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Showing papers on "Leading edge published in 1984"


Journal ArticleDOI
TL;DR: In this article, the lift and power requirements for hovering insect flight are estimated by combining the morphological and kinematic data from papers II and III with the aerodynamic analyses of papers IV and V.
Abstract: The lift and power requirements for hovering insect flight are estimated by combining the morphological and kinematic data from papers II and III with the aerodynamic analyses of papers IV and V. The lift calculations are used to evaluate the importance in hovering of two distinct types of aerodynamic mechanisms: (i) the usual quasi-steady mechanism, where the circulation for lift is primarily determined by translation of the wing, and (ii) rotational mechanisms, where the circulation is largely governed by wing rotation at either end of the wingbeat. Power estimates are compared with the available measurements of metabolic rate during hovering to investigate the role of elastic energy storage, the maximum mechanical power output of the flight muscles, and the muscle efficiency. The quasi-steady mechanism proves inadequate for the lift requirements of hover-flies using an inclined stroke plane, and for a ladybird beetle and a crane-fly hovering with a horizontal stroke plane. Observed angles of attack rule out lift enhancement by unsteady modifications to the quasi-steady mechanism, such as delayed stall, but the rotational lift mechanisms proposed in paper IV seem consistent with the kinematics. The rotational mechanisms rely on concentrated vortex shedding from the leading edge during rotation, with attachment of that vorticity as a leading edge separation bubble during the subsequent half-stroke. Strong leading edge vortex shedding should result from delayed pronation for the hover-fly, a near fling and partial fling for the ladybird, and profile flexion for the crane-fly (the flex mechanism). The kinematics for the other insects hovering with a horizontal stroke plane are basically the same as for the anomalous crane-fly, and the quasi-steady mechanism cannot be accepted for them while rejecting it for the crane-fly. All of these insects flex their wings in a similar manner during rotation, and could use the flex mechanism for lift generation. The implication is that most, if not all, hovering animals do not rely on quasi-steady aerodynamics, but use rotational lift mechanisms instead. It is not possible to reconcile the power estimates with the commonly accepted values of both the mechanochemical efficiency of insect flight muscle (about 25%) and its maximum mechanical power output (about 20 W N $^{-1}$ of muscle). Maximum efficiencies of 12-29% could be obtained only if there is no elastic storage of the kinetic energy of the flapping wings, but this would require more than twice the accepted value for maximum mechanical power output. The available evidence suggests that substantial elastic storage does occur, and that the maximum mechanical power output is close to the accepted value. If so, then the efficiency of both fibrillar and non-fibrillar flight muscle is likely to be only 5-9%.

466 citations


Journal ArticleDOI
TL;DR: In this paper, the aerodynamic forces acting on a delta wing, mounted on a free-to-roll sting-balance apparatus, were measured, and the helium-bubble flow visualization technique was used to gain some insight into the periodic motion of the separated leading edge vortices.
Abstract: The aerodynamic forces acting on a delta wing, mounted on a free-to-roll sting-balance apparatus, were measured. Two wing planforms having leading edge sweeps of 76 and 80 deg were tested, but only the wing with the 80 deg sweep would undergo periodic self-induced roll oscillation. The time dependent forces and roll angles for this wing were then recorded for various test conditions. In these tests a considerable drop in the average normal force of the free-to-roll wing was measured, relative to the normal force obtained in the static tests. Also, the helium-bubble flow visualization technique was used to gain some insight into the periodic motion of the separated leading edge vortices.

138 citations


Journal ArticleDOI
TL;DR: In this article, the interaction between flow and flow-induced acoustic resonances near rigid plates with semi-circular leading edges located in a hard-walled duct is described, and the rate of growth of the vortices is determined by an instantaneous Kutta condition applied over part of the cycle.

65 citations


01 Nov 1984
TL;DR: In this article, a scheme for investigating the parallel blade vortex interaction (BVI) has been designed and tested, which involves setting a vortex generator upstream of a nonlifting rotor so that the vortex interacts with the blade at the forward azimuth.
Abstract: A scheme for investigating the parallel blade vortex interaction (BVI) has been designed and tested. The scheme involves setting a vortex generator upstream of a nonlifting rotor so that the vortex interacts with the blade at the forward azimuth. The method has revealed two propagation mechanisms: a type C shock propagation from the leading edge induced by the vortex at high tip speeds, and a rapid but continuous pressure pulse associated with the proximity of the vortex to the leading edge. The latter is thought to be the more important source. The effects of Mach number and vortex proximity are discussed.

57 citations


Patent
31 Dec 1984
TL;DR: In this article, a swept wing having a leading edge flap which in its deployed position forms a slot with the forward end portion of the wing is described, where an elongate strip is positioned on the forward portion of wing in a manner that when the flap is deployed to form the slot, this strip protrudes into the airstream that passes upwardly through the slot.
Abstract: A swept wing having a leading edge flap which in its deployed position forms a slot with the forward end portion of the wing. An elongate strip is positioned on the forward portion of the wing in a manner that when the flap is deployed to form the slot, this strip protrudes into the airstream that passes upwardly through the slot. This creates a stall condition in the area of the strip to produce the desired pitch characteristics for safe recovery from stall. In the cruise configuration, where the flap is positioned against the leading edge of the wing, this strip is aerodynamically concealed.

51 citations


Patent
19 Oct 1984
TL;DR: In this article, a flip-flop is used to store input data on both the leading and the trailing edges of a clock pulse, which allows data to be stored on both leading and trailing edges.
Abstract: A flip-flop stores input data on both the leading and trailing edges of a clock pulse. The flip-flop includes a data path responsive to the leading edge of a clock pulse and a second data path responsive to the trailing edge of a clock pulse, thereby allowing data to be stored on both the leading edge and the trailing edge of a clock pulse.

45 citations


Book ChapterDOI
01 Jan 1984
TL;DR: The positive pressure gradient, downstream of the suction peak at the leading edge of an airfoil at incidence, may induce large perturbations on the general pattern of the flow as discussed by the authors.
Abstract: The positive pressure gradient, downstream of the suction peak at the leading edge of an airfoil at incidence, may, under some conditions, induce large perturbations on the general pattern of the flow.

40 citations


Patent
23 Apr 1984
TL;DR: In this article, a perturbation device is used to control the separation shedding of those vortices and manipulate their frequency and pairing, which results in different growth rates of the vorticles downstream of the device and thus the lift produced by the large bound vortice may be controlled.
Abstract: The lift generated by delta wings is due primarily to large vortices associated with the flow separation near the leading edge. The invention includes a perturbation device to control the separation shedding of those vortices and manipulate their frequency and pairing. This results in different growth rates of the vortices downstream of the device and thus the lift produced by the large bound vortices may be controlled. If the invention is applied to both leading edges, the total lift of the wing will be altered; if the perturbation is preferentially applied on only one side of the wing, the moment around the roll axis of the aircraft is controlled. A first embodiment uses a piston coupled to a cavity and slot to produce the desired perturbation. Alternative embodiments are described which achieve the results without moving parts.

36 citations


Patent
26 Oct 1984
TL;DR: In this paper, an electro-impulse de-icing device for use in an airfoil of an aircraft that includes a system having an energy storage device connected via a triggering device to a set of coils each embodying a coil construction in the form of a spirally wound ribbon coil member whose planar dimension is pressed against an interior surface in the leading edge of the aircraft.
Abstract: What is proposed is an electro-impulse de-icing device for use in an airfoil of an aircraft that includes a system having an energy storage device connected via a triggering device to a set of coils each embodying a coil construction in the form of a spirally wound ribbon coil member whose planar dimension is pressed against an interior surface in the leading edge of the airfoil, and wherein the coil sets are arranged in a linear manner along the long axis of the airfoil and are energized simultaneously and sequentially via an interlocking pattern from the wing tips or from the fuselage of the aircraft with each coil set being triggered twice from about three to five seconds apart.

36 citations


Patent
20 Aug 1984
TL;DR: In this article, an improved composite material leading edge/spar member for an aircraft control surface, and an efficient method for manufacturing the same is also provided, which is of a lighter and stronger construction offering dimensional stability.
Abstract: This invention relates to an improved composite material leading edge/spar member for an aircraft control surface, and the like. The present invention provides a one-piece composite leading edge/spar member that is of a lighter and stronger construction offering dimensional stability, and an efficient method for manufacturing the same is also provided. A one-piece leading edge/spar member (12) includes a forward leading edge portion (22), and an aft spar portion (23). The forward leading edge and the aft spar portions are connected together as a continuous one-piece tubular member of composite material. The forward leading edge portion (22) may be rounded, and the aft spar portion (23) may include an aft web portion (24) and first and second rebate portions (26, 28). The rebate portions (26, 28) connect the web portion (24) to the rounded forward leading edge portion (22), and provide surfaces for the attachment of skin surface members (16, 18) thereto.

35 citations


Journal ArticleDOI
TL;DR: In this paper, the similarity equations for combined forced and free convection flow over a horizontal plate when the wall temperature is inversely proportional to the square root of the distance from the leading edge are solved by introducing a scaling similar to that for the Blasius equation.
Abstract: The similarity equations for combined forced and free convection flow over a horizontal plate when the wall temperature is inversely proportional to the square root of the distance from the leading edge are solved by introducing a scaling similar to that for the Blasius equation. The technique is also applied to the local similarity equations for the case of a constant wall temperature.

Proceedings ArticleDOI
01 Jan 1984
TL;DR: In this paper, a Lamb-like analytical vortex having a finite core is chosen to interact with a thick and a thin (NACA 64A006) airfoil independently in transonic flow.
Abstract: A perturbation form of an implicit conservative, noniterative numerical algorithm for the two-dimensional thin layer Navier-Stokes and Euler equations is used to compute the interaction flow-field of a vortex with stationary airfoil. A Lamb-like analytical vortex having a finite core is chosen to interact with a thick (NACA 0012) and a thin (NACA 64A006) airfoil independently in transonic flow. Two different configurations of vortex interaction are studied, viz., (1) when the vortex is fixed at one location in the flowfield, and (2) when the vortex is convecting past the airfoil at freestream velocity. Parallel computations of this interacting flowfield are also done using a version of the Transonic Small Disturbance Code (ATRAN2). A special treatment of the leading edge region for thin airfoils is included in this code. With this, the three methods gave qualitatively similar results for the weaker interactions considered in this study. However, the strongest interactions considered proved to be beyond the capabilities of the small disturbance code. The results also show a far greater influence of the vortex on the airfoil flowfield when the vortex is stationary than when it is convecting with the flow.

Journal Article
TL;DR: In this article, the use of variable incidence angle delta wing leading edge "vortex flaps" for supersonic cruise and maneuvering performance improvements in fighter aircraft is discussed, and it is speculated that the vortex flap may be applicable to multimission fighters, and promote STOL performance.
Abstract: Prompted by the extensive experience obtained with vortex lift-generating leading edges in the SR-71, Concorde and F-16 supersonic aircraft, development efforts have recently been made toward the use of variable incidence angle delta wing leading edge 'vortex flaps' for supersonic cruise and maneuvering performance improvements in fighter aircraft. Vortex lift flaps have been wind tunnel tested on scale models, and it has been noted that a variety of effects can be obtained through the use of folding, hinged, and tabbed flap designs. Flap planforms can, moreover, be varied in length and in total area, as well as segmented, to yield unique combinations of drag reduction, vortex generation, longitudinal stability, and vortex flow reattachment. It is speculated that the vortex flap may be applicable to multimission fighters, and promote STOL performance.

Journal ArticleDOI
TL;DR: In this article, a two-dimensional steady inviscid flow past an inclined flat plate with a forward-facing flap attached to the rear edge is considered for the case when a vortex sheet separates from the leading edge of the flat plate and reattaches at the leading end of the flap, with uniform vorticity distributed between the vortex sheet and the body.
Abstract: Two-dimensional steady inviscid flow past an inclined flat plate with a forward-facing flap attached to the rear edge is considered for the case when a vortex sheet separates from the leading edge of the flat plate and reattaches at the leading edge of the flap, with uniform vorticity distributed between the vortex sheet and the body. Solutions are found for a particular geometry and a range of values of the vorticity. The method used to calculate the flow is an extension of a free-streamline method widely used in cases where the velocity is a constant on the separating streamline.

Journal ArticleDOI
TL;DR: In this article, an unsteady vortex lattice method is presented for the calculation of the aerodynamic forces acting on lifting surfaces undergoing complex three dimensional motion of a slender delta wing.
Abstract: An unsteady vortex lattice method is presented for the calculation of the aerodynamic forces acting on lifting surfaces undergoing complex three dimensional motion. For the present case the nonsymmetric motion of a slender delta wing was considered and the resulting lateral characteristics were calculated. The flow separation line was specified along the wing leading edge and the emanating vortex sheet shape and rollup was then calculated. Numerical results are presented for the combined high angle of attack and side slip condition and for the wing constant roll and coning motions.

Patent
07 Aug 1984
TL;DR: In this article, a fast voltage pulse is applied to a transducer which comprises a composite of multiple layers of alternately polarized piezoelectric material, and these layers are bonded together and positioned over the curved leading edge of an aircraft wing structure.
Abstract: A fast voltage pulse is applied to a transducer which comprises a composite of multiple layers of alternately polarized piezoelectric material. These layers are bonded together and positioned over the curved leading edge of an aircraft wing structure. Each layer is relatively thin and metallized on both sides. The strain produced in the transducer causes the composite to push forward resulting in detachment and breakup of ice on the leading edge of the aircraft wing.

Patent
06 Apr 1984
TL;DR: In this paper, a motor-driven fan with a hub adapted to be driven by a motor, a plurality of fan blades provided on the hub to extend in radial directions, and a shroud including a ring-shaped portion encircling the fan blades and staying members for supporting the ringshaped portion is described.
Abstract: A motor-driven fan including a hub adapted to be driven by a motor, a plurality of fan blades provided on the hub to extend in radial directions, a shroud including a ring-shaped portion encircling the fan blades and stay members for supporting the ring-shaped portion, each of the fan blades being formed at a tip end thereof with a deflector which is bent in a direction of rotation of the fan by a width which increases from a leading edge to a trailing edge of the blade.

Patent
18 Jul 1984
TL;DR: In this paper, a vacuum media capturing and retention system for a drum type printer or recorder is described, which includes a vacuum drum with two regions of vacuum passages, one for capturing the leading edge of the media and the second for retaining the trailing edge of media.
Abstract: A vacuum media capturing and retention system for a drum type printer or recorder is disclosed. The apparatus includes a vacuum drum with two regions of vacuum passages, one for capturing the leading edge of the media and the second for retaining the trailing edge of the media. When the leading edge of the media is initially captured the vacuum level in the drum is at one level. After the leading edge of the media is captured the vacuum level is dropped to a lower level until the trailing edge of the media is captured. Following the capture of the media trailing edge, the vacuum level within the drum is again increased to retain the media thereto during the copying or recording operation of the overall device.

Patent
20 Mar 1984
TL;DR: In this article, a cylindrical mast provides an aerodynamically shaped leading edge automatically oriented into relative wind, and a smooth shape behind the mast automatically adjusting for changes in trim of the sail.
Abstract: A sail on a cylindrical mast provides an aerodynamically shaped leading edge automatically oriented into relative wind, and a smooth shape behind the mast automatically adjusting for changes in trim of the sail. Flexible rib pairs opposite the mast are clamped tantentially to full length battens, the battens defining the shape of the ribs and the orientation of the leading edge.

Journal ArticleDOI
TL;DR: In this article, the tilt with height of the leading edge of seven mesoscale convective lines in GATE is determined by two independent methods, when averaged over time and along the line axis, the tilt is found to be surprisingly shallow, between 20 and 35 degrees from the horizontal.
Abstract: The tilt with height of the leading edge of seven mesoscale convective lines in GATE is determined by two independent methods. When averaged over time and along the line axis, the tilt is found to he surprisingly shallow, between 20 and 35 degrees from the horizontal. This is distinct from the slopes of the individual towers, which can be much steeper. The line leading-edge slope corresponds to the ratio of the vertical to horizontal velocity, relative to the line motion, of “representative” embedded convective cores.

Patent
13 Dec 1984
TL;DR: In this paper, the inlet for a temperature measuring probe mounted in the leading edge of a strut or vane is constructed to project beyond the leading-edge into the flow stream being measured and having the end scarfed in the direction of flow stream.
Abstract: The inlet for a temperature measuring probe mounted in the leading edge of a strut or vane is constructed to project beyond the leading edge into the flow stream being measured and having the end scarfed in the direction of the flow stream. This measuring probe has particular utility where the flow direction changes as in gas turbine power plant.

Journal ArticleDOI
TL;DR: In this paper, the results of extensive experimental studies of the structure of three-dimensional flow in a region of interaction of asymmetrically developing incompressible turbulent boundary layers by a longitudinal flow around corner configurations are presented.
Abstract: The results of extensive experimental studies of the structure of three-dimensional flow in a region of interaction of asymmetrically developing incompressible turbulent boundary layers by a longitudinal flow around corner configurations are presented. The character of the originating secondary flows is analysed depending on the degree of the flow asymmetry and on the geometry of the leading edge corner. The mechanisms of origin, subsequent development and transformation of secondary flows along the length of a model are discussed. In particular, it is shown that a one-vortex scheme of the flow gradually transforms into a two-vortical one with increasing distance from the leading edge corner.

Patent
Robert J. Russell1
03 Apr 1984
TL;DR: In this article, a frequency and time measurement circuit is provided with a delay means for effectively delaying the leading edge of a pulse, where a register is clocked by the trailing edge of the pulse to take a snapshot of how far it has progressed through the delay means.
Abstract: A frequency and time measurement circuit is provided with a delay means for effectively delaying the leading edge of a pulse. A register is clocked by the trailing edge of the pulse to take a snapshot of how far the leading edge of the pulse has progressed through the delay means. During a calibration phase, a reference pulse of constant length is used to take a reference reading. During a measurement phase, the measurement reading is taken on the unknown pulse whose clock frequency or time period is to be determined. By comparing the reference reading with the measurement reading, the relative clock frequency or time of the unknown pulse can be determined.

Patent
13 Apr 1984
TL;DR: In this article, a drive link preceding the cutting link includes a guide portion with an inclined leading edge that corresponds with the leading edge of the depth gauge, and a shallow V shaped opening is formed between the depth gauges and drive link guide portion to assist the cutting links in tracking in the kerf.
Abstract: A gulletless saw chain having a cutting link with a cutter portion that is configured to be top sharpenable. A depth gauge portion is positioned in close proximity to the cutting edge corner of the cutter portion. The depth gauge is laterally offset to position the outer most edge of the depth gauge at the corner of the cutting edge to thereby control side penetration as well as depth penetration of the cutting edge. A drive link preceding the cutting link includes a guide portion with an inclined leading edge that corresponds with the leading edge of the depth gauge. A shallow V shaped opening is formed between the depth gauge and drive link guide portion to assist the cutting link in tracking in the kerf.

Journal ArticleDOI
TL;DR: In this article, a droplet trajectory computer code is used to predict the water droplet impingement characteristics of several low- and medium-speed airfoils, and the authors analyzed the maximum impeding efficiency, total collection efficiency, and limits of impingements as functions of the airfoil geometry and freestream conditions.
Abstract: A droplet trajectory computer code is used to predict the water droplet impingement characteristics of several low- and medium-speed airfoils. The maximum impingement efficiency, total collection efficiency, and limits of impingement are analyzed as functions of the airfoil geometry and freestream conditions. The airfoil geometry is represented by leading edge radius, maximum thickness, maximum camber, and angle of attack. The analysis shows that the primary effects are an increase in maximum impingement efficiency with a decrease in leading edge radius, a reduction in total collection efficiency for thicker airfoils, and a change in the limits of impingement for airfoils of different maximum camber.

Proceedings ArticleDOI
01 Jun 1984
TL;DR: In this paper, a thin-layer Navier-Stokes code capable of predicting steady state viscous flows is applied to complicated three-dimensional flow fields, and the results indicate that the present method can capture the physical phenomenon well.
Abstract: A 'thin-layer' Navier-Stokes code capable of predicting steady state viscous flows is applied to complicated three-dimensional flow fields. The code is written in a generalized coordinate system, and a recently developed grid generation procedure is used for the flow-field discretization. Application is made to the vortical flow over a delta wing at high angle of attack, and the computed results are compared with experimental results. The results indicate that the present method can capture the physical phenomenon well. It is observed that a leading-edge separation vortex is formed over the wing, as is a secondary separation vortex near the leading edge. The flow field behind the trailing edge is also well described. Application is also made to the transonic flow over the Shuttle configuration. The result appears to be reasonable even though no experimental data are available for comparison. These results indicate that the present approach is capable of computing complicated three-dimensional flow fields.


Journal ArticleDOI
TL;DR: In this paper, the interaction of sound with the leading and trailing edges of a nominally lossless acoustic liner is examined in the presence of mean flow, and it is concluded that there is a net production of acoustic energy at a trailing edge for all subsonic mean flow Mach numbers M.

Patent
23 Nov 1984
TL;DR: In this article, the authors described a high speed parallel combinational line in which containers (8) are wrapped with plastic labels (10), each having an outer surface and an unneride which is next to the container (10) and comprising a solid polymer layer or a foam polymer layer.
Abstract: Apparatus and methods are disclosed for a high speed par duction line in which containers (8) are wrapped with plastics labels (10) each having an outer surface and an un nerside which is next to the container (10) and comprising a fi nt solid polymer layer (20) or a foam polymer layer (60), incl nding means (23, 38, 45) for moving a leading edge (61) of a abel (10) to the periphery (12) of a rotating vacuum drum (5), means for applying a solvent, such as methylene chic ide when the polymer is polystyrene, to the underside of the layer to form finite areas (65) on the leading label edge (61) nd a finite area (66) on the trailing edge (68). The finite areas 65, 66) have therein a rapidly soldifying tacky solution of the bolymer in the solvent, the tacky viscous solutions rapidl solidifying to form an adhesive bond. The solvent- applie label (10) is quickly moved to a label wrapping statior vhere it is wrapped around a container (8), the finite areas (66) on the leading edge (61) tacking the label (10) to the cor t iner (8), and the finite area (66) on the trailing edge (68) fo ning a cohesive bond on the seam formed by the overlap: ed label ends.

Patent
21 May 1984
TL;DR: In this paper, the structural skins are secured to the leading edge and the trailing edge portions employing a bonding material and a molding system in which the skins are held in contact with the cores without sufficient pressure, temperature, and time to secure complete bonding.
Abstract: An aircraft or sailboat structure and the method of manufacturing it in which the wing is formed of an elongated leading edge core of lightweight formable cellular material having an aerodynamically configured semi-circular forward surface and a substantially planar rearward vertical surface. A thin structural impervious skin is bonded to the leading edge core forward surface, an elongated trailing edge core formed of lightweight formable cellular material with a thin structural impervious skin bonded to the trailing edge upper and lower aerodynamic surfaces. The trailing edge portion has a substantially vertical forward surface, the vertical surfaces of the leading edge and trailing edge portions being secured to each other to complete the wing. The structural skins are secured to the core portions employing a bonding material and a molding system in which the skins are held in contact with the cores without sufficient pressure, temperature, and time to secure complete bonding.