Maximum Lift-drag Ratio Research Articles

Aerodynamic characteristics of sharp elliptic cones in a viscous hypersonic gas flow

The results of an experimental investigation of the aerodynamic characteristics of elliptic cones for M???=12.5 and Re0=(0.78–1.52)·104 are given. The effect of the apex angle of the cone and the ellipticity coefficient on the value of the maximum lift-drag ratio is considered. It is shown that in a viscous gas flow the function K(α) can be determined by assigning the quantity Kmax and the corresponding angle of incidence. The experimental data are compared with the results of calculations.

縦湾曲Ｖ型オッターボードの流体特性

The hydrodynamic characteristics of a vertical V type otter board, which has been widely used recently by Japanese trawlers, were studied using a model with a dihedral angle and a sweepback angle. The model with 309cm2 wing area and 14.1% camber ratio were rigged for an attack angle ranging from -5° to 90°. The lift, drag and moment were measured by a three-component balance on a circulating water tank. Results showed that the maximum lift coefficient was 1.27 while the maximum lift-drag ratio was 4.03 when the stall angle was 22°. The range of the common attack angle sustaining 75% of maximum lift-drag ratio was comparatively wide (17°), and variation of the coefficient of pressure center was only 10%. It follows that this type of otter board is of good stability.

円型オッターボードの流体学的研究 ＩＩ 迎角およびヒールアングルの変化による円型オッターボードの性能と安定性

The efficiency and stability of simplified plastic saucer-shaped otter board models with seven kinds of camber (0, 5, 7.5, 10, 15, 20, 25%) were studied. Models were rigged for an attack angle of between 0° and 50° and for an inward heel angle of between 0° and 20° at 5-degree intervals. The horizontal lift, drag and moment were measured by a three component load cell in a circulation-type test tank. Lift and drag coefficients, lift-drag ratio and coefficient of pressure centre were then calculated.The lift and drag coefficients became smaller when the angle of heel was gradually increased from 0° to 20°. The coefficient of pressure centre increased with increase of the camber. Considering the mean lift-drag ratio which was calculated using the width of 5° on both sides of the attack angle at the maximum lift-drag ratio for all models, the optimum camber of the otter board was from 5 to 7% while the most effective heel angle was 5° inwards. However, otter boards with higher camber of 13-23% seemed to be more stable judging from both the width of attack angle at 75% of the maximum lift-drag ratio and the mean coefficient of pressure centre within 5° on each side of the attack angle at the maximum lift-drag ratio.

キャンバス製拡網装置，ウイングパラカイトの流体特性

A canvas-made cambered wing parakite with ribs was designed as a net-mouth opening device for practical use. To carify its hydrodynamic characteristics, a flume experiment was conducted on the variations of the camber ratio, the number of ribs and the vertical curvature at a constant aspect ratio. Results showed that a wing parakite with 10 ribs (camber ratio 17%) was highly efficient. When this parakite was set with 6.5% vertical curvature, the maximum lift coefficient was 1.14 and the maximum lift-drag ratio was 3.35. The performance of this wing parakite was comparable to that of an ordinary cambered upright otter board.

円型オッターボードの流体力学的研究 ＩＩＩ ブラケットを取り付けた円型オッターボードの揚抗特性

The characteristics of lift and drag of the saucer-shaped otter board were studied using models with five kinds of cambers (0, 5, 10, 15, 20%). The models attached with appendages were rigged for an attack angle of between 0°and 30°and for an inward heel angle of between 0°and 10°at 5-degree intervals. The horizontal lift, drag and moment were measured by a three-component load cell in a circulating test tank. The lift and drag coefficients, lift-drag ratio and coefficient of pressure centre were then calculated.Only from the mean lift-drag ratio which was narrowly defined and calculated using the width of 5°on both sides of the attack angle at the maximum lift-drag ratio for all models, it was difficult to evaluate the efficiency of the otter boards because the variation of the mean lift-drag ratio at given different cambers was not significant. Therefore we judged the stability of the otter boards both from the width of attack angle at 75% of the maximum lift-drag ratio and from the coefficient of pressure centre. As a result, the otter boards with cambers of between 15% and 18% and with an attack angle of between 10°and 30°were stable and better than the others.

Effect of viscosity on the lift-drag ratio of a thin blunt wing at hypersonic rates of flow round it

The effect of viscosity on the carrying properties of hypersonic aircraft appears at great flight altitudes, where an important factor is the interaction of the laminar boundary layer with inviscid flow. In the present study the method of bands is used to make an approximate calculation of this effect for a regime of weak viscous interaction [1]. The results of [2] are used for conditions of inviscid flow round a body. The local coefficient of friction and coefficients of the additional pressure induced by the boundary layer are determined from the data for a plate of infinite width [3]. Simple relationships are obtained which make it possible to estimate the effect of viscosity on the magnitude of the maximum lift-drag ratio and the value of the angle of attack corresponding to it. The results are given of an experimental study of hypersonic flow round a plane triangular wing in a broad range of Reynolds numbers, and these confirm the relationships obtained and indicate the region in which they are applicable.

Conical wing of maximum lift-drag ratio in a supersonic gas flow

The calculation of supersonic flow past three-dimensional bodies and wings presents an extremely complicated problem, whose solution is made still more difficult in the case of a search for optimum aerodynamic shapes. These difficulties made it necessary to simplify the variational problems and to use the simplest dependences, such as, for example, the Newton formula [1–3]. But even in such a formulation it is only possible to obtain an analytic solution if there are stringent constraints on the thickness of the body, and this reduces the three-dimensional problem for the shape of a wing to a two-dimensional problem for the shape of a longitudinal profile. The use of more complicated flow models requires the restriction of the class of considered configurations. In particular, paper [4] shows that at hypersonic flight velocities a wing whose windward surface is concave can have the maximum lift-drag ratio. The problem of a V-shaped wing of maximum lift-drag ratio is also of interest in the supersonic velocity range, where the results of the linear theory of [5] or the approximate dependences of the type of [6] can be used.

Compressor Cascade Optimization based on Inverse Boundary Layer Method and Inverse Cascade Method : 2nd Report, An Inverse Boundary Layer Method and Wind-Tunnel Tests of Optimized Compressor Cascade with High Loading

An aerodynamic approach to an optimum compressor cascade in a two-dimensional incompressible flow is described on the basis of two inverse problems ; namely, an inverse boundary layer problem in order to produce the optimum surface velocity distribution and an inverse cascade problem in order to obtain the blade section which realizes a prescribed velocity distribution. A new method for the former problem is developed in this paper; namely, the momentum equation is integrated for a prescribed shape factor distribution in order to get an unseparated turbulent flow approaching the equilibrium state. An inverse cascade design method is introduced by combining the thus obtained optimum surface velocity distribution with the inverse cascade method proposed in the previous report. Highly loaded compressor cascade designed by this method was tested in a low speed cascade wind-tunnel. Reasonable agreement between the theory and the experiments is obtained and the maximum lift-drag ratio is about 1.4 times as high as that of corresponding NACA 65 series cascade at design operation.

二次元の有限空どうキャビテーション翼型の最適化に関する一考察

In this paper, an optimum problem of supercavitating hydrofoils at nonzero cavitation number is treated by the linearized theory. Namely, the purpose of this paper is to determine the foil profile which has minimum drag coefficient under the given lift coefficient, angle of attack, foil length, and cavitation number. Optimum profiles are determined by using calculus of variation. The foil configuration is limited to the so-called two-term and four-term hydrofoils.The foil configuration and the lift-drag ratio are obtained under various given above conditions.The results obtained in this paper are summerized as follows:(1) When the lift coefficient, angle of attack, and foil length are fixed, the lift-drag ratio of the optimum hydrofoil with nonzero cavitation number is greater than that with zero cavitation number.(2) The difference of the lift-drag ratio between the two-term and four-term hydrofoil is only a few percents. Consequently, it may be seen that the results of the optimum hydrofoils are dominant in the problem of the optimum hydrofoils.(3) It is seen that the foil configurations which have the maximum lift-drag ratio in the optimum hydrofoils with same lift coefficient, attack of angle, and foil length are almost independent of the cavitation number.

Optimal design of hydrofoil and marine propeller using micro-genetic algorithm (μGA)

This paper presents results from the application of the genetic algorithm (GA) technique to the design optimization of hydrofoil and marine propeller incorporating potential based boundary element method (BEM). Although, larger population size as implemented by simple genetic algorithm (SGA) could find the optimal individual after a fewer number of generations than smaller population size, it is penalized by a longer amount of time to evaluate fitness in every generation. An investigation is, therefore, conducted in this research to implement micro genetic algorithm (μGA) with a very small population, and with simple genetic parameters, in order to achieve faster convergence to better solution from generation to generation. The technique is applied here to optimize hydrofoils of different plan forms, e.g., rectangular, elliptical, trapezoidal etc. Firstly, the hydrofoil design parameters, such as, angle of incidence, maximum thickness and camber ratios, aspect ratio, taper ratio, angle of sweep etc. are initialized randomly and the generated hydrofoil is analyzed by potential based boundary element method. GA then updates the design parameters over generation after generation and finally, finds an improved hydrofoil of maximum lift-drag ratio or minimum drag coefficient satisfying some design constraints. An improved blade or hydrofoil section is also designed by GA satisfying some design constraints. Finally, the technique is applied to the optimum design of marine propeller. In this study, μGA is found useful and prospective tool for the design optimization of hydrofoil and marine propeller due to its faster convergence. Keywords: Genetic algorithm, boundary element method, hydrofoil, propeller, design optimization  doi: 10.3329/jname.v1i1.2038 Journal of Naval Architecture and Marine Engineering 1(2004) 47-61

Experimental aerodynamcis of a rotor entry vehicle.

An unpowered entry vehicle model has been tested at Mach numbers 0.10 to 3.54 at angles of attack from 15° to 90°. The tests included variations of blade collective and cyclic pitch angles. A summary of the autorotative equilibrium speed, forces, and moments is presented. The results indicate that adding the to the capsule improved vehicle performance throughout most of the Mach number range. Maximum lift drag ratio was substantially improved at low Mach numbers. Large pitching moments were produced by the rotor, requiring the use of flaps for longitudinal trim. Control phasing was unusual compared to the predicted response of an ideal rotor but did not change grossly with forward flight speed.

A Method of Reducing Aeroelastic Effects of Highly Swept Wings

The greatest efficiency for a lifting surface at supersonic speeds, according to the theoretical considerations of reference 1, can be attained if the leading edge is swept well behind the Mach cone and the highest aspect ratio which is structurally possible is employed. Such a wing, designed for a Mach number of 3.0, would have 80 deg. of sweepback. Aeroelastic effects have < been shown 3 to be considerable for a wing with 60deg of sweepback and designed for a Mach number of 2.0. The wing shown was found theoretically to have considerable loss in maximum lift-drag ratio attributable to aeroelasticity. This wing has 12-per cent-thick Clark-Y airfoils normal to the wing leading edge. If it were of solid aluminum and flying at a dynamic pressure of 2,400 lbs./sq.ft. (flexibility parameter qb(exp. 4) /El(0) = 7.8), analysis indicates that the wing would deflect so as to reduce the maximum lift-drag ratio about 30 per cent.

The Problem of Obtaining High Lift-Drag Ratios at Supersonic Speeds

The importance of the lift to drag ratio is well known to all aircraft designers since it gives, to a great extent, the aerodynamic efficiency of the airplane. Aerodynamic efficiency, however, is only one component of the grand compromise that a completed airplane represents. At subsonic speeds, lift-drag ratios of well over 200 have been measured in wind tunnels on airfoil sections; but few powered aircraft have attained (L/D) value of 20. It is invariably true that the requirements of stability and control, structure, and flight operation all contribute to reducing the design (L/D) (sub max)) considerably below those exotic values which can be predicted from unrestricted aerodynamic theory. If, however, a certain range or operating efficiency is required, there is most certainly a minimum (L/D) (sub max)) value for which the goals are just attainable. If we examine the range equation we see that range is proportional to the lift-drag ratio, the thermopropulsive efficiency, and the logarithm of the initial to final weight ratio. The appearance of the lift-drag ratio as a linear factor in the range equation indicates that every attempt should be made to increase (L/D) (sub max)); however, the search for higher (L/D)max may lead to strange and unorthodox configurations. Most frequently, such configurations are ruled out by the adverse effects of their geometry on the weight ratios. In the present paper, we will deal with the maximum lift-drag ratio problem for conventional configurations having a wing and a body in close proximity to each other. No attempt will be made to select a particular configuration as being the best. However, the promising direction to go from the aerodynamic view will be stressed with the understanding that the other factors may outweight the aerodynamics

Choice of Airfoils for Rotating-Wing Aircraft

T E National Advisory Committee for Aeronautics has for some time been directing its efforts toward the improvement of safety in flight, and with that purpose in view has done extensive research on rotating-wing aircraft at the Langley Memorial Aeronautical Laboratory. At present an extensive program of research on rotating wings is under way in the propellerresearch wind tunnel, where autogiro and gyroplane models 10 feet in diameter are to be tested to determine the influence of varying such basic properties of the rotor as the pitch angle, the airfoil section, the plan form, and the blade mass. Similar tests are being made on a model of a cyclogiro rotor 8 feet in diameter. The following analysis of the choice of airfoils for these rotors is supported by work that has already been completed; much valuable information concerning this and related subjects is anticipated from the current program. Rotating-wing aircraft may be divided into two main classes: those normally employing power-driven rotors for sustentation, such as the helicopter, helicogyre, and cyclogiro; and those employing autorotating wings for sustentation, such as the autogiro and gyroplane. The autogiro and helicopter are familiar types. The helicogyre is an aircraft supported by a power-driven lifting propeller which is rotated by means of an additional propeller on each blade of the main screw. The cyclogiro is supported by a paddlewheel rotor on each side of the fuselage, rotating about the lateral axis. The gyroplane is quite similar aerodynamically to the autogiro except that the blades on the gyroplane rotor are free to rotate only about the span axis, and the opposite blades are rigidly joined; lift on opposing sides of the rotor is equalized by rotation of a blade pair about its span axis. The aerodynamic characteristics of an airfoil section required for the optimum performance of a rotating wing are the same regardless of the type under consideration. I t is true, however, that the choice of the proper airfoil is more critical for the autorotating systems than for the power-driven; for this reason, the following discussion will be concerned with the autogiro and gyroplane rotors. The aerodynamic similarity between these two types is so complete that the analysis applies with equal validity to both systems. The autogiro is a windmill of low pitch operating at large angles of yaw and maintaining a condition of zero aerodynamic torque during a state of steady autorotation. This condition means essentially that the average moment, during one revolution, of the blade element chord forces about the axis of rotation is zero, the chord force on any element being the sum of two components of opposite sign, and being derived from the lift and drag of the element. The torque variation with rotor speed is such that a decrease in speed in any state of operation generates an accelerating torque, and conversely; the rotation is therefore stable. The optimum airfoil for a rotor of given geometrical form is defined as the airfoil that gives the largest maximum lift-drag ratio of the rotor. I t has been shown by Lock (British R. & M. 1127) that by consideration of the energy losses in the rotor, the ratio of drag to lift can be expressed as