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CFD based positioning and calibration of helicopter air data system
No full textThis paper presents air data system positioning and calibration activities of T625 Gökbey helicopter via computational fluid dynamics analyses. Air data boom and pitot static probe placement is performed by exploring the critical flight conditions including the effect of main rotor downwash and fuselage aerodynamic characteristics. CFD analyses are performed for all possible conditions covering certification flight envelope and feasible locations are defined for all probes. Main rotor downwash is modeled by using actuator disk model in Siemens STAR CCM+ and ANSYS Fluent together with fuselage. Pressure error correction (PEC) flight tests are performed and flight data is compared with CFD
Operator state monitoring for workload prediction and management
No full textOngoing efforts to modernize the U.S. Army is resulting in the development of the next generation of rotary aircraft under the Future Vertical Lift (FVL) program. FVL missions will be characterized by increased agility, degraded visual environments (DVE) and optionally piloted vehicles (OPVs) in complex, highly contested and dynamically changing environments. New technologies and automation in the cockpit allow aviators to be more effective in completing their missions in the modern dynamic battlefield. Autonomous systems have the potential to contribute to improvements in operational safety, efficiency and effectiveness but have also introduced additional human factors engineering considerations. These technologies provide pilots with appropriate and timely information and support, while avoiding overloading with excessive clutter and information. At the same time, excessive automation can lead to overloading/ underloading, leading to automation misuse, complacency, and loss of situational awareness (SA). Adaptive decision aiding systems have the potential to enhance operators’ capabilities by recognizing situations, external (environment) and internal (operator state) and providing subsequently real-time adaptation of the aircraft controls and human/ machine interfaces. A pre-requisite to the development of such adaptive decision aiding systems is the real-time monitoring and identification of the operator’s performance and mental state in terms of workload and situation awareness. Being multidimensional, latent factors, workload (WL) and SA need to be inferred through observable variables such as subjective assessments, task-based metrics, and psychophysiological measures. Of particular interest for FVL are techniques and technologies that enable real-time WL and SA assessment, for realistic missions in simulator and/or real flight conditions. The present research aims to provide a methodology to manipulate WL and SA in an operationally relevant mission in a fixed-platform UH60 simulator, evaluate the usability, diagnosticity, sensitivity and reliability of various performance metrics in situ using novel approaches for the data analysis and validate real-time predictive models of WL. An experiment was designed to manipulate WL and SA by using two levels of flight control level of automation (LOA) and two levels of obstacle cueing symbology during a degraded visual environment (DVE) medical evacuation (MEDEVAC) mission. The level of WL was further manipulated by the presence of obstacles and aircraft survivability equipment (ASE) threat events (radar and missile warnings). Five UH60M Army experimental test pilots participated in the simulation at the U.S. Army rotorcraft in flight laboratory RIFL system integration laboratory (SIL) at Fort Eustis, VA. Preliminary analyses validate the WL driver’s selection, and the usability of the real-time subjective WL report using a modified Bedford rating scale, used to compute the spare capacity operations estimator (SCOPE). A novel approach to statistical analyses is proposed, that will allow to determine the relative weight of each metric to the final WL and SA estimates, and support performance modeling
New method for the presizing of heavy lift civil transport helicopters
Get PDFIn this work, a new method based on an iterative and multi-level process is used for presizing of heavy lift helicopters having a capacity of 90 passengers over a range of at least 1000Km. This method is based on an iterative and multi-level process. It allows to define in broad outlines several dimensioning characterized by a series of parameters, starting from mission specification and helicopter characteristics in the form of modeling. The models used in this study, are based on a combination of statistical and physical laws. Some components of the heavy lift helicopter configuration are similar to those of an airplane. Thus, for this reason, the statistical laws of weight relative to a transport plane are applied to these organs. The results obtained were compared with the values obtained by the NASA NDARC tool for the same helicopter configuration. The difference of the parameters does not exceed 8%, giving an average relative difference of 4%
A non-linear unsteady vortex lattice method for aeroelastic rotor loads evaluation
Get PDFThe present work aims to extend the capabilities of DUST, a mid-fidelity aerodynamic solver developed at Politecnico di Milano, for the aerodynamic simulation of flight conditions characterised by flow separations. With this aim, a novel numerical element was implemented in the solver obtained by a coupling between the potential unsteady vortex lattice method and viscous aerodynamic data of airfoil sections available from two-dimensional high-fidelity CFD simulations or experimental wind-tunnel tests. The paper describes the mathematical formulation of the method and the results of a comprehensive validation of the novel numerical element performed by comparison with both high-fidelity CFD simulations results and experimental data. In particular the validation test cases included the evaluation of the airloads of a fixed rigid wing, the flutter speed of a wedged wing and the aerodynamic performance of the full scale proprotor of the XV-15 tiltrotor operating in hover condition, forward flight in helicopter mode and airplane mode
Are eVTOL aircraft inherently more susceptible to the vortex ring state than conventional helicopters?
Get PDFThere is currently extensive interest worldwide in developing small, lightweight, electrically powered, multi-rotor vertical takeoff and landing aircraft. The aim is to use these new vehicles to carry a small number of passengers on short-range intra-urban missions, for instance as part of a passenger ferry service between an airport and a downtown commuter hub. The concern is that these aircraft might have certain characteristic design features that, in combination with the environmental conditions that they will experience, will render them particularly susceptible to a potentially hazardous operating regime, known as the Vortex Ring State, especially during their descent and landing. This paper extends our classical understanding of the basic physics that underpins the Vortex Ring State in order to assess the likely impact of this phenomenon on the safety and operational characteristics of this new class of vehicle
Flight performance of multi-rotor configuration tail rotors
No full textTo better understand and predict the flight performance of multi-rotor configurations of tail rotors controlled via collective pitch or rotor speed, a flight performance tool is derived. The tool includes a tail rotor model, an aerodynamic interference model, and a trim method. The vertical configuration of a multi-rotor tail rotor can effectively take advantage of aerodynamic interference to reduce the required power. The five-rotor configuration with fixed rotor speed reduces the power by 36.7%. More rotors are preferable from the point of view of power consumption. Too many rotors are unnecessary, since the extra benefit obtained is very diminished. Varying the rotor speed is better for performance improvement compared with varying the collective pitch, since lower rotor speed leads to rotor power reduction. The five-rotor configuration with fixed collective pitch reduces the power by 53.3%. The severe aerodynamic interference between the rotors leads to the longitudinal configuration of multi-rotor configuration having much poorer performance. The four-rotor configuration in a “plus” arrangement achieves better performance than the cross four-rotor configuration or a vertical four-rotor configuration
Safety landing strategy investigation for Urban-Air-Mobility Vehicles using inverse simulation approach
No full textThe UAM systems have recently become the focus in the rotorcraft academia and industry. The advent of the UAM could significantly reduce ground-level traffic and carbon emissions. NASA report indicated [1] that by 2030 there could be as many as 1.25 billion UAM flights a year. In anticipation of this increase, more than 150 UAM vehicles are currently under developmen
Fully FEM-based simulation approach for advanced helicopter interior noise design using noise sources extracted from flight test data
No full textApart from exterior noise emissions which are subject of the type certification of a helicopter, also the noise perception inside the cabin poses major design challenges in rotorcraft development. In particular, rotating components such as rotors, drive shafts, engine components and gears are commonly known sources of sound. Of particular relevance are those sources whose frequency range interferes with that of human voice, for which the Speech Interference Level (SIL) is a widely used metric. In the recent past, availability of computational resources as well as development of efficient and robust numerical solution methods have experienced a steep gradient. This paves the way for the use of Fine Element Methods (FEM) to simulate acoustic wave propagation for successively higher frequencies in ever larger volumes such as helicopter cabins. With the aim of designing effective measures to optimize the SIL4 noise level of a helicopter cabin we present the applicability of a full FEM-based acoustics simulation approach. The presented model is capable to cover the full frequency range bounded by the SIL4 range. To describe location and strength of the acoustic sources, we exploit measurement data recorded during regular flight test campaigns allowing to compute equivalent accelerations for the major sources of sound. Using the AW09 prototype helicopter as a practical example, the acoustic performance in terms of SIL4 reduction is investigated for two treated configurations: One with a carpet and a second with carpet and a ceiling panel. The materials are acoustically described by frequency-dependent absorption coefficients from literature. As a result, the reduction potential of the carpet is quantified to range between ? 1.2 and 1.8 SIL4dB and up to approx. 11.5 SIL4dB for the case with carpet and ceiling panel. The great potential of model lies in its implementation in a multiphysics simulation environment. This allows for example to include more complex interaction effects such as acoustic-structure coupling as well as consideration of structures like acoustic metamaterials
Experimental investigation of the aerodynamic interaction between overlapping propellers in tandem for eVTOL airplane-mode flight conditions
Get PDFThe latest trends of Urban Air Mobility (UAM) pushed the aeronautical community towards the eVTOL concept, i.e. electrical vertical take-off and landing aircraft. Electrical power, tilt-wing configuration and multiple propellers in tandem configuration (i.e. with the propellers placed one after the other) are the key features of such concept. In particular, the presence of multiple propellers working at close range introduces a new challenge, i.e. the investigation of the aerodynamic interaction between front propeller slipstreams and rear propellers. The present work aims to investigate the main physical aspects of this phenomenon in a typical eVTOL configuration in airplane mode. A dedicated wind tunnel testing campaign was performed to investigate deeply the interaction between two co-rotating tandem propellers at fixed axial distance and variable lateral separation. The tests included both thrust and torque measurements of the propellers and Particle Image Velocimetry (PIV) surveys. Load measurements showed a significant loss in the rear propeller performance as a function of the overlapping ratio between the propellers. Furthermore a dedicated spectral analysis of wind tunnel thrust signals outlined high amplitude fluctuations in partial overlapping configurations. The collected experimental results represent a reference database for the validation of numerical codes implemented during the design phase of such vehicles. In particular, some experimental data were compared with results obtained by the mid-fidelity aerodynamic solver DUST relying upon Vortex Particle Method (VPM) in order to enhance the comprehension of the phenomenon. The analysis of the numerical results allowed to access the flow behaviour involving the front propeller slipstream and the rear propeller disk, which is responsible of the massive losses experienced by the rear propeller
An energy-based trim procedure for multirotor VTOLS
Get PDFThe aim of the proposed paper is the development of a general approach capable of determining the set of trim commands, aerodynamic controls surfaces actuation and/or engine thrust regulation, that allow specific steady-state flight conditions of non-conventional VTOLs, under given performance constraints. Specifically, an energy-based trim algorithm is introduced, based on the minimization of a cost function. This approach is particularly interesting in that, in case of multi-rotor system, it allows to determine the control settings such to guarantee the required flight condition while using the redundant controls to optimise selected target functions, as for instance performance or noise emission. The proposed approach will be applied to a quadcopter configuration, for validation purposes, and a hexacopter configuration for which a comparison with a conventional trim procedure will be performed. Three different control strategies are applied: a pure rotor angular velocity control, a pure blade collective pitch control and a combined angular velocity and blade collective pitch control