Showing papers on "Lift-induced drag published in 1972"

A Method for Reducing the Base Drag of Wings with Blunt Trailing Edge

Abstract: To study the possibilities of reducing the base drag of profiles with a blunt trailing edge, experiments were performed in two low-speed wind-tunnels at the DFVLR-AVA, Gottingen, some on models between walls and some on rectangular wings with an aspect ratio of 2.5. The results show that the mean base pressure can be increased, and so the base drag reduced, by using a special form of the blunt trailing edge. The variation of local base pressure along the span, and the way in which this variation is influenced by the form of the trailing edge, is also shown. Some results for the total drag and lift are also indicated.

On the Aerodynamics of Wake Vortices

Abstract: : The effect of wing span loading on the development of fully rolled up wing trailing vortices is discussed. It is shown that parabolic wing loadings produce potential flow maximum core rotary speeds which are finite and less than fifty percent of the downwash speeds at the plane of symmetry. The development of turbulent cores is analyzed and core growth is predicted to occur as the two thirds power of time whereas the peak velocities fall off as the inverse one third power. Axial flow effects of the wing profile drag and lifting system are shown to lead to axial jets on the vortex axis which may either follow the aircraft or exceed the free stream velocity depending on the ratio of profile drag to induced drag.

Aerodynamic effects of leading-edge serrations on a two-dimensional airfoil

Abstract: An investigation was conducted to determine the flow field and aerodynamic effects of leading-edge serrations on a two-dimensional airfoil at a Mach number of 0.13. The model was a NACA 66-012 airfoil section with a 0.76 m (30 in.) chord, 1.02 m (40 in.) span, and floor and end plates. It was mounted in the Ames 7- by 10-Foot Wind Tunnel. Serrated brass strips of various sizes and shapes were attached to the model in the region of the leading edge. Force and moment data, and photographs of tuft patterns and of oil flow patterns are presented. Results indicated that the smaller serrations, when properly placed on the airfoil, created vortices that increased maximum lift and angle of attack for maximum lift. The drag of the airfoil was not increased by these serrations at airfoil angles of attack near zero and was decreased at large angles of attack. Important parameters were serration size, position on the airfoil, and spacing between serrations.

Wind Load on Cylinder with Spanwise Protrusion

Abstract: Drag and lift forces for circular cylindrical bodies with two types of spanwise protrusions were measured in a wind tunnel in the transition range of Reynolds numbers (10 4 to 10 5 ), with the protrusion size varying from 0.004 to 0.006 of the cylinder diameter. The data show that the two protuberance shapes, a trip-wire and an overlap, are nearly identical in their effect on the aerodynamic characteristics, and that their effect depends much more on location than on size. It was found that the drag coefficient could vary by ±40% and that the lift coefficient could be as high as 0.7, depending on the location of the protuberance, or equivalently on the angle of attack. By using hot-wire anemometry to study the flow field, these significant variations in C D and C L were revealed to be associated with fundamental changes in the boundary-layer flow, caused by the interaction of the protrusion with the surrounding fluid motion.

Reduction of wave drag by antisymmetric arrangement of wings and bodies.

Abstract: The wave interference effects for bodies or wings in a mirror-symmetric arrangement, and in an antisymmetric arrangement are discussed. It is shown that while in the case of a mirror-symmetric arrangement large adverse interference effects can be observed, antisymmetric arrangements provide comparatively much smaller wave drags. The single continuous wing panels also adapt themselves more readily to varying angles of obliquity, and hence, to varying flight speeds. A detailed review is presented of the previous work on the aerodynamic properties and flight stability of oblique elliptic wing combinations. A possible mode of application of these combinations to transport aircraft operating at moderate supersonic speeds is suggested.

Drag characteristics of a disk-gap-band parachute with a nominal diameter of 1.65 meters at Mach numbers from 2.0 to 3.0

Abstract: Supersonic wind-tunnel tests were conducted with disk-gap-band parachute models having a nominal diameter of 165 meters and geometric porosities of 100, 125, and 150 percent Canopy inflation characteristics, angles of attack, and drag performance are presented for deployment behind forebody base extensions which were free to oscillate in pitch and yaw The effect of increasing suspension-line length on canopy motions and drag performance is included, and the drag performance of a model with 125 percent geometric porosity is compared with results from flight tests of a parachute with a nominal diameter of 1219 meters

Aerodynamic properties of spherical balloon wind sensors.

Abstract: First-order theory of fluctuating lift and drag coefficients for aerodynamically induced motions of rising and falling spherical balloon wind sensors

Two-Dimensional Subsonic Wind Tunnel Investigations of a Cambered 30- Percent Thick Circulation Control Airfoil

Abstract: : A relatively thick Circulation Control (CC) elliptic airfoil section with thickness-to-chord ratio of 030 and a circular arc camber of 15 percent at the midchord was tested subsonically to determine its aerodynamic properties as a midspan blade section on a blown helicopter rotor The two-dimensional tests established the section's ability to generate the required lift at low and negative incidence Lift coefficients up to 65 were produced at moderate momentum coefficient C sub mu equal to or less than 024 High drag of the unblown bluff ellipse was greatly reduced by the application of very moderate blowing, and equivalent efficiencies of 47 (including power required for blowing) were generated at C sub l approximately equal to 19 The section's performance was found to be heavily influnced by upper and lower aft surface flow separations, especially at the larger positive and negative angles of attack In addition, both low Reynolds number and an increase in slot height were detrimental to section lift capability Nevertheless, the ability to operate at high lift coefficients essentially independent of angle of attack, and with large lift augmentation for relatively low blowing, promises to provide an effective blade section for heavy lift application

Newtonian lift and drag of blunt-cone cylinder bodies.

Abstract: 5 Jones, R. T., "Theoretical Determination of the Minimum Drag of Airfoils at Supersonic Speeds," Journal of the Aeronautical Sciences, Vol. 19, No. 12, Dec. 1952, pp. 813-822. 6 Carmichael, R. L., Castellano, C. R., and Chen, C. F., "The Use of Finite Element Methods for Predicting the Aerodynamics of WingBody Combinations," Analytic Methods in Aircraft Aerodynamics, NASA SP 228, 1969, pp. 37-51. 7 Smith, J. H. B., "Lift/Drag Ratios of Optimized Slewed Elliptic Wings at Supersonic Speeds," The Aeronautical Quarterly, Vol. XII, Aug. 1961, pp. 201-218. 8 Jones, R. T., "Aerodynamic Design for Supersonic Speeds," Proceedings of the First International Congress in the Aeronautical Sciences, Advances in Aeronautical Sciences, Pergamon Press, New York, 1959, pp. 34-51. 9 Kuchemann, D., "Aircraft Shapes and Their Aerodynamics," Proceedings of the 2nd I.C.A.S., Advances in Aeronautical Sciences, Vol. 34, Pergamon Press, New York, 1962, pp. 221-252. 10 Holdaway, G. H. and Hatfield, E. W., "Transonic Investigation of Yawed Wings of Aspect Ratios 3 and 6 With a Sears-Haack Body and With Symmetrical and Asymmetrical Bodies Indented for a Mach Number of 1.2," RM A58C03, 1958, NACA. 11 Campbell, J. P. and Drake, H. M., "Investigation of Stability and Control Characteristics of an Airplane Model With Skewed Wing in the Langley Free-Flight Tunnel," TN 1208, 1947, NACA. 12 Lee, G. H., comments appended to Kuchemann, D., "Aircraft Shapes and Their Aerodynamics," Proceedings of the 2nd I.C.A.S. Advances in Aeronautical Sciences, Vol. 3-4, Pergamon Press, New York, 1962, pp. 221-252. 13 Lee, G. H., "Slewed Wing Supersonics," The Aeroplane, Vol. 100, March 1961, pp. 240-241.

Supersonic lifting systems

Abstract: The present invention relates to a method and apparatus for reducing the drag, and thereby increasing the ratio of lift/drag of supersonic wings above that achievable with conventional swept wings. The invention is characterized by the fact that the drag reduction is achieved as a result of a mutual interaction among multiple lifting surfaces in a manner which results in lower drag than is achieved by a single lifting surface at the same lift.

Exploratory investigation of factors affecting the wing tip vortex

Abstract: An investigation was conducted in the Langley full-scale tunnel to study some factors affecting the tip vortex of a wing. It was found that there was a pronounced effect of Reynolds number on the tip-vortex core size. An attempt was made to determine what aerodynamic parameters, such as lift, drag, or induced drag, influence the size of the vortex core, but no particular function of the parameters was found to be superior to all others. Various spoilers placed on the upper and lower surfaces of the wing to increase the boundary-layer thickness resulted in a reduction in the vorticity as determined from the tuft grid. Various solid objects placed in the vortex core downstream of the wing tip seemed to decrease the vorticity within the vortex core.

Wind-tunnel Investigation of Effects of Rear Upper Surface Modification on a NASA Supercritical Airfoil

Abstract: Wind tunnel tests were conducted at Mach numbers from 0.60 to 0.81 to examine the effects on supercritical airfoil of modifying the rear upper surface to reduce the magnitude of an intermediate off design second velocity peak. The modification was accomplished by increasing the upper surface curvature around the 50 percent chord station and reducing the curvature over approximately the rearmost 30 percent of the airfoil while maintaining the same trailing edge thickness.

Effect of nozzle lateral spacing on afterbody drag and performance of twin-jet afterbody models with convergent-divergent nozzles at Mach numbers up to 2.2

Abstract: Twin-jet afterbody models were investigated by using two balances to measure the thrust-minus-total drag and the afterbody drag, separately, at static conditions and at Mach numbers up to 2.2 for an angle of attack of 0 deg. Hinged-flap convergent-divergent nozzles were tested at subsonic-cruise- and maximum-afterburning-power settings with a high-pressure air system used to provide jet-total-pressure ratios up to 20. Two nozzle lateral spacings were studied, using afterbodies with similar interfairing shapes but with different longitudinal cross-sectional area distributions. Alternate, blunter, interfairings with different shapes for the two spacings, which produced afterbodies having identical cross-sectional area progressions corresponding to an axisymmetric minimum wave-drag configuration, were also tested. The results indicate that the wide-spaced configurations improved the flow field around the nozzles, thereby reducing drag on the cruise nozzles; however, the increased surface and projected cross-sectional areas caused an increase in afterbody drag. Except for a slight advantage with cruise nozzles at subsonic speeds, the wide-spaced configurations had the higher total drag at all other test conditions.

Transonic wall interference effects on bodies of revolution.

Abstract: Efforts to develop a near sonic transport have placed renewed emphasis on obtaining accurate aerodynamic force and pressure data in the near sonic speed range. Comparison of wind-tunnel and flight data obtained for a blunt-nose body of revolution showed significant discrepancies in drag levels near Mach 1 - apparently due to wind-tunnel wall interference. Subsequent tests of geometrically similar bodies of revolution showed that increasing the model-to-test-section blockage ratio from 0.00017 to 0.0043 resulted in altered drag curve shapes, delayed drag divergence, and 'transonic creep' from subsonic drag levels due to increased wall interference.

Effect of nozzle lateral spacing on afterbody drag and performance of twin-jet afterbody models with cone plug nozzles at Mach numbers up to 2.20

Abstract: Twin-jet afterbody models were investigated by using two balances to measure separately the thrust minus total drag and the afterbody drag at Mach numbers of 0.0 and 0.50 to 2.20 for a constant angle of attack of 0. Translating shroud cone plug nozzles were tested at dry and maximum afterburning power settings with a high-pressure air system used to provide jet total-pressure ratios up to 20.0. Two nozzle lateral spacings were studied by using afterbodies with several interfairing shapes. The close- and wide-spaced afterbodies had identical cross-sectional area distributions when similar interfairings were installed on each. Nozzle cant angles of -5, 0, and 5 degrees were investigated. The results show that the highest overall performance was generally obtained with the close-spaced afterbody, basic interfairings (no base), and uncanted nozzles.

Jet-Flapped Wings in Very Close Proximity to the Ground

Abstract: The method of matched asymptotic expansions is applied to the problem of jet-flapped wings of finite span in very close proximity to the ground. For the linearization of this problem, the order of small parameters, the angle of attack and jet deflection, are assumed to be smaller than the ratio of the ground clearance to the root chord. This linearized problem is solved as a direct problem represented by a source distribution on the upper surface of the wing and jet sheet with concentrated sources around the leading and side edges plus a separate confined channel flow region under the wing and jet sheet. The two-dimensional, jet-flapped airfoil is examined in detail, and the calculated lift coefficients lie within 5% of corresponding results by Lissaman.1 In the three-dimensional case, a simple analytic solution is obtained for a flat plate semi-elliptic wing with a straight trailing edge, zero angle of attack and uniform momentum distribution of the jet. Spanwise lift distributions and lift coefficients are derived and the distributions of the jet momentum are discussed for minimum induced drag.

Nacelle-airframe interference at low supersonic Mach numbers.

Abstract: The aerodynamic interference between the propulsion system and airframe for a low supersonic transport with wing-mounted nacelles is examined. Both a flowfield analysis and the equivalent body approach were used to predict the interference lift, drag, and pitching moment as functions of nacelle size, shape, and position. The results indicate that the interference lift and pitching moment, as well as drag, must be included in the analysis to properly assess the interference effects. In addition, the performance of the basic wing was found to play an important role in determining the effectiveness of the interference lift in reducing the net installation drag. Based on a conservative prediction, the interference effects can reduce the installed propulsion system drag to 40% of the isolated drag of the nacelles. Furthermore, including the interference effects in the optimization of the engine cycle from a thermodynamic and weight standpoint can result in a considerable reduction in the net propulsion system weight fraction (fuel plus engines) while increasing the optimum engine bypass ratio of a typical transport vehicle.

Lift and Drag Forces Due to Wave Action on Elevated Platforms

Abstract: The study was conducted for the purpose of describing lift and drag forces exerted upon a structure with plane vertical sides and a horizontal bottom by shallow water waves which approach the structure with normal incidence and pass beneath it. Results of the study are presented in graphical form. Some degree of generalization is achieved through the relation of dimensionless parameters, which contain physical quantities pertinent to the problem. The graphs show maximum and minimum relative values of lift force and values of drag force for various values of relative wave height, relative clearance, relative width of structure, and relative length of structure.

Wing of given volume with maximum lift/drag ratio in hypersonic flow

Abstract: Results are presented of the numerical solution of the problem of a triangular wing of given volume having maximum aerodynamic efficiency in hypersonic flow. In calculating the aerodynamic characteristics of lifting bodies in hypersonic viscous gas flow it is often assumed that the pressure coefficient on the surface of the body is given by the Newton law [1, 2], while the friction coefficient is constant. These assumptions make i t possible to formulate the variational problem of bodies with optimal characteristics as the problem of the extremal value of a functional which can be expressed explicitly. However, even for simple problems the Euler equations will be nonlinear partial differential equations whose solution can be obtained only in certain particular cases. Therefore the additional assumption is usually made that the wing is slender, which makes it possible to solve certain simple variational problems with the aid of the analytic methods. But this assumption restricts severely the class of permissible wing forms and does not permit obtaining a complete picture of the dependence of the aerodynamic characteristics of the optimal bodies on the various parameters. The numerical method of local variations [3], used in the following, makes it possible to solve certain variational problems without imposing any limitations on the relative dimensions of the wings. Let us assume that the pressure coefficient Cp on the ~,ing surface (Fig. 1) is given by the Newton law with a modifying factor N(M co), the friction Coefficient cj = const and the upper and lower surfaces of the wing are given by the respective functions Yi Y* (x, z) and Y2 = Y2( x, z). We use the dimensionless variables ~ = x/b0, = y /V • z = 2 z / l . Here b0, l, and V are, respectively, the width span, and volume of the wing. Then the wing drag and lift coefficients and the wing volume are given by the functions (bars over letters are dropped)