapunov stability theory and designed adaptive control laws. It is not only ensured that the outputs of the aircraft system can track the given trajectories, but also ensured that the tracking errors can converge to approximately zero within a finite time. Finally, the validity of the designed adaptive control laws is verified through three numerical examples. It can be obtained that the finite-time tracking problems of the given aircraft system can be achieved at 18.8766 s and 14.6340 s under the given parameters. The results are consistent with the theoretical analysis. In addition, under the control laws proposed in this work, the aircraft system can achieve tracking after 9.443 s and 9.674 s and the tracking errors are basically close to zero, which is significantly superior to other control methods considered in this work.

Neuroadaptive Dynamic Surface Asymptotic Tracking Control of a VTOL Aircraft with Unknown Dynamics and External Disturbances

This work studies the asymptotic tracking control problem of a vertical take-off and landing (VTOL) aircraft with unknown dynamics and external disturbances. The unknown nonlinear dynamics of the VTOL aircraft are approximated via the introduction of radial basis function neural networks. Then, the weight update laws are designed. Furthermore, the parameter update control laws are presented to deal with the errors generated during the approximation process and the external disturbances of the aircraft system. Moreover, first-order filters are introduced to avoid repeated differentiation of the designed virtual control laws, thereby effectively eliminating the “complexity explosion” problem caused by traditional backstepping control. Based on the application of the neural network control method, dynamic surface control technique, weight update laws and parameter update control laws, neuroadaptive dynamic surface control laws for the aircraft system are finally proposed. Theoretical analysis shows that the proposed control law can ensure that the aircraft system asymptotically tracks the reference trajectories and the tracking errors can converge to a small neighborhood of zero by choosing the appropriate designed parameters. Finally, simulation examples are provided to verify the effectiveness of proposed control laws.

Target Tracking Control of UAV Through Deep Reinforcement Learning

This study presents an innovative reinforcement-learning-based control algorithm for a vertical take-off and landing (VTOL) aircraft under wind disturbances. In our approach, the tracking control problem of the VTOL aircraft is formulated as a Markov decision process, and the appropriate system state, reward function, and soft update method are presented. To improve the control accuracy under wind disturbances, three kinds of wind fields were added in the learning environment to expand the exploration space and simulate the effect of wind disturbances on the flight control. Moreover, to ensure the tracking accuracy and the practical implementation, a quantum-inspired experience replay strategy was developed based on quantum computation theory. In this strategy, the preparation operation scheme was designed to encourage the exploration and speed up the convergence. The depreciation operation method was developed to enrich the sample diversity, which increased the robustness of the controller and allowed the control strategy learned in the numerical simulations to be directly transferred into real-world environments. Numerical simulations, hardware-in-the-loop experiments, and real-world flight experiments were conducted to evaluate the performance and merits of the proposed method. The results demonstrated high accuracy and effectiveness and good robustness of the proposed control algorithm in terms of standoff target tracking control and flight stability.

A smooth control allocation method for a distributed electric propulsion VTOL aircraft test platform

AbstractDistributed electronic propulsion (DEP) aircraft with vertical take‐off and landing (VTOL) ability mostly equipped with multiple redundant tiltable propulsors, which are used to provide not only thrusts, but also control torque in all flight mode. The features make the control allocation problem of these aircraft both complex and important. Therefore, this paper proposes: (і) a prototype platform for DEP VTOL aircraft that allows researchers to design and analyse control allocation strategies, and (іі) a uniform hierarchical control allocation method that can be adapted to both MC and FW modes. The platform contains ten fully actuated thrusters, which are distributed in the scaled geometry of a typical DEP‐VTOL aircraft. The proposed control allocation strategy uses hierarchical structure to avoid high‐dimensional matrix operations for the redundant actuators. The additional constraints on the thrust and tilt angles of the actuators are addressed by adopting cascade generalized inversion (CGI) to force decompensation (FD)‐based methods by a coordinate transformation. A novel smooth strategy through Schur Complement is also presented to achieve steady and smooth transition from MC to FW mode. Finally, the proposed method is implemented in the authors’ novel platform in both simulations and flight experiments to demonstrate its effectiveness and smoothness.

Conceptual design and sizing optimization based on minimum energy consumption of lift-cruise type eVTOL aircraft powered by battery and fuel cell for urban air mobility

In conceptual studies and prototypes of aerial vehicles for Urban Air Mobility, batteries are generally adopted as only energy sources. However, batteries have a long charging time that is not suitable for consecutive flights, and a low energy density that limits the range and flight time of the aircraft. For this reason, the hybrid propulsion solution consisting of a battery and a fuel cell has attracted attention in aviation in recent years. This study proposes the conceptual design of a VTOL (Vertical Take-Off and Landing) aircraft for passenger transportation in metropolitan areas by the synergic optimization of the aircraft configuration and the sizing of the propulsion system aimed at minimizing the power request in cruise. In the proposed conceptual design method, VTOL type aircraft is powered by either the battery or the fuel cell according to the flight phase. A multivariate nonlinear optimization problem using as goal the minimization of the fuel cell size is solved. The optimal values of battery size, wing loading, aspect ratio, endurance speed, aircraft weight, maximum lift coefficient, disk loading, rotor solidity, and zero-lift drag coefficient are determined from the solution of the optimization problem.

Modeling and optimization of the energy system for series hybrid electric fixed-wing VTOL

In this paper, the fixed-wing vertical take-off and landing (VTOL) aircraft is studied. Based on the typical mission profile, the flight process of fixed-wing VTOL aircraft is divided into rotor mode and fixed-wing mode, and the dynamic models of the two modes are established respectively. The power transmission model of the series hybrid electric system is established, the concept of hybridization for power (Hp ) is introduced, and an optimization method of power allocation based on Hp is proposed. The optimization method is verified by simulation, and the results show that, compared with the pure electric energy system, the performance of the optimized hybrid energy system is improved obviously.

Fuzzy Logic-Based Energy Management Strategy of Hybrid Electric Propulsion System for Fixed-Wing VTOL Aircraft

An energy management strategy for a series hybrid electric propulsion system designed for a fixed-wing vertical take-off and landing (VTOL) aircraft is presented in this paper. The proposed method combines an ideal operating line (IOL) and fuzzy logic. Fuzzy logic is used to dynamically and optimally allocate the output power of the generator and the battery pack according to the power requirement of the aircraft and the SOC of the battery pack. The IOL controller is used to optimize the internal combustion engine (ICE) operating point to improve the fuel economy of the system. The detailed aircraft model and energy system model are established. The flight process of a 100 kg scale VTOL aircraft under a typical mission profile is simulated. The simulation results show that running the ICE based on IOL can greatly improve its efficiency The introduction of fuzzy logic to optimize the power allocation of the generator and battery pack improves the overall efficiency of the system. The feasibility and effectiveness of the energy management strategy proposed in this paper are verified, and the design ideas and analysis methods are provided for the energy management of a hybrid electric aircraft.

Minimizing deflection on the yaw axis on VTOL type air-vehicles with three rotors

This study provides an effective solution to the problem of deflection on yaw axes of air-vehicles capable of three-rotor Vertical Take-Off and Landing (VTOL). Most VTOL aircraft are produced with five rotors in national context. Four of these rotors are used for landing and taking off and are positioned to balance each other. The other rotor is positioned to fly with fixed wings. Therefore, no deviation in the yaw axis is experienced during descent-off. Three rotor VTOL configurations are available as an alternative to five rotor VTOL air-vehicles. This study is available through the three rotor VTOL prototypes that we have developed. The biggest drawback of three rotor VTOLs is the instability due to the position of the rotors during takeoff. This instability has been eliminated and three rotor VTOLs have been more advantageous than other configurations.

Blade Shape Optimization and Analysis of a Propeller for VTOL Based on an Inverse Method

With the rapid development of vertical takeoff and landing (VTOL) aircraft, the blade design of a propeller suitable for VTOL aircraft with a wide range of operating conditions has become a challenging and popular task. This paper proposes a multi-objective optimization framework for a VTOL propeller using an inverse design method at the cruising stage, which is developed from the Betz optimum theory and blade element momentum theory (BEMT). Different from passing studies, the maximum thrust-to-weight ratio at hover (MTWRH) is taken as one of the two objectives in this paper, which is closely related to the wind-resistance capability and maneuverability during takeoff and landing. The other objective is the energy consumption of the whole mission profile. A fixed pitch propeller (FPP) and a variable pitch propeller (VPP) are both optimized using the proposed framework for the Vahana A3 tilt-wing aircraft and validated by the computational fluid dynamics (CFD) method. The influences of the level flight energy ratio, hover disk loading and cruising speed toward the optimization result are analyzed, respectively. The results show that the MTWRH has a significant impact on the optimization result both for the FPP and VPP. A comparison between the two propeller forms validates the advantages of the VPP both in energy saving and takeoff maneuverability. The quantitative rules of this advantage with the level flight energy ratio are calculated to provide a reference for choosing the appropriate form. Overall, the methodology and general rules presented in this paper support the propeller optimization and form selection for VTOL aircraft.

Numerical Prediction of Convective Heat Flux on the Flight Deck of Naval Vessel Subjected to a High-Speed Jet Flame from VTOL Aircraft

This study examines the heat flux and convective heat transfer generated when a vertical take-off and landing (VTOL) aircraft takes off and lands on the flight deck of a naval vessel. A procedure for analyzing the convective heat transfer imposed on the deck by the high-temperature and high-velocity impingement of a VTOL jet is described. For the analysis, the jet velocity and the deck arrival temperature were calculated by applying computational fluid dynamics (CFD), assuming that the heat flow is an impingement jet. The relationships between the diameter of the jet, the speed of impingement, and the exhaust temperature of VTOL are introduced to assess the inlet condition. Heat flow was analyzed using CFD techniques, and Reynolds-averaged Navier–Stokes (RANS) and k-ε models were applied to model the turbulent motion. A procedure for evaluating the convection coefficient and convective heat flux from the calculated local velocity and temperature is presented. Simultaneously, a method for compensating the convection coefficient considering the singular velocity at the stagnation point is proposed. Furthermore, the accuracy was verified by comparing the convective heat flux and deck temperature predicted using CFD with the existing experimental studies. Finally, by applying finite element analysis (FEA) based on the thermal-structural interaction, the magnitude of thermal deformation due to conductive temperature and heat flux was presented as a design application of the flight deck.

Sizing and Mission Profile Analysis of the Hybrid-Electric Propulsion System for Retrofitting a Fixed Wing VTOL Aircraft

Hybrid-electric technology can be expected to improve the performance of fixed wing vertical takeoff and landing (VTOL) aircraft. In this paper, we demonstrated a method of retrofitting a single-energy propulsion system prototype with a hybrid-electric propulsion system. Since the hybrid-electric system has several working modes, the optimal design results have strong coupling with mission performance. Therefore, we propose an analysis method of the mission profile to determine the design point. Finally, the payload-range sensitivity is studied. The results show that the hybrid-electric propulsion system can greatly increase the mission profile of aircraft. The analysis method of the mission profile also provides perspective for the hybrid-electric propulsion system design.

Vertiports: Ready for Take-off … And Landing

While aviation has been used in transportation for decades, the use of vertical takeoff and landing (VTOL) aircraft for large-scale, low-cost, green, sustainable, and integrated mobility in populated areas is a new phenomenon. Despite the importance of ground infrastructure for embarkation and disembarkation of passengers, cargo, and mail, questions remain on how these “vertiports” are or should be regulated and how they will relate to existing regulated ground infrastructure such as aerodromes, airports, and heliports. Therefore, several questions arise: what is a vertiport; how do vertiports relate to other aviation infrastructure; what are the legal implications of having different terms; what laws apply to vertiports? This Article seeks to address these questions from a European Union (EU) perspective by looking at the rise of civil VTOL aircraft and the need for vertiports. Following this, the Article analyzes the current and pro-posed legal landscapes in the EU. This analysis shows how vertiports are currently regulated and highlights the steps that still need to be taken. An examination of the different terms that exist and their definitions is also undertaken. This highlights the similarities and differences that exist between the different terms, thus allowing the relevant laws to be appropriately identified and their scope understood. Finally, the Article looks at some of the legal consequences of introducing the term “vertiport” by focusing on specific EU aviation-based regulations. Thus, this shows the real-life implications of the questions posed.

A high-fidelity aeroacoustic simulation of a VTOL aircraft in an urban air mobility scenario

This paper concerns a high fidelity computational approach for the prediction of the acoustic impact of a VTOL vehicle operating in a urban area. The aerodynamic problem is solved with a free-wake vortex lattice boundary element method whereas the challenging acoustic scattering problem by a large urban area is carried out by coupling a Ffowcs Williams and Hawkings approach (FW-H) with a Boundary Element Method (BEM), accelerated with an Adaptive black-box Fast Multipole Method (AbbFMM). This work also demonstrates the set-up of a comprehensive numerical chain for assessing the noise of vertical take-off and landing (VTOL) vehicle during their whole operations meanwhile producing highly accurate noise shielding predictions when they are approaching in proximity of the urban areas.