Showing papers on "Blade pitch published in 1978"

Wind turbine generator pitch control system

Abstract: Wind energy is used to drive a wind turbine, which is in turn connected to an electrical generator to produce electrical power. The pitch angle of the wind turbine blades is controlled in a closed loop manner to maintain either a constant generator speed for isolated power generating stations or when the generator is synchronized to the load, or constant generator output power or shaft torque when the generator is connected to an electrical grid. Open loop acceleration and deceleration schedules are provided to minimize blade stress and shaft torque variations during start up and shutdown transients, limiting blade angle excursions as a function of wind velocity and speed. The schedules may be implemented either electronically or by a suitably programmed digital computer. The gains in the speed, torque and power loop controls are scheduled as a function of average wind velocity to optimize stability and response. An anticipatory blade angle schedule responsive to instantaneous wind velocity is added to the desired blade angle reference from the closed loop controls to minimize transient excursions in output power or generator speed resulting from wind gusts.

Wind turbine generator acceleration control

Abstract: A power generating system includes a wind turbine driven generator, the wind turbine having a wind turbine driven rotor with a variable pitch angle blade. Stresses on the system during startup and shutdown are minimized by scheduling the blade angle as a function of the rotor speed and wind velocity to provide a minimum blade angle relative to the fully powered blade angle during rotor acceleration, and to provide a minimum blade angle relative to the fully powered blade angle during rotor deceleration.

Wind turbine generator having integrator tracking

Abstract: A power generating system includes a wind turbine driven generator, the wind turbine having a wind driven rotor with a plurality of variable pitch angle blades. The blade angle is scheduled during acceleration and deceleration of the wind turbine by open loop controls to minimize stresses, and is scheduled during powered operation by closed loop controls to maintain desired torque or speed. The closed loop controls contain an integrator which produces an integral blade angle control signal. The scheduled blade angle is fed back to the integrators through an integrator tracking network to maintain the integral blade angle control signal at all times within a preselected range relative to the scheduled blade angle.

Surge-accepting accumulator transmission for windmills and the like

Abstract: An alternator, powered by a wind rotor having pitch changeable blades, is maintained at a fixed speed despite variations in wind speed and cyclic perturbations in rotor shaft speed due to rotor dynamics. In one embodiment, a geared speed increaser, coupling the rotor to the alternator, is mounted for reversible rotation relative to the rotor shaft. A fluid transfer means, such as a torque motor, coupled to a pressurized accumulator, applies such a torsional reaction to the speed increaser to permit its rotation at a rate which accommodates the difference between the instantaneous rotor shaft speed and that rotor shaft speed corresponding to the alternator's fixed speed. The fluid transfer means and accumulator means together permit a maximum angular displacement of the speed increaser sufficient to provide a time interval in which the rotor blade pitch may be corrected and the rotor shaft returned to normal speed. Pitch changes are effected, in part, responsive to rotation of the speed increaser.

Modeling of Manoeuvring Behaviour of Ships with a Propeller Idling, Boosting and Reversing

Abstract: Frequent use of the engine telegraph is not unusual when manoeuvring in and out of harbours, or navigating through a narrow waterway. The captain may let the ship proceed by herself with the propeller idling, brake her by reversing the propeller, or actuate the engine shortly with the helm hard-over to correct the heading.Naturally, these operations cause a significant headway change, and at the same time introduce quite an extensive variation in propeller slip, which considerably affects the rudder effectiveness. We reduced the well-known coupled equations of forward, sway and yaw motion of a ship, Eq. (2. 1), into a simple mathematical model of ship response in such manoeuvres. Those are Eqs. (2. 10), (2. 20) and (2. 25).We make use of the existing knowledge on the rudder-to-yaw response in steady steaming as well as of a somewhat modified self-propulsion tank test to determine the propeller performance. The effect of propeller slip on the rudder effectiveness and the hydrodynamic force exerted by a reversing propeller are also investigated.According to the free-sailing model experiments, two VLCCs and one container ship model, the present simple mathematical model of ship response proved successful.

Method and apparatus for generating electricity from a fixed pitch wind wheel

Abstract: A method and apparatus for generating electricity from wind energy, wherein a wind wheel is connected to drive an energy converter which effects a torque reaction on the wind wheel proportional to the square of the rotational speed of the wheel, so that the wheel may be operated at fixed blade pitch and the blade tip speed will be proportional to the wind speed. The wind wheel may be connected to drive an electric generator to generate electrical energy in synchronism with mains supply.

Speed and collective pitch bias of helicopter longitudinal cyclic pitch

Abstract: A bias actuator, such as an extensible link, in the longitudinal cyclic pitch channel of a helicopter is provided with inputs as a function of airspeed multiplied inversely with collective pitch, and as a function of the rate of change of collective pitch stick position, so as to enforce positive angle of attack and speed stability and positive static pitch trim gradient and to decouple collective pitch from the longitudinal cyclic pitch channel at cruise airspeeds, the invention compensates, inter alia, adverse control effects of tail stabilizer surfaces at cruise speeds. A pair of indicators display bias commands and actual bias responses.

Investigation of Interior Noise in a Twin-Engine Light Aircraft

Abstract: This paper describes experimental studies of interior noise in a twin-engine, propeller-driven, light aircraft. An analytical model for this type of aircraft is also discussed. Results indicate that interior noise levels in this aircraft due to propeller noise can be reduced by reducing engine rpm at constant airspeed (about 3 dB), and by synchrophasing the twin engines/propellers (perhaps up to 12 dB). Ground tests show that the exterior noise pressure imposed on the fuselage consists of a complex combination of narrow-band harmonics due to propeller and engine exhaust sources. This noise is reduced by about 20-40 dB (depending on the frequency) by transmission through the sidewall to the cabin interior. The analytical model described uses modal methods and incorporates the flat-side geometrical and skin-stringer structural features of this light aircraft.

Surface pressure measurements at the tip of a model helicopter rotor in hover

Abstract: Surface pressures were measured near the tip of a hovering single-bladed model helicopter rotor with two tip shapes The rotor had a constant-chord, untwisted blade with a square, flat tip which could be modified to a body-of-revolution tip Pressure measurements were made on the blade surface along the chordwise direction at six radial stations outboard of the 94 percent blade radius Data for each blade tip configuration were taken at blade collective pitch angles of 0, 618 and 114 degrees at a Reynolds number of 736,000 and a Mach number of 025 both based on tip speed Chordwise pressure distributions and constant surface pressure contours are presented and discussed

Reverse velocity rotor system for rotorcraft

Abstract: A blade control method and means for helicopter rotors which increases heopter speed by mixing two/rev. control motion with one/rev. cyclic and collective motion through mechanical summation is provided. Both rotary and vertical motions are imparted to an inner control shaft and these motions are combined to impart vertical oscillatory motions to the rotor head which motions increase the thrust developed by the helicopter rotor.

Model helicopter device

Abstract: A model helicopter device wherein a countertorque generated in the helicopter body by changes in the revolution of a main rotor is canceled by substantially detecting the acceleration of the revolution of the main rotor and automatically adjusting the pitch of tail rotor blades in accordance with the detected acceleration.

Automatic regulating device for keeping constant the speed of wind-powered propellers

Abstract: This invention relates to an automatic regulating device for wind-powered propellers having blades which are connected to the propeller hub by torsion springs and are self-adjustable in dependence of the wind forces acting on the blades and returnable by action of the torsion springs. The distinctive feature of the invention is that the torsion spring connecting each blade with the propeller hub has a substantial portion of its length pre-stressed between two abutment points situated on a radius from the propeller axis and radially spaced from each other. The abutment points permit twisting the blade about its longitudinal axis from an initial position by wind forces against action of the prestressed torsion spring. The abutment points are both fixed either in relation to the blade or in relation to the hub.

Variable-pitch rotor, specially for a rotary-wing aircraft

Abstract: The invention relates to a variable-pitch rotor, specially for a rotary-wing aircraft. Each blade of the rotor is connected to the hub by a flexible connecting member comprising a radial bundle of fibres, each agglomerated by a resin and secured together by a vulcanized elastomer. A rigid tubular sleeve surrounds the connecting member without contact thereto. The outer end of the tubular sleeve is secured to the root part of the blade and its inner end is secured to a rigid ring, to which a blade pitch control lever is externally articulated. Spherical ball and socket joint members are inserted between the rigid ring and rigid parts of the rotor hub. Frequency adaptors are associated with the ball and socket joint members.

Redundant rotor blade retention system

Abstract: A redundant rotor blade retention system is disclosed. A secondary load path is provided in the event the primary load path of the rotor blade retention system fails. Both the primary and the secondary load path permit rotation of the rotor blade about its pitch axis. The rotor blade is connected to a shaft which forms a portion of the rotor hub. The shaft is pivotally connected to the housing of the rotor hub by a tie-bar, tension-torsion strap, or the like. Flanges which form an integral part of the hub housing and the shaft overlap and are spaced apart from one another. In the event the tie-bar or tension-torsion strap fails, the flanges come in contact with one another and act as a secondary load path. Lubrication is provided so that relative motion about the rotor blade pitch axis may occur between the two flanges thus permitting rotor blade pitch motion.

Rotor blade support setup for rotary wing aircraft

Abstract: A composite bearingless helicopter rotor system utilizes one single and only flexible strap as at least the principal wing support, and also preferably has also a blade pitch shaft. The line of shear centers of the flexible strap, the line of shear centers of the blade pitch shaft, and the pitch axis each lie somewhere along the one straight line, or substantially so. The cross section of the flexible strap may vary but in each case it is one which is asymmetrical relative to a line through its center of gravity and parallel to the axis of rotation of a rotor, and in each case the line of shear centers of the flexible strap, the line of shear centers of the blade pitch shaft and the pitch axis all are spaced from the line of centers of gravity of the flexible strap. A number of examples of varying specific overall configurations of flex straps and blade pitch shaft will be found described and illustrated herein, of which an example is that in FIG. 15 and the text relating thereto, in which at the leading edge there is a gapped dome in the cross section of the flex strap, following which the cross section comes straight back in legs on both sides with a web straight across between in the further part and the blade pitch shaft is a solid shaft at the trailing edge between the ends of the legs.

On methods for application of harmonic control

Abstract: The paper presents data which confirm the effectiveness of higher harmonic blade pitch control in substantially reducing helicopter rotor vibratory hub loads. The data are the result of recent tests on a 2.7-m model conducted in the Langley Research Center's transonic dynamics wind tunnel. Several predictive analyses developed in support of the NASA program are shown capable of accurately predicting both amplitude and phase of the higher harmonic control input required to nullify a single 4/rev force or moment input. The use of multiple blade feathering inputs in the design of a flightworthy higher harmonic control system is discussed.

An improved computational procedure for determining helicopter rotor blade natural modes

Abstract: An existing computer program, used for predicting the natural frequencies and mode shapes of helicopter rotor blades, was refined to improve program accuracy and versatility. The program is based on the Holzer-Myklestad approach adapted for rotating beams. Coupled vertical (out-of-plane), horizontal (in-plane), and torsional mode characteristics were determined for a variety of hub and blade configurations. The resulting program is documented by presenting the recursion equations and techniques for determining natural frequencies and mode shapes, input data requirements, and descriptions of various program outputs. The accuracy of the program is demonstrated by comparing computed results with exact solutions to classical problems and experimental data.

Pitch control system for helicopter rotor blades

Abstract: A system is disclosed for controlling the pitch angle of helicopter rotor blades to compensate for differences in lift generated by advancing and retreating blades during translational flight or due to gust loading of individual blades. Each rotor blade is free to move about its pitch axis to achieve an adjustable balance between a pitching moment exerted by the blade and centrifugal force exerted by weights rotating with the blade system. Collective and cyclic pitch commands from the pilot are transmitted through a conventional swash plate to a linkage which adjusts the relationship of the pitching-moment and centrifugal forces which produces a balanced condition. The system maintains near-constant blade lift as the blade rotates, and minimizes blade distortion and asymmetric coning, thereby significantly reducing vibration arising from a shifting of the center of mass of the rotor-blade system away from the center of rotation.

Design considerations for propellers in a cavitating environment

Abstract: Cavitation adds a dimension to propeller operation that necessitates rational design practice to approach a good balance of craft requirements. This paper discusses propeller characteristic format to reduce the computation time to make performance predictions and propeller selection for partially and fully cavitating conditions. In addition, maximum propeller thrust and torque loading limits are defined for four different blade section shapes, including recommended design limits.

Floating pressure control of fractionator system

Abstract: Method and apparatus are disclosed for the automatic adjustment of the fractionation column pressure in a fractionator system which employs total condensation of overhead vapor and a liquid full reflux accumulator to thus float the column pressure above minimum column pressure. The set point of a condensder fan pitch controller, which manipulates the blade pitch of the condenser fan, is automatically adjusted in response to a desired offset of condensate subcooling from the overhead bubble point temperature which is repeatedly automatically calculated in response to analysis of the overhead product composition and pressure. The set point of a pressure controller, which manipulates the overhead product control valve to adjust column pressure, is automatically adjusted in response to a fan pitch signal from the condenser fan pitch controller and a desired fan pitch set point. Appropriate limits and overrides are also disclosed to prevent sudden changes in column pressure which might upset system operation.

A theoretical technique for analyzing aeroelastic stability of bearingless rotors

Abstract: A technique is introduced for aeroelastic stability analysis of certain hingeless helicopter rotors termed bearingless because of their lack of a pitch-change bearing. The rotor is modeled as three or more rigid blades, each joined to the hub by means of a flexible appendage known as the flexbeam or strap. The pitch-control system twists the flexbeam to provide blade pitch change. The analysis is capable of treating effects of several different pitch-control configurations, geometic nonlinearities associated with the equilibrium deflected shape of the flexbeam, and the built-in angular offsets of the flexbeam and blade. Numerical results are presented for a variety of system parameters. The stability of the system in both hub-fixed motion and coupled rotor-body motion is considered. System parameters can be chosen to stabilize most soft in-plane configurations for the hub-fixed case. The same parameters will also, under certain conditions, stabilize the coupled rotor-body system in hovering flight (air resonance). When the rotorcraft is in ground contact, however, at zero thrust, it appears that these parameters are not as effective in stabilizing the system (ground resonance).

A note on multicyclic control by swashplate oscillation

Abstract: It was shown that for two, three, or four bladed rotors, simple oscillation of the nonrotating swashplate controls can produce prescribed blade pitch schedules of the sort which were suggested for vibration alleviation. Equations were given which relate the swashplate motions to the resulting blade pitch schedules.

Full scale experience relating to the propeller and its environment

Abstract: This paper presents some of the full scale experience and conclusions relating to propeller problems which have been gained from the many investigations undertaken by Lloyd's Registe of Shipping. Among the subjects discussed are the influence of the hull after-body on the wake and its consequent effects on propeller induced excitation of the hull and shafting systems, propeller cavitation and full scale experience in the use of highly skewed propellers as a means of reducing propeller excitation. Some comment is also made on service experience with flow correcting devices. The problems discussed here and ensuing comments are based upon a broad spectrum of ship types and are not those peculiar to any one class of ship.

Compressible flow about helicopter rotors

Abstract: Two theoretical methods for helicopter rotors or propellers in subsonic flow are presented, namely a lifting-line theory for a helicopter rotor in vertical climb, hovering or in slow descent, or a propeller in steady forward flight or operating statically, and a disk approximation for a helicopter rotor in forward flight or a propeller in yaw. In both methods, the compressibility of the air is taken into account. First, the problem of a vertically moving rotor is treated with the method of matched asymptotic expansions. In the second case, the rotor is approximated by a disk of continuous thrust and in-plane force distributions, which are assumed to be known. Its wake is represented by a semi-infinite cylinder of distributed vorticity. Formulas for the induced velocity field are derived.

Apparatus for automatically cutting piping

Abstract: PURPOSE:To cut an outer periphery of a pipe by fixing a cutting machine to the pipe to be cut in a narrow space and automatically feeding a blade pitch by pitch.

Control of wind turbine generators connected to power systems

Abstract: A unique simulation model based on a Mode-O wind turbine is developed for simulating both speed and power control An analytical representation for a wind turbine that employs blade pitch angle feedback control is presented, and a mathematical model is formulated For Mode-O serving as a practical case study, results of a computer simulation of the model as applied to the problems of synchronization and dynamic stability are provided It is shown that the speed and output of a wind turbine can be satisfactorily controlled within reasonable limits by employing the existing blade pitch control system under specified conditions For power control, an additional excitation control is required so that the terminal voltage, output power factor, and armature current can be held within narrow limits As a result, the variation of torque angle is limited even if speed control is not implemented simultaneously with power control Design features of the ERDA/NASA 100-kW Mode-O wind turbine are included