Showing papers on "Helicopter rotor published in 1985"

Helicopter obstacle detector

Abstract: A pulsed Doppler radar mounted adjacent to the tip of a helicopter rotor blade for sensing obstacles in the helicopter path. The rotor tip velocity shifts the frequency of radar echos so that, through pulsed Doppler radar techniques, the echos from obstacles can be separated from clutter.

Solution method for a hovering helicopter rotor using the Euler equations

Abstract: A method for the calculation of the flow field of a helicopter rotor blade in hover is presented. The approach uses a finite volume solution of the three dimensional Euler equations for the blade near field. In the Euler solver the velocity field is decomposed into two parts. One is the induced velocity of the vortex wake extending below the blade, found from a free wake calculation procedure. The other part is the unknown additional velocity field of the rotor blade. This approach eliminates numerical diffusion of the rolled up wake vorticity due to truncation error and artificial viscosity. Also, the effects of the far wake are included in the limited computational domain. Solutions are presented for an isolated wing and a model helicopter rotor and compared to experiment.

Performance and loads data from a hover test of a full-scale XV-15 rotor

Abstract: A hover test of a full-scale XV-15 rotor was conducted at the Outdoor Aerodynamic Research Facility at Ames Research Center. The primary objective of the test was to obtain accurate measurements of the hover performance of the original, metal-blade XV-15 rotor system. Data were acquired for rotor tip Mach numbers ranging from 0.60 to 0.73. This report presents data on rotor performance, rotor wake downwash velocities, and rotor loads.

Numerical solution of the full-potential equation for rotors and oblique wings using a new wake model

Abstract: A three-dimensional, full-potential, quasi-steady code TFAR1 is proposed for calculating the transonic flow past a lifting helicopter rotor blade and oblique wing. The TFAR1 uses a two-dimensional nonlinear wake-model that allows a jump in velocity potential to propagate with the local fluid flow in the wake. Rotor calculations were made for a single blade at an advance ratio of 0.3, a rotational tip Mach number of 0.7, and at 0-degree incidence. A 1/7-scale model of the Cobra Operational Load Survey (OLS) rotor blade is calculated, and the pressure distributions are compared to the measurements for azimuth angles 0, 30, 60, 90, 120, and 150 degrees at the 95 percent spanwise station of the OLS blade. Furthermore, an oblique wing with Korn airfoil was calculated at the high transonic free-stream Mach number of 0.9791, zero incidence, and yaw angle of 40 degrees. The TFAR1, coupled with a helicopter performance code CAMRAD (Johnson, 1981), provides a full-potential code for calculating the entire flow field for a multiple-bladed rotor in transonic lifting forward flight.

The use of active controls to augment rotor/fuselage stability

Abstract: The use of active blade pitch control to increase helicopter rotor/body damping is studied. Control is introduced through a conventional nonrotating swashplate. State variable feedback of rotor and body states is used. Feedback parameters include cyclic rotor flap and lead-lag states, and body pitch and roll rotations. The use of position, rate, and acceleration feedback is studied for the various state variables. In particular, the influence of the closed loop feedback gain and phase on system stability is investigated. For the rotor/body configuration analyzed, rotor cyclic inplane motion and body roll-rate and roll-acceleration feedback can considerably augment system damping levels and eliminate ground resonance instabilities. Scheduling of the feedback state, phase, and gain with rotor rotation speed can be used to maximize the damping augmentation. This increase in lead-lag damping can be accomplished without altering any of the system modal frequencies. Investigating various rotor design parameters (effective hinge offset, blade precone, blade flap stiffness) indicates that active control for augmenting rotor/body damping will be particularly powerful for hingeless and bearingless rotor hubs.

Electric air-driven helicopter

Abstract: A helicopter has a low profile electric motor mounted in each of the rotor blades to drive a cross-flow fan which draws air in through a slot at the leading edge of the blade and forces it out through an opposing slot adjacent the trailing edge of the blade to provide the thrust for rotating the rotor blade. An engine is located in the fuselage of the helicopter for driving an electric generator to produce the electricity supplied to the motors mounted in the blades. In addition, yaw control is achieved without the necessity of tail structure or a tail rotor using a small electric motor driving or absorbing power from the main rotor shaft. Both the yaw control motor and the main rotor shaft tilt together as a rigid unit. Pitch and roll control is achieved without the necessity of aerodynamic surfaces by movement of the main rotor support mast about a gimbal bearing support located above the center of gravity of the helicopter.

Helicopter air-spring vibration absorber

Abstract: A tunable vibration absorber in a helicopter rotor hub arrangement with a central mass suspended in a symmetrical outer casing over the rotor hub, including an air spring for variably stiffly supporting said central mass in three dimensions.

Wide-field shadowgraph flow visualization of tip vortices generated by a helicopter rotor

Abstract: The vortex trajectory and vortex wake generated by helicopter rotors were visualized using a wide-field shadowgraph technique. Use of a retro-reflective Scotchlite screen made it possible to investigate the flow field generated by full-scale tail rotors. Tip vortex trajectories were visible in shadowgraphs for a range for tip Mach number of 0.38 - 0.60. The effect of the angle of attack was substantial. At an angle of attack greater than 8 degrees, the visibility of the vortex core was significant even at relatively low tip Mach numbers. The theoretical analysis of the visibility was carried out for a rotating blade. This analysis demonstrated that the visibility decreases with increasing dimensionless core radius (ro/c) and increases with increasing tip Mach number. Based on this investigation, it is concluded that the wide-field shadowgraph flow visualization technique should be feasible to study the flow field generated by a large main rotor in a wind tunnel and in an outdoor full-scale test stand. Of note is that the shadowgraph technique could easily be used with other on-going tests such as aerodynamic performance study, noise measurements, velocity measurements with LDV or hot-wire anemometer, local pressure measurement on the rotor surface, etc.

Helicopter rotor blade made from a multispar composite material with torsion compartments and a process for manufacturing same

Abstract: The invention provides a helicopter rotor blade made from a composite material whose multistrut resistant framework adjacent the leading edge is disposed so as to form two superimposed compartments.

Optimization methods applied to the aerodynamic design of helicopter rotor blades

Abstract: This paper describes a formal optimization procedure for helicopter rotor blade designs which minimizes hover horsepower while assuring satisfactory forward flight performance. The approach is to couple hover and forward flight analysis programs with a general purpose optimization procedure. The resulting optimization system provides a systematic evaluation of the rotor blade design variables and their interaction, thus reducing the time and cost of designing advanced rotor blades. The paper discusses the basis for and details of the overall procedure, describes the generation of advanced blade designs for representative Army helicopters, and compares designs and design effort with those from the conventional approach which is based on parametric studies and extensive cross-plots.

Coupled helicopter rotor/body aeromechanical stability comparison oftheoretical and experimental results

Abstract: This paper presents the results of an analytical study aimed at predicting the aeromechanical stability of a helicopter in ground resonance, with the inclusions of aerodynamic forces. The theoretical results are found to be in good agreement with the experimental results, available in the literature, indicating that the coupled rotor/fuselage system can be represented by a reasonably simple mathmatical model.

Effect of ground and/or ceiling planes on thrust of rotors in hover

Abstract: The thrust produced by a helicopter rotor hovering near ground and/or ceiling planes is investigated experimentally and theoretically. In the experiment, the thrust was measured on a 0.324-m-diam rotor operating between floor and ceiling planes which were located from 6 to 0.08 diam from the rotor disk. In the first theoretical model studied, the incompressible and inviscid flow induced by a sequence of vortex cylinders, located above and below the rotor to simulate the rotor wake and its interaction with the floor and ceiling planes, was considered. Comparison with experiment showed that this model overpredicts the change in thrust caused by the proximity of the walls. Therefore, a second arrangement of vortex cylinders was introduced which provides a more accurate prediction of the ground and ceiling effects on the thrust of the rotor in hover. The applicability of these results to a vented wind tunnel is also discussed.

Helicopter main rotor blade having a short span slot near the tip end

Abstract: A helicopter main rotor blade having built-in twist for improved hover performance is provided with a trailing-edge, short span slot near the tip end of the blade for upwardly directing a stream of pressurized air therefrom. The upward ejection of air from the slot untwists the blade, which will enhance the forward flight performance of the blade. A method of modulating the ejection of air from the slot is disclosed for antivibratory control.

Performance Degradation of Helicopter Rotor in Forward Flight Due to Ice

Abstract: This study addresses the analytical assessment of the degradation in the forward flight performance of the front rotor Boeing Vertol CH47D helicopter in a rime ice natural icing encounter. The front rotor disk was divided into 24 15-deg sections and the local Mach number and angle of attack were evaluated as a function of azimuthal and radial location for a specified flight condition. Profile drag increments were then calculated as a function of azimuthal and radial position for different times of exposure to icing, and the rotor performance was re-evaluated including these drag increments. The results of the analytical prediction method, such as horsepower required to maintain a specific flight condition, as a function of icing time have been generated. The method to illustrate the value of such an approach in assessing performance changes experienced by a helicopter rotor as a result of rime ice accretion is described.

Apparatus for control of collective and cyclic pitch of the blades of a rotor

Abstract: Apparatus for controlling both collective and cyclic pitch of blades of a helicopter rotor comprises a non-rotating plate which is connected via a fixed caliper and servo controls to a fixed housing and to which is attached the internal ring of a ball race bearing. The external ring of the bearing carries a rotating plate, which is connected by means of rotating caliper or links to each of the rotors and by means of pitch rods to control levers for adjusting the pitch of the blades. The non-rotating plate is fixed to external armatures of laminated joint pieces which are mounted slidingly up and down a guide base. The collective pitch is controlled by sliding the assembly of non-rotating plate and joint pieces up or down the guide base while the cyclic pitch is controlled by inclining the assembly relative to the main rotor shaft. This inclination involves deformations in the laminated joints.

Helicopter gust alleviation, attitude stabilization, and vibration alleviation using individual-blade-control through a conventional swash plate

Abstract: The novel active control system presented for helicopter rotor aerodynamic and aeroelastic problems involves the individual control of each blade in the rotating frame over a wide range of frequencies (up to the sixth harmonic of rotor speed). This Individual Blade Control (IBC) system controls blade pitch by means of broadband electrohydraulic actuators attached to the swash plate (in the case of three blades) or individually to each blade, using acceleratometer signals to furnish control commands to the actuators. Attention is given to IBC's application to blade lag, flapping, and bending dynamics. It is shown that gust alleviation, attitude stabilization, vibration alleviation, and air/ground resonance suppression, are all achievable with a conventional helicopter swash plate.

Low vibration helicopter rotor

Abstract: A low vibration helicopter rotor including a four-bar linkage arrangement which permits the straight line connecting the center of gravity of each pair of diametrically opposed rotor blades to intersect the rotor hub geometrical center at all cyclic conditions.

Analyses and tests for design of an electro-impulse de-icing system

Abstract: De-icing of aircraft by using the electro-magnetic impulse phenomenon was proposed and demonstrated in several European countries. However, it is not available as a developed system due to lack of research on the basic physical mechanisms and necessary design parameters. The de-icing is accomplished by rapidly discharging high voltage capacitors into a wire coil rigidly supported just inside the aircraft skin. Induced eddy currents in the skin create a repulsive force resulting in a hammer-like force which cracks, de-bonds, and expels ice on the skin surface. The promised advantages are very low energy, high reliability of de-icing, and low maintenance. Three years of Electo-Impulse De-icing (EIDI) research is summarized and the analytical studies and results of testing done in the laboratory, in the NASA Icing Research Tunnel, and in flight are presented. If properly designed, EIDI was demonstrated to be an effective and practical ice protection system for small aircraft, turbojet engine inlets, elements of transport aircraft, and shows promise for use on helicopter rotor blades. Included are practical techniques of fabrication of impulse coils and their mountings. The use of EIDI with nonmetallic surface materials is also described.

The UH-1H helicopter icing flight test program: An overview

Abstract: An ongoing joint NASA/Army program to study the effects of ice accretion on unprotected helicopter rotor aerodynamic performance is discussed. This program integrates flight testing, wind tunnel testing, and analytical modeling. Results are discussed for helicopter flight testing in the Canadian NRC hover spray rig facility to measure rotor aero performance degradation and document rotor ice accretion characteristics. The results of dry wind tunnel testing of airfoil sections with artificial ice accretions and predictions of rotor performance degradation using available rotor performance codes and the wind tunnel data are presented. An alternative approach to conducting future helicopter icing flight programs is discussed.

Investigation of the Steady-State Response of a Dual-Rotor System With Inter-Shaft Squeeze Film Damper

Abstract: This paper presents an analysis of the steady-state unbalance response of a dual-rotor gas turbine engine with a flexible intershaft squeeze film damper using a simplified transfer matrix method. The simplified transfer matrix method is convenient for the evaluation of the critical speed and response of the rotor system with various supports, shaft coupling, intershaft bearing, etc.The steady-state unbalance response of the rotor system is calculated for different shaft rotation speeds. The damping effects of an intershaft squeeze film damper with different radial clearances under various levels of rotor unbalance are investigated.Copyright © 1985 by ASME

A Blade Loss Response Spectrum for Flexible Rotor Systems

Abstract: A shock spectrum procedure is developed to estimate the peak displacement response of linear flexible rotor-bearing systems sugjected to a step change in unbalance (i.e., a blade loss). A progressive and a retrograde response spectrum are established. These blade loss response spectra are expressed in a unique non-dimensional form and are functions of the modal damping ratio and the ratio of rotor spin speed to modal damped whirl speed. Modal decomposition using complex modes is utilized to make use of the unique feature of the spectra for the calculation of the peak blade loss displacement response of the rotor system. The procedure is applied to three example systems using several modal superposition strategies. The results of each are compared to true peak displacement obtained by a separate transient response program.

Analysis of the Vibration of the Input Bevel Pinion in RAN (Royal Australian Navy) Wessex Helicopter Main Rotor Gearbox WAK143 Prior to Failure.

Abstract: : Following the crash of an RAN Wessex helicopter caused by the catastrophic fatigue failure of the input spiral bevel pinion in the main rotor gearbox, routine recordings of the gearbox vibration have been analyzed by ARL. It has been shown that conventional spectral analysis of the vibration is unable to give adequate indication of the presence of the fatigue crack but that an alternative technique of vibration analysis called signal averaging can give warning of the crack 42 hours before failure. Enhancement of the signal average using a computer enables detection of the crack as early as 103 hours before failure.

Helicopter destruction system employing cables

Abstract: A method and apparatus for destroying helicopters is disclosed and relies on launching cables (7) above a helicopter (1) which cables (7) are tailored to a specific helicopter to maximize the probability of ingestion of the cable into the helicopter rotor system (3, 5) thus providing a low cost, highly efficient helicopter destruction system.

All composite, constant speed universal joint for use in a shaft driven tiltable main rotor for a helicopter

Abstract: A universal joint for use in a pitch cone rotor system in a helicopter is comprised of crossed lift beams, one beam of which is coupled to the rotor hub and the other beam of which is coupled to the driven rotor shaft. The two crossed lift beams are coupled to each other through a cruciform case. The cruciform case in turn is coupled to each of the crossed lift beams by means of a plurality of flexures. The flexures and cruciform case are made of composite fiber materials and the flexures are soft enough to permit angular and translational deflections of the crossbeams with respect to each other thereby tending to smooth out and reduce sudden changes in rotor speed between the shaft and rotor system and thereby tending to make rotor speeds more uniform. The crossed lift beams are further coupled together at the center of their crossing by a flexible elastomeric tension link which conducts rotor loads between the two beams when the rotor develops negative lift loads on the ground and in flight. A hollow laminated elastomeric compression fitting is placed between the beams at their center to transmit the rotor lift force between them.

Aeroelastic model helicopter rotor testing in the Langley TDT

Abstract: Wind-tunnel testing of a properly scaled aeroelastic model helicopter rotor is considered a necessary phase in the design development of new or existing rotor systems. For this reason, extensive testing of aeroelastically scaled model rotors is done in the Transonic Dynamics Tunnel (TDT) located at the NASA Langley Research Center. A unique capability of this facility, which enables proper dynamic scaling, is the use of Freon as a test medium. A description of the TDT and a discussion of the benefits of using Freon as a test medium are presented. A description of the model test bed used, the Aeroelastic Rotor Experimental System (ARES), is also provided and examples of recent rotor tests are cited to illustrate the advantages and capabilities of aeroelastic model rotor testing in the TDT. The importance of proper dynamic scaling in identifying and solving rotorcraft aeroelastic problems, and the importance of aeroelastic testing of model rotor systems in the design of advanced rotor systems are demonstrated.

Method and apparatus for tracking a helicopter rotor or other rotating mass

Abstract: A helicopter has means for giving a prominent display or graphical representation of the rate of revolution of the rotor or of the value of m/R where m is the number of rotor blades and R is the rotor cyclic time, while it is also possible to display measurements of the vibration amplitude at the frequency l /R, or m/R against %RRPM. This kind of display has not previously been thought necessary for helicopter operation but has been discovered to be most useful in correcting instrument readings in adjusting helicopter rotors for any lack of balance, and in adjusting balancing weights so that there will be a minimum vibration at the rotor speed at which it is intended to fly the helicopter.

Device comprising cyclic plates driven by flexible blades, for controlling a helicopter rotor

Abstract: A device comprising cyclic plates driven by flexible blades for controlling a helicopter rotor. The device comprises upper flexible curved blades pivotably mounted on the rotor shaft, above the rotary plate, and pivotably mounted by a ball joint on the rotary plate, so as to cause it to rotate with the rotor shaft and at least one lower flexible curved blade, pivoting on an element of the structure of the helicopter and pivotably mounted by a ball joint on the non rotary plate, so as to secure it against rotation. The transverse stiffness of the blades ensures centering of the plates whereas the longitudinal flexibility of the blades and their end pivot point allow the blades to follow the axial translational and tilting movements imparted to the plates by pilot controls pivotably mounted to the non rotary plate, and transmitted to levers controlling the angle of attack of the rotor blades by means of links pivotably mounted to the rotary plate.

Hover and Forward Flight Acoustics and Performance of a Small-Scale Helicopter Rotor System.

Abstract: A 2.1-m diam., 1/6-scale model helicopter main rotor was tested in hover in the test section of the NASA Ames 40- by 80- Foot Wind Tunnel. Subsequently, it was tested in forward flight in the Ames 7- by 10-Foot Wind Tunnel. The primary objective of the tests was to obtain performance and noise data on a small-scale rotor at various thrust coefficients, tip Mach numbers, and, in the later case, various advance ratios, for comparisons with similar existing data on full-scale helicopter rotors. This comparison yielded a preliminary evaluation of the scaling of helicopter rotor performance and acoustic radiation in hover and in forward flight. Correlation between model-scale and full-scale performance and acoustics was quite good in hover. In forward flight, however, there were significant differences in both performance and acoustic characteristics. A secondary objective was to contribute to a data base that will permit the estimation of facility effects on acoustic testing.

Tension/compression rod arrangement for damping helicopter rotor blade oscillations

Abstract: Apparatus for damping blade lead/lag motion on a hingeless helicopter rotor assembly, including a hub, blades and flexbeam(s) interposed between the root end of the blades and the hub. Rigid, radial links extend the length of the flexbeams for attachment to the outboard ends thereof. Lead/lag motion at the outboard end of the flexbeam causes flexbeam bending, which is converted to radial translation of the links. This radial translation of the links and likewise the blade lead/lag motion is damped by damper means connected between the inboard ends of the links and the hub.