Showing papers on "Lift-induced drag published in 1994"

Lift enhancement of an airfoil using a Gurney flap and vortex generators

Abstract: Experimental measurements of surface pressure distributions and wake profiles were obtained for an NACA 4412 airfoil to determine the lift, drag, and pitching-moment coefficients for various configurations. The addition of a Gurney flap increased the maximum lift coefficient from 1.49 up to 1.96, and decreased the drag near the maximum lift condition. There was, however, a drag increment at low-to-moderate lift coefficients. Additional nose-down pitching moment was also generated by increasing the Gurney flap height. Good correlation was observed between the experiment and Navier-Stokes computations of the airfoil with a Gurney flap. Two deploy able configurations were also tested with the hinge line forward of the trailing edge by one and 1.5 flap heights, respectively. These configurations provided performance comparable to that of the Gurney flap. The application of vortex generators to the baseline airfoil delayed boundary-layer separation and yielded an increase in the maximum lift coefficient of 0.34. In addition, there was a significant drag penalty associated with the vortex generators, which suggests that they should be placed where they will be concealed during cruise. The two devices were also shown to work well in concert.

Variable-complexity aerodynamic optimization of a high-speed civil transport wing

Abstract: A new approach for combining conceptual and preliminary design techniques for wing optimization is presented for the high-speed civil transport (HSCT). A wing-shape parametrization procedure is developed which allows the linking of planform and airfoil design variables. Variable-complexity design strategies are used to combine conceptual and preliminary-design approaches, both to preserve interdisciplinary design influences and to reduce computational expense. In the study, conceptual-design-level algebraic equations are used to estimate aircraft weight, supersonic wave drag, friction drag, and drag due to lift. The drag due to lift and wave drag are also evaluated using more detailed, preliminary-design-level techniques. The methodology is applied to the minimization of the gross weight of an HSCT that flies at Mach 3 with a range of 6500 mi.

Quantitative low-speed wake surveys

Abstract: Theoretical and practical aspects of conducting three-dimensional wake measurements in large wind tunnels are reviewed with emphasis on applications in low-speed aerodynamics. Such quantitative wake surveys furnish separate values for the components of drag such as profile drag and induced drag, but also measure lift without the use of a balance. In addition to global data, details of the wake flowfield as well as spanwise distributions of lift and drag are obtained. This article demonstrates the value of this measurement technique using data from wake measurements conducted on a variety of low-speed configurations including the complex high-lift system of a transport aircraft.

Aerodynamic corrections for the flight of birds and bats in wind tunnels

Abstract: Few wind tunnel studies of animal flight have controlled or corrected for distortions to behaviour, physiology or flight aerodynamics representing the difference between flight in the tunnel and flight in free air. Aerodynamic correction factors are derived based on lifting-line theory and the method of images for an animal flying freely within closed- and open-section wind tunnels; the method is very similar to that used to model flight in ground effect, and as in ground effect the corrections to induced drag may be substantial. These correction factors are used to estimate bound wing circulation, drag and mechanical power for comparison with free flight, and to derive testable predictions of optimum flight strategies for an animal in a tunnel. In an open-section tunnel, mechanical power is increased compared to free flight, and the animal should fly at the tunnel centre. In a closed tunnel mechanical power is usually reduced, and substantial savings are available, particularly at low speeds, if the animal flies close to the tunnel roof. Anecdotal observations confirm that birds and bats adopt this strategy. The mechanical power-speed curve in a closed tunnel is flatter than the curve for free flight, and this may explain the flat metabolic power-speed curves for birds and bats obtained in some measurements.

Drag and wake modification of axisymmetric bluff bodies using Coanda blowing

Abstract: This work investigates the ability of Coanda jet blowing to modify the base pressure of a cylindrical body aligned axially in a flow, and thereby, produce overall drag reduction. It is found that blowing through one or two slot jets concentric to the outer body circumference can significantly influence the entire base flow region. The recirculating wake is eliminated and is replaced by freestream fluid entrained by the Coanda blowing. Base pressure rises significantly and leads to drag reduction of up to 30% beyond the thrusting action of the Coanda jet. A comparison between the power savings through drag reduction and the power requirement of the Coanda jet demonstrates that net benefits are attainable at certain body geometries and flow conditions. By judiciously selecting the jet blowing velocity, it is possible to produce a nearly flat wake velocity profile requiring little net power. RAG reduction of immersed bodies is a subject with a long history, leading to the early concept of streamlining. The net drag force on a body may be considered the sum of viscous drag and pressure drag forces. For streamlined aero- dynamic and hydrodynamic bodies, the pressure drag is small, and current research is directed towards the application of laminar flow control (e.g., suction), turbulent viscous drag reduction (e.g., riblets and large eddy breakup devices (LEBUs)), and the use of nonlinear aerodynamics for induced drag reduction (e.g., winglets or crescent wing planforms). For bluff bodies, on the other hand, streamlining is usually not an option for reducing drag because the bluff shape is often dictated by other constraints. This situation is particu- larly true for trucks, buses, and most automobiles. For bluff bodies then, where pressure drag dominates, drag reduction is primarily through base flow modification, including flow separation control using airfoils, the use of plates, cavities, base bleed, and suction/blowing. Bluff bodies may be considered of two general classifica- tions—high and low aspect ratio. The former may be modeled as bodies of large span relative to a characteristic height, and are generally two-dimensional in nature. Examples would be the classic cylinder in crossflow, or a symmetric airfoil with a thick, blunt trailing edge. Drag reduction for such bodies has been performed1"3 with drag reductions of up to 64% reported in the literature. Low aspect ratio bodies have also been studied. Such bodies are characterized by three-dimensionality or axisymmetry, with a sphere being the classic example. Other examples would be cylinders of rectangular or circular cross section aligned axially in the flow direction. Work on drag reduction of such bodies has been reported in Refs. 4-12. A variation of these studies would include inclined base regions such as fast-back auto- mobiles and cargo transport aircraft. During the energy crisis of the seventies, renewed interest in vehicle drag led to many important new findings which are summarized in the books

Prediction of ice shapes and their effect on airfoil drag

Abstract: Calculation of ice shapes and the resulting drag increases are presented for a NACA 0012 airfoil. The calculations were made using a combination of modified LEWICE and interactive boundary-layer codes for a wide range of values of parameters such as airspeed and temperature, the droplet size and liquid water content of the cloud, and the angle of attack of the airfoil. Based on experimental data, an improved correlation of equivalent sand-grain roughness was developed. Calculated ice shapes are in good agreement with experimental data for rime ice, but some differences are shown between predictions and experimental data for glaze ice. Calculated drag coefficients generally follow trends shown by the experimental data.

In-flight lift-drag characteristics for a forward-swept wing aircraft and comparisons with contemporary aircraft)

Abstract: Lift (L) and drag (D) characteristics have been obtained in flight for the X-29A airplane (a forward swept-wing demonstrator) for Mach numbers (M) from 0.4 to 1.3. Most of the data were obtained near an altitude of 30,000 ft. A representative Reynolds number for M = 0.9, and a pressure altitude of 30,000 ft, is 18.6 x 10(exp 6) based on the mean aerodynamic chord. The X-29A data (forward-swept wing) are compared with three high-performance fighter aircraft: the F-15C, F-16C, and F/A18. The lifting efficiency of the X-29A, as defined by the Oswald lifting efficiency factor, e, is about average for a cantilevered monoplane for M = 0.6 and angles of attack up to those required for maximum L/D. At M = 0.6 the level of L/D and e, as a function of load factor, for the X-29A was about the same as for the contemporary aircraft. The X-29A and its contemporaries have high transonic wave drag and equivalent parasite area compared with aircraft of the 1940's through 1960's.

Dynamic Ground Effects Flight Test of an F-15 Aircraft

Abstract: Flight tests to determine the changes in the aerodynamic characteristics of an F-15 aircraft caused by dynamic ground effects are described. Data were obtained for low and high sink rates between 0.7 and 6.5 ft/sec and at two landing approach speeds and flap settings: 150 kn with the flaps down and 170 kn with the flaps up. Simple correlation curves are given for the change in aerodynamic coefficients because of ground effects as a function of sink rate. Ground effects generally caused an increase in the lift, drag, and nose-down pitching movement coefficients. The change in the lift coefficient increased from approximately 0.05 at the high-sink rate to approximately 0.10 at the low-sink rate. The change in the drag coefficient increased from approximately 0 to 0.03 over this decreasing sink rate range. No significant difference because of the approach configuration was evident for lift and drag; however, a significant difference in pitching movement was observed for the two approach speeds and flap settings. For the 170 kn with the flaps up configuration, the change in the nose-down pitching movement increased from approximately -0.008 to -0.016. For the 150 kn with the flaps down configuration, the change was approximately -0.008 to -0.038.

Drag Reduction for Turbulent Flow over a Projectile: Part I

Abstract: A numerical study is made to analyze the drag performance of a secant-ogive-cylinder-boattail projectile in the transonic Mach number regime between 0.91 and 1.20. To improve the projectile's performance, two drag reduction methods, boattailing and base bleed, are applied. The effectiveness of each method and the combination of both methods are studied by varying the values of parameters such as boattail angle, bleed quantity, and bleed area. The computed distributions of surface pressure coefficient of the projectile with different boattail angles are in close agreement with experimental data. Computed drag components and the total drag of the projectile are accurate by comparison with experimental data and semiempirical predictions. The optimal boattail angle for total drag reduction is predicted to be at about 5-7 deg. The method of combining boattailing and base bleed can become an effective method for total drag reduction.

Aerodynamic design of supersonic cruise wings with a calibrated linearized theory

Abstract: The design of supersonic cruise wings for minimum drag due to lift is examined in this study. The aerodynamic design method is based on a supersonic linearized theory modified to include corrections for attainable leadingedge thrust and vortex forces. A semiempirical design and estimation method has been developed to account for the deficiencies of the linearized theory which tends to overestimate the required amount of twist and camber and predicts an unattainable level of performance. Comparisons of theoretical and experimental results showed that the semiempirical method provides for the selection of the amount of twist and camber required for maximum performance at cruise and gives a good estimate of the level of performance.

Power Augmentation Effects of a Horizontal Axis Wind Turbine With a Tip Vane—Part 2: Flow Visualization

Abstract: We present a discussion of the physics of the flow discussed in our first report. By visualizing the flow around the tip vane, the following results were drawn: 1) The strength of the tip vortex, the induced drag and turbulence on the blade tip can be diminished with a tip vane. 2) The inflow rate to the rotary surface of wind turbine can be increased with the tip vane

Drag structure for fishing reel

Abstract: A drag structure for a fishing reel comprising a drag assembly, and a drag control element for contacting said drag assembly to produce a drag force. The drag control element is adjustably movable toward and away from said drag assembly and switchable between an operational position in which to vary the drag force and an inoperational position in which not to produce the drag force. The drag control element includes means for informing the angler that the drag control element is switched to the inoperational position.

Study on wings of flying microrobots

Abstract: The conventional method for calculating aerodynamic forces generated on objects is based on the aerodynamics in the high Reynolds number flow, like the airflow around the wings of airplanes, because little is known about the low Reynolds number flow. Using this method to calculate the aerodynamic force acting on a flying microrobot, the obtained results may differ from the actual values. For analysis of this difference. The large-scale models of wings for flying microrobots were made, whose wing lengths are 3 cm and 1.5 cm respectively. With these wings the experiments were done in the low Reynolds number flows (Re=385, 752). The drag forces measured in these experiments were compared with the ones from calculations. As a result, in both flows, the measured values were larger than the calculated one. Using semiconductor surface machining technology, we also fabricated a flapping mechanism with the wings that generate the difference of the drag forces during upstroke and downstroke movements. >

Flow Characteristics of the Main Nozzle in an Air-Jet Loom Part II: Measuring High Speed Jet Flows from the Main Nozzle and Weft Drag Forces

Abstract: In this research, the jet-flow characteristics under tank pressures of 2 ∼ 6 kgf/cm2 were studied to obtain basic data for an optimal design of the main nozzle in an air- jet loom. Furthermore, wef...

On the boundary-layer control through momentum injection: Studies with applications

Abstract: The concept of moving surface boundary-layer control, as applied to a Joukowsky airfoil, is investigated through a planned experimental programme complemented by numerical studies. The moving surface was provided by rotating cylinders located at the leading edge and/or trailing edge as well as top surface of the airfoil. Results suggest that the concept is quite promising, leading to a substantial increase in lift and a delay in stall. Depending on the performance desired, appropriate combinations of cylinder geometry, location and speed can be selected to obtain favourable results over a wide range of angle of attack. Next, effectiveness of the concept in reducing drag of bluff bodies such as a two-dimensional flat plate at large angles of attack, rectangular prisms and three-dimensional models of trucks is assessed through an extensive wind tunnel test-programme. Results show that injection of momentum through moving surfaces, achieved here by introduction of bearing-mounted, motordriven, hollow cylinders, can significantly delay separation of the boundary-layer and reduce the pressure drag. The momentum injection procedure also proved effective in arresting wind-induced vortex resonance and galloping type of instabilities. A flow visualization study, conducted in a closed-circuit water tunnel using slit lighting and polyvinyl choride tracer particles, adds to the wind-tunnel and numerical investigations. It shows, rather dramatically, the effectiveness of the moving surface boundary-layer control (MSBC).

Main wing of supersonic aircraft

Abstract: PURPOSE: To provide vortex drag reduction effect which is equal to that obtained when a wing end is extended, reduce induced drag, and increase lift/ drag ratio without extending an end of a wing which is thin and long vertically and unique to a supersonic aircraft. CONSTITUTION: In a main wing of a supersonic aircraft which flies at Mach number of 1-5, a winglet is mounted in non-plane manner by making a rear fringe coincide with a wing end section of the main wing, and the plane shape of the winglet is trapezoidal type having low aspect ratio. The winglet having front fringe retraction angle ΛLE is formed in such a way that ΛLE. winglet>=ΛM≡COS (1/M), and cant angle ϕ is in a scope of 90>ϕ>=70 deg.. Furthermore, mounting angle θ is 0-1 deg., chord length Cr.w of a wing root section of the winglet is in a scope of Ct>=Cr.w>=Ct/2 in which it is smaller than chord length Ct of the wing end section of the main wing and larger than a half of the chord length Ct, and the ratio λ of the chord length Cr.w of the wing root section of the winglet to the chord length Ct.w of the wing end is in a scope of 0.5>=λ>=0.2 so that the main wing of the supersonic aircraft has the shape in which torsion distribution is not provided in the winglet.

Helicopter Performance Evaluation (HELPE) Computer Model

Abstract: : A HELicopter Performance Evaluation (HELPE) computer model has been developed. The model is empirically based on the energy balance method. For a helicopter at a given mission, the model computes for a helicopter at given weight and flight conditions, the maximum possible level speed, its maneuverability in a turn, and its hover and climb capabilities in the in-ground and out-of-ground effects modes. The code also computes the speeds of maximum endurance in the air and of maximum range for the helicopter. Thrust, Induced drag, Profile drag, Tail rotor, Parasitic drag, Turn radius, Rate of turn, Vertical rate of climb, Maneuverability, Bank angle

Induced Drag Prediction for Wing-Tail and Canard Configurations through Numerical Optimisation.

Abstract: Abstract A computational procedure has been developed in order to predict aerodynamic interference between lifting surfaces, and to devise configurations which best meet given aerodynamic requirements. The procedure, which couples an aerodynamic solver with a numerical optimisation routine, is useful in the preliminary design of aircraft. The essential features of the aerodynamic code and of the optimisation routine are described, along with the coupling criteria. Some of the most significant predictions obtained in induced-drag minimisation for wing-tail and canard configurations are described and discussed.

Improvement of the low-speed control authority of an AUV through hull shaping

Abstract: Often it is necessary to operate an autonomous underwater vehicle (AUV) under conditions where the specific gravity of the vehicle varies by as much as 3%. For AUV systems without a variable ballast system that have to operate at low speeds, this can severely restrict the operational envelope of the system. This paper explores the limits on control authority as a function of vehicle speed and specific gravity for a typical AUV and then shows the effect of increasing the hull elliptic cross-section on vehicle control. Increasing hull lift through various devices is shown to be propulsion-limited as a result of the increase in induced drag. An example is shown where the drag of the vehicle at its lowest speed is higher than the drag at its maximum speed.

A New Drag Measurement System for Wind Tunnel Testing of the Racing Bicycle and Rider to Determine a Low Drag Configuration.

Abstract: : This study investigated the application of splitter plate effects to reduce the aerodynamic drag of the racing bicycle and rider system. A sensitive, low-force, beam-type, single-component balance was developed to provide drag measurements accurate to within 0.053 N (0.012 lbf). The performance of the new system was verified by comparing the measured drag on a three-dimensioaal, right-circular cylinder model, 0.127 m (5.0 in) in diameter and 0.610 m (24 in) long, with the results from a commercial balance and a other similar data. The bicycle and rider model consisted of a full-scale mannequin comprising only the hips, legs and feet, mounted on a regulation 0.48 m (19 in) size bicycle. Rotation of the wheels and a stationary ground plane were also simulated. Two frame configurations in conjunction with a disk type wheel were tested to determined the lowest drag configuration for narrow and wide spacing of the rider's legs. The results show that for the standard tube construction frame, the conventional wisdom to streamline as much as possible prevails. When an aerodynamic frame was tested, the overall drag was reduced. Although the standard spacing still provided the lowest drag configuration, any further streamlining showed an increase in drag.

Low-speed longitudinal aerodynamic characteristics of a flat-plate planform model of an advanced fighter configuration

Abstract: A flat-plate wind tunnel model of an advanced fighter configuration was tested in the NASA LaRC Subsonic Basic Research Tunnel and the 16- by 24-inch Water Tunnel. The test objectives were to obtain and evaluate the low-speed longitudinal aerodynamic characteristics of a candidate configuration for the integration of several new innovative wing designs. The flat plate test allowed for the initial evaluation of the candidate planform and was designated as the baseline planform for the innovative wing design study. Low-speed longitudinal aerodynamic data were obtained over a range of freestream dynamic pressures from 7.5 psf to 30 psf (M = 0.07 to M = 0.14) and angles-of-attack from 0 to 40 deg. The aerodynamic data are presented in coefficient form for the lift, induced drag, and pitching moment. Flow-visualization results obtained were photographs of the flow pattern over the flat plate model in the water tunnel for angles-of-attack from 10 to 40 deg. The force and moment coefficients and the flow-visualization photographs showed the linear and nonlinear aerodynamic characteristics due to attached flow and vortical flow over the flat plate model. Comparison between experiment and linear theory showed good agreement for the lift and induced drag; however, the agreement was poor for the pitching moment.

Applications and Developments of Wing-TipDevices to Reduce Drag

Abstract: use of wing tip devices to reduce drag of the wing is an important part of studies about aircraft drag reduction. This paper presents synthetically the new developments about the research work of the drag reduction technology by wing-tip devices. In the discussion, emphasis is given to the investigation and applications of principle, speciality and design technology for "wing tip sails", "winglet" and "sheared wing tip",which are three typical wing tip devices. The results of the investigation indicate that wing tip devices mentioned above produce substantially greater reduction in the induced drag at near design condition than would a "wing tip extension". Comparison and analysis made for various devices show that drag reduction for the complex "wing tip sail" is more effective than that for simple "winglet" and "sheared wing tip", which can be applied conveniently to the aircraft. It is important to select wing tip devices available for different aircrafts. Finally, development prospects are commented on and looked ahead on the most recent research and developments.

Experimental Study on Aerodynamic Characteristics of PAR-WIG

Abstract: To understand the aerodynamic characteristics of power- augmented-ram wing-in-ground (PAR-WIG), measurements of lift, drag and moment acting on a low aspect wing were carried out in a towing tank. A pair of model propellers were arranged in front of the wing, the Reynolds number was approximately 3x105. It is shown that lift and drag of the wing increase remarkably due to the PAR effect when the wing is close to the water surface. The lift drag ratio decreased considerably. The trailing edge flap works to significantly increase the PAR effect. The lift gradient versus angle of attack becomes negative value at large angle of attack. Further studies such as flow visualization and pressure measurement on the wing surface are necessary to understand the mechanism of the PAR effect.

The FC-1D: The profitable alternative Flying Circus Commercial Aviation Group

Abstract: The FC-1D was designed as an advanced solution for a low cost commercial transport meeting or exceeding all of the 1993/1994 AIAA/Lockheed request for proposal requirements. The driving philosophy behind the design of the FC-1D was the reduction of airline direct operating costs. Every effort was made during the design process to have the customer in mind. The Flying Circus Commercial Aviation Group targeted reductions in drag, fuel consumption, manufacturing costs, and maintenance costs. Flying Circus emphasized cost reduction throughout the entire design program. Drag reduction was achieved by implementation of the aft nacelle wing configuration to reduce cruise drag and increase cruise speeds. To reduce induced drag, rather than increasing the wing span of the FC-1D, spiroids were included in the efficient wing design. Profile and friction drag are reduced by using riblets in place of paint around the fuselage and empennage of the FC-1D. Choosing a single aisle configuration enabled the Flying Circus to optimize the fuselage diameter. Thus, reducing fuselage drag while gaining high structural efficiency. To further reduce fuel consumption a weight reduction program was conducted through the use of composite materials. An additional quality of the FC-1D is its design for low cost manufacturing and assembly. As a result of this design attribute, the FC-1D will have fewer parts which reduces weight as well as maintenance and assembly costs. The FC-1D is affordable and effective, the apex of commercial transport design.