Special Issue "Rotorcraft"

A special issue of Aerospace (ISSN 2226-4310). This special issue belongs to the section "Aeronautics".

Deadline for manuscript submissions: closed (31 October 2021) | Viewed by 12118

Special Issue Editor

Dr. Jacopo Serafini
E-Mail Website
Guest Editor
Department of Engineering, Roma Tre University, Via della Vasca Navale, 79, 00144 Roma, Italy
Interests: aerodynamics, aeroelasticity, flight dynamics, aeroacoustics of rotorcraft; structural characterization and shape sensing; electric aircraft/rotocraft
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Although representing a relatively small market segment in the aeronautical sector, rotary wing aircraft has historically been deeply studied due to the peculiar technical and scientific challenges they propose. In recent years, the sector has dramatically changed due to the introduction of several types of rotorcraft, ranging from multicopter to compound helicopters and tiltrotors, enlarging the spectrum of operations. This has been made possible by the advancement of the various disciplines involved in the design of rotary wing aircraft. However, several issues still remain open, requiring theoretical and technological development. Moreover, many of the theories developed for rotorcraft have found another field of application, especially in the wind turbine sector.
This Special Issue aims to present the most recent advancement in the disciplines related to rotorcraft, including but not limited to:

  • Aerodynamics
  • Aeroelasticity
  • Autonomous flight
  • Electric rotorcraft
  • Flight dynamics and simulation
  • Flight control systems/navigation systems
  • Crashworthiness/ditching
  • Health and usage monitoring and predictive maintenance
  • Innovative rotorcraft design
  • Multicopters
  • Noise
  • Operations
  • Rotorcraft–pilot interactions
  • Sensors and avionics
  • Structures and materials
  • Transmissions
  • Vibrations

Dr. Jacopo Serafini
Guest Editor

Manuscript Submission Information

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Published Papers (8 papers)

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Research

Article
Generalized Quantitative Stability Analysis of Time-Dependent Comprehensive Rotorcraft Systems
Aerospace 2022, 9(1), 10; https://doi.org/10.3390/aerospace9010010 - 24 Dec 2021
Viewed by 801
Abstract
Rotorcraft stability is an inherently multidisciplinary area, including aerodynamics of rotor and fuselage, structural dynamics of flexible structures, actuator dynamics, control, and stability augmentation systems. The related engineering models can be formulated with increasing complexity due to the asymmetric nature of rotorcraft and [...] Read more.
Rotorcraft stability is an inherently multidisciplinary area, including aerodynamics of rotor and fuselage, structural dynamics of flexible structures, actuator dynamics, control, and stability augmentation systems. The related engineering models can be formulated with increasing complexity due to the asymmetric nature of rotorcraft and the airflow on the rotors in forward flight conditions. As a result, linear time-invariant (LTI) models are drastic simplifications of the real problem, which can significantly affect the evaluation of the stability. This usually reveals itself in form of periodic governing equations and is solved using Floquet’s method. However, in more general cases, the resulting models could be non-periodic, as well, which requires a more versatile approach. Lyapunov Characteristic Exponents (LCEs), as a quantitative method, can represent a solution to this problem. LCEs generalize the stability solutions of the linear models, i.e., eigenvalues of LTI systems and Floquet multipliers of linear time-periodic (LTP) systems, to the case of non-linear, time-dependent systems. Motivated by the need for a generic tool for rotorcraft stability analysis, this work investigates the use of LCEs and their sensitivity in the stability analysis of time-dependent, comprehensive rotorcraft models. The stability of a rotorcraft modeled using mid-fidelity tools is considered to illustrate the equivalence of LCEs and Floquet’s characteristic coefficients for linear time-periodic problems. Full article
(This article belongs to the Special Issue Rotorcraft)
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Article
A Continuous Multivariable Finite-Time Super-Twisting Attitude and Rate Controller for Improved Rotorcraft Handling
Aerospace 2022, 9(1), 6; https://doi.org/10.3390/aerospace9010006 - 22 Dec 2021
Viewed by 675
Abstract
This paper synthesizes a continuous, multivariable, finite-time-convergent, super-twisting attitude and rate controller for rotorcraft with the objective of providing desired handling qualities and robustness characteristics. A sliding manifold is defined in the system state space to represent ideal attitude and rate command response [...] Read more.
This paper synthesizes a continuous, multivariable, finite-time-convergent, super-twisting attitude and rate controller for rotorcraft with the objective of providing desired handling qualities and robustness characteristics. A sliding manifold is defined in the system state space to represent ideal attitude and rate command response dynamics of relative degree one with respect to the command input. Subsequently, robust command tracking is achieved via the synthesis of a multivariable super-twisting flight controller, which renders the plant states convergent on to the defined sliding manifold in finite-time and in the presence of matched external disturbance input. To validate the efficacy of the controller, simulation results are presented based on a nonlinear, higher-order rotorcraft model operating in turbulence. True system convergence to the sliding manifold from an untrimmed state is shown to lie within the theoretically predicted finite-time convergence bound. Furthermore, simulations with a linear quadratic flight controller are also presented for performance comparison with the proposed super-twisting flight controller. Full article
(This article belongs to the Special Issue Rotorcraft)
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Article
X-ray Computed Tomography Method for Macroscopic Structural Property Evaluation of Active Twist Composite Blades
Aerospace 2021, 8(12), 370; https://doi.org/10.3390/aerospace8120370 - 30 Nov 2021
Viewed by 732
Abstract
This paper describes an evaluation of the structural properties of the next-generation active twist blade using X-ray computed tomography (CT) combined with digital image processing. This non-destructive testing technique avoids the costly demolition of the blade structure. The CT scan covers the whole [...] Read more.
This paper describes an evaluation of the structural properties of the next-generation active twist blade using X-ray computed tomography (CT) combined with digital image processing. This non-destructive testing technique avoids the costly demolition of the blade structure. The CT scan covers the whole blade region, including the root, transition, and tip regions, as well as the airfoil blade regions, in which there are spanwise variations in the interior structural layout due to the existence of heavy instrumentation. The three-dimensional digital image data are processed at selected radial stations, and finite element beam cross-section analyses are conducted to evaluate the structural properties of the blade at the macroscopic level. The fidelity of the digital blade model is first assessed by correlating the estimated blade mass with the measured data. A separate mechanical measurement is then carried out to determine the representative elastic properties of the blade and to verify the predicted results. The agreement is found to be good to excellent for the mass, elastic axis, flap bending, and torsional rigidity. The discrepancies are less than 2.0% for the mass and elastic axis locations, and about 8.1% for the blade stiffness properties, as compared with the measured data. Finally, a sensitivity analysis is conducted to clarify the impact of modeling the sensor and actuator cables, nose weight, and manufacturing imperfections on the structural properties of the blade. Full article
(This article belongs to the Special Issue Rotorcraft)
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Article
The Control Algorithm and Experimentation of Coaxial Rotor Aircraft Trajectory Tracking Based on Backstepping Sliding Mode
Aerospace 2021, 8(11), 337; https://doi.org/10.3390/aerospace8110337 - 09 Nov 2021
Viewed by 633
Abstract
In view of the uncertainty of model parameters, the influence of external disturbances and sensor noise on the flight of coaxial rotor aircraft during autonomous flight, a robust backstepping sliding mode control algorithm for the position and attitude feedback control system is studied [...] Read more.
In view of the uncertainty of model parameters, the influence of external disturbances and sensor noise on the flight of coaxial rotor aircraft during autonomous flight, a robust backstepping sliding mode control algorithm for the position and attitude feedback control system is studied to solve the trajectory tracking problem of an aircraft in the case of unknown external interference. In this study, a non-linear dynamic model based on a disturbed coaxial rotor aircraft was established for an unknown flight. Then, a non-linear robust backstepping sliding mode controller was designed, which was divided into two sub-controllers: the attitude controller and the position controller of the coaxial rotor aircraft. In the controller, virtual control was introduced to construct the Lyapunov function to ensure the stability of each subsystem. The effectiveness of the proposed controller was verified through numerical simulation. Finally, the effectiveness of the backstepping sliding mode control algorithm was verified by flight experiments. Full article
(This article belongs to the Special Issue Rotorcraft)
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Article
Experimental Study of the Aerodynamic Interaction between Side-by-Side Propellers in eVTOL Airplane Mode through Stereoscopic Particle Image Velocimetry
Aerospace 2021, 8(9), 239; https://doi.org/10.3390/aerospace8090239 - 30 Aug 2021
Cited by 2 | Viewed by 822
Abstract
Side-by-side propellers characterise the architecture of most new electric aircraft (eVTOLs) designed in recent years for urban air mobility. The aerodynamic interaction between side-by-side propellers represents one of the key phenomena that characterise the flow field and performance of these novel aircraft configurations. [...] Read more.
Side-by-side propellers characterise the architecture of most new electric aircraft (eVTOLs) designed in recent years for urban air mobility. The aerodynamic interaction between side-by-side propellers represents one of the key phenomena that characterise the flow field and performance of these novel aircraft configurations. The present article describes the main results of a wind tunnel campaign that aimed to investigate the flow features that characterise this aerodynamic interaction, with a particular application to cruise flight conditions in eVTOLs. With this aim, stereo particle image velocimetry (PIV) measurements were performed in the wake of two co-rotating propeller models in a side-by-side configuration. The three-dimensional flow surveys provided detailed insights into the flow physics of the interacting propellers, with a particular focus on the interactional effects on the trajectory of the tip vortices and the wake topology provided at two different advance ratios by reproducing a moderate and a fast cruise speed of eVTOLs in urban areas. Full article
(This article belongs to the Special Issue Rotorcraft)
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Article
In-Flight Test Campaign to Validate PIO Detection and Assessment Tools
Aerospace 2020, 7(9), 136; https://doi.org/10.3390/aerospace7090136 - 10 Sep 2020
Viewed by 1592
Abstract
This paper describes a joint research campaign conducted by the German Aerospace Center (DLR) and the National Research Council Canada (NRC) to explore methods and techniques to expose rotorcraft pilot-induced oscillations (PIOs) during flight testing. A flight test campaign was conducted at NRC [...] Read more.
This paper describes a joint research campaign conducted by the German Aerospace Center (DLR) and the National Research Council Canada (NRC) to explore methods and techniques to expose rotorcraft pilot-induced oscillations (PIOs) during flight testing. A flight test campaign was conducted at NRC using the Bell 205 experimental aircraft. Results show that, particularly for the lateral axis, ADS-33 tasks can be successfully applied to expose PIO tendencies. Novel subjective and objective criteria were used during the test campaign. PIO prediction boundaries of the objective phase-aggression criteria (PAC) detection algorithm were validated through results obtained. This was the first use of PAC with data recorded in-flight. To collect subjective feedback, the aircraft–pilot coupling (APC) scale was used. This was the first use of the novel scale in-flight and received favourable feedback from the evaluation pilot. Modifications to ADS-33 mission tasks were found to successfully improve the ability to consistently expose PIOs. Full article
(This article belongs to the Special Issue Rotorcraft)
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Article
Mathematical Modelling of Gimballed Tilt-Rotors for Real-Time Flight Simulation
Aerospace 2020, 7(9), 124; https://doi.org/10.3390/aerospace7090124 - 28 Aug 2020
Cited by 2 | Viewed by 1901
Abstract
This paper introduces a novel gimballed rotor mathematical model for real-time flight simulation of tilt-rotor aircraft and other vertical take-off and landing (VTOL) concepts, which improves the previous version of a multi-purpose rotor mathematical model developed by ZHAW and Politecnico di Torino as [...] Read more.
This paper introduces a novel gimballed rotor mathematical model for real-time flight simulation of tilt-rotor aircraft and other vertical take-off and landing (VTOL) concepts, which improves the previous version of a multi-purpose rotor mathematical model developed by ZHAW and Politecnico di Torino as part of a comprehensive flight simulation model of a tilt-rotor aircraft currently implemented in the Research and Didactics Simulator of ZHAW and used for research activities such as handling qualities studies and flight control systems development. In the novel model, a new formulation of the flapping dynamics is indroduced to account for the gimballed rotor and better suit current tilt-rotor designs (XV-15, V-22, AW-609). This paper describes the mathematical model and provides a generic formulation as well as a specific one for 3-blades proprotors. The method expresses the gimbal attitude but also considers the variation of each blade’s flapping due to the elasticity of the blades, so that the rotor coning angle can be represented. A validation of the mathematical model is performed against the available literature on the XV-15 Tilt-rotor aircraft and a comparison between the previous model is provided to show the improvements achieved. The results show a good correlation between the model and the reference data and the registered performance allow real-time flight simulation with pilot and hardware in the loop. Full article
(This article belongs to the Special Issue Rotorcraft)
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Article
Cabin Layout Optimization for Vibration Hazard Reduction in Helicopter Emergency Medical Service
Aerospace 2020, 7(5), 59; https://doi.org/10.3390/aerospace7050059 - 15 May 2020
Cited by 3 | Viewed by 2464
Abstract
Helicopter Emergency and Medical Service (HEMS) vehicles require a specially configured cabin that supports the quick transport of a rescue team to the site of an emergency and return of patients back to a full capacity hospital, while sustaining the patients’ health using [...] Read more.
Helicopter Emergency and Medical Service (HEMS) vehicles require a specially configured cabin that supports the quick transport of a rescue team to the site of an emergency and return of patients back to a full capacity hospital, while sustaining the patients’ health using specifically designed, but otherwise state-of-the-art life-support equipment. The effectiveness and safety of the service may be challenged by the vibratory level, which could be improved by optimally positioning the affected subjects within the cabin. However, the bare dynamical response of the airframe can lead to erroneous evaluation of vibration performance, since pilots, crew, patients, and medical equipment dynamically interact with the helicopter through their interfaces with the structure. Therefore, layout optimization of a HEMS vehicle for low vibration requires the capability to efficiently analyze a large set of candidate coupled helicopter-interface-subject configurations, reaching a suitable trade-off between model detail and computational cost. This work presents an effective vibration rating of medical helicopters to support vibration hazard reduction by minimization of cabin interior accelerations. The tool is able to model high-fidelity rotorcraft aeroservoelasticity, easily connect formulations representing the dynamics of humans, equipment, and their interfaces, and calculate the vibration performance of the resulting coupled models. The approach is applied to a medium-weight helicopter to find its lowest vibration HEMS configuration. It is demonstrated that the optimal positioning of HEMS subjects can significantly reduce vibration hazard and improve operation safety, nearly as effectively as the application of vibration attenuation solutions with a fixed cabin layout. Full article
(This article belongs to the Special Issue Rotorcraft)
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