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Development and validation of a fast mid-fidelity comprehensive analysis tool for generic e-VTOL configurations
No full textThis paper presents development and validation of a mid-fidelity fast vortex rotorcraft comprehensive analysis tool specialized for flight mechanics and handling quality analysis of multiple rotor configurations having severe interactional aerodynamics. Mid-fidelity simulation framework includes Vortex Particle Method (VPM) accelerated by GPU and coupled with a Generic Air Vehicle Model (GAVM) which is a mathematical model for analysis of generic configurations such as propeller aircrafts, conventional and unconventional rotorcrafts, multi-rotor and tilt-rotor eVTOL configurations. This work presents the development, integration and validation stages for a mid-fidelity aerodynamics and flight mechanics comprehensive analysis framework for further research specialized for eVTOL design, performance, control design and handling quality analysis by modeling correct rotor wake dynamics and interactions. Simulation cases are presented including rotor-rotor, rotor-body and rotor-lifting surfaces interactions for conventional helicopter and multi-rotor configurations. In addition to the development and integration, several validation cases are presented that are covering rotor in hover, rotor in edgewise flight, propeller in axial flight and rotor-body interactions. Detailed comparisons with direct CFD solutions are presente
Rotor Control Equivalent Turbulence Input (RCETI) models
Get PDFThis paper presents a first step toward the generalization of the hover/low-speed Control Equivalent Turbulence Inputs (CETI) models for different helicopter configurations. The rotor hub-loads are used as the outputs to which the turbulence-related spectra are matched in order to achieve this. Furthermore, the rotor swash-plate deflections are considered as inputs to create what is referred to herein as the Rotor Control Equivalent Turbulence Inputs (RCETI) model. Development of an RCETI model, that provides rotor loads spectra similar to those produced by vertical turbulence, is carried out using a representative model of the UH-60 helicopter in FLIGHTLAB®. The effect of altering the rotor parameters on the RCETI model is studied and presented in the paper
HORUS - High Operational Reliability For Unmanned Systems
No full textIn an effort to increase Unmanned Aerial Vehicles (UAV) mission safety and reliability, this paper introduces the HORUS prototype. HORUS is a small hardware device that allows UAVs to be flown with two Commercial Off The Shelf (COTS) Flight Control Units (FCU) instead of a single one traditionally. The HORUS device offers the possibility to manually switch from one FCU to the other but also to switch autonomously if the UAV gets out of the allowed geographic boundaries or out of its defined flight envelope. Although envelope protection or geofencing features are commonly available on COTS FCUs, they are generally not robust to sensor or FCU failures. But, as a result of its design, which has been developed following manned aviation safety process guidelines, the HORUS device offers high reliability and integrity. In this context, the main objective of this paper is to introduce the HORUS concept, to describe the software and hardware architectures and to demonstrate its functionality by showing some flight test results
Dynamic stability and control of rotorcraft for suspended load transportation: an analytical approach
Get PDFIn the present paper a fully–analytical framework is outlined to investigate the effects of cable–suspended loads on rotorcraft. In particular, the dynamics of an isolated multirotor is first investigated by including the complete model of the electric propulsion system. Then, system description is extended to the presence of a suspended load, thus generating non–actuated degrees of freedom. In order to provide the complete slung–load system with a closed– loop desired behavior, an auxiliary controller is proposed to restore or even improve the initial multirotor dynamics, while stabilizing load oscillations with prescribed behavior. To this end, closed–form expressions are derived to design the auxiliary controller gains, based on the knowledge of a limited set of parameters which include the position of the cable hook point. A test case is proposed relative to a commercial–off–the–shelf hexarotor whose propulsion units have been characterized by an experimental campaign performed at University of Bologna premises
Evaluation of a Head-Mounted Display and advanced flight control laws for helicopter ship deck landing
Get PDFWithin the maritime environment, helicopters can be used for a wide variety of missions including rescue missions, transport of personnel and material as well as for surveillance and reconnaissance. To perform such tasks on open sea and to expand the onshore refueling range, ship deck landings are necessary. Adverse weather conditions, such as high winds, fog and precipitation lead to strong ship movements and create a turbulent environment on the ship’s landing deck. Combined with few visual cues, ship deck operations put a high workload on pilots which can compromise flight safety. To support pilots during ship deck operations a symbology concept was integrated into the previously developed head-mounted display (HMD) based on a Microsoft HoloLens 2. Three advanced flight control modes were developed for the approach phase. Results from a simulator campaign with pilots in a realistic scenario indicate that the handling qualities can degrade with the HMD and only the relative translational rate command (RTRC) is suited as advanced control mode for ship deck operation
Flight path generation for a helicopter in tail rotor failure condition
No full textThe objective of this study is to generate viable flight trajectories for a helicopter with a failed tail rotor. A generic helicopter model using the FLIGHTLAB software is utilized for tail rotor failure simulation. For a conventional helicopter, there is a certain forward flight speed threshold, above which the vertical tail is sufficient to generate the required anti-torque during forward flight. Tail rotor failures above and below this threshold speed are treated in simulations. Optimal trajectories that brings the helicopter from autorotation to level flight for low speed failures; and from level flight to a predefined location for high speed failures are found. The path generation process is performed in the MATLAB environment with an open-source trajectory optimization tool, OptimTraj. The trajectories are obtained for different scenarios by using linear system dynamic models as constraints
Prevention of retreating blade stall by asymmetrically generated lift: Free-flight investigations with a fully autonomous helicopter testbed
No full textHelicopters in forward flight experience highly asymmetrical flow conditions. While transonic effects on the advancing side of the rotor are responsible for a high generation of drag and noise, the retreating side operates in low-speed flow at high angles of attack, close to dynamic stall. This inherent aerodynamic dissymmetry of the main rotor could be counteracted with the intentional generation of asymmetrical lift on the fuselage. To gather more information about the effects of asymmetrical lift and their consequences for the rotor, a UAV helicopter testbed was developed and equipped with a four-axis autopilot system, which enables it to perform fully autonomous flights using GPS waypoints. As a result, the measurements can be conducted in precisely defined flight conditions which can be maintained over long periods of time. Consequently, the averaged data reach a very high level of accuracy that could not be achieved with conventional, manually controlled systems. Successful tuning of the PID loops and other controller parameters for low and high-speed flight (up to 125 km/h fully autonomous cruise flight) was conducted. A remotely adjustable horizontal stabilizer was used to investigate different situations of asymmetric lift. Due to gyroscopic effects of the rotor, a phase shift has to be taken into account, which means that the lift should not be produced directly on the retreating side. The results prove that asymmetrically generated lift can indeed counteract and even overcompensate for the natural rotor asymmetry of a helicopter in forward flight. The retreating blade operates at significantly lower angles of attack, leaving a greater margin to dynamic stall, which allows for lower rotor speeds and therefore resolves the transonic problems of manned helicopters on the advancing side. As a result, either higher flight speeds or lower fuel consumption and noise emissions (eliminated HSI noise) can be achieved
Prop-blade section design optimization using weight/dynamic characteristic surrogate model with skin/spar design variable
Get PDFFor prop-blade section design optimization, an analysis procedure was established to generate a weight/dy-namic characteristic surrogate model based on the general blade section design procedure. The general blade section design procedure consists of requirement analysis, cross-section design, section properties analysis, dynamic characteristics/load analysis and structure analysis to check all requirements are satisfied. Based on this procedure, the database was created by performing section design variable input value generation, section shape and finite element data generation, section properties analysis and dynamic characteristic analysis se-quentially. And an artificial neural network algorithm was applied to create a surrogate model of estimated weight and dynamic characteristics with a control prop-blade section design variable. The prop-blade section configuration has consisted of skin, C-spar and form. Section design variable was decided to a thickness of skin(Skin-t), a thickness of spar(Spar-t) and chordwise length of spar(Spar-l) from the leading edge. A data-base of design variable input values for the creation of a surrogate model was generated using the space-filling method, which is a kind of design of experience and design input variables were generated within a limited range by setting the ranges and constraints of each variable in consideration of the actual prop blade manufacturing characteristics. The weight/dynamic characteristics surrogate model derived through this pro-cess was applied to the genetic algorithm and the optimal cross-sectional shape that satisfies the dynamic characteristic requirements and weight minimization was derived
Experimental investigation of UAV rotor aeroacoustics and aerodynamics with computational cross-validation
Get PDFThe study provided a base of comparison of known computational techniques with different fidelity levels for performance and noise prediction of a single, fixed-pitch UAV rotor operating with varying flight parameters. The range of aerodynamic tools included blade element theory, potential flow methods (UPM, RAMSYS), liftingline method (PUMA) and Navier-Stokes solver (FLOWer). Obtained loading distributions served as input for aeroacoustic codes delivering noise estimation for the blade passing frequency on a plane below the rotor. The resulting forces and noise levels showed satisfactory agreement with experimental data, however differences in accuracy could be noticed depending on the computational method applied. The wake influence on the results was estimated based on vortex trajectories from simulations and those visible in Background Oriented Schlieren (BOS) pictures. The analysis of scattering effects showed that influence of ground and rotor platform on aeroacoustic results was observable even for low frequencies
Toward smart air mobility: control system design and experimental validation for an unmanned light helicopter
No full textLight helicopters are used for a variety of applications, attracting users from the private and public market segments because of their agility and convenient storage capabilities. However, most light helicopters on the market today are designed and manufactured with technologies dating back to the 1980s, with safety issues to be addressed by advanced design methods, more powerful engines, and innovative solutions. In this regard, the DISRUPT (Development of an innovative and safe ultralight, two–seater turbine helicopter) project, lead by Curti Aerospace Division (Italy) and co–funded by EU H2020 program, represents a state–of–the–art concept for a novel ultralight helicopter, equipped with a ballistic parachute. In order to validate the first parachute ejection in a safe scenario, a dronization process was selected as a viable solution to be performed in collaboration with the University of Bologna. In the present paper, the steps followed to transform the helicopter into an unmanned vehicle are detailed according to the Model–Based Design approach, with particular attention to the mathematical modeling, the control system design, and the experimental validation. Obtained results also demonstrate the feasibility of using a civil helicopter first as a remotely–piloted system and then as an highly–automated personal transportation system, in the direction of smart and sustainable air mobility