Showing papers on "Blade pitch published in 1994"

Reduction of Helicopter BVI Noise, Vibration, and Power Consumption Through Individual Blade Control

Abstract: A wind tunnel test was conducted with a full-scale BO 105 helicopter rotor to evaluate the potential of open-loop individual blade control (IBC) to improve rotor performance, to reduce blade vortex interaction (BVI) noise, and to alleviate helicopter vibrations. The wind tunnel test was an international collaborative effort between NASA/U.S. Army AFDD, ZF Luftfahrttechnik, Eurocopter Deutschland, and the German Aerospace Laboratory (DLR) and was conducted under the auspices of the U.S./German MOU on Rotorcraft Aeromechanics. In this test the normal blade pitch links of the rotor were replaced by servo-actuators so that the pitch of each blade could be controlled independently of the other blades. The specially designed servoactuators and IBC control system were designed and manufactured by ZF Luftfahrttechnik, GmbH. The wind tunnel test was conducted in the 40- by 80-Foot Wind Tunnel at the NASA Ames Research Center. An extensive amount of measurement information was acquired for each IBC data point. These data include rotor performance, static and dynamic hub forces and moments, rotor loads, control loads, inboard and outboard blade pitch motion, and BVI noise data. The data indicated very significant (80 percent) simultaneous reductions in both BVI noise and hub vibrations could be obtained using multi-harmonic input at the critical descent (terminal approach) condition. The data also showed that performance improvements of up to 7 percent could be obtained using 2P input at high-speed forward flight conditions.

Pitch-regulated vertical access wind turbine

Abstract: A cross flow wind turbine comprising a rotor mounted for rotation about a vertical axis and a plurality of blade assemblies mounted on the rotor. Each blade assembly comprises a blade of aerofoil section mounted vertically for pivotal movement about a vertical shaft. The turbine also includes a device for measuring the direction of the apparent fluid velocity, a shaft encoder for measuring the blade angle and a control system to set the blade angle such that the lift component of the aerodynamic forces on the blade contributes positively to the driving torque on the rotor.

A Higher Harmonic Control Test in the DNW to Reduce Impulsive BVI Noise.

Abstract: A model rotor acoustic test was performed to examine the benefit of higher control (HHC) of blade pitch to reduce blade-vortex interaction (BVI) impulse noise. A 40-percent dynamically scaled, four-bladed model of a BO-105 main rotor was tested in the German-Dutch Wind Tunnel (DNW). Acoustic measurements were made in a large plane underneath the rotor employing a traversing in-flow microphone array in the anechoic environment of the open test section. Noise characteristics and noise directivity patterns as well as vibratory loads were measured and used to demonstrate the changes when different HHC schedules (different modes, amplitudes, phases) were applied. Dramatic changes of the acoustic signatures and the noise radiation directivity with HHC phase variations are found. Compared to the baseline conditions (without HHD), significant mid-frequency noise reductions of as much as 6 dB are obtained for low speed descent conditions where BVI is most intensive. For other rotor operating conditions with less intense BVI there is less or no benefit from the use of HHC. Low frequency loading noise and vibratory loads, especially at optimum noise reduction control settings, are found to increase.

Analysis of a higher harmonic control test to reduce blade vortex interaction noise

Abstract: A noise study using an aeroelastically scaled BO-105 rotor was conducted in the German-Dutch Wind Tunnel to examine the use of higher harmonic control (HHC) of blade pitch to reduce impulsive blade-vortex interaction (BVI) noise. The noise directivity was measured over a large plane underneath the rotor using a traversing inflow microphone array. Noise and vibration measurements were made for a range of matched rotor operating conditions where prescribed (or open loop) HHC pitch, at various amplitudes and phases, was superimposed on normal (baseline) collective and cyclic trim pitch. Acoustic data are presented for 3, 4, and 5P HHC applied to a typical landing approach rotor operating condition where BVI noise is normally intense. Noise reductions of up to 6 dB were found for the advancing side BVI noise radiating upstream of the rotor, and also for the retreating side BVI noise radiating below and downstream of the rotor. The relative levels between the sides were modified by HHC control phase. To help give insight to the physics of the HHC/BVI noise problem, highresolution loading and noise prediction results are presented for comparison to the data. The predictions are based on a new high-resolution version of the CAMRAD rotor performance program under development at Langley, called HIRES.

Ram air turbine with secondary governor

Abstract: A ram air turbine is provided for use in driving electric and/or hydraulic power systems in an aircraft, wherein the ram air turbine includes primary and secondary speed control governors. The primary governor includes centrifugal flyweights for cam-actuated adjustment of the pitch angle of a turbine blade or blades, within a selected adjustment range, to achieve substantially constant turbine speed in response to varying air speed and/or load. The secondary governor preloads the turbine blade or blades to a selected midrange pitch angle in the at-rest condition, wherein the midrange pitch angle is chosen for faster turbine acceleration on deployment to the desired full-speed rotation. The secondary governor controls blade pitch angle until the turbine reaches a selected rotational speed, after which the primary governor regulates and adjusts blade pitch angle within the selected adjustment range.

Control mechanism for RAM air turbine

Abstract: A control mechanism is provided which feathers the propeller blade pitch during stopping and stores restart energy in the blade pitch governor mechanism. Deceleration to the feathered mode is aided by the airstream. During restart, excess stored energy is used to increase reliability, but is then dissipated mechanically, as by a flywheel mechanism, to maintain low internal impact stresses. More specifically, where single governor spring is used for controlling the pitch of all propeller blades, a braked ball screw device is used to compress that spring during stoppage. Upon restart, the governor spring expands and causes blade pitch change. The ball screw arrangement then dissipates a large portion of the excess energy through torque transmission to mechanical components.

Recent studies of rotorcraft blade-vortex interaction noise

Abstract: Recent results are presented from several research efforts aimed at the understanding of rotorcraft blade-vortex interaction (BVI) in terms of the noise generation, directivity, and control. The results are based on work performed by NASA Langley Research Center researchers, both alone and in collaboration with other research organizations. Based on analysis of a simplified physical model, the critical parameters controlling BVI noise generation have been identified. The detailed mapping of the acoustic radiation field of a model rotor in a wind tunnel has revealed the extreme sensitivity of directivity to rotor advance ratio and disk attitude. The control and reduction of BVI noise through the use of higher harmonic pitch control is discussed.

Variable propeller for boat

Abstract: A sleeve 18 spline-fitted in an outer periphery of a propeller shaft 4 is connected to a propeller boss 12 for surrounding the outer periphery of the sleeve by a damper rubber 20 interposed in superposed relation therebetween, and in a recess formed in the outer periphery of the propeller boss 12 so that a bottom surface thereof comes near the outer periphery of the damper rubber 20, propeller blades are rotatably supported on a blade shaft 33 parallel to the propeller shaft 4. With this arrangement, it is possible to provide a compact variable propeller for a boat which can be mounted on a relatively short propeller shaft and which is provided with a torque limiting device.

Application of nonlinear control to a HAWT

Abstract: Wind energy is one of the most promising sources of renewable energy for the UK. Over the last two decades there has been rapid development of the technology, and in the UK several commercial wind farms are in operation with more under construction. The standard commercial design of wind turbine is a horizontal axis grid-connected up-wind machine with a rating of approximately 300 kW. The rotor usually has two or three blades, and in pitch regulated machines the pitch angle of either the full span of the blades or just the outer tips can be varied. The application of a nonlinear controller to a typical two-bladed machine with full-span pitch control is investigated in the present paper. It is known that this particular configuration of wind turbine presents a more demanding control problem than alternative configurations, and the benefits of a more sophisticated control system are therefore expected to be greater in the two-bladed case. >

Measurement around a rotor blade excited in pitch, part 2: unsteady surface pressure

Abstract: This paper describes measurements of chordwise distributions of unsteady pressure at three radial locations on a stiff two-bladed teetering model helicopter rotor in hover, with the blades executing simple harmonic pitch oscillations about the quarter-chord pitch axis. The objective of the present work is to provide a data base to correlate the measured unsteady blade pressure distributions with dynamic inflow to establish the validity or deficiencies of available analytical methods for predictions of unsteady aerodynamic phenomena. The effect of dynamic inflow on rotor unsteady surface pressure has been

Marine propeller device with current fin

Abstract: PURPOSE: To improve propeller efficiency by attaching a current fin to the rear of a propeller and arranging the current of a swirl caused in the rear of the propeller. CONSTITUTION: Eight current blades 11a-11h are radially protruded from a fin boss 14 disposed in the rear of a propeller and concentrically to a propeller bossing. The intermediates of the blades 11a-11h are intercoupled through an intermediate ring 13, the two upper blades 11a and 11b are coupled to struts 12a and 12b protruded from a ship hull 1 and the flow straightening blades 11a-11h are attached in the rear of the propeller and in this way, the rotating flow by the propeller is collected or reduced by the current blades to improve propeller efficiency. Further, like a device with its current blades installed in front of the propeller, the speed of inflow to the propeller is prevented from delaying and this constitution also improves the efficiency of the propeller alone. COPYRIGHT: (C)1995,JPO

Block apparatus and method for changing dozer blade pitch

Abstract: A dozer blade pitch adjustment apparatus has a mounting lug and a block supported by the lug for setting a dozer blade at a first pitch or a second pitch. In the improvement, the lug has a mounting surface and the block has a first face contacting such mounting surface when the blade is set at the first pitch. A second face of the block contacts the mounting surface when the blade is set at the second pitch. The block has a surface portion between the lugs and such portion faces generally upwardly when the blade is set at either pitch. A new method for changing the pitch of the blade is also disclosed.

Blade pitch change mechanism

Abstract: A lightweight and compact apparatus is provided for altering and controlling the pitch of a plurality of rotating blades during rotation using a mechanical clutch and gear arrangement driven by a rotational speed differential between the blade drive shaft and the blades. A first set of clutches and gears controls the direction of rotational power to the pitch change mechanism and is disengaged from rotation when desired blade pitch is established. A second set of clutches and gears controls the speed of rotational power applied to the pitch change mechanism. This pitch change mechanism includes a failsafe capability against pitch change through disengagement of the directional clutches except when needed, and an inherent rotational lock resulting from the rate change clutches' bias to simultaneous engagement. Variation of that speed of rotational power permits coarse and fine pitch adjustments at variable rates.

Analysis and vibration control of a helicopter rotor blade

Abstract: A study of helicopter blade vibration control is presented in this work. The blade is modelled by the finite element method and it is considered as a rotating beam undergoing the coupling motions of flapping, lead-lagging, axial stretching and torsion. The blade model also considers a pretwist angle, offset between mass and elastic axes and isotropic material. The finite element matrices are obtained by energy methods and a linearization procedure is applied to the resulting expressions. The linearized aerodynamic loading is calculated for hover and the state-space approach is used to design the control system. The eigenstructure assignment by output feedback is used in the blade reduced model resulting from the application of the expansion method by partial fractions. The simulations for open and closed-loop systems are presented, having exhibited good response qualities, and they show that output feedback is a good alternative for helicopter vibration attenuation. >

Mechanisms of Vibration and BVI Noise Reduction by Higher Harmonic Control

Abstract: The sources of helicopter rotor vibration and noise are presented and the mechnisms of higher harmonic blade pitch control to reduce vibration and noise are explained using experimental data from a wind tunnel test with the Bo 105 model rotor. Rotor simulation results are shown for validation.

Wind turbine with passive control.

Abstract: In a wind turbine which is provided with a rotor having a number of rotor blades (1), each of which has a main part (2) situated near the rotary shaft of the rotor and a separate tip (3) which is rotatable relative to the main part about the longitudinal axis of the rotor blade (1). Each rotor blade (1) is provided with a control mechanism which is designed in such a way that the angular position (angle of attack) of the end part of the rotor blade is controlled depending on the speed of rotation of the rotor. The control mechanism comprises a tension-torsion element (11) made from a non-isotropic (anisotropic or othotropic) material, the longitudinal axis of which runs essentially in the same direction as the longitudinal axis (9) of the rotor blade, and which twists under the influence of an axial tensile force (centrifugal force on the end part of the rotor blade). The tension-torsion element (11) is expediently in the form of an elongated tube which is made up of layers of fibre-reinforced plastic, the fibres of the tension-torsion element being oriented in such a way that the tube twists under the influence of an axial tensile force.

Wind power plant - has horizontal axis rotor with blades adjustable in angle and vibration damping becoming harder as angle increases

Abstract: The wind power plant has a rotor with at least one blade (1) fastened to a horizontal shaft (4). It can be adjusted in inclination to the radial axis (6). The resulting pressure point (8) lies behind the radial axis, with regard to the direction of rotation (9). There is a hydraulic or pneumatic damper to smooth out blade vibration about the radial axis. It is connected between a point on the hub and a point on the shaft. The damping becomes harder as the blade inclination is increased. The blades may have fins and each blade has its own controller with a cam or toggle link. ADVANTAGE - Improved control of blade angle, giving better operationo

Model testing of an optimally designed propeller with two-sided shifted end plates on the blades

Abstract: Model tests were carried out in order to investigate the hydrodynamic behaviour of an unconventional screw propeller with end plates. The end plate for each blade consists of two parts, one part attached to the pressure side of the blade tip, the other to the suction side. At the junction the end plate parts are positioned in a relatively shifted way with respect to each other. The propeller was optimized with respect to uniform inflow using variational calculus and was designed by lifting-surface theory. Open water experiments in a deep water towing tank were performed with the end plate propeller and with a state-of-the-art conventional propeller, used for reference. An unconventional propeller with the end plates not yet fitted to the blades was also examined. Cavitation tests were carried out in a cavitation tunnel for uniform inflow. The experimental results clearly revealed that the unconventional propeller with end plates meets some important design objectives, including the objective that a gain in propulsion efficiency can be achieved. Also the propeller is free of cavitation within considerable margins around realistic levels of pressure and loading.

Applications of cyclic pitch thrusters

Abstract: A cyclic pitch propulsion system is an advanced propulsor concept that offers several advantages when compared to conventional propeller systems. The cyclic pitch system produced both thrust and manoeuvring forces so that conventional control surfaces can be eliminated. In addition, the cyclic pitch capability can be used to reduce unsteady forces on the propeller that can cause undesirable vibrations on the ship. The unsteady panel method program USAERO is demonstrated as an analysis tool for this type of propulsor, two example calculations are presented, and a real implementation of cyclic pitch is described.

Variable pitch boat prop

Abstract: A variable pitch boat prop includes a hub fixed to the prop shaft, a sleeve surrounding the hub and having bearings which receive stub shafts from a plurality of blades. The stub shafts pivot in the bearings, so that the blade pitch can change. Pinion teeth formed on the stub shafts mate with respective toothed racks fixed to the hub and disposed at an acute angle to the hub axis. The center of pressure of each blade is offset downstream from the stub shaft axis, so that dynamic pressure on the blades tends to decrease blade pitch, while the rack and pinion tend to increase blade pitch. These opposing moments are at equilibrium at different blade pitches, according to the speed of the boat and the prop shaft torque. Blade pitch increases automatically as speed increases, and decreases at load increases.

Ship position automatic holding method

Abstract: PURPOSE:To hold a ship in the specified position by generating thrust appropri ately by a bow thruster in addition to thrust for moving a stern laterally on the spot, and controlling two rudders and a bow thruster by signals from other ship position measuring devices. CONSTITUTION:When a hull is shifted from the specified object position or attitude by the action of external force on the hull, a ship position difference computing device 13 detects and computes the shift grade, speed and acceleration. A ship position setting control indicator 8 controls the rotating positions of two rudders 17, the rotating speed (or blade pitch quantity) of a propeller 16, and/or the discharge direction and rotating speed (or pitch quantity) of a bow thruster 9 through a steering angle control computing element 6 and a bow thruster controller 10 in such a way as to put this shift swiftly back into the original specified position or attitude.

Propeller shaft for the drive line of a motor vehicle

Abstract: The invention relates to a propeller shaft for the drive line of a motor vehicle with driven rear axle and front-mounted engine drive-connected thereto by way of the propeller shaft, which engine, in the event of an impact acting on it in the direction of the rear axle, is axially supported against the rear axle by the propeller shaft. At the same time the propeller shaft is designed so that its joints are immovably braced by the impact force so that their angle does not vary and the impact force cannot lead to buckling of the propeller shaft.

Process and apparatus for cutting up by shearing of elements of a nuclear installation

Abstract: A process and apparatus for cutting up an element used in the construction of a nuclear installation for dismantling. The element is placed on a support and pushed toward a shearing tool having a blade pitch angle of 30°. As the element is pushed, the blade performs a first shearing operation. Then a releasing stop controlled by a jack releases the element from the blade. Operation continues until the element is cut up.

Rotor blade of rotor

Abstract: PURPOSE:To provide a rotor blade having a low resistance coefficient in a region with a comparatively low Mach number by specifying the base blade thickness and forming a part to a designated angular distance in a specified sectional form in the sectional form of the rotor blade of a rotor. CONSTITUTION:In a rotor, it is necessary that in order to balance the lift on the whole of a rotary surface of a rotor blade, the elevation angle is made small in positions a, b having high airspeed and the elevation angle is made large in positions a', b' with low airspeed. In the light of the above situation, the blade is formed in such a manner that the base blade thickness is 12% angular distance, and concerning coordinate points on the upper surface of the blade from the blade front edge about 90% angular distance, the blade thickness is increased to retreat the maximum blade thickness position, the curvature distribution is concetrated on the central part and optimized, and a flow-up device is provided on the rear edge part. Thus, the vacuum peak in the vicinity of the front edge near Mach number of 0.6 and lift coefficient of 0.6 is moderated to reduce resistance coefficient and decrease the head-down pitching moment.

Experimental performance and comparison of performance prediction methods for a trochoidal propeller model

Abstract: A three-bladed, 150 mm orbit diameter model trochoidal propeller was tested at atmospheric pressure in a cavitation tunnel. The tests included forward propeller operations at rotational speeds of 150 and 200 rpm and bollard pull tests at speeds from 100 to 200 rpm. Results are presented of thrust and torque coefficient and propulsive efficiency over a range of advance ratio. Results from two theoretical analysis methods for cycloidal propellers were compared with particular emphasis on their effectiveness in predicting performance of this trochoidal propeller. Mendenhall and Spangler's discrete vortex method for cycloidal propeller performance was modified to: a) calculate the angle of attack changes at each propeller blade directly from the induced velocities due to all vortices in the flow representing the wake and other blades; b) calculate lift and drag on the blades from various models and experimental section data; and c) include an approximate model for stall hysteresis of a blade section operating into and out of stall (dynamic stall). Multiple streamtube momentum theory was used with experimental blade section data. Results show that both methods predict the global induced velocities of the propeller at the blades to similar levels of accuracy. However the accuracy of performance prediction is limited because: a. the methods do not adequately calculate the three dimensional performance of the blades in unsteady flow below stall; and b. the performance of the blade section in three dimensional unsteady flows through and above stall is unknown.

Drive for counter-rotating propellers, esp. for ship - applies opposite torque to propellers and can be controlled to change propeller speeds

Abstract: The propeller driver is kept in a torsionless position, and applies opposite torque to provide variable rotation for propellers. Several drivers can be directly coupled or coupled through gears to reduce or increase propeller speed. Torque is applied to one propeller and counter-torque is provided by the second propeller. The counterbalancing of the propellers provides for force equilibrium, and obviates the need for several gears. Several gears can be included, but they are optional. Two or more motors can be used and the direction of rotation of the motors affects the redn. or increase in propeller speed. ADVANTAGE - Reduced vibration and power loss.

Dynamically Tuned Blade Pitch Links for Vibration Reduction

Abstract: A passive vibration reduction device in which the conventional main rotor blade pitch link is replaced by a spring/damper element is investigated using a comprehensive rotorcraft analysis code. A case study is conducted for a modern articulated helicopter main rotor. Correlation of vibratory pitch link loads with wind tunnel test data is satisfactory for lower harmonics. Inclusion of unsteady aerodynamics had little effect on the correlation. In the absence of pushrod damping, reduction in pushrod stiffness from the baseline value had an adverse effect on vibratory hub loads in forward flight. However, pushrod damping in combination with reduced pushrod stiffness resulted in modest improvements in fixed and rotating system hub loads.

Propeller syncro-pulsing

Abstract: Indexing a propeller blade so it leads intake valve timing by a specific amount causes an increase in engine power. The proper indexing allows the high energy propeller wake in the form of an acoustic wave to be ingested by the induction system and arrive at the intake valve just as the valve is opening. When the Wave arrives just as the valve is opening, the wave causes a momentary increase in manifold pressure which adds pumping potential to force additional airflow into the engine cylinders which results in a power increase. This technique called propeller syncro-phasing causes the propeller blade to behave as a "zero stage supercharger". Adding a trailing edge extension to the propeller blade chord at the radius corresponding to the induction inlet causes a local increase in slipstream total energy adding additional energy to the induction airflow resulting in additional engine power. There has been no device marketed to exploit either of these two phenomena, nor has there been any publication which speaks of this technique that I have seen. In this regard propeller syncro-pulsing is unique.