Showing papers on "Lift-induced drag published in 1997"

Dragonfly flight. I. Gliding flight and steady-state aerodynamic forces.

Abstract: The free gliding flight of the dragonfly Sympetrum sanguineum was filmed in a large flight enclosure. Reconstruction of the glide paths showed the flights to involve accelerations. Where the acceleration could be considered constant, the lift and drag forces acting on the dragonfly were calculated. The maximum lift coefficient (CL) recorded from these glides was 0.93; however, this is not necessarily the maximum possible from the wings. Lift and drag forces were additionally measured from isolated wings and bodies of S. sanguineum and the damselfly Calopteryx splendens in a steady air flow at Reynolds numbers of 700-2400 for the wings and 2500-15 000 for the bodies. The maximum lift coefficients (CL,max) were 1.07 for S. sanguineum and 1.15 for C. splendens, which are greater than those recorded for all other insects except the locust. The drag coefficient at zero angle of attack ranged between 0.07 and 0.14, being little more than the Blassius value predicted for flat plates. Dragonfly wings thus show exceptional steady-state aerodynamic properties in comparison with the wings of other insects. A resolved-flow model was tested on the body drag data. The parasite drag is significantly affected by viscous forces normal to the longitudinal body axis. The linear dependence of drag on velocity must thus be included in models to predict the parasite drag on dragonflies at non-zero body angles.

Drag Prediction and Transition in Hypersonic Flow

Abstract: This paper discusses progress on issues such as instability studies, nose-bluntness and angle-of-attack effects, and leading-edge-contamination problems from theoretical, computational, and experimental points of view. Also included is a review of wind-tunnel and flight data, including high-Re flight transition data, the levels of noise in flight and in wind tunnels, and how noise levels can affect parametric trends. A review of work done on drag accounting and the role of viscous drag for hypersonic vehicles is also provided.

In-flight adaptive performance optimization (APO) control using redundant control effectors of an aircraft

Abstract: Practical application of real-time (or near real-time) Adaptive Performance Optimization (APO) is provided for a transport aircraft in steady climb, cruise, turn descent or other flight conditions based on measurements and calculations of incremental drag from a forced response maneuver of one or more redundant control effectors defined as those in excess of the minimum set of control effectors required to maintain the steady flight condition in progress. The method comprises the steps of applying excitation in a raised-cosine form over an interval of from 100 to 500 sec. at the rate of 1 to 10 sets/sec of excitation, and data for analysis is gathered in sets of measurements made during the excitation to calculate lift and drag coefficients C L and C D from two equations, one for each coefficient. A third equation is an expansion of C D as a function of parasitic drag, induced drag, Mach and altitude drag effects, and control effector drag, and assumes a quadratic variation of drag with positions δ i of redundant control effectors i=1 to n. The third equation is then solved for δ iopt the optimal position of redundant control effector i, which is then used to set the control effector i for optimum performance during the remainder of said steady flight or until monitored flight conditions change by some predetermined amount as determined automatically or a predetermined minimum flight time has elapsed.

Development of a universal wake survey data analysis code

Abstract: A universal wake survey data analysis code which is compatible with different types of wake data acquisition systems has been developed. The theories of Maskell and Betz are used. Their basic approach is to rewrite the drag and lift integrals in terms of flow variables measured inside the wake region. Quantitative wake surveys allow separate measurements of profile drag, induced drag, and lift, including sectional distributions of lift and drag. Some wake survey data analysis results are also discussed in order to demonstrate the general capabilities of the currently developed code.

I. gliding flight and steady-state aerodynamic forces

Abstract: The free gliding flight of the dragonfly Sympetrum sanguineum was filmed in a large flight enclosure. Reconstruction of the glide paths showed the flights to involve accelerations. Where the acceleration could be considered constant, the lift and drag forces acting on the dragonfly were calculated. The maximum lift coefficient (CL) recorded from these glides was 0.93; however, this is not necessarily the maximum possible from the wings. Lift and drag forces were additionally measured from isolated wings and bodies of S. sanguineum and the damselfly Calopteryx splendens in a steady air flow at Reynolds numbers of 700‐2400 for the wings and 2500‐15 000 for the bodies. The maximum lift coefficients (CL,max) were 1.07 for S. sanguineum and 1.15 for C. splendens, which are greater than those recorded for all other insects except the locust. The drag coefficient at zero angle of attack ranged between 0.07 and 0.14, being little more than the Blassius value predicted for flat plates. Dragonfly wings thus show exceptional steady-state aerodynamic properties in comparison with the wings of other insects. A resolved-flow model was tested on the body drag data. The parasite drag is significantly affected by viscous forces normal to the longitudinal body axis. The linear dependence of drag on velocity must thus be included in models to predict the parasite drag on dragonflies at non-zero body angles. Summary

Comparison of smart wing concepts for transonic cruise drag reduction

Abstract: A method is being developed to employ TERFENOL to optimize the shapes of wings for minimum drag during transonic cruise Potential advantages include enhanced UAV attack and surveillance capabilities through increased dash speed, longer loiter, and extended range as well as decreased fuel expenditures for transport aircraft Two smart-wing concepts were compared: an adaptive wing with the capability to change the shape of the wing box and a smart trailing edge that modifies camber while maintaining a smooth upper surface While the adaptive wing provides the most capability to change the structural shape to minimize shock- induced drag, when actuator- and structural-weight penalties were considered as well as reliability and maintenance, it was determined that the smart trailing edge is the better concept Numerical optimization of a simplified smart trailing edge determined the optimum configuration and optimum deflections for minimum drag The system has the potential to extend the range of a small-fuselage large-wing UAV bomber by 9% and increase its loiter time by 11% Magnetic and electronic design improvements to the TERFENOL linear-wave motor have been identified that will enable us to miniaturized it for UAV applications while doubling its actuation force and speed, and halving its power

Rapidly-convertible roadable aircraft

Abstract: A fixed wing aircraft that can be automatically and rapidly converted to a roadway vehicle within seconds while driving in the highway, comprising a one-piece wing rotatably mounted on top of the fuselage The aircraft features a 3-horizontal-surface design allowing good pitch stability and damping in a very short fuselage, stall-resistant feature and reduction in induced drag at cruise speed The aircraft's wing is enlargeable with additional wing tip segments allowing boost in aspect ratio hence improving efficiency at high loads The vehicle has low center of gravity, four wheels with independent suspension, nose-height leveling for take-off and landing, and anti-sway mechanism in order to prevent roll-over in a tight turn Ground propulsion is by both a ducted fan and hydraulic rear wheel drive allowing rapid accleration in the roadable mode

Nonlinear Longitudinal Stability of a Symmetric Aircraft

Abstract: The longitudinal stability of a symmetric aircraft is examined beyond the well-known linearization about a steady mean state, leading to the phugoid and short-period modes The exact equations of longitudinal motion of a symmetric aircraft are considered, ie, balance of longitudinal and transverse force (without side force ) and balance of pitching moment; the drag terms included are friction and lift-induced drag, plus nonsymmetric lift ‐ drag polar; the mass density is taken as a constant, as well as thrust along the e ight path Elimination would lead to a fourth-order nonlinear differential equation for the angle of attack relative to the angle of zero pitching moment, if the acceleration of the e ight-path angle is neglected, and the e ight-path angle is moderate In the case of a small e ight-path angle, it simplie es to a thirdorder differential equation, containing a set of nonlinear corrections, to a second-order linear equation, specifying sinusoidal oscillation of the relative angle of attack It is shown, by a small perturbation method, that forced oscillations occur at its harmonics (viz double or triple frequency ), and free oscillations can have decaying or growing amplitude In the case of statically stable aircraft, the oscillations have a short period and grow or decay slowly In the case of statically unstable aircraft the growth is rapid, as in a pilot-induced oscillation

Semi-Empirical Vortex Step Method for the Lift and Induced Drag Loading of 2D or 3D Wings

Abstract: The familiar "vortex step" method for calculating the spanwise distribution of lift, lift slope, and aerodynamic center position is reviewed and enhanced to more accurately locate the wing aerodynamic center and to accommodate arbitrary spanwise variations of sweep, chord, twist, camber, flaps, and dihedral. Lifting and downwash line position and shape are adjusted to account for semi-empirical effects of planform and airfoil properties. Vector and matrix methods are then applied to solve for the spanwise distribution of lift normal to the spar, or for the required twist to obtain a prescribed loading. For induced drag, an "apparent downwash" method is proposed to reveal the negative induced drag of winglets. Then, predicted 2D and 3D wing characteristics are compared to test data. Finally, the methods are applied to the design and analysis of unique wing configurations.

Design and wind tunnel test results of a flapped laminar flow airfoil for high-performance sailplane applications

Abstract: A laminar flow airfoil with camber changing flap, named DU89-1.34 / 74, has been designed and windtunnel tested for application in the high-performance sailplanes ASH-26E and ASW-27 produced by Alexander Schleicher Segelflugzeugbau, Germany. The ASH-26E is an 18m span selflaunching sailplane with retractable propellor and the ASW-27 is a 15m span FAI competition sailplane. Primary objectives were: low drag at a specified range of lift coefficients and Reynolds numbers, no abrupt loss of lift beyond the upper boundary of the low drag bucket at high lift conditions - to avoid bad handling and climbing qualities in thermal flight conditions, gradual stalling characteristics, and a maximum lift coefficient insensitive to leading edge contamination. These requirements have been met, as verified experimentally, by the design of long laminar flow regions on the upper and lower surface and, at increasing angle of attack, a controlled growth of the turbulent separated area while transition moves forward to the leading edge. Flap deflections and artificial transition were integrated from the start into the design. Flexible slot sealings save drag and, at the high speed flap settings, the sealing on the lower surface enables the boundary layer to remain laminar up to 95% chord, where pneumatic turbulators cause transition. In comparison with the well-known Wortmann sailplane airfoil FX62-K-737/77,the new airfoil shows superior performance.

Determination of Drag From Three-Dimensional Viscous and Inviscid Flowfield Computations

Abstract: A momentum balance approach is used to extract the drag from flowfield computations for wings and wing/bodies in subsonic/transonic flight. The drag is decomposed into vorticity, entropy, and enthalpy components which can be related to the established engineering concepts of induced drag, wave and profile drag, and engine power and efficiency. This decomposition of the drag is useful in formulating techniques for accurately evaluating drag using computational fluid dynamics calculations or experimental data. A formulation for reducing the size of the region of the crossflow plane required for calculating the drag is developed using cut-off parameters for viscosity and entropy. This improves the accuracy of the calculations and decreases the computation time required to obtain the drag results. The improved method is applied to a variety of wings, including the M6, W4, and Ml65 wings, Lockheed Wing A, a NACA 0016 wing, and an Elliptic wing. The accuracy of the resulting drag calculations is related to various computational aspects, including grid type (structured or unstructured) , grid density, flow regime (subsonic or transonic), boundary conditions, and the level of the governing equations (Euler or Navier-Stokes ). The results show that drag prediction to within engineering accuracy is possible using computational fluid dynamics, and that numerical drag optimization of complex aircraft configurations is possible.

Leading edge channel for enhancement of lift/drag ratio and reduction of sonic boom

Abstract: The leading edges of wings, nose assemblies, tails, fins, struts, and other components of aircraft, atmospheric entry vehicles and missiles in which the leading edge is blunted and the flight Mach number is supersonic, are provided with passive airflow channel, resulting in significantly reduced wave drag and total drag, significantly increased lift-to-drag ratio, and reduced sonic boom.

POST-STALL FLOW CONTROL ON AN AIRFOIL BY LOCAL UNSTEADY FORCING Part I. Lift, Drag, and Pressure Characteristics

Abstract: By using a Reynolds-averaged two-dimensional computation of a turbulent flow over an airfoil at poststall angles of attack, we show that the massively separated and disordered unsteady flow can be effectively controlled by a local unsteady excitation with low-level power input. In a certain range of post-stall angles of attack and forcing frequency, the unforced random separated flow can become periodic or quasi-periodi c, associated with a strong lift enhancement, which opens a promising possibility for one to fly beyond the static stall till to a much higher angle of attack. The same local control also leads to, in some situations, a reduction of the drag. On a part of the airfoil the pressure fluctuation is suppressed as well, which would be beneficial for higha buffet control. The computations confirm the physical principles for controlling a massively separated unsteady flow proposed by Wu, Vakili, and Wu (Prog. Aerospace Sci. 28 (1991), 73-131) and are in qualitative agreement with several recent post-stall flow control experiments. In Part I of this two-part paper, we examine the characteristics of lift, drag, and surface pressure without and with control, focusing mainly on the effect of forcing frequency and angles of attack. The necessary conditions for unsteady control to be successful are identified.

Aerodynamic optimization study of a mission adaptive wing for transport aircraft

Abstract: A theoretical preliminary study to evaluate the aerodynamic performance of a variable camber wing (VCW) for transport aircraft has been performed. The study has been concentrated on the potential use of such wing to reduce induced drag in a wide lift variation range and on its performance to produce high lift for landing. As a reference, similar analysis have been made for the conventional wing of same planform, equipped with modern high lift devices. To perform the evaluations, a constrained direct optimization method has been used, composed of a vortex lattice analysis method coupled to a multivariable function minimizer algorithm. To simulate idealized camber variation, basic elastic deformation solutions have been produced with a linear finite element method for flat plates, to assure minimum structural feasibility guidelines. Within the limitations and simplified modeling assumed for this preliminary study, it has been concluded that an increase of 0.023 on the Oswald efficiency factor might be expected over the basic wing. Also, to have high lift performance comparable to conventional current wing designs, deformable camber airfoil wing sections would have to produce maximum lift coefficients much higher than equivalent airfoils with plain leading and trailing edge flaps.

Zero-lift drag characteristics of afterbodies with a square base

Abstract: Results of zero-lift drag characteristics of afterbodies with a square base relevant to missile and projectile applications at several transonic Mach numbers and Mach 2 are presented. These afterbodies, at zero incidence, generate vortical flows upstream of the base like that on the lee side of a delta wing at incidence. The measurements made consisted primarily of afterbody drag using a balance and base pressure and extensive surface flow visualization studies were carried out to infer features associated with vortex flows. Results of base pressure, boat-tail profile drag, and total afterbody drag are presented and compared with results from the axisymmetric counterpart involving circular arc and conical boat tailing having the same base area. Some aspects of the flow features on square-base afterbodies are discussed as well.

Studies of vortex flaps for different sweepback angle delta wings

Abstract: Low speed windtunnel measurements were made on a 50° delta wing with leading edge vortex flaps. Improvements in the lift/drag ratio were obtained by deflecting the leading edge vortex flap. Comparisons were made between the previously measured 60° and 70° delta wing results and the present 50° wing results. Improvements in the lift/drag ratio of the 50° delta wing were attained over a wider lift coefficient range than for the 70° delta wing. The highest lift/drag ratio for the 50° delta wing is achieved when the flow attaches to the flap surface without any large area of separation. Estimations of the aerodynamic forces were also made using a quasi-vortex lattice method coupled with the leading edge suction analogy for the 50° 60° and 70° delta wings

Effect of riblets on axisymmetric base pressure

Abstract: Experiments have been performed assessing riblet effects on axisymemtric base pressure at low speeds. The tests were conducted in the 0.91-m-diam. low-speed wind tunnel at a freestream velocity of 20 m/s. It is shown that, with a large-scale or massive separation, riblets do not decrease the base drag at low speeds; on the other hand, there is a progressive increase in base drag with h+ and the drag penalty is about 8 percent for the optimized drag reducing riblet. Riblets may provide a small pressure or base drag reduction on streamlined bodies with a sharp trailing edge like an airfoil or turbine blade, because the effects of viscous-induced displacement thickness will be lower on the riblet surface.

Numerical Solution Of The Lifting Surface Equation

Abstract: The piecewise-constant vorticity method of Tuck* for solution of the lifting surface integral equation determines accurately integrated quantities such as the lift produced by planar lifting surfaces. Here a modification to this method is presented whereby the leading-edge singularity strength and leading-edge suction force, and hence the induced drag, may also be calculated accurately.

Lee waves and hydrodynamical loads due to the motion of a submerged horizontal circular cylinder in a three-layer fluid

Abstract: Laboratory experiments and analytical studies investigating the interaction of two-dimensional, uniform stratified flow with a submerged horizontal circular cylinder are presented. Measurements were made of the interfacial waves formed behind the cylinder towed horizontally at constant speeds, and of the drag and lift forces exerted on the cylinder. An analytical linear model that describes the wave field and the associated wave induced drag force is formulated. In this model, the water is modeled as a uniform flow of three layers of inviscid and immiscible fluids. A solution is found for the case of the cylinder located in the upper layer. The experiments showed that large amplitude first mode internal waves are generated when the cylinder is towed at about one half of the long wave celerity of first mode waves, and that drag and lift forces change significantly with stratification. The analytical model demonstrates the role of a finite stratified layer. For the shorter waves it predicts wave lengths wel...

A device for the reduction of the aerodynamic drag of cycles and similar, with air injection in the wake

Abstract: A device for the reduction of the aerodynamic drag of cycles and similar, consisting of a pipe (1), passing through the frame (T), and provided with an air intake (2) arranged in the front part between the wheel (RA) and the handle-bar (M), and the outlet (3) below the saddle, so as to reduce the aerodynamic drag determined by the cycler's body, with air injection in the wake.

Vortex Structures and Span Loadings from Alleviated-Wake Measurements

Abstract: In an effort to find efficient wing designs that shed non-hazardous vortex wakes, an analysis is made of data taken in the wakes of three configurations of a subsonic transport. The study begins with the observation that alleviated-wake configurations often shed vortex wakes that induce about the same rolling-moment coefficient on following aircraft of all sizes. In order to determine the span loadings that correspond to these downstream vortex wakes, the analysis first finds the vortex structures that make up the measured downwash distributions. An inverse Betz method is then used to derive the corresponding span loadings. Analysis of these span loadings, and consideration of the induced drag and the energy in various wakes, yields information on some of the characteristics and penalties associated with the design of wings for less hazardous wakes. It is recommended that tools be developed for an optimization process that includes drag, wing-root bending moment, weight, complexity, etc. and the design of vertical and horizontal lifting surface for vortex wakes that have an acceptable hazard. Nomenclature