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Analytical Modeling of a Cyclorotor in Hovering State
Abstract
In the paper it is proposed and described in detail a mathematical model that is able to assist in the design of cycloidal rotors. The method is formulated on a semi-empirical way including unsteady aerodynamic effects that are based on first principles. It is able to predict the overall generated thrust and the power required by the operation of the cycloidal rotor. The model also includes a kinematic package that can provide an instantaneous design and animation of the cycloidal rotor under different regimes of operation. For validation it was addressed three different rotor configurations where it was varied several rotor parameters, namely: pitch amplitude; pitching axis location; blade chord; airfoil thickness; phase angle of eccentricity. It was shown that the proposed model is able to provide a good estimation of thrust and power when compared with the experimental data from these different sources, showing that the semi-empirical approach could be applied in a more general way.
... The dynamic pitching provided by the four-bar linkage mechanism is expressed by the following equations [13]: ...
... This mechanism, which has proved well for cyclogyros used in aeronautical propulsion [13][14][15][16][17][18], is simple, reliable, and has the ability to self-adjust the turbine dynamics as a function of the rotating speed of the rotor and also on the direction and magnitude of the incoming wind. It is noted that the system kinematics also allows for an asymmetric pitching schedule of the blades, which could be beneficial since the frontal area of the rotor operates at a different angle of attack than the rear region. ...
... To this end, data for a cyclogyro of similar dimensions as the wind turbine, operating in propulsion mode (V wind ¼ 0), are used. This configuration, here denominated IAT21-L3 rotor, was analyzed as a part of an European research project, which aimed to develop the cyclogyro technology as a mean of propulsion for small and medium size aircraft [13,18,[20][21][22][23]. It is obvious that the results obtained for the IAT21-L3 rotor do not faithfully represent the features of a VAWT, since in propulsion mode energy is being provided and not extracted from the flow. ...
In this paper, four key design parameters with a strong influence on the performance of
a high-solidity variable pitch vertical axis wind turbine (VAWT) operating at low
tip-speed-ratio (TSR) are addressed. To this aim, a numerical approach, based on a
finite-volume discretization of two-dimensional (2D) unsteady Reynolds-averaged
Navier–Stokes (URANS) equations, on a multiple sliding mesh, is proposed and validated
against experimental data. The self-pitch VAWT design is based on a straight-blade Darrieus
wind turbine with blades that are allowed to pitch around a feathering axis, which
is also parallel to the axis of rotation. The pitch angle amplitude and periodic variation
are dynamically controlled by a four-bar linkage system. We only consider the efficiency
at low and intermediate TSR; therefore, the pitch amplitude is chosen to be a sinusoidal
function with a considerable amplitude. The results of this parametric analysis will
contribute to define the guidelines for building a full-size prototype of a small-scale wind
turbine of increased efficiency. [DOI: 10.1115/1.4032794]
... The airfoils depict an increase in C p with t/c as seen through Fig. 19(b), and this observation suggests that for a given k, upon increasing the blade thickness, the performance of the rotor seems to be promising. Apart from this, they have also examined the effect of b through a controlled pitching mechanism as suggested by Leger et al. 94 Their findings suggest that using the proposed pitching mechanism, the rotor generates a relatively higher torque compared to fixed b while operating a low k. Furthermore, it is to be noted that the rotor with six blades produces a higher torque compared to lesser number of blades. ...
... 59 At low k, the pitching mechanism for VAWT generates higher torque. 94 ...
The utility of small wind turbines (SWTs) covering horizontal and vertical-axis types as off-grid, standalone, and decentralized energy supplement systems has gained market attention. Such turbines primarily operate at low Reynolds number ( Re) and low tip speed ratio ( λ) conditions. Under such circumstances, the design, development, and testing of SWTs have become a tedious task, mainly due to the lack of precise aerodynamic knowledge of SWT. The present article reviews the fundamental aspects of SWT, including airfoil selection criteria, blade design, and aerodynamic improvement through passive flow control and augmentation techniques. The article also reports several classes of potential airfoils that can be employed in the design of SWTs. The airfoils considered operate mainly in the range of Re = 0.3 x 10 ⁵ to 3 x 10 ⁵ and λ = 0.5 to 6. Besides the classical approach, the article showcases the prospects of several bioinspired profiles/shapes that are meant for SWTs operating at low Re and λ conditions. Towards the end, various design constraints and applicability of SWTs are summarized.
... At this time, a European consortium, under the project CROP (Cycloidal Rotor Optimized for Propulsion), developed several works which allowed the undertaking of various important conclusions regarding the use of cycloidal rotors in commercial aircrafts. Under this project, various works were performed, including analytical studies [27,28], numerical simulations [13,29,30] and experimental tests [31], and demonstrated that cycloidal rotors can be integrated with helicopters, allowing an increase in efficiency to about 60%, or with wings, allowing an efficiency increase of about 40% [32]. In a follow-up of this project, Habibnia and Pascoa [33][34][35] numerically studied the operation of cycloidal rotors under diverse conditions and altitudes, and demonstrated the possibility of optimizing these devices by implementing artificial neural network algorithms. ...
Airships are a method of transportation with reduced fuel consumption and great potential for different applications. However, these aerial vehicles still present considerable control and maneuverability problems. To overcome these issues, in the current work, we propose the use of plasma-enhanced cycloidal rotor thrusters to increase the controllability and maneuverability of airships. Numerical simulations are carried out to demonstrate the potential of plasma actuators to enhance the efficiency and thrust vectoring capabilities of cycloidal rotors. The fluid dynamics of the flow effects created via the operation of the cycloidal rotor is analyzed with and without plasma actuation. In addition, smart combined plasma actuation is proposed to further optimize the plasma-coupled cycloidal rotor device. The results demonstrated that by using this novel approach, the lift coefficient was increased by about 27%. To summarize, the obtained results for a rotational speed of 100 rpm are compared with results for 200 rpm, and it is demonstrated that for lower rotational speeds, the plasma effect is increased and more significant. This allows us to conclude that airships are an ideal application for plasma-enhanced cycloidal rotors, because since the lift is mostly generated via aerostatic principles, the plasma-enhanced thruster can be operated at lower rotational speeds and effectively increase the controllability and maneuverability of the aerial vehicle.
... A European Union project entitled "CROP" was developed with the intention to work on aerodynamic efficiency, optimizations and designing the most promising configurations of cyclorotors as propulsion systems. Under this project, Leger et al. [17][18][19] made detailed analytical studies to detect the optimal mechanical dimensions under specific operating conditions. Their model was able to compute the dynamic and kinematic behavior of a UAV-scale cyclorotor operating at hover. ...
The present study demonstrates an improved performance of cycloidal rotors by actively controlling the pitching oscillations and rotational speeds. The computational fluid dynamics (CFD) coupled with artificial neural network (ANN) were the methodologies used in the optimization analysis for the hover-state operation rather than the take-off mode under ground effects [1]. The former is carried out to obtain numerical predictions at various operating conditions for an UAV-scale cyclorotor. The oscillating-rotating blades and the corresponding flowfield is computed unsteadily along the complete circular trace for performance considerations. From CFD simulations, the optimum operational state is predicted for a 30∘ and 500 (rpm) pitch angle and rotating speed, respectively. On a second step, by training the ANN with the CFD database at various operating conditions and parameters, the ANN was then capable of analyzing the optimum states for operating at different conditions. The pitching oscillation schedule is then optimized for each rotational speed by using ANN and for each azimuthal location over the traversing trace. This will imply to perform on-board control in active mode for the blades, rather than assigning constant pitching oscillations for all operating states. This active control concept showed to be a potential approach to enhance the cyclorotor efficiency by 12 percent in average.
... A European Union project entitled "CROP" was developed with the intention to work on aerodynamic efficiency, optimizations and designing the most promising configurations of cyclorotors as propulsion systems. Under this project, Leger et al. [17][18][19] made detailed analytical studies to detect the optimal mechanical dimensions under specific operating conditions. Their model was able to compute the dynamic and kinematic behavior of a UAV-scale cyclorotor operating at hover. ...
The present study demonstrates an improved performance of cycloidal rotors by
actively controlling the pitching oscillations and rotational speeds. The computational
fluid dynamics (CFD) coupled with artificial neural network (ANN) were the
methodologies used in the optimization analysis for the hover-state operation rather
than the take-off mode under ground effects [1]. The former is carried out to obtain
numerical predictions at various operating conditions for an UAV-scale cyclorotor. The
oscillating-rotating blades and the corresponding flowfield is computed unsteadily
along the complete circular trace for performance considerations. From CFD
simulations, the optimum operational state is predicted for a 30◦ and 500 (rpm) pitch
angle and rotating speed, respectively. On a second step, by training the ANN with the
CFD database at various operating conditions and parameters, the ANN was then
capable of analyzing the optimum states for operating at different conditions. The
pitching oscillation schedule is then optimized for each rotational speed by using ANN
and for each azimuthal location over the traversing trace. This will imply to perform onboard
control in active mode for the blades, rather than assigning constant pitching
oscillations for all operating states. This active control concept showed to be a potential
approach to enhance the cyclorotor efficiency by 12 percent in average.
... The Cycloidal Rotor Optimized for Propulsion (CROP) project (CROP 2013b), a project under the European Union FR7 framework license, held cyclorotors as the optimizing target. Leger et al. (2015Leger et al. ( , 2016 studied the different operating principles of a cyclorotor at a hovering state using an analytic approach. Furthermore, in another numerical work, they predicted the presence of threedimensional effects, tip leakage, and main flow structure considerations when equipped with endplates (Xisto et al. 2014b). ...
... The blade numerical domain exchange information with the rotor domain through a sliding mesh as well as the rotor and the environment domains. Each blade region moves according to Eq. (3) [33] which describes the blade pitch angle variation [ ] imposed by the mechanical system shown in Fig. 6. ...
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.
A three-dimensional (3D) unsteady Reynolds averaged Navier–Stokes (URANS) computational fluid dynamics (CFD) toolkit for cycloidal rotors was developed and used to perform a parametric study. It included blade aspect ratio, side disks, pitch mechanism, blade camber, and shaft size. The influence of the pitch rod length showed the importance of the lift distribution between the upstream and downstream parts of the rotor cylinder. The application of blade camber significantly affected thrust and power, while having a limited effect on efficiency. A similar effect was obtained by varying the pitch rod lengths. The presence of a central axis in the rotor had a negligible effect on efficiency. The most significant impact on efficiency came from the side disks, which behaved similarly to winglets on fixed-wing aircraft. However, changing the aspect ratio of the blades showed a similar response to that of aircraft wings, but with a smaller effect, making it conceivable to fly a square-bladed cyclorotor without side disks. To verify the CFD model, a cycloidal rotor was also built using 3D printed parts and carbon fiber tubing. It was then operated on a test rig where thrust and power were measured for speeds ranging from 408 to 2528 RPM. On the test bench, the blades were pitched with a uniform asymmetric mechanism. The maximum nose-up pitch angle in upstream of the rotor axis was 34.8°. Due to its rotation around the rotor and its pitching in the opposite direction, the maximum nose-up pitch angle of the downstream blade was 38.6°. The obtained rotor thrust and power curves and the flow visualization around the rotor confirmed the validity of the CFD toolkit.
In the operation of cycloidal rotors the flow structure deformation, and associated curvature, limits the possibility of achieving an optimum working point. In this study, first, we started by performing a detailed analysis of the start-up characteristics of a cycloidal rotor in order to identify the evolution of kinematic and dynamic characteristics of its operation. Afterwards, we identified the effects of applying multiple plasma boundary layer control, of dielectric barrier discharge type. This application is defined in both sides of the blades, since in cyclorotor movement they change from pressure to suction side over one blade rotation. A control law is defined to regulate the operation of the plasma actuators as the rotor blade move in azimuthal direction. The coupled multiphysics simulation of the cyclorotor and plasma flow is performed by adding to Fluent two user define functions to model the complex cyclorotor movement and the plasma momentum effect. The k- SST turbulence model is used in the computations. The study is performed for a cyclorotor comprised of six NACA 0016 blade profiles that rotate at 200 rpm. The results demonstrate the advantage of using multiple plasma actuators in order to control the blade flow field. In particular, the configuration with six actuators, three in each side, was the most effective, by improving the thrust by 2.3%, as compared to the base case, and achieving a reduction in power requirements of 0.9%.
Cycloidal rotors have shown to be susceptible to achieve larger efficiency
enhancements while being subjected to various designs and operating conditions. In
this work an improvement on the performance of a UAV-scale cycloidal rotor is
demonstrated at hovering mode and for various operating conditions with three endwall
designs. The novel concept of actively controlling the pitching oscillations at different
rotational speeds is obtained from a coupled methodology of computational fluid
dynamics (CFD) and artificial neural network (ANN). In this approach, rather than a
free-sided rotor, the effects of employing single and double endwalls are targeted for
optimizing the operation at hover-state, whereas, the previous work focused on
forward-flight and lift-up phases (Habibnia Rami and Pascoa 2021). A detailed
database from numerous combinations of operating conditions is obtained from CFD
predictions. Over eighteen principal parameters are processed and computed along
the continuous 360◦ circular trace, which is showing novel results. Subsequent to
performing a precise database from the rotating-oscillating blades under various
operating conditions for all the three designs, the ANN approach is trained from the
CFD data for optimization analysis and to propose the optimum pitching schedules by
using a parametric study on the cyclorotor performance at each operating condition.
Since each design can be used in its specific application, the optimum operating state
for each of the endwall designs is further illustrated and reported as a baseline data.
The coupled analysis from CFD and ANN methodologies, reports the efficiency
achieved with free-sides, doubled endwalls, and single-side endwall, respectively.
Moreover, employing a single-side endwall results in 18.8% efficiency, and the doublesided
model in 13.6% efficiency reduction as compared with the free-sided cyclorotor.
The computations on horizontal and vertical force productions are revealing an 8% and
11% higher horizontal force for free-sides design than those of double-endwall and
single-endwall models, and an average of 7% and 16% higher values in vertical force
generation in double-endwall model compared with free-sided and single-endwall
designs.
This study analyzes the effect of DBD plasma actuators on the unsteady flow of a cycloidal rotor with six blades of NACA 0016 type using computational fluid dynamics (CFD). The flow field modeling is performed through a sliding mesh technique that was used with k-ω SST turbulence model. The plasma body force generated by a dielectric barrier discharge DBD actuator is modeled with the phenomenological Shyy's model. The impact of plasma actuators on the flow is studied using two actuators located on the upper and bottom surfaces of the airfoil in each of the cyclorotor blades. Three cases are studied: actuation off; actuation over the upper surface of the blades; actuation over the bottom surface of the blades. The vorticity field and the evolution of the lift, thrust and power consumption are analyzed for when a control law is designed that combines both actuations based on the two last cases. The results show that the use of the proposed control law for plasma actuation improves the cyclorotor lift peak value per blade in 11% and the overall thrust by 1.5%. It is also demonstrated that the plasma actuator mitigates the virtual camber on the cyclorotor, this effect is named counter-virtual camber. We show that DBD actuators produce a reduction on the recirculation bubble at the blades suction surface. This effect is important to reduce the thickness of the blades, bringing improvements in terms of mitigating unsteady periodic mass acceleration in cyclorotors.
div class="section abstract"> The current paper presents the numerical study of the downwash flowfield characteristics in a cycloidal rotor at close-ground altitudes. In an aircraft equipped with this kind of thruster, the downwash flow plays significant role in different flight modes. The interaction of this downwash jet with ground in effective altitudes is studied using CFD simulations in OpenFOAM. Several operating conditions such as pitching oscillation angles, rotation speeds and height levels are all considered in this work. The results declare that close-ground operating states affects the performance of cyclorotors. The vertical and horizontal forces of a single blade is also analyzed in a complete cycloid in different operating conditions. A lead and lag in maximum and minimum extremes of force curves of a single blade is obtained while being subjected to different functional conditions. The presented results highly support an active control methodology to be taken for both pitching oscillations and rotation speeds as essential strategy for operating at optimum state.
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Cycloidal rotor is a rotor whose blades pitch around the pitching axis and revolve around the rotor shaft that is parallel to blade. It can generate omni-directional thrust with high efficiency. In this paper, the numerical simulation models were validated by the wind tunnel experiments. Then physics of the cycloidal rotor in forward flight was studied. The effects of blade number and advance ratio were qualitatively discussed based on the numerical simulation results. Results of the analysis indicate that the rotor with more blades will result in smoother force curve, so that there will be lower vibration. However, the rotor with three or four blades will be the most efficient. The maximum forward flight efficiency is obtained from medium-to-high advance ratio. The efficiency is comparable with that of a screw propeller at the same Reynolds number. At low advance ratio, the peak lift on the blade can be observed when the blade is located at the lower left part of its trajectory. This is caused by positive blade pitch angle and relatively large inflow speed, which is similar to the downwash in the rotor cage under hovering status. From medium-to-high advance ratio, the thrust and lift primarily originated from the plunging motion of the blade. If the advance ratio is high enough, there will be negative horizontal force and positive torque, which means that the blade is taking energy from the inflow. Resultant force of the horizontal and vertical force does not vary too much with the advance ratio. But with the advance ratio approaching 1.0, the direction of the resultant force will point upwards and no horizontal force can be observed.
In this work, four key design parameters of cycloidal rotors, namely the airfoil section;
the number of blades; the chord-to-radius ratio; and the pitching axis location, are
addressed, both having a strong effect on the rotor aerodynamic efficiency. To this aim,
an analytical model and a numerical approach, based on a finite-volume discretization
of 2D unsteady RANS equations on a multiple sliding mesh, are proposed and
validated against experimental data. A parametric analysis is then carried out
considering a large-scale cyclogyro, suitable for payloads above 100 kg, in hovering
conditions. Results demonstrate that the airfoil thickness significantly affects the rotor
performance; such a result is partly in contrast with previous findings for small- and
micro-scale configurations. Moreover, it will be shown that increasing the number of
blades could result in a decrease of the rotor efficiency. The effect of chord-to-radius
will demonstrate that c/R values of around 0.5 result in higher efficiency. Finally it is
found out that for these large systems, in contrast with MAV-scale cyclogyros, the
generated thrust increases as the PA is located away from the leading edge, up to
35% of chord length. Further the shortcomings of using simplified analytical tools in the
prediction of thrust and power in non-ideal flow conditions will be highlighted and
discussed.
In the present paper, the sloshing resistance performance of a huge-size LNG carrier's insulation system is evaluated by the fluid-structure interaction (FSI) analysis. To do this, the global-local analysis which is based on the arbitrary Lagrangian-Eulerian (ALE) method is adopted to accurately calculate the structural behavior induced by internal LNG sloshing of a KC-1 type LNG carrier insulation system. During the global analysis, the sloshing flow and hydrodynamic pressure of internal LNG are analyzed by postulating the flexible insulation system as a rigid body In addition, during the local analysis, the local hydroelastic response of the LNG carrier insulation system is computed by solving the local hydroelastic model where the entire and flexible insulation system is adopted and the numerical analysis results of the global analysis such as initial and boundary conditions are implemented into the local finite element model. The proposed novel analysis techniques can potentially be used to evaluate the structural integrity of LNG carrier insulation systems.
In the following paper we introduce PECyT system for enhancing the aerodynamic efficiency of cycloidal rotors. For that purpose the incorporation of Dielectric Barrier Discharge plasma actuators for active flow control on a pitching airfoil, under deep-stall conditions, will be assessed using a numerical tool. Two different arrangements of DBD actuators will be analysed, namely single-and multi-DBDs configurations. For the single-DBD plasma actuator the effect of different modes of actuation on the lift coefficient will also be studied. We will show that the multi-DBD actuator, in a steady-actuation mode, could delay stall and allows for a faster reattachment of the flow. However during the downstroke phase of the pitching cycle the unsteady operation of a single-DBD gives us the best results in terms of lift coefficient.
Performance and flowfield measurements were conducted on a small-scale cyclorotor for application to a micro air vehicle. Detailed parametric studies were conducted to determine the effects of the number of blades, rotational speed, and blade pitching amplitude. The results showed that power loading and rotor efficiency increased when using more blades; this observation was found over a wide range of blade pitching amplitudes. The results also showed that operating the cyclorotor at higher pitching amplitudes resulted in improved performance, independently of the number of blades. A momentum balance performed using the flowfield measurements helped to quantify the vertical and sideward forces produced by the cyclorotor; these results correlated well with the force measurements made using load balance. Increasing the number of blades increased the inclination of the resultant thrust vector with respect to the vertical because of the increasing contribution of the sideward force. The profile drag coefficient of the blade sections computed using a momentum deficit approach correlated well with typical values at these low chord Reynolds numbers. Particle image velocimetry measurements made inside the cage of the cyclorotor showed that there are rotational flows that, when combined with the influence of the upper wake on the lower half of the rotor, explain the relatively low efficiency of the cyclorotor.
The flying wing is a promising concept for the mid long-term commercial aviation. After the previously published conceptual design of a 300-seat class flying wing, the present article carries out a parametric analysis to optimize its planform and analyse the suitable cruise conditions to achieve the highest efficiency of such configuration. The figures of merit chosen for the optimization are the direct operating cost and the maximum take-off weight per passenger, for a specified constant range of 10 000 km. The design has to respect five relevant constraints: wingspan (limited to 80 m), cabin width, wing tip chord, number of passengers, and cruise lift coefficient. The optimum aircraft fulfilling all constraints cruises at 45 000-47 000 ft and M = 0.82, has an aspect ratio of 6.3 and taper ratio of 0.10, and carries about 280 passengers in three-class seating. This aircraft is about 20 per cent more efficient than conventional wide bodies of similar size, in terms of trip fuel.
This study describes the control mechanism of a VTOL UAV cyclocopter. The cycloidal blades system (CBS), which is a thrust system of cyclocopter is composed of several blades rotating about a horizontal axis. To generate the required thrust, the pitch angles of the blades are periodically oscillated by a pitch control mechanism. And it can change both the magnitude and the direction of the thrust almost instantly. For the thrust control mechanism of the cyclocopter, the mathematical model is derived, and the control forces to control the magnitude and direction of the thrust are determined. In addition, it is designed and developed by radio-controlled actuators.
After reporting observations on the flight of gulls which indicated that the wing top moves with a cycloidal motion, the author proceeds to an analysis of this type of motion as it might be applied to the propulsion of aircraft. Various aspects of cycloidal propellers, including their efficiency, are discussed, and their application to heavier-than-air and lighter-than-air craft is urged. The advantages of this method of propulsion are discussed. Tests of model and full-size propellers are referred to, but are not included in the paper.
This paper describes design and experimental works of a 100kg-or-heavier cyclocopter. A cyclocopter is a VTOL aircraft that has the Cycloidal Blade Systems (CBS). This system consists of a horizontal axis and several blades, which make it possible to change direction and magnitude of a thrust vector. The cyclocopter developed in this study has two CBS rotors and a horizontal tail rotor. To reduce drag, the cyclocopter has end plates, improved shape of trailing edge, and control arm. A new concept of control mechanism is proposed that uses a cam path. A stable hovering flight test is performed under tethered condition.
The viability of cycloidal rotor (cyclocopter) concept for developing hover-capable micro-air vehicles was analyzed through performance and flow field measurements. Detailed parametric studies were conducted to identify the dependence of the rotor performance on the amplitude of the blade pitch, blade airfoil profile, blade flexibility, and rotational speed. All experiments were conducted using a three-bladed, model scale cyclocopter that was tested up to the design rotational speed of 2,000 RPM. While higher pitch angles were found to increase the power loading (thrust/power) of the cyclocopter, the bending and torsional flexibility of the blades deteriorated the performance. Similarly, fixed camber proved to be detrimental to the rotor performance. Thrust measurements suggested the presence of a sidewise force (along with the vertical lift), similar to those found with lifting cylinders. Digital particle image velocimetry (DPIV) measurements made in the wake of the cyclocopter provided evidence of wake skewness, resulting in sideward force. The thrust produced by the cyclocopter was found to increase with a geometric pitch of 45° without showing any signs of stall. This behavior was explained through DPIV measurements that showed the presence of high induced velocities, resulting from the trailing tip vortices. These velocities are comparable to the rotor blade velocities, reducing substantially the aerodynamic angles of attack experienced by the rotor blades, thereby, preventing the occurrence of stall. DPIV measurements also identified several interesting flow features that include the presence of a leading edge vortex, similar to a dynamic stall vortex. The slipstream boundary obtained by following the path of the tip vortices was found to contract, as expected for a lifting rotor.
This paper describes the systematic performance measurements conducted to understand the role of rotor geometry and blade pitching kinematics on the performance of a microscale cycloidal rotor. Key geometric parameters that were investigated include rotor radius, blade span, chord, and blade planform. Because of the flow curvature effects, the cycloidal-rotor performance was a strong function of the chord/radius ratio. The optimum chord/radius ratios were extremely high, around 0.5-0.8, depending on the blade pitching amplitude. Cycloidal rotors with shorter blade spans had higher power loading (thrust/power), especially at lower pitching amplitudes. Increasing the solidity of the rotor by increasing the blade chord, while keeping the number of blades constant, produced large improvements in power loading. Blade planform shape did not have a significant impact, even though trapezoidal blades with a moderate taper ratio were slightly better than rectangular blades. On the blade kinematics side, higher blade pitching amplitudes were found to improve the power loading of the cycloidal rotor. Asymmetric pitching with a higher pitch angle at the top than at the bottom produced better power loading. The chordwise optimum pitching axis location was observed to be around 25-35% of the blade chord. The power loading of the optimized cycloidal rotor was higher than that of a conventional microrotor.
This article presents a model of rotor-fixed wing hybrid aircraft, which can operate as a helicopter as well as transition to fixed-wing flight. The control mission includes: hover, vertical take-off and landing, forward flight, from hover to forward flight, and vice versa. A backstepping-basedbased control method for the aircraft is designed to keep the flying height invariant during mode transitions from hover to forward flight and vice versa. The other control missions mentioned are not considered in this article.
This paper summarizes the state of knowledge of cyclogyro theory and development in order
to aid those working on researching and designing cyclogyros. A cyclogyro is a horizontal-
axis rotary-wing aircraft. While no cyclogyros have ever been successfully flown, the concept
offers an alternative to helicopters and other VTOL aircraft with several potential advantages.
Research on cyclogyro development was first begun in the 1930's and at least one prototype
was actually built. With the recent interest in small UAV’s and the
development of lightweight electric motors and batteries, interest in the cyclogyro has been
renewed in the last decade. There exists a considerable void between modern works and the
significant amount of research and testing was performed in the first half of the twentieth
century. Many of the early reports are difficult to locate, and there is a lack of continuity
between the works in this field. The goal of this work is to present an overview of the several
widely varied sources in order to reduce the likeliness of redundant efforts, encourage
collaboration and advancement, and help facilitate cyclogyro evaluation in light of modern
materials and technologies.
In this paper, calculus of variations and combined blade element and momentum theory (BEMT) are used to demonstrate that, in hover, when neither root nor tip losses are considered; the rotor, which minimizes the total power (MPR), generates an induced velocity that varies linearly along the blade span. The angle of attack of every blade element is constant and equal to its optimum value. The traditional ideal twist (ITR) and optimum (OR) rotors are revisited in the context of this variational framework. Two more optimum rotors are obtained considering root and tip losses, the ORL, and the MPRL. A comparison between these five rotors is presented and discussed. The MPR and MPRL present a remarkable saving of power for low values of both thrust coefficient and maximum aerodynamic efficiency. The result obtained can be exploited to improve the aerodynamic behaviour of rotary wing micro air vehicles (MAV). A comparison with experimental results obtained from the literature is presented.
A cyclorotor (also known as a cyclocopter or cyclogiro) is a rotating-wing system where the span of the blades runs parallel to the axis of its rotation. The pitch angle of each of the blades is varied cyclically by mechanical means such that the blades experiences positive angles of attack at both the top and bottom positions of the azimuth cycle. The resulting time-varying lift and drag forces produced by each blade can be resolved into the vertical and horizontal directions. Varying the amplitude and phase of the cyclic blade pitch can be used to change the magnitude and direction of the net thrust vector produced by the cyclorotor. Compared to a conventional rotor, each spanwise blade element of a cyclorotor operates at similar aerodynamic conditions (i.e., at similar flow velocities, Reynolds numbers, and angles of incidence), and so the blades can be optimized to achieve the best aerodynamic efficiency. Moreover, because the blades are cyclically pitched once per revolution (1/rev), unsteady flow mechanisms may delay blade stall onset and in turn may augment the lift produced by the blades. Albeit proposed to MAV-scale, its use on large scale vehicles turns problematic, and we proposed in this paper to address their stopovers. Furthermore, since the thrust vector of a cyclorotor can be instantaneously set to any direction perpendicular to the rotational axis, a cyclorotor-based air vehicle may ultimately show better maneuverability and agility as compared to a classical powered conventional rotor system. One major drawback of a cyclorotor is its relatively large rotating structure which might offer a weight penalty when compared to a conventional 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.
ABSTRACT The cycloidal blades system is a thrust propulsion system that consists of several blades rotating about a horizontal axis perpendicular to the direction of normal flight. In order to generate the thrust required, the pitch angles of the individual blades to the tangent of the circle of the blade’s path are varied by a pitch control mechanism,installed in the cycloidal blades system so designed ,that the periodic oscillation of the blades about their span axis may ,be changed both in amplitude and in phase angle. Therefore, the cycloidal blades system is able to vector its high thrust anywhere,within a 360° arc parallel to the propellers plane of rotation. This characteristic enables the cycloidal blades system to take off and land vertically, hover and fly forwardly by simple adjustment of blades pitch angles.
Abstract Acyclocopter,propelled by the ,cycloidal blade system, which can be described as a horizontal rotary wing, is a new concept of VTOL vehicle. In this paper, cyclocopter rotor system is optimized for design variables such as radius of rotor, rotating speed, maximum pitch angle, chord and span of blade, number of blades and airfoil. To apply response surface methodology, datum acquired by STAR-CD for aerodynamic ,design ,variables and MSC/NASTRAN for ,structural ,ones. Genetic algorithm is used to find the optimal values from the constructed,response ,surface ,while ,objective functions are thrust, required power and stress of blade.
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 new concept of vertical takeoff and landing aircraft. The cycloidal blade system, which can he described as a horizontal rotary wing, offers powerful thrust levels and a unique ability to change the direction of the thrust almost instantly. This paper investigates the development of the cyclocopter with four rotors, file aircraft was designed through computational fluid dynamics and finite element structural analyses. Elliptic blades and a swash plate were applied to the rotor system to improve the rotor performance and control mechanism. Efficient dc brushless motors and lithium-polymer batteries were used for power transmissions. Almost all parts of the rotor blades and fuselage were manufactured out of composite material. Thrust and required power were measured experimentally on the test bed. The experimental result shows that the cyclocopter on produce sufficient thrust for both hovering and low-speed forward flight.
The cycloidal propeller, which can be described as a horizontal rotary wing, offers powerful thrust levels, and a unique ability to change the direction of the thrust almost instantly. In this work, cycloidal propulsion system was designed and implemented with sinusoidal low pitch system to investigate the fundamental characteristics of hovering states. Before experimental study, computational analysis was made in commercial CFD tool, CD Adopco/Star- CD. This work gives schematic view of flow field around rotor. And it predicts the load variation on a blade with respect to revolution and the total thrust from cycloidal rotor, at specific condition. CFD analysis also makes it possible to check the camber effect. The propulsion system was built up with sinusoidal low pitch control mechanism. Thrust, power and efficiency were measured for various conditions of parameter setting. It was accomplished by designing the equipment which can change the rotational radius, number of blade, phase angle of eccentricity and amplitude of eccentricity.
Among the purely aeronautical applications, near-horizontal axis as well as horizontal axis devices are considered. The former cover the radial-lift propeller or 'self-propelling' wing; the latter cover Magnus effect and related systems; cyclogiro systems and horizontal-axis propeller systems with cyclic pitch. A limited investigation of non-aeronautical applications of HARWAS is also made, which covers wing-rotor type windmills, cyclogiro windmill turbines, Magnus effect ship propulsion and cycloidal ship propulsion. Approximately 1200 references are listed. A series of cross-index tables is also included to provide a quick means for the reader to determine the content and availability of the references. An analysis of the various lift systems pertinent to the HARWAS field is made with a view to potential air vehicle applications. Over 20 original aeronautical applications are identified and evaluated in the light of recent advances in power plants, transmissions and lightweight structural techniques. This analysis points out the extraordinary variety of HARWAS and identifies promising new aeronautical systems. A preliminary performance and design study of two promising HARWAS concepts is also reported. The two concepts are the STOL logistics aircraft using a rotating airfoil flap and the amplified high-pitch cyclogiro for application to the composite aircraft mission.
BOSCH Aerospace, Inc., (BOSCH Aerospace) and subcontractor MSU RASPET Flight Research Laboratory (RASPET) accomplished successful development and testing of a prototype Curtate Cycloidal Propeller during the SBIR Phase 1 effort which concluded on October 31, 1998. This propulsion concept holds significant promise for adaptation to UAV VTOL operations. Thrust levels demonstrated were substantially higher than achievable by the best screw type propellers, and approximately equal to those of high end helicopters. Vectoring of thrust through a 3600 arc, and low noise characteristics throughout the RPM range were demonstrated. Also accomplished was identification of efficiency gain techniques that may increase the overall thrust by approximately 30%.
An experimental investigation was conducted to study the flow around a cycloidal propeller. Flow fields were obtained using a particle image velocimetry system whose data acquisition was synchronized with the propeller’s angular position. The chord-based Reynolds number was Re
c = u
rc/υ = 1.4 × 104, where u
r is the rotational velocity of the propeller and c is the chord length of the airfoil. Flow characteristics such as mean velocity, vorticity and the RMS value of velocity fluctuation were derived from the measurements. The results demonstrated the presence of a downwash around the propeller during the generation of lift. Detailed observations around each airfoil visualized distinct vortex shedding and reattaching flow at certain phase angles of the propeller.
Graphical Abstract
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.
This paper presents an experimental study on the development of a cyclogyro-based flying robot with a new variable angle of attack mechanism. A cyclogyro is a flying machine supported in the air by power-driven rotors that rotate about a horizontal axis, like the paddle-wheels of a steamboat. Machines of this type have been designed by some companies but there has been no record of any successful flights. Our design starts with a new variable angle of attack mechanism with an eccentric (rotational) point in addition to a rotational point connecting to a motor. The main feature of the mechanism with the eccentric rotational point is the ability to change attack of angles in accordance with the wing positions (as determined by the rotational angles of the cyclogyro) without actuators. The design parameters (wing span, the number of wings, and eccentric distance) of the flying robot are determined through a series of experiments. Experimental results show that the cyclogyro-based flying robot with the new variable angle of attack mechanism is capable of generating sufficient lift force for flying.
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