Showing papers on "Blade pitch published in 1971"

Rotor with variable angle blades

Abstract: A support, actuation, and balancing structure for rotor blades in a variable blade angle axial flow fan, compressor or turbine as may be used in a turbojet or turbofan engine. The supporting structure may include a shaft attached to each rotor blade and restrained from outward radial travel, under high centrifugal loading, by the inwardly facing surfaces of two spaced apart discs. Actuation may be provided by at least one fluid powered piston which controls blade angulation through rotation of one disc member relative to the other. Centrifugally controlled balancing means may also be provided to insure a uniform flow condition through the blades by maintaining the blades in a stable position of angulation upon disengagement of the actuator. Each rotor blade preferably includes a central axis about which the blade angle is varied, and which is in close proximity to the intersection of the leading edge of the blade with the blade tip.

Helicopter type vehicle

Abstract: The invention discloses a helicopter type vehicle having coaxial counter rotating propellers above the cabin of the vehicle, each propeller being fixed in pitch as opposed to conventional helicopter propellers which vary in pitch during rotation of the propeller. The counter rotating propellers provide lift for lifting the vehicle from the surface, and forward thrust on the vehicle is developed by shifting the center of gravity of the vehicle to tilt the axis of rotation of the propellers with the shifting of the center of gravity of the vehicle being accomplished in at least one instance, by mounting the propeller drive motors adjacent the respective propellers and rotating the motors bodily about the axis of rotation of the propellers.

Helicopter rotor pitch control system

Abstract: A blade pitch control assembly in accordance with the invention comprises an inner disc rotating with the rotor shaft and an outer non-rotating connected connected to the first disc by a bearing and which can be tilted by pitch variation control means.

Controllable pitch maripropeller

Abstract: A hub for a controllable pitch marine propeller has a one-piece casting mounting the blade spindles, irreversible pitch controllable mechanism, and a rotary motor control and gear reducer. Although low in weight and small in overall size, exceptionally precise control over blade angles is maintained and wear is minimized.

Propeller Noise at Low Tip Speeds

Abstract: : The study comprises an analytical and experimental investigation of the vortex noise generated by low-tip speed propellers. intially, the treatment of the subject is focussed on an examination of the origins of broadband noise and the methods by which these can be analytically represented. Subsequent noise measurements on simple-design propellers indicate how the typical spectra in the Strouhal frequency range are significantly influenced by an extensive range of high order harmonics of the blade passage frequency, and a treatment of this harmonic content is included in this study report. The broadband and harmonic components of noise data, obtained from propellers with blade number and blade angle variations, have been analyzed in detail and noise prediction methods have been derived for each. It is postulated that the noise source mechanisms may be associated with unstable laminar flow separation (or transition) at the blade surfaces. The report also includes a set of graphical procedures by which both harmonic and random spectral details of the radiated noise can be calculated by tip Mach numbers in the range 0.2 to 0.6.

Yieldable blades for propellers

Abstract: A blade design for propellers of watercraft wherein the blades of the propeller are weakened in the line of impact but retain substantially all of their strength along the line of hydrodynamic load. Such a weakening permits the blades of a propeller to shear off or yield upon impact with an object without damage to the motor, shaft or pitch changing mechanism.

Rotor overload protection

Abstract: Overloading of rotor blades in a vertical lift aircraft such as a helicopter is avoided by limiting blade pitch to a value below that at which permissible loading will obtain. Strain in the blade pitch rods is monitored and used, together with the rate of change thereof as a pitch limit control signal to limit the effect of pilot control on the actual pitch of the rotor blades. In one embodiment, the strain in the rotor pitch push rods is compared against a lower threshold load value, and an excess causes the rate of change of the strain to be utilized as one input to the pitch limiting control signal; the load is also compared to an upper threshold, and an excess causes the actual load to be used as a second input to the pitch limit control signal. The pitch limit control signal in one embodiment is applied directly to the collective pitch outer loop (or major control loop), but is further modified when applied to the longitudinal cyclic pitch outer control loop. The further modification multiplies the limiting signal with air speed and pitch rate to prevent unwanted longitudinal pitch input at low air speeds, particularly as a result of excess commands in collective pitch.

Rotors for rotary winged aircraft

Abstract: This invention relates to a hub for a rigid rotor of a rotary winged aircraft and includes means for varying the blade angle of attack of each blade of a rotor as each blade rotates around the path traced out by the rotor to bring about a non-sinusoidal cyclic pitch change whilst independently allowing a sinusoidal cyclic pitch control to be superimposed thereon through the medium of a spider, the means being associated with each of the blade roots and includes a spindle for each blade, the spindles being equidistantly mounted for rotational movement in a rotatable component of the hub, and at their inner ends are each in spiral-splined engagement with a plunger whose inner end bears on a fixed cam and whose outer periphery has a predetermined peripheral profile to enable, for each blade, the blade angle of attack in relation to its azimuth position to be varied to suit the speed of the rotary winged aircraft.

Flight Evaluation of Elastomeric Bearings in an AH-1 Helicopter Main Rotor

Abstract: : Presented in this report are the results of a flight test program conducted to evaluate elastomeric bearings in the main rotor of an AH-1G helicopter. An experimental main rotor was fabricated and tested using only elastomeric bearings in both the flapping and pitch change axes. With this rotor, the flapping bearings carry the rotor drive and lift loads and allow the flapping motions. Two pitch change bearings were used in each grip to carry the blade bending and shear loads and transfer the blade centrifugal force to the rotor yoke. These bearings also accommodate the blade collective and cyclic pitch change motions. Torsional, radial, and axial load deflection curves are given for the flapping and pitch change bearings. In addition, the results from a limited endurance test program are included for the pitch change bearing. The purpose of the endurance tests was to assure that bearing metal parts would not fail prior to elastomer shredding. Thus, visual inspection of the elastomeric bearings was considered sufficient for safety-of-flight during the test program. The test results have shown the feasibility of elastomeric bearings for helicopter main rotor applications.

Principles of mechanisms used in controllable pitch propellers

Abstract: A controllable pitch propeller has a central hub which serves not only for the attachment of the blades but also contains the mechanical components to make the blades rotate. Inside the hub a translation motion is transformed into rotation of the blades. This involves large actuating forces, some times amounting to three times the total thrust on the propeller. Various types of blade suspension systems are described. The principles of crank-conrod, crack-slot, slot-pin and double-acting mechanisms are discussed in relation to their historical origin and development to modern conceptions. It is concluded that a sliding slot mechanisms with slots in the rotating parts has favorable characteristics for application in normal and feathering propellers.

An experimental investigation of the helicopter rotor blade element airloads on a model rotor in the blade stall regime

Abstract: A wind tunnel test program was conducted on an eight foot diameter model rotor system to determine blade element airloads characteristics in the unstalled and stalled flight regimes. The fully articulated model rotor system utilized three blades with a Vertol 23010-1.58 airfoil section, the blades being 1/7.5 scale models of the Ch-47C rotor blades. Instrumentation was incorporated at the blade 75% radial station to measure pressure and skin friction distributions, surface streamline directions and local angle of attack. The test program was conducted in three phases; non-rotating, hover and forward flight at advance ratios of 0.15, 0.35 and 0.60. Test data were analyzed with respect to providing insight to the mechanisms affecting blade stall, particularly retreating blade stall during forward flight conditions. From such data, an assessment was made as to the applicability of current theoretical analyses used for the prediction of blade element airloads in the stall regime.

Cyclic Pitch Control on a V/STOL Tilt Wing Aircraft

Abstract: : The report presents the key results of a model wing tunnel test program that was directed towards investigating the use of cyclic pitch propellers as the low speed longitudinal control system of a four propeller V/ STOL tilt wing transport-type aircraft. The almost linear pitch control effectiveness of this system through transitional flight and in-ground effect along with the correlation with theory is discussed, and the moderate power increase associated with its use is shown.

Propeller induced excitation forces

Abstract: This publication comprises a summing up of available pro- cedures for the estimation of propeller induced excitation forces and a critical examination of their ability to assess such forces acting on the ship. Reasons are given why hull wakes cannot be applied for estimation of cavitation performance and hull forces without correction for scale, propeller induction effects and operation in waves. Methods are suggested for estimation of such effects. By the concept of equivalent wake it is shown that the propeller induction effects for the test case considered does not alter the hull wake with propeller blade in vertical upwards position. Means are illustrated by which the propeller may transfer large amounts of energy to the hull under conditions for cavitation inception. It is demonstrated that the blade frequency part of the forces may be properly assessed by direct application of hull wakes only. The random part of the wake, however, needs to be included by application of statistical methods. Most of the methods discussed appear to be able to provide us with reasonable results at the projecting stage if the wake input to the computer resembles the velocity distribution actually experienced by the propeller.

Helicopter cyclic and collective pitch mechanism

Abstract: An apparatus for changing both the cyclic and collective pitch of each blade of a rigid rotor helicopter with a single differential gear mechanism. To change the collective pitch, a spider element is moved up or down which simultaneously actuates the differential gear mechanism for each blade in order to change its pitch collectively To change the cyclic pitch, a seesaw type linkage is actuated and applies a torque to the swash plate and control gyro of the helicopter. The control gyro supports lateral arms and the applied torque changes their plane of rotation. Linkages connected between each of the control arms and differential gear mechanisms react to this change in the plane of rotation and actuate the appropriate differential gear mechanisms to cyclically change the pitch of the blades.

A method for minimizing the occurrence of cavitation on propellers in a wake

Abstract: In this paper some indications are given as to how current propeller design practices may be modified to obtain improved cavitation properties for the moderately loaded screw propeller operating in a wake. Some general rules concerning the choice of propeller diameter, rotative speed, direction of rotation, blade area ratio, radial load distribution, etc. are discussed. The largest part of the paper, however, deals with a method to determine propeller pitch, blade thickness and camber in accordance with obtaining maximum latitude to variations in the angle of attack. It is postulated that for minimizing cavitation occurrence it is ineffective to determine pitch, thickness and camber solely by means of providing for the required strength, the required lift and a non-cavitating condition at shock free entry of the flow. The variation in the angle of attack, an inherent property of the non-uniform velocity field in which the screw propeller works, must also be accounted for. By incorporating the outlined quasi-stationary blade section shaping method in modern propeller design, the proper compromise between the conflicting characters of thick sections (with large possible cavitation-free angle of attack variations) and thin sections (free of cavitation at low cavitation numbers at shock-free entry of the flow) is made. This paper is a further development and another result of continuous and persistant research carried out at the Netherlands Ship Model Basin into the adaptation of the propeller to the wake to obtain optimum results.

Exciting-Force Operators for Ship Propellers

Abstract: The unsteady transfer functions or vibratory-exciting force and moment operators for any ship propeller are found by a procedure which employs an existing computer program. These functions can then be applied to any given radial variation of a spatially varying hull wake or inflow to yield three forces, three moments, and the blade bending moments. With these operators (which can be found once and for all for a systematic series of propellers), the task of predicting the vibratory-exciting forces and moments acting on the bearings of a particular ship is reduced to a simple calculation that can be made with a desk calculator in a matter of minutes. Thus, once a complete set of operators are obtained from the elaborate computer program, subsequent applications to any specific wakes does not require the computer program. Application of the method to a 5-bladed propeller is given in a worked example using simple formulas and tabulated values of the operators.

New method for the prediction of propeller thrust

Abstract: The author shows that the propeller thrust can be divided into two parts in the same way as the ship resistance using the dimensionless thrust coefficient. According to this, the necessary propeller thrust of the ship can be exactly determined by a linear extrapolation of the measured results of two different models.

Performance and Acoustic Testing of a Variable Camber Propeller

Abstract: : The report presents the test results obtained from a series of performance and acoustic near-field measurements on a propeller fitted with a variable camber feature. The subject propeller effects a change in camber by deflecting a flap positioned along the 72% chordal line of each blade. The tests were conducted on a 10,000 horsepower electric whirl rig. The tests represent the only test data available on this unique propeller configuration which is considered to have good potential for V/STOL applications.