Showing papers on "Leading edge published in 1974"

Investigation of Acoustic Effects of Leading-Edge Serrations on Airfoils

Abstract: This paper presents and interprets a series of extensive studies of the application of leading-edge serrations as a device for reducing the vortex noise radiated from stationary and rotating airfoils in low Reynolds number flow. In these studies, a variety of serrations were attached at selected locations near the leading edge of stationary and rotating airfoils. The noise levels of the airfoils were reduced considerably with the serrations attached. An explanation of the aeroacoustic flow mechanisms involved is given.

Hydromechanics of lunate-tail swimming propulsion

Abstract: This paper investigates the non-uniform motion of a thin plate of finite aspect ratio, with a rounded leading edge and sharp trailing edge, executing heaving and pitching oscillations at zero mean lift. Such vertical motions characterize the horizontal lunate tails with which cetacean mammals propel themselves, and the same motions, turned through 90° to become horizontal motions of sideslip and yaw, characterize the vertical lunate tails of certain fast-swimming fishes. An oscillating vortex sheet consisting of streamwise and spanwise components is shed to trail behind the body and it is this additional feature of the streamwise component resulting from the finiteness of the plate that makes this study a generalization of the two-dimensional treatment of lunate-tail propulsion by Lighthill (1970). The forward thrust, the power required, the energy imparted to the wake and the hydromechanical propulsive efficiency are determined for this general motion as functions of the physical parameters defining the problem: namely the aspect ratio, the reduced frequency, the feathering parameter and the position of the pitching axis. The dependence of the thrust coefficient and propulsive efficiency on these physical parameters, for the complete range of variation consistent with the assumptions of the problem, has been depicted graphically.

Extension of leading-edge-suction analogy to wings with separated flow around the side edges at subsonic speeds

Abstract: A method for determining the lift, drag, and pitching moment for wings which have separated flow at the leading and side edges with subsequently reattached flow downstream and inboard is presented. Limiting values of the contribution to lift of the side-edge reattached flow are determined for rectangular wings. The general behavior of this contribution is computed for rectangular, cropped-delta, cropped-diamond, and cropped-arrow wings. Comparisons of the results of the method and experiment indicate reasonably good correlation of the lift, drag, and pitching moment for a wide planform range. The agreement of the method with experiment was as good as, or better than, that obtained by other methods. The procedure is computerized and is available from COSMIC as NASA Langley computer program A0313.

Aircraft anti-icing plenum

Abstract: The leading edge of the jet engine nacelle is provided with structure to prevent the formation of ice particles at the inlet of the jet engine. The nacelle is split into leading and trailing chambers and there is a partition separating the chambers, the leading one of which includes the anti-icing apparatus. The leading chamber includes a double skin generally facing interiorly toward the jet engine and that double skin defines the nacelle therebetween which permits the passage of the hot gases which heat the outer skin from the inside thereof. Conduit means controllably pass hot exhaust gases from the jet engine to within the leading chamber from where they pass into a cell via a series of spaced apertures formed in the inner double skin. A series of spaced channels are formed between the inner and outer skins and connect the leading and trailing chambers. Those channels pass the spent heating gases into the trailing chamber which includes the structural acoustical sandwich comprising inner and outer skins separated by a layer of honeycomb core. The outer skin is apertured for acoustic purposes and the spent gases pass through those apertures and are discharged.

A Conceptual Study of Leading-Edge-Vortex Enhancement by Blowing

Abstract: A conceptual wind-tunnel-test program has been conducted to verify that blowing a stream of highpressure air over a swept-wing surface in a direction roughly parallel to the leading edge enhances the vortex system. The blowing is shown to intensify the leading-edge vortex and thus delay the deleterious effects of vortex breakdown to higher angle of attack. As a result, the vortex-lift is significantly increased and, as the blowing rate is increased, appears to approach the value predicted by the Polhamus suction-analogy for thin wings.

Boundary layer control and anti-icing apparatus for an aircraft wing

Abstract: A boundary layer control (BLC) and anti-icing apparatus for an aircraft wing comprising a duct in thermal communication with the leading edge (nose) of the wing and a leading edge flap is disclosed. The duct carries relatively high temperature air bled from the engines, and ejects this air through BLC nozzles and anti-icing orifices located in the lower portion of the nose. The leading edge flap is movable between a stowed position in the wing and an operative position adjacent to the leading edge of the wing. When in the stowed position the high temperature air in the duct functions to prevent ice formation on the wing, as does the ejected air which attaches to the wing skin and flows over the top of the wing, thereby wiping away water droplets. When in the operative position, the adjacent surfaces of the leading edge flap and the nose of the wing form an ejector nozzle that mixes the BLC nozzle ejected air with ambient air and then ejects the mixed air over the wing surface to provide boundary layer control. In addition, when the leading edge flap is in its operative position, thermal anti-icing mixing tubes receive the air ejected through the anti-icing orifices, mix it with ambient air and convey the mixed air to a spray tube located in the nose of the leading edge flap. The still warm mixed air is discharged from the spray tube, through orifices, into the nose of the leading edge flap. The air in the leading edge flap may be ejected over the top of the flap to provide additional boundary layer control, if desired.

Airplane wing camber control

Abstract: The angular configuration of a fluid control surface, with respect to the relative direction of fluid flow, is controlled by selectively heating the structural portions of only one side of the control surface to expand the structural members on the one side with respect to the structural members on the other side for warping the control surface generally from its leading to its trailing edge. Particularly, the camber of an airplane wing is changed by this selective heating for controlling the wing portion lift. Preferably, wires extend generally from the leading edge to the trailing edge of the wing as wing structural members closely adjacent the upper and lower surfaces of the wing, with both sets of wires being prestressed to provide an intermediate camber for the wing portion when the upper and lower wires are the same temperature, a generally symmetrical wing configuration when only the lower wires are heated, and a high lift maximum camber when only the upper wires are heated. The wires may be electrically heated by the passage of current therethrough, closely adjacent the wing surface for air cooling, deeply embedded in the wing structure for insulation, or contained within concentric tubes conducting a cooling or heating fluid. Further, the wires may be organic synthetic fibers with electrically conductive material embedded in them for thermal expansion, or a composite of electrically conductive and non-electrically conductive fibers for thermal expansion, or composed of an electrostrictive material to shorten upon the passage of electrical current, or of composite structure as above mentioned, with an electrostrictive component for shortening with the passage of a current.

Multi-chambered cellular structure and method for manufacture

Abstract: A fiber-reinforced plastic article of manufacture having a multi-chambered, cellular structure with an outer shell having a fluid foil shape with a leading edge having a smooth radius of curvature and a trailing edge [noncircular]cross section over a substantial portion of its length and containing therein an inner shell which extends between at least two opposite interior walls of said outer shell thereby defining at least two chambers within said article, the walls of said shells being composed of a plastic having embedded therein at least on layer of a continuous roving of a fibrous reinforcement material, said at least one layer comprising two adjacent thicknesses of said roving with the rovings being in parallel alignment in each thickness and the rovings being in parallel alignment in each thickness and in diagonal orientation between thicknesses and with the rovings in the outer shell being continuous and unbroken over the leading edge of said foil shape.

Method of and apparatus for preventing leading edge shocks and shock-related noise in transonic and supersonic rotor blades and the like

Abstract: This disclosure is concerned with novel rotor blade and similar foil designs that, by critical skewing of intermediate blade regions where the airflow is supersonic, prevents leading edge shocks and shock-related noise.

Extension of a vortex-lattice method to include the effects of leading-edge separation

Abstract: Vortex-lattice methods have been used successfully to obtain the aerodynamic coefficients of lifting surfaces without leading-edge separation. It is shown how an existing vortex-lattice method can be modified to include the effects of leading-edge separation. The modified version is then used to calculate the aerodynamic loads on a highly swept delta wing. The results are compared with Peckham's (1958) experimental data.

Inversion of sweep‐frequency sky‐wave backscatter leading edge for quasiparabolic ionospheric layer parameters

Abstract: A method is presented for the derivation of quasiparabolic ionospheric layer parameters from a set of three data points on the leading edge of a sweep-frequency sky-wave backscatter ionogram. The method is illustrated with a numerical example. Possible extensions of the method are discussed.

Variable leading edge stator vane assembly

Abstract: A variable leading edge stator vane assembly, particularly suited for use in a bypass gas turbine engine as a last stage fan stator, includes vane spindles on each end of the movable portion which are rotatably disposed in the gas path walls and which are large relative to the thickness of the airfoil so that they extend downstream of the movable portion; the stationary portion of the vane has its leading edge pinned into cavities positioned on the axis of rotation of the vane spindles and its trailing edge secured directly to the flow path walls.

Tractor-trailer aerodynamic drag reducer

Abstract: A device for reducing the aerodynamic drag on a tractor-trailer is mounted on the tractor roof and includes an upwardly inclined rearwardly extending top surface having its leading edge faired into the tractor roof The device has side walls which extend generally vertically to connect the outer edge of the top surface of the device with the roof of the tractor A central portion of the leading edge is recessed rearwardly of a roof mounted equipment device and defines a central top surface portion which extends upwardly from the recessed leading edge into tangency with the top surface Laterally spaced walls depend vertically from the inboard edges of the top surface portions spaced laterally of the central top surface portion and merge with the central top surface portion and the tractor roof to cooperate therewith and with the roof mounted equipment device to define a recessed channel which imparts a low drag streamline curvature to the airflow An opening is provided in the central top surface portion to receive a rearward portion of an air conditioning unit within the confines of the drag reducing device

Actuating system for wing leading-edge slats

Abstract: The invention relates to a leading-edge slat actuating system comprising an intermediate slat having a trailing edge and hingedly connected to a beam fast with the main wing, a front slat hingedly connected to the beam and a leading edge hingedly connected to the front slat, characterized in that the system includes: a first jack having one end hingedly connected to a non-moving point on the wing structure and its other end hingedly connected to a moving point fast with the front slat; two rods on either side of the jack, having their hinge-points located on the one hand on the leading edge of the front slat, in an outer part of the undersurface thereof, and at non-moving points on the beam on the other; a second jack having one end hingedly connected to a non-moving point on the wing structure and its other end hingedly connected to a point moving with the trailing edge of the intermediate slat, the jacks and rods being so arranged that when the jacks are in their extended position the slats are extended to form two slits one of which lies between the intermediate slat and the wing and the other between the front slat and the intermediate slat.

Heat Transfer Due to Shock Wave Turbulent Boundary Layer Interactions on High Speed Weapon Systems

Abstract: : Three-dimensional shock wave turbulent boundary layer interactions caused by a fin-plate configuration were investigated experimentally and analytically. Wind tunnel tests were conducted at a Mach number of 3.71 and the interactions were studied at near full scale conditions by mounting one of several fins normal to the tunnel sidewall in the naturally turbulent, 6 inches thick sidewall boundary layer. Tests were conducted primarily with a sharp leading edge planar fin, although blunt and blunt swept planar fins were also used. The experimental data were used to develop new analytical and correlation procedures.

The effect of canard leading edge sweep and dihedral angle on the longitudinal and lateral aerodynamic characteristic of a close-coupled canard-wing configuration

Abstract: A generalized wind-tunnel model, with canard and wing planforms typical of highly maneuverable aircraft, was tested in the Langley high-speed 7- by 10-foot tunnel at a Mach number of 0.30. The test was conducted in order to determine the effects of canard sweep and canard dihedral on canard-wing interference at high angles of attack. In general, the effect of canard sweep on lift is small up to an angle of attack of 16 deg. However, for angles of attack greater than 16 deg, an increase in the canard sweep results in an increase in lift developed by the canard when the canard is above or in the wing chord plane. This increased lift results in a lift increase for the total configuration for the canard above the wing chord plane. For the canard in the wing chord plane, the increased canard lift is partially lost by increased interference on the wing.

Wind power plant

Abstract: A power plant of the windmill type is provided which includes a multi-arm horizontal propellor unit mounted for rotation about a vertical axis. Each propellor vane of the unit includes an external shell configured to form an elongated trough with an open trailing edge. A webbing is mounted within the shell to form a series of cells which are exposed through the open trailing edge. The shell has a parabolic cross section, and its leading edge has an airfoil shape. The propellor unit responds to wind from any direction so that the need for wind tracking mechanisms is obviated. Moreover, the construction is such that gyroscopic vibrations due to wind changes are also minimized.

Sheet jam detector for electrophotographic copying machine

Abstract: Timers measure the length of time for the leading edge of the first copy sheet to reach a sensing point at the discharge side of the machine after the copy operation is started and de-energize the machine if the measured time is longer than a predetermined time value, indicating that the first sheet jammed and did not reach the sensing point. If the first sheet reaches the sensing point in less than the predetermined time indicating proper feeding thereof, the length of time between the sensing of the leading edge and the trailing edge of the first sheet at the sensing point is measured, and the machine is deenergized if the measured time is longer than another predetermined value, indicating that the first sheet jammed at the sensing point. If the first sheet passes the sensing point normally (the machine is not de-energized), the length of time between the sensing of the trailing edge of the first sheet and the leading edge of the second sheet at the sensing point is measured, and the machine is de-energized if the measured time is longer than still another predetermined value, indicating that the second sheet jammed and did not reach the sensing point. If the second sheet passes the sensing point normally (the machine is not de-energized), the latter two operations are alternately performed for subsequent sheets until a jam is detected and the machine de-energized or the copying operation is completed without a jam.

Airfoil leading edge structure with boundary layer control

Abstract: The airfoil has jaws on the front face of the front spar therein, and the jaws have a boundary layer control duct supported therein which is slotted along the forward side thereof. The slot has coextensive, relatively upper and lower lips projecting outboard from the upper and lower edges thereof, the upper of which lips extends reentrantly upwardly and distantly away from the upper edge of the slot, and forms the overside of the leading edge of the airfoil. The lower lip forms a throat with the upper lip, outboard from the slot, and in addition, has a deflector thereon which forms a convergent nozzle or nozzles with the upper lip, through which the throat discharges upwardly over the outer surface of the upper lip. The lower lip also serves as a hold-down surface for a section of skin which forms the underside of the leading edge of the airfoil.

Pivoted pad bearing apparatus and method for bidirectional rotation

Abstract: A pivoted pad journal bearing for and method of supporting a journal member for bidirectional rotation. A separate oil distribution groove is provided in the journal bearing face of the pivoted bearing pad contiguous but spaced from each of the respective opposite circumferentially spaced first and second edges of the bearing pad. For one direction of rotation of the journal, the first edge will be the ''''leading'''' edge, while the second edge will be the ''''trailing'''' edge. For the opposite direction of rotation, the converse will be true. The bearing pad includes a pivotal support permanently located midway between the first and second edges. A low pressure oil supply is connected through lines of substantially equal frictional loss to each of the opposite oil distribution grooves. For any given direction of rotation of the journal, each pivoted bearing pad will automatically tilt in such manner as to provide a larger spacing at the leading edge of the pivoted bearing pad for the particular direction of rotation, to thereby insure proper development of the oil wedge between the rotating journal and the pivoted bearing pad. The frictional loss at the incoming oil channel at the leading edge of the bearing is less due to the wider spacing at the leading edge, and most of the oil flow will automatically be directed to the incoming oil channel, eliminating the need for elaborate valving to control oil flow at the incoming oil channel for each pivoted bearing pad. A minimum of two pivoted bearing pads is required to support the rotating journal.

Four Space Shuttle Wing Leading Edge Concepts

Abstract: A heat-pipe-cooled Space Shuttle orbiter wing leading edge was compared and evaluated against three alternate leading edge candidates: a refurbishable ablative design, and two other reusable versions employing coated columbium and carbon-carbon high-temperature segments. Each candidate concept was shown feasible in the Phase B environment. The reusable versions were all found to cost nearly the same and substantially less than the nonreusable ablative version. However, since current Shuttle trajectories produce higher heating rates than those used in this study, the carbon-carbon and heat pipe concepts are now the prime candidates for Shuttle leading edge thermal protection.

Lithographic plate bending arrangement

Abstract: A bending jig for lithographic plates to provide precise bends in the leading edge and trailing edge thereof. The lithographic plate to be bent is supported on a plate support mounted in a support frame and a leading edge anvil and a trailing edge anvil are provided adjacent opposite ends of the plate support. Positioning means are provided for accurately positioning each lithographic plate in the jig in order that the bends may be made accurately and repetitively in lithographic plates. Bending bars are provided for moving in lithographic plate bending relationship to the leading edge anvil and trailing edge anvil to provide the bends in the plate required for mounting the plate accurately in the cylinder of an offset press.

Radial flow compressors

Abstract: A radial flow compressor is described in which the diffuser entrance is uniquely contoured to minimize losses attributable to the differences in absolute flow angle of the high velocity air discharged from the compressor impeller, such differences existing across the width of the impeller discharge flow path. The diffuser comprises a plurality of vanes which split the circumferential impeller discharge into discrete, tangential, diffusion channels. Each vane is wedge shaped and has suction and pressure surfaces on opposite sides of the leading edge thereof. The leading edge is angled, or swept, relative to the direction of air flow. The suction surface is angled relative to the impeller axis so that, marginally of the leading edge, it is more tangential at the shroud side of the flow path then at the hub side thereof and an essentially uniform impingement angle of approximately 0* is obtained along the width of the suction surface.

Copier with leading edge image control

Abstract: An image producing process of a document copier is controlled by means detecting a low average intensity of reflected light during initial stages of scan of an original being copied to produce a low density or light copy adjacent the leading edge of the copy sheet passing through the machine thereby minimizing paper feed difficulties associated with the passage of copy having a dense leading edge through a contact fuser.

Development of a computer program to obtain ordinates for NACA-6 and 6A-series airfoils

Abstract: A computer program was developed to produce the ordinates for airfoils of any thickness, thickness distribution, or camber in the NACA 6- and 6A-series. For the 6-series and for all but the leading edge of the 6A-series, agreement between the ordinates obtained from the new program and previously published values is generally within .00005 chord. Near the leading edge of the 6A-series airfoils, differences up to .00035 chord are found.

On the Unsteady Supersonic Cascade With a Subsonic Leading Edge—An Exact First Order Theory—Part 1

Abstract: This paper presents, in two parts, the theoretical predictions of the aerodynamic forces acting on slowly oscillating airfoils in a supersonic cascade with a subsonic leading edge. The analysis is based on the assumption of an inviscid, two-dimensional and linearized flow. In the first part of the paper, the flow field ahead of the cascade is considered. An initial value problem is posed and, from the periodicity requirement in the cascade, the problem is reformulated in terms of integral equations. Solution of the integral equations, accurate to the first order of a frequency parameter, are obtained in closed form. In the limit of the steady flow, the unsteady flow analysis yields a mathematical verification of the unique incidence effect. Based on this proof, a simple rule is presented for the airfoil suction surface contour satisfying steady flow requirement ahead of the cascade. The complete aeroelastic problem, including the solution for the flow field between the blades and the trailing interference zone, is treated in Part 2.

Engine mounting and boundary layer control fluid supply apparatus

Abstract: A midwing aircraft employs a unique configuration for mounting three high bypass turbofan engines. All three engines are mounted so that a portion thereof projects forwardly of the leading edge of the airfoil on which they are mounted and so that the chordal plane of the airfoil longitudinally bisects the engine. The exhaust from each of the engines is directed by two nozzles. Internal bifurcators split both the turbine exhaust and the fan exhaust from each of the engines evenly between the two nozzles. A pair of channels in each of the wing mounted engines intercepts a portion of the fan effluent and directs it rearwardly into boundary layer control supply plenums in the wing structure. Valve mechanisms for opening and closing the channels are mounted in the forward portions of the channels. Check valves are also provided in each of the channels to prevent backflow of fluid from the supply plenums into the channels. The engines are mounted on the airfoils by a pair of box beams that run along the interior longitudinal sides of each of the engine nacelles. The turbine portion of the turbofan engines is mounted to the inner sides of the box beams at a location forwardly of the leading edge of the airfoils. The box beams can be shrouded to serve as the fluid inlet channels for the fluid supply plenums. The rear portion of the box beams are removably affixed to ribs or flanges extending forwardly from the front main spar of the wing.

Methods for the Design and Analysis of Jet-Flapped Airfoils

Abstract: Methods for solving both the direct and inverse jet flap airfoil potential flow problems are described. The direct airfoil analysis method is a completely nonlinear iterative method which is applicable to either thick or thin airfoils of arbitrary shape. The very general surface singularity formulation has been extended to include multielement airfoils, ground effects, nonuniform freestreams, inlet flows, jet entrainment effects, etc. Comparisons are given with the results of previous linear and nonlinear methods as well as with experimental data. The inverse (design) method is a more approximate method in which camber and thickness distributions are designed separately. Section shapes are shown for several airfoils designed to have only very small regions of adverse pressure gradient. Nomenclature c = length of airfoil chord cp = coefficient of pressure d = coefficient of lift cu = coefficient of jet momentum h = height of airfoil leading edge above ground plane R = radius of curvature of the jet sheet s = coordinate along the jet sheet t = airfoil thickness V = local flow speed V = average flow speed across a vortex sheet Vj - jet flow speed Vn = component of velocity normal to a surface V = freestream flow speed x = coordinate parallel to the freestream = coordinate perpendicular to the freestream = jet deflection angle at the trailing edge relative to the airfoil chord line 7 = strength of a vortex sheet 0 = local angle of inclination of the jet sheet relative to the freestream 0 = velocity potential