Showing papers on "Lift-induced drag published in 1980"

Joined wing aircraft

Abstract: An aircraft having a fuselage and a pair of first airfoils in the form of wings extending outwardly from the vertical tail and a pair of second airfoils in the form of wings extending outwardly from the forward portion of the fuselage at a lower elevation than the first airfoils. The second wings extend rearwardly having a positive dihedral so that the tip ends of the second airfoil are located in close proximity to and may overlap the tip ends of the first wings. The pairs of wings along with the fuselage present a double triangle or diamond shape in both front elevational view and top plan view. A winglet structurally connects the tip ends of the corresponding first wings and second wings, and these winglets have airfoil surfaces which extend vertically substantially beyond the tip ends of the first and second wings in order to minimize the effects of induced drag and also to augment directional stability of the aircraft. In addition, a unique wing structure is disclosed where the average thickness varies along the chord of the wing to enhance resistance to the component of lift acting normal to the spanwise plane containing the centroids of the airfoils.

Prandtl's biplane theory applied to canard and tandem aircraft

Abstract: Prandtl's biplane theory for elliptic loadings is generalized to apply to nonelliptic spanwise load distributions. The induced drag is calculated by assuming an infinite stagger distance so all of the mutually induced drag acts upon the rear surface which has no effect upon the front surface. Consequently, the mutually induced drag is calculated by integrating the Trefftz-plane downwash of the front surface over the independent load distribution on the rear surface. This procedure is verified by explicit solutions that give the same mutually induced drag irrespective of the fore and aft location of the larger span when carrying either an elliptic or a uniform load distribution. It was found that the mutually induced drag was less when the larger span had a uniform load distribution, but the total induced drag was not decreased because of the additional self-induced drag produced by the change from the ideal elliptic loading to a uniform loading. However, when the larger span carried a uniform loading it allowed the smaller span, when either fore or aft, to support more of the aircraft's weight at the minimum induced drag condition.

Preliminary design characteristics of a subsonic business jet concept employing an aspect ratio 25 strut braced wing

Abstract: The advantages of replacing the conventional wing on a transatlantic business jet with a larger, strut braced wing of aspect ratio 25 were evaluated. The lifting struts reduce both the induced drag and structural weight of the heavier, high aspect ratio wing. Compared to the conventional airplane, the strut braced wing design offers significantly higher lift to drag ratios achieved at higher lift coefficients and, consequently, a combination of lower speeds and higher altitudes. The strut braced wing airplane provides fuel savings with an attendant increase in construction costs.

Grooves reduce aircraft drag

Abstract: Aerodynamic drag can be reduced by many small longitudinal grooves machined in aircraft skin. Experiments show that grooves parallel to airflow reduce drag by 4 to 7 percent. Reduced drag translates into reduced engine power required to overcome drag and ultimately to lower fuel consumption.

Wing flapping with minimum energy

Abstract: For slow flapping motions it is found that the minimum energy loss occurs when the vortex wake moves as a rigid surface that rotates about the wing root - a condition analogous to that determined for a slow-turning propeller. The optimum circulation distribution determined by this condition differs from the elliptic distribution, showing a greater concentration of lift toward the tips. It appears that very high propulsive efficiencies are obtained by flapping.

Design considerations of advanced supercritical low drag suction airfoils

Abstract: Supercritical low drag suction laminar flow airfoils were laid out for shock-free flow at design freestream Mach = 0.76, design lift coefficient = 0.58, and t/c = 0.13. The design goals were the minimization of suction laminarization problems and the assurance of shock-free flow at freestream Mach not greater than design freestream Mach (for design lift coefficient) as well as at lift coefficient not greater than design lift coefficient (for design freestream Mach); this involved limiting the height-to-length ratio of the supersonic zone at design to 0.35. High design freestream Mach numbers result with extensive supersonic flow (over 80% of the chord) on the upper surface, with a steep Stratford-type rear pressure rise with suction, as well as by carrying lift essentially in front- and rear-loaded regions of the airfoil with high static pressures on the carved out front and rear lower surface.

Induced drag ideal efficiency factor of arbitrary lateral-vertical wing forms

Abstract: A relatively simple equation is presented for estimating the induced drag ideal efficiency factor e for arbitrary cross sectional wing forms. This equation is based on eight basic but varied wing configurations which have exact solutions. The e function which relates the basic wings is developed statistically and is a continuous function of configuration geometry. The basic wing configurations include boxwings shaped as a rectangle, ellipse, and diamond; the V-wing; end-plate wing; 90 degree cruciform; circle dumbbell; and biplane. Example applications of the e equations are made to many wing forms such as wings with struts which form partial span rectangle dumbbell wings; bowtie, cruciform, winglet, and fan wings; and multiwings. Derivations are presented in the appendices of exact closed form solutions found of e for the V-wing and 90 degree cruciform wing and for an asymptotic solution for multiwings.

Performance improvement of delta wings at subsonic speeds due to vortex flaps

Abstract: Subsonic wind tunnel tests were conducted to determine performance improvements possible from the use of leading edge vortex flaps (LEVF) on delta wings. Various flap sizes and deflection angles were examined and lift-to-drag ratio improvements of up to 40% were found at moderate angles of attack on 60 deg and 75 deg swept wings. The LEVF is concluded to be effective in moving the wing's leading edge vortex onto the flaps, tilting the vortex-induced force vector forward to produce a thrust or reduce the wing's drag while maintaining attached flow and lift on the wing's upper surface.

Higher order farfield drag minimization for a subcritical wing design code

Abstract: A higher order Trefftz plane model of the undistorted interacting wing wakes of two symmetric subsonic planforms has been developed and integrated with an existing vortex lattice wing design code. The Trefftz plane calculation provides continuous, piecewise quadratically varying bound circulations, which are then interpolated in the nearfield vortex lattice representation of the wing. Integration of the surface slopes for a specified chord loading function provides the design wing camber surfaces. This paper outlines the theoretical development and presents comparisons between results obtained using the present theory and (1) previous exact solutions for minimum induced drag and (2) previous wing designs obtained using a discrete vortex wake moded.

An Extension of Blade Element Momentum Theory to Incorporate Nonlinear Lift and Drag Coefficients

Abstract: : An expression for the steady induced inflow velocity is obtained from blade element and momentum theory considerations The lift coefficient is allowed to be a quadratic function of angle and attack and the drag coefficient, incorporated through a perturbation procedure, can be any arbitrary function of angle and attack A principal range of interest is identified in which the function inflow versus blade pitch angle is single valued The results reduce to the classic formula found in textbooks when the lift coefficient is linear and drag is ignored

Afterbody Drag. Volume 1. Drag of Conical and Circular Arc Afterbodies without Jet Flow

Abstract: : The results of the afterbody drag study are presented in four volumes. Volume 1 includes a series of charts that enable the drag of conical and circular arc afterbodies without jet flow to be determined.

Fuel Consumption of a Strutted vs Cantilever-Winged Short-Haul Transport with Aeroelastic Considerations

Abstract: A preliminary design of a short-haul aircraft using a strut-braced wing was made to study the possibility of block fuel savings caused by the decrease in wing weight allowed by the use of a strut. A computer-aided wing loads and stress analysis was performed to determine the wing weight savings. It was found that the wing weight savings are not large in this aircraft and the induced drag decrease is offset by the strut parasite drag. The final cantilever and strutted configurations have essentially equal block fuel consumptions. A calculated strut flutter velocity was close enough to the flight envelope to warrant design consideration.

Combination of Aileron and Flap Deflection for Minimum Induced Drag Roll Control

Abstract: Induced drag has a significant impact on the performance of flight vehicles. If a considerable amount of the airborne time is spent in maneuvering flight, optimization of vehicle performance requires the minimization of drag associated with maneuvering. In this study only the increment in induced drag due to aircraft lateral control and lateral control induced adverse yaw is analyzed theoretically, using all induced drag minimizing three-dimesional potential flow computer program. The effects of varying single segment aileron span and employment of double segment ailerons with an optimum combination of inboard and outboard corltrol surface deflection angles and the merits of differentiating the upward and downward aileron deflection angles are investigated. The influence of wing induced sidewash onto the vertical tail induced drag due to aircraft yaw trim side forces is accounted for. The optimum size of conventional ailerons is found to be in the order of 70% semispan. Double-segment aileron systems exhibit a slightly lower induced drag incremetlt. They also require smaller control deflection angles and, therefore, should yield additional reductions in viscous profile drag.

Application of the Joined Wing to Cruise Missiles.

Abstract: : The joined wing is a new airplane and missile configuration comprising two wings, a fuselage, and a fin, arranged such that the wings form diamond shapes both in plan view and in front view. Advantages claimed for the joined wing include lightness, stiffness, low induced drag, low wave drag, high trimmed maximum lift coefficient, reduced parasite drag, and good stability and control, plus 'built-in' direct lift and sideforce capabilities. Comparisons are made of three cruise missile configurations: (1) conventional, (2) joined wing, and (3) joined wing plus canard. The latter configurations yield large advantages in range, maneuverability, and terrain-following. Optimal control theory is employed to calculate the terrain-following accuracy of each configuration. (Author)

An experimental investigation of three dimensional low speed minimum interference wind tunnel for high lift wings

Abstract: As a means to achieve a minimum interference correction wind tunnel, a partially actively controlled test section was experimentally examined. A jet flapped wing with 0.91 m (36 in) span and R = 4.05 was used as a model to create moderately high lift coefficients. The partially controlled test section was simulated using an insert, a rectangular box 0.96 x 1.44 m (3.14 x 4.71 ft) open on both ends in the direction of the tunnel air flow, placed in the University of Washington Aeronautical Laboratories (UWAL) 2.44 x 3.66 m (8 x 12 ft) wind tunnel. A tail located three chords behind the wing was used to measure the downwash at the tail region. The experimental data indicates that, within the range of momentum coefficient examined, it appears to be unnecessary to actively control all four sides of the test section walls in order to achieve the near interference free flow field environment in a small wind tunnel. The remaining wall interference can be satisfactorily corrected by the vortex lattice method.

A study of wing body blending for an advanced supersonic transport

Abstract: Increases in supersonic cruise lift drag ratio were sought at Mach numbers 2.2 and 2.7 using wing body planform and thickness blending. Constrained twist and camber optimization was performed in the presence of nacelles. Wing and fuselage thickness distributions were optimized for either minimum volume wave drag or minimum total pressure wave drag. The zero leading edge suction lift drag ratios were determined for three wing planforms. The magnitude of the effect of leading edge suction on attainable lift drag ratio was defined on one planform and estimation of available leading edge suction was made.

Pressure Distributions on Some Delta Wings at M=4.

Abstract: : Complete pressure distributions are presented for a series of delta wings tested through an incidence range at a Mach number of 4. The results have been integrated to obtain lift and drag coefficients and the values found are in good agreement with the trend from measurements on similar wings at lower Mach numbers. Some of the models were designed to test a possible method of engine/airframe integration. The results show that it is possible to add volume to the rear of the wing without increasing the drag of the forebody, thus confirming the proposed method of integration. (Author)

Simplified solution of the compressible lifting surface problem

Abstract: A simplified application of planar lifting-surface theory is presented for determining the load (distribution on finite wings in compressible subsonic flow. Classical theoretical forms are used to define functions for the pressure coefficient distribution. The Kernel function integral is evaluated in a closed form/finite summation manner, resulting in a well-behaved coefficient matrix similar to that obtained in vortex lattice theory. The Mangier-type singularity is avoided. Chordwise and spanwise integrals for lift and induced drag are reduced to simple summation, with the number of terms equal to the number of collocation points used. Analytical results are compared with experimental data and with other methods; quick convergence and computational efficiency are illustrated. b c c ccd

Thrust and Drag in Supersonic Flow with Heat Addition

Abstract: The concepts of drag and thrust and of their influence on the wake of a body at first were developed for subsonic flow processes only. If we disregard in this context the special case of the induced drag of an airfoil, the drag manifests itself mainly in the wake of the body, where the air flows downstream with a reduced velocity but at practically the ambient pressure p =p ∞ . On the other hand, thrust is obtained if one succeeds to generate increased wake velocities. This concept is derived from the fact that the pressure downstream of the body adjusts very fast to the ambient pressure. With the assumption p = p ∞ one gets from the momentum equation the well known relation for the thrust S $$S{\text{ }} = {\text{ }}G\left( {w - {w_{\infty }}} \right) $$ (1) where w ∞ is the approach velocity, w is the downstream velocity, and G means the mass flow per unit of time which experiences a velocity increase of w−w ∞ . The upstream and downstream velocities are assumed to have the same directions. Eq. (1) can be used also as equation for the drag.

Hydrofoil Craft Drag Polar

Abstract: Adaptation of the friction and wave drag components to the classic aerodynamic drag polar are shown with accommodation for the weight/center-of-gravity envelope. The parametric forms of the drag, power, and specific range and endurance curves are shown and related to the traditional dimensional forms. The relationship between the drag polar and the propulsion is indicated.

Downwash and induced drag corrections for a lifting wing at low speeds in a circular‐section wind tunnel

Abstract: Analytical solutions for the downwash and induced drag wall corrections are given for a finite lifting‐rolling wing at low speeds in a circular test‐section wind tunnel. The spanwise lift distribution is represented by a Fourier cosine series instead of the Fourier sine series as has been the general practice in the literature so far. Unlike the sine distributions, the cosine distributions do not produce a singularity in shed vorticity at the wing tips and hence these are considered more realistic in mimicking actual lift distributions. For a given lift, comparisons are made for tunnel corrections for uniform, elliptic, and parabolic lift distributions (the last being an example of cosine distributions) to highlight the fact that tip loadings have a primary influence on the magnitude of tunnel corrections at large wing span: tunnel test‐section diameter ratios, and thus must be correctly represented. Similar comparisons are made for a given rolling moment at zero lift for the simplest of the antisymmetric...