Showing papers on "Lift-induced drag published in 1977"

Optimization of Flexible Wing Structures Subject to Strength and Induced Drag Constraints

Abstract: An optimization procedure for designing wing structures subject to stress, strain, and drag constraints is presented. The optimization method utilizes an extended penalty function formulation for converting the constrained problem into a series of unconstrained ones. Newton's method is used to solve the unconstrained problems. An iterative analysis procedure is used to obtain the displacements of the wing structure including the effects of load redistribution due to the flexibility of the structure. The induced drag is calculated from the lift distribution. Approximate expressions for the constraints used during major portions of the optimization process enhance the efficiency of the procedure. A typical fighter wing is used to demonstrate the procedure. Aluminum and composite material designs are obtained. The tradeoff between weight savings and drag reduction is investigated.

The use of wing tip sails to reduce vortex drag

Abstract: Windtunnel measurements of the flow around the tip tanks of a model of a Morane-Soulnier Paris aircraft have been used to design cambered and twisted auxiliary surfaces, each only 0.4% to 0.6% of the wing area, which unwound the tip vortices formed at incidence and in so doing experienced a thrust, effectively reducing the vortex drag. Flight tests on a Paris aircraft showed that three such sails per tip tank increased the effective aspect ratio of the wing by over 40%. The increase in the overall lift-drag ratio at a lift coefficient of 0.35 was 21% and the maximum lift-drag ratio increased from 12.5 to 15.8. More recent windtunnel tests have shown that sails have a similar effect when fitted to plain wing tips. The results suggest that three or four sails spiralled round the rear half of each wing tip will give best results. These encouraging results suggest that far more windtunnel, flight and design work should be done to realise the potential savings in drag and fuel. Starting in 1946 as the College of Aeronautics, the Cranfield Institute of Technology was granted university status in 1969. In 1993 it changed its name to Cranfield University.

Minimum drag wing configuration for aircraft operating at transonic speeds

Abstract: A wing extension or tip fin is disclosed wherein the tip fin is joined to an aircraft wing to form a nonplanar wing configuration which minimizes induced drag during both low speed and high speed operation of an aircraft. The tip fin which is of generally trapezoidal geometry, extends streamwise along the end of the aircraft wing and is canted to project upwardly and outwardly therefrom. Additionally, the tip fin is twisted to toe-out relative to the freestream direction with the angle of twist varying along the lower portion of the tip fin length. Viewed from the side, the tip fin has a sweep angle at least equal to the sweep angle of the aircraft wings with the leading edge of the tip fin intersecting the wing tip chord at a position aft of the wing leading edge. A strake which extends along the upper surface of the wing from the wing leading edge to the tip fin leading edge, forms a smooth transition between the wing and tip fin. To provide maximum aerodynamic efficiency, the length and cant angle of the tip fin are established to reduce the induced drag of the wing-tip fin combination below that exhibited by the wing alone or by a conventional wing of area and span equivalent to that of the combined wing-tip fin. Interference and compressibility drag of the combined wing-tip fin is minimized by controlling the chordwise position of the tip fin and by the strake which not only provides an aerodynamically smooth wing to tip fin transition, but establishes a vortical flow pattern that maintains boundary layer attachment under high speed flight conditions. Further, the area of the tip fin is established for minimum profile drag, the variation in tip fin thickness ratio further minimizing interference drag and the tip fin twist compensates for spanwise loading on the wing to reduce induced drag.

Optimal Flight-Path-Angle Transitions in Minimum-Time Airplane Climbs

Abstract: If dependence of drag D on lift L is suppressed by calculating the induced drag corresponding to L weight W, the minimum-time climb path, obtained either by the energy state analysis or by Green's Theorem, leads, as is well known, to discontinuities in the flight-path angle 7. This requires, of course, an unreasonable increase in lift, positive or negative! If the reciprocal of maximum L/D is treated as a small parameter e, dependent on Mach number, a more complete analysis reveals that the discontinuities in 7 are replaced by transitional "boundary layers" on time scales of order e l / 2 , during which L/D is of order e ~ //: rather than e ~.

Reduced drag airfoil platforms

Abstract: A flow directing apparatus for use in an axial flow turbomachine is disclosed. Techniques for reducing aerodynamic drag along the walls of the flow directing apparatus are developed. In one embodiment, rotor blades have multiplanar platform surfaces which reduce aerodynamic drag pressure losses at the interface between each blade platform and the adjacent structure.

An overview of concepts for aircraft drag reductions

Abstract: A current overview of aerodynamic drag reduction concepts which have potential for reducing aircraft fuel consumption is presented. The discussion shows where the greatest percentages of aircraft fuel is burned and what areas have the greatest potential for fuel conservation. The paper deals with aerodynamic improvements and touches only briefly on structural and propulsion improvements. Concepts for reducing pressure drag (i.e., roughness, wave, interference, and separation drag), drag due to lift/induced drag, and skin-friction drag at subsonic and supersonic speeds are emphasized.

Constrained Flow Past Cavitating Bluff Bodies

Abstract: An experimental program has been carried out to determine the effects of wall interference on the drag and vortex shedding characteristics of cavitating two-dimensional triangular prisms and circular cylinders. The former shapes were chosen to eliminate effects of Reynolds number in interpreting the results. Direct pressure measurements were made to estimate the drag force. The vortex shedding frequency of the cavitating bodies was recorded with the help of a pressure transducer. The gap velocity u1 and the jet contraction velocity uj are shown to be the proper velocity scales to form the drag coefficients and Strouhal numbers for the bluff shapes tested. The drag coefficient was found to increase due to wall interference effects when partial cavitation conditions prevailed. The trend of the drag coefficient data indicated that wall interference effects are relatively small at very low cavitation numbers (σ → σch ) which correspond to choking conditions. As choking conditions are reached, the vortex shedding from the cavitating source becomes intermittent and finally vortex shedding ceases.

A wind-tunnel investigation of the effects of flap span and deflection angle, wing planform and a body on the high-lift performance of a 28 degrees swept wing

Abstract: : Lift, drag and pitching moment have been measured over an extensive range of configurations of the high-lift system on a wing of basic aspect ratio 835 and with a trailing-edge planform extension and a body added The results were analysed and compared with two linear-theory prediction methods The measured increments in lift generated by the various elements of the high-lift system were lower than the predicted levels An exploratory analysis of the drag results showed that the lift-dependent drag factor was considerably underestimated by linear theory, particularly when the slat was deployed The limitations of the planar vortex sheet used in the theory and the neglect of viscous effects are suggested as the principal reasons for the differences between experiment and theory Deflection of the flap produced a load, which acted at a distance forward of the mean quarter chord of the flap, that was practically independent of incidence and flap span The wing/body interference effect was insensitive to flap span and there was some evidence of a download being generated on the rear body when the high-lift system was deployed The performance of the high-lift system was downgraded when the wing planform was extended in the root region and this was attributed to the greater non-uniformity of the spanwise loading (Author)

Calculations, and comparison with an ideal minimum, of trimmed drag for conventional and canard configurations having various levels of static stability

Abstract: Classical drag equations were used to calculate total and induced drag and ratios of stabilizer lift to wing lift for a variety of conventional and canard configurations. The Flight efficiencies of such configurations that are trimmed in pitch and have various values of static margin are evaluated. Classical calculation methods are compared with more modern lifting surface theory.

Stowable airfoil structure

Abstract: The stowable airfoil structure is a tapered, high aspect ratio, retractable and foldable wing for aircraft which provides minimum aerodynamic drag during launch and minimum space for ground storage. The airfoil utilizes a forward leading edge box section to which is attached a plurality of spanwise channels hinged together for movement in a chordwise direction. Retraction of these elements takes place by the utilization of suitable actuators so as to move the hinged elements forwardly in a nested position thereby substantially reducing the width of the wing or airfoil which is then folded to lie along side the fuselage of an aircraft.

Methods for Reducing Subsonic Drag Due to Lift

Abstract: The results of repeat experimental research on methods for reducing subsonic drag due to lift are discussed. The NASA supercritical airfoils and their application to structurally practical wings with increased aspect radio are described. A design approach and experimental results for wing-tip-mounted winglets are presented. Several methods for utilizing the thrust of jet engines to provide reductions in the drag due to lift are also discussed.

Flight-measured lift and drag characteristics of a large, flexible, high supersonic cruise airplane

Abstract: Flight measurements of lift, drag, and angle of attack were obtained for the XB-70 airplane, a large, flexible, high supersonic cruise airplane. This airplane had a length of over 57 meters, a takeoff gross mass of over 226,800 kilograms, and a design cruise speed of Mach 3 at an altitude of 21,340 meters. The performance measurements were made at Mach numbers from 0.72 to 3.07 and altitudes from approximately 7620 meters to 21,340 meters. The measurements were made to provide data for evaluating the techniques presently being used to design and predict the performance of aircraft in this category. Such performance characteristics as drag polars, lift-curve slopes, and maximum lift-to-drag ratios were derived from the flight data. The base drag of the airplane, changes in airplane drag with changes in engine power setting at transonic speeds, and the magnitude of the drag components of the propulsion system are also discussed.

Effect' of winglets on a first-generation jet transport wing

Abstract: SUMMARY OF RESULTS A wind-tunnel investigation of winglets mounted on the tip of a 0.07-scale KC-135A jet transport model wing has been conducted. Configurations with an upper winglet only and with upper and lower winglets are compared with a simple wing-tip extension which is designed to produce the same increase in bending moment at the wing root (at a lg load factor) as do the winglets. Data are pre- sented at four high subsonic Mach numbers and one low subsonic Mach number, and indicate the following conclusions: 1. Both winglet configurations reduce induced drag by approximately 20 per- cent at design cruise conditions. The tip extension reduces induced drag by about 10 percent at design conditions. 2. At cruise conditions winglets produce improvements in lift-drag ratio of about 9 percent. improvement in lift-drag ratio. At the same conditions the tip extension produces a 4-percent 3. The negative increments in pitching-moment coefficient due to the wing- lets are less than those produced by the tip extension. 4.

Effect of nonlifting empennage surfaces on single-engine afterbody/nozzle drag at Mach numbers from 0.5 to 2.2

Abstract: The effect of empennage interference on the drag characteristics of a model with a single engine fighter aft end with convergent-divergent nozzles was studied. The dry and maximum afterburning nozzle power settings were investigated. A high pressure air system was used to provide jet total pressure ratios up to 20.0. In an attempt to quantify and reduce adverse empennage interference and decrease aft-end drag, several empennage arrangements (variable tail surface location), contour bump configurations, and locally contoured afterbodies were investigated. The results of the investigation indicate that empennage interference effects can be significant at transonic and supersonic speeds. The most effective means of reducing adverse empennage interference is the proper relocation of individual tail surfaces. The aft or conventional empennage arrangement produced the highest aft-end drag at all conditions investigated.

Slot injection for skin-friction drag reduction

Abstract: A description and analysis of slot injection in low-speed flow, slot injection in high-speed flow, a discussion of aircraft applications, and possibilities for future improvements of slot drag reduction capability are presented.

Theoretical Aspects of Dromedaryfoil.

Abstract: : A new airfoil design (called a dromedaryfoil) has been developed using a single hump on a modified supercritical airfoil for limiting the center of pressure excursion and maximizing the drag divergence Mach number. Derivation of the hump is based on isentropic compression in the fore part and incipient separation in the rear. The former leads to a weakened shock wave and the latter to high pressure recovery after the shock. The shock will theoretically locate at the peak of the hump to form a fixed pressure pattern under different flight speeds. The shock foot will be inclined at a deflection angle of the hump measured from the normal of the fore hump surface at the peak. Theoretical results indicate considerably shorter center-of-pressure travel for a dromedaryfoil than for a supercritical airfoil with equal wave drag. However, improper humping would be penalized by increased wave drag. At high supercritical flows, the shock strength would be limited by (M sub 1 sin beta)max = 1.483. Experimental verification of theoretical predictions is planned. (Author)

Nacelle Integration Study on a Mach-2.2 Supersonic Cruise Aircraft

Abstract: Results of a propulsion system integration study performed on a Mach-2.2 advanced supersonic cruise aircraft are discussed. A study configuration developed in a joint NASA-Douglas supersonic technology program was used as the baseline airframe to study the detailed problems of inlet-nacelle -airframe integration at Mach 2.2. Numerous inlet-nacelle combinations were examined in a preliminary screening study. Promising configurations were evaluated in a nacelle installation study in which structural weight and installed wave drag were traded leading to the selection of an axisymmetric single-engine pod installation as the most promising configuration. A detailed nacelle shape study was conducted, and a wing reflex was designed. A cooperative NASA-Douglas wind-tunnel test of the refined nacelle with both mixed and external compression inlets was conducted with the nacelles installed on both a refined baseline wing and a reflexed wing. An installation drag penalty equal to 4.3% of the baseline wing-body drag was observed for the external compression inlet over the mixed compression inlet. Wing reflexing improved the trimmed wing-body-nacelle drag by 3.0% of the wing-body drag. Good agreement was observed between calculated and experimental increments in induced drag due to nacelle installation.

Subsonic and supersonic aerodynamic characteristics of a supersonic cruise fighter model with a twisted and cambered wing with 74 deg sweep

Abstract: A wind tunnel investigation has been conducted to determine the longitudinal and lateral aerodynamic characteristics of a model of a supersonic cruise fighter configuration with a design Mach number of 2.60. The configuration is characterized by a highly swept arrow wing twisted and cambered to minimize supersonic drag due to lift, twin wing mounted vertical tails, and an aft mounted integral underslung duel-engine pod. The investigation also included tests of the configuration with larger outboard vertical tails and with small nose strakes.

Aerodynamic loads near cranks, apexes, and tips of thin, lifting wings in incompressible flow

Abstract: The calculation of the incompressible and irrotational flow in the vicinity of tips and corners of thin, lifting wings is considered. It is shown that the important characteristics of the flow are governed by an eigenvalue problem, which is nonlinear at the trailing edge because of the shed wake (assumed to be in the wing plane). A new solution method was devised because either the existing methods were not valid for the trailing edge case or they would have required excessive amounts of computer time. The new method, which is fundamentally different than the previous ones, was used to calculate solutions for a number of cases, including some for which correct answers had not previously been obtained. Two of these solutions were used to determine the validity of drag and leading-edge-suction distributions near the tips of a delta wing and a swept wing as calculated by using both the vortex lattice method and a kernel function method. The calculations for the swept wing resolved the question of whether or not the induced drag should be zero at the wing tip.

An investigation of induced drag reduction through over-the-wing blowing

Abstract: An investigation has been conducted in the Langley 16-foot transonic tunnel to verify analytically predicted benefits in climb and cruise performance due to blowing the jet exhaust over the wing for a transport configuration. A wing-body model - powered-nacelle rig combination was tested at Mach numbers of 0.5 and 0.8 at angles of attack from -2 to 4 deg and jet total pressure ratios from jet off to 3 or 4 (depending on Mach number) for a variety of nacelle locations relative to the wing. Results from this investigation show that the induced drag for the wing-body (nacelles were nonmetric) was reduced for virtually all configurations. In addition to the experimental results, comparisons of the data with available prediction methods are included to show their validity and capabilities.

Effects of deflected thrust on the longitudinal aerodynamic characteristics of a close-coupled wing-canard configuration

Abstract: The effects of power on the longitudinal aerodynamic characteristics of a close-coupled wing-canard fighter configuration with partial-span rectangular nozzles at the trailing edge of the wing were investigated. Data were obtained on a basic wing-strake configuration for nozzle and flap deflections from 0 deg to 30 deg and for nominal thrust coefficients from 0 to 0.30. The model was tested over an angle-of-attack range from -2 deg to 40 deg at Mach numbers of 0.15 and 0.18. Results show substantial improvements in lift-curve slope, in maximum lift, and in drag-due-to-lift efficiency when the canard and strakes have been added to the basic wing-fuselage (wing-alone) configuration. Addition of power increased both lift-curve slope and maximum lift, improved longitudinal stability, and reduced drag due to lift on both the wing-canard and wing-canard-strake configurations. These beneficial effects are primarily derived from boundary-layer control due to moderate thrust coefficients which delay flow separation on the nozzle and inboard portion of the wing flaps.

Drag evaluation of the Bellanca Skyrocket II

Abstract: The Bellanca Skyrocket II, possessor of five world speed records, is a single engine aircraft with high performance that has been attributed to a laminar flow airfoil and an all composite structure. Utilization of composite materials in the Skyrocket II is unique since this selection was made to increase the aerodynamic efficiency of the aircraft. Flight tests are in progress to measure the overall aircraft drag and the wing section drag for comparison with the predicted performance of the Skyrocket. Initial results show the zero lift drag is indeed low, equalling 0.016.

Aerodynamic characteristics of wing-body configuration with two advanced general aviation airfoil sections and simple flap systems

Abstract: Aerodynamic characteristics of a general aviation wing equipped with NACA 65 sub 2-415, NASA GA(W)-1, and NASA GA(PC)-1 airfoil sections were examined. The NASA GA(W)-1 wing was equipped with plain, split, and slotted partial- and full-span flaps and ailerons. The NASA GA(PC)-1 wing was equipped with plain, partial- and full-span flaps. Experimental chordwise static-pressure distribution and wake drag measurements were obtained for the NASA GA(PC)-1 wing at the 22.5-percent spanwise station. Comparisons were made between the three wing configurations to evaluate the wing performance, stall, and maximum lift capabilities. The results of this investigation indicated that the NASA GA(W)-1 wing had a higher maximum lift capability and almost equivalent drag values compared with both the NACA 65 sub 2-415 and NASA GA(PC)-1 wings. The NASA GA(W)-1 had a maximum lift coefficient of 1.32 with 0 deg flap deflection, and 1.78 with 41.6 deg deflection of the partial-span slotted flap. The effectiveness of the NASA GA(W)-1 plain and slotted ailerons with differential deflections were equivalent. The NASA GA(PC)-1 wing with full-span flaps deflected 0 deg for the design climb configuration showed improved lift and drag performance over the cruise flap setting of -10 deg.

Effects of deflected thrust on the stability and performance characteristics of a close-coupled canard fighter configuration

Abstract: The effect of deflected thrust on the stability and performance of a close-coupled canard fighter configuration are presented. These results were obtained at low speeds in the Langley V/STOL tunnel. Transonic as well as low-speed results are also presented for an unpowered close-coupled canard and a supercruiser configuration. The V/STOL tunnel data indicate an increase in maximum lift and reductions in drag due to lift with the addition of two-dimensional vectored thrust at the wing inboard trailing edge. The longitudinal pitchup associated with the unpowered configuration at higher angles of attack was significantly reduced with power.

Determining the Lift and Drag Distributions on a Three-Dimensional Airfoil from Flow-Field Velocity Surveys

Abstract: The application of the incompressible momentum integral equation to a three-dimensional airfoil was reviewed to interpret the resulting equations in a way that suggests a reasonable experimental technique for determining the spanwise distributions of lift and drag. Consideration was given to constraints that must be placed on the character of the vortex wake structure shed by the wing, to provide the familiar relationship between lift and bound vorticity. It is shown that the induced drag distribution is not directly measurable, but can be obtained, via the lift distribution, approximately for a deflected wake and exactly for a planar wake. Moreover, it is shown that it is only necessary to survey a short distance above and below the wing trailing edge. Examples are presented for several typical loading distributions and the results of a numerical simulation of the suggested experiment are discussed.

Performance Prediction Method for a Wing-in-Ground Effect Vehicle with Blowing Under the Wing.

Abstract: : Recent efforts in theoretical analysis and experimental observations have moved the concept of power-augmented flight in ground effect toward practicality With the addition of lift and drag due to external airflow, end-plate leakage, water skin friction, wave drag effects, and wave clearance constraints, a flow model can be made capable of effective comments The analysis shows that there are wave drag and wave clearance related limits to many aspects of the vehicle configuration The most important of which are cruising height and aspect ratio, in that they have a very large effect on transport efficiency Unfortunately, the low flying high aspect ratio cases are ruled out due to wave impact problems Testing of a point design vehicle, arrived at through the use of analysis such as the one of this report, needs to be performed as final verification of the accuracy of the design procedure (Author)

Some contributions to aerodynamic theory for vertical axis wind turbines

Abstract: A review and modest extensions are described of quasisteady aerodynamic theory for performance prediction on Darrieus-type turbines. Results are given for both parallel-axis and curved-blade configurations. Blade stall and variable inflow are neglected; it is hypothesized that unsteady effects support the former approximation down to lower values of tip-speed ratio than hitherto believed. Both profile and induced drag are included, and their influences on power and downwind force are expressed in terms of elliptic integrals. Comparisons are presented with power data from the Sandia 2-m turbine. Three values of profile drag coefficient are employed, and it is argued that numbers in the range CD() =0.015-0.017 are most appropriate to the example chosen. Finally, a linearized analysis of unsteady flow effects on performance is summarized. Calculations suggest that they may be larger than might be expected in view of the low operating reduced frequencies of these machines.

An Aerodynamic Investigation of a Forward Swept Wing

Abstract: : This study consisted of modeling and wind tunnel testing of a high speed, subsonic, low aspect ratio, forward swept wing with an advanced supercritical airfoil section for the purpose of determining its lift, drag, and pitching moment characteristics as compared to a similar aft swept wing. Tests were conducted at Mach numbers of 0.63 to 0.93 in the Air Force Flight Dynamics Laboratory's Trisonic Gasdynamic Facility located at Wright-Patterson Air Force Base, Ohio. Two wing configurations, forward and aft swept, were tested and compared to computer predictions provided by the Unified Subsonic-Supersonic Program (Woodward's Version B). The results indicated that the forward swept wing was capable of higher useable angles of attack while maintaining a lower drag coefficient for angles of attack below eight degrees. Wind tunnel test results are presented in graphical and tabular form for use in future design studies of similar aerodynamic configurations.