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NEXTTRIP Interactional aerodynamic assessment of an advanced tilt rotor configuration
No full textAbstract This paper reports on the goals accomplished by the NEXTTRIP Consortium in response to the Topic JTICS2-2017-CFP06-FRC-01-15 titled “Interactional Aerodynamic Assessment of Advanced Tilt Rotor Configuration”. The aim of the project was to assess different empennage configurations for the Next Generation Civil Tilt Rotor, NGCTR, by a large scale wind tunnel experiment, share knowledge and skills across the European partners and to provide guidance to the Integrated Technology Demonstrator (ITD) leaders through CFD-optimised and cost-effective solutions. The investigation, test and evaluation of a new empennage configuration for the NGCTR Technology Demonstrator were conducted in the DNW 9.5-by-9.5 m large low speed facility (LLF) in Marknesse, the Netherlands. Although the wind tunnel campaign was mainly focused to determine the stability and control characteristic of the powered, 1/5th scale model of the NGCTR, tests were also conducted to study the following effects of varying the basic configuration: effect of a V-tail and T-tail empennage, effect of elevator trim, effect of lateral-directional control, effect of power, interactional effect of rotor on/rotor off and effect of nacelle angle. Additional and innovative aspect of the experimental campaign was the application of the Particle Image Velocimetry based on Helium Filled Soap Bubbles, or HFSB, on large scale by using a seeding rake on 3-by-3 meters and up to 60 m/s. The test results were used in parallel to develop and validate a CFD methodology, based on multi-objective genetic algorithm, to optimise the V-tail empennage. Moreover, the project led to a fruitful exchange of ideas, expertise and knowledge, strengthening the bonds between JU partners
Advanced analysis method of electric propulsion system for UAM vehicles
Get PDFThis article proposes an advanced analysis method of the electric propulsion system for UAM vehicles. Three modules are constructed to consider the electrical characteristics of electric devices. The motor-analysis module is developed based on the permanent magnet synchronous motor (PMSM)'s control strategies: maximum torque per ampere (MTPA), field weakening (FW), and maximum torque per voltage (MTPV). The inverter-analysis module uses the linear loss model for the power semiconductors. Based on the near-linear discharge model, the battery-analysis module was constructed to consider the voltage drop. In addition, the eVTOL aircraft sizing is performed in two cases depending on the type of analysis method for the electric propulsion system. The comparative study based on the sizing results demonstrates the necessity and the capability of the proposed analysis method for the electric propulsion system
A mathematical model for landing a single-rotor helicopter with a wheeled chassis in standard conditions and special cases
Get PDFAt the present stage of development of the design of modern aviation equipment, in conditions of fierce rivalry, there are obvious trends to reduce the design time, to lower the final cost, as well as to increase the safety of the product being designed. One of the ways to solve this problem, along with increasing the functionality of the calculation software, is to reduce the volume of certification work by replacing full - scale stand and flight tests with mathematical modeling
Helicopter flight dynamic axis coupling identification
Get PDFThe paper reviews the research that combines dedicated modelling approaches in a nonlinear environment with parameter estimation and system identification methods to pursue two goals simultaneously. First, the improvement of helicopter axis coupling prediction capabilities and second, to gain an insight into the physical mechanisms leading to the phenomena by analysing the identification results. Axis coupling behaviour of helicopters is discussed and the knowledge of the phenomena is compiled to lay the foundation for the modelling and simulation task. The specific modelling approach applied is based on the Parametric Wake Distortion (PWD) theory that yielded a closed mathematical formulation for the treatment of pitch-roll cross coupling. In order to make use of this combined nonlinear analytical/parametric formulation, system identification and parameter estimation methods are used to quantify the effects involved. The methods based on the maximum likelihood output error estimation are presented and explained. The actual optimisation task is applied to BO 105 flight test data and is thoroughly analysed with regard to the stated objectives. The method proved to be suited to support the goals postulated for this research. As per the two stated goals, the results are interpreted twofold. The improvement of simulation fidelity and the conclusions to be obtained regarding the involvement of the addressed physical effects. The resulting values of the estimated parameters of the optimized result yields an insight into the participation of the addressed phenomenon in the improvement of the simulation result. The paper concludes with an assessment of the methods
The use of computational fluid dynamics in the investigation of stall onset on tilt-rotor blades
Get PDFAn experimental setup has been designed to examine rotor blade stall flutter. The blade had to be designed so that it does not exceed the maximum permissible load on the rotor rig to be employed for wind tunnel tests, while maximising the blade loading to allow for the blade to be excited. An original set of blades where first tested to examine the possibility of their reuse. On discovery that they required too much power to drive them at the required collective computational fluid dynamics (CFD) was used to aid a new desig
Evaluation of Control Equivalent Turbulence Input (CETI) models for hover and forward flight
Get PDFThis paper details developments in Control Equivalent Turbulence (CETI) Input models. Using these models, control inputs are calculated that generate aircraft angular and vertical rates in calm conditions equivalent to those when flying in atmospheric turbulence. In this paper, previous efforts to generate CETI models for the EC135 in hover are extended to include dependency with respect to forward flight speed and flight altitude. The paper describes the flight tests conducted in turbulent conditions, the extraction of the equivalent control input traces and their power spectral densities, and the determination of the desired turbulence models. The paper also presents validation of the derived turbulence models. This is performed through piloted simulation trials conducted in the Air Vehicle Simulator (AVES) at DLR. Results showed the appropriateness of developed CETI models to simulate atmospheric turbulence over the flight envelope
JAXA-ONERA-DLR cooperation: Results from rotor optimization in hover
Get PDFA cooperation on the aerodynamic optimization of helicopter rotors has been formed by JAXA, ONERA and DLR. This work represents the conclusions drawn from the first phase: optimization of a hovering rotor. The HART-II blade is first investigated with low-fidelity tools and compared against state-of-the art CFD simulations. Following up on this, the HART-II blade chord distribution and twist are optimized with the low-fidelity tools as well as CFD. Due to observed differences in the outcome of the CFD simulations for the low-fidelity optimized blades by the partners, a deeper investigation of the effects of the turbulence modelling approach, elasticity and grid topology is undertaken. The outcome is that the chosen flight condition is close to thrust of the maximum Figure of Merit and the vortex triggered separation on the outboard sections of the blade has to be modelled correctly. In this study, the blade grids had the most noticeable effect on the results, followed by the turbulence model and elasticity. With respect to the optimization, care must be taken when optimizing with low-fidelity methods, whereas CFD optimized blades were found to lead to more robust designs even though they have only been optimized for a single point. Reason is the more accurate modelling of the stall phenomenon with respect to geometrical changes
Advanced pilot modeling for rotorcraft handling qualities investigation in turbulent wind
No full textTurbulent wind is known notoriously that can significantly deteriorate rotorcraft performance and handling qualities for manoeuvring flight. However, research on this topic is rarely reported largely due to the lack of an effective analytical tool. This paper develops a pilot model to explore the effect of turbulent wind on rotorcraft handling qualities. The proposed pilot model consists of three components: a compensatory control model for attitude stabilization, a preview control model for trajectory tracking, and a tau guidance model for trajectory planning. Model accuracy assessment indicates that the new pilot model can plan and track a desired trajectory conforming to pilot’s tau guidance strategy and predict credible handling qualities capturing the effect of the vestibular system and a flight control system. Handling qualities analysis for a slalom task in turbulent wind shows that the new pilot model predicts the effect of mean wind on rotorcraft manoeuvring aggressiveness and yaw control performance by changing required ground speed and the airflow through the tail rotor. Atmospheric turbulence significantly deteriorates the task with increased turbulence intensities. Flight control system can significantly improve the tracking performance and HQs in turbulent wind but saturation due to limited authority in aggressive operation reduces the effect of the flight control system
Accurate and flexible formulation of a dual-solver hybrid CFD framework
Get PDFVarious hybrid computational fluid dynamics (CFD) methods have recently been developed which couple Navier-Stokes solvers to vortex-based solvers for cost-effective rotorcraft aeromechanical analysis. Previous hybrid methods have had implementation issues which result in in-accurate and/or inflexible frameworks. Methodological approaches to CFD/free-wake coupling that address these issues and are unique among other hybrid CFD methods are introduced, including rotor tracking, blade deformation treatment, unsteady free-wake boundary pressure, boundary characteristic treatment, boundary value interpolation, and single gridded blade (SGB) simulation. These improvements are implemented into the OVERFLOW-CHARM hybrid CFD framework and their impact is demonstrated using three example scenarios: vortex advection, wing-integrated propulsion, and a rotor in hover. The new methods quantifiably improve the quality of the hybrid CFD solutions in these cases and enhance the generality of the framework to problems related to future vertical lift
A study to examine effects of the inflow interference on induced power using combined momentum and simple vortex theory inflow model
Get PDFThis paper uses a recently developed combined momentum theory and simple vortex theory (CMTSVT) inflow model to study effects of rotor-on-rotor inflow interference on induced power predictions for different multi-rotor configurations with varying overlapping areas. The validation with the Harrington coaxial rotor shows that this analytical model, although simple, can capture the overall rotor-on-rotor wake interference effects in the estimation of rotor power, without a need for its coupling with a blade element rotor model. The first harmonic self-induced and interference inflow components of individual rotors are also available for further exploration of the different multi-rotor configurations. Hence, the CMTSVT model can serve as a viable tool for rapid estimation of rotor-on-rotor interference on overall power required in the early design stages of vehicle configuration and sizing trade studies