Showing papers on "Blade pitch published in 1976"

Dynamics of Wind Generators on Electric Utility Networks

Abstract: Dynamic interaction of wind-turbine-driven generators on electric utility networks was studied by computer simulation. Nonlinear representations of wind-turbine and various drive train elements and Park equation representations of synchronous and induction generators were implemented. An infinite capacity network was assumed. Time history responses for various system configurations were computed using as the input function severe wind gust data added to cyclical torque variations occurring at turbine blade frequency. Results indicated that severe transient mechanical and electrical stresses can be induced for certain system configurations. Best results were obtained by interposing rate or damped compliant couplings between the wind turbine and a synchronous generator. The induction generator did not appear to require such means. Blade pitch control (or equivalent) was required to limit output above rated wind velocities for wind turbines configured to produce maximum mum specific power. The blade pitch control loop must exhibit high performance to limit transient overshoots. An aerodynamically limited turbine driving an induction generator exhibited good response without the need for blade pitch control, but at the cost of increased turbine rotor diameter. Further work is indicated, taking into account wind-turbine aeroelastic effects, finite capacity networks, and other factors.

Method and apparatus to determine need for rotor blade pitch adjustment and/or blade substitution

Abstract: The output of an aircraft propulsion or lift rotor blade out-of-track pick-up is processed in such a way as to enable quick determination of need for blade pitch adjustment, the approximate amount of such adjustment to optimize reduction of out-of-track vibration, and the need for blade substitution when such optimized reduction is insufficient.

Overspeed control arrangement for vertical axis wind turbines

Abstract: This invention is an overspeed control arrangement for vertical axis wind turbines employing normally vertically positioned rotor blades, said control arrangement allows the rotor blades to tilt either forward or backwards to form a swept wing configuration, at wind turbine speeds beyond the design rpm. When the rotor blade is in a highly swept wing configuration its high drag and low lift reduces the turbine rotor torque to zero and eliminates excessive overspeeding and structural damage. The rotor blade can tilt about a radial or nearly so, tilt-support arm, mounted on a concentric bearing, the tilting starts at the feathering design rpm which is controlled by the geometric position of the combined center of gravity of both rotor blade and tilt-support arm. The control arrangement is automatic and passive and does not require the use of springs, pulleys or levers.

Advanced control system for a rotor and/or a compound or rotary wing vehicle

Abstract: The control system includes a sensing mechanism by which a true pure signal from flapping bending activity resulting from an external load force on a rotor blade in a rotor system is generated and fed back to a gyroscope which then precesses to return a correcting feathering motion to the rotor blade through a swashplate. Such generation is developed by the sensing mechanism which comprises a cantilevered beam or spring system secured at its one end to a fixed hub arm about which the blade feathers and having its other end operatively connected to the gyroscope. The gyroscope is positioned outside of a high force blade feathering loop and is independently sized from the rotor to which it is coupled. The system also provides for pilot command input to produce a control feathering motion to a pair of blades independently of the sensing means.

Variable pitch mechanism for fan blades

Abstract: In a variable pitch fan assembly having a plurality of fan blades mounted in a rotor for rotation about their longitudinal axes and a drive shaft for rotatively driving the rotor, the pitch varying mechanism has a planetary gear train connected to each fan blade to rotate the latter to change the pitch or angle of attack of the blades, actuator means for effecting bi-directional rotation of the planetary gear train and a no-back, bi-directional brake interposed between the actuator means and the planetary gear train to transmit pitch-changing rotation from the actuator means to the planetary gear train and lock the planetary gear train to the rotor and prevent transmission of blade torque loads to the actuator means during steady state operation when no blade pitch-change is being effected.

Aeroelastic analysis for helicopter rotor blades with time-variable, non-linear structural twist and multiple structural redundancy: Mathematical derivation and program user's manual

Abstract: The differential equations of motion for the lateral and torsional deformations of a nonlinearly twisted rotor blade in steady flight conditions together with those additional aeroelastic features germane to composite bearingless rotors are derived. The differential equations are formulated in terms of uncoupled (zero pitch and twist) vibratory modes with exact coupling effects due to finite, time variable blade pitch and, to second order, twist. Also presented are derivations of the fully coupled inertia and aerodynamic load distributions, automatic pitch change coupling effects, structural redundancy characteristics of the composite bearingless rotor flexbeam - torque tube system in bending and torsion, and a description of the linearized equations appropriate for eigensolution analyses. Three appendixes are included presenting material appropriate to the digital computer program implementation of the analysis, program G400.

Noise produced by turbulent flow into a propeller or helicopter rotor

Abstract: than can be applied to calculate the instantaneous sound spectrum produced by the rotor at each azimuthal rotor position, and this instantaneous spectrum can be averaged over the azimuthal rotor position to find an averaged far-field sound spectrum. In taking this average, account must be taken of the different amount of retarded time that the rotor spends at each azimuthal rotor position. Further discussion of this point is given in another paper.4 A further factor taken into account in the analysis is the existence of blade-to-blad e correlation. If a given turbulent eddy is chopped by more than one rotor blade, the blade-toblade correlation leads to narrow-band noise peaked around the rotor harmonics. The far-field sound for an airfoil moving in rectilinear motion through a turbulent flow can be expressed in terms of a single wavevector component of the turbulence. The presence of blade-to-blade correlations requires that the single wavevector component be replaced by a summation over several wavevector components. This summation generally is carried out numerically for the calculations presented herein, but, if the frequency of interest is high enough, the summation can be replaced by an integral that can be evaluated in closed form; i.e., the blade-to-blade correlation becomes unimportant, and the result reduces to that for a single blade in rectilinear motion. The preceding description of the procedure for calculating the far-field sound applies to the sound produced by a spanwise segment of the rotor. This segment must have a spanwise dimension small enough so that the velocity does not vary significantly over the segment but large enough so that the loading correlation from segment to segment is not significant. This latter assumption is consistent with the highfrequency assumption mentioned previously, since high frequency corresponds to small correlation length. Thus, to find the noise contributed by the entire rotor, an integral over span must be performed.

Propeller or a set of wings for a wind mill

Abstract: A propeller for a wind mill comprising a rotable supported hub with at least one mainly radially extending blade having a cross section in the shape of a "wing profile", each blade being provided with at least one auxiliary blade with a cross section in the shape of wing profile and being positioned such that said auxiliary blade will generate a "ventury effect" by which a part of the fluid, which normally should pass outside the propeller disc area, is drawn into the propeller.

Elastomeric bearing test machine

Abstract: Apparatus and method for testing elastomeric bearings used for mounting articulated rotor blades on the main rotor head of a helicopter wherein the blade is held stationary and the rotor hub is moved to subject the bearing to simulated flight loads and motions simultaneously, including centrifugal loading and blade flapping, lead-lag, and pitch change motions.

Aircraft propeller and blade pitch control system

Abstract: A propeller hub supports a plurality of angularly disposed propeller blades which are movable by a hydraulic cylinder between a high pitch position and a reverse position through a low pitch position. Hydraulic fluid is supplied to the cylinder from a governor unit driven by the aircraft engine, and a fluid pressure responsive relief valve controls the pressure of the hydraulic fluid. The pressure responsive relief valve is manually adjustable by the aircraft pilot to change the fluid pressure at which the valve responds in order to change the pitch of the propeller blades. The fluid pressure must be increased above a predetermined normal operating limit for actuating the cylinder against the bias of a spring within the propeller to move the blades to their reverse pitch position. In addition, a centrifugally actuated lock unit prevents actuation of the cylinder and movement of the blades to their reverse pitch position until the speed of the propeller is reduced to a slow idle. The pressure responsive relief valve also incorporated hydraulic means to assure that the valve responds immediately to the pilot's command.

Front end loader attachment

Abstract: A blade mounting assembly for mounting a blade on a front end loader vehicle to provide the desired attributes of a bulldozer. The blade is pivotally mounted on a U-shaped frame which is pivotally mounted on the push beam assembly of the front end loader. The front end loader hydraulic motors are used to control blade pitch, and hydraulic motors mounted on the frame are used to control blade angle. The geometry of the assembly allows setting blade tilt by combining blade pitch and angle.

Flexure having pitch flap coupling

Abstract: A flexure for connecting the root end of a rotor end of a rotor blade to a rotor hub in a bearingless rotor assembly. The flexure inherently induces a change in pitch angle in accordance with a change in flap angle. The flexure, which may form an integral portion of the rotor blade, is constructed of a composite material made of fibers secured to one another by a bonding agent. The fibers are arranged in two sets. The variation of the blade pitch angle in accordance with the blade flap angle is accomplished by either varying the number of fibers between the two sets or varying the angle of each set to the longitudinal axis of the flexure, or both.

Marine propulsion plant with reversible propeller shaft connected thereto

Abstract: When reversing a marine power plant, due consideration must be given to the fact that the inertia of the ship will continue to force the ship through the water during a moment of time after the shut down of the prime mover, with the propeller then acting as a water turbine tending to rotate the propeller shaft in the same direction as before. If the propulsion plant includes a gas turbine and a reversing gear, the reversing gear is designed in such a manner that the part thereof connected to the turbine will represent, in use, a smaller inertia than the part connected to the propeller shaft, with the propeller shaft together with the propeller attached thereto representing a considerable rotating body. By suitable selection of the means engaging the parts of the reversing gear in their respective working positions for ahead and astern running, respectively, it will be possible to disengage the turbine part of the gear, to brake this part and then to re-engage the gear parts in their new relative position, thereafter braking the propeller connected part by the power of the turbine and finally bringing the whole system to rotate in the desired direction.

Rotors for a screw rotor machine

Abstract: A pair of cooperating rotors for a screw rotor machine, comprising a main rotor with a dedendum and a gate rotor with an addendum. One flank of each gate rotor land is generated inside the pitch circle of the gate rotor by the crest of the main rotor land and is generated outside the pitch circle by a portion of the main rotor inside the pitch circle and is formed to sealingly cooperate with the main rotor land so that gear action is obtained only outside the pitch circle of the gate rotor and inside the pitch circle of the main rotor.

Integrated helicopter flight control

Abstract: A helicopter rotor control mechanism is provided in which cyclic and collive rotor control functions are performed by a single integrated control having three degrees of freedom and operable by either or both hands of the pilot as desired. The integrated control comprises a floor mounted control column rotatable about a fore and aft collective pitch control axis and a pair of hand grips mounted for rotation about two independent cyclic control axes (by one or both hands of the operator) in a control head assembly mounted on the upper end of the floor mounted control column. The floor column and control head effect displacement of collective pitch, cyclic pitch and cyclic roll output rods for ultimate control of the helicopter rotor.

Roto-wing jet airplane

Abstract: A jet aircraft is equipped with powered helicopter type rotor blades and control mechanisms whereby it can take off and land vertically, yet in horizontal flight can operate at speeds and altitudes typical of jet aircraft. The rotor blades are foldably retractable to a compact locked, trailing position for horizontal travel and are readily unfoldable by a manually operated control mechanism within the aircraft. While the rotors are rotating, the blade pitch can be selectively controlled and, on power failure, will be automatically controlled to provide for same direction autogyro rotation. In one form, the wings and stabilizers are tiltable between substantially horizontal positions for normal horizontal flight and substantially vertical positions for vertical flight. The craft is ground supported by flexible legs.

Model helicopter throttle governor/collective pitch control apparatus

Abstract: A throttle governor/collective pitch control apparatus for radio controlled model helicopters for proportionally controlling either the model helicopter rotor speed or the rotor collective pitch, including sensing and timing means determining the rotor speed and any changes thereof, comparison means for comparing a subsequently sensed rotor speed with a first sensed rotor speed and developing an error signal, and control means responsive to the error signal to provide a control signal proportional to any changes in the rotor speed. In the throttle governor mode any variations in rotor speed result in a proportional control signal to vary the model helicopter throttle so as to maintain constant rotor speed. In the auto-collective mode changes in rotor speed result in a proportional control signal coupled to the collective pitch servo for proportionally varying the model helicopter collective pitch.

Blade pitch control mechanism for helicopters

Abstract: Pitch control linkage for the upper rotor of coaxial counterrotating rotors utilizes conventional swashplate, control rod and servomotor elements for changing blade pitch but without the conventional rotating and non-rotating scissors for reacting swashplate torque This is accomplished by the use of rotating and non-rotating walking beams and combination torque reacting control rods between the walking beams and the rotatable and non-rotatable swashplate elements Means are also disclosed for shimming the rotatable walking beams to achieve pre-track adjustment of the pitch of individual blades

Feathering propeller especially for sailing boats

Abstract: Feathering propeller particularly for auxiliary engines of sailing boats. The propeller comprises a device for transmitting a rotary and a positioning motion to the blades including planetary gear means for converting an angular motion of the drive shaft into an angular motion for inclining the propeller blades and means for halting the angular motion to halt the blades at the required inclination and render the blades of such inclination rigid both with the relative hub and with the drive shaft.

Investigation of a bearingless helicopter rotor concept having a composite primary structure

Abstract: Experimental and analytical investigations were conducted to evaluate a bearingless helicopter rotor concept (CBR) made possible through the use of the specialized nonisotropic properties of composite materials. The investigation was focused on four principal areas which were expected to answer important questions regarding the feasibility of this concept. First, an examination of material properties was made to establish moduli, ultimate strength, and fatigue characteristics of unidirectional graphite/epoxy, the composite material selected for this application. The results confirmed the high bending modulus and strengths and low shear modulus expected of this material, and demonstrated fatigue properties in torsion which make this material ideally suited for the CBR application. Second, a dynamically scaled model was fabricated and tested in the low speed wind tunnel to explore the aeroelastic characteristics of the CBR and to explore various concepts relative to the method of blade pitch control. Two basic control configurations were tested, one in which pitch flap coupling could occur and another which eliminated all coupling. It was found that both systems could be operated successfully at simulated speeds of 180 knots; however, the configuration with coupling present revealed a potential for undesirable aeroelastic response. The uncoupled configuration behaved generally as a conventional hingeless rotor and was stable for all conditions tested.

Collar for redirecting propeller energy

Abstract: A rigid cylindrical collar with an inside diameter slightly larger than the outside diameter of a propeller which is mounted over a propeller and is used singly or in combination with a flexible extension thereto for maximizing the efficiency of propeller blades. The invention is adaptable to watercraft or to aircraft so as to prevent water or air from slipping off the ends of propeller blades so as to redirect energy lost as a result of slipping off the ends of propeller blades in the direction useful for advancing a water or air vehicle. The flexible extension is usable primarily on large watercraft, such as tug boats, ocean vessels and barges, and the like, and could be used with or without a rudder in order to steer a boat in the direction desired.

Axial fan with automatically controlled variable pitch blades

Abstract: A fan impeller for axial flow having automatically variable-pitch blades ached to a rotatable hub for attaining maximum lift and inhibiting stall in a varying back pressure regime. The blades are attached for rotation about their axes to the hub, and are connected through a crank and link to a drive shaft. The hub is attached to the drive shaft to permit relative axial movement, but to preclude relative rotational movement. Varying back pressure moves the blades and the hub in variable blade rotation planes, causing changes in blade pitch. Springs and dash-pots, connecting the hub and shaft, act axially to give non-linear restoring forces and damping to the blade pitch changes.

Optimum propellers with cavity-drag and frictional-drag effects

Abstract: In a variational problem for the optimum pitch distribution of a propeller, the Euler differential equation with Munk's displacement theory is utilized. Effects of frictional-drag and cavity-drag are considered through simple approximate relations of drag-lift ratio and the circulation. Simple relations between the optimum pitch distributions and the drag-lift ratio are obtained both for free-running and wake- adapted propellers.

Aircraft control system providing hardover protection and full control authority

Abstract: In a helicopter a servo system connected to operate in parallel with the rotor blade pitch controlling linkages and also to receive autopilot generated signals directing maneuvers. The system limits the autopilot control over the blade pitch or position in the short term and permits full control over the long term.

Control system for variable pitch axial fan for utility boiler

Abstract: The disclosed system detects the pressure rise across the fan and the flow rate in the system and integrates signals corresponding thereto, and outputs a signal to indicate to the user when the pressure rise exceeds a given level for a corresponding flow rate to warn of a condition within a given degree of a stall condition. The system outputs another signal to block any increase in fan blade pitch and substitutes a decrease pitch signal in response to a predetermined closer approach to a stall condition so that the pitch of the blades is reduced to a position in which the pressure rate rise and flow rate are reduced to a safe level with respect to a stall condition. The system also includes means responsive to the predetermined closer approach to stall to prevent the user from feeding a blade pitch increase signal following a reduction in the pressure rise across the fan until the user resets a bistable device.

Self-feathering propeller

Abstract: A self-feathering propeller for use on sail boats having an auxiliary power source. The propeller blades are rotated automatically to working pitch positions to provide an ahead or an astern thrust in accordance with the direction of rotation of the propeller shaft. When the shaft is stationary and water flow is substantially parallel to the shaft axis, as when the boat is under sail, the blades are automatically feathered thereby to minimize resistance to movement of the boat.

The analysis of controllable pitch propeller characteristics at off-design conditions

Abstract: Model tests were conducted to study the effect of cavitation and wake field on blade loading. Blade geometry is discussed and a numerical analysis method is described. Controllable pitch propeller hydrodynamics are then dealt with, and the last section is devoted to practical aspects of cp-propeller design.

Static stress measurements on a series of skewed propeller blades with and without forward rake

Abstract: : Static strains were measured in a systematic series of five marine propeller blades. The propeller blades have projected skew angle at the blade tip equal to zero, 36 degrees and 72 degrees without rake, and 36 and 72 degrees with sufficient forward rake to place the locus of the section midchord in the propeller plane. This combination of skew and rake is called warp. The primary experiments were conducted with the blades under uniform loading applied with air pressure using specially constructed chambers. Limited supplemental experiments were conducted using concentrated loads. The experimental results under uniform loading were correlated with modified beam theory. Both the experimental results and the modified beam theory indicate that for all the skewed and warped propeller blades evaluated, the largest value of the maximum principal stress is no greater than 1.20 times the maximum prinicipal stress on the unskewed propeller.