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Showing papers on "Helicopter rotor published in 1970"


Patent
10 Jul 1970
TL;DR: A convertible composite engine capable of either shaft horsepower or thrust generation and split-powered operation in which partial thrust and partial shaft horsepower is generated is described in this article, where the engine is concentric about a single centerline and includes two coaxial free turbines, one driving a bypass fan and the other a shaft horsepower take-off, such as is commonly used to drive a helicopter rotor drive shaft.
Abstract: A convertible composite engine capable of either shaft horsepower or thrust generation and split-powered operation in which partial thrust and partial shaft horsepower is generated. The engine is concentric about a single centerline and includes two coaxial free turbines, one driving a load such as by-pass fan and the other a shaft horsepower take-off, such as is commonly used to drive a helicopter rotor drive shaft. A single gas generator provides compressed and heated gases to the coaxial free turbines with the total amount of gases provided determined by the total power required from the two free turbines and the split of gas flow through each free turbine determined by the position of the variable inlet guide vanes at the inlet to each turbine.

28 citations


Patent
13 Mar 1970
TL;DR: In this paper, an elastomeric rotor mounting structure for a helicopter blade is provided, where a blade grip is coupled to a yoke structure by means of radial-thrust elastomers and the yoke is connected to the rotor hub.
Abstract: An elastomeric rotor mounting structure for a helicopter blade is provided. In the mounting, a blade grip is coupled to a yoke structure by means of radial-thrust elastomeric bearings and the yoke structure is connected to the rotor hub. The elastomeric bearings simplify the rotor design and eliminate the need for bearing lubrication.

28 citations


ReportDOI
01 May 1970
TL;DR: In this paper, an aerodynamic model is constructed for the application of the properties of dynamic stall of airfoils to the calculation of the airloads and blade motion of helicopter rotor blades.
Abstract: : An aerodynamic model is constructed for the application of the properties of dynamic stall of airfoils to the calculation of the airloads and blade motion of helicopter rotor blades. Dynamic stall occurs on an airfoil undergoing pitching motion at high angle of attack, and is characterized by peak section lift and moment much larger than the corresponding static stall loads. A method is developed for the solution of the equations of motion of a rotor blade by means of harmonic analysis. The effect of dynamic stall on the blade torsional motion at high advance ratio is examined, and comparison is made with the limited experimental data available. An increase in the dynamic stall angle is shown to significantly decrease the amplitude of the pitch motions.

27 citations


Journal ArticleDOI
TL;DR: In this paper, the cyclic changes in the blowing jet were measured and the results indicated that the leading-edge jet does not disturb the flow and actually furnishes some additional reaction force to the lift.
Abstract: and agree well with the semiempirical expression previously determined. Most encouraging results were obtained from an experiment performed on the elliptical airfoil of 18% thickness ratio with dual symmetrical jets. These results indicate that the leading-edge jet does not disturb the flow and actually furnishes some additional reaction force to the lift. Hence, the important application of the elliptical airfoil (or oval airfoil) with dual jets to the retreating blade of a helicopter rotor is evident. Furthermore, the results of aerodynamic response measurements of the model to cyclic changes in the blowing jet are surprisingly encouraging. The cyclic valve was tested at frequencies equivalent to twice that of the rotational speed of a conventional helicopter blade, and the response of the lift was found to be excellent with negligible delay. The response of the drag as well as the chordwise pressure distribution to the cyclic changes in the blowing jet were also found to be very good. These results clearly indicate that the periodic variation of lift on the airfoil can be fulfilled by cyclic variation of the jet momentum; hence, the circulation control problem is reduced to simply the problem of pressure control inside the model.

25 citations


Patent
07 Dec 1970
TL;DR: In this paper, a plurality of slots are employed on the upper surface of the air foil to blow a thin sheet of air tangentially across the surface and around the trailing edge.
Abstract: The rotating blades on a helicopter are in the shape of a cambered elliptical airfoil with blunt edges. A plurality of slots are employed on the upper surface of the air foil to blow a thin sheet of air tangentially across the surface of the foil and around the trailing edge. Circulation control is achieved by the tangential blowing as the sheet of air adheres to the surface and travels around the trailing edge, detaching beneath the trailing edge at a location determined by the intensity of blowing. The effect of the tangential blowing is relocation of the stagnation stream lines producing increased lift on the foil. The air supplied to the slots is modulated with respect to the azimuth position of the rotor and the speed of the rotating blade so that cyclic control over the lift of the rotor can be accomplished without altering the blade attitude.

23 citations


ReportDOI
01 Dec 1970
TL;DR: In this paper, a computer program was written to calculate the velocity field and streamlines of a UH-1 rotor in order to examine the sensitivity of blade load calculations to wake geometry, an existing airloads program was modified to accept the computed wake geometry.
Abstract: : It is assumed that a helicopter rotor in forward flight can be represented by a flat plate. Expressions are developed relating the pressure field to the steady aerodynamic thrust and moment and the time-dependent flapping moment. This pressure field satisfies the zero pressure condition at the center and edge of the disc, the first and second harmonic variation in lift, and Laplace's equation. A computer program was written to calculate the velocity field and streamlines. Two sample cases corresponding to high- and low- speed conditions for the UH-1 rotor were chosen for computation. Both cases showed the tip-vortex phenomenon. In order to examine the sensitivity of blade load calculations to wake geometry, an existing airloads program was modified to accept the computed wake geometry. A comparison of results of this modified program with experimental data indicated that the effect of distorted wake is greater at low advance ratios than at high advance ratios. The reduced sensitivity at high advance ratios may be due to the wake being blown farther behind the rotor and/or the predominance of other aeroelastic parameters.

22 citations


Journal ArticleDOI
TL;DR: In this article, a theory is developed and used for determining the influence of compressibility on the aerodynamic forces acting on helicopter rotor blades when oscillating in hovering flight, and the usual two-dimensional mathematical model of the flow is adopted in which a section of the reference rotor blade and its helical wake is replaced by an airfoil with a straight wake and a system of regularly spaced infinite wakes below, the amount of spacing depending on the downward flow induced by the rotor and the number of blades.
Abstract: : A theory is developed and used for determining the influence of compressibility on the aerodynamic forces acting on helicopter rotor blades when oscillating in hovering flight. The usual two-dimensional mathematical model of the flow is adopted in which a section of the reference rotor blade and its helical wake is replaced by an airfoil with a straight wake and a system of regularly spaced infinite wakes below, the amount of spacing depending on the downward flow induced by the rotor and the number of blades. (Author)

21 citations


Patent
26 Mar 1970
TL;DR: In this paper, a HELICOPTER control system with a UNITIZED ROTOR and a TRANSMISSION ASSEMBLY for a CRAFT USING COAXIAL COUNTER-ROTATING ROTORS is described.
Abstract: DISCLOSED IS A HELICOPTER CONTROL SYSTEM HAVING A UNITIZED ROTOR AND TRANSMISSION ASSEMBLY FOR A CRAFT USING COAXIAL COUNTER-ROTATING ROTORS. THE ASSEMBLY IS GIMBAL MOUNTED SO THAT THE TRANSMISSION ACHIEVES DIRECTIONAL CONTROL WITHOUT ALTERING BLADE PITCH AND THE ROTOR HEAD IS OF SIMPLIFIED CONSTRUCTION TO ACHIEVE COLLECTIVE CONTROL OF THE BLADES.

18 citations


Patent
03 Feb 1970
TL;DR: In this paper, an improved attachment for a ROTOR BLADE in a Rotating Wing AirCRAFT has been discussed, which provides a low COST, light weight, low maintenance, and low maintenance.
Abstract: THIS INVENTION RELATES TO AN IMPROVED ATTACHMENT FOR A ROTOR BLADE IN A ROTATING WING AIRCRAFT HAVING A SEMIRIGID ROTOR SYSTEM. MORE PARTICULARLY, THE INVENTION PROVIDES A LOW COST, LIGHTWEIGHT, LOW MAINTENANCE ROTOR SYSTEM EMBODYING ALL OF THE DESIRED CHARACTERISTICS OF THE SEMI-RIGID HUB BUT WITH A MINIMUM CHANCE OF FATIGUE OR FAILURE.

14 citations


Patent
19 Jan 1970
TL;DR: In this article, a helicopter with a fixed wing on each of which is located an engine has a central horizontal rotor connected to both engines, as is a tail rotor, and a third rotor blade is mounted directly on the wing opposite to that of the tail rotor to blance the torque of the rotor.
Abstract: A helicopter with a fixed wing on each of which is located an engine has a central horizontal rotor connected to both engines, as is a tail rotor. A third rotor blade is mounted directly on the wing opposite to that of the tail rotor to blance the torque of the tail rotor.

14 citations


ReportDOI
01 Mar 1970
TL;DR: In this article, an analytical study was conducted to determine if available unsteady normal force and moment aerodynamic test data could be used in conjunction with existing helicopter rotor aeroelastic and variable inflow analyses to provide a method for predicting the stall flutter response of a helicopter rotor blade.
Abstract: : An analytical study was conducted to determine if available unsteady normal force and moment aerodynamic test data could be used in conjunction with existing helicopter rotor aeroelastic and variable inflow analyses to provide a method for predicting the stall flutter response of a helicopter rotor blade. For this purpose, incompressible unsteady aerodynamic data for an NACA 0012 airfoil executing pure sinusoidal pitching motions were employed. To apply such data under rotor blade operating conditions where multiharmonic motions and velocity variations exist, the data were expressed as functions of instantaneous section angle of attack, angular velocity, and angular acceleration. In addition, scaling procedures were developed in an attempt to account for the effects of compressibility. Limited application of the resulting analysis to define the aeroelastic characteristics of several blade designs showed that significant self-excited torsional oscillations of the stall flutter type could, in fact, be predicted for certain combinations of flight conditions and blade designs. Correlation studies, to evaluate the ability of the analysis to predict control loads, were performed with CH-53A maneuvering flight test data and with level flight test data from the NH-3A (S-61F).

Patent
02 Mar 1970
TL;DR: In this paper, a helicopter rotor has weights, one for each blade, mounted on arms which are pivoted remote from the axis of rotation of the rotor, connected through adjustable linkage mechanism with their respective blade horns in such manner that the system including all moving parts involved in the blade pitch motion can be turned to a desired frequency which is equal to the basic frequency of the blade vibration due to forward flight of the helicopter.
Abstract: A helicopter rotor has weights, one for each blade, mounted on arms which are pivoted remote from the axis of rotation of the rotor. The weights are connected through adjustable linkage mechanism with their respective blade horns in such manner that the system including all moving parts involved in the blade pitch motion can be turned to a desired frequency which is equal to the basic frequency of the blade vibration due to forward flight of the helicopter. When the tuned system is excited by aerodynamic vibratory forces at the tuned frequency, a pitch vibration of the blade results which leads to the generation of additional aerodynamic forces tending to cancel the original vibrational forces.

Journal ArticleDOI
TL;DR: In this paper, the nature of flapping torsion flutter of a helicopter blade in forward flight is discussed and the essential complication in the analysis is the presence of periodic coefficients in the equations of motion; approximate solutions are obtained by use of a perturbation procedure.
Abstract: The nature of flapping torsion flutter of a helicopter blade in forward flight is discussed. The essential complication in the analysis is the presence of periodic coefficients in the equations of motion; approximate solutions are obtained by use of a perturbation procedure. An unusual behaviour of the flutter equations which occurs when the fundamental frequency of flutter is a half-integer multiple of rotational speed is studied. Two different instability mechanisms can be distinguished and are related to the two energy sources in the system, namely the rotation of the rotor and the forward speed of the helicopter. It is found that forward flight can have a significant stabilising influence on flutter and that, as the tip speed ratio increases, flutter occurs predominantly at half-integer frequencies. The results are confirmed by the use of a numerical method.

Patent
18 May 1970
TL;DR: In this paper, the rotor rotor system is equipped with a rotor retention member which is compressible and torsionable in installation and operation of a helicopter rotor system, the torsional stiffness of the member decreasing with increasing rotor blade speed, the compressible stress not exceeding the strength of the material out of which the member is fabricated.
Abstract: In a helicopter rotor system, a hub assembly including a blade retention member which is compressible and torsionable in installation and operation of such rotor system, the torsional stiffness of the member decreasing with increasing rotor blade speed, the compressible stress not exceeding the strength of the material out of which the member is fabricated. Its inboard end is fixedly connected to either the rotor blade or a movable hub enveloping it at its inboard end, while its outboard end is fixedly connected to the fixed hub or extension thereof in the rotor system. Means are also provided in the system for isolating bearing means supporting the blade from the blade retention member. The member itself comprises a plurality of rails spacedly disposed radially equidistant from a common centerline coincident with the feathering axis for the blade.

Patent
23 Nov 1970
TL;DR: In this paper, a helicopter lighting system for night formation flying is described, which includes a first light unit attached to the main helicopter rotor in the vicinity of its tip and a second light unit at a location thereon spaced inwardly from the tip.
Abstract: The invention relates to helicopter lighting systems particularly for night formation flying. The system includes a first light unit attached to the main helicopter rotor in the vicinity of its tip and a second light unit attached to the main helicopter rotor at a location thereon spaced inwardly from the tip. Upon rotation of the helicopter rotor, the light units provide a light pattern providing a quickly discernible indication to an observer of the attitude of the helicopter and of any change in heading thereof relative to the observer.

01 Jun 1970
TL;DR: In this paper, a computer program for determining characteristic functions of aeroelastic instabilities of helicopter rotor in forward flight is presented, which can be used to determine the flight characteristics of a helicopter rotor.
Abstract: Computer program for determining characteristic functions of aeroelastic instabilities of helicopter rotor in forward flight


Patent
26 Jan 1970
TL;DR: A HELICOPER BLADE COMPRISING a PLURALITY of BONDED COMPONENTS forming a UNITARY STRUCTURE HAVING A LONGITUDINALLY EXTENDING PORTION, A GRADUAL TRANSITIONAL PORTion and a HOLLOW TUBE-LIKE Portion.
Abstract: A HELICOPER BLADE COMPRISING A PLURALITY OF BONDED COMPONENTS FORMING A UNITARY STRUCTURE HAVING A LONGITUDINALLY EXTENDING PORTION, A GRADUAL TRANSITIONAL PORTION AND A HOLLOW TUBE-LIKE PORTION. THE HOLLOW ROOT PORTION OF THE BLADE IS SECURED TO A ROTOR.

ReportDOI
01 Jan 1970
TL;DR: In this article, the effects of mass flow injection on the vortex strength, swirl velocity distribution, vortex core pressure, and vortex core size and the induced drag on the blade were evaluated.
Abstract: : Numerous research efforts have been conducted by different investigators to alter the characteristics of the tip vortex generated by a helicopter blade in order to alleviate the blade-vortex interaction problem as well as the noise problem associated with impulsive loading. The analytical investigation shows that it should be possible to significantly alter the characteristics of the trailing tip vortex for all flight conditions in a beneficial manner by injecting an airstream directly into the forming tip vortex. Analytical expressions were developed for the initial and final states of the vortex in order to evaluate the effects of mass flow injection on the vortex strength, swirl velocity distribution, vortex core pressure, vortex core size and the induced drag on the blade. On the basis of the results that were obtained, it was shown that the required mass flow may be obtained from centrifugal pumping action by venting the blade and therefore the desired modification can be obtained apparently without significant performance penalties which would be unacceptable. (Author)

Journal ArticleDOI
TL;DR: In this paper, a helicopter rotor aeroelastic stability in forward flight with periodically varying parameters analyzed by Hill type infinite determinant, exemplifying helicopter rotor stability in the forward flight.
Abstract: Dynamic systems stability with periodically varying parameters analyzed by Hill type infinite determinant, exemplifying helicopter rotor aeroelastic stability in forward flight


Journal ArticleDOI
TL;DR: This analysis provides a transient rotor solution in which integration out the blade is accomplished every five rotor azimuth degrees and the lift and drag coefficients are continuously calculated at all points along the blade.
Abstract: An accurate real-time simulation of a helicopter rotor can be achieved on a high-speed analog computer. By using repetitive operation and integrating along each blade every 2.5 milliseconds, the double integration required to determine rotor torque, thrust, moment, and rearward and sideward rotor forces is accomplished. The lift and drag coefficients are continuously calculated at all points along the blade. The same analog equipment used to calculate quantities for one blade is used for other blades by chang ing appropriate initial conditions. This analysis provides a transient rotor solution in which integration out the blade is accomplished every five rotor azimuth degrees. One console of a Hybrid Systems, Inc., SS-100 Analog/Hybrid Computer is used for the rotor solution.

01 Jan 1970
TL;DR: In this article, flight tests on a hingeless rotor compound helicopter were conducted to determine level flight and maneuvering characteristics of a single-rotor helicopter with a single rotor.
Abstract: Flight tests on hingeless rotor compound helicopter to determine level flight and maneuvering characteristics

ReportDOI
01 Jul 1970
TL;DR: In this paper, a rotor was instrumented to measure stagnation point location, radial flow direction, and pressure distributions, which were then used to determine angle of attack; effective airfoil profile; section normal force, chord force, and pitching moment; and stall and unsteady aerodynamics effects.
Abstract: : Aerodynamic data were measured at one blade radius station as the initial phase of a program designed to define the aerodynamic environment over the entire rotor disc. The rotor was instrumented to measure stagnation point location, radial flow direction, and pressure distributions. These data were then used to determine angle of attack; effective airfoil profile; section normal force, chord force, and pitching moment; and stall and unsteady aerodynamics effects. The test data were compared with two-dimensional empirical data and theory. Four cases were analyzed in some detail. They showed the variations in airfoil pressure, angle of attack, and radial flow as functions of aximuth and advance ratio. Deviations in the pressure distributions between test data and theory are believed to be due to the rotor wake and unsteady aerodynamic effects.

01 Dec 1970
TL;DR: The AH-1G helicopter as discussed by the authors is a two-bladed, semi-rigid, 'door hinge' type with the stabilizer bar removed and the engine is derated to 1100 shp due to the maximum torque limit of the main transmission.
Abstract: : The AH-1G helicopter manufactured by Bell Helicopter Company (BHC) was designed specifically to meet the US Army requirements for an armed helicopter. Tandem seating is provided for a two-man crew. The main rotor system is a two-bladed, semi-rigid, 'door hinge' type with the stabilizer bar removed. The engine is derated to 1100 shp due to the maximum torque limit of the main transmission. Distinctive features of the AH-1G are: the narrow fuselage (36 inches), the stub midwing with four external store stations, the integral chin turret. The flight control system is of the mechanical, hydraulically boosted, irreversible type with conventional helicopter controls in the aft cockpit (pilot station). The controls in the forward cockpit (copilot/gunner station) consist of conventional antitorque pedals and sidearm collective and cyclic controls. An electrically operated force trim system is connected to the cyclic and directional controls to induce artificial feel and to provide positive control centering.

Patent
22 Apr 1970
TL;DR: A rotor hub for a mechanically driven helicopter rotor comprises laminated ties connected at their outboard ends to blade attachment members 1 and at their inboard end to parallel sleeves 3 normal to the axes both of the ties and of rotation, the sleeves 3 comprising part of a central frame transmitting drive to the blades.
Abstract: 1,189,136. Helicopter rotor. COSTRUZIONI AERONAUTICHE GIOVANNI AGUSTA S.p.A. 17 Oct., 1969, No. 23363/67. Heading B7W. [Also in Division F2] A hub for a mechanically driven helicopter rotor comprises laminated ties 4 connected at their outboard ends to blade attachment members 1 and at their inboard ends to parallel sleeves 3 normal to the axes both of the ties and of rotation, the sleeves 3 comprising part of a central frame transmitting drive to the blades. Blade pitch is variable as members 2 are rotatable about axes radial of the rotor.



01 Nov 1970
TL;DR: In this article, the results of an analytical study to determine the application of a blown flap device called the Variable Deflection Thruster (VDT) to a helicopter rotor are presented and analyzed.
Abstract: : The results of an analytical study to determine the application of a blown flap device called the Variable Deflection Thruster (VDT) to a helicopter rotor are presented and analyzed. The study is part of a longer-range program to investigate and develop control techniques for stabilization of the higher harmonic modes of helicopter rotor blades. A high-speed digital computer program was used to calculate the aerodynamic characteristics and performance of a Sikorsky CH-34 rotor system as though equipped with a blown two-dimensional section. The study was made over a range of rotor flight profiles and operating parameters including advance ratio, shaft angle of attack, blade pitch, tip Mach number, jet deflection angle and blowing rate. Performance of the blown rotor is compared to the conventional CH-34 rotor to illustrate VDT application effectiveness. Results show that the operating lift capability and propulsive force of the CH-34 rotor are increased when the rotor is equipped with a blown device. A preliminary analysis of the attenuation of rotor hub-shear variation by programmed blowing is also shown. In all cases, improved performance through application of blown control requires additional power. (Author)

Journal ArticleDOI
TL;DR: The Lanchester Lecture on the topic of helicopters as mentioned in this paper has been a great honour and just now a wonderful chance to be asked to give the Lanchester lecture on the subject of helicopters.
Abstract: To be asked to give the Lanchester Lecture, on the topic of helicopters, is a great honour and just now a wonderful chance. We all know of Lanchester's basic contributions to our knowledge of the way in which lift is generated by the creation of a vortex system. For fixed wings the flow patterns are now known and the theories are in the third stage of refinement. But on helicopters, although it has been the topic of intensive research for fifteen years or more, the subject is much farther back. The results obtained are fascinating technically and pictorially and I would cheerfully discuss them for hours. But our understanding is far from complete and I have regretfully decided to throw away a wonderful chance and leave the topic to a less formal occasion.