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Flight performance estimation for eVTOL quadcopter configurations
Get PDFThe present study attempts to compare flight performance of the most popular eVTOL (electrical Vertical Take-Off and Landing) aerodynamic configurations of our days. This study gives a theoretical evaluation of the possible VTOL design of different configurations with full electric or hybrid power plant aimed at the urban mobility applications. Conventional rotorcraft, quadcopters, tiltrotor and tiltwing aircrafts with open rotors and ducted fans have been considered. Different eVTOL design available structural elements mass distributions were found. Flight performance of the eVTOL with full electric and hybrid power plants is estimated. Power available and required for speed envelope from hover to maximal speed modes are calculated. Optimal specific parameters of fully electric and hybrid power plant elements (batteries, generators, electric motors, etc.) are defined to provide acceptable eVTOL flight performance
Dynamics of span morphing helicopter rotor
No full textVariable span morphing rotor blade can vary its radius during the flight and can improve the flight performance and flight dynamics significantly. In this study, the dynamics of a span morphing rotor blade is modeled and analysed. A telescopic-box beam type mechanism is considered for realizing the span morphing blade. The telescopic wing had two beams, a primary beam attached to the rotor hub and a secondary beam that can morph along radial direction. The dynamics induced by span morphing is captured as moving loads over the primary beam. The morphing dynamic equations are derived using the approximate energy methods. The effect of key morphing parameters such as span morphing speed, magnitude of morphing loads and rotor speed on the flap dynamic response of primary beam are studied. Results show that the speed of span morphing has significant impact on the flap dynamic response. Also, the magnitudes of span morphing loads have considerable impact. In contrast, rotor speed during span morphing has inverse effects on the flap response because of the coupled effect of loss of centrifugal stiffness and addition of morphing induced dynamic loads. Therefore, in general, the morphing induced dynamics plays a significant role in the design of span morphing rotor
Rotorcraft simulation fidelity improvements through augmented rotor inflow
No full textIn rotorcraft research, the prediction of correct off-axis response using a simulation model is a challenging task, particularly for hover and low-speed flight. This can be attributed to the complex aeromechanical behavior exhibited by a rotorcraft, including the unsteady and hysteretic nature of the main rotor wake and its coupling with the fuselage and empennage in manoeuvring flight. A traditional approach to improve the off-axis response prediction is to include the manoeuvre wake distortion effect arising from the variation of the induced inflow through the rotor disc. Various approaches have been developed to deal with this phenomenon but usually demand prerequisites of high levels of expertise and profound aerodynamic knowledge. This paper presents a new and practical approach to capturing this wake distortion through an augmented rotor inflow model. The proposed model is integrated into a nonlinear simulation using the FLIGHTLAB environment. The response comparisons between the simulation and flight test in hover indicate the good quality of the proposed model. The results reported are part of ongoing research at Liverpool and its partner Institutions into rotorcraft simulation fidelity for predicting dynamic behaviour for operationally-relevant mission-task-elements
Application of linear and nonlinear model predictive control for reducing helicopter cross-couplings
No full textSingle rotor helicopters have strong cross couplings manifested in the response to control between longitudinal and lateral-directional commands. These couplings cannot be eliminated by static considerations of control phasing since the cross coupling is a function of the frequency content of the control input. This paper proposes a model predictive control (MPC) method to alleviate the strong helicopter cross-couplings (e.g., roll due to pitch control and pitch and roll due to collective control). The advantage of using MPC is that this well-known discrete method in optimal control has the powerful capability of inclusion of look-ahead information about the frequency content of the input and states constraints. The paper investigates both whether linear and nonlinear MPC are suitable for online application to helicopters cross-couplings reduction. It is demonstrated that both linear and nonlinear MPC are effective methods in reducing cross-coupling effects on a Bolkow Bo-105 helicopter even when external disturbances and model errors are present. Using the ADS-33 handling qualities (HQs) criteria on crosscouplings, the paper demonstrates that Level 2 and 3 HQs of the uncontrolled helicopter are improving to Level 1 HQs once the MPC controller is switched on with almost ideal off-axis rate response corresponding to no couplings. Furthermore, compared to a classical proportional-integral-derivative (PID) controller, the MPC performs 55 percent to 80 percent better than the PID with and without simulation model uncertainty or disturbance introduced in the controller
A propeller blade design for experimental stall flutter investigations
No full textWith the development of modern propellers for low acoustic emissions and high performance, the influence of propeller aeroelasticity at low speed, highly loaded conditions may induce stall flutter. Therefore, this must be examined to ensure safe operations. To this end, a propeller blade design has been developed which aims to induce torsional stall flutter in a controlled experimental environment. The design has been developed using rigid and elastic CFD, with the results and process presented within this paper. The main objective is to use the final design and test data for validation of CFD and other aeroelastic method
Evaluation of rotorcraft Pilot Induced Oscillations (PIO): results from a DLR/NRC collaborative project
No full textPilot-induced oscillations (PIOs) still pose a significant risk to safety of rotorcraft operations, particularly as no formal evaluations are conducted during test and evaluation programs. Usually during experimental flight testing if PIOs are observed, additional testing and evaluations are conducted. This paper details results from a joint research effort undertaken by researchers at the National Research Center Canada (NRC) and the German Aerospace Center (DLR) to investigate and test novel methods and techniques to assess PIOs occurring in rotorcraft. The efforts included modifications to test processes and the use of PIO detection and prediction criteria. The research was conducted using both a ground-based simulation facility and a research helicopter. Results of the campaign showed the suitability of a novel subjective assessment scale and a PIO detection algorithm. This was confirmed through both objective and subjective assessment. Furthermore, modifications to ADS-33 mission task elements were also considered to improve the applicability to testing for PIOs
Helicopter rotor performance improvement by piecewise dynamic blade twist
Get PDFPiecewise dynamic twist is studied as a method for reducing rotor power and improving rotor performance. A rotor performance calculation model is established based on the anisotropic composite moderate deformation beam model and used to power prediction and flow field analysis at different flight speeds. The theoretical prediction is consistent with the flight test data, which verifies the validity of the analysis model. The blade is divided into inner and outer segments in the radius direction according to the airfoil distribution of UH-60 helicopter. The effect and its mechanism of the piecewise dynamic twist on the rotor power is investigated from the point of view of the angle of attack and lift-to-drag ratio distribution over the disk. Overall, the effect is proportional to the amplitude of the dynamic twist, changes periodically with the phase angle, and increases first and then decreases with the flight speed. A set of piecewise dynamic blade twist schemes are obtained by the traversal method, which are better than the linear negative twist scheme at any flight speed
Tail-shake risks assessment & mitigation by wind-tunnel tests on air-intake installation on a heavy-weight helicopter configuration
Get PDFIn this work, the key role of the upper-deck design including engine installation as a potential source of tail-shake is at focus. The work is based on a Wind-Tunnel Test (WTT) campaign performed at the Airbus Helicopters’ Marignane wind tunnel facilities on a high-fidelity minibody fuselage at scale 1:3.5 representing a generic heavy-helicopter upper deck. Two different engine intake installations for a Power Unit (PU) have been investigated; in a first configuration, the air intake is implemented at the pylon-fairing trailing edge. The second configuration consists in positioning two air intakes on each side of the pylon fairing, close to the maximum cross-section location. Different measurement methods to evaluate aerodynamic interactions and wake sources are proposed. They consist in flow-separation assessments from surface oil flow visualizations, time-resolved particle image velocimetry (PIV) measurements, as well as unsteady skin-pressure measurements at the cowlings. Tail-shake related indicators are then proposed. Basically, a configuration which produces strong vortices characterized by a broadband spectral signature is believed to gather all the conditions for tail-shake to emerge. The flow over the baseline configuration (i.e. without air intake) is first analyzed for various combinations of angle of attack and sideslip, highlighting four different areas of flow separation at the cowlings. The complex flow topology around the upper deck is then assessed, which includes a spectral analysis of the flow unsteadiness in the time-resolved PIV planes. The influence of the air intakes (operating or not) is then evaluated. When located at the pylon-fairing trailing edge, the impact of the operating air intake on the engine-cowlings dynamic pressure and the flow-field topology is spectacular. The air intake is shown to be responsible for the generation of an intense broadband wake interacting with the pylon-fairing lip vortices, which is believed to be a potential severe source of tail-shake. The second air-intake configuration is also not favorable, because it requires enlarging the pylon fairing by 100 mm to integrate ducts from the inlets to the PU, which generates an intense wake similarly to a blunt body. At last, a mitigation mean is proposed for the first configuration. It demonstrates a significant reduction of the wake intensity and broadband signature at the source
Aerodynamic analysis of rotor/propeller wakes interactions on high speed compound helicopter
Get PDFIn the context of the development of high speed compound helicopters, the main rotor may not be an efficient propulsive device at high speeds and a propeller has to be added in order to reach high advancing velocities. On such configuration, at low speed, the propellers are in strong interactions with the main rotor wake which affects their performance and aircraft maneuverability. The present work numerically investigates the aerodynamics of the rotor / propeller interaction on rotorcraft similar to the Racer from Airbus Helicopters. Through the comparison of two different levels of modeling it is shown that at high advance ratio, a simple free wake model is suitable to give most of the interaction effects, while in hover, a full CFD unsteady computation is necessary to precisely capture all the unsteadiness of the interaction. By comparing two different CFD solvers it also demonstrates that the results are highly sensitive to the choosen numerical setup. This paper also outlines the different behaviors of the propeller when it is fully inside the rotor wake or out of it, and therefore the need for a precise control of the rotorcraft in the transition between hover to fast forward fligh
Rotor power savings with active camber actuation varying baseline rotor properties and operating conditions
Get PDFA variation of helicopter main rotor properties was investigated with regard to their effects on active camber induced power savings using a comprehensive analysis model including elastic blade modeling and free vortex wake analysis. A Bo 105 main rotor was used as the baseline rotor in this work. This study was aimed at analyzing the transferability of results on active camber induced power savings to other rotor systems, while also identifying design targets for a rotor designated to be operated with an active camber system. A range of advance ratios from 0 to 0.35 was investigated. Active camber actuation on the modified baseline rotors was examined with regard to the absolute power variation compared to the original baseline rotor, and the relative power variation compared to the modified baseline rotor. The rotor blade torsional stiffness did not prove to be an important design parameter to optimize rotor power at high-speed flight using active camber. Only the relative rotor power savings from active camber notably depended on the blade torsional stiffness. The built-in twist of the baseline Bo 105 rotor was identified to be below the optimum. This lack of efficiency was compensated by active camber. Therefore, active camber yielded a reduced capability to improve rotor power for higher geometric built-in blade twist, especially for low advance ratios. Increased efficiency of the baseline rotor, however, did not necessarily reduce the efficiency gain from active camber. This was shown in case of varying the number of rotor blades and the blade taper ratio, where greater baseline rotor efficiency still resulted in an increase of relative power savings from active camber. A reduction in rotational speed resulted in significant rotor total power savings, but had a negative effect on the power savings from active camber. However, active camber was able to ameliorate detrimental effects from a reduced rotor rotational speed on thrust and stall margins