Showing papers on "Lift-induced drag published in 1970"

An analytic solution for two- and three-dimensional wings in ground effect

Abstract: : The method of matched asymptotic expansions is applied to the problem of a ram wing of finite span in very close proximity to the ground. The general lifting surface problem is shown to be a direct problem, represented by a source-sink distribution on the upper surface of the wing and wake, with concentrated sources around the leading and side edges plus a separate confined channel flow region under the wing and wake. The two-dimensional flat plate airfoil is examined in detail and results for upper and lower surface pressure distribution and lift coefficient are compared with a numerical solution. A simple analytic solution is obtained for a flat wing with a straight trailing edge which has minimum induced drag. To lowest order, this optimally loaded wing is an elliptical wing with a lift distribution which is linear along the chord. The resultant total spanwise lift distribution is parabolic. An expression for the lift coefficient at small clearance and angle of attack, valid for moderate aspect ratio, is derived. The analytic results are compared with numerical results from lifting surface theory for a wing in ground effect; reasonable agreement is obtained. (Author)

Some Trim Drag Considerations for Maneuvering Aircraft

Abstract: The results of a preliminary analytical and experimental study of trim drag characteristics at maneuvering lift coefficients have been summarized. The study included aft-tail configurations at subsonic and supersonic speeds and canard configurations at subsonic speeds. It is shown that the tail load required to minimize trim drag is highly dependent on the wingbody drag-due-to-lift characteristics with examples presented for both the full and zero leading-edge suction cases. For the high drag case (corresponding to zero leading-edge suction), which tends to be typical at high maneuvering lift coefficients and high speeds, rather large uploads on the tail are required to reduce the trim drag problem. The analytical predictions of trim drag characteristics compare well with the experiment for the aft-tail configuration. At supersonic speeds, reductions in down tail load required to trim, obtained by increasing tail volume and thereby allowing a favorable rebalancing of the aircraft, result in relatively large reductions in trim drag for aft-tail configurations. At subsonic speeds, the experimental studies for the canard configuration exhibit considerably higher trim drag than the analytical prediction as a result of canard stall.

Two Dimensional Subsonic Wind Tunnel Tests on a 20 Percent Thick, 5 Percent Cambered Circulation Control Airfoil

Abstract: : An experimental program was undertaken to develop circulation control, high lift airfoils for rotary wing vehicle application. The basic method used to eject a thin jet sheet of air tangentially over the rounded trailing edge of a thick airfoil, usually of modified elliptic cross section. The jet sheet remains attached to the rounded trailing edge, separating, eventually, on the underside. The report presents results for cambered ellipse. Lift, drag and section equivalent lift-drag ratio data are presented which indicate that this model is one of the most efficient high lift airfoils yet tested.

Slotted diffuser system for reducing aircraft induced drag

Abstract: A wing assembly for increasing lift and reducing drag is disclosed comprising (1) an inboard conventional primary wing panel, and (2) an outboard secondary wing panel which is aftswept and comprised of a cascade of airfoil elements. The inboard panel is provided with a constant lift distribution which is dropped sharply at the knee or juncture with the outer panel, shedding a substantially concentrated vortex at the knee rather than at the wing tip. The sweep of the outer panel deflects the flow carrying this vorticity outboard, and its cascade airfoil elements then operate in the upflow outboard thereof. The cascade elements of the outer panel are stacked vertically above to the rear, so that the vorticity shed from each element generates a spanwash providing an incremental lift and thrust on the next element aft and above, which, in turn, because of its sweep deflects the vorticity underneath outboard, providing a greater effective span. The cascade splits the vortex into a vertical stack of vortex sheets, which laminate into an expanded size, slowly turning vortex core. The energy and corresponding induced drag of the vortex pair shed from this improved wing assembly is less because the vortex cores are (a) expanded, and (b) displaced outboard.

On the Minimum Induced Drag of Ground-Effect Wings

Abstract: An approximate theory, which yields the minimum induced drag of a planar wing with end-plates in ground effect, is presented. As a check on the accuracy of the method, it is compared with the exact linearised theory in the case of end-plates of vanishing depth (planar configuration). This shows that, within the limitations of the linearised lifting-surface theory, the present method is accurate in the range of wing heights of interest. In Section 5 the theory is compared with experiment. In this comparison two interpretations of the theory are employed. The first assumes that the vortex trace is the projection of the trailing edge of the configuration onto a plane normal to the direction of motion when the wing incidence is zero. The second is different from this only in that no constraint is placed on the wing incidence. Of the two interpretations the first is found to be in better agreement with experiment than the second for the planar configuration. However, the opposite is found to be true when end-plates of sufficient depth are fitted. A reason for this is proposed in Section 5.

Optimum lift-drag ratio for a ram wing tube vehicle

Abstract: Munk's theorem specifying the downwash condition for minimum drag is generalized to include lifting surfaces operating in proximity to solid boundaries. A simple method for finding the optimum lift distribution on a wing above an infinite flat plane is developed. The optimum configuration for a ram wing in a tube is found, and by means of a simple transformation this is mapped into the previously obtained solution for a wing in ground effect. An expression for the induced power required is calculated, and it is shown that there is a favorable effect on this requirement for the case of tube vehicles which have significant blockage ratios. Experimental results are presented which demonstrate that at very small clearances the theory must be modified to include viscous effects, and because of these effects ram wings in tubes usually have lower induced power requirements than the inviscid theory would indicate. Nomenclature AR = aspect ratio A t = cross-sectional area of tube b = wing span = vehicle width Cof — induced drag coefficient CL = lift coefficient Di = induced drag F = volume flux

Study of modification of rotor tip vortex by aerodynamic means

Abstract: : Numerous research efforts have been conducted by different investigators to alter the characteristics of the tip vortex generated by a helicopter blade in order to alleviate the blade-vortex interaction problem as well as the noise problem associated with impulsive loading. The analytical investigation shows that it should be possible to significantly alter the characteristics of the trailing tip vortex for all flight conditions in a beneficial manner by injecting an airstream directly into the forming tip vortex. Analytical expressions were developed for the initial and final states of the vortex in order to evaluate the effects of mass flow injection on the vortex strength, swirl velocity distribution, vortex core pressure, vortex core size and the induced drag on the blade. On the basis of the results that were obtained, it was shown that the required mass flow may be obtained from centrifugal pumping action by venting the blade and therefore the desired modification can be obtained apparently without significant performance penalties which would be unacceptable. (Author)

Effects of ground proximity on the longitudinal aerodynamic characteristics of an unswept aspect-ratio-10 wing

Abstract: Ground proximity effects of unswept aspect ratio 10 wing on longitudinal aerodynamic characteristics

The use of aerodynamic lift for application to high speed ground transportation

Abstract: The problem of a wing flying in very close proximity to a solid boundary, the so-called 'ram wing,' is reviewed and a new solution is found using the method of matched asymptotic expansions. The effect of the wing upper and lower surface coordinates on the resulting pressure distribution is shown explicitly for the case of a two-dimensional airfoil. It is shown that for very small clearance ratios a very simple expression is valid for the lift coefficient. On the basis of this simplification on analytic solution is obtained for the case of a flat-plate airfoil operating above a sinusoidal ground plane, which gives the forces and moments due to ground bumps. The longitudinal dynamics of a tracked vehicle designed to utilize aerodynamic lift are then investigated. Attention is focused on the case in which the vehicle body is a lifting surface operating in a rectangular guideway. It is found that, as with an airplane, a single wing gives unacceptable stability characteristics and some kind of stabilizing surface is required. Sample calculations are made for the case of a vehicle with a canard which show that adequate ride quality may be obtained with a reasonably smooth guideway. Some of these ideas are extended to three dimensions. An analytic solution is obtained for the case of a flat elliptical wing with a straight trailing edge which has the minimum induced drag for a given lift. A similar solution is obtained for the case of a wing in a tube. (Author)

Effect of Rotor Blade Root Cutout on Vertical Drag

Abstract: : Tests were conducted to determine the effect of rotor blade root cutout on the vertical drag of winged rotorcraft. Rotor thrust and torque were measured on isolated model rotors with blade root cutouts of 10 and 50 percent radius and were compared to the values obtained when a model fuselage and wings of three different planform areas were located below the rotor disc. Vertical drag was recorded on all airframe configurations with both sets of root cutout blades. The test data revealed a decrease in vertical drag for all airframe configurations when tested with the blades having 50 percent root cutout. The largest vertical drag reduction was measured for a small wing located high on the fuselage. The 4 percent figure of merit penalty due to 50 percent blade root cutout of the isolated rotor was diminished to 2 to 3 percent for most conditions when the reduction in vertical drag was taken into consideration.

Aerodynamic characteristics of a large-scale model with a lift fan mounted in a 5 per cent thick triangular wing, including the effects of BLC on the lift fan inlet

Abstract: Aerodynamic characteristics of large-scale model with lift fan mounted in 5 percent thick triangular wing

Theoretical investigation of the lift and drag characteristics of flexible parawings at subsonic speeds

Abstract: A theoretical analysis supplemented with an experimental program has been conducted to determine the lift and drag characteristics of NASA-type parawings. The results of the experimental program showed that the flowfield at a given spanwise station is nearly two-dimensional and that the aerodynamic characteristics of a parawing are similar to those of a conventional wing. As a consequence, it was concluded that the lifting-line theory for conventional wings should yield a suitable prediction for parawing aerodynamics even though the parawings have low aspect ratios. Thus, lifting-line theory was applied to several parawing configurations to determine the lift, induced drag, center of pressure, etc. The skin-friction drag was estimated so that the total drag as well as the lift-to-drag ratios could be calculated. Comparison of theory and experiment indicates that the lifting line theory provides an adequate estimate of parawing aerodynamics within the linear range of the lift curve. In addition, a technique based on the center of pressure results has been devised to predict the angle-of-attack at which trailing edge nutter begins.

Lifting Line Theory of a Wing in Uniform Shear Flow

Abstract: In the axial type fans and compressors, the velocity distribution relative to the blades is generally not uniform. Therefore, in the practical applications, it is important to find the characteristics of the wing in non-uniform flow. In this investigation, the characteristics of a finite large aspect ratio wing in uniform shear flow with the velocity varying in the spanwise direction are analyzed by the singularity method which is different from the method adopted by von Karman and Tsien. As the result, the characteristics of arbitrary wings are obtained concretely, and, at the same time, the physical difference between the characteristics of wings in uniform shear flow and those in uniform potential flow is clarified. Furthermore, the wing planform and its aerodynamic forces satisfying the condition of the minimum induced drag are given analytically.

Drag and Performance of Several Aerodynamic Decelerators at Mach Number 8.

Abstract: : An experimental investigation was conducted at Mach number 8 and at simulated pressure altitudes ranging from 130,000 to 145,000 ft to determine the drag, stability, and performance of flexible aerodynamic decelators located in the wake of a strut-mounted cone forebody. The investigation was conducted at temperatures below and above that required to prevent air liquefaction in the wind tunnel test section because many of the decelerators were designed to withstand only the lower temperature. Data are presented which show an increase in drag coefficient with increasing trailing distance (x/D or approx. = 3.5. Wake convergence was generally noted to coincide with a significant increase in decelerator drag with increasing trailing distance or with decreasing pressure altitude. Wake pressure and total temperature survey data are presented which show the symmetrical nature of the wake and the effects of the forebody mounting struts as well as operation below the air liquefaction temperature. (Author)