Showing papers on "Lift-induced drag published in 1975"

Aerodynamic properties of an insect wing section and a smooth aerofoil compared.

Abstract: IN this communication I report measurements of lift and drag forces acting on corrugated aerofoils. The chordal profile of the wings in many orders of insects is corrugated1 and I have used scale models of a wing section of this type found in the hover fly Syrphus balteatus (Diptera, Syrphidae). The experimental profile is shown in Fig. 1d. The life-size chord length is 2.9 mm, and occurs 3.7 mm distal to the wing-root hinge, in a total unilateral wing length of 11.5 mm. (There is no special reason either for selecting this particular section or for choosing S. balteatus.) The model profiles were 22 times life size (chord length = 6.4 cm) and were made of stainless steel 100 µm thick. They were built to uniform chordal profile, with spans of 7.17 cm or 3.39 cm, giving aspect ratios of 1.12 and 0.53, respectively—both very low. An attempt was made to model the thick leading edge vein of the real wing by constructing the model leading edge from a stainless steel rod (diameter 1.7 mm).

Flow Forces on a Cylinder Near a Wall or Near Another Cylinder

Abstract: : Lift, drag and pressure distributions have been measured on cylinders (of various cross-section shapes) near a wall. It is found that as the cylinder approaches the wall its drag decreases and a lift (away from the wall) develops. A similar development occurs for two cylinders approaching each other (in a plane perpendicular to the flow) but in this case there is a range of gap sizes for which the flow is asymmetrical and the forces on the two cylinders are different. The asymmetry is associated with an instability in the near-wake flow, and it can be flipped (switched) by small disturbances. The results are of interest for the effects of wind on cylindrical structures parallel to the ground, for pairs of structures, like stacks, near each other, etc. (Author)

Approximate solution of minimum induced drag of wings with given structural weight

Abstract: light reaching the photomultiplier. If one beam is unaffected but the other is deflected in the vertical plane, a smaller net change in the photomultiplier current would result. In full-scale operation over a runway, the laser beams should propagate above and parallel to the runway. Existing runway approach light towers on both ends of the runway could be used to house the necessary system of mirrors. This would not, therefore, add any new protruding structures adjacent to the runway. The beam separation and height above ground are variables which must be determined for best system response to a vortex. For safety, the laser wavelength should be selected such that the light beams would not transmit through the aircraft windshields. The laboratory tests described above indicate that, in principle, a full-scale system of this type should be able to detect wingtip vortices over a runway.

On vortex strength and drag in bluff-body wakes

Abstract: In a recent paper (Griffin & Ramberg 1974) the authors studied the vortex-street wakes behind forced vibrating rigid cylinders. All experimental conditions were within the regime of wake capture or synchronization between the vibration and vortex frequencies. Both mean and fluctuating velocities in the wake together with the length of the vortex formation region were measured as functions of vibration amplitude and frequency at a Reynolds number of 144. The viscous vortex strength, age and spacing at this Reynolds number were then obtained by matching a model for the vortex street with the mean and r.m.s. velocity profiles obtained from hot-wire measurements. These results are employed here to determine the steady drag force on the vibrating cylinder by means of the von Karman drag formulation. The drag coefficients determined in this way are in agreement with the recently published direct force measurements of Tanida, Okajima & Watanabe (1973) and Griffin, Skop & Koopmann (1973) at Reynolds numbers of 80, 500-900 and 4000. From these results a direct relation is drawn between the increased drag on resonantly vibrating structures and changes in the vortex strength, spacing and formation in their wakes.

Wind energy concentrators

Abstract: The herein described horizontal and vertical wind energy concentrators are structurally simple and light and are capable of concentrating the wind energy at least six times with very high efficiency. This permits a corresponding reduction in the frontal area of the wind turbine and increases its speed without sacrifice in wind energy harnessed. The wind energy concentrator is a high lift, short aspect ratio wing, which is designed to maximize the induced drag. This induced drag takes the velocity out of the wind but transforms the wind energy into rotational energy present in the shed vortex system. The design is such that most of this rotational energy can be harnessed by a small high speed wind turbine placed in the rolled up wing tip vortex.

Light aircraft lift, drag, and moment prediction: A review and analysis

Abstract: The historical development of analytical methods for predicting the lift, drag, and pitching moment of complete light aircraft configurations in cruising flight is reviewed. Theoretical methods, based in part on techniques described in the literature and in part on original work, are developed. These methods form the basis for understanding the computer programs given to: (1) compute the lift, drag, and moment of conventional airfoils, (2) extend these two-dimensional characteristics to three dimensions for moderate-to-high aspect ratio unswept wings, (3) plot complete configurations, (4) convert the fuselage geometric data to the correct input format, (5) compute the fuselage lift and drag, (6) compute the lift and moment of symmetrical airfoils to M = 1.0 by a simplified semi-empirical procedure, and (7) compute, in closed form, the pressure distribution over a prolate spheroid at alpha = 0. Comparisons of the predictions with experiment indicate excellent lift and drag agreement for conventional airfoils and wings. Limited comparisons of body-alone drag characteristics yield reasonable agreement. Also included are discussions for interference effects and techniques for summing the results above to obtain predictions for complete configurations.

Transonic equivalence rule: a nonlinear problem involving lift

Abstract: The inviscid transonic flow past a thin wing having swept leading edges, with smooth lift and thickness distributions, is shown to possess an outer nonlinear structure determined principally by a line source and a line doublet. Three domains (the thickness-dominated, the intermediate, and the lift-dominated), representing different degrees of lift control of the outer flow, are identified; a transonic equivalence rule valid in all three domains is established. Except in one domain, departure from the Whitcomb-Oswatitsch area rule is significant; the equivalent body corresponding to the source effect has an increased cross-sectional area depending nonlinearly on the lift. This nonlinear lift contribution results from the second-order corrections to the inner (Jones) solution, but produces effects of first-order importance in the outer flow. Of interest is an afterbody effect dependent on the vortex drag, which is not accounted for by the classical transonic small-disturbance theory.

Two-Dimensional Subsonic Wind Tunnel Evaluation of a 20-Percent-Thick Circulation Control Airfoil

Abstract: : A circulation control uncambered elliptic airfoil section with a thickness-to-chord ratio of 0.20 was tested subsonically to determine its aerodynamic characteristics. Lift coefficients up to 5 were produced at momentum coefficients, of 0.24. The initially high unblown drag coefficients, characteristic of bluff trailing edge airfoils, were greatly reduced at low values of momentum coefficient. It was therefore possible to produce equivalent lift-to-drag ratios in excess of 30 when Cl = 1.0. The ability to produce high lift coefficients essentially independent of angle of attack is indicated by the results of this investigation.

A comprehensive plan for helicopter drag reduction

Abstract: Current helicopters have parasite drag levels 6 to 10 times as great as fixed wing aircraft. The commensurate poor cruise efficiency results in a substantial degradation of potential mission capability. The paper traces the origins of helicopter drag and shows that the problem (primarily due to bluff body flow separation) can be solved by the adoption of a comprehensive research and development plan. This plan, known as the Fuselage Design Methodology, comprises both nonaerodynamic and aerodynamic aspects. The aerodynamics are discussed in detail and experimental and analytical programs are described which will lead to a solution of the bluff body problem. Some recent results of work conducted at the Naval Ship Research and Development Center (NSRDC) are presented to illustrate these programs. It is concluded that a 75-per cent reduction of helicopter drag is possible by the full implementation of the Fuselage Design Methodology.

Theoretical aerodynamics of upper-surface-blowing jet-wing interaction

Abstract: A linear, inviscid subsonic compressible flow theory is formulated to treat the aerodynamic interaction between the wing and an inviscid upper-surface-blowing (USB) thick jet with Mach number nonuniformity. The predicted results show reasonably good agreement with some available lift and induced-drag data. It was also shown that the thin-jet-flap theory is inadequate for the USB configurations with thick jet. Additional theoretical results show that the lift and induced drag were reduced by increasing jet temperature and increased by increasing jet Mach number. Reducing jet aspect ratio, while holding jet area constant, caused reductions in lift, induced drag, and pitching moment at a given angle of attack but with a minimal change in the curve of lift coefficient against induced-drag coefficient. The jet-deflection effect was shown to be beneficial to cruise performance. The aerodynamic center was shifted forward by adding power or jet-deflection angle. Moving the jet away from the wing surface resulted in rapid changes in lift and induced drag. Reducing the wing span of a rectangular wing by half decreased the jet-circulation lift by only 24 percent at a thrust coefficient of 2.

Wind Tunnel Development of the Dragfoiler - A System for Reducing Tractor-Trailer Aerodynamic Drag

Abstract: Dragfoiler II, an effective and practical add-on aerodynamic drag reducing system for tractor-trailers, has been developed. Wind tunnel tests with 1/16- and 1/7-scale tractor-trailer models were used to determine empirical design guidelines for the Dragfoiler II's side elevation and planform shapes. Optimum designs for various combinations of tractor roof height and length, trailer height, and tractor-to-trailer gap length gave zero-yaw drag reductions between 30 and 35%. At a yaw angle of 10 deg, the percentage drag reductions were about half those at 0 deg. Off-design performance and the effects of trailer side-edge geometry were investigated.

Opportunities for aerodynamic-drag reduction

Abstract: Methods for reducing aerodynamic drag to improve aircraft performance and reduce fuel consumption are discussed. The techniques considered are: (1) pressure drag reduction, (2) supercritical airfoils, (3) subcritical airfoils, (4) induced drag reduction by over-the-wing blowing and increased aspect ratio, and (5) friction drag reduction by laminar flow control and slot injection. It is stated that a 50 percent reduction from current drag values is expected through the application of these techniques.

Trim Drag in the Light of Munk's Stagger Theorem

Abstract: Munk's stagger theorem holds that the induced drag of a multiplane is independent of the streamwise position (the stagger) of its lifting elements so long as the gap/span ratios and the element/element lift ratios are specified. In particular, a monoplane-tailplane or a monoplane-foreplane (canard)arrangement can be regarded as a biplane of zero gap and the trim drag due to tailplane download or foreplane upload can be readily calculated. The trim drag penalty is the same for both configurations. Relations are given for trim drag estimates for various practical arrangements.

Jet-Wing Lifting-Surface Theory Using Elementary Vortex Distributions

Abstract: A lifting-surface theory for jet wings based on a finite-element method—the method of elementary vortex distribution or the EV D method—is presented. The method utilizes a set of independent but overlapped elementary horseshoe vortex distributions to represent the wing and jet sheet, and satisfies a set of mixed-type boundary conditions on both the wing and jet sheet. The solution includes chordwise and span wise loading distributions, from which sectional and total aerodynamic quantities (e.g., lift, pitching moment, induced drag, etc.) are derived. In view of the finite-element approach, the method can, in general, be applied to jet wings of arbitrary planform, camber, twist, partial-span flaps, and arbitrary trailing-edge jet-momentum distribution. The present method also reduces to a conventional lifting-surface theory when the jet momentum is zero. An extensive comparison has been made of solutions derived with the EVD method with other theoretical and experimental data for jet wings and conventional wings. Good agreement has been observed in the chordwise and span-wise loadings as well as total aerodynamic coefficients.

Angle-of-Attack Control of Drag for Slender Re-entry Vehicle Recovery

Abstract: A method is described in which drag increase due to angle of attack is used to decelerate a slender,highballistic-coefficient re-entry vehicle for recovery. The angle of attack and drag increase are produced by the application of a controlled wind-fixed yaw moment which causes dynamic undamping of the angle of attack. A small yaw moment can induce large circular coning motion for which the drag is predictable. It is shown that sufficient deceleration for recovery can be obtained after the vehicle has experienced high stagnation pressures for nosetip and heat-shield testing. Practical implementation of the recovery system is discussed.

Reduction of trimmed drag

Abstract: Methods are reported for reducing the aircraft drag coefficient for a given aircraft lift coefficient, or speed. The emphasis is placed in determining the load distribution between the wing-body combination and the tail which reduces overall drag coefficient. Furthermore, a technique is presented which allows the determination of various aerodynamic and geometric parameters to permit the best location to satisfy inherent stability requirements. Included in the method is the calculation of sensitivity coefficients which indicate the importance of various parameters in achieving specified goals. Preliminary results indicate that such an approach is feasible.

Transonic aerodynamic characteristics of the 10-percent-thick NASA supercritical airfoil 31

Abstract: Refinements in a 10 percent thick supercritical airfoil (airfoil 31) have produced significant improvements in the drag characteristics compared with those for an earlier supercritical airfoil (airfoil 12) designed for the same normal force coefficient of 0.7. Drag creep was practically eliminated at normal force coefficients between about 0.4 and 0.7 and was greatly reduced at other normal force coefficients. Substantial reductions in the drag levels preceding drag divergence were also achieved at all normal force coefficients. The Mach numbers at which drag diverges were delayed for airfoil 31 at normal force coefficients up to about 0.6 (by approximately 0.01 and 0.02 at normal force coefficients of 0.4 and 0.6, respectively) but drag divergence occurred at slightly lower Mach numbers at higher normal force coefficients.

The effect of Reynolds number on the boattail drag of two wing-body configurations

Abstract: An investigation has been conducted in the Langley 1/3-meter transonic cryogenic tunnel to determine the effects of varying Reynolds number on the boattail drag of wing-body configurations at subsonic speeds. Two boattailed cone-cylinder nacelle models were tested with a 60 deg delta wing at an angle of attack of 0 deg. Reynolds number, based on model length, was varied from about 2.5 million to 67 million. Even though the presence of the wing had large effects on the boattail pressure coefficients, the results of this investigation were similar to those previously found for a series of isolated boattails. Boattail pressure coefficients in the expansion region became more negative with increasing Reynolds number, while those in the recompression region became more positive. These two effects were compensating, and as a result, there was virtually no effect of Reynolds number on boattail pressure drag.

Theoretical and experimental study of a new method for prediction of profile drag of airfoil sections

Abstract: Theoretical and experimental studies are described which were conducted for the purpose of developing a new generalized method for the prediction of profile drag of single component airfoil sections with sharp trailing edges. This method aims at solution for the flow in the wake from the airfoil trailing edge to the large distance in the downstream direction; the profile drag of the given airfoil section can then easily be obtained from the momentum balance once the shape of velocity profile at a large distance from the airfoil trailing edge has been computed. Computer program subroutines have been developed for the computation of the profile drag and flow in the airfoil wake on CDC6600 computer. The required inputs to the computer program consist of free stream conditions and the characteristics of the boundary layers at the airfoil trailing edge or at the point of incipient separation in the neighborhood of airfoil trailing edge. The method described is quite generalized and hence can be extended to the solution of the profile drag for multi-component airfoil sections.

Effects of nozzle interfairing modifications on longitudinal aerodynamic characteristics of a twin jet, variable wing sweep fighter model

Abstract: A wind-tunnel investigation has been made to determine the effects of nozzle interfairing modifications on the longitudinal aerodynamic characteristics of a twin-jet, variable-wing-sweep fighter model. The model was tested in the Langley 16-foot transonic tunnel at Mach numbers of 0.6 to 1.3 and angles of attack from about minus 2 deg to 6 deg and in the Langley 4-foot supersonic presure tunnel at a Mach number of 2.2 and an angle of attack of 0 deg. Compressed air was used to simulate nozzle exhaust flow at jet total-pressure ratios from 1 (jet off) to about 21. The results of this investigation show that the aircraft drag can be significantly reduced by replacing the basic interfairing with a modified interfairing.

Some comments on trim drag

Abstract: A discussion of data of and methods for predicting trim drag is presented. Specifically the following subjects are discussed: (1) economic impact of trim drag; (2) the trim drag problem in propeller driven airplanes and the effect of propeller and nacelle location; (3) theoretical procedures for predicting trim drag; and (4) research needs in the area of trim drag.

Aerodynamic characteristics of a tandem wing configuration of a Mach number of 0.30

Abstract: An investigation was conducted to determine the aerodynamic characteristics of a tandem wing configuration. The configuration had a low forward mounted sweptback wing and a high rear mounted sweptforward wing jointed at the wing tip by an end plate. The investigation was conducted at a Mach number of 0.30 at angles of attack up to 20 deg. A comparison of the experimentally determined drag due to lift characteristics with theoretical estimates is also included.

Evaluation of viscous drag reduction schemes for subsonic transports

Abstract: The results are described of a theoretical study of viscous drag reduction schemes for potential application to the fuselage of a long-haul subsonic transport aircraft. The schemes which were examined included tangential slot injection on the fuselage and various synergetic combinations of tangential slot injection and distributed suction applied to wing and fuselage surfaces. Both passive and mechanical (utilizing turbo-machinery) systems were examined. Overall performance of the selected systems was determined at a fixed subsonic cruise condition corresponding to a flight Mach number of free stream M = 0.8 and an altitude of 11,000 m. The nominal aircraft to which most of the performance data was referenced was a wide-body transport of the Boeing 747 category. Some of the performance results obtained with wing suction are referenced to a Lockheed C-141 Star Lifter wing section. Alternate designs investigated involved combinations of boundary layer suction on the wing surfaces and injection on the fuselage, and suction and injection combinations applied to the fuselage only.

The Drag and Oscillating Transverse Force on Vibrating Cylinders due to Steady Fluid Flow

Abstract: When a cylinder is exposed to cross-flow, oscillating transverse forces act on the cylinder in addition to the nearly steady drag forces. If the cylinder is elastic or elastically supported, the oscillating transverse or lift forces will cause flow induced vibrations of the cylinder. These vibrations, in turn, will cause significant changes in the drag forces as well as in the lift forces itself which initially caused the flow induced vibrations. This article develops a theory with which the drag and lift forces acting on vibrating cylinders can be predicted. The theory is based upon a simplified, hypothetical, two-dimensional wake model. The stipulated assumptions restrict the validity of the theory to small amplitude vibrations in the frequency range at which “lock-in” occurs, i.e. at which the vibration prescribes the vortex shedding frequency.