Variable Pitch Rotors Research Articles

Comparison of aerodynamic and aeroacoustic characteristics of fixed-pitch and variable-pitch rotors

This research conducts a comparative analysis of the aerodynamic and aeroacoustic characteristics of fixed-pitch and variable-pitch controlled multirotors [i.e., revolution per minute (RPM) and collective pitch control]. The study encompasses single-, twin-, and quad-rotor configurations under hovering flight conditions. The unsteady blade motion is modeled as a function of RPM and pitch, fluctuating with frequency and amplitude. To comprehensively account for wake interaction effects, a free-wake vortex lattice method combined with acoustic analogy is utilized. The findings reveal that unsteady blade motion and wake interaction effects cause fluctuations in thrust and tip vortex trajectory. The thrust and tip vortex behavior exhibited greater instability in response to RPM fluctuations than to pitch fluctuations. Consequently, the axial unsteady loading noise was more pronounced under RPM fluctuations compared to pitch fluctuations. In both twin- and quad-rotor configurations, the wake interaction significantly influenced the characteristics of thrust and tip vortex behavior. In addition, spectral analysis demonstrated that the frequencies of unsteady blade motion and wake interaction determine the frequencies of thrust and tip vortex fluctuations as well as unsteady loading noise.

Performance based systematic design methodology for development and flight testing of fuel engine powered quadrotor Unmanned Aerial System for industrial applications

This paper presents a systematic study of the design optimization, development, vibration analysis and flight testing of a single power plant variable pitch quadrotor Unmanned Aerial System (UAS) for industrial applications. The use of variable pitch rotors enables the use of a two-stroke internal combustion engine for powering the four rotors through a mechanical transmission. The proposed methodology is described by carrying out the design of a quadrotor UAS with 2–3 kg payload capacity and have endurance in excess of one hour. The study is conducted in a systematic manner. First, the design of rotors is optimized for minimum power consumption during hover as well as forward flight condition using physics based simulation developed and validated for this purpose. From the rotor optimization, an untwisted rotor blade with taper ratio of 0.6 and aspect ratio of 10 appeared to be an optimal choice for the current design. Next, the powerplant selection is carried out based on the optimized rotor designed earlier. Next, two different approaches for mechanical power transmission design is considered: torque tube-bevel gear and belt–pulley system based designs. The transmission system designed using belt and pulley was nearly 14% lighter and showed greater tolerance to manufacturing imperfections. Next, two prototypes are designed and its static and dynamic analysis is carried out to ensure its airworthiness. A Proportional Integral Derivative (PID) based attitude controller is developed using quarternions for attitude stabilization and trajectory tracking to test the flight in simulation and then subsequently on the actual vehicle by implementing it on PixHawk autopilot board. Finally, system integration is carried out to build two prototypes of engine powered quadrotor UAS. Then, vibration data is recorded using the sensors onboard to conduct the vibration analysis and design an efficient vibration isolator. Performance analysis is also, carried out to estimate the speed for best endurance (11 m/s) and best range (27 m/s) for the variable pitch quadrotor designed. The estimated best endurance achieved is 2.2 h and estimated best range is more than 150 km. This design revisits and solves the challenge of developing an agile helicopter without cyclic pitch control which was first explored nearly a century ago.

Relative rotor phasing for multicopter vibratory load minimisation

AbstractThis study focuses on vibration reduction for quadcopters and octocopters with elastic, two-bladed, fixed-speed, variable-pitch rotors through the use of relative rotor phasing. The study defines phase modes such as a pitch phase mode with relative phasing between the front and aft rotors, a roll phase mode with relative phasing between the left and right rotors, and a differential phase mode with relative phasing between the clockwise and counter-clockwise spinning rotors for both the quadcopter and the octocopter, as well as additional higher harmonic phase modes for the octocopter. Parametric studies on individual phase modes indicate that, for the quadcopter in forward flight, the pitch and roll phase modes can almost entirely eliminate the 2/rev vibratory forces (at the aircraft level), but the 2/rev vibratory moments cannot be minimised at the same time. By simultaneously using multiple phase modes, a Pareto front can be generated and a solution selected based on the relative emphasis on force or moment vibration reduction. For the octocopter, it was observed that individual higher harmonic modes (specifically the 2cor 2smodes) could almost entirely eliminate both the 2/rev vibratory forces and moments, simultaneously. Compared with vibration levels in forward flight that might, on average, be expected if the rotors were randomly phased, a 62% reduction of a composite vibration index can be achieved on a quadcopter, and complete elimination of vibration was achievable on an octocopter, with appropriate rotor phasing.

Design methodology and performance analysis of conical rotors for dry screw vacuum pumps

Abstract The conical rotor, as an alternative internal compression structure, has shown the potential to enhance the performance of screw vacuum pumps further. In view of no available literature examining the design of them, to fill this gap, mathematical models for the generation and analysis of conical rotors were established in this paper. The generation process was based on a design implementing a rotor profile cluster and a conical helix. The analysis model reflected the geometric characteristics and thermodynamic performance of conical rotors. The effect of key parameters in conical rotors was investigated, and the difference between conical rotors and variable-pitch rotors was revealed. Results showed that with the increase in the conical angle the internal volume index enlarged while both the specific power and pumping speed decreased. To achieve greater internal compression, more rotor stages were needed. The rotor performance could be improved by changing the distribution of the tooth width angle for the rotor profile cluster at a certain inlet pressure. In comparison with the variable-pitch rotor, the specific power was lower for the conical rotor at a close pumping speed.

Performance Comparison of Quadcopters with Variable-RPM and Variable-Pitch Rotors

Use of variable-pitch rotors was compared against variable-RPM rotors on a 2-kg (20 N) quadcopter in simulation. To generate 5 N of thrust in hover while maintaining a 2:1 maximum thrust-to-weight ratio, the variable-pitch rotor required 29% more power. At low climb rates the variable-RPM rotor requires less power, but near its maximum rate it required more power than the variable-pitch rotor. The maximum climb rate for the variable-pitch rotor was up to 70% greater than that of the variable-RPM rotor. A quadcopter equipped with variable-pitch rotors required more power to operate compared to the aircraft with variable-RPM rotors over its operational airspeed range. The variable-pitch quadcopter required 30% more power at best-endurance speed and had 18% less range than the variable-RPM quadcopter (at maximum-range speed). The 1/rev root drag shear was 42% larger for the variable-RPM rotor, and the 2/rev H- and Y-forces were 37% and 50% larger. The 2/rev thrust vibration was 6.5% smaller for the variable-RPM rotor, and the hub pitching and rolling moments were 11% and 9% smaller, respectively. Unlike the quadcopter equipped with variable-pitch rotors, the quadcopter equipped with variable-RPM rotors experienced a beating phenomenon in the aircraft-level vibratory loads.

Force Analysis for a Variable-Pitch Rotor Meshing Pair in Twin-Screw Vacuum Pump Generating on CNC Turning Machine

The variable pitch twin-screw vacuum pump has more advantage than the uniform pitch twin-screw vacuum pump. Its energy efficiency and volumetric compression ratio are specifically high. Under the cyclic gas pressure and working temperature, the rotors of vacuum pump often deform and interfere that lead to noise, vibration and rotor abrasion. In this paper, a 3D model of the variable pitch rotor generating by CNC turning process is constructed to reasonably estimate the rotor load and deformation in operation. The contact force have been analyzed to show the advantages of variable pitch rotors.

Optimisation of screw spindle vacuum pumps with variable rotor pitch regarding load-lock operation

Screw spindle vacuum pumps are characterised by high suction speed and the ability to achieve high pressure ratios in a dry running process. If the dimensions of the pump are comparable to the volume of the system’s receiver, evacuation only takes a few seconds. For this reason, a typical application for screw spindle vacuum pumps is the evacuation of a load-lock chamber in a predefined time during a clocked production process. In order to reduce power consumption, screw spindle vacuum pumps with an internal change of volume are used almost exclusively. These pumps are commonly with variable pitch rotors. In this article, a new approach for optimisation of variable pitch rotors in consideration of the requirements of the load-lock process is presented. A dimensionless energetic efficiency is defined based on an idealised load-lock process, this parameter is maximised by the optimisation algorithm. The rotor pitch progression, an important factor in pump performance, is approximated by segments of constant pitch at the suction and discharge sides with a linear decrease in between. The overall wrap angle, the minimum rotor pitch, the crown circle diameter, the root circle diameter, and the circumferential speed are constant for the optimisation, during which the rotor length and load-lock pressure are varied. Optimisations are carried out for double-lobed cycloid profiles. The optimisations result in selection of internal volume ratios which are significantly below a theoretical calculated value for the idealised lock-lock process. This is explained by the internal clearances and details of compression process. The studies reveal a positive influence of the rotor length on the load-lock efficiency, this is because the proper rotor length leads to an uniform compression. It is also shown that the wrap angle of the segment on the suction side should be kept low.

Deforming grid generation and CFD analysis of variable geometry screw compressors

The most common type of twin screw machines are twin screw compressors. These normally contain rotors of uniform pitch and profile along the rotor length. However, in some cases such as in twin screw vacuum pumps with very large pressure ratios, the variable pitch rotors are often used to improve efficiency. The limited use of rotors with variable pitch and/or section profile is mainly due to manufacturing constraints. In order to analyse the performance of such machines by means of Computational Fluid Dynamics (CFD), it is necessary to produce a numerical mesh capable of calculating 3D transient fluid flows within their working domains.An algebraic grid generation algorithm applicable to unstructured grid, Finite Volume Method (FVM) for variable pitch and variable profile screw machines is described in this paper. The grid generation technique has been evaluated for an oil free air compressor with “N” profile rotors of 3/5 lobe configuration. The performance was obtained by calculations with commercial CFD code. The grid generation procedure provides mesh of the required quality and results from CFD calculations are presented to compare performance of constant pitch rotors, variable pitch rotors and variable profile rotors. The variable pitch and variable profile rotors achieve steeper internal pressure rise and a larger discharge area for the same pressure ratio. Variable pitch rotors achieve reduced sealing line length in high pressure domains.

Design and Modelling of a Quadrotor Helicopter with Variable Pitch Rotors for Aggressive Manoeuvres

This article presents the design of a low inertia, variable pitch quadrotor helicopter intended to investigate control problems associated with aggressive manoeuvres. In this paper a rotor pitch controlled quadrotor is designed and modelled to address performance limiting issues associated with conventional speed controlled quadrotors. The helicopter is designed to minimise the rotational inertia and maximise the vehicle bandwidth. Simple design and control measures are used to linearise the body attitude dynamics during all operating regions, aiding in complex acrobatic flight. The decoupled high performance capabilities are demonstrated by simulating a controlled 180° cross-axis roll.

Patent abstracts

In UK patent 2261203 Keith Ralbert Sherriff describes a VTOL light aircraft. Two variable pitch rotors are housed one behind the other within the fuselage to draw air through front intakes and through intake louvres in the top of the fuselage, and expel it through controllable flaps in the bottom of the fuselage and/or through a rear exhaust nozzle. The rotors are inclined to the fuselage horizontal plane and rotate in opposite directions. In the hover, yaw control is by vanes in the exhaust nozzle and lateral control by a weight movable spanwise within the wing, while differential pitch control of the rotors is used for pitch control of the aircraft. The pilot lies in a prone position.