Showing papers on "Lift-induced drag published in 1974"

Feasibility study of the transonic biplane concept for transport aircraft application

Abstract: Investigations were conducted to evaluate the feasibility of a transonic biplane consisting of a forward-mounted swept-back lower wing, a rear-mounted swept-forward upper wing, and a vertical fin connecting the wings at their tips. This wing arrangement results in significant reductions in induced drag relative to a monoplane designed with the same span, and it allows for a constant-section fuselage shape while closely matching an ideal area distribution curve for M = 0.95 cruise. However, no significant reductions in ramp weight were achieved for the biplane relative to a monoplane with the same mission capability. Flutter analyses of the biplane revealed both symmetric and antisymmetric instabilities that occur well below the required flutter speed. Further studies will be required to determine if acceptable flutter speeds can be achieved through the elimination of the instabilities by passive means or by active controls. Configurations designed for other missions, especially those with lower Mach numbers and lower dynamic pressures, should be examined since the geometries suitable for those design constraints might avoid the weight penalties and flutter instabilities which prevent exploitation of induced drag benefits for the configuration studied.

Method and apparatus for controlling tip vortices

Abstract: A jet engine disposed at and preferably in front of the tip end of an airplane wing with exhaust flow intercepting and rotating counter to tip vortex flow to reduce vortex induced drag, the angle of rotation of exhaust flow being cyclically variable to dissipate the vortex flow. The tip engine assists in powering the aircraft.

Vehicle flow direction vanes

Abstract: Vehicle Flow Direction Vanes for reducing the rear vacuum induced drag on moving vehicles and thus increase mileage performance on the order of 20 percent. Aft, and forward, mounted flow direction vanes are attached to flat-back vehicles to deflect air flow into the drag producing reduced pressure area rearwardly of the vehicle. The basic shape of the vane is based upon the criteria that a line tangent to the curved surface at any point does not exceed an angle of 30° to the main airstream to avoid local separation.

Supercirculation effects induced by vectoring a partial-span rectangular jet

Abstract: Thrust-induced supercirculation effects from thrust vectoring have indicated a potential for not only increasing maneuverability of fighter aircraft but also as a means of improving cruise performance. The current study investigated a partial-span rectangular jet-exhaust nozzle located at the wing trailing edge that acts similar to a jet flap by increasing lift due to supercirculation. This paper summarizes experimental studies including the effects of nozzle deflection angle, wing camber, and nozzle shape and exit location on lift, drag and load distributions. The results indicate that significant increases in thrust-induced lift along with substantial decreases in drag are possible.

Inviscid drag at transonic speeds

Abstract: A systematic asymptotic expansion procedure is introduced into the Euler equations to obtain the transonic, small-disturbance potential equation and corresponding relation for the drag. The relation consists of an integral around any contour enclosing the body and an integral along all shocks contained within the contour. Interpretations are given for the origin of the pressure drag due to shock waves, lift, and wind-tunnel boundaries. Numerical procedures are discussed for evaluating these quantities from finite-difference relaxation calculations. Computed results are included for various contours, and results are compared with some experimental data.

Drag reduction obtained by rounding vertical corners on a box-shaped ground vehicle

Abstract: A box-shaped ground vehicle was used to simulate the aerodynamic drag of delivery vans, trucks, and motor homes. A coast-down method was used to define the drag of this vehicle in a configuration with all square corners and a modified configuration with the four vertical corners rounded. The tests ranged in velocity from 30 miles per hour to 65 miles per hour, and Reynolds numbers ranged from 4.4 x 1,000,000 to 1.0 x 10 to the 7th power based on vehicle length. The modified configuration showed a reduction in aerodynamic drag of about 40 percent as compared to the square cornered configuration.

Drag reductions obtained by modifying a box-shaped ground vehicle

Abstract: A box-shaped ground vehicle was used to simulate the aerodynamic drag of high volume transports, that is, delivery vans, trucks, or motor homes The coast-down technique was used to define the drag of the original vehicle, having all square corners, and several modifications of the vehicle Test velocities ranged up to 65 miles per hour, which provided maximum Reynolds numbers of 1 times 10 to the 7th power based on vehicle length One combination of modifications produced a reduction in aerodynamic drag of 61 percent as compared with the original square-cornered vehicle

An Analytical Study of the Effects of Jets Located More Than One Jet Diameter Above a Wing at Subsonic Speeds

Abstract: A procedure has been developed to calculate the effects of blowing two jets over a swept tapered wing at low subsonic speeds The algorithm used is based on a vortex lattice representation of the wing lifting surface and a line sink-source distribution to simulate the effects of the jet exhaust on the wing lift and drag The method is limited to those cases where the jet exhaust does not intersect or wash the wing The predictions of this relatively simple procedure are in remarkably good agreement with experimentally measured interference lift and interference induced drag

Subsonic and supersonic longitudinal stability and control characteristics of an aft tail fighter configuration with cambered and uncambered wings and uncambered fuselage

Abstract: An investigation has been made in the Mach number range from 0.20 to 2.16 to determine the longitudinal aerodynamic characteristics of a fighter airplane concept. The configuration concept employs a single fixed geometry inlet, a 50 deg leading-edge-angle clipped-arrow wing, a single large vertical tail, and low horizontal tails. The wing camber surface was optimized in drag due to lift and was designed to be self-trimming at Mach 1.40 and at a lift coefficient of 0.20. An uncambered or flat wing of the same planform and thickness ratio was also tested. However, for the present investigation, the fuselage was not cambered. Further tests should be made on a cambered fuselage version, which attempts to preserve the optimum wing loading on that part of the theoretical wing enclosed by the fuselage.

Two-Dimensional Subsonic Evaluation of a 15-Percent Thick Circulation Control Airfoil with Slots at Leading and Trailing Edges,

Abstract: : A 15-percent-thick circulation control elliptical airfoil section with slots at both leading and trailing edges for tangential blowing was evaluated in a subsonic wind tunnel to determine its potential for high-speed (300-400 knot) helicopter rotor systems. Fore-and-aft slot utilization were determined by local flow direction over the blade as it revolved around the azimuth. Aerodynamic performance was not affected by the addition of an unblown leading edge slot except beyond the usable positive angle of attack range where some loss in lift and increase in drag were noted. At equal plenum pressures, simultaneous blowing from the leading and trailing edges resulted in a decrease in lift, an increase in drag, and a more positive pitching moment than for trailing edge blowing alone. (Modified author abstract)

Theoretical prediction of thick wing and pylon-fuselage-fanpod-nacelle aerodynamic characteristics at subcritical speeds. Part 1: Theory and results

Abstract: The theoretical development and the comparison of results with data of a thick wing and pylon-fuselage-fanpod-nacelle analysis are presented. The analysis utilizes potential flow theory to compute the surface velocities and pressures, section lift and center of pressure, and the total configuration lift, moment, and vortex drag. The skin friction drag is also estimated in the analysis. The perturbation velocities induced by the wing and pylon, fuselage and fanpod, and nacelle are represented by source and vortex lattices, quadrilateral vortices, and source frustums, respectively. The strengths of these singularities are solved for simultaneously including all interference effects. The wing and pylon planforms, twists, cambers, and thickness distributions, and the fuselage and fanpod geometries can be arbitrary in shape, provided the surface gradients are smooth. The flow through nacelle is assumed to be axisymmetric. An axisymmetric center engine hub can also be included. The pylon and nacelle can be attached to the wing, fuselage, or fanpod.

Boundary-layer transition and displacement thickness effects on zero-lift drag of a series of power-law bodies at Mach 6

Abstract: Wave and skin-friction drag have been numerically calculated for a series of power-law bodies at a Mach number of 6 and Reynolds numbers, based on body length, from 1.5 million to 9.5 million. Pressure distributions were computed on the nose by the inverse method and on the body by the method of characteristics. These pressure distributions and the measured locations of boundary-layer transition were used in a nonsimilar-boundary-layer program to determine viscous effects. A coupled iterative approach between the boundary-layer and pressure-distribution programs was used to account for boundary-layer displacement-thickness effects. The calculated-drag coefficients compared well with previously obtained experimental data.

Comparisons of two-dimensional shock-expansion theory with experimental aerodynamic data for delta-planform wings at high supersonic speeds

Abstract: An investigation has been conducted to explore the potential for optimizing airfoil shape at high supersonic speeds by utilizing the two-dimensional shock-expansion method. Theoretical and experimental force and moment coefficients are compared for four delta-planform semispan wings having a leading-edge sweep angle of 65 deg and incorporating modified diamond airfoils with a thickness-chord ratio of 0.06. The wings differ only in airfoil maximum-thickness position and camber. The experimental data are obtained at Mach numbers of 3.95 and 4.63 and at a Reynolds number of 9.84 million per meter. A relatively simple method is developed for predicting, in terms of lift-drag ratio, the optimum modified diamond airfoil at high supersonic and hypersonic speeds.

Warping of delta wings for minimum drag

Abstract: A study was conducted of the possibility to use the results obtained by Bera (1974) in the design of wings of low drag. The case in which the wings are subjected to a given lift is investigated. The results of the study are presented in a number of graphs showing conical twist distributions, basic wing camber surfaces, optimum wing camber surfaces, and sample spanwise pressure distribution of basic and minimum drag shapes

The influence of wind shear on aerodynamic coefficients

Abstract: The purpose of this study is to investigate the influence of wind shear on the lift, drag, roll and yaw moments of a wing in a horizontal wind gradient at various elevations and roll angles. The models of wind shear considered are those proposed by Leurs (1973) for atmospheric flow over horizontally homogeneous and uniform terrain. A general series solution for the distribution of lift along the wing span following the method of Houghton and Brock (1970) is employed to compute the loads and moments on the airfoil. Results of the computations indicate that wind shear can have a significant effect on the rolling and yawing moments of the wing of an aircraft flying with one wing low in the atmospheric boundary layer. These moments are directly influenced by the magnitude of the wind gradient in the neutral atmosphere reflected by the magnitude of the friction velocity. The effect of wind shear on lift and drag is negligible. Stability of the atmosphere tends to increase the magnitude of the rolling moment while decreasing its variation with elevation.

Theoretical prediction of thick wing and pylon-fuselage-fanpod-nacelle aerodynamic characteristics at subcritical speeds. Part 2: Computer program description

Abstract: The procedures required to operate the thick wing and pylon-fuselage-fanpod-nacelle computer program are presented. The program computes surface velocities and pressure, section loads, and total configuration loads and pitching moment. Potential flow theory is used to compute the surface pressures and the associated lift, moment, and vortex drag. The skin friction drag is also computed.

Low Speed Wind Tunnel Test of Jet Flaps and Floating Wingtip Ailerons on a Fighter Wing.

Abstract: : An 18% scale semispan fighter wing was tested at low speed in various configurations to assess improvements in lift and roll control. A full span jet flap achieved a CL 14% higher than current aircraft. Floating wingtip ailerons provided undiminished roll control up through high angles of attack. Parameters measured were angle of attack, lift coefficient, drag coefficient, pitching moment, rolling moment, and yawing moment.

High Lift Characteristics of an Airfoil Placed in a Narrow Channel

Abstract: Aerodynamic characteristics of an airfoil moving in a narrow channel bounded by two parallel walls, i.e. ground and ceiling, are studied theoretically and experimentally. Lift acting on an airfoil at a positive attack angle increases as the airfoil approaches either ground orceiling. This study deals with the combination of ground and ceiling effects to realize a high lift wing. A theory is presented for the calculation of two-dimensional inviscid flow around an arbitrary airfoil placed in a narrow channel, using singularity method in which proper circulation is distributed directly on the airfoil contours. Sample calculation shows the influences of ground and ceiling on the lift and moment coefficients of the airfoil. Two-dimensional experiment is conducted to measure the pressure distribution of airfoil, from which lift and pressure drag coefficients are evaluated. Theoretical and experimental results are compared and the characteristics of this kind of high lift wings are discussed.

Use of a pitot-static probe for determining wing section drag in flight at Mach numbers from 0.5 to approximately 1.0

Abstract: The use of a pitot-static probe to determine wing section drag at speeds from Mach 0.5 to approximately 1.0 was evaluated in flight. The probe unit is described and operational problems are discussed. Typical wake profiles and wing section drag coefficients are presented. The data indicate that the pitot-static probe gave reliable results up to speeds of approximately 1.0.