Showing papers on "Lift-induced drag published in 1986"

Airfoil aerodynamics in icing conditions

Abstract: Methods of analyzing and experimentally measuring the effect of ice accretion on airfoil sections are presented. Empirical and analytical methods for predicting airfoil performance degradation due to ice are discussed. Ice simulation techniques for aerodynamic testing are presented and compared to data with actual ice accretions. The results show that simulation techniques to imitate the effect of ice on airfoil performance work well in most cases. Comparisons between predicted and measured airfoil performance with ice accretions are presented. For rime ice cases, the predictions compared well with experiments; but for glaze ice, a need for improved methods are seen.

Auxiliary wing tips for an aircraft

Abstract: Auxiliary winglets or control surfaces for aircraft wings are tiltable ab an axis extending in the flight direction and about an axis extending substantially perpendicularly to the flight direction. The auxiliary wing tips have a configuration which assure a wing surface continuity, especially when the tips are in their normal wing extending position, but also in any other position of the winglets. Additionally, at least the leading auxiliary winglets are located upstream of the elastic wing axis, as viewed in the flight direction and they have a forward sweep or negative sweepback. The combination of these features permits a simultaneous reduction of induced drag and of stress caused by wind gusts, and for increasing the effectiveness of the wing's ailerons. Thus, these auxiliary winglets have three advantages simultaneously.

A fundamental study of drag and an assessment of conventional drag-due-to-lift reduction devices

Abstract: The integral conservation laws of fluid mechanics are used to assess the drag efficiency of lifting wings, both CTOL and various out-of-plane configurations. The drag-due-to-lift is separated into two major components: (1) the induced drag-due-to-lift that depends on aspect ratio but is relatively independent of Reynolds number; (2) the form drag-due-to-lift that is independent of aspect ratio but dependent on the details of the wing section design, planform and Reynolds number. For each lifting configuration there is an optimal load distribution that yields the minimum value of drag-due-to-lift. For well designed high aspect ratio CTOL wings the two drag components are independent. With modern design technology CTOL wings can be (and usually are) designed with a drag-due-to-lift efficiency close to unity. Wing tip-devices (winglets, feathers, sails, etc.) can improve drag-due-to-lift efficiency by 10 to 15% if they are designed as an integral part of the wing. As add-on devices they can be detrimental. It is estimated that 25% improvements of wing drag-due-to-lift efficiency can be obtained with joined tip configurations and vertically separated lifting elements without considering additional benefits that might be realized by improved structural efficiency. It is strongly recommended that an integrated aerodynamic/structural approach be taken in the design of (or research on) future out-of-plane configurations.

Airfoil large-eddy breakup devices for turbulent drag reduction

Abstract: It was determined from the present LaRC experiments that tandem, airfoil-shaped large eddy breakup (LEBU) devices can reduce local skin friction as much as 30 percent with a recovery region extending more than 100 boundary layer thicknesses downstream. These airfoils experience near laminar skin friction device drag and produce net drag reductions of up to 7 percent. In contrast to the thin plates used in previous experiments, these airfoils are more than 1000 time stiffer and hence have the potential to withstand the real flight environment (dynamic pressure 36 times larger than in low-speed wing tunnels). In addition, the higher Reynolds numbers of the present tests indicate drag reduction performance is at least as good (or better) as at lower Reynolds numbers.

Aerodynamic measurements of an airfoil with simulated glaze ice

Abstract: An experimental study has been conducted in the OSU subsonic tunnel to measure the detailed aerodynamic characteristics of an airfoil with simulated glaze ice. A special model was built with interchangeable leading edges to be used in this study. One leading edge is that of a NACA 0012, while the other is a simulation of a glaze ice accretion measured in the NACA Lewis Icing Research Tunnel. The model was instrumented with a dense distribution of surface pressure taps to provide excellent detail around the ice shapes and reattachment point. A traversing total pressure probe was used to document the boundary layer characteristics on the NACA 0012 section. The ice shape caused a severe lift and drag penalty, reducing the maximum lift by over 50 percent and causing a 300 percent increase in drag. Surface pressure distributions revealed a large lower surface separation in addition to the expected large upper surface separation.

Fluid flow control device

Abstract: A fluid flow control device controllably maintains attached flow in the region of a body having a contour of rapid curvature utilizing tangential fluid discharge slots, positioned just upstream from the separation line, which issue a thin jet sheet to energize the boundary layer and entrain the surrounding flow. When applied to the aft fuselage of an aircraft, the device reduces separation and vortex drag at cruise and provides control forces and moments during low speed operation of the aircraft.

Experimental investigation of rotorcraft hub and shaft fairing drag reduction

Abstract: A wind-tunnel test was conducted to obtain data on several rotorcraft hub and shaft fairing drag reduction configurations. Aerodynamic loads and moments were acquired for each test configuration. Limited wake pressure measurements and flow visualization (tuft) photographs were obtained for some configurations. All hub and shaft fairing configurations were tested on a 1/5-scale XH-59A model fuselage. Both coaxial and single rotor configurations were tested. All rotor assemblies were modeled with nonrotating hardware. The drag reduction methods tested included cambered elliptical hub fairings, several different shaft fairings, and strakes. Test data show that significant drag reductions can be attained with certain fairing configurations. The lowest drag values for the single rotor configurations were obtained for a cambered elliptical hub fairing with a large thickness airfoil shaft fairing. The lowest coaxial configuration drag values were obtained with cambered elliptical hub fairings and a long chord intermediate shaft fairing.

Aerodynamic characteristics of two-dimensional wing configurations at angles of attack near -90 deg

Abstract: : Wind tunnel tests were conducted to determine the drag og two-dimensional wing sections operating in a near-vertical flow condition. Various leading-and trailing-edge configurations, including plain flaps of 25, 30, and 35% chord were tested at angles of attack from-75 to -105deg. Reynolds numbers examined ranged from approximately 0.6 to 1.4 million. The data were obtained using a wind tunnel force and moment balance system and arrays of chordwise pressure orifices. The results showed that significant reductions in drag, beyond what would be expected by virtue of the decreased frontal area, were obtainable with geometries that delayed flow separation. Rapid changes in drag with angle of attack were noted for many configurations. The results, however, were fairly insensitive to Reynolds number variations. Drag values computed from the pressure data generally agreed with the force data within 2%. Keywords: Download; Two-dimension wing; Leading edge; trailing edge; Wing flap; Wing slots; Wing slats; Wing spoiler.

Over-the-wing propeller

Abstract: This invention is an aircraft 10 with a system for increasing the lift-drag ratio over a broad range of operating conditions. The system positions the engines and nacelles 15 over the wing 12 in such a position that gains in propeller 16 efficiency is achieved simultaneously with increases in wing lift and a reduction in wing drag. Adverse structural and torsional effects on the wings 12 are avoided by fuselage mounted pylons which attach to the upper portion of the fuselage 11 aft of the wings. Similarly, pylon-wing interference is eliminated by moving the pylons to the fuselage. Further gains are achieved by locating the pylon surface area aft of the aircraft center-of-gravity, thereby augmenting both directional and longitudinal stability. This augmentation has the further effect of reducing the size, weight and drag of empennage components 13. The combination of design changes results in improved cruise performance and increased climb performance while reducing fuel consumption and drag and weight penalties.

Zero-Lift Wave Drag of Complex Aircraft Configurations

Abstract: WAVDRAG calculates supersonic zero-lift wave drag of complex aircraft configurations. Numerical model of aircraft used throughout design process from concept to manufacturing. Incorporates extended geometric input capabilities to permit use of more accurate mathematical model. Engineer defines aircraft components as fusiform or nonfusiform in terms of traditional parallel contours or nonintersecting contours in any direction. Laterally asymmetric configurations simulated. WAVDRAG calculates total drag and wave-drag coefficient of specified aircraft configuration.

Aircraft drag prediction and reduction. Addendum 1: Computational drag analyses and minimization; mission impossible?

Abstract: The Special Course on Aircraft Drag Prediction was sponsored by the AGARD Fluid Dynamics Panel and the von Karman Institute and presented at the von Karman Institute, Rhode-Saint-Genese, Belgium, on 20 to 23 May 1985 and at the NASA Langley Research Center, Hampton, Virginia, USA, 5 to 6 August 1985. The course began with a general review of drag reduction technology. Then the possibility of reduction of skin friction through control of laminar flow and through modification of the structure of the turbulence in the boundary layer were discussed. Methods for predicting and reducing the drag of external stores, of nacelles, of fuselage protuberances, and of fuselage afterbodies were then presented followed by discussion of transonic drag rise. The prediction of viscous and wave drag by a method matching inviscid flow calculations and boundary layer integral calculations, and the reduction of transonic drag through boundary layer control are also discussed. This volume comprises Paper No. 9 Computational Drag Analyses and Minimization: Mission Impossible, which was not included in AGARD Report 723 (main volume).

Advanced natural laminar flow airfoil with high lift to drag ratio

Abstract: An experimental verification of a high performance natural laminar flow (NLF) airfoil for low speed and high Reynolds number applications was completed in the Langley Low Turbulence Pressure Tunnel (LTPT). Theoretical development allowed for the achievement of 0.70 chord laminar flow on both surfaces by the use of accelerated flow as long as tunnel turbulence did not cause upstream movement of transition with increasing chord Reynolds number. With such a rearward pressure recovery, a concave type deceleration was implemented. Two-dimensional theoretical analysis indicated that a minimum profile drag coefficient of 0.0026 was possible with the desired laminar flow at the design condition. With the three-foot chord two-dimensional model constructed for the LTPT experiment, a minimum profile drag coefficient of 0.0027 was measured at c sub l = 0.41 and Re sub c = 10 x 10 to the 6th power. The low drag bucket was shifted over a considerably large c sub l range by the use of the 12.5 percent chord trailing edge flap. A two-dimensional lift to drag ratio (L/D) was 245. Surprisingly high c sub l max values were obtained for an airfoil of this type. A 0.20 chort split flap with 60 deg deflection was also implemented to verify the airfoil's lift capabilities. A maximum lift coefficient of 2.70 was attained at Reynolds numbers of 3 and 6 million.

Combined, nonlinear aerodynamic and structural method for the aeroelastic design of a three-dimensional wing in supersonic flow

Abstract: An iterative procedure for the static aeroelastic design of a flexible wing at supersonic speeds has been developed. The procedure combines a nonlinear, full-potential solver (NCOREL) with an equivalent plate structural analysis method. The NCOREL method yields significantly improved aerodynamic estimates compared to linear theory. The equivalent plate structural analysis method demonstrates an order of magnitude reduction in computer memory and execution time compared to finite-element methods. A highly swept wing is analyzed at high lift using this aeroelastic procedure. The results indicate that the wing deforms favorably due to aerodynamic loading and, consequently, that the inviscid drag levels do not vary at the required lift coefficient although the angle of attack varies significantly. A sensitivity analysis of the type required for optimization studies was also performed with the aeroelastic design procedure.

Potential influences of heavy rain on general aviation airplane performance

Abstract: Recent NASA wind tunnel tests of airfoils in a simulated rain environment under extremely heavy rain conditions have shown reductions in maximum lift and increases in drag. Conventional airfoils were tested with and without high lift devices and tests of laminar-flow airfoils without high-lift devices were conducted. Both types of airfoils indicated performance decrements when exposed to a simulated heavy rain environment. For the laminar flow airfoil, the rain influence was observed to occur throughout the angle of attack range, whereas for the conventional airfoil in a high lift configuration, the rain influence occurred mostly at the higher angles of attack. The performance decrement for the laminar-flow airfoil appeared to be a result of laminar-to-turbulent boundary-layer transition whereas the performance penalty for the conventional airfoil appeared to be the result of premature separation. The results of these tests are presented and the implication of the results to general aviation airplanes are discussed.

Canard/tail comparison for an advanced variable-sweep-wing fighter

Abstract: Equivalent canard and tail control surfaces are compared on an advanced, carrier-based fighter/attack aircraft featuring variable wing sweep and vectorable, two-dimensional nozzles. Evaluations of stability and control characteristics, trimmed drag due to lift, minimum takeoff rotation speeds, and carrier approach speeds are presented. The results show that the canard configuration has substantially less supersonic trim drag and a lower carrier approach speed, which can yield appreciable takeoff weight savings, but the tail configuration exhibits better stability and control characteristics with less development risk.

Drag-reduction characteristics of aft-swept wing tips

Abstract: Results are presented of a study conducted to analyze the potential aerodynamic improvements which can be obtained with aft-swept wing tips at subsonic speeds. A review and summary of previous swept-tip applications and studies are given. Additionally, the through evolution optimized tail-fin shapes of fast-cruising aquatic animals are examined as well as the wing planform shapes of sea birds. These superior long-distance travellers both display lifting-surface planform shapes with increased leading-edge sweep towards the tip. These observations and analytical results obtained with a nonlinear surface-panel method demonstrate that substantial induced-drag improvements can be obtained through the adoption of planform shapes with highly-tapered aft-swept tips.

Study of the propeller with small blades on the blade tips (1st Report)

Abstract: A new type propeller derived from “winglets” was investigated. This propeller is also fitted small blades at the blade tips likely to “winglets”, so we named it “bladelets”. These are for the purpose of reducing induced drag from tip vorteces. This paper, as the first report, mainly presents the results of the series tests which are concerned with the arrangement of these small blades. Propeller open test, flow visualization and flow velocity measurements were performed, and one of the best arrangement of “bladelets” were found out. The results looks 1 or 4% better compared the efficiency of “bladelet propeller” with that of the original one within the bound of real working condition.

Transient induced drag

Abstract: In the present treatment of the calculation of forces on a wing that is suddenly brought into motion at a constant speed, attention is given to the unsteady potential's contribution to the force balance. Total bound vorticity is produced at the initial impulse. The results obtained are independent of wing aspect ratio; as time increases, this effect on the drag force becomes smaller as the vortex emanating from the trailing edge is left behind. The second contributor to induced drag is the spanwise vorticity shedding that results from the spanwise load distribution of three-dimensional wings. This contribution grows with time as the length of the wake grows.

The numerical solution of flow around a rotating circular cylinder in a uniform flow.

Abstract: Fluid-dynamic forces on a rotating circular cylinder in a uniform flow were obtained by numerically solving the vorticity transport equation. the ranges of calculation are from 20 to 100 for the Reynolds number, Re, and from 0 to 2 for the specific rotating speed, |V0|, the ratio of the peripheral speed of the cylinder to the uniform velocity. The results of calculation show that the temporal-mean lift coefficient is nearly independent of Re and is proportional |V0|. On the other hand, the temporal-mean pressure drag coefficient increases proportionately to V02 and that increment is due to induced drag in two-dimensional flow, while the skin-friction drag is independent of V0. The amplitude of the temporally fluctuating lift coefficient is maximum at |V0|e0.5 which is larger when Re is larger. The amplitude and frequency seem to be strongly affected by the width of the formation region.

Nonplanar vortex lattice method for analysis of complex multiple lifting surfaces

Abstract: A method for determining the aerodynamic characteristics of complex multiple lifting surfaces in inviscid subcritical flows has been developed and programmed on UNIVAC 1100/60 computer. 13; Each lifting surface is represented by a network of non-planar horse shoe vortices distributed on the mean surface and trailing to infinity. The strengths of these vortices are determined by requiring the flow to be parallel to the surface at a number of control points. The force due13; to a vortex segment is calculated as the vector product of local velocity and the vortex strength multiplied by density.13; The programme can handle wings with breaks and span wise segmented flaps in leading and trailing edges, local dihedral, camber and twist. The code can be used to compute lift, induced drag and pitching moments for any lifting planar of non-planar surfaces and surfaces in combination13; like wing-canard or wing-horizontal tail. The programme has been validated for a number of configurations for which experimental data is available.

An experimental study of the lift, drag and static longitudinal stability for a three lifting surface configuration

Abstract: The experimental procedure and aerodynamic force and moment measurements for wind tunnel testing of the three lifting surface configuration (TLC) are described. The influence of nonelliptical lift distributions on lift, drag, and static longitudinal stability are examined; graphs of the lift coefficient versus angle of attack, the pitching moment coefficient, drag coefficient, and lift to drag ratio versus lift coefficient are provided. The TLC data are compared with the conventional tail-aft configuration and the canard-wing configuration; it is concluded that the TLC has better lift and high-lift drag characteristics, lift to drag ratio, and zero-lift moments than the other two configurations. The effects of variations in forward and tail wind incidence angles, gap, stagger, and forward wind span on the drag, lift, longitudinal stability, and zero-lift moments of the configuration are studied.

Maximum lift/drag ratio of flat plates with bluntness and skin friction at hypersonic speeds

Abstract: Newtonian theory is used to derive a simple expression for the maximum lift/drag ratio of flat plates with bluntness and skin friction at hypersonic speeds. The bluntness drag is assumed to be independent of angle of attack. Because the effect of skin friction is of second order over the angle of attack range for maximum lift/drag ratio, it was assumed constant. As an example, the expression is applied to the Space Shuttle.

Planform effects for low-fineness-ratio multibody configurations at supersonic speeds

Abstract: An experimental and theoretical investigation of planform effects on a low-fineness ratio multibody configuration has been conducted in NASA Langley Research Center's Unitary Plan Wind Tunnel at Mach numbers 1.6, 1.8, 2.0, and 2.16. Experimental and theoretical values of lift, drag, and pitching moment were obtained on three configurations which varied in outboard panel planform only. The three variations were at 65 deg delta, a 70/66 deg cranked arrow, and a 20 deg trapezoidal planform . The purpose of the study was to determine the effect of wing planform on the supersonic aerodynamics and to evaluate the ability of two existing linearized-theory aerodynamic methods to predict these effects. Experimental data showed that the planforms produced the lift, drag-due-to-lift, and pitching-moment characteristics typically found on single-body configurations. However, the data also showed that planform has a minimal influence on zero-lift drag, which is not typical of single-body configurations. Theoretical aerodynamic analysis indicated that codes based on linearized theory adequately predicted the effect of planform on the supersonic aerodynamics.

Analytical observations on the aerodynamics of a delta wing with leading edge flaps

Abstract: The effect of a leading edge flap on the aerodynamics of a low aspect ratio delta wing is studied analytically. The separated flow field about the wing is represented by a simple vortex model composed of a conical straight vortex sheet and a concentrated vortex. The analysis is carried out in the cross flow plane by mapping the wing trace, by means of the Schwarz-Christoffel transformation into the real axis of the transformed plane. Particular attention is given to the influence of the angle of attack and flap deflection angle on lift and drag forces. Both lift and drag decrease with flap deflection, while the lift-to-drag ratioe increases. A simple coordinate transformation is used to obtain a closed form expression for the lift-to-drag ratio as a function of flap deflection. The main effect of leading edge flap deflection is a partial suppression of the separated flow on the leeside of the wing. Qualitative comparison with experiments is presented, showing agreement in the general trends.

All-wing light aircraft

Abstract: In order to make possible an aircraft of high mechanical strength with a low structural weight and maximum lift performance with a low overall drag, an all-wing composite system is created which, in plan view and end view, exhibits a delta-shaped wing composite. The circumferential rear edge profile is formed such that an acceleration of the flow occurs in the rear region of the profile, which increases the coefficient of lift and prevents boundary-layer separation in the useful incidence-angle range. The departure of the tip vortex wake is made possible at 70 % of the span width in order to ensure a low induced drag in the region of high coefficients of lift. Longitudinal stabilisation is carried out without auxiliary surfaces by means of a specific centre of gravity position, such that the system rises or falls in brief changes in the incident flow, without moving about the pitch axis, and in consequence produces a particularly favourable flight path behaviour.

All-wing elliptical ring configuration

Abstract: In order to provide a climbing performance flight system which additionally permits good cruise performance, sub-surfaces are connected to form an elliptical-ring all-wing system. The result of this is that: - the induced drag is considerably reduced by surface-related, continuous pressure-difference reversal of the translation flow and incidence-angle-independent zero distribution of the lift in the region of the maximum span in all flight conditions, - the total drag remains low as a result of the absence of further control/stabilisation surfaces, - as a consequence of the static stability produced by a fully-integrated, vertically staggered leading surface, thermally or dynamically dependent incident-flow changes result in a particularly low-drag parallel shift of the respective trimmed-flight attitude without system movement about the pitch axis and/or stabilisation phugoids, as a result of which all incident-flow changes automatically and optimally lead to an altitude gain, - absolutely non-critical stall behaviour results from the aerodynamically and mass-dynamically balanced lift distribution, - the all-wing design permits maximum mechanical strength with low structural weight, - the all-wing design can be used both in the UL region and in the other flight-system region, - the all-wing design can be combined - cost effectively - with very different fuselages without losing its specific flight performance and flight characteristics. t