VTOL Aircraft Research Articles

Attitude Tracking Control for VTOL Aircraft with Uncertain Disturbances Based on Adaptive Neural Network ADRC Method

Attitude Tracking Control for VTOL Aircraft with Uncertain Disturbances Based on Adaptive Neural Network ADRC Method

Bird strike analysis of new composite inlet for tilt rotor aircraft

Bird strikes are an important phenomenon to consider when designing and servicing aircraft structures. Most major bird strike incidents result in aircraft propulsion damage. Because an engine is the sole thrust-providing system of an aircraft, the effect of bird strikes on engine inlets and systems must be investigated and mitigated to the maximum extent. Especially in the case of (vertical take-off and landing) VTOL aircraft, such as an aircraft with tilting rotors, this effect is critical from the point of view of the operation, from the point of view of flight mechanics and the overall control of the aircraft. This work aims to propose the proof of resistance of a new composite air inlet for a new tilting rotor aircraft, which is experimentally verified and supported by numerical simulations performed on flat and simple curved test panels. The new, very effective method was used to calibrate the composite material model, which is further used in the following numerical simulations.

Flight Verification of Automatic Flight and Transition System for Lift/Cruise Thrust Type VTOL Aircraft

Flight Verification of Automatic Flight and Transition System for Lift/Cruise Thrust Type VTOL Aircraft

Investigation on the Airworthiness of a Novel Tri-Rotor Configuration for a Fixed Wing VTOL Aircraft

In this paper, a novel tri-rotor configuration is proposed with the goal of granting vertical take-off and landing capabilities to a future concept of tiltrotor, fixed-wing, aircraft while minimizing the overall mass of the propulsive system and the amount of aerodynamic drag developed during horizontal flight. The novelty of the presented configuration is related not only to the thrust vectoring capabilities of all three rotors but also to the constraints surrounding the action of the rear rotor, which will be required to provide thrust during both vertical and horizontal flight stages while drawing power from an internal combustion engine fixed inside the aircraft's fuselage. Another distinctive feature of the proposed configuration is related to the 20/80 thrust distribution which exists between the front and rear rotors respectively in vertical flight, unlike the more conventional approach of having all three rotors evenly loaded. The proposed rotorcraft configuration was then translated into a test vehicle which was subjected to several stages of ground and flight testing, with the ultimate goal of evaluating the airworthiness of this multi-rotor configuration as a concept. This process also encompasses the development of a custom flight control firmware in PX4, required to operate not only this vehicle but also any other multi-rotor or Vertical Take-Off and Landing system with such configuration. Finally, a frequency-response based system identification technique is applied to the collected flight data as to obtain a suitable flight dynamics model for future autopilot tuning.

Full envelope nonlinear flight controller design for a novel electric VTOL (eVTOL) air taxi

AbstractOn-demand urban air transportation gains popularity in recent years with the introduction of the electric VTOL (eVTOL) aircraft concept. There is an emerging interest in short/medium range eVTOL air taxi considering the critical advantages of electric propulsion (i.e. low noise and carbon emission). Using several electric propulsion systems (distributed electric propulsion (DEP)) has further advantages such as improved redundancy. However, flight controller design becomes more challenging due to highly over-actuated and coupled dynamics. This study defines and resolves flight control problems of a novel DEP eVTOL air taxi. The aircraft has a fixed-wing surface to have aerodynamically efficient cruise flight, and uses only tilting electric propulsion units to achieve full envelope flight control via pure thrust vector control. The aircraft does not have conventional control surfaces such as aileron, rudder or elevator. Using pure thrust vector control has some design benefits, but the control problem becomes more challenging due to the over-actuated and highly coupled dynamics (especially in transition flight). A preliminary flight dynamics model is obtained considering the dominant effects at hover and high-speed forward flight. Hover and forward flight models are blended to simulate the transition dynamics. Two central challenges regarding the flight control are significant nonlinearities in aircraft dynamics during the transition and proper allocation of the thrust vector control specifically in limited control authority (actuator saturation). The former challenge is resolved via designing a sensor-based incremental nonlinear dynamic inversion (INDI) controller to have a single/unified controller covering the wide flight envelope. For the latter one, an optimisation-based control allocation (CA) approach is integrated into the INDI controller. CA requires special attention due to the pure thrust vector control’s highly coupled dynamics. The controller shows satisfactory performance and disturbance rejection characteristics. Moreover, the CA plays a vital role in guaranteeing stable flight in case of severe actuator saturation.

Correlation analysis of lift fan lip feature geometry and aerodynamic performance

In hover, the lip of a lift fan plays a crucial role, contributing to nearly half of the lift for the VTOL aircraft power plant. Thus, investigating the geometric parameters that influence lip performance is of significant importance. In this study, four types of lift fan lips were designed, tailored to meet specific application requirements. Numerical analysis, validated through experimental data, was employed to examine the flow field and the geometric factors that lead to variations in lip performance. Based on the findings, the relationship between lip geometric parameters and aerodynamic performance was thoroughly investigated and confirmed. The results demonstrate that, at a rotational speed of 10 000 r/min, the non-dimensional lift and non-dimensional mass flow of the lemniscate lip exhibit improvements of 33% and 9.5%, respectively, compared to lips designed based on NACA65. Among the various lip configurations, it is found that the performance parameters of the lip are optimal when the slope of the inner surface equaled twice the slope of the lemniscate. On the other hand, when the slope deviated from this optimal value, whether greater or lesser, a reduction in lip performance was observed. Specifically, at a rotational speed of 10 000 r/min, the lip designed based on a lemniscate slope could increase the total lift of the lift fan by 5.6% when compared to the lemniscate lip.

Longitudinal Aerodynamic Characteristics of Ducted Fan Propelled Fixed-Wing VTOL Aircraft Hovering in Ground Effect

The aerodynamic performances and control characteristics of vertical takeoff and landing aircraft will be significantly affected by the ground effect during takeoff and landing. The longitudinal aerodynamic characteristics and main flow features of a fixed-wing vertical takeoff and landing aircraft hovering in ground effect are investigated in this paper, using Multiple Reference Frame based numerical simulations. The aircraft is propelled by three ducted fans. Results show that the overall morphology of the flow is characterized by a fountain, ground vortex, reingestion, and recirculation. When the thrust distribution between the front and aft ducted fans changes, the flow features change as well. As the aircraft approaches the ground, the ducted fan thrust decreases, the fuselage lift increases, and the total lift first decreases and then increases. The maximum lift increases by 9.6% and the minimum lift decreases by 3.0% compared with that out-of-ground effect. The magnitude of the drag is about 1% of the lift, which has little influence on the aircraft’s performance. The pitching moment gradually changes from the equilibrium state to a significant nose-up moment. The total power consumed increases at a specific rotational speed.

Secure state estimation and actuator attack reconstruction for cyber‐physical systems based on sliding‐mode observer

AbstractIn this paper, the secure state estimation attack and reconstruction problems are considered for linear cyber‐physical systems (CPSs) under actuator attacks and unknown disturbances. By introducing a continuous sliding mode observer with an exponential reaching law strategy, the dynamic quality of approach motion is greatly improved and the chattering is eliminated. Then by transforming the original system into a special attack channel separation form so that an improved sliding mode observer with disturbance compensation is obtained to solve the secure state estimation problem. In addition, with the obtained observer's information, not only the actuator attack can be reconstructed but also the estimation of the disturbance can be obtained. Meanwhile, the influence of disturbance estimation error on attack reconstruction can be attenuated. Finally, simulations on a VTOL aircraft are presented to verify the effectiveness of the proposed scheme.

A controller management scheme for active fault-tolerant tracking: Linear discrete-time systems

This paper proposes an active fault-tolerant control (FTC) approach based on the controller management and virtual actuator idea for linear discrete-time systems subject to unknown L2-bounded disturbances, input constraint, and time-varying additive actuator faults. The closed-loop faulty system, which includes the modified nominal controller, the fault and state estimator, and the virtual actuator, suppresses the effects of disturbances and faults, while ensuring input-constraint satisfaction. The management of the nominal controller is performed through an online optimization method – in the form of a standard quadratic programming problem – by manipulating the reference input and intervening in the nominal controller evolution. The proposed method proves the input-to-state stability (ISS) criterion of the overall closed-loop faulty system. The problem of minimizing the ultimate bound of the ISS criterion is formulated in terms of tractable linear matrix inequality (LMI) conditions that allow the fault and state estimation errors to converge to a small neighborhood of the origin. To illustrate the capabilities and advantages of the proposed control strategy, comparative simulation results are presented for a flexible joint robotic system, tracking control of a DC motor’s angular velocity, and the multivariable VTOL aircraft.

New Backstepping Control of Nonlinear Uncertain Systems with Application to the Vtol Aircraft

New Backstepping Control of Nonlinear Uncertain Systems with Application to the Vtol Aircraft

Discrete-time Flatness-based Controller Design using an Implicit Euler-discretization

In this contribution, we present a constructive method to derive flat sampled-data models for continuous-time flat systems through an implicit Euler-discretization. We show how the sampled-data model can be used subsequently for a flatness-based controller design, and illustrate our results with the well-known planar VTOL aircraft example.

Cloud-Based Event-Triggered Predictive Control for Heterogeneous NMASs Under Both DoS Attacks and Transmission Delays

A novel compensation control method for heterogeneous multiagent systems under Denial-of-Service (DoS) attacks and transmission delays is investigated in this article. This control method has all the advantages of the cloud-based computation strategy, the adaptive event-triggered strategy, and the predictive control scheme. The adaptive event-triggering mechanism can adjust the event numbers adaptively, the predictive control can reduce or eliminate the negative effects brought out by both DoS attacks and transmission delays actively, while the cloud-based computation strategy can eliminate the negative effects completely as the same as there are no DoS attacks and transmission delays. Through the interval decomposition skill and the augmented system modeling method, the compensated geschlossenes system model is established. Moreover, the joint design for the feedback gain matrices and the event-triggered parameters is implemented. In the simulation part, five VTOL aircraft are used to demonstrate the theoretical results.

Effect of Rotor Tilt on the Gust Rejection Properties of Multirotor Aircraft

In order to operate safely in windy and gusty conditions, multirotor VTOL aircraft require gust resilience. This paper shows that their gust rejection properties can be improved by applying a small amount of fixed outward rotor tilt. Standard aerodynamic models of the rotors are incorporated into two dynamic models to assess the gust rejection properties. The first case is a conceptual birotor planar VTOL aircraft. The dependence of the trim and stability on the tilt angle are analyzed. The aircraft is stabilized using a pole-placement approach in order to obtain consistent closed-loop station-keeping performance in still air. The effect of gusts on the resulting response is determined by simulation. The second case study is for a quadrotor with a 10° outward rotor tilt. The aerodynamic coefficients are analyzed for trimmed station-keeping over a range of steady wind speeds. An LQR controller is used to apply station-keeping that includes integral action, and the gust responses are again obtained using simulation. The results show that the outward rotor tilt causes the aircraft to pitch down into a lateral gust, providing lateral force that opposes the gust and so significantly improving the gust rejection properties.

Preliminary Sizing of Electric-Propulsion Powertrains for Concept Aircraft Designs

The drive towards a greener and more sustainable future is encouraging the aviation industry to move towards increasing electrification of its fleet. The development of electric propulsion technologies also requires new approaches to assess their viability in novel configurations. A methodology is proposed which consists of four sub-procedures; powertrain modelling, performance analysis, aerodynamic modelling, and sizing. This approach initially considers powertrain modelling using AIAA symbol representations, and a review of the available literature establishes state-of-the-art component values of efficiency, specific power, specific energy, and specific fuel consumption. The sizing procedure includes a mission and aerodynamic analysis to determine the energy and power requirements, and it relies on a mass regression model based on full-electric, hybrid, VTOL and fixed-wing aircraft found in the literature. The methodology has been applied to five case studies which are representative of a wide range of missions and configurations. Their predicted masses from the sizing procedure have been validated against their actual masses. The predicted total mass shows generally good agreement with the actual values, and in addition, accurate values for active mass have been predicted. A sensitivity analysis of the sizing procedure suggests that future work may include a more accurate analysis of aerodynamics and mission if the methodology were to be applied for selecting aircraft concepts.

PD control of VTOL aircraft trajectory tracking based on double-loop design

In this design, a VTOL aircraft system is used as the controlled object. Aiming at the trajectory tracking problem of its position and attitude output, a trajectory tracking control method based on double closed-loop PD control is adopted to design. The trajectory tracking system of VTOL aircraft is decomposed into a track tracking subsystem and a roll tracking subsystem. At the same time, a double closed-loop PD control structure based on position outer loop and attitude inner loop is constructed, and a PD controller based on feedforward compensation is designed. The pole assignment method is used to set and select PD parameters. The stability of the double closed-loop system is ensured by the engineering method of making the reaction speed of the inner loop greater than that of the outer loop. Then, MATLAB software is used to simulate whether the control system can track the given trajectory. Simulation results show that this method simplifies the design process of the control system and makes certain that VTOL aircraft can track arbitrary trajectory outputs with three state outputs as soon as possible, thus meeting the needs of underactuated VTOL aircraft for arbitrary trajectory tracking.

A Study on Hover Performance of Ducted Fans for an Unmanned VTOL Aircraft

In this study, ground tests and numerical analysis were performed to verify the hover performance of the second ducted fan model designed by this research team. Shape of the duct inner surface was asymmetric in longitudinal direction, and considering various aspects such as test site or costs for test operation, a 40% scaled-down model of the ducted fan was adopted for this study. Both the results of the tests and the analysis were found to be coherent, and it was verified that the ducted fan was verified to be well designed to achieve the targeted performance. Furthermore, the performance of this ducted fan was compared with that of the symmetric one to determine the effects of the difference in the duct shape on the performance. It was observed that the symmetric ducted fan performs better in hovering flight, although the asymmetric ducted fan was sufficiently satisfied with the design intention.

Design and analysis of solar-powered VTOL aircraft system for surveillance

UAVs today are used for a variety of applications, from recreational aviation to advanced world defense. Aside from a host of applications, modern UAVs are plagued by the age-old problem of limited range, due to battery power. Studies have suggested that more energy is used between the vertical departure phase and the arrival phase. To reduce this, the potential solution can be used in the form of VTOL UAVs introduced into the air. This may reduce the energy lost during direct and indirect climbs and this effectively increases the range. Along with this using a solar powered aircraft will take us towards a sustainable option. In this paper, we did the analysis, calculations and market research of the propulsion system and proposed the best combination of electronics required for the successful flight of a UAV. The design and evaluation of a wing are presented in this paper with combination of solar and battery power. We also aimed at building a vertically launching aircraft to save power. The presented wing is capable of producing a lift of 7kg and can be used for a surveillance aircraft. Key Words: solar-powered, VTOL, aircraft, lift, drag, payload, surveillance

Hover Performance Analyses of Coaxial Co-Rotating Rotors for eVTOL Aircraft

Hover performance analyses of coaxial co-rotating rotors (or stacked rotors), which can be used as lifting rotors for electric VTOL (eVTOL) aircraft, are conducted here. In this study, the rotorcraft comprehensive analysis code, CAMRAD II, is used with the general free-wake model. The generic coaxial co-rotating rotor without the blade taper and built-in twist is considered as the baseline rotor model, and the rotor is trimmed to match a prescribed rotor thrust value. The hover performance, including the rotor power and Figure of Merit (FM), is investigated for various index angles, axial spacings, blade taper ratios, and built-in twist angles. A maximum FM value is obtained near an index angle of 0° and 10° when the axial spacing is below and above 5.27%R, respectively. When the index angle is 0° and axial spacing is 1.44% R, the maximum increments in the FM are 3.03% and 6.06%, respectively, for a rotor with a blade taper ratio of 0.8 and a built-in twist angle of −12°. Therefore, this simulation study demonstrates that the hover performance of coaxial co-rotating rotors can be changed by adjusting the index angle or the axial spacing.

A novel passively coupled VTOL aircraft for arbitrary flying attitude

In this paper we present a novel VTOL aircraft design which evolves from our previous work on passively coupled systems. This can be seen as an improvement over our previous drone topology since the present one allows the main hub of the drone to assume any arbitrary orientation, while the center of mass of the main hub is stabilized at a desired point. This design manages to decouple the movement of the center of mass by the movement of the orientation. Therefore the reference for the center of mass of the main hub is independent by the reference for the orientation of the main hub at any point of the trajectory. We derive in detail the full nonlinear model using D’Alembert’s principle and propose a fully nonlinear control techniques composed of two cascaded controllers. The inner loop controller performs an additional optimization step to assign commands to eight rotors such that six variables are fully controlled. The outer loop controller upon solving a nonlinear algebraic equation provides the required references to the inner loop controller such that a six degrees of freedom reference (trajectory of the c.o.m and attitude of main body) is followed with vanishing error. Simulations of the mathematical model as well the proposed control law for different types of trajectories are also presented.

Modelling Green VTOL Concept Designs for Reliability and Efficiency

All-electric and hybrid-electric aircraft are a future transport goal and a possible ‘green’ solution to increasing climate-related pressures for aviation. Ensuring the safety of passengers is of high importance, informed through appropriate reliability predictions to satisfy emerging flight certification requirements. This paper introduces another important consideration related to redundancy offered by multiplex electric motors, a maturing technology which could help electric aircraft manufacturers meet the high reliability targets being set. A concept design methodology is overviewed involving a symbolic representation of aircraft and block modelling of two important figures of merit, reliability, and efficiency, supported by data. This leads to a comparative study of green aircraft configurations indicating which have the most potential now, and in the future. Two main case studies are then presented: an electric tail rotor retrofitted to an existing turbine powered helicopter (hybrid) and an eVTOL aircraft (all-electric), demonstrating the impact of multiplex level and number of propulsion channels on meeting target reliabilities. The paper closes with a summary of the important contribution to be made by multiplex electric machines, well as the advancements necessary for green VTOL aircraft sub-systems, e.g., power control unit and batteries, to improve reliability predictions and safety further.