Showing papers on "Leading edge published in 1977"

Viscous sheets advancing over dry beds

Abstract: The unsteady creeping motion of a thin sheet of viscous liquid as it advances over a gently sloping dry bed is examined. Attention is focused on the motion of the leading edge under various influences and four problems are discussed. In the first problem the fluid is travelling down an open channel formed by two straight parallel retaining walls placed perpendicular to an inclined plane. When the channel axis is parallel to the fall line there is a progressive-wave solution with a straight leading edge, but inclination of the axis generates distortions and these are calculated. In the second problem a sheet with a straight leading edge travelling over an inclined plane penetrates a region where the bed is uneven, and the subsequent deformation of the leading edge is followed. The third problem considers the flow down an open channel of circular cross-section (a partially filled pipe) and the time-dependent shape of the leading edge is calculated. The fourth problem is that of flow down an inclined plane with a single curved retaining wall. These problems are all analysed by assuming that a length characteristic of the geometry is large compared with the fluid depth divided by the bed slope, and all the solutions display extreme sensitivity to the data.

Hydromechanics of lunate-tail swimming propulsion. Part 2

Abstract: This paper investigates the propulsive performance of the lunate tails of aquatic animals achieving high propulsive efficiency (the hydromechanical efficiency being defined as the ratio of the work done by the mean forward thrust to the mean rate at which work is done by the tail movements on the surrounding fluid). Small amplitude heaving and pitching motions of a finite flat-plate wing of general planform with a rounded leading edge and a sharp trailing edge are considered. This is a generalization of Chopra's (1974) work on model rectangular tails. This motion characterizes vertical oscillations of the horizontal tail flukes of some cetacean mammals. The same oscillations, turned through a right angle to become horizontal motions of side-slip and yaw, characterize the caudal fins of certain fast-swimming fishes; viz. wahoo, tunny, wavyback skipjack, etc., from the Percomorphi and whale shark, porbeagle, etc., from the Selachii. Davies’ (1963, 1976) method of finding the loading distribution on the wing and generalized force coefficients, through approximate solution of an integral equation relating the loading and the upwash (lifting-surface theory), is used to find the total thrust and the rate of working of the tail, which in turn specify the hydromechanical swimming performance of the animals. The physical parameters concerned are the tail aspect ratio ((span)2/planform area), the reduced frequency (angular frequency x typical length/forward speed), the feathering parameter (the ratio of the tail slope to the slope of the path of the pitching axis), the position of the pitching axis, and the curved shapes of the leading and trailing edges. The variation of the thrust and the propulsive efficiency with these parameters has been discussed to indicate the optimum shape of the tail. It is found that, compared with a rectangular tail, a curved leading edge as in lunate tails gives a reduced thrust contribution from the leading-edge suction for the same total thrust; however, a sweep angle of the leading edge exceeding about 30° leads to a marked reduction of efficiency. Another implication of the present analysis is that no negative work is involved in the actual oscillation of the tail.The present results are used to obtain an estimate of the drag coefficient for the motion of the animals, based on observed data and the computed thrust. The results show some evidence of differences between the CD's for cetacean mammals and scombroid fish respectively. Some discussion of this difference is also given.

Noise and Surface Pressure Response of an Airfoil to Incident Turbulence

Abstract: A theoretical and experimental investigation of the nosie and unsteady surface pressure characteristics of an isolated airfoil in a uniform mean velocity, homogeneous, nearly isotropic turbulence field was conducted. Experiments were performed with a 23-cm chord, two-dimensional, NACA 0012 airfoil in the UTRC Acoustic Research Tunnel over a Mach number range of 0.1 to 0.5. Far-field noise spectra and directivity as well as surface pressure spectra and cross-spectra were obtained. Incident turbulence statistics were documented. Theory applied to predict far-field noise and surface pressure characteristics from measured inflow turbulence statistics showed good agreement with measurement over the dominant frequency range for all Mach numbers investigated. The theoretical formulation represents a first-principles solution providing absolute level prediction without recourse to empirical or adjustable constants. It takes into account compressibility as well as source noncompactness effects. Correlation measurements demonstrated that all chordwise portions of the airfoil radiated directly to the far-field, but that the leading edge was the dominant noise producing region. b c c0 d / g kx,ky,kz

A skin friction meter, using the viscosity balance principle, suitable for use with flat or curved metal surfaces (based on thickness measurement)

Abstract: An oil film is placed on a surface over which gas is flowing, and moves under the influence of skin friction. The skin friction meter to be described makes use of the fact that, at time t after the start of the flow with skin friction tau , the thickness y of oil of viscosity mu at a point x close downstream of the leading edge is y= mu x/ tau t. A laser beam focused at position x, reflects partly from the oil surface and partly from the metal substrate. The reflected beams are focused on a photocell and the pen recorder output gives an interferometric record of y against t. To permit accurate setting of the position x, a second laser beam is used which is set at the upstream oil edge, x=0. The results obtained show good agreement with theory, repeatability and consistency. The meter can be used with any polished metal surface, whether flat or curved, and provides versatile and potentially accurate method for skin friction measurement.

Two-dimensional wind-tunnel tests of a NASA supercritical airfoil with various high-lift systems. Volume 2: Test data

Abstract: Three high lift systems for a 93 percent blunt based, supercritical airfoil were designed, fabricated, and wind tunnel tested A method for calculating the viscous flow about two dimensional multicomponent airfoils was evaluated by comparing its predictions with test data A comparison of high lift systems derived from supercritical airfoils with high lift systems derived from conventional airfoils is presented The high lift systems for the supercritical airfoil were designed to achieve maximum lift and consisted of: (1) a single slotted flap, (2) a double slotted flap and a leading edge slat, and (3) a triple slotted flap and a leading edge slat Aerodynamic force and moment data and surface pressure data are presented for all configurations and boundary layer and wake profiles for the single slotted flap configuration The wind-tunnel models, test facilities and instrumentation, and data reduction are described

Variable camber leading edge flap

Abstract: Tailoring the contour and chord length of a variable camber leading edge flap for the tapered wing of an aircraft is aimed at improving the aircraft's low speed performance particularly for takeoff and landing. Each segment of a spanwise series of leading edge flap segments has a constant chord flexible panel and a spanwise tapered leading edge or bullnose member. By using different chord flexible panels in adjacent flap segments, together with a tapered bullnose, the effective chord length and contour of the variable camber leading edge flap can be varied smoothly in the spanwise direction without resorting to different flap linkage mechanisms at each spanwise station. Further, through the change in cross-sectional shape of the bullnose member along the semi-span of the wing, a change in the effective flap angle (angle-of-incidence of the flap-chord relative to the wing-chord plane) is also produced. For additional variation in the flap angle in a spanwise direction along the leading edge of the fixed wing section, a twist can be imparted to the constant chord flexible panel through a slight variation in the degree of angular rotation of common flap linkage mechanisms attached to each end of the flap segment; however, the greatest amount of change in flap angle is accomplished through the change in cross-sectional shape of the bullnose member and only a slight amount is due to the variation in the degrees of angular rotation of the linkage mechanism.

Minimum drag wing configuration for aircraft operating at transonic speeds

Abstract: A wing extension or tip fin is disclosed wherein the tip fin is joined to an aircraft wing to form a nonplanar wing configuration which minimizes induced drag during both low speed and high speed operation of an aircraft. The tip fin which is of generally trapezoidal geometry, extends streamwise along the end of the aircraft wing and is canted to project upwardly and outwardly therefrom. Additionally, the tip fin is twisted to toe-out relative to the freestream direction with the angle of twist varying along the lower portion of the tip fin length. Viewed from the side, the tip fin has a sweep angle at least equal to the sweep angle of the aircraft wings with the leading edge of the tip fin intersecting the wing tip chord at a position aft of the wing leading edge. A strake which extends along the upper surface of the wing from the wing leading edge to the tip fin leading edge, forms a smooth transition between the wing and tip fin. To provide maximum aerodynamic efficiency, the length and cant angle of the tip fin are established to reduce the induced drag of the wing-tip fin combination below that exhibited by the wing alone or by a conventional wing of area and span equivalent to that of the combined wing-tip fin. Interference and compressibility drag of the combined wing-tip fin is minimized by controlling the chordwise position of the tip fin and by the strake which not only provides an aerodynamically smooth wing to tip fin transition, but establishes a vortical flow pattern that maintains boundary layer attachment under high speed flight conditions. Further, the area of the tip fin is established for minimum profile drag, the variation in tip fin thickness ratio further minimizing interference drag and the tip fin twist compensates for spanwise loading on the wing to reduce induced drag.

Apparatus for handling flexible sheet material of different sizes

Abstract: A low inertia rotary drum supports sheets of paper of different sizes for transport and processing. The drum has a plurality of leading edge ports formed in its surface along the length of the drum. A vacuum is selectively applied to one or more of the ports in accordance with the dimension of the paper in the direction of the length of the drum. The drum has a plurality of sets of trailing edge ports formed in its surface with each of the sets being disposed a predetermined arcuate distance from the set of leading edge ports in accordance with the other dimension of the paper. Each set of trailing edge ports has the ports arranged longitudinally along the drum and parallel to the set of leading edge ports. Only one set of trailing edge ports extends for the same length as the set of the leading edge ports. One of the sets of the trailing edge ports has a vacuum applied thereto with the same number of ports of the trailing edge set having the vacuum applied thereto as the number of the leading edge ports.

Two-Dimensional Subsonic Wind Tunnel Evaluation of Two Related Cambered 15-Percent Thick Circulation Control Airfoils

Abstract: : Two circulation control cambered elliptic airfoil sections with a thickness-to-chord ratio of 0.15- and 1.0-percent circular arc camber were evaluated subsonically to determine their aerodynamic characteristics. The two models, designated NCCR 1510-7067N and NCCR 1510-7567S, have a common leading edge but different Coanda surfaces.

Numerical Computations of Orbiter Flowfields and Laminar Heating Rates

Abstract: Numerical computations of flowfields and laminar heating rates around the Space Shuttle Orbiter windward surface, including the root of the wing leading edge, are presented to illustrate the sensitivity of these calculations to several flowfield modeling assumptions. Specifically, results obtained using the axisymmetric analogue concept to predict "three-dimensional" heating rates, in conjunction with exact three-dimensional inviscid flowfield solutions and two-dimensional boundary-layer analysis, show the sensitivity of boundary-layer edge conditions and heating rates to considerations of: 1) the inviscid flowfield "entropy layer," 2) equilibrium air vs chemically and vibrationally frozen flow, and 3) nonsimilar terms in ttie boundary-layer computations. In addition, a cursory comparison between flowfield predictions (made at critical points in the current design trajectory) obtained from these methods and current Orbiter design methods has established a benchmark for selecting and adjusting these and future design methodologies.

Apparatus for the successive release of items of mail from a stack

Abstract: In apparatus for the successive discharge and conveyance, along a conveying path, of items of mail from a stack by a continuously driven conveying device and an externally controllable removal member arranged to transport successive items from the stack to the region of action of the conveying device, the desired spacing between successive items is established by the provision of a first sensing unit disposed between the stack and the conveying device to define a first measuring path extending along the conveying path and to provide an output signal indicative of the length of the portion of the first measuring path traversed by the leading edge of an item presently being conveyed by the removal device, a second sensing unit disposed downstream of the first sensing unit, along the conveying path, to define a second measuring path offset from the first measuring path, along the conveying path, by a distance corresponding to the desired spacing between successive items, and to provide an output signal indicative of the length of the portion of the second measuring path traversed by the leading edge or trailing edge of an item being conveyed by the conveying device, and a control member connected to place the removal device into operation upon production of output signals indicating that the length of the portion of the second measuring path traversed by the leading or trailing edge of an item is equal to the length of the portion of the first measuring path traversed by the leading edge of the immediately following item.

Aircraft folding airfoil system

Abstract: A folding airfoil for an aircraft in which the wing or stabilizer airfoil n be folded and contained entirely within the fuselage of the aircraft. The airfoil comprises a series of elongated sheet metal channel sections of generally C-shaped cross section with the cross sectional dimension of successive channels decreasing so that each can nest entirely within an adjacent channel. The channels are each pivotally connected at the root end to the aircraft fuselage structure at spaced intervals along the chord line of the extended airfoil and the end sections of the channels are pivotally connected to each other such that the channels are pivotable between (1) an extended position extending spanwise of the extended airfoil to lie in tandem one behind the other, with adjacent channels partially overlapping and (2) a retracted or folded position in which the channels are nested within the leading edge channel section and lie along the chord line of the extended airfoil along the line of channel root end pivotal connections.

Fan shroud arrangement

Abstract: The mechanism shown and described herein is a cooling fan and associated dual shroud arrangement including (1) a rotating shroud comprised of a ring secured to the outer tips of the fan blades and a bell-mouthed inlet formed on the leading edge of the ring, and (2) a stationary shroud secured at one end or edge thereof to the radiator and terminating at the outer end thereof in an annular edge in front or upstream of the bell-mouthed inlet. A predetermined clearance is defined between the stationary shroud and the bell-mouthed inlet, effective to provide a smooth recirculating airflow around the rotating shroud and back into the main airflow stream, thereby substantially eliminating tip-vortex characteristics and resultant tip-clearance noise, and without unsteady flow interactions that cause rotational noise. In one alternate embodiment, the radiator is used in lieu of the stationary shroud for cooperation with the bell-mouthed inlet.

Method and apparatus for obtaining useful work from wave energy

Abstract: An apparatus and method for obtaining useful work from or with waves includes a buoyant body having a leading edge and a trailing edge, and a convex upper surface extending between the leading and trailing edges. The upper surface is configured with a gradually sloping shape from the leading edge toward the trailing edge and terminates at the trailing edge in a sharply oppositely sloping surface, whereby the circular or orbital motion of water particles in waves is converted by the upper surface to linear flow of the water particles, and waves traveling across the surface from the leading to the trailing edge are not damped or extinguished by backwash of waves from the trailing edge toward the leading edge. Upstanding structures on the upper surface define open-ended venturi-shaped water flow channels across the upper surface which increase the velocity of the linear flow of water across the upper surface, and water-driven devices are disposed in the water flow channels to obtain work from the accelerated linear flow of water. The buoyant body floats at the surface of the body of water, with the upper surface of the buoyant body disposed beneath and substantially parallel to the surface of the water, and the configuration of the buoyant body is such that it undergoes both pitching and heaving motion as waves move therepast. Devices may be attached to the buoyant body and/or positioned therewithin to obtain work from the pitching and heaving motion of the buoyant body.

Turbine shroud support

Abstract: Hot gas recirculation is eliminated between the trailing edge of a turbine shroud and the leading edge of a downstream vane by a tongue-and-groove interconnection between the two parts and a passage of cooling air through the interconnection to exhaust against the vane outer band and flow into the main gas stream. The shroud with its supporting structure is thereby maintained at substantially uniform temperatures around its circumference so as to present a round, close-tolerance relationship to its circumscribed turbine blade row.

Magnetic head-slider assembly

Abstract: A multi-channel magnetic head-slider assembly having a ceramic member having a bottom slider face which is adapted to ride on a thin fluid film a predetermined distance above a moving media wherein the slider face has a hollowed out, central area having a wedge shaped inner surface formed in the interior of the bottom slider face which defines a first and second parallel planar fluid bearing support rail which extend in spaced parallel alignment along the side of the ceramic member and each of which have one end which terminates in sloped surface defining a leading edge relative to the moving media and each of which terminate in and are integral with a third flat fluid support surface forming a trailing edge which is perpendicular to said first and second fluid bearing support rails and a plurality of magnetic transducers having a preselected gap width and predetermined spacing are mounted on the end of the ceramic member at the trailing edge of the ceramic member with the gap of each head adjacent to and in alignment with said third flat support surface forming a plurality of tracks with a moving media wherein the width of each track is substantially equal to the preselected gap and the spacing between the tracks is substantially equal to the predetermined spacing between magnetic transducers is shown.

Snowmelt: A Two-Dimensional Turbulent Diffusion Model

Abstract: The melt from a ripe snowpack due to sensible and latent heat flux is considered. The problem is two- dimensional; the snow field has a well-defined leading edge. The equations that describe the airflow over the snow are the conservation of momentum, sensible heat, and water vapor. The turbulent diffusion is formulated by semi-empirical turbulence theory. The solution shows the manner in which the point melt varies downwind from the leading edge and the average melt varies with the fetch of the snowpack for varying degrees of atmospheric stability conditions. The results indicate that a reasonably accurate estimate of total melt can be achieved by using the one-dimensional formulae with temperature, humidity, and velocity measurements taken over the central part of the snow field.

Airfoil for controlling refueling boom

Abstract: An airfoil used in a ruddevator assembly for controlling movement of an aircraft refueling boom, where there are two airfoils (i.e. ruddevators) mounted to the boom, each at a dihedral angle of about 42°. Each airfoil has an outboard section, which is an advanced technology cambered airfoil for high lift at transonic speeds, with a raked wing tip. The inboard portion of the airfoil has a forwardly extending strake-like member having a sharp leading edge which in planform comprises three sections. There is a curved forward edge section and two rearwardly extending edge sections, which in operation are positioned at high sweep angles. The side edge portions of the strake-like member create vortices which travel over the inboard portion of the airfoil to augment lift over a wide range of surface deflection of the airfoil (i.e., angle of attack). The inboard vortex also smooths the flow over the boom housing, and another aerodynamic feature is that the hinge moments exerted on the airfoil are relatively linear over a wide range of deflection, thus enhancing the control characteristics of the ruddevator assembly.

Thrust reverser for an asymmetric aircraft exhaust nozzle

Abstract: A thrust reverser is provided for use with an asymmetric aircraft gas turbine engine exhaust nozzle. The thrust reverser includes a movable aerodynamic flap downstream of the asymmetric nozzle casing which is rotatable about one pivot in order to effect in-flight thrust vectoring through deflection of the exhaust stream, and which is also independently rotatable about another pivot to effect thrust reversing. In the reverse thrust mode, the leading edge of the flap is immersed into the exhaust stream, thereby splitting the stream into two portions, one of which is deflected upward and forward by a turning vane incorporated into the leading edge of the flap, and the other portion of which is deflected downward and forward by a hinged lip connected to the flap trailing edge. The thrust reverser thus permits the exhaust stream to be ejected in the vertical plane to produce reverse thrust without an accompanying pitch moment even though the exhaust nozzle is not symmetrical in the vertical plane.

Blade or vane for a gas turbine engine

Abstract: A hollow blade or vane for a gas turbine engine is provided with a longitudinally extending, hollow thickened portion in its wall adjacent the leading edge. This hollow thickened portion acts as an integral strut and relieves the leading edge of some loads.

Canard type aircraft

Abstract: The present canard type of aircraft comprises steering rudder elements which are tiltable substantially about the leading edge of each wing of the aircraft, whereby the respective edge of the rudder element extends alongside said leading edge of the respective wing. Another edge of the rudder element extends alongside a surface portion of the fuselage or body of the aircraft in close conformity with said surface portion, but movable relative thereto. A sealing may be inserted between the rudder element and the fuselage in such a manner that said movement is permitted.

Propelling nozzle for means of transport in air or water

Abstract: The invention relates to the propulsion of transport vehicles in air or water, which involves the new use of a nozzle comprising an internal surface, a curved surface merging into the internal surface, a narrowed throat in the internal surface located towards the leading edge of the nozzle, a jacket surrounding the internal surface, an annular internal slot located in the internal surface between the curved surface and the narrowed throat and communicating with the jacket. The fluid under pressure is supplied through the slot the arrangement of the slot being such that the fluid is ejected at an acute angle of under 45° to the direction of the exit flow tangentially to the curved surface.

Stagnation Region Gas Film Cooling for Turbine Blade Leading-Edge Applications

Abstract: An experimental investigation was conducted to model the film-cooling performance for a turbine-vane leading edge using the stagnation region of a cylinder in cross flow. Experiments were conducted with a single row of spanwise-angled coolant holes for a range of the coolant blowing ratio with a freestream-to-wall temperature ratio of about 2.1 and a Reynolds number of 170,000, characteristic of the gas-turbine environment. Data from local heat-flux measurements are presented for coolant-hole injection angles of 25, 35, and 45 deg with the row of holes located at three positions relative to the stagnation line on the cylinder. Results show the spanwise (hole-to-hole) variation of heat-flux reduction due to film cooling and indicate conditions for the optimum film-cooling performance.

Obstruction sensing edge for a bifolding door

Abstract: An obstruction sensing edge for a bifolding door includes a body secured to the door. The body defines an internal fluid chamber that is in fluid communication with a fluid actuated switch. The switch controls the opening and closing of the door. Defined on the body portion is an edge portion including a leading edge and side portions extending from the leading edge to the body portion. The leading edge and body portion are fabricated of elastomeric material such that upon engagement of the leading edge with an obstruction, the internal chamber is deformed changing the volume thereof and actuating the switch. The edge portion includes elongated fins extending transversely to the sides of the edge portion such that upon complete closing of the door, the fins seal the door.

Aircraft wing lift augmentation device

Abstract: A wing duct near and parallel to the leading edge of an aircraft wing receives air from the jet engines of the craft. The wing duct is spiral-like in cross section with an exit slit for directing high velociy air rearwardly over the dorsal wing surface and toward the trailing edge of the wing. A vertically movable slat matching the contour of the wing adjacent to the duct covers the exit slit leading from the duct when in a lowered position. The slat is raised automatically by the high velocity air stream blasting out of the exit slit and the slat directs this air stream rearwardly and prevents it from flowing forwardly. The slat is attached to the top of a gridwork through which the high velocity air stream from the exit slit must flow and the gridwork, in conjunction with the elevated slat, produces laminar flow of air across the top of the wing and minimizes turbulence. When the slat is retracted to lie flush against the top of the wing, the gridwork enters a wing recess or well immediately rearwardly of the duct. The slat can be retracted by a state of the art hydraulic mechanism in the wing which allows extension of the slat and gridwork responsive to the air stream coming from the exit slit.

Variable camber flap

Abstract: A variable camber leading edge flap and linkage mechanism for allowing two different extended operating positions of the flap, i.e. a landing position whereat an aerodynamic slot is formed between the aft edge of the flap and the fixed leading edge of the wing, coupled with a relatively steep flap angle relative to the wing chord plane; and a take-off position whereat the aerodynamic slot is closed and the flap angle is less than at the landing position. Also, a pair of cam mechanisms are interposed between linkages and sequenced in their operating functions to alternately restrain and release certain of the linkage members in order to open or close the aerodynamic slot and change the flap angle in a manner that insures that air loads acting on the variable camber flap do not cause linkage oscillation and flap instability. Further, through ball joint connections between the flap member and its actuating linkage mechanism, and by altering the degree of angular rotation of the spanwise spaced sets of flap linkage mechanisms, the flap panel can be made to twist torsionally spanwise along the wing leading edge providing a variable flap angle and aerodynamic slot to improve the aerodynamic efficiency of the wing and flap combination.

Fertilizer applying knife assembly

Abstract: A fertilizer knife assembly is capable of being connected to an agricultural implement and is operative for flow of fertilizer into a furrow opened by the knife assembly. A wear point of cast chrome alloy iron has a leading portion and a shoe portion in engagement with and secured by welding to a leading edge and a free end respectively of an elongated shank capable of being connected to an agricultural implement. An elongated fertilizer tube is positioned adjacent a trailing edge of the shank and has one end portion thereof secured to a trailing end of the shoe portion of the wear point. An elongated shield is spaced from and surrounds an exterior surface of the fertilizer tube and has opposite side edges thereof secured to the shank trailing edge by hard facing welding in a manner to protect the fertilizer tube and define an air space surrounding the same.