Showing papers on "Lift-induced drag published in 2003"

The design of winglets for high-performance sailplanes

Abstract: Although theoretical tools for the design of winglets for high-performance sailplanes were initially of limited value, simple methods were used to design winglets that gradually became accepted as benefiting overall sailplane performance. To further these gains, an improved methodology for winglet design has been developed. This methodology incorporates a detailed component drag buildup that includes the ability to interpolate input airfoil drag and moment data across operational lift coefficient, Reynolds number, and flapsetting ranges. Induced drag is initially predicted using a relatively fast multi- lifting line method. In the final stages of the design process, a full panel method, including relaxed-wake modeling, is employed. The drag predictions are used to compute speed polars for both level and turning flight. The predicted performance is in good agreement with flight-test results. The straight and turning flight speed polars are then used to obtain cross-country performance over a range of thermal strengths, sizes, and shapes. Example design cases presented here demonstrate that winglets can provide a small, but important, performance advantage over much of the operating range for both span limited and span unlimited high-performance sailplanes.

Aircraft Drag Reduction-A Review

Abstract: The paper summarizes the state of the art in aeronautical drag reduction across the speed range for the conventional drag components of viscous drag, drag due to lift and wave drag. It also describes several emerging drag-reduction approaches that are either active or reactive/interactive and the drag reduction potentially available from synergistic combinations of advanced configuration aerodynamics, viscous drag-reduction approaches, revolutionary structural concepts and propulsion integration.

Design, development and testing of a morphing aspect ratio wing using an inflatable telescopic spar

Abstract: This paper discusses the design, development and testing of an inflatable telescopic wing that permits a change in the aspect ratio while simultaneously supporting structural wing loads. The key element of the wing consists of a pressurized telescopic spar that can undergo large-scale spanwise changes while supporting wing loadings in excess of 15 lbs/ft. The wing cross-section is maintained by NACA0012 rib sections fixed at the end of each element of the telescopic spar. Telescopic skins are used to preserve the spanwise airfoil geometry and ensure compact storage and deployment of the telescopic wing. A small scale telescopic wing assembly was tested in a free jet wind tunnel facility at a variety of Reynolds numbers (182000, 273000, 363000 and 454000). The telescopic wing was deployed from 7 inches to 15”. Experimental wind tunnel results were compared to rigid fixed wing test specimen to compare the performance of the telescopic wing. Preliminary aerodynamic results are promising for the variable aspect ratio telescopic wing. Overall, the telescopic wing at maximum deployment did incur a slightly larger drag penalty and a reduced lift to drag ratio. Thus, it may be possible to develop UAVs with variable aspect ratio wings using inflatable telescopic spars and skin sections. Graduate Research Assistant, Aerospace Engineering Dept. † Undergraduate Student, Aerospace Engineering Dept. Associate Professor, Aerospace Engineering Dept., Associate Fellow of AIAA Nomenclature a Lift curve slope a0 Theoretical lift curve slope a Angle of attack (degrees) a i Induced angle of attack (degrees) AR Aspect ratio b Wingspan (ft) c Chord length (ft) cf Specific fuel consumption CL Lift coefficient CD Drag coefficient CD,0 Induced Drag coefficient at α = 0 CD,i Induced Drag coefficient e Span efficiency factor E Endurance ID Inside Diameter l Length L Lift force m Mass (lbs) ? Propeller efficiency μ Viscosity OD Outside Diameter P Pressure (Psi) q Dynamic pressure R Range Re Reynolds Number ? Density (lbs/ft ) S Surface area of the wing t Thickness (ft) V Speed (ft/s) W0 Gross weight (with full fuel an payload) W1 Empty weight (lbs) 8 Freestream

Lifting-Line Analysis of Roll Control and Variable Twist

Abstract: A more practical form of an analytical solution that can be used to predict the roll response for a wing of arbitrary planform with arbitrary spanwise variation of control surface deflection and wing twist is presented. This infinite series solution is based on Prandtl 's classical lifting-line theory and the Fourier coefficients are presented in a form that only depends on wing geometry. The solution can be used to predict rolling and yawing moments as well as the lift and induced drag, which result from control surface deflection, rolling rate, and wing twist. The analytical solution can be applied to wings with conventional ailerons or to wings utilizing wing-warping control. The method is also applied to full-span twisting control surfaces, named "twisterons," which can be simultaneously used to provide roll control, high-lift, and minimum induced drag. A closed-form solution for optimum twist in a wing with linear taper is also presented. Nomenclature An = coefficients in the infinite series solution to the lifting-line equation an = planform contribution to the coefficients in the infinite series solution to the lifting-line equation b =w ingspan bn = twist contribution to the coefficients in the infinite series solution to the lifting-line equation Di C = induced drag coefficient L C = lift coefficient α , L C = wing lift slope α , ~ L C = airfoil section lift slope f L C δ , = change in wing lift coefficient with respect to flap deflection t L C δ , = change in wing lift coefficient with respect to twisteron deflection " C = rolling moment coefficient p C , " = change in rolling moment coefficient with respect to dimensionless rolling rate δ , " C = change in rolling moment coefficient with respect to control surface deflection m

Flight dynamic simulation assessment of a morphable hyper-elliptic cambered span winged configuration

Abstract: As part of the Morphing Project in the Aerospace Vehicle Systems Technology Program, NASA is conducting biomimetics research aimed at the study of natural morphologies that may prove beneficial for advanced flight systems. Wind tunnel tests were conducted in 2002 to compare three biologically inspired wing designs with a planar elliptic wing; theoretically considered the best planar configuration for the least induced drag. All wings had the same aspect ratio and wing span. One of the wings, referred to as a Hyper-Elliptic Cambered Span (HECS) due to its continuously varying span-wise curvature, demonstrated that although it had nearly a 10 percent increase in surface area it provided a lift-to-drag increase of as much as 15 percent. Because of its beneficial aerodynamic properties, the Hyper-Elliptic Cambered Span wing has been chosen as a focus concept for wing morphing (continuous physical shape change) research. To be of potential use on a vehicle, morphing concepts must allow for adequate stability and control properties. Flight control designs must be validated in simulation and eventually in flight. This paper presents the development of a non-linear, CFDbased, dynamic vehicle simulation incorporating a morphable Hyper-Elliptic Cambered Span wing. This vehicle utilizes a continuous (hingeless, gapless) morphable panel along the trailing edge of the wing and a continuous moveable wing tip for pitch, roll, and yaw control. The simulation is used as the basis for the assessment of vehicle stability and control characteristics and the viability of using wing morphing for primary maneuver control. Linear state space models of the vehicle associated with typical trimmed level flight conditions are also presented.

Airlifting surface division

Abstract: This airlifting surface division idea provides for division airlifting surfaces resulting in low induced and interference drag. It can be applied to aircraft wings and helicopter and windmill rotor blades to significantly reduce induced drag when compared to prior art. Also, it can be used for new concepts of large subsonic and hypersonic aircraft to significantly reduce their overall drag and external dimensions when compared to prior art, simultaneously providing for very good pitch maneuver and longitudinal stability of such aircraft.

Fluid forces on kayak paddle blades of different design

Abstract: Three kayak paddle blades of different design (Conventional, Norwegian, Turbo) were tested in a low-speed wind tunnel at a maximum chord Reynolds number of Re = 2.2–2.7 × 105 (corresponding to speed through water of ≈1 m/s). The mean drag force and side force acting on each blade were measured, as the yaw and pitch angles were varied. The results were compared with those recorded for a finite rectangular flat plate of similar area and aspect ratio. For zero pitch angle of the blades, the results indicate that the drag coefficient was mostly independent of the blade design as the yaw angle was varied between ± 20°, with only the Norwegian blade design displaying a marginally higher drag coefficient than either of the other two blades or the flat plate. Increasing the pitch angle to 30°, while maintaining the yaw angle at zero, resulted in a 23% reduction of the drag coefficient for the flat plate, but only a 15% reduction of the drag coefficients for the three blades. For all designs, the drag coefficient reduction followed a simple cosine relationship as the pitch angle or yaw angle was increased. The wind tunnel experiments revealed that the side force coefficients for all three paddle blade designs were entirely independent of the blade design and were indistinguishable from those recorded for a flat plate. In summary, the study showed that the nondimensional force coefficients are largely independent of the paddle blade design.

Aerodynamic Drag of Engine-Cooling Airflow With External Interference

Abstract: This report examines the aerodynamic drag and external interference of engine cooling airflow Much of the report is on inlet interference, a subject that has not been discussed in automotive technical literature It is called inlet spillage drag, a term used in the aircraft industry to describe the change in inlet drag with engine airflow The analysis shows that the reduction in inlet spillage drag, from the closed front-end reference condition, is the primary reason why cooling drag measurements are lower than would be expected from free stream momentum considerations In general, the free stream momentum (or ram drag) is the upper limit and overstates the cooling drag penalty An analytical expression for cooling drag is introduced to help the understanding and interpretation of cooling drag measurements, particularly the interference at the inlet and exit Empirical thrust coefficients, which represent the interferences, are introduced as a practical representation of the interaction to the exterior pressure distribution Comparisons to experimental measurements on three vehicles are presented to illustrate the concepts

High efficiency tip vortex reversal and induced drag reduction

Abstract: Methods for increasing the performance of a foil ( 100 ) by using tip droop ( 102 ) having an inward directed camber capable of generating an inward directed lifting force on the tip droop ( 102 ) in order to control spanwise flow conditions adjacent the tip ( 112 ) of a foil ( 100 ). Methods for varying the inward lifting shape of a tip droop ( 102 ) are provided along with methods for varying the angle of attack and camber of the tip droop ( 102 ) as the angle of attack of the foil ( 100 ) is changed and as spanwise flow conditions vary.

Aerodynamic Coefficients for a Parafoil Wing with Arc Anhedral - Theoretical and Experimental Results

Abstract: One main characteristic of gliding parachutes is the arc anhedral, i.e. the spanwise curvature of the wing. This paper presents an approach for the theoretical calculation of the aerodynamic coefficients of such wings based on the extended lifting line theory. In order to check the confidence of this theoretical approximation, the aerodynamic coefficients are validated using real flight tests data coming from ALEX flight experiments. The paper compares the theoretical with the experimental results and discusses the differences between both. Abbreviations and Nomenclature ALEX Small Autonomous Parafoil Landing Experiment DLR German Aerospace Center DOF Degrees Of Freedom CP Center of Pressure e0, e anhedral angle b, c, R span, chord, line length S, Λ reference area, aspect ratio V air speed α, β angle of attack, angle of side slip p, q, r body-fixed angular rates φ, θ, ψ Euler angles ρ air density (ρ0 = 1.225 kg/m3) x, y, z geometric position X, Y, Z forces in bodyfixed axis L, D, Y lift, drag, side force L, M, N rolling, pitching, yawing moment Γ, γ circulation (vortex strength) η, θ integration variables αi, αg induced, geometric angle of attack αZL zero lift angle a0 airfoil lift curve slope a1, a2 Fourier coefficients k, k1, k2 lifting line parameter e Oswald efficiency factor CL , CD aerodynamic lift/drag coefficients CLα wing lift curve slope CDi induced drag coefficient CY side force coefficient Cm pitching moment coefficient Cl, Cn rolling/yawing moment coefficient CYβ side force derivative wrt. side slip (other derivatives analogous) δl, δr left/right control deflection δs, δa symmetric/asymmetric deflection bk width of deflected trailing edge ek mean anhedral angle (deflection) lk distance to wing center ∆αZL shift of the zero lift angle ∆CD0δ additional profile drag ∩ local parafoil axis (subscript) k deflected trailing edge (subscript) d distribution (frontscript) fk_ correction factor (frontscript) Introduction For the simulation and the dynamic stability analysis of a parafoil-load system a mathematical model is required that accounts for the kinetics and aerodynamics of the vehicle. In contrast to the well known kinetic relationships there is still some uncertainty in the determination of aerodynamic coefficients for ram-air parachute canopies. Past investigations have either evaluated the aerodynamic coefficients from wind tunnel tests [1,2,3,4], have taken airplane aerodynamics as a model [5] or have used numerical methods to compute them for a concrete wing configuration [4,6,7,8]. For airplane wings, a common approach is to use Prantl lifting line theory and it’s extension by Weissinger (extended lifting line theory) to compute the aerodynamic coefficients [9]. In the past, this theory has been applied to gliding parachutes by Gonzalez [10] (numerical implementation of the Multhopp procedure for an AIAA-2003-2106 __________________________________________ * Research Scientist, Mathematical Methods and Data Handling Branch, Member AIAA Copyright © 2003 by T. Jann, published by the American Institute of Aeronautics and Astronautics, Inc. with permission. 17th AIAA Aerodynamic Decelerator Systems Technology Conference and Seminar 19-22 May 2003, Monterey, California AIAA 2003-2106 Copyright © 2003 by Thomas Jann. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. 2 arched wing) and Iosilevskii [11] (theoretical study on the aerodynamics of a paraglider). This paper presents an approach for the theoretical calculation of aerodynamic coefficients based on the extended lifting line theory for an elliptical rigid wing with arc anhedral. As result, simple formulas are derived that allow easily to compute the aerodynamic derivatives (including lateral and dynamic derivatives) for different wing aspect ratios and curvatures. In this context also the aerodynamic effects responsible for the typical behavior of an arched wing will be discussed. However, because the flexibility of the parafoil canopy is neglected, the computed coefficient should only be understood as rough estimates rather than precise values. Nevertheless, they provide a set of consistent aerodynamic parameters that can be used as starting point for simulation and system identification. In order to check the confidence of the theoretical approximation, the aerodynamic coefficients are validated using real flight tests data coming from ALEX flight experiments [12,13, 14]. The vehicles were equipped with an extensive flight test instrumentation package including GPS, inertial and airdata sensors, magnetometer and actuator position transducers. In the past, 20 remotely and autonomously controlled flight tests were conducted dropping the vehicle from a helicopter at 600 to 2000 m. The acquired flight test data led to a database which is evaluated using system identification methods. In this validation procedure the parameters of a 6-DoF parafoil-load model are adjusted to match simulation with real flight test results. The paper compares the theoretical with the experimental results and discusses the differences between both. Figure 1: ALEX in Flight Model of the Parafoil Wing Once inflated a ram-air parachute is essentially a wing with low aspect ratio [15]. While early parafoils always had a rectangular planform, in modern constructions tapered, semi-elliptical or elliptical planforms became more common. Arc Anhedral One main characteristic of gliding parachutes is the arc anhedral, i.e. the spanwise curvature of the wing, produced by the suspension lines joined together in the confluence points. The anhedral causes a side force which is required to spread the flexible wing and produce a stable shape. The amount of anhedral (anhedral angle e0) is a function of the ratio of line length R and span b.

Investigation of Tip Vortex on Aerodynamic Performance of a Micro Air Vehicle

Abstract: Tip vortex induces downwash movement that reduces the effective angle of attack. When a wing has a relatively low aspect ratio, such as that employed by the micro air vehicle (MAV), the induced drag by the tip vortex is relatively large and therefore the aerodynamic performances of the vehicle are deteriorated. In this paper we study the MAV wing aerodynamics using the endplate to help probe the tip vortex effects. The investigation is facilitated by solving the Navier-Stokes equations around a rigid wing with a root chord Reynolds number of 9x10. It is confirmed that with modest angle of attack, the endplate can reduce the downwash, and therefore increase the effective angle of attack and the lift. However, as the angle of attack becomes higher than 15, the wing tip vortex is stronger and the endplate can no longer affect the vortex structure to improve lift. Furthermore, drag also increases along with the endplate.

Survey and Analysis of Research on Supersonic Drag-Due-to-Lift Minimization With Recommendations for Wing Design

Abstract: A survey of research on drag-due-to-lift minimization at supersonic speeds, including a study of the effectiveness of current design and analysis methods, has been conducted. The results show that a linearized theory analysis with estimated attainable thrust and vortex force effects can predict with reasonable accuracy the lifting efficiency of flat wings. Significantly better wing performance can be achieved through the use of twist and camber. Although linearized theory methods tend to overestimate the amount of twist and camber required for a given application and provide an overly optimistic performance prediction, these deficiencies can be overcome by implementation of recently developed empirical corrections. Numerous examples of the correlation of experiment and theory are presented to demonstrate the applicability and limitations of linearized theory methods with and without empirical corrections. The use of an Euler code for the estimation of aerodynamic characteristics of a twisted and cambered wing and its application to design by iteration are discussed.

Vortex Generator Installation Drag on an Airplane Near Its Cruise Condition

Abstract: A method is discussed for predicting the drag increment caused by the installation of a blade-type vortex generator (VG) on a transonic-transport airplane. The original Nash and Bradshaw magnie cation concept of roughness drag is extended to cover compressible e ows and then is applied to VG blades to estimate the VG installation drag on an airplane. Thedrag of a VG blade placed on a wing will beamplie ed dueto thegrowth of the boundary layerwith distance along thewing surface. Nash and Bradshaw showed that thedegree of magnie cation cannot be approximated simply by the ratio of local to freestream dynamic pressure ( q effect). To demonstrate the magnie cation effects, some VG installation drag analyses for transonic-transport airplane models are performed using the new magnie cation factor formula. It can be seen that the agreement between these predicted drag increments and the wind-tunnel test results is good, but the drag increment based on the q effect is seriously underestimated.

New model of decelerating bluff-body drag

Abstract: A new model of the drag force generated by a freely decelerating bluff body is presented. The model is based, mainly, on the premise that the wake of an object accelerating downwind in a moving fluid is identical to that of the same object decelerating in the fluid at rest. After arguing for the drag of a wind drifter to depend only on a power function of its speed relative to the wind, a Galilean transformation is used to provide a formula for decelerating body drag of the form F D ∼ V β . The value of exponent β is dependent on the amount of external force applied to the body, as well as on its initial and final drag coefficients and its initial speed. By implication, this exponent depends on the specific history of the motion. Applications to powered and unpowered vehicles trailing a parachute or any other high-drag devices are presented and discussed

On the Equation Satisfied by a Steady Prandtl-Munk Vortex Sheet

Abstract: We show the the voricity distribution obtained by minimizing the induced drag on a wing, the so called Prandtl-Munk vortex sheet, is not a travelling-wave weak solution of the Euler equations, contrary to what has been claimed by a number of authors. Instead, it is a weak solution of a non-homogeneous Euler equation, where the forcing term represents a "tension" force applied to the tips. This is consistent with a heuristic arguement due to Saffman. Thus, the notion of weak solution captures the correct physical behavior in this case.

The design of winglets for high-performance sailplanes

Abstract: Although theoretical tools for the design of winglets for high-performance sailplanes were initially of limited value, simple methods were used to design winglets that gradually became accepted as benefiting overall sailplane performance. As understanding was gained, improved methods for winglet design were developed. The current approach incorporates a detailed component drag buildup that interpolates airfoil drag and moment data across operational lift-coefficient, Reynolds-numbe{, and flap-deflection ranges. Induced drag is initially predicted using a relatively fast multiple lifting-line method. In the final stages of the design process, a full panel method, including relaxed-wake modeling, is employed. The drag predictions are used to compute speed polars for both level and turning flight. The predicted performance is in good agreement with flight-test results. The straight- and turningflight-speed polars are then used to obtain average crosscountry speeds as they depend on thermal strength, size, and shape, which are used to design the winglets that provide the greatest gain in overall performance. Flight-test measurements and competition results have demonstrated that the design methods produce winglets that provide an important performance advantage over much of the operating range for both span-limited and span-unlimited highperformance sailplanes.

Method for reducing the drag of blunt-based vehicles by adaptively increasing forebody roughness

Abstract: A method for reducing drag upon a blunt-based vehicle by adaptively increasing forebody roughness to increase drag at the roughened area of the forebody, which results in a decrease in drag at the base of this vehicle, and in total vehicle drag.

スクラムジェットエンジンの3分力測定 1)マッハ4から8飛行条件におけるエンジン抗力

Abstract: Aerodynamic performance of scramjet engines was measured by using 0.44-m-long models in a M6.7 wind tunnel. Drags and wall pressure distributions were measured to evaluate the total pressure and friction drag in the engine internal flow. The internal drag of the models with various struts was dicussed. The internal and the external drags, the pressure and the friction drags were estimated. Consistency between the force balance measurements and the pressure measurements was examined. The internal drag obtained from the force balance agreed with that based on the wall pressure measurements.

The development of a PrandtlPlane aircraft configuration

Abstract: A PrandtlPlane aircraft configuration is based on the concept of “Best Wing System”. Reference is made to a theoretical result published by Prandtl in 1924, showing that the lifting system with the minimum induced drag, under certain conditions, is a wing box in the front view. The properties of the Prandtl’s Best Wing System are independent from the sweep angles of the wings and, then, an aircraft configuration based on these properties is valid also for the transonic range. This configuration, in honour of Prandtl, has been named as "PrandtlPlane". In order to develop a PrandtlPlane configuration, a large amount of aerodynamic analyses is needed. These computations can be carried out by means of Boundary Element method or CFD (Computational Fluid Dynamics) codes. The main problem connected to the application of the aerodynamic codes is the shape generation of the aircraft; even more so, in the case of such a complex configuration. At the University of Pisa, a proper code, named MSD (Multiple Shape Design), has been set up to generate any aerodynamic PrandtlPlane configuration. MSD is a parametric geometry generator which uses features typical of the commercial CAD codes for solid modelling, as extrusions, holes, intersections and generation of wing/wing and wing/body fillets, etc.. The last version of MSD makes use of NURBS (Non Uniform Rational B-Splines) geometrical entities. By means of MSD code and a CFD code, the PrandtlPlane configuration was developed. The application of the methodology is shown with reference to a very large aircraft. The configuration was changed having in mind both the Prandtl results on the best wing system (same total lift and same lift distribution on the two wings, butterfly shaped lift on the vertical wings) and the static stability of flight. The paper shows that, in general, the condition of static stability of flight could reduce the aerodynamic efficiency. The paper shows also that PrandtlPlane configurations exist in which the aircraft is stable as far as flight mechanics is concerned and, at the same time, the front and the rear wings are equally loaded. This configuration is completely different from a very large conventional aircraft. This PrandtlPlane concept is applicable to any kind of aircraft, when proper modifications are introduced. As an example, a two seat ultra light aircraft is presented. A scaled wind tunnel model was tested at the Technical University of Torino and some results are presented in this paper.

Aerodynamic Drag Reduction of a Racing Motorcycle Through Vortex Generation

Abstract: Aerodynamic Drag Reduction of a Racing Motorcycle through Vortex Generation

Aerodynamic Drag and Drag Reduction

Abstract: An assessment of the role of fluid dynamic resistance and/or aerodynamic drag and the relationship to energy use in the United States is presented. Existing data indicates that up to 25% of the total energy consumed in the United States is used to overcome aerodynamic drag, 27% of the total energy used in the United States is consumed by transportation systems, and 60% of the transportation energy or 16% of the total energy consumed in the United States is used to overcome aerodynamic drag in transportation systems. Drag reduction goals of 50% are proposed and discussed which if realized would produce a 7.85% total energy savings. This energy savings correlates to a yearly cost savings in the $30Billion dollar range.

Wing-tip-to-wing-tip aerodynamic interference

Abstract: The aerodynamic interaction of finite wings flying in very close proximity is investigated experimentally. Docked wings are also examined. Tests were carried out in a water tunnel and Particle Image Velocimetry (PIV) was employed to generate velocity data along Trefftz planes. The results indicate that vortex lines “jump”, or reconnect from one wing tip to the next, even in cases of some physical separation. These data can be used to calculate lift and drag and our calculations indicate significant reductions in drag.

A Relationship Between Wave Drag and Induced Drag

Abstract: A formulation for the induced drag of a wing in subsonic or transonic flow is derived from entropy considerations. This approach shows how wave drag and induced drag are related. The new formulation is cast in a form similar to that used in the classic induced drag derivation thus allowing a theoretical comparison of the two approaches. If there are no shock waves in the flow the two formulations agree theoretically only in the case of an elliptic wing loading, although calculations indicate that the quantitative difference may be relatively small. If shock waves are present they can increase or decrease the induced drag leading to the idea of a reduction in the sum of induced and wave drag by a judicious tailoring of the flow over the wing.

The evolution of sailplane wing design

Abstract: As the sport of soaring initially focused on exploiting ridge winds to maintain altitude, and the level of structural technology was unable to allow large spans, the low sink rates required were achieved by wings having large areas and fairly low aspect ratios. By the late 1920's, the discovery of thermals led to the use of climb/glide sequences for cross-country soaring. Thus, the trade-off between low induced drag for climb and low profile drag for cruise became a critical issue in the design of sailplane wings. Theoretical guidance for these designs was provided primarily by the lifting-line theory of Ludwig Prandtl and the minimum induced drag, elliptical loading result of Max Munk. During this time, the need for greater spans and higher aspect ratios led to structural advancements in the primarily wooden airframes and the development of some very interesting wing geometries, such as the distinctive gull wings that were then popular. The evolution of wing design through this period continued slowly until the introduction of new materials and laminar flow wing sections led to very rapid advancements beginning in the late 1950's. The use of glass-reinforced plastic structures, and later carbon-reinforced plastic, allowed designers to incorporate much larger aspect ratios than had been possible earlier. By the rnid 1970's, the computational capabilities had improved io the extent that lifting-surface theories, such as vortex-lattice and panel methods, were utilized in the design process. In additiory non-linear methods were developed that could not only account for non-rigid wakes, but also optimize the wing geometry to achieve the greatest cross-country performance. These developments led to the adaptation of planforms having straight trailing edges and on to non-planar wing geometries and the, now commonplace, use of winglets. While it is not at all clear what directions wing design in the future will take, it will no doubt be influenced by technological developments such as the use of boundary-layer suction for laminar-flow control and conformable/adaptable wing geometries that "morph" to the optimum configuration for any given flight situation.

Using Drag to Hover

Abstract: Unlike a helicopter, an insect can, in theory, use both lift and drag to stay aloft. Here we show that a dragonfly uses mostly drag to hover by employing asymmetric up and down strokes. Computations of a family of strokes further show that using drag can be as efficient as using lift at the low Reynolds number regime appropriate for insects.

Effects of Various Fillet Shapes on a 76/40 Double Delta Wing from Mach 0.18 to 0.7

Abstract: The effects of linear, diamond, and parabolic fillets on a double delta wing were investigated in the NASA Langley 7 x 10 ft High Speed Tunnel from Mach 0.18 to 0.7 and angles of attack from 4 deg. to 42 deg. Force and moment, pneumatic pressures, pressure sensitive paint, and vapor screen flow visualization measurements were used to characterize the flow field and to determine longitudinal forces and moments. The fillets increased lift coefficient and reduced induced drag without significantly affecting pitching moment. Pressure sensitive paint showed the increase in lift is caused by an increase in suction and broadening of the vortex suction footprint. Vapor screen results showed the mixing and coalescing of the strake fillet and wing vortices causes the footprint to broaden.

High-performance propeller

Abstract: A high-performance propeller has one hub and a plurality of blades, characterized in that a double-side or a single-side arc brim is provided at the tip of each blade. The propeller of the invention can provide a small induced drag and convert the centrifugal force to the effective force so as to increase the differential pressure near the tip of blades and thereby increase the acting force on blades. Under the condition of same power consumption, it has been tested for the large propeller in the type of lateral inclination that the amount of flow is increased about 12% SIMILAR 17%, which is equivalent to save energy 40% SIMILAR 70%. Since the fluid dynamic performance presents the aspect ratio approaching infinity, the width of the blades can be increased whereas the induced drag is not increased. Applying the method of increasing the area of the blades and decreasing the velocity of outflow fluid, the effect on saving of energy can be further improved greatly on the present basis.

Sailboat hull and method for reducing drag caused by leeway

Abstract: A shaped hull with a fixed angle keel with respect to the hull that when heeled, orients the keel to an angle of attack substantially related to the heel angle. The angle of attack being sufficient to create on the keel a lateral force substantially equal and opposite to the lateral force derived from the wind. The submerged portion of the hull, however, remains symmetrical and oriented parallel to the course sail as is its associated drag contribution vector. Thereby reducing or substantially eliminating the lateral force generated by the hull and the associated drag contribution. The movement of the shaped hull induces a lateral force on the keel without generating a lateral force and its associated drag on the hull, thus providing a sailboat with reduced drag without resorting to the prior art methods and their associated disadvantages.

Side Flow Stabilization of a Stepped-Nose Obstacle (Experimental Documentation)

Abstract: A stepped-nose with various step lengths and heights, attached to a square cylinder, can significantly reduce the drag coefficient compared to that of the square cylinder. The underlying physics are that (1) the vortices trapped in the step regions produce the thrust forces acting on the step surfaces facing against the uniform stream which cancel the drag force acting on the front surface of the stepped-nose obstacle, and (2) the tangent reattachment of the flow separating from the front surface edges to the side surfaces of the main body decreases the suction pressure acting on the back surface of the main body. In the present study, these favorable effects of the stepped-nose are experimentally documented by presenting the measurement results of surface pressure coefficient, streamwise velocity, and turbulence intensity of side flow and flow visualization pictures. It is demonstrated that when step height takes a value of about one-tenth of the main body length, there is a rather wide range of step length, for which the net drag force acting on the stepped-nose almost vanishes and the side flow is stabilized by the stepped-nose.