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GLIDING BIRDS: REDUCTION OF INDUCED DRAG BY WING TIP SLOTS BETWEEN THE PRIMARY FEATHERS

GLIDING BIRDS: REDUCTION OF INDUCED DRAG BY WING TIP SLOTS BETWEEN THE PRIMARY FEATHERS

For a particular combination of base wing and wing tip, a computer program chose a random value for angle of attack from an appropriate range and calculated the mean value of drag for this angle from the equation of the fitted curve for drag. The program then chose a random value for drag from a normal distribution with a mean equal to the mean value of drag and the same standard deviation as that of the original data around the fitted curve. Twenty-five repetitions of this Monte Carlo simulation generated a set of data that itself was fitted with a least-squares curve. The program repeated the entire procedure to fit five such curves to the drag data. The equations for these curves varied because of the variation of the drag measurements around the original fitted curve. The program used a similar procedure to generate five curves for lift at different angles of attack.
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Low-Order Modeling of Wing-Tip Vortices Using an Augmented Vortex Lattice Method.

Low-Order Modeling of Wing-Tip Vortices Using an Augmented Vortex Lattice Method.

Wing-tip flow effects become increasingly significant in the prediction of forces and moments on a wing as the aspect ratio decreases. Similar to the attached leading-edge vortex of delta wings, the wing-tip vortex is characterized by a separated flow structure that is not included in conventional vortex lattice method (VLM) models. These models assume fully-attached flow at the tip, and therefore fail to capture what portion of the wing-tip vortex exists as a free vortex upstream of the trailing edge. Even at small angles of attack, some degree of the shear layer separation that feeds the free tip vortex can and generally does occur. The most significant consequence of this attached vortex structure is the increased suction, and therefore, normal force developed near the wing tips. This increased normal force results in a supplementary lift known as “vortex lift” (and “vortex drag”), which acts in addition to the “linear lift” associated with fully-attached flow. For low-aspect-ratio wings this effect on lift, as well as all forces and moments, is significant.
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Optimization and design of an aircraft’s morphing wing tip demonstrator for drag reduction at low speed, Part I – Aerodynamic optimization using genetic, bee colony and gradient descent algorithms

Optimization and design of an aircraft’s morphing wing tip demonstrator for drag reduction at low speed, Part I – Aerodynamic optimization using genetic, bee colony and gradient descent algorithms

The MDO 505 wing demonstrator was developed based on a real aircraft wing tip structure, fully equipped with an aileron, but without a winglet. Therefore, respecting the struc- tural requirements was as important as achieving the aerody- namic objectives. The length of the morphing upper surface was restricted by the front and rear spars’ positions, and the positions of the actuators were determined based on the mor- phing surface length. The actuators’ maximum and minimum displacements were determined in an iterative process between aerodynamic optimization and morphing surface structural optimization, in which a compromise was reached between the main aerodynamic objectives (influencing the transition region on the upper-surface of the wing): the structural objec- tives for a structurally rigid morphing surface, and the need to minimize the actuator forces and size.
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Mean flow and turbulence measurements in the near field of a fighter aircraft wing-tip vortex at high Reynolds number and transonic flow conditions

Mean flow and turbulence measurements in the near field of a fighter aircraft wing-tip vortex at high Reynolds number and transonic flow conditions

The model construction involved the assembly of three major components: a stainless steel central section with a one piece wing box, an aluminium alloy forebody with integral leading edge extensions (LEX) and a stainless steel rear fuselage. These components were assembled through bolted and spigotted joints. Through-flow air inlets were fitted without using any internal chokes (ie. fully open). Vertical fins were bolted to the rear fuselage. Due to mechanical interference with the articulated sting used to support the measurement probe, the horizontal stabilators were removed. However, since all measurements were well upstream of the location of the stabilators, this was not expected to have any effect on the results. Boundary layer transition strips were placed on the wings, LEX, vertical fins and forebody of the model. Due to the particular wing geometry, the flow structure in the vicinity of the wing-tip can be expected to be considerably more complex than that typically investigated in tip vortex studies using rectangular half- wings of symmetrical profile. AIM-9 sidewinders were mounted on the wing-tips as shown in Figure 2, and thus the resulting flow was due to the interaction of the wing-tip vortex, the wake of the main body of the missile (similar to an ogive cylinder), and the additional vortical flow generated by the canards and fins of the AIM-9. The underwing of the model was clean (ie. no stores or pylons were installed). Wing flaps were bolted to the wing box and set to zero deflection.
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Reduction of Induced Drag Using Wing Tip Propeller

Reduction of Induced Drag Using Wing Tip Propeller

is 1.3m/s for the angle of attack of 4° and 1.7m/sec for the angle of attack of 6°. The RPM of the wingtip propeller to cancel the circulation at the wing tip was calculated as 570 RPM and 760 RPM for angle of attack of 4° and 6° respectively by taking no slip condition and assuming there is no frictional torque. Experiment is done for wing with/without wingtip propeller of RPM higher than the calculated vales for different angle of attack of 4° and 6° at freestream velocity of 15 m/s. Due to the speed constrain of the wind tunnel, 15 m/s flow velocity were chosen. And because of the small plastic propeller fitted into the wing, experiment was done for small angle of attacks (α ≥ 6°). Otherwise propeller will be pulled away from the wing by the freestream air flow.
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Experimental investigation of wing tip vortices in the near-field

Experimental investigation of wing tip vortices in the near-field

Some of the recent experimental investigations include the work of Sun and Daichin [7], where the influence of the ground effect on the wing tip vortices was investigated on a NACA0012 wing. Ahmadi-Baloutaki et al. [8] carried out experiments on the effect of the external free-stream turbulence in the near-field of a wing-tip vortex using hot-wire anemometry, which showed that the increase of the external free-stream turbulence tends to increase the vortex diffusion.

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Drag reduction by wing tip slots in a gliding Harris' hawk, Parabuteo unicinctus

Drag reduction by wing tip slots in a gliding Harris' hawk, Parabuteo unicinctus

The drag of a bird gliding at equilibrium in a tilted wind tunnel can be calculated from from the bird’s weight and the angle of tunnel tilt (Pennycuick, 1968). This technique was used to measure the effect of removing the tip slots on the hawk’s drag. However, to show that that the slots reduce drag by vertical vortex spreading requires wing theory and additional measurements, some of which cannot be made on living birds. I made the feasible measurements, estimated the remaining quantities and used wing theory to show that the hawk’s tip slots did reduce drag by spreading vorticity vertically. A sensitivity analysis showed that this finding does not change when the estimated quantities range over plausible values.
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Increased selection response in larger populations. I. Selection for wing-tip height in Drosophila melanogaster at three population sizes.

Increased selection response in larger populations. I. Selection for wing-tip height in Drosophila melanogaster at three population sizes.

9%, 16% and 21% in small, medium and large lines, respectively. Thus similar selection pressure was more effective in larger lines. T h e realized heritabilities for the whole e[r]

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Formation and near-field dynamics of a wing tip vortex

Formation and near-field dynamics of a wing tip vortex

161 Effects of Boundary Layer and Tip Geometry Vortex lines of opposite sign annihilate each other Vortex lines coming from the wing surface boundary layer Rectangular Tip Case Vortex li[r]

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Induced airflow in flying insects I  A theoretical model of the induced flow

Induced airflow in flying insects I A theoretical model of the induced flow

these tip losses amounts to assuming that the aerodynamic effect of wing tip is small compared to the chordwise circulation and that each section of the wing continues to generate lift all along the span. As first pointed out by Prandtl (Prandtl and Tietjens, 1957) this assumption may not be valid at points closer to the tip of a finite wing, where a tip vortex enhances leakage of the fluid around the airfoil tip thus significantly reducing the ability of that region to generate any lift. In the framework described above, the effect of tip vortices is not considered explicitly, but is implicitly incorporated through the measured lift coefficients, which include the effect of tip vorticity on the finite wings and through the semi-elliptic distribution resulting from the loss of lift at wing tips.
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Mechanism of Generation and Collapse of a Longitudinal Vortex System Induced around the Leading Edge of a Delta Wing

Mechanism of Generation and Collapse of a Longitudinal Vortex System Induced around the Leading Edge of a Delta Wing

Characteristics of the longitudinal vortex are well reflected by pressure coefficients on the wing surface. The fast flows at the wing tip are rapidly separated, but the rotational radius is small. Since the centrifugal force has the property that it is proportional to the square of the velocity and is in inverse proportion to the rotational ra- dius, this causes the tip of the longitudinal vortex to induce the largest negative pressure. As a result, the wing tip has the lowest pressure coefficients as shown in Figure 8. The pressures in the longitudinal vortex gradually tend to recover due to the diffusion of the vorticity and convection of flows. In addition, the existence of two vortices is confirmed by distribution of pressure coefficients as shown in red chain lines of Figure 8. These two red chain lines have much to do with a pair of vortices shown in Figure 7. The characteristics of equi-contour lines of pressure coefficients in Figure agree well with the experimental results of actual vehicle by Ogawa [13] [14].
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Moments of Inertia of Bat Wings and Body

Moments of Inertia of Bat Wings and Body

For low inertia, wing span should be small but wing-tip length index T\ should be large long hand wings, wing-tip shape index /should be small pointed tips and aspect ratio AR should be [r]

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Computational Prediction of Tip-Vortex of a Swept Wing

Computational Prediction of Tip-Vortex of a Swept Wing

Abstract: The near-field flow structure of a wing tip vortex behind a sweptback and tapered NACA 0015 wing was investigated using Computational Fluid Dynamics (CFD) code at Re of 1.81 x 105. In this paper, Numerical simulations of the tip vortices was carried out at a geometric angle of attack 8° and the numerical results of tangential velocity of tip vortex is compared with the experimental result done by P. Gerontakos and T. Lee at McGill University low speed wind tunnel at the velocity equal to 35 m/s. The numerical result that was obtained by using CFD code shows a good agreement with the experimental result. The coordinates of the vortex-core location are closely captured along the downstream of flow and the variation of the vortex flow quantities with different angle of attack are investigated. Also circulation at three different downstream location of the trailing edge are calculated.
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Conceptual Design and Performance Optimization of a Tip Device for a Regional Turboprop Aircraft

Conceptual Design and Performance Optimization of a Tip Device for a Regional Turboprop Aircraft

An increasing number of aircraft is equipped with wing tip devices, which either are installed by the aircraft manufacturer at the production line or are retrofitted after the delivery of the aircraft to its operator. Installation of wing tip devices has not been a popular choice for regional turboprop aircraft and the novelty of the current study is to investigate the feasibility of retrofitting the British Aerospace (BAe) Jetstream 31 with an appropriate wing tip device (or winglet) to increase its cruise range performance, taking also into account the aerodynamic and structural impact of the implementation. To the best of the knowledge of the authors, no previous study exists which has attempted to assess the winglet retrofit of an existing aircraft type of similar size and operating profile. The optimal winglet design achieved a 2.38% increase of the maximum range by reducing the total drag by 1.19% at a mass penalty of 3.25%, as compared with the baseline aircraft configuration. Other designs were found to be more effective in reducing the total drag, but the structural reinforcement required for their implementation outweighed the achieved performance improvements. Since successful winglet retrofit programs for typical short to medium range narrow body aircraft report even more than 3% of block fuel improvements, undertaking the project of installing an optimal winglet design to the BAe Jetstream 31, should also consider a Direct Operating Cost (DOC) assessment on top of the aerodynamic and structural aspects of the retrofit.
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ENERGY SAVINGS IN FORMATION FLIGHT OF PINK FOOTED GEESE

ENERGY SAVINGS IN FORMATION FLIGHT OF PINK FOOTED GEESE

The large-format (56 mm 3 56 mm) negatives were printed onto Ilford A5 squared paper (15 cm 3 15 cm). Measurements were taken from the prints with vernier callipers (accurate to 0.1 mm). The implications of this accuracy for the error in estimated wing-tip spacing and depth varied from picture to picture. The higher a skein flew, the less precise the estimates became, because bill-to-tail length on the film decreased with increasing height, making the scale larger, hence 0.1 mm on a photograph represented a correspondingly larger actual distance. Enlarging the negatives further, however, induced other errors since the images became progressively less defined. On average, we estimated that 0.1 mm was equivalent to 1.7 cm.
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Biomechanical strategies for mitigating collision damage in insect wings: structural design versus embedded elastic materials

Biomechanical strategies for mitigating collision damage in insect wings: structural design versus embedded elastic materials

A comparison of yellowjacket and bumblebee wing morphologies suggests that these two species rely on alternative biomechanical strategies for mitigating wing damage due to collisions. Wing veins provide the structural support for insect wings (Wootton, 1992), and hymenopteran wings typically possess a similar complement of major veins and vein junctions (Fig. 1). Despite possessing many of the same veins and vein junctions, however, the distribution of these structures within the wing can vary substantially between species. In yellowjackets, the veins extend all the way to the wing tip, supporting the distal-most region of the wing (Fig. 1A). In contrast, bumblebee wing veins are withdrawn to more proximal regions of the wing and do not extend much beyond 75% of the wing span (Fig. 1C), leaving the entire distal region unreinforced and more continuously flexible than the veined yellowjacket wing tip. Thus, whereas a costal break is necessary in yellowjackets to allow an otherwise rigid wing to buckle upon contact with an obstacle (Fig. 4A,B; supplementary material Movies 1, 2), we presume that it is less important in bumblebees, as their vein-less wing tip is inherently more flexible overall (Fig. 4C; supplementary material Movie 3). However, just because a costal break is less important for mitigating wing wear in bumblebees, this is not a sufficient explanation for its absence in the bumblebee wing, when other hymenoptera representatives display both withdrawn wing veins and a costal break (Danforth, 1989; Danforth and Michener, 1988). The absence of a costal break in bumblebees may have nothing to do with wing wear per se, but might instead relate to biomechanical constraints on the costal break associated with flapping flight.
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Airport Noise Pollution: A Remedy for the Adjacent Land Owner

Airport Noise Pollution: A Remedy for the Adjacent Land Owner

The court stated, "We are unable to accept the premise that recovery for inter- ference with the use of land should depend on anything as irrelevant as whether the wing tip o[r]

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Induced Drag Savings From Ground Effect and Formation Flight in Brown Pelicans

Induced Drag Savings From Ground Effect and Formation Flight in Brown Pelicans

Altitudes close to the water and wing tip spacing WTS, distance perpendicular to the flight path between wing tips of adjacent birds at maximum span were measured for brown pelicans duri[r]

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Precision and Dynamics of Positioning by Canada Geese Flying in Formation

Precision and Dynamics of Positioning by Canada Geese Flying in Formation

A method is described for reconstructing perspective-distorted film images of geese flying in V formations to allow measurements of wing tip spacing WTS, the distance between wing tips o[r]

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Wake structure and wing kinematics: the flight of the lesser dog faced fruit bat, Cynopterus brachyotis

Wake structure and wing kinematics: the flight of the lesser dog faced fruit bat, Cynopterus brachyotis

downstroke as well as over large parts of the upstroke. In spite of its long-term presence, the tip vortex diminishes considerably later in the upstroke, and disappears totally at the end of the upstroke, suggesting that the overall wake pattern is one of successive ring vortices rather than a continuous vortex structure, although gaps between the rings are small. The position of the tip vortex is strongly correlated with the wingtip position during the downstroke, although positioned slightly inwards and below the tip location. Simultaneous to the formation of the tip vortex, a counter-rotating vortex, V2, develops at the beginning of the downstroke. V2 increases in strength simultaneously with V1, but disappears gradually towards mid- downstroke. V2 is located in close proximity to the body, and shows vertical displacement similar to V1 over the course of its existence, most probably because of the strong downward momentum of the flow behind the bat. However, unlike V1, for which the vertical and horizontal location is closely related to the wing tip position, V2 shows very little horizontal displacement, suggesting its origin more closely related to body position rather that the fifth digit trajectory. During the first half of the upstroke, V1 shifts medially and loses strength as well as its distinct contour. At the end of the upstroke, a second vortex pair, V3 and V4, appears in the distal wing region, with the more proximal vortex of the pair, V3, rotating in the same direction as the inward-shifted tip vortex, V1. The appearance of vortex pair V3 and V4 is similar to the pair identified in the wake of Glossophaga soricina (Hedenström et al., 2007). The vertical
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