Showing papers on "Helicopter rotor published in 1983"

Soft inplane bearingless helicopter rotor

Abstract: This invention relates to helicopter rotors and more particularly to rotor mounting involving a composite fiber-reinforced unitary yoke with resilient inplane restraints.

In-flight monitoring of composite structural components such as helicopter rotor blades

Abstract: The apparatus comprises one or more acoustical transducers associated with a particular interchangeable rotor blade for monitoring acoustic emissions emitted by the rotor blade under operating stress. The output of the transducers is connected to a computer associated with the particular aircraft. The transducer output signals are processed by the computer and filtered to allow real time stress return level readings so as to accumulate a count of critical acoustic emissions which are indicative of progressive irreversible structural fatigue or damage to the interchangeable rotor blade.

Interactions of Airfoils with Gusts and Concentrated Vortices in Unsteady Transonic Flow

Abstract: Unsteady interactions of concentrated vortices and distributed free-stream gusts with a stationary airfoil have been analyzed in two-dimensional transonic flow. A simple method of introducing such disturbances has been implemented numerically in the well-known transonic small-disturbance code LTRAN2, and calculations have been performed for two important classes of current aerodynamic problems. The first, which demonstrates many of the essential features of the interactions between helicopter rotor blades and their trailing-vortex wakes, is that of a discrete potential vortex convecting past an airfoil. The second is the response of a transonic airfoil to a transverse periodic gust, with and without the alleviation that can be achieved by the proper active control motion of a trailing-edge flap. In both cases, unsteady effects are found to play important roles in the shock-wave motion, in the overall flow-field development, and consequently, in the air loads on the airfoil.

An aeroacoustic model for high-speed, unsteady blade-vortex interaction

Abstract: A three-dimensional aeroacoustic model is developed to predict the sound pulse radiated by the passage of a helicopter blade over a potential vortex. The linearized analysis assumes that either the blade-vortex separation is small or that the blade-tip Mach number is close to 1, or both, so that an acoustically noncompact situation exists. The three-dimensional blade loading due to blade-vortex interaction is constructed through a spanwise superposition of two-dimensional solutions with strength linearly increasing from hub to tip. Such a loading overestimates somewhat the strength of tip region dipoles in the acoustic calculation that follows. The final expression for the predicted far-field signature is obtained in closed form, and thus permits a relatively inexpensive calculation of the directivity of peak acoustic pressures in three dimensions.

Helicopter Rotor Wake Geometry and Its Influence in Forward Flight. Volume 1. Generalized Wake Geometry and Wake Effect on Rotor Airloads and Performance.

Abstract: An analytic investigation to generalize wake geometry of a helicopter rotor in steady level forward flight and to demonstrate the influence of wake deformation in the prediction of rotor airloads and performance is described. Volume 1 presents a first level generalized wake model based on theoretically predicted tip vortex geometries for a selected representative blade design. The tip vortex distortions are generalized in equation form as displacements from the classical undistorted tip vortex geometry in terms of vortex age, blade azimuth, rotor advance ratio, thrust coefficient, and number of blades. These equations were programmed to provide distorted wake coordinates at very low cost for use in rotor airflow and airloads prediction analyses. The sensitivity of predicted rotor airloads, performance, and blade bending moments to the modeling of the tip vortex distortion are demonstrated for low to moderately high advance ratios for a representative rotor and the H-34 rotor. Comparisons with H-34 rotor test data demonstrate the effects of the classical, predicted distorted, and the newly developed generalized wake models on airloads and blade bending moments. Use of distorted wake models results in the occurrence of numerous blade-vortex interactions on the forward and lateral sides of the rotor disk. The significance of these interactions is related to the number and degree of proximity to the blades of the tip vortices. The correlation obtained with the distorted wake models (generalized and predicted) is encouraging.

Synthesized airfoil data method for prediction of dynamic stall and unsteady airloads

Abstract: A detailed analysis of dynamic stall experiments has led to a set of relatively compact analytical expressions, called synthesized unsteady airfoil data, which accurately describe in the time-domain the unsteady aerodynamic characteristics of stalled airfoils. An analytical research program was conducted to expand and improve this synthesized unsteady airfoil data method using additional available sets of unsteady airfoil data. The primary objectives were to reduce these data to synthesized form for use in rotor airload prediction analyses and to generalize the results. Unsteady drag data were synthesized which provided the basis for successful expansion of the formulation to include computation of the unsteady pressure drag of airfoils and rotor blades. Also, an improved prediction model for airfoil flow reattachment was incorporated in the method. Application of this improved unsteady aerodynamics model has resulted in an improved correlation between analytic predictions and measured full scale helicopter blade loads and stress data.

Helicopter rotor wake geometry and its influence in forward flight. Volume 2: Wake geometry charts

Abstract: Isometric and projection view plots, inflow ratio nomographs, undistorted axial displacement nomographs, undistorted longitudinal and lateral coordinates, generalized axial distortion nomographs, blade/vortex passage charts, blade/vortex intersection angle nomographs, and fore and aft wake boundary charts are discussed. Example condition, in flow ratio, undistorted axial location, longitudinal and lateral coordinates, axial coordinates distortions, blade/tip vortex intersections, angle of intersection, and fore and aft wake boundaries are also discussed.

Model helicopter rotor high-speed impulsive noise: Measured acoustics and blade pressures

Abstract: A 1/17-scale research model of the AH-1 series helicopter main rotor was tested. Model-rotor acoustic and simultaneous blade pressure data were recorded at high speeds where full-scale helicopter high-speed impulsive noise levels are known to be dominant. Model-rotor measurements of the peak acoustic pressure levels, waveform shapes, and directively patterns are directly compared with full-scale investigations, using an equivalent in-flight technique. Model acoustic data are shown to scale remarkably well in shape and in amplitude with full-scale results. Model rotor-blade pressures are presented for rotor operating conditions both with and without shock-like discontinuities in the radiated acoustic waveform. Acoustically, both model and full-scale measurements support current evidence that above certain high subsonic advancing-tip Mach numbers, local shock waves that exist on the rotor blades ""delocalize'' and radiate to the acoustic far-field.

Helicopter rotor transmission systems

Abstract: A fast forward flight helicopter is provided with a multiple speed helicopter rotor transmission. The transmission allows a variation in main rotor RPM or tail rotor RPM or both, dependent upon the desired flight conditions, while maintaining satisfactory lift and performance. With this means, noise is controlled without loss of aerodynamic performance. In one embodiment a helicopter is provided with a transmission for interconnecting the power input shaft through the main rotor shaft and tail rotor shaft in common. The transmission employed is a planetary gear transmission. A brake means is provided for clutching the planetary gear transmission from a first and second transmission speed so that power is continuously delivered, and shifting is accomplished in a smooth manner, thereby allowing the helicopter to remain in smooth flight. In another embodiment the main rotor is driven through the planetary gear transmission and the tail rotor is directly driven. In another embodiment a no-tail-rotor (NOTAR) helicopter is driven by the planetary gear system with the main rotor system being directly driven.

Fuel control for controlling helicopter rotor/turbine acceleration

Abstract: The difference in the speed (54, 56) of a helicopter gas engine (20), free turbine (40) from a reference speed (62, 64) generates (80) a desired acceleration signal (81). The difference (82) in actual turbine acceleration (84, 86) from desired acceleration is integrated (100) to provide an engine fuel command signal (67-73) whenever (88) the speed error signal exceeds (90) a predetermined threshold magnitude.

Collective and cyclic in-mast pitch control system for a helicopter

Abstract: A compact, rugged, streamline, stiff, pitch control system is devised in a helicopter by concentrically nesting a cyclic pitch control tube and collective pitch control tube within the drive shaft and stationary mast of a helicopter rotor system. The collective pitch control tube terminates in an upper inclined flange which engages a stationary swashplate by means of a bearing member disposed in an inclined bearing raceway in the stationary swashplate. The stationary swashplate in turn is rotatably coupled through a universal joint to the cyclic pitch control tube. Relative rotation of the cyclic pitch control tube with respect to the collective pitch control tube adjusts the stationary swashplate to a selected inclination with respect to the longitudinal axis of the control tubes and of the helicopter mast. A rotating swashplate is rotatably coupled to the stationary swashplate and transmits the angular orientation of the stationary swashplate to the pitch case of each rotor blade as appropriate. The cyclic pitch control tube and collective pitch control tube are rotatably coupled to each other to permit relative angular rotation, but otherwise can be displaced vertically in the direction of the mast as a collective unit, thereby vertically displacing the stationary swashplate and hence the rotating swashplate to effect collective pitch control for all of the blades of the rotor system.

Helicopter engine control with rotor speed decay anticipator

Abstract: The speed (54, 56) of the free turbine (40) of a helicopter engine (20) is compared (103) with the speed (105, 106) of the helicopter rotor (10) to indicate (101, 102) autorotation, and the deceleration (108) of the rotor above a threshold magnitude (110) is utilized (81, 68, 69) to increase fuel flow (72) to the engine in anticipation of rotor speed droop which would otherwise occur during recovery from the autorotation maneuver

Trends of Reynolds number effects on two-dimensional airfoil characteristics for helicopter rotor analyses

Abstract: The primary effects of Reynolds number on two dimensional airfoil characteristics are discussed. Results from an extensive literature search reveal the manner in which the minimum drag and maximum lift are affected by the Reynolds number. C sub d sub min and C sub l sub max are plotted versus Reynolds number for airfoils of various thickness and camber. From the trends observed in the airfoil data, universal scaling laws and easily implemented methods are developed to account for Reynolds number effects in helicopter rotor analyses.

Pendulum for damping or eliminating low excitation frequencies

Abstract: Low excitation frequencies of a structural component, for example of a heopter rotor blade or the like, are damped or eliminated by a pendulum device connected to the component, the excitation frequency or frequencies of which are to be damped or eliminated. In a helicopter rotor blade the pendulum device is preferably connected to the blade neck near the rotor head. The pendulum device has a plurality of pendulum bodies coupled to each other for forming a multiple pendulum in which these pendulum bodies are so tuned relative to each other that the multiple pendulum has several eigenfrequencies.

Aeroelastic tailoring of rotor blades for vibration reduction in forward flight

Abstract: Modern structural optimization techniques are applied to vibration reduction of helicopter rotor blades in forward flight. The objective function minimized consists of the oscillatory vertical hub shears or the hub rolling moments at one particular advance ratio. The behavior constraints are the frequency placements of the blade and the requirement that aeroelastic stability margins, in hover, remain unaffected by the optimization process. The aeroelastic stability and response analysis is based on a fully coupled flap-lag-torsional analysis of the blade. The vertical hub shears and rolling moments used as the objective function are obtained by appropriate integration of the loads acting along the span of the blade combined with a transformation to a hub fixed coordinate system, and a summation over the total number of blades. Numerical results for both a stiff-in-plane and a soft-in-plane configuration are presented, indicating that structural optimization yields the highest benefits when applied to soft-in-plane blade configuration. The results indicate substantial (15-40 percent) reduction in vibration levels, as well as a blade which is 20 percent lighter than the initial design.

Helicopter rotor control system with integrated hub

Abstract: A rotor control system for a helicopter in which the conventional swashplate is eliminated and the rotor hub is integrated to include an actuator for each rotor blade. Two arrangements are employed, each of which utilizes a hydraulic circuit. One arrangement is a hydromechanical arrangement with stick control, while the other arrangement is an electro-hydraulic fly by wire arrangement. The latter does not employ a swashplate, while the former employs a modified swashplate. The controls, like the actuators, are mounted in the rotor hub, and the hydraulic lines and fiber optics pass through the rotor drive shaft to the rotor hub.

Hubless, hingeless and bearingless helicopter rotor system

Abstract: A helicopter rotor system in which a plurality of rotor blades are attached to the rotor mast. Each blade has a spar formed of fibers bundled and bonded together inside a skin. These fibers are divided into two bundles, each of which has a bight with a bend and two arms that double back into the spar. The bights are joined to the mast by spaced-apart attachments. The attachments may be plate-like, and can be shaped to provide initial coning and camber angles.

Helicopter rotor system and method

Abstract: A rotor hub system for a helicopter in which the rotor hub and pitch housing are fabricated predominately of composite material, the flap hinge, pitch hinge and lead-lag hinge contain elastomeric bearings and one step blade folding in either the forward or aft direction using the same drive system. The rotor hub includes closed loop straps which define generally opposed lugs of the flap hinge, and the pitch housing includes a pair of closed loop straps which define the lugs of the lead-lag hinge and a lug of the flap hinge. The use of composite materials as the predominant material of the rotor hub and the pitch housing results in a highly load redundant structure permitting a reduction in size and number of parts, a reduction in drag, and an increase in reliability and safety.

Analysis and correlation of the test data from an advanced technology rotor system

Abstract: Comparisons were made of the performance and blade vibratory loads characteristics for an advanced rotor system as predicted by analysis and as measured in a 1/5 scale model wind tunnel test, a full scale model wind tunnel test and flight test. The accuracy with which the various tools available at the various stages in the design/development process (analysis, model test etc.) could predict final characteristics as measured on the aircraft was determined. The accuracy of the analyses in predicting the effects of systematic tip planform variations investigated in the full scale wind tunnel test was evaluated.

Method of displaying detected information about a rotating mass

Abstract: In a method of detecting the deflection of the blades 13 of a helicopter rotor as it rotates, a beam 14 of radiation from a transmitter/receiver 11 encounters the tips of the rotating blades which send reflected signals to the receiver. The phase difference due to deflection of the blade tip can be used to give a measure of the deflection of each blade, and that can be displayed graphically as shown in FIGS. 7-10 for the various blades at various speeds. In a related method of measuring deflections of the blades 111 for a tail rotor, a laser beam transmitter 16 in FIG. 14 has its reflected beam 122, 123 from an undeflected blade 111 or a deflected blade 111' received by a particular receiver in a linear array 119 of receivers so that the particular receiver gives an indication of the amount of deflection.

Labyrinth seal forces on a whirling rotor

Abstract: An experimental investigation of air labyrinth seal forces on a subsynchronously whirling model rotor is described and test results are given for diverging, converging, and straight two-strip seals. The effects of pressure drop, provide basic experimental data needed in the development of design methods for predicting and preventing self-excited whirl of turbine rotors and other machines having labyrinth seals. The total dynamic seal forces on the whirling model rotor are measured accurately by means of an active damping and stiffness system that is adjusted to obtain neutral whirl stability of the model rotor system. In addition, the whirling pressure pattern in the seal annulus is measured for a few test conditions and the corresponding pressure forces on the rotor are compared with the total measured forces. This comparison shows that either radial and axial pressure gradients in the seal annulus or drag forces on the rotor are significant. Comparisons made between the measured seal forces and theoretical results show that present theory is inadequate.

Toy land vehicle and aircraft combination

Abstract: A self-propelled military type land vehicle with a power take-off friction coupling in the form of a rotating cannon fits into and is retained in a helicopter shell with the power coupling driving the helicopter rotor. A releasable latch carried by the helicopter retains the vehicle within the helicopter shell and in driving engagement during simulated flight. The helicopter has a hand grippable depending tail support with a trigger disposed near the support for effecting release of the land vehicle and disengagement of the power take-off coupling from the rotor without braking the rotor.

Transient Vibration of High-Speed, Lightweight Rotors Due to Sudden Imbalance

Abstract: In the field of rotor dynamics, increased attention is being given to the transient response analysis of the rotor, since the effects of impact loading and vibrations of the rotor arising from blade loss can be studied by a time transient solution of the rotor system. As recent trends in rotating machinery have been directed towards lightweight, high-speed flexible rotors, the effect of flexibility on transient response analysis is becoming of increasing importance. In the present paper, a transient vibration analysis is carried out on a flexible-disk/flexible-shaft system or rigid-disk flexible-shaft system subjected to a sudden imbalance that is assumed to represent the effect of blade loss. To solve the basic equation governing a rotating flexible disk the Galerkin’s method is used, and the equation of motion of the rotor system is numerically solved by employing the Runge-Kutta-Gill’s method. Experiments were conducted on a model rotor having a blade loss simulator; the shaft vibrations were also measured. The validity of the anaytical results was demonstrated by comparison with the experimental results.

Method of producing apertures in fibre-reinforced articles such as helicopter rotor blades

Abstract: A method of producing apertures in fibre-reinforced articles is described and consists of locally heating an area of the unconsolidated article and piercing the heat-softened area using a tapered piercing tool. Following withdrawal of the tool, an aperture retaining means is inserted to retain the shape of the aperture during a subsequent consolidation operation. The method ensures that all of the strength bearing fibres are retained and also that none of the fibres is severed, and is particularly suited to the formation of attachment apertures at the root end of a helicopter rotor blade.

Rotor/body aerodynamic interactions

Abstract: A wind tunnel investigation was conducted in which independent, steady state aerodynamic forces and moments were measured on a 2.24 m diam. two bladed helicopter rotor and on several different bodies. The mutual interaction effects for variations in velocity, thrust, tip-path-plane angle of attack, body angle of attack, rotor/body position, and body geometry were determined. The results show that the body longitudinal aerodynamic characteristics are significantly affected by the presence of a rotor and hub, and that the hub interference may be a major part of such interaction. The effects of the body on the rotor performance are presented.

Vibration damper and in particular frequency adapter for a helicopter blade

Abstract: The device comprises two rigid elements 1a, 1b, 2 and an elastomer mass 10 interposed therebetween so as to be deformed when the elements move relative to each other in a longitudinal direction. The device includes a closed space with a restriction element 16 defining two chambers 23, 24 whose volumes vary inversely upon movement of the chamber walls, the two chambers being interconnected by one or more passages, the empty space being filled with a viscous fluid material so as to produce a damping effect in the passages. Application to helicopter blade frequency adapters.

Investigation of the Effect of Blade Sweep on Rotor Vibratory Loads.

Abstract: The effect of helicopter rotor blade planform sweep on rotor vibratory hub, blade, and control system loads has been analytically investigated. The importance of sweep angle, sweep initiation radius, flap bending stiffness and torsion bending stiffness is discussed. The mechanism by which sweep influences the vibratory hub loads is investigated.

Optimum design of rotor blades for vibration reduction in forward flight

Abstract: Modern structural optimization techniques are applied to vibration reduction of helicopter rotor blades in forward flight. The objective function minimized consists of the oscillatory vertical hub shears or the hub rolling moments at one particular advance ratio. The behavior constraints are the frequency placements of the blade and the requirement that aeroelastic stability margins, in hover, remain unaffected by the optimization process. The aeroelastic stability and response analysis is based on a fully coupled flap-lag-torsional analysis of the blade. Numerical results are presented for some typical soft-in-plane hingeless rotor configurations indicating a 15-40 percent reduction in vibration levels, as well as a blade which is 20 percent lighter than the initial design. These results imply that structural optimization techniques can yield substantial practical benefits in the design process of rotor systems.