Showing papers on "Leading edge published in 1976"

Large amplitude lunate-tail theory of fish locomotion

Abstract: The two-dimensional theory of lunate-tail propulsion is extended to motions of arbitrary amplitude, regular or irregular, so that an accurate comparison may be made with the actual lunate-tail propulsion of scombroid fishes and cetacean mammals. There is no restriction at all on the amplitude of motion but the tail's angle of attack relative to its instantaneous path through the water is assumed to remain small. The theory is applied to the regular finite amplitude motion of a thin aerofoil with a rounded leading edge to take advantage of the suction force and a sharp trailing edge to ensure smooth tangential flow past the rear tip. This can represent the vertical motions of the horizontal lunate tails of large aspect ratio with which cetacean mammals propel themselves or the horizontal undulations of the vertical lunate tails of certain fast fishes. The dependence of the thrust, the hydromechanical propulsive efficiency and the energy wasted in churning up the eddying wake on the reduced frequency, the angle of attack and the amplitude of motion is exhibited.

Lifting body aircraft for V/STOL service

Abstract: An unexpectedly high augmentation of aerodynamic lift for a given amount of power in STOL operation of a V/STOL aircraft is achieved by combining the unique features of a lifting body with those of a "jet flap", i.e. an aerodynamic mechanism in which a slipstream is directed over a deflected flap. Specifically, a movable flap is located on the trailing edge of the lifting body, and a tiltable propeller, which propels the aircraft in the normal manner in cruising, may be tilted, in low-speed flight, in order to direct air toward the leading edge of the flap and over the upper surface thereof. The movement of a large mass of air at a higher velocity over the upper surface of the flap maintains the air flow over the flap in an attached condition, and entrains and energizes the lower-velocity boundary layer on the airfoil forward of the flap, thereby producing an augmentation in lift. The lifting body lends itself especially to lift augmentation in that, for a given lifting surface area, the low aspect ratio of the lifting body gives rise to a much greater lift augmentation than would be afforded by a high aspect ratio surface.

Rotary device driven by a moving fluid

Abstract: A rotary device driven by a moving fluid, such as water or air, for generating a rotary movement comprises a cylindrical or frusto-conical rotor having a vertical axis, the rotor having a plurality of identical blades distributed around the periphery of the rotor, each blade having a symmetrical aerodynamic profile and being mounted so as to freely rotate about a substantially vertical axis parallel to its leading edge. The device may be used to power a screw driven boat, a wheeled vehicle or other machinery.

Analysis of leading-edge separation bubbles on airfoils

Abstract: The small separation bubbles which form near the leading edge of airfoils prior to the onset of leading-edge stall have been analyzed in detail, including the effects of viscous-invis cid interaction. The separated laminar shear layer, transitional flow, and turbulent reattaching flow are represented by an integral formulation. A correlation of local shear-layer parameters has been developed for determining the onset of transition in the laminar shear layer. Solutions are obtained using an iterative procedure, with strong interaction effects limited to the immediate vicinity of the separation bubble. Five different cases are analyzed, varying both angle of attack and Reynolds number. Results are in good agreement with wind tunnel measurements.

Overspeed spoilers for vertical axis wind turbine

Abstract: An overspeed spoiler for vertical axis wind turbines of the type having straight or curved airfoil blades attached to a vertical shaft formed by a relatively thin flat blade shaped spoiler element hinge mounted on the trailing edge, leading edge, or at a central position of a portion of the airfoil section with the element having two portions one of which is held flush or against a surface by spring means with a surface of the blade towards the turbine rotor axis and the other lies substantially parallel to the chordline of the airfoil, the weight and configuration of the element being such that a predetermined turbine rotor speed the element rotates against the spring force because of centrifugal action and takes up a position generally transverse to the air flow direction such as to cause much increased drag and control overspeeding of the rotor.

Airfoil tip vortex control

Abstract: Device for diminishing tip vortices in an aircraft. For the purpose of diminishing the tip vortices generated by aircraft there are provided retractable foils at or near the airfoil, as wing, tips in question and projecting upwardly and/or downwardly therefrom. The operation of the retractable foils is satisfactory if such foils are parallel to the centerline of the aircraft but it is preferable if such foils are angled slightly with respect thereto, such as if the leading edge of the upper foil is angled approximately 10° inwardly toward the fuselage of the aircraft and the bottom foil is oppositely angled also approximately 10°. The retractable foils, in addition to diminishing wing tip vortices, also when used on wing tips improve the rate of climb of an aircraft at a given engine setting and appear to diminish the area over which the major amounts of noise generated by the aircraft will be dispersed. The foils may be fully retractable into the aircraft wing, but if not fully retracted, they will each provide a small streamlined ridge projecting upwardly and/or downwardly adjacent the tip of the aircraft wings which will improve the lift characteristics of the wings by diminishing air flow around the end of the wings sufficiently to move than compensate for the drag otherwise created. The foils are also advantageously applicable to other aircraft components, such as flaps, stabilizers or elevators.

Dual wedge fluid thrust bearing including wave spring

Abstract: A dual wedge thrust bearing for holding two relative rotating members in spaced relation includes a wave spring which supports both a thick flexible plate and a thin flexible plate stacked in that order between the cooperating bearing surfaces of the members. By securing the leading edge of the thin plate to the member on which the wave spring rests and in spaced relation to the cooperating bearing surface, a wedge-shaped passage is formed to create a fluid bearing which is efficient for low speeds and loads. At high speeds and loads, when the thin plate would have sagged making an inefficient wedge, the thick plate deflects against the spring at its leading edge to form a more efficient wedge-shaped opening between it and the cooperating bearing surface.

Automatic header adjustment for harvesters

Abstract: A vine crop, e.g. tomato harvester is disclosed which has a crop processing mechanism that is movable through a field and a rearwardly and upwardly inclined elevator or header that is pivotally connected to a forward end of the processing mechanism. A leading edge of the elevator is proximate the ground and a level control wheel is vertically movably connected to the header and positioned forward of its leading edge. The wheel is defined by a multiplicity of tines, the free ends of which engage the ground so that the wheel rolls over the ground as the harvester moves through the field. The tines have a longitudinally convex configuration facing in the direction of rotation of the wheel. A control mechanism is actuated by relative vertical movements of the wheel for raising and lowering the leading edge of the elevator in response to ground surface irregularities sensed by the wheel.

Aerodynamic characteristics of slender wings with sharp leading edges - A review

Abstract: This paper presents an overview of the current state-of-the-art regarding slender wings with sharp leading edges; i.e., wings characterized by the presence of leading edge separation at most angles of attack. Several theoretical methods are discussed in detail and their results are compared with experimental data. Both steady and some unsteady flows are considered. No one theory adequately predicts all aspects of the flow process, and more work is needed, particularly in the fields of vortex control and unsteady flow.

Collecting device for a swimming pool

Abstract: A floating support defines an open area, and it removably holds a net adjacent that open area. That floating support holds the leading edge of that net below the surface of a circulating body of water in a swimming pool, but it holds the trailing edge of that net above that surface so objects which are floating on and moving with that body of water will move into and be held by that net. That net is light in weight, and it can be raised vertically from the floating support for emptying. Also, a floating barrier extends forwardly from that floating support to guide floating objects toward that floating support and to help provide an additional enclosed area, immediately ahead of that floating support, within which floating objects can be trapped.

Boundary layer control system for aircraft

Abstract: An improved boundary layer control system is particularly useful in applications where controlled air is to be injected into a boundary layer region adjacent to a surface of an aircraft wing. The controlled air is obtained from an air source having a temperature and a pressure which are substantially greater than ambient temperature and pressure, such as that obtained from a jet engine bleed air source. A number of manifolds are located in spanwise arrangement along the wing and serve to conduct the air from the source to a plurality of nozzle penums, each of which includes a plurality of spanwise-spaced apertures for injecting air into a portion of the boundary layer region. The manifolds are interconnected by compressible bellows and are mounted so that respective inboard ends are fixed and respective outboard ends are free to move longitudinally. At least one nozzle plenum is interconnected with and supported by each manifold through use of a pair of flexible, outboard feeder ducts and an intermediate, non-flexible feeder duct. The plurality of apertures are located in a front wall member of each nozzle plenum which is located in a spanwise slot in the leading edge of the wing and maintained substantially flush with the leading edge of the wing by upper and lower, spanwise tongues which are received in corresponding upper and lower spanwise grooves in the portions of the wing adjacent to the slot. Apparatus is also disclosed to limit the relative transverse movement of each nozzle plenum with respect to its associated manifold, to bleed controlled air from the plurality of manifolds when a substantial number of the apertures of the nozzle plenums are obstructed due to ice or the like, and to seal a separation between adjacent nozzle plenums to prevent substantial airflow between the exterior airstream and the wing interior.

Heat transfer from a hot film in reversing shear flow

Abstract: The two-dimensional thermal boundary layer over a finite hot film embedded in a plane insulating wall, with a shear flow over it which reverses its direction, is analysed approximately using methods similar to those previously developed for viscous boundary layers (Pedley 1976). The heat transfer from the film is calculated both for uniformly decelerated and for oscillatory wall shear, and application is made to predict the response of hot-film anemometers actually used to measure oscillatory velocities in water and blood. The results predict that the velocity amplitude measured on the assumption of a quasi-steady response will depart from the actual amplitude at values of the frequency parameter St greater than about 0·3 (St = ΩX0/U0, where Ω = frequency, U0 = mean velocity, X0 = distance of hot film from the leading edge of the probe). This is in good agreement with experiment. So too is the shape of the predicted anemometer output as a function of time throughout a complete cycle, for cases when the response is not quasi-steady. However, there is a significant phase lead between the predicted and the experimental outputs. Various possible reasons for this are discussed; no firm conclusions are reached, but the most probable cause lies in the three-dimensionality of the velocity and temperature fields, since the experimental hot films are only about 2·5 times as broad as they are long, and are mounted on a cylinder not a flat plate.

Correction factory techniques for improving aerodynamic prediction methods

Abstract: A method for correcting discrete element lifting surface theory to reflect given experimental data is presented. Theoretical pressures are modified such that imposed constraints are satisfied while minimizing the changes to the pressures. Several types of correction procedures are presented and correlated; (1) scaling of pressures; (2) scaling of downwash values; and (3) addition of an increment to the downwash that is proportioned to pressure. Some special features are included in these methods and they include: (1) consideration of experimental data from multiple deflection modes, (2) limitation of the amplitudes of the correction factors, and (3) the use of correction factor mode shapes. These methods are correlated for cases involving all three Mach Number ranges using a FORTRAN IV computer program. Subsonically, a wing with an oscillating partial span control surface and a wing with a leading edge droop are presented. Transonically a two-dimensional airfoil with an oscillating flap is considered. Supersonically an arrow wing with and without camber is analyzed. In addition to correction factor methods an investigation is presented dealing with a new simplified transonic modification of the two-dimensional subsonic lifting surface theory. Correlations are presented for an airfoil with an oscillating flap.

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.

Stack forming device

Abstract: The stack forming device according to the invention comprises a traction surface which is rotatably driven. The portion of the trailing edge of a sheet to be stacked is kept in contact with the traction surface so that the trailing edge of the sheet is displaced in synchronism with said surface. This displacement is carried out over a period which follows the abutment of the leading edge of the sheet against a stop provided on a stacking platform. As a consequence the sheet acquires a convex configuration and is finally propelled against the platform or the preceding sheet after release by the traction surface. The device may be equipped with supplementary blowers in order to facilitate the release from the traction surface. It is of particular interest for high speed stacking of photographic film sheets, preferably double-side coated ones.

Compactor wheel with cross-shaped tips

Abstract: A compactor wheel comprises sets of tips each disposed in circumferential alignment therearound with the leading edge of a tip of one set being substantially aligned with the trailing edge of a tip of an adjacent set. Each tip comprises a body portion having a cross-shaped tip portion secured in upstanding relationship thereon to include a first tip portion extending circumferentially and a second tip portion extending transversely relative to the first tip portion and disposed intermediate the ends thereof. A tapered surface and concavity are formed on each lateral side of the first tip portion to dispel material outwardly therefrom during compaction of soils or the like. A plurality of circumferentially aligned blades are positioned on each lateral side of the compactor wheel.

Breakaway fan blade

Abstract: A fan blade having a breakaway leading edge positioned on the spar and shell that constitute the main structure of the blade, the leading edge being adapted to break away, in part at least, upon being struck by a large foreign object, with the shell providing an acceptable leading edge after the breakaway.

Comparison of a two-dimensional shock impingement computation with experiment

Abstract: Results of computations of two-dimensional viscous blunt-body flowfields with an impinging shock wave, with a time-dependent finite-difference method employed to solve the complete set of Navier-Stokes equations, are compared with experimental results. The experimental results were obtained in a 20-inch hypersonic tunnel with a planar shock impinging on the cylindrical leading edge of a fin, hence with the shock parallel to the centerline of the leading edge, so that type III and type IV interference patterns were generated. Close agreement is found. The overall effects of smoothing and grid size on the calculations are determined. A 31 x 51 mesh is adequate for wall pressure values (except in peaked regions).

The Aerodynamic Characteristics of Wrap-around Fins at Mach Numbers of 0.3 to 3.0.

Abstract: : Results of investigations into many of the geometric and flow parameters influencing the aerodynamics of wrap-around fins are presented in this report. Particular emphasis is placed on defining static and dynamic roll characteristics between Mach numbers of 0.3 to 3.0. Among the geometric parameters highlighted are fin span, aspect ratio, leading edge sweep, leading edge shape, fin opening angle, and afterbody geometry. Comparisons of static stability, dynamic stability, and drag are made between the flat and the wrap- around fin. Problems associated with measurement of wrap-around fin rolling mounts are also discussed. An overview of the wrap-around fin roll moment characteristics are presented as an aid for making estimates and establishing testing techniques. This report supercedes RD-73-17.

Airplane with two superposed wings

Abstract: This invention relates to an improvement in an airplane having two superposedly-arranged upper and lower sweptback wings which together form a closed frame, with reference to a front view thereof, the improvement comprising a rhombic shape of the frame with the upper wing having a negative V-position and the lower wing having a positive V-position, both of the wings being rearwardly sweptback, and the upper wing being more markedly sweptback than the lower wing, and at least the leading edge of the upper wing being positioned forward of the lower wing.

Numerical computation of the hypersonic leading edge problem using the Burnett equations

Abstract: The hypersonic rarefied flow near the sharp leading edge of a flat plate is computed for the first time using a finite‐difference solution of the complete, unsteady Burnett equations. The computation is advanced in time from the initial conditions until the steady‐state solution is reached. The computational region extends from the leading edge to the strong‐interaction regime. Schamberg’s second‐order wall slip and temperature jump boundary conditions are employed at the wall. The numerical results are compared with experimental data, a Monte Carlo simulation, and a finite‐difference solution of the complete Navier–Stokes equations. Based on these comparisons, it is evident that the Burnett equations in conjunction with Schamberg’s second‐order boundary conditions give a much less accurate description of the rarefied flow field near the leading edge than do the Navier–Stokes equations.

Effects of wing leading-edge radius and Reynolds number on longitudinal aerodynamic characteristics of highly swept wing-body configurations at subsonic speeds

Abstract: An investigation was conducted in the Langley low turbulence pressure tunnel to determine the effects of wing leading edge radius and Reynolds number on the longitudinal aerodynamic characteristics of a series of highly swept wing-body configurations. The tests were conducted at Mach numbers below 0.30, angles of attack up to 16 deg, and Reynolds numbers per meter from 6.57 million to 43.27 million. The wings under study in this investigation had leading edge sweep angles of 61.7 deg, 64.61 deg, and 67.01 deg in combination with trailing edge sweep angles of 0 deg and 40.6 deg. The leading edge radii of each wing planform could be varied from sharp to nearly round.

Wing and reduced airspeed system for jet aircraft

Abstract: A thin, high performance swept wing of the tapered type with an improved leading edge characterized by (1) camber that increases from a minimum near the wing root to a maximum near the wing tip, and (2) substantially a constant leading edge radius extending substantially across the wing span which defines a "blunt" contour. The wing in combination with a T-tail aircraft with a stick shaker/pusher activated by a rate of change of angle of attack sensor and optionally a strake between the leading edge and a wing tip tank which intrinsically combine to define a system that enhances aircraft performance by reducing minimum airspeed without impairing aircraft performance at high subsonic Mach (M) numbers.

Method and apparatus for making helically seamed tubing

Abstract: A thin perforate, helically wound welded edge tubing is used as a filter core for a roving wound filter. The slightly roughened external edges of the spirally formed welded joint greatly adds to the ability of securing the fiber roving to the tube and prevents relative slippage therebetween. Also, the invention comprehends an apparatus for, and a method of making the helically seamed tube by first drawing a sheet metal from a supply and raising two lateral edges thereof to form flanges. The material can be guided in a helical path by engaging the inside of the flanges so that the trailing edge abuts the leading edge. The abutted edges are heated so that the flanges themselves provide the filler for a weld on the exterior surface thereof. Drive rollers are provided to move the welded tube from the welding area and to torque the tube to prevent edge separation prior to the cooling of the weld.

Process of forming a projectile by folding a resilient tubular member and filling same with payload

Abstract: A process of making and filling an envelope shaped as a ring airfoil for use as a projectile. The envelope is formed of resilient material into a tubular shape with an outer wall portion and an inner wall portion located along the tubular extent thereof with a foldable portion therebetween. The walls are relatively moved to form a payload cavity by moving the inner wall to nest within the outer wall by folding at the foldable portion with the ends contiguous. The foldable portion forms the leading edge of the airfoil. The trailing edge is formed by joining the contiguous ends. Payload filling and final sealing steps complete the airfoil projectile shape.

Trolling depth controller

Abstract: A trolling depth controller having a body with a generally delta wing pattern and an air-foil cross section, the primary camber being on the lower surface and the nose being weighted. An upper fin includes a plurality of holes along its rearwardly sloping leading edge for attachment of the towing line. A lower, rearwardly sloped fin also includes a plurality of holes, at least some of which are positioned along a trailing edge for attachment of the towed lure or bait line.

Quench determination in liquid scintillation counting systems

Abstract: Method and apparatus for measuring the degree of quench in a liquid scintillation sample by irradiating the sample with a standard source, such as a cesium-137 gamma source, to produce a Compton scattered electron distribution exhibiting a Compton edge configuration as the leading edge thereof. For increasing the quench levels in the sample, the Compton edge shifts to lower pulse height values and the extent of this shift is indicative of the degree of quench. To measure the degree of quench, a unique point on the Compton edge, namely the point at which the second derivative of the edge is zero (i.e. the inflection point), is measured for the quenched sample and the pulse height value corresponding to the inflection point is determined. The pulse height value is compared with the pulse height value determined for a calibration standard in a similar manner, the difference in pulse height values indicating the degree of quench.

Blood serum bearing film with position indicating mark

Abstract: A plurality of spaced blood serum samples are disposed on a serum-bearing film having a leading and trailing edge. The blood serum samples are disposed in an array and each blood serum sample has a leading and a trailing edge. A position-indicating mark is disposed forward of the leading edge of the sample closest to the leading edge of the film by a distance representative of the spacing between adjacent ones of the samples.

A lifting surface theory for the analysis of nonplanar lifting systems

Abstract: A new nonlinear, nonplanar lifting surface theory is presented. The method is regarded as a lifting surface theory in that the effects of wing thickness are neglected, but none of the usual small perturbation assumptions inherent in most other lifting surface theories are made. The method represents nonplanar lifting systems by distributed vorticity, including the leading edge singular behavior characteristic of thin wings. The method is well suited to the computation of induced drag of nonplanar systems because leading edge suction is calculated from the leading edge singularity. The method has been used to compute the induced drag benefit of winglets (vortex diffusers), and the agreement with NASA experimental data is excellent.