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Vertical take-off and landing (VTOL) unmanned aircrafts are the newest and rapidly developing topic which is not only capable of improving Unmanned Aerial Vehicles (UAV) potential but also to create new use cases. This paper proposes a new convertible VTOL concept designed to obtain optimum flight characteristics for monitoring or flying over long objects. The distinctive feature of the proposed design is a combination of a flying wing with a longitudinal bicopter. The aircraft folds the wings down along the main axis of the aircraft during vertical take-offs and landings to descend the center of gravity and increase stability in bicopter mode. The convertible plane maximizes performance during horizontal flight while maintaining vertical take-off and landing capabilities. The design has been implemented in prototype, and the internal systems and the airframe have been designed and manufactured. As a result, the calculated technical characteristics of the UAV including wind resistance capability were described, the principal elements and components of the design were discussed, and the flight tests of the prototype created were conducted and results presented. Furthermore, the advantages and disadvantages of the concept are reviewed and further development of the project is discussed. The conducted work allows us to confirm the assumption that the developed concept can be used for real-world monitoring missions and to continue developing the concept for a full-scale UAV.   [ABSTRACT FROM AUTHOR]

This paper presents the application of a multidisciplinary approach for the preliminary design and evaluation of the potential improvements in performance and environmental impact through the utilization of compressed (CGH2) and liquefied (LH2) hydrogen fuel for a civil tilt-rotor modelled after the NASA XV-15. The methodology deployed comprises models for rotorcraft flight dynamics, engine performance, flight path analysis, hydrogen tank and thermal management system sizing. Trade-offs between gravimetric efficiency, energy consumption, fuel burn, CO 2 emissions, and cost are quantified and compared to the kerosene-fuelled rotorcraft. The analysis carried out suggests that for these vehicle scales, gravimetric efficiencies of the order of 13% and 30% can be attained for compressed and liquid hydrogen storage, respectively leading to reduced range capability relative to the baseline tilt-rotor by at least 40%. At mission level, it is shown that the hydrogen-fuelled configurations result in increased energy consumption by at least 12% (LH2) and 5% (CGH2) but at the same time, significantly reduced life-cycle carbon emissions compared to the kerosene counterpart. Although LH2 storage at cryogenic conditions has a higher gravimetric efficiency than CGH2 (at 700 bar), it is shown that for this class of rotorcraft, the latter is more energy efficient when the thermal management system for fuel pressurization and heating prior to combustion is accounted for. [Display omitted] • A civil tilt-rotor is retrofitted for liquid and gaseous hydrogen fuel. • The hydrogen-fuelled rotorcraft are compared against the kerosene-fuelled counterpart. • Performance and environmental assessment is conducted at payload-range and mission level. • Liquid hydrogen offers higher gravimetric densities but its requirement for heating penalizes performance. [ABSTRACT FROM AUTHOR]

A new robust adaptive mixing control (RAMC) is proposed in order to accomplish trajectory tracking of a tilt-rotor unmanned aerial vehicle (UAV) configuration. This kind of system is a hybrid aerial vehicle that combines advantages of rotary-wing aircraft, like hovering flight and vertical take-off and landing (VTOL), and those of fixed-wing aircraft, as improved forward flight. Although the VTOL and cruise flight regimes present different dynamic behaviors, in this work a unified, highly coupled, nonlinear model is developed to cope with the considered tilt-rotor UAV full flight envelope, that is, the axial flight, hovering, transition/cruise and turning flight. The modeling is performed via Euler–Lagrange formulation considering the tilt-rotor UAV as a multi-body system and taking into account aerodynamic effects and the dynamics of the tilting servomotors. Accordingly, in order to comply with the trajectory tracking requirements and improve the tilt-rotor UAV forward flight, this paper presents a novel robust adaptive mixing controller which is formulated to deal with linear parameter-varying (LPV) systems dependent on not known a priori large parameters but measured or estimated online, and also to provide robustness against unknown disturbances. Additionally, a rigorous closed-loop stability analysis is performed. The controller performance is validated with numerical experiments conducted using a high fidelity simulator developed on Gazebo and Robot Operating System (ROS) platforms. • A tilt-rotor UAV multi-body dynamic model formulated via the Euler–Lagrange approach. • A new robust AMC for polytopic uncertain systems in the state-space. • RAMC synthesis for full flight envelope trajectory tracking of a tilt-rotor UAV. • Stability proof of the new RAMC for the full flight envelope trajectory tracking. [ABSTRACT FROM AUTHOR]

Aeroacoustics radiation is one of the main sources of tilt-rotor aircraft interior noise. In order to reduce the noise radiation on the surface of tilt-rotor aircraft fuselage, an active rotor control technology based on Higher Harmonic Control (HHC) is proposed. Its control effect is verified by simulation and the control mechanism is studied at the same time. Firstly, a tilt-rotor aeroacoustics prediction model is established based on FW-H equation and Beddoes unsteady aerodynamic model. And the accuracy of the above model is verified according to the flight test data of the XV-15 tilt-rotor aircraft. Furthermore, taking XV-15 as the object, a simulation research of rotor aeroacoustics active control is carried out in both airplane mode and helicopter mode. The simulation research reveals that: the HHC can suppress the aeroacoustics radiation of tilt-rotor to the fuselage through the principle of sound pressure cancellation. By applying appropriate control inputs, the maximum aeroacoustics radiation can be reduced by 9.2 dB in airplane mode; and the maximum aeroacoustics radiation can be reduced by 13.5 dB in helicopter mode. [ABSTRACT FROM AUTHOR]

In order to suppress the near field aeroacoustics radiation on the fuselage wall of the tilt-rotor aircraft, a noise suppression method is proposed based on the rotor phase control. Firstly, based on the free wake model and panel method, a tilt-rotor near field aeroacoustics calculation model is established considering the interference between the rotors and the wing. Then, taking the XV-15 tilt-rotor aircraft as object, a simulation research is carried out in both hover and cruise conditions, and the influence of the rotor phase difference (RPD) on the near field aeroacoustics radiation is studied. The results show that the Overall Sound Pressure Level (OASPL) of aeroacoustics radiation on the fuselage wall can be effectively reduced by the rotor phase control, but the introduction of RPD will also aggravate the aerodynamic interference between the rotors, and have some negative impact on the noise suppression effect. In hover condition, the aerodynamic interference is most serious, and the noise suppression effect of the rotor phase control is relatively poor. In cruise condition, because of the distant inflow, the interference between the rotors and wing is relieved, and the rotor phase control can achieve better noise suppression effect. The OASPL of aeroacoustics radiation on the fuselage wall can be reduced by 10.2 dB at most in hover condition, and up to 15 dB in cruise condition. The simulation results demonstrated a significant effect of rotor phase control on near field aeroacoustics suppression of tilt-rotor aircraft. [ABSTRACT FROM AUTHOR]

This paper investigates the aeroelastic performance of a thrust-vectored system on aerostat vehicle, which is characterized by capsule-beam-rotor or capsule-wing-rotor configuration. The distinct inherent and environmental factors, like rotor tilt, wing sweep, air condition etc., are taken into account. The variation principle is utilized to establish the governing equations, where the aerodynamic loads of wing and rotor which highly couple with the structural deformations are modeled with accordant accuracies. The physical model is applied, which is especially appropriate for the aeroelastic analyses of tilt-rotor systems in low-speed flight condition. The Rayleigh-Ritz method is employed to derive the frequency-domain modal solutions. The case studies consider three contrastive models to investigate the aeroelastic mechanisms by means of parametric analyses. The results show that, except for the installation geometries of rotor, all the distinct parameters cause implications on the amplitudes and trends of modal frequencies and damping rates; the rotor rotation interacts with the structural deformations severely, leading to the occurrence of complicated coupling phenomenon; in addition, the relevant parameters also show optimizable potentials to postpone the aeroelastic instabilities. [ABSTRACT FROM AUTHOR]

A nonlinear unsteady aerodynamics model is coupled with a three degree of freedom quadplane to control the forward and backward transition between hover and steady level flight. The unsteady lift and drag forces are modeled using a lumped vortex model for flat plates. Two variants for the quadplane are considered: (i) a pusher and (ii) a tilt-rotor configuration in the absence of control surfaces to assess the controllability for altitude, attitude and forward speed. Conventional PID control is applied to generate the control inputs. The simulation results conclude that the pusher quadplane configuration is effortless to control as all the selected states are controllable, whereas for the tilt-rotor configuration, even though the vehicle is stable, altitude control is significantly more challenging due to one less control input when compared to the pusher configuration. [ABSTRACT FROM AUTHOR]