Showing papers on "Leading edge published in 1979"

Experiments on the Weis-Fogh mechanism of lift generation by insects in hovering flight. Part 1. Dynamics of the ‘fling’

Abstract: From a series of experiments using simplified mechanical models we suggest certain minor modifications to the Weis-Fogh (1973)–Lighthill (1973) explanation of the so-called ‘clap and fling’ mechanism for the generation of large lift coefficients by insects in hovering flight. Of particular importance is the production and motion of a leading edge, separation vortex that accounts for virtually all of the circulation generated during the initial phase of the ‘fling’ process. The magnitude of this circulation is substantially larger than that calculated using inviscid theory. During the motion that subsequently separates the wings, the vorticity over each of them is convected and combined to become a tip vortex of uniform circulation spanning the space between them. This combined vortex moves downwards as a part of a ring, of large impulse, that is then continuously fed from quasi-steady separation bubbles that move with the wings as they continue to open at a large angle of attack. Such effects are able to account for the large lift forces generated by the insect.

Laminar natural convection over a frustum of a cone

Abstract: The problem of laminar, natural convection flow over a vertical frustum of a cone is treated in this paper. The thermal boundary condition at the wall include both the constant wall temperature and the constant wall heat flux cases. The governing differential equations are solved by a combination of quasilinearization and finite-difference methods. Numerical solutions are obtained for a range of Prandtl numbers. The solutions are found to approach to the solutions for a full cone if the flow is far downstream or the radius of the cross-section at the leading edge is very small.

Wing leading edge high lift device

Abstract: A wing leading edge high-lift generating device in the form of a spanwise slat segment having both an upper and a lower surface, faired into an airfoil configured leading edge of a relatively stationary portion of the wing therebehind and movable with respect thereto by a downwardly extending hinge arm pivotally related to a downwardly extending hinge bracket from the wing within a fairing structure which also includes an actuator between the hinge arm and bracket for biasing the hinge arm connected to the leading edge device away from and downwardly with respect to the hinge bracket of the wing about the pivotal connection therewith. Further, the wing leading edge slat device has a large cavity formed between the upper and lower surfaces thereof, which cavity is readily adaptable for the insertion of a large duct for blowing pressurized air through a nozzle and an aerodynamic slot formed between the leading edge slat and the relatively stationary airfoil configured leading edge of the wing therebehind when the leading edge slat is moved outwardly and downwardly. In another embodiment the leading edge slat has its movement guided by an extendable track.

Estimation of Attainable Leading-Edge Thrust for Wings at Subsonic and Supersonic Speeds

Abstract: The factors which place limits on the theoretical leading edge thrust are identified. An empirical method for the estimation of attainable thrust is presented. The method is based on the use of simple sweep theory to permit a two dimensional analysis, the use of theoretical airfoil programs to define thrust dependence on local geometric characteristics, and the examination of experimental two dimensional airfoil data to define limitations imposed by local Mach numbers and Reynolds numbers. Comparisons of theoretical and experimental aerodynamic characteristics for a series of wing body configurations are examined.

The influence of relaxation on shock detachment

Abstract: By establishing that the length scale governing the detachment of a shock wave from a wedge is the distance from the leading edge to the sonic line, and by considering the view of observers with different length scales, it is predicted that the detachment distance increases gradually with wedge angle for relaxing flow and more rapidly in a perfect gas. Both of these features are confirmed by experiments in the free-piston shock tunnel. The influence of other length scales is discussed. The phenomenon is related to a relaxation effect in which a subsonic layer grows from the translational-rotational shock as the wedge inclination is increased beyond the frozen sonic point.

Automatic web tying apparatus

Abstract: An apparatus and process for automatically making a spiral wrapped unitary package having a ring type or tied closure. In the apparatus a series of loads, each containing a plurality of units are fed one load at a time onto a turntable adjacent a material dispenser with the leading edge of the material from the dispenser being formed into a rope-like configuration by a roper mechanism and held by a clamp mechanism mounted on the turntable. The material is opened to its full web width, stretched and is spirally wrapped around the load at which time it is again formed into another rope-like configuration by the roper mechanism, and is positioned adjacent the leading edge where it is mechanically joined to the leading edge of the material by a ring type or tied closure. The roped material is then released from the clamp mechanism mounted on the turntable and the material is allowed to return to its memory position. The clamp mechanism again clamps the leading edge for the next load and the material is severed from the wrapped load.

Time similarity analysis of unsteady buoyant plumes in neutral surroundings

Abstract: A time similarity formulation of the flow equations for unsteady plumes is shown to exist only when the buoyancy flux at the source varies as a power function of time. The time similarity equations for unsteady plumes are solved numerically. It is shown that the velocity of the leading edge of the plume is less (at most the 0·42 fraction) than the velocity inside the plume behind its leading edge; this observation is consistent with Turner's (1962) results on the behaviour of a starting plume with constant buoyancy flux at the source. Finally, experimental results of axial temperature histories in the buoyant plume generated by a fast-growing fire are compared with the theoretical predictions.

Three-position variable camber flap

Abstract: A wing leading edge variable camber flap for an airplane, the flap having a pivoted bullnose and flap extension and retraction linkage mechanism for sequencing the flap into three positions of operation: a stowed position for high speed cruise operation of the airplane; a first forwardly and downwardly extended flap position whereat an aerodynamic slot is formed between the trailing edge of the flap and the relatively fixed leading edge of the wing, coupled with a steep flap angle-of-deflection of the flap relative to the wing chord plane, for low speed landing operation of the airplane; and a further forwardly extended second position whereat the trailing edge of the flap is moved to an abutment relation with the leading edge of the wing to seal off the aerodynamic slot, to form a substantially aerodynamically continuous upper surface and the flap angle-of-deflection being less than the landing position, for creating less drag during take-off operation of the airplane.

Actuating apparatus for a flap system having an upper surface blowing powered lift system

Abstract: A trailing edge flap moveable from a stowed position behind a wing to a downwardly and rearwardly extending position to deflect jet exhaust from an upper surface blowing jet engine downwardly and rearwardly to augment lift. The actuating mechanism rotates the flap about a variable radius which maintains the upper surface of the flap in contact with and generally in tangential alignment with the trailing edge of the upper surface of the wing. This mechanism comprises forward and rear radius links pivotally mounted at their lower ends to a stationary mounting arm, and extending upwardly and divergently therefrom to attach to the flap. In two embodiments, the rear radius link has its pivot end mounted to a moveable member which in turn enables the flap to be rotated so that its forward end moves downwardly. Thus, in its fully deployed position, the flap can be rotated to form a slot between the aft end of the wing and the leading edge of the flap.

Method and apparatus for measuring time

Abstract: A time duration is measured precisely and with high resolution by making three time measurements as shown in FIG. 5. The time difference t A between the leading edge of a start signal and the next following leading edge of a constant frequency time base signal is measured. The number "n" of the following leading edges is then counted including the leading edge of the time base signal following a stop signal. The number n is multiplied by the period T Q of the time signal. The time difference t E between the leading edge of the stop signal and the next following leading edge of the time base signal is measured. The real time difference Δt is then calculated as follows Δt=t A +n·T Q -t E . A three part real time measurement is performed to correct the calculated result for drift and aging. Calibration measurements are made and the respective calibration factors are used in calculating the final results. The respective circuit arrangement includes a start channel, a stop channel, and the corresponding supporting circuits.

Apparatus for covering panels with sheet material

Abstract: A stiff rectangular panel is placed centrally on an adhesive coated rectangular sheet of covering material with marginal edge portions of the sheet extending beyond the panel edges. The panel and sheet are conveyed on a first pass through a roller press and on such pass a leading edge portion of the sheet is engaged by weighted pivoted folding plate segments which fold or turn the edge portion of the sheet upwardly and around the leading edge of the panel and down onto the top face of the panel where the tack of the adhesive holds the folded edge portion of the covering sheet temporarily in place. Immediately following this, a stationary stiff brush engages the folded edge portion of the sheet and presses it tightly against the top face of the panel while the brush bristles simultaneously tuck the opposite end portions of the folded sheet snugly against the advancing longitudinal edges of the panel. On a reverse pass through the press at a lower elevation, the opposite edge portion of the sheet is folded and tucked in the same manner, followed by two additional passes of the product through the press at successively lower levels in a direction at right angles to the first and second passes to complete the folding and tucking of the remaining adhesive coated edge portions of the covering sheet.

Real Flow Limitations in Supersonic Airplane Design

Abstract: angle of attack for this example i s found to be approximately 15 degrees. Experience indicates that the airstream normally Experimental studies, including pressure measurements, will not be able to flow around the leading edge at this large force measurements and flow visualization techniques, have angle of attack without flow separation. This i s particularly shown that predicted aerodynamic performance levels of supertrue for the thin airfoils that are characteristic of supersonic sonic wings can be achieved only when the flow remains wing designs. This leading.edge flow separation completely attached over the entire wing surface. alters the character o f the flow pattern over the wing. The nature of the breakdown of potential flow on supersonic wings is discussed and illustrated with experimental f low visualization pictures and wind-tunnel data. Various types of flow breakdown are examined. Simplified flow analogies that explain these flow phenomena are developed. Practical procedures that ensure design for attached flow at prescribed con. ditions are described. Flow analogies are used to explore the impact of various airplane design parameters on the breakdown of attached flow. 1.0 Introduction The design of efficient, very highly swept supersonic wings is one of the more difficult problems in aeronautics. These highly swept wings are of interest because they have the potential, according to theory, o f having relatively low drag a t super. sonic lifting conditions. LWell known supersonic wing theory' indicates that the leading edge of a wing must be a t an angle of sweepback greater than the angle weak shockwaves make with the free stream a t corresponding Mach numbers to achieve low drag a t lifting conditions. Sweepback angles of 70 to 75 degrees are necessary for Mach numbers in the range of 2.0 to 3.0 Theoretical predictions indicate that an airplane with a wing of such high sweep would have an advantage of approximately 15 to 20 percent in liftldrag ratio when compared to an airplane having a much lower sweepback angle (for example, 50 degrees). When i t was first attempted to substantiate these very encouraging predictions with wind-tunnel models, it was found that the experimental results did not confirm them a t all. Subsequent examinations revealed that the low drag predicted by theory was not achieved because the flow pattern around the wings, implicit in theory, did not occur in practice. Viscosity, which normally has a relatively small effect on the overall f low over wings a t normal cruise lift conditions, had a rather substantial effect on these highly swept wings. Consider as an example a wing a t Mach 3.0 and a t an angle of attack of 4 degrees-typical supersonic conditions. With the wing swept 75 degrees to achieve low drag, the Mach number component normal t o the leading edge i s 0.78. Hence near the wing leading edge, a recognized subsonic flow condition i s produced. The leading edge flow is governed by the angle normal to the leading edge. Using simple sweep theory. the normal !d Leadingedge flow separation i s only one of the reasons why the predicted low drag levels o f highly swept wings could not be obtained. The flow over the wing, which i s a t a relatively low pressure, must adjust t o freestream pressure through a shock wave at the trailing edge. If the theoretical f low requires too large a pressure rise, trailing-edge separation occurs. Again the flow pattern postulated by theory cannot occur and the theoretical drags cannot be achieved. Similar problems can occur on other partsof sucha highly swept wing. The establishment o f a f low consistent with theoretical low drag is, therefore, contingent on the response of the boundary layer to potentially severe conditions a l l over the wing. The development and behavior of highly swept wing boundary layers under complicated three-dimensional flow conditions is not amerable to theoretical calculations. Necessary wing design limitations cannot be defined strictly on the basis of analytical studies, and therefore had t o be developed from experimental test programs. This paper presents a comprehensive set o f design conditions that can be used to define efficient, highly swept super. sonic wings. I f these conditions are applied as constraints to theoretical calculations, the flow pattern resulting from analysis would not have a very large effect on the wing boundary layers and the theoretical flow, and drag, could be expected to be obtained in practice. The results presented in this paper are based on work that began in the la te 1950s and was carried through the U.S. SST program until cancellation of the program in 1971. The object of the work was to develop methods for the design of efficient supersonic wings. More recently. interest in the design of such wings has been renewed both for eventual commercial' and military3 applications. For the latter case, not only does the designer require low drag a t cruising conditions, but he also requires a reasonable flow at higher l i f t coefficients associated with military maneuvers. A review of design methods to accomplish this is therefore timely and appropriate, and forms the subject of this paper. In Section 2 the basic characteristics of supersonic wing planforms are discussed, pointing out the advantages of highly swept wings in supersonic flow. This i s followed by a review of experimental results illustrating the basic flow problems of highly swept wings. The potential effects of warping the sur. face of such wings, (e.g., camber and twist) are discussed in

Shapes for rotating airfoils

Abstract: This invention is an airfoil which has particular application to the blade or blades of rotor aircraft and aircraft propellers. The airfoil thickness distribution, camber and leading edge radius is shaped to locate the airfoil crest at a more aft position along the chord, and to increase the freestream Mach number at which sonic flow is attained at the airfoil crest. The upper surface of the airfoil has a general reduction in the surface slope back to the maximum ordinate which is about 40 percent of the airfoil chord. The reduced slope causes a reduction in velocity at the airfoil crest at lift coefficients from zero to the maximum lift coefficient. The leading edge radius is adjusted or shaped so that the maximum local Mach number at 1.25 percent chord and at the designed maximum lift coefficient is limited to about 0.48 when the Mach number normal to the leading edge is approximately 0.20. The lower surface leading edge radius is shaped so that the maximum local Mach number at the leading edge is limited to about 0.29 when the Mach number normal to the leading edge is approximately 0.20 and the lift coefficient is in the range of 0.0 to -0.2. This design moves the drag divergence Mach number associated with the airfoil to a higher Mach number over a range of lift coefficients resulting in superior aircraft performance.

Flow deflector blades

Abstract: A flow deflector blade primarily for mounting within the efflux of an aircraft propulsion fan so that a change of flow direction can be effected, includes a leading edge member, a trailing edge member, a leaf spring member of arcuate form connecting the two, and filler portions of rubber bonded to each side of the leaf spring member shaped to provide a desired blade contour.

Suppression of Aerodynamically Induced Cavity Pressure Oscillations

Abstract: A flight test program was performed to gain further insight into the phenomenon of flow‐induced pressure oscillations in cavities and to evaluate the effectiveness of various suppressure concepts. The cavity tested was rectangular with dimensions of 17 in. long, 8.5 in. deep, and 8.75 in. wide. It was instrumented with microphones, static pressure ports, and a thermocouple. The flight speeds ranged from Mach number 0.6 to 1.3 at pressure altitudes of 3000, 20 000, and 30 000 ft. The suppression devices tested included leading edge spoilers and deflectors and trailing edge ramps and deflectors. Several combinations of these were tested. The results indicate that the flow‐induced pressure oscillations in a cavity, can be significantly reduced with leading edge spoilers in conjunction with a trailing edge ramp. A 20‐dB reduction was achieved for the predominant modal frequency. Other combinations of the suppression devices afforded some reduction, but the spoiler–ramp combination proved most effective.

Device for automatically guiding and regulating travel of bottles or the like in a conveying system

Abstract: In a system for conveying bottles or like articles, bottles being conveyed in single file along two or more separate paths are caused to merge and travel in single file along a single path by a device comprising arcuate guide passages and star wheels rotatably supported in concentric relation thereto, each star wheel having a plurality of teeth with respective outer tips lying in a rotational path extending partly into the guide passage, each tooth having a special profile shape defined by leading and trailing edges, the leading edge having a concave arcuate shape of a radius of curvature which substantially corresponds to the radius of said circular cross section and extending from the tip inward to smoothly join the inner end of the trailing edge of the forwardly adjacent tooth, said trailing edge having a convex curved shape and extending outward to the tip of said adjacent tooth, said leading and trailing edges thereby forming a fair S-shaped curve.

Pressure Gradient and Leading-Edge Effects on the Corner Bounday Layer

Abstract: Results are presented of velocity and pressure measurements made in the initially laminar boundary layer in a streamwise corner formed by two flat plates at 90° to each other set at various incidences. The leading edges of the plates were sharp in contrast to earlier tests with an aerofoil type leading edge. It was found impossible to obtain a steady enough flow for useful measurements to be made at zero incidence and pressure gradient, a small incidence associated with a favourable pressure gradient was necessary. This is believed to be because of the development of separation bubbles at the sharp leading edge at very small incidences due to small variations of flow direction to be expected in a wind tunnel. The profiled nose used in earlier tests afforded flow conditions much closer to the ideal theoretical model involving zero pressure gradient, but it is argued that any nose however shaped may introduce disturbances in the form of characteristic secondary flows that may well determine the downstream response of the boundary layer. In any case the corner flow is highly unstable at all but very low Reynolds numbers, and in the absence of a region of favourable pressure gradient a Reynolds number in terms of distance downstream of the leading edge greater than about 105 is unlikely to be attained in practice with the flow remaining smooth and laminar.

Leading edge vortex-flap experiments on a 74 deg delta wing

Abstract: Exploratory wind tunnel tests are reported on a 74 deg. delta wing model. The potential of a vortex flap concept in reducing the subsonic lift dependent drag of highly swept, slender wings is examined. The suction effect of coiled vortices generated through controlled separation over leading edge flap surfaces to produce a thrust component is discussed. A series of vortex-flap configurations were investigated to explore the effect of some primary geometric variables.

Responses of single units in the monkey superior colliculus to moving stimuli.

Abstract: 1. Single unit responses of pan-directional cells to moving and stationary flashing stimuli were studied in the superficial layers of the superior colliculus in paralysed, anaesthetized rhesus monkeys. The aim of this study was to see how far cell responses to moving stimuli fit in with what would be expected from their responses to stationary flashing stimuli. 2. Both the leading and the trailing edge of a moving stimulus evoke a transient response. If the diameter of moving light spots is increased the strength of the leading edge response increases, reaches a maximum and decreases to a constant value which is similar to the behaviour of the on response when the diameter of flashing spots is increased. The strength of the trailing edge response increases and reaches the same strength as that of the leading edge response. If the width of a long moving slit is increased, the strength of the leading edge response is the same at all slit widths, while the strength of the trailing edge response shows a course similar to that of the trailing edge response if the spot diameter is increased. If the length of a wide moving slit is increased both the leading and the trailing edge responses decrease. These results indicate that the strength of both leading and trailing edge responses is dependent on the degree the inhibitory surround is activated. 3. The leading and the trailing edge of a stimulus evoke their responses at the same position in the receptive field independent of the direction of movement. 4. Increasing the velocity of a moving stimulus shows that in general the leading edge response is present up to higher velocities than the trailing edge response independent of the sign of contrast. The burst duration to moving stimuli decreases with increasing stimulus velocity and appears to be determined by the time a moving edge is present in the receptive field centre. When this time becomes shorter than 10--20 ms, the burst duration for moving stimuli is constant and about the same as for flashing stimuli. This indicates that, although spatial receptive field properties can vary considerably, temporal receptive field properties show a strong similarity among different units. 5. The response latencies to light and dark moving edges are the same, which in turn are about equal to the response latencies to stationary flashing stimuli. 6. Stimulation experiments show that the general response characteristics to moving stimuli can be predicted by using a set of receptive field parameters derived from responses to stationary flashing stimuli. The most important variable of moving stimuli appears to be the period of time a moving contour is present within the receptive field centre, besides the degree of activation of the inhibitory surround.

Method and apparatus for a web edge tracking flaw detection system

Abstract: A web of moving material is successively scanned by a light source, such as a laser beam, and changes of intensity of the transmitted, reflected or scattered light from the material is detected to provide an indication for discerning flaws in the web. A once per scan line digital signal from the scanner controls a voltage controlled oscillator connected in a phased locked loop which is used for controlling the generation of a precision ramp analog voltage that follows the angular scan position of the light source on the material. The light signal from the web is applied to a comparator for providing a digital pedestal signal in which the first light passing the comparator is the leading edge of the web while the last light passing during a scan line is the trailing edge or the end of the web. If no pedestal signal is present indicative of a break in the web, a synthetic maximum width pedestal signal is substituted to enable the inspection system to continue to function. The digital pedestal signal or synthetic maximum width pedestal signal and the precision ramp are applied to leading and trailing edge, position-to-voltage converters. The precision ramp voltage is sampled and held by the voltage converters which generate leading and trailing edge position analog voltage outputs. These voltage outputs are applied to a leading and trailing edge cross web, down web position tracking rate filter which is controlled by edge position tracking rate and web speed circuits. The filtered leading and trailing edge outputs are applied to margin set circuits and then are converted by voltage-to-edge, position converter circuits into digital active scan pulses that accurately define and track the active scan interval of interest where flaws are to be detected.

Blade profile for rotary wing of an aircraft

Abstract: The present invention relates to a blade profile for rotary wing of an aircraft, comprising, between the leading edge and the trailing edge, a convex upper surface and a non-concave lower surface, wherein, at the point of maximum curvature of the leading edge, the radius of curvature Ro is approximately defined by the expression Ro=1.7 C. emax 2, in which C represents the chord and emax the relative thickness of said profile and the portion of lower surface adjacent the leading edge extends to about 20% of the chord from said leading edge and presents a very small general curvature decreasing continuously in the direction of the trailing edge up to the point of minimum curvature of the lower surface. The invention is more particularly applicable to obtaining rotary wings, for example for helicopters, capable of very high performances both when hovering, and in high speed flight, as well as during manoeuvres.

Feed mechanism for continuous and cut form paper

Abstract: A cut form paper transport apparatus in a belt printer includes driven exit friction rollers disposed for rolling engagement with a pressure roller pivotally supported on a pair of support arms which carry a deflector or guide plate spaced above the platen and disposed for engagement with the leading edge of a sheet of paper as it leaves the printing region for deflection of the leading edge into an exit path tangent to the platen and such that the leading edge of the sheet moves between the exit friction rollers and the pressure roller for engagement thereby when the sheet is in the exit path. Mounted on the deflector plate is a pair of adjustment rollers disposed for rolling engagement with the outer surface of the platen for adjusting the position of the deflector plate with respect to the platen.

Method of manufacturing rotor blade

Abstract: A rotor blade is manufactured by making a soft alloy into a blade body with a curved section, joining a hard alloy to the leading edge of the blade body, coating the back side surfaces of the leading and trailing edge portions of the blade by alternately giving at least one coat each of a Ni-Cr-B-Si alloy and WC by spraying and fusing the coats onto the backing surfaces, and then coating the entire front side surface of the blade in the same way.

Material characteristics of Space Shuttle reinforced carbon-carbon

Abstract: Reinforced carbon-carbon with an oxidation-resistant coating is used as the thermal protection system for the Space Shuttle Orbiter high-temperature wing leading edge and nose cap surfaces. The reinforced carbon-carbon system is capable of multimission reuse, and, in addition, provides a smooth external moldline while transmitting aerodynamic loads to the fuselage forward bulkhead and wing spar through mechanical attachments. This paper describes the material and processes developed, strength and thermal/physical properties which characterize performance.

Apparatus for preparing fresh farinaceous pastes

Abstract: In an apparatus for preparing fresh food paste of the type including a vessel having a bottom and forming a mixing and kneading chamber, the vessel having a closed side wall of circular cross section which is symmetrical about an axis passing centrally through the chamber, a rotatable member mounted within the chamber for rotation about the vertical axis, a drive for rotating the member in a given direction, blades located within the chamber and operatively connected to the rotatable member in a position extending away from the vertical axis, wherein the improvement comprises: the blades including a kneading blade extending into close confronting space relation with the vessel side wall and having a lower surface with leading and trailing edges defined by the given direction of rotation, the trailing edge having a normal position adjacent the vessel bottom and being moveable away from the bottom and the leading edge being positioned at a substantially greater distance from the bottom than the normal position of the trailing edge; and a device for biasing the trailing edge towards the vessel bottom for causing the kneading blade to exert downward pressure on paste forming ingredients between the kneading blade's lower surface and the vessel bottom during the rotation of the rotatable member to effect the kneading of those ingredients.

Method of lapping webs

Abstract: A method of lapping webs wherein two series of web sections are advanced, reversely folding a portion of each section about a transverse line adjacent the section leading edge to lap a portion of the preceding section adjacent the trailing edge, and retarding one series relative to the other.