Showing papers on "Lift-induced drag published in 1976"

A design approach and selected wind tunnel results at high subsonic speeds for wing-tip mounted winglets

Abstract: Winglets, which are small, nearly vertical, winglike surfaces, substantially reduce drag coefficients at lifting conditions. The primary winglet surfaces are rearward above the wing tips; secondary surfaces are forward below the wing tips. This report presents a discussion of the considerations involved in the design of the winglets; measured effects of these surfaces on the aerodynamic forces, moments, and loads for a representative first generation, narrow body jet transport wing; and a comparison of these effects with those for a wing tip extension which results in approximately the same increase in bending moment at the wing-fuselage juncture as did the addition of the winglets.

icle 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 DEG to the main airstream to avoid local separation

A vortex-lattice method for the mean camber shapes of trimmed noncoplanar planforms with minimum vortex drag

Abstract: A new subsonic method has been developed by which the mean camber surface can be determined for trimmed noncoplanar planforms with minimum vortex drag. This method uses a vortex lattice and overcomes previous difficulties with chord loading specification. A Trefftz plane analysis is utilized to determine the optimum span loading for minimum drag, then solved for the mean camber surface of the wing, which provides the required loading. Sensitivity studies, comparisons with other theories, and applications to configurations which include a tandem wing and a wing winglet combination have been made and are presented.

Theoretical determination of the minimum drag of airfoils at supersonic speeds

Abstract: A method is reported for determining mathematically the combined disturbance field, and in certain cases the minimum drag, of wings at supersonic speeds. The simplest analytic example is provided by the wing of elliptic planform, which achieves its minimum drag when the lift is distributed uniformly over the surface. With a symmetrical distribution of thickness, the requirement of minimum drag for a given total volume is found to lead to profiles of constant curvature.

Analysis of coast-down data to assess aerodynamic drag reduction on full-scale tractor-trailer trucks in windy environments

Abstract: A data reduction procedure is presented and successfully used to analyze coastdown data obtained in a windy environment to provide a measure of the aerodynamic drag on a full-scale tractor-trailer combination as a function of the yaw angle of the vehicle. Comparison with wind tunnel measurements suggests that the wind-tunnel provides a reasonable simulation of the effects of winds on vehicle drag. The highest drag reductions that were measured in the presence of winds were obtained with a streamlined fairing/gap seal combination. /GMRL/

Numerical method to calculate the induced drag or optimum loading for arbitrary non-planar aircraft

Abstract: A simple unified numerical method applicable to non-planar subsonic aircraft has been developed for calculating either the induced drag for an arbitrary loading or the optimum aircraft loading which results in minimum induced drag. The method utilizes a vortex lattice representation of the aircraft lifting surfaces coupled with the classic equations and theorems for computing and minimizing induced drag. Correlation of results from the numerical method with non-planar solutions obtained from other more complex theories indicates very good agreement. Comparison of the induced-drag computations using the numerical method with experimental data for planar and non-planar configurations was also very good.

Airfoil Section Drag Reduction at Transonic Speeds by Numerical Optimization

Abstract: A practical procedure for the design of low drag, transonic airfoils is demonstrated. The procedure uses an optimization program, based on a gradient algorithm coupled with an aerodynamic analysis program, that solves the full, non-linear potential equation for transonic flow. The procedure is useful for the design of retrofit modifications for drag reduction of existing aircraft as well as for the design of low drag profiles for new aircraft. Results are presented for the modification of four different airfoils to decrease the drag at a given transonic Mach number.

Design and Analysis of Winglets for Military Aircraft

Abstract: : A study of the design and analysis on winglets for military Aircraft has been completed. The program consisted of investigating analytically winglet concepts for application to the KC-135 and C-141 designing and building winglets for an 0.035 and 0.070 scale model KC-135, and conducting a structural feasibility investigation of the winglet installation on the KC-135. The analysis of the winglets showed a 14% reduction in induced drag for the KC-135 and a 11% reduction for the C-141. The structural design study of the KC-135A winglet installation estimated a 592 lb weight increase. An 8.4% improvement was estimated in M(L/D) sub MAX and an 8.1% improvement in range factor for the KC- 135A. An 0.070 scale half span KC-135 wind tunnel model has been tested in the NASA 8 Ft Transonic Tunnel. Preliminary unpublished test data have substantiated the analytical procedures used by The Boeing Company to determine the aerodynamic characteristics and performance benefits from winglets on the KC-135 aircraft.

Drag reducer for lift surface of aircraft

Abstract: One or more aerodynamic bodies of preselected shape and placement are employed on the lower surface of an aircraft wing or other aerodynamic lifting surface for the purpose of reducing its drag. These anti-drag bodies singly or collectively provide a reduction in the lower speed profile drag of the associated lifting surface, an increase in its lift at a given angle of attack, and an increase in its critical Mach number.

Aerodynamic Design of a Mach 2.2 Supersonic Cruise Aircraft

Abstract: The McDonnell Douglas Corporation has conducted numerous Mach 2.2 supersonic aircraft design and in- tegration studies in support of the NASA Supersonic Cruise Aircraft Research (SCAR) program. This program traces the evolution of a baseline study configuration and an improved performance configuration through several aerodynamic design and trade study cycles. The impact of real-world constraints on configuration design is discussed. Previous studies have not addressed the Mach 2.2 cruise design condition and this work has resulted in a structurally feasible configuration capable of achieving £/D's in excess of 9 at this cruise Mach number. The purpose of this paper is to present the resulting design and wind-tunnel test results for two configurations. The wind-tunnel test results are compared to the analysis methods. N 1972, interest was renewed both at NASA and in the industry in conducting technology assessment studies on supersonic cruise aircraft. The NASA Supersonic Cruise Aircraft Research (SCAR) program emerged late in 1972, charged with the task of identifying, through aircraft design studies, key technologies whose pursuit would lead to im- proved aerodynamic efficiency, reduced operating costs, and environmental compatibility for typical next-generation supersonic cruise configurations. McDonnell Douglas (MDC) reassessed the entire spectrum of supersonic travel beginning with a market analysis and a review of technology available at various design Mach numbers. Results of these preliminary design studies indicated that a 273-passenger, Mach 2.2 aircraft offered the best mix of low operating costs, productivity, near-term technology materials, and reduced program risk for typical supersonic transport con- figurations. 1 Using this as a starting point, McDonnell Douglas conducted numerous aerodynamic studies, trade studies, and sizing studies in support of the SCAR program.2'3 A baseline study configuration, shown in Fig. 1, emerged, which was a structurally feasible arrow-wing configuration promising good cruise L/D's. Subsequent studies indicated that improved performance was available through wings optimized to reduce configuration trim drag. In 1975, a cooperative MDC-NASA wind-tunnel test program was conducted in which the performance of the study baseline configuration and an improved-perf ormance configuration was substantiated, and the analytical techniques used in their design were validated. Methods of Analysis The primary analytical tools used in the aerodynamic design and analysis of the McDonnell Douglas advanced supersonic cruise aircraft configuration have been the Woodward program4 and the Douglas Arbitrary Body Wave Drag Program.5 The McDonnell Douglas version of the Woodward program has been extensively modified to im- prove its versatility. In the SCAR studies it was used in both the inverse (optimization) and direct (analysis) modes. Wings were designed by optimizing the wing camber distributions for minimum drag due to lift at specified CL's, with and without specified pitching moments. Wings were primarily optimized as wings alone extended to the fuselage centerline, but some optimizations were done in the presence of the fuselage. Drag due to lift and wing-body pitching moments were computed by direct analysis of wing-body combinations including wing thickness effects. Wing panels were spaced equally spanwise and chordwise on both wings alone and wings exterior to the fuselage. All wings were represented by 9 spanwise and 12 chordwise panels, which is sufficient for converged solutions. Biquadratic interpolation was used to determine exterior wing camber distributions from wing-alone optimizations, and vice versa. A typical Woodward wing-body paneling scheme is shown in Fig. 2. Although not depicted on Fig. 2, the Woodward program was used in the full configuration mode to calculate wing-body pitching moments, including the ef- fects of forebody lift. Configuration zero-lift wave drag was calculated using the McDonnell Douglas-developed Arbitrary Body Wave Drag Program which calculates, based on the area rule theory,6'7 the wave drag of completely arbitrary configurations. All analyses were performed on full wing-body and wing-body- nacelle configurations at their cruise attitudes. While the program can accept cambered fuselages with exact cross sections, it has been determined that cambered fuselages with

A lifting surface theory for the analysis of nonplanar lifting systems

Abstract: A new nonlinear, nonplanar lifting surface theory is presented. The method is regarded as a lifting surface theory in that the effects of wing thickness are neglected, but none of the usual small perturbation assumptions inherent in most other lifting surface theories are made. The method represents nonplanar lifting systems by distributed vorticity, including the leading edge singular behavior characteristic of thin wings. The method is well suited to the computation of induced drag of nonplanar systems because leading edge suction is calculated from the leading edge singularity. The method has been used to compute the induced drag benefit of winglets (vortex diffusers), and the agreement with NASA experimental data is excellent.

Aircraft aerodynamic design and evaluation methods

Abstract: This paper presents some practical methods for the aerodynamic design and evaluation of conventional aircraft. High-lift methodology which provides improved takeoff and landing and transonic maneuvering performance is discussed. Also, new techniques for estimating and minimizing cruise pressure drag are presented. These include a far-field theory to minimize trimmed induced drag, theories to estimate the spanwise variation of drag due to thickness and lift, and a far-field theory to estimate total pressure drag. In addition to the description of methods, aerodynamic design procedures are outlined and results from both the design and evaluation methods are presented.

The Body Shape of Minimum Drag

Abstract: After a short review of the work done in the past to reduce the aerodynamic drag of a body moving in the vicinity of the ground, a new theoretical method is developed in order to determine the shape of the body when a certain lift distribution is imposed. Considerations on the induced drag suggest that the total lift is zero as also should be zero the pitching moment for stability reasons. These conditions together with that of gradual variation of the area and shape of the cross sections of the body lead to the determination of the basic shape of the body. A model was realized and tested on the Pin infarina wind tunnel. /GMRL/

Optimization and design of three-dimensional aerodynamic configurations of arbitrary shape by a vortex lattice method

Abstract: A new method based on vortex lattice theory has been developed which can be applied to the combined analysis, induced drag optimization, and aerodynamic design of three-dimensional configurations of arbitrary shape. Geometric and aerodynamic constraints can be imposed on both the optimization and the design process. The method is compared with several known analytical solutions and is applied to several different design and optimization problems, including formation flight and wingtip fins for the Boeing KC-135 tanker airplane. Good agreement has been observed between the theoretical predictions and the wind tunnel test results for the KC-135 modification.

Applications of vortex lattice theory to preliminary aerodynamic design

Abstract: Some applications of the vortex-lattice theory to the preliminary aerodynamic design and analysis of subsonic aircraft were presented. These methods include the Rockwell-Tulinius vortex-lattice theory for estimating aerodynamic characteristics, a Trefftz plane optimization procedure for determining the span loads for minimum induced drag, and a modification of the Trefftz plane procedure to estimate the induced drag for specified span loads. The first two methods are used to aerodynamically design aircraft planforms, twists, and cambers, and the latter method is used to estimate the drag for components such as flaps and control surfaces. Results from the theories for predicting lift and pitching moment, drag due to lift, and the drag of control surfaces are compared with experimental data. This data was obtained on a general aviation model with flaps and a close-coupled canard-wing model.

U.S. Army Helicopter Design Datcom Volume 1. Airfoils

Abstract: : This report contains airfoil data of interest for rotor applications. The data is presented in the form of lift, drag, and pitching moment coefficients and, in most cases, it covers the complete Mach number range from low subsonic to supercritical flow conditions. An introductory section presents airfoil data trends and information pertaining to the source and usefulness of such data.

A wing-jet interaction theory for USB configurations

Abstract: The aerodynamic interaction between the wing and an inviscid upper-surface blowing (USB) thick jet with Mach number nonuniformity is treated within the framework of a linear inviscid subsonic compressible flow theory. A two-vortex-sheet model for the jet surface is used to represent the induced flowfields inside and outside the jet. Comparison of the predicted results with experimental data shows good agreement in lift, induced drag, and pitching moment. It is shown that the thin jet flap theory is inadequate for USB configurations with thick jet.

Challenge to advanced technology transport aircraft systems

Abstract: From the point of view of providing a potential for improved economic performance, six areas of advancing technology are particularly significant: supercritical aerodynamics, friction drag reduction, induced drag reduction, active controls, composite materials, and improved specific fuel consumption. Some potential solutions for future all-new advanced technology transport systems are examined.

Experimental effects of fuselage camber on longitudinal aerodynamic characteristics of a series of wing-fuselage configurations at a Mach number of 1.41

Abstract: An experimental investigation was conducted to evaluate a method for the integration of a fighter-type fuselage with a theoretical wing to preserve desirable wing aerodynamic characteristics for efficient maneuvering. The investigation was conducted by using semispan wing fuselage models mounted on a splitter plate. The models were tested through an angle of attack range at a Mach number of 1.41. The wing had a leading edge sweep angle of 50 deg and an aspect ratio of 2.76; the wing camber surface was designed for minimum drag due to lift and was to be self trimming at a lift coefficient of 0.2 and at a Mach number of 1.40. A series of five fuselages of various camber was tested on the wing.

Minimum induced drag of ground effect wings

Abstract: Kida and Miyai's theory, which treats theoretically the problem of the minimum induced drag of nonplanar ground effect wings, is refined and extended. The gap clearance between the wing tip and the ground is assumed to be so small that the method of matched asymptotic expansions may be used. Except for this restriction, this method has a remarkable flexibility in wing front-view geometry. The theory is applied to some typical cases such as semielliptic, rectangular, and triangular ground effect wings over flat surface and a flat plate in a rectangular guide way. Special attention is concentrated on the two limiting cases with very high and low front views. Kida and Miyai's errors are corrected.

Advanced airfoil design empirically based transonic aircraft drag buildup technique

Abstract: To systematically investigate the potential of advanced airfoils in advance preliminary design studies, empirical relationships were derived, based on available wind tunnel test data, through which total drag is determined recognizing all major aircraft geometric variables. This technique recognizes a single design lift coefficient and Mach number for each aircraft. Using this technique drag polars are derived for all Mach numbers up to MDesign + 0.05 and lift coefficients -0.40 to +0.20 from CLDesign.

Cruise aerodynamics of USB nacelle/wing geometric variations

Abstract: Experimental results are presented on aerodynamic effects of geometric variations in upper surface blown nacelle configurations at high speed cruise conditions. Test data include both force and pressure measurements on two and three dimensional models powered by upper surface blowing nacelles of varying geometries. Experimental results are provided on variations in nozzle aspect ratio, nozzle boattail angle, and multiple nacelle installations. The nacelles are ranked according to aerodynamic drag penalties as well as overall installed drag penalties. Sample effects and correlations are shown for data obtained with the pressure model.

Minimum trim drag design for interfering lifting surfaces using vortex-lattice methodology

Abstract: A new method has been developed by which the mean camber surface can be determined for trimmed noncoplanar planforms with minimum vortex drag under subsonic conditions. The method uses a vortex lattice and overcomes previous difficulties with chord loading specification; it uses a Trefftz plane analysis to determine the optimum span loading for minimum drag, then solves for the mean camber surface of the wing which will provide the required loading. Pitching-moment or root-bending-moment constraints can be employed as well at the design lift coefficient. Sensitivity studies of vortex-lattice arrangement have been made with this method and are presented. Comparisons with other theories show generally good agreement. The versatility of the method is demonstrated by applying it to (1) isolated wings, (2) wing-canard configurations, (3) a tandem wing, and (4) a wing-winglet configuration.

A linearized theory method of constrained optimization for supersonic cruise wing design

Abstract: A linearized theory wing design and optimization procedure which allows physical realism and practical considerations to be imposed as constraints on the optimum (least drag due to lift) solution is discussed and examples of application are presented. In addition to the usual constraints on lift and pitching moment, constraints are imposed on wing surface ordinates and wing upper surface pressure levels and gradients. The design procedure also provides the capability of including directly in the optimization process the effects of other aircraft components such as a fuselage, canards, and nacelles.

Low froude number hydrodynamic performance of a flat plate hydrofoil

Abstract: Results of towing tank experiments are presented for lift, drag, moment, and center of pressure of an aspect ratio 4, rectangular planform, 5.21% thick, flat plate hydrofoil attached to a large strut and pod and operated beneath the free surface of water. The nominal range of the chord Froude number was 0.5 to 3.5 with corresponding chord Reynolds numbers of 740,000-5,200,000. Tests included foil submergence depths ranging from 0.25 to 3.5 chord lengths, and foil angles of attack varying from 0 -8 deg. These data fill an important gap in our experimental knowledge of near-surface, low speed hydrofoil performance. Experiments indicate that there are significant changes in lift and drag for operation at shallow and moderate submergences in the low chord Froude number range, especially around 0.75 to 1.5. Prediction of residual drag coefficients for an 18-foot-chord hydrofoil operating at constant lift shows that the wavemaking drag is significant and that the trend of increase in residual drag at froude numbers ranging from 3.5 down to 1.75 appears to be roughly parallel to the trend of induced drag alone. However, the magnitudes of residual drag coefficients are rather large, and there are indications that interference wave drag, due to the presence of a strut and a pod, is an important feature of the low speed drag variation.

A Parametric Analysis of Winglet Effects.

Abstract: : A two part study was undertaken. In the first part, winglet effects were examined on a variety of wing planforms. A nonplaner lifting surface computer program was used to calculate aerodynamic coefficients including lift, induced drag, wing pitching moment, and wing root bending moment coefficients. Typical cruise flight conditions were examined and the coefficients calculated for the wing alone were compared to those obtained for the wing with winglets installed. The calculations were then repeated as the wing aspect ratio, sweep angle, and dihedral angle were varied. Winglet size and orientation remained constant. The percentage induced drag reduction was found to be the greatest on the wing with the highest aspect ratio and wing sweep angle (27.5% for an aspect ratio 7, 45 degree swept wing). Percentage induced drag reduction increased slightly with increasing positive dihedral angle. The greatest incremental drag reduction occurred with the lowest aspect ratio, highest swept wing. The second study examined the effects of winglet cant angle on induced drag reduction. Winglet cant angle on two separate wings was varied from -3 degrees to +3 degrees in an attempt to find an optimum value. The model used in this analysis ignored viscous effects and indicated that positive cant angles (leading edge inboard yielded the greatest reductions in induced drag. (Author)