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Feasibility Assesment: A Cycloidal Rotor to Replace Conventional Helicopter Technology
Abstract
A mathematical model is presented for the solution of the aerodynamic performances of a cycloidal rotor. It is solved algebraically for the cases where the forces and incoming wind velocity share the same direction. The model is validated against experimental data coming from three different sources. It is then used to evaluate the viability of using a cycloidal rotor as a replacement for the traditional tail rotor of a helicopter. By doing so, power is saved by the helicopter having non-null advance ratios. The savings reach 50% at an advance ratio of 0.33. It was found that imposing a constant cycloidal rotor angular velocity does not reduce the efficiency and that high pitch angles are the most efficient. The experimental data indicates that three dimensional effects have an influence on the cycloidal rotor performance. A three dimensional Euler fluid dynamic analysis confirms the experimental findings. Copyright © (2014) by the Royal Aeronautical Society. All rights reserved.
... They assessed the potential of cycloidal rotors to be used in large-size unmanned or small-size manned vehicle propellers. Previous work by the current authors led to the development of various models for the study of the cycloidal rotor under different configurations (Gagnon et al., 2014a(Gagnon et al., , 2014b(Gagnon et al., , 2014c. ...
... The scope of this paper is to study the implementation of a cycloidal rotor as the replacement of the tail rotor on otherwise conventional helicopters. It has been previously shown that the configuration is aerodynamically efficient (Gagnon et al., 2014a(Gagnon et al., , 2014b. This paper further studies the implementation feasibility by studying the efficiency of the cycloidal rotor airfoils under various operating conditions. ...
... A computational fluid dynamics model is used to evaluate the importance of the three-dimensionality of the rotor flow. The proposed concept is shown in Figure 2. It was chosen after inspecting the aerodynamics of three configurations which were reported in previous works (Gagnon et al., 2014a(Gagnon et al., , 2014b. ...
Purpose-Few modeling approaches exist for cycloidal rotors because they are a prototypal technology. Thus, the purpose of this study was to develop new models for their analysis and validation. These models were used to analyze cycloidal rotors and a helicopter that uses them instead of a tail rotor. Design/methodology/approach-Three different models were developed to study the aerodynamic response of cycloidal rotors. They are a simplified analytical model resolved algebraically; a multibody model resolved numerically; and an unsteady computational fluid dynamics (CFD) model. The models were validated using data coming from three different experimental sources, each with rotor spans and radii of roughly 1 m. The CFD model was used to investigate the influence of rotor arms. The efficiency and the stability of the rotor in different configurations were studied. An aeroelastic multibody simulation was used to verify the influence of flexibility on the rotor response. Findings-The analyses suggested that cycloidal rotors can increase the efficiency of a helicopter at high velocities while flexibility reduces it and may lead to instabilities. Research limitations/implications-These models do not consider the effect of boundary layer friction on the trailing vortices generated by the rotor blades. Practical implications-These models allow a four-step aerodynamic optimization procedure. First, a range of optimized configurations is obtained by the analytical model. Second, the multibody model refines that range. Third, the CFD model detects eventual problematic blade interactions. Originality/value-The models presented should serve researchers and industrials looking for a means to measure the performance of cycloidal rotors concepts. The results presented also guide an initial cycloidal rotor design.
... They receive a lot of attention because of their ability to instantly change the direction of their thrust in a 360 • plane perpendicular to the cylinder's axis. Recent research by the authors identified a strong potential for better handling and lower energy consumption of aircraft through the use of cycloidal rotors using analytical rigid [13] and flexible [14] solutions, fixed [15] and free (untethered) [16] multibody dynamics models, and bi-and tridimensional computational fluid dynamics [17,18]. This paper thus attempts to further investigate two promising aircraft models which rely on cycloidal rotors to provide better control and potentially reduce energy consumption. ...
Multibody dynamics models of a helicopter and two cy-cloidal rotor aircraft concepts capable of vertical takeoff and landing (VTOL) are constructed. The first concept aircraft is a helicopter equipped with two lateral cycloidal rotors acting as a replacement for its tail rotor and is named the Heligyro. The other concept is named the Quadricyclogyro and is propelled exclusively by four cycloidal rotors whose axes are aligned. The autopilot algorithm is implemented as a proportional, integral, and derivative (PID) controller and is tuned using a genetic optimization algorithm directly on the multibody models. Aircraft vibration and energy requirements are monitored and fed as penalty functions to the genetic algorithm. The time-domain responses of the aircraft attempting to follow mission paths of variable complexity obtained from the literature are studied. Overall , the tuned VTOL aircraft are able to reproduce the requested routes with good accuracy if a certain speed threshold is respected .
... The variation in the phase angle and amplitude of movement allows, respectively, changes in the thrust direction and thrust magnitude [5][6][7][8]. This remarkable feature allows the use of the cycloidal rotor for propulsion, lift, and air vehicles control in both military and civilian applications [9][10][11][12]. Thus, an air vehicle whose main source of propulsion and lift is the cycloidal rotor, can take off and land vertically, hover, and may move in any perpendicular direction to the rotating axis [13][14][15][16][17]. ...
Cycloidal rotors have the inherent ability to provide vectorized thrust with fast reaction times. However, their present efficiency levels restricts their routinely use as propulsion elements for air-vehicles. Efforts have been made to improve the performance of cycloidal rotors through the optimal combination of its geometric parameters. In the present work the performance improvement of cycloidal rotors is demonstrated using a different approach, namely by imposing an unsteady change on the dynamics and structure of the vortices developed around the blades. This required change on the flow field, around the blades, was applied by adding an harmonic vibration to the traditional cycloidal movement of the blades, thus causing the blades to vibrate as they describe their oscillating pitch movement. This research on the effect of harmonic vibration, on lift and drag coefficients, was done first for a single blade profile, and later for a full cycloidal rotor, and is based on the Takens reconstruction theorem and Poincaré map. Therefore, diverse test cases and conditions were considered: a single static airfoil, an oscillating blade profile, and a complete cycloidal rotor. We concluded that the optimal combination of harmonic vibration parameters, specifically; amplitude, phase angle and vibration frequency, under adequately tuned design conditions, can have a beneficial effect on cycloidal rotor performance.
This paper presents some aspects concerning the 2D RANS numerical modeling of a Darrieus cross flow marine turbine. Two main features of the modeling are studied. The first deals with the influence of the near wall grid density on the numerical results. Most of the available literature concerning the occurrence of stalling foils emphasizes the need for a fine grid mesh at wall fitting y+ around the unity or less at the first near wall cell center. Nevertheless, in the case of a Darrieus turbine, the influence of this parameter has not yet been studied precisely. In particular, the exact y+ specification is not known, and its influence either on the global turbine performance or on the local flow field, has not been outlined. The present work provides insight into the y+ influence in a 2D Darrieus turbine and deals with its maximum acceptable value. The second feature concerns the ability of a 2D modeling to represent, the actual 3D flow in the turbine. The power coefficients CP are compared to those obtained in the hydrodynamic LEGI tunnel on a small scale model. The experimental power coefficients are presented with their associated precision. The comparisons show a medium tip speed ratio range around the nominal point for which the instantaneous ratio of the experimental and numerical power coefficients is a constant significantly lower than 1 regardless of the azimuthal position of the blades. This constant ratio is thought to be representative of the tip and arm-blade junctions losses.
In the following paper we perform an unsteady CFD analysis of the effect of several two dimensional blade geometrical parameters in the performance of CROP. The values will be analysed in terms of power loading (Thrust/Power) vs Disk Load (Thrust/Disk Area). The geometric parameters that we investigate include: blade thick-ness; rotor solidity (number of blades); and pitching amplitude.
This paper describes the effect of some design parameters on the performance of a Giromill vertical axis wind turbine. A Giromill wind turbine has been designed, manufactured and tested. The turbine performance has been investigated with varying the design parameters such as, pitch angle, number of blades, airfoil type, turbine radius and its chord length. Then, the results were used for the comparison between the performance achieved while changing the design parameters.Vast number of experiments have been performed with changing the above mentioned parameters. The effect of each parameter on the power coefficient and torque coefficient has been studied and explanation of the results was also discussed. It has been found that the pitch angle, turbine radius and chord length have a significant effect on turbine power coefficient.The maximum power coefficient obtained in this research was 25% using turbine radius of 40cm, chord length 15cm, pitch angle of 10°, airfoil type NACA 0024, and four blades (which is found to be the best configuration in this study). For the effect of pitch angle, the obtained maximum power coefficient is decreasing, this decrease in performance was due to increasing in the pitch angle above 10° and also due to decreasing it below this value showing the high effect of pitch angle. It was also noticed that, when decreasing the turbine radius to 20cm at 0° pitch angle the maximum power coefficient is much decreased. Moreover, decreasing the chord length to 12cm at 10° pitch angle decreases the maximum power coefficient significantly, which again show the high effect of turbine radius and chord length. In order to compare the effect of airfoil type; the blades with NACA 4420 were used compared to NACA 0024 at the same above parameters of turbine radius 40cm, chord length 15cm, pitch angle of 10° and four blades. The maximum power coefficient obtained was 15%. Finally, the effect of the number of blades have been investigated using two, three and four blades at 0° pitch angle and the same other above parameters of turbine radius 40cm, chord length 15cm and airfoil type NACA 0024. The obtained maximum power coefficients were decreased significantly when decreasing the number of blades from four to two blades.
This work discusses the possibility to use the cycloidal rotor technology to provide anti-torque to otherwise conventional helicopter designs. A simple analytical model of cycloidal rotor aeromechanics is provided to support its sizing. The analytical model is validated using other approaches of increasing complexity and experimental results. Three anti-torque configurations are considered: a single vertical axis rotor at the tail, a single longitudinal axis rotor at the tail, and two sideways axis rotors at both sides of the airframe. The first and the last configurations are analyzed in more detail. The required power for anti-torque capabilities is compared to that of a conventional rotor and possible advantages are discussed in terms of added lift and thrust and better control capabilities. Copyright© 2014 by the American Helicopter Society International, Inc. All rights reserved.
The vortex shedding characteristics of finite aspect ratio plunging wings, set to a zero geometric angle of attack, have been examined using force, particle image velocimetry and volumetric velocimetry measurements. Dual mode deflected jets have so far only been observed for two-dimensional airfoils. In this study, we investigate whether one can observe this phenomenon with finite aspect ratio wings, to significantly improve the time-averaged lift by exploiting the proper deflection mode. A gradual transition between the existence of these deflection modes in the 2D case and its absence on a finite aspect ratio wing is observed by gradually increasing the spacing between the tip of the wing and endplate. We believe that tip vortices may be preventing the formation of these deflected jets. Volumetric measurements illustrate that intertwined vortex loops are formed downstream of the wing, consisting of trailing edge and tip vortices. A double helix structure is observed within the trailing edge vortex, allowing the two consecutive loops to remain interconnected.
This work presents aerodynamic and aeroelastic models used to investigate the behavior of a cycloidal rotor scaled for personal transportation applications. Three different models are considered. The impact of solidity on performance is evaluated using a two-dimensional RANS viscous flow model with the boundary layer fully resolved. An aeroelastic multibody model is used to further evaluate the effects of aeroelasticity on the performance of the rotor.
This paper describes the aeroelastic model to predict the blade loads and the average thrust of a micro-air-vehicle-scale cycloidal rotor. The analysis was performed using two approaches: one using a second-order nonlinear beam finite element method analysis for moderately flexible blades and a second using a multibody-based large-deformation analysis (especially applicable for extremely flexible blades) incorporating a geometrically exact beam model. An unsteady aerodynamic model is included in the analysis with two different inflow models: single streamtube and double-multiple streamtube inflow models. For the cycloidal rotors using moderately flexible blades, the aeroelastic analysis was able to predict the average thrust with sufficient accuracy over a wide range of rotational speeds, pitching amplitudes, and number of blades. However, for the extremely flexible blades, the thrust was underpredicted at higher rotational speeds, and this may be because of the overprediction of blade deformations. The analysis clearly showed that the reason for the reduction in the thrust-producing capability of the cycloidal rotor with blade flexibility may be attributed to the large nosedown elastic twisting of the blades in the upper half cylindrical section, which is not compensated by a noseup pitching in the lower half-section. The inclusion of the actual blade pitch kinematics, unsteady aerodynamics, and flow curvature effects was found crucial in the accurate lateral force prediction.
This paper presents the results of a flight simulator test campaign aimed at understanding the effect of high-frequency dynamics associated with helicopter aeroservoelasticity on the proneness to rotorcraft-pilot couplings and specifically to pilot-assisted oscillations. Linearised aeroservoelastic models representative of helicopters in hover and in forward flight have been flown in a full motion flight simulator by trained test pilots, performing selected mission task elements. The handling qualities of the vehicles have been intentionally degraded by modifying the gearing ratios between the control inceptors and the flight controls and by introducing time delays representative of realistic fly-by-wire flight control systems. Clear evidence of pilot-induced oscillations has been found while performing the roll step manoeuvre, especially with the soft-inplane hingeless helicopter with a lightly damped main rotor first regressive lead-lag mode. Based on subjective pilot ratings and objective measures, the aeroservoelastic models require higher pilot workload than corresponding rigid-body models. The repeatable occurrence of an unstable pilot-assisted oscillation event with only one test pilot flying the aeroservoelastic model has been explained by the interaction of the pilot's involuntary biodynamic feedthrough, identified by specific experiments, and the above mentioned regressive lead-lag mode.
A combined experimental and numerical study of a cyclogiro, rotor operating at Reynolds numbers,about 40,000 has been conducted. The study reveals complex flow field with complex (unsteady) interactions between the blades and the wakes of other blades. In spite of this complexity, time-averaged integral forces acting on the rotor can be predicted by a simple momentum theory, properly corrected for thrust-producing area of the rotor and for large Magnus effect. The effective thrust producing area was estimated to be about half of its projected area, suggesting that the effectiveness of a cyclogiro rotor may be comparable with that of a heavy-loaded helicopter rotor.
A cyclocopter propelled by a cycloidal blade system is a concept of vertical takeoff and landing (VTOL) vehicle that has excellent hovering characteristics. The cycloidal blade system, which can be described as a horizontal rotary-wing, offers good thrust levels and a unique ability to change the direction of the thrust almost instantly. In this study, an unmanned, scaled cyclocopter was designed and developed by an optimization process. Flight esperiments and numerical analyses were performed to show that the cycloidal blade system can be used as a viable propulsion system. The esperimental results of the cyclocopter show good agreement with analytical predictions showing its potential as a VTOL vehicle.
This paper investigates an advanced vertical axis turbine to enhance power generation from water energy. The turbine, known as a cycloidal water turbine, is a straight-bladed type adopting a cycloidal blade system that actively controls the rotor blades for improved turbine efficiency, according to the operating conditions. These characteristics enable the turbine to self-start and produce high electric power at a low flow speed, or under complex flow conditions. A parametric study has been carried out by CFD analysis, with various characteristics including different number of blades, chord length variations, variety of tip speed ratios, various hydrofoil shapes, and changing pitch and phase angles. Optimal parameters have been determined, and the performance of the turbine has achieved approximately 70% better performance than that of a fixed pitch turbine. An experimental study has also been carried out which shows that the results correlate quite well with the theoretical predictions although the power output was reduced due to the drag forces of the mechanical devices. Another numerical optimization was carried out to improve the rotor performance by adopting an individual blade control method. Controllable pitch angles were employed to maximize the rotor performance at various operating conditions. The optimized result obtained using genetic algorithm and parallel computing, shows an improvement in performance of around 25% compared with the cycloidal motion.
Simplified unsteady aerodynamic and inertial force models were developed for a cycloidal propeller system operating at small forward speeds. These models were used to support the development of a VTOL concept demonstrator vehicle. The nature of the blade motion showed that interactions between the blades could be neglected to first order. The downwash through the rotor could not be neglected because of the induced angle of attack caused by the downwash. The total force was compared with wind tunnel data produced by Wheatley in the 30's and a ground test system developed for this project. It was found that the estimates produced by the model agreed with the total force and power to within 10% for the Wheatley data. Agreement between the model and the current tests was within 5% for the total force and power. The inertial loads were used to design the blade structure, the support structure, and the blade motion system. It was found that the inertial loads were much larger than the aerodynamic loads. The aerodynamic effect of forward motion or wind moving toward the propeller was defined. It was modeled as a constant velocity induced flow through the propeller that induced an angle of attack of the blades. It was found that the cycloidal propeller was very susceptible to wind gusts, but that the resultant force from the wind gust could be easily damped out. The same forward motion model was used to simulate downwash. By modeling the downwash as a constant velocity flow through the propeller, the lift and thrust of the propeller was linked to the induced flow velocity. The effect of the induced flow velocity was then linked back to its effect on the lift and thrust produced by the propeller. Mode of access: Internet via the World Wide Web. System requirements: Internet connectivity; World Wide Web browser software; Adobe Acrobat Reader. Title from title screen. Electronic book in PDF. Thesis (M.S.)--Mississippi State University. Department of Aerospace Engineering. Includes bibliographical references.