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At least 271 records · Page 15

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NASA NTRS1979

Calculation of the longitudinal aerodynamic characteristics of upper-surface-blown wing-flap configurations

An investigation has been carried out to develop an engineering method for predicting the longitudinal aerodynamic characteristics of wing-flap configurations with upper surface blown (USB) high lift devices. Potential flow models of the lifting surfaces and the jet wakes are combined to calculate the induced interference of the engine wakes on the wing and flaps. The wing may have an arbitrary planform with camber and twist and multiple trailing edge flaps. The jet wake model has a rectangular cross section over its entire length and it is positioned such that the wake is tangent to the upper surfaces of the wing and flaps. Comparisons of measured and predicted pressure distributions, spanload distributions, and total lift and pitching-moment coefficients on swept and unswept USB configurations are presented for a wide range of thrust coefficients and flap deflection angles.

Mendenhall, M. R.↗

NASA NTRS1980

Works on theory of flapping wing

It is shown mathematically that taking account of the boundary layer is the only way to develop a theory of flapping wings without violating the basic observations and mathematics of hydromechanics. A theory of thrust generation by flapping wings can be developed if the conventional downstream velocity discontinuity surface is replaced with the observed Karman type vortex streets behind a flapping wing. Experiments show that the direction of such vortices is the reverse of that of conventional Karman streets. The streets form by breakdown of the boundary layer. Detailed analysis of the movements of certain birds and insects during flight 'in place' is fully consistent with this theory of the lift, thrust and drag of flapping wings. Further directions for research into flight with flapping wings are indicated.

Golubev, V. V.↗

NASA NTRS1982

Wind-tunnel investigation of vortex flaps on a highly swept interceptor configuration

A subsonic wind-tunnel investigation of the application of vortex flaps to a supersonic interceptor configuration is described. Experimental results are presented which indicate the aerodynamic effects of vortex-flap deflection, trailing-edge flap deflection, vortex flap chord and span, vertical stabilizers, and a highly cambered leading edge designed for attached flow. Data presented include longitudinal forces and moments, upper-surface pressure distributions, and oil- and smoke-flow visualization photographs. It is concluded that a full-span deployable vortex flap can provide a substantial performance improvement for this and other similar configurations.

Schoonover, W. E., Jr.↗

NASA NTRS1983

Nonlinear aerodynamic modeling of flap oscillations in transonic flow - A numerical validation

The regime of validity of a nonlinear aerodynamic force and moment formulation, based on concepts from nonlinear functional analysis and applicable to a transonic airfoil with a deflecting flap, is investigated. A time-dependent finite difference technique is used to evaluate the aerodynamic data of the formulation in terms of specified, characteristic motions. Flap-motion histories are generated from the flap inertial equations of motion, with aerodynamic reactions specified by the moment formulation. The motion histories depicting the cases of decaying and growing flap oscillations are compared with histories generated through simultaneous, coupled solution of the fluid-dynamic equations and flap inertial equations of motion. The range of applicability of the formulation is discussed.

Chyu, W. J.↗

NASA NTRS1984

Vortex flaps - Advanced control devices for supercruise fighters

Prompted by the extensive experience obtained with vortex lift-generating leading edges in the SR-71, Concorde and F-16 supersonic aircraft, development efforts have recently been made toward the use of variable incidence angle delta wing leading edge 'vortex flaps' for supersonic cruise and maneuvering performance improvements in fighter aircraft. Vortex lift flaps have been wind tunnel tested on scale models, and it has been noted that a variety of effects can be obtained through the use of folding, hinged, and tabbed flap designs. Flap planforms can, moreover, be varied in length and in total area, as well as segmented, to yield unique combinations of drag reduction, vortex generation, longitudinal stability, and vortex flow reattachment. It is speculated that the vortex flap may be applicable to multimission fighters, and promote STOL performance.

Lamar, J. E.↗

NASA NTRS1984

Force and moment measurements on a 74 deg delta wing with an apex flap

Results are presented of a subsonic experimental investigation of an apex flap concept on a 74 deg swept delta wing with trailing-edge flaps. The apex flap comprised approximately 6 percent of the wing area forward of a transverse hinge, allowing for upward and downward deflection angles from +40 deg to -20 deg. Upward deflection forces leading-edge vortex formation on the apex flap, resulting in an increased lift component on the apex area. The associated nose-up moment balances the nose-down moment due to trailing-edge flaps, resulting in sizeable increase in the trimmed lift coefficient particularly at low angles of attack. Nose-down apex deflection may be used to augment the pitch control for rapid recovery from high-alpha maneuvers. This report presents the balance data without analysis.

Buter, T. A.↗

NASA NTRS1983

Low-speed tests of a high-aspect-ratio, supercritical-wing transport model equipped with a high-lift flap system in the Langley 4- by 7-meter and Ames 12-foot pressure tunnels

The Ames 12-Foot Pressure Tunnel was used to determine the effects of Reynolds number on the static longitudinal aerodynamic characteristics of an advanced, high-aspect-ratio, supercritical wing transport model equipped with a full span, leading edge slat and part span, double slotted, trailing edge flaps. The model had a wing span of 7.5 ft and was tested through a free stream Reynolds number range from 1.3 to 6.0 x 10 to 6th power per foot at a Mach number of 0.20. Prior to the Ames tests, an investigation was also conducted in the Langley 4 by 7 Meter Tunnel at a Reynolds number of 1.3 x 10 to 6th power per foot with the model mounted on an Ames strut support system and on the Langley sting support system to determine strut interference corrections. The data obtained from the Langley tests were also used to compare the aerodynamic charactertistics of the rather stiff, 7.5-ft-span steel wing model tested during this investigation and the larger, and rather flexible, 12-ft-span aluminum-wing model tested during a previous investigation. During the tests in both the Langley and Ames tunnels, the model was tested with six basic wing configurations: (1) cruise; (2) climb (slats only extended); (3) 15 deg take-off flaps; (4) 30 deg take-off flaps; (5) 45 deg landing flaps; and (6) 60 deg landing flaps.

Morgan, H. L., Jr.↗

NASA NTRS1983

An aerodynamic analysis computer program and design notes for low speed wing flap systems

The expanded capabilities for analysis and design of low speed flap systems afforded by recent modifications of an existing computer program is described. The program provides for the simultaneous analysis of up to 25 pairs of leading-edge and trailing-edge flap deflection schedules. Among other new features of the program are a revised attainable thrust estimation method to provide more accurate predictions for low Mach numbers, and a choice of three options for estimation of leading-edge separation vortex flow effects. Comparison of program results with low speed experimental data for an arrow wing supersonic cruise configuration with leading-edge and trailing-edge flaps showed good agreement over most of the range of flap deflections. Other force data comparisons and an independent study of airfoil and wing pressure distributions indicated that wind-tunnel measurements of the aerodynamic performance of twisted and cambered wings and wings with leading-edge flaps can be very sensitive to Reynolds number effects.

Carlson, H. W.↗

NASA NTRS1986

Analytical observations on the aerodynamics of a delta wing with leading edge flaps

The effect of a leading edge flap on the aerodynamics of a low aspect ratio delta wing is studied analytically. The separated flow field about the wing is represented by a simple vortex model composed of a conical straight vortex sheet and a concentrated vortex. The analysis is carried out in the cross flow plane by mapping the wing trace, by means of the Schwarz-Christoffel transformation into the real axis of the transformed plane. Particular attention is given to the influence of the angle of attack and flap deflection angle on lift and drag forces. Both lift and drag decrease with flap deflection, while the lift-to-drag ratioe increases. A simple coordinate transformation is used to obtain a closed form expression for the lift-to-drag ratio as a function of flap deflection. The main effect of leading edge flap deflection is a partial suppression of the separated flow on the leeside of the wing. Qualitative comparison with experiments is presented, showing agreement in the general trends.

Oh, S.↗

NASA NTRS1985

Effects of jet flap on AV8-B 'Harrier' performance

This paper examines the effects of fitting various jet-flap configurations to an AV8-'Harrier II' Baseline aircraft using two NASA developed computer codes. The first code predicts the ground roll of an AV8-B with a partial span jet-flap, a full span jet-flap, a partial span internally blown-flap, and a full span internally blown-flap as well as the Baseline configuration. The second code used was a mission performance estimation routine called ACSYNT (Aircraft Synthesis). This code models each configuration on a standard mission so that the relative merits may be determined.

Hahn, A. S.↗

NASA NTRS1987

Applicability of linearized-theory attached-flow methods to design and analysis of flap systems at low speeds for thin swept wings with sharp leading edges

Low-speed experimental force and data on a series of thin swept wings with sharp leading edges and leading and trailing-edge flaps are compared with predictions made using a linearized-theory method which includes estimates of vortex forces. These comparisons were made to assess the effectiveness of linearized-theory methods for use in the design and analysis of flap systems in subsonic flow. Results demonstrate that linearized-theory, attached-flow methods (with approximate representation of vortex forces) can form the basis of a rational system for flap design and analysis. Even attached-flow methods that do not take vortex forces into account can be used for the selection of optimized flap-system geometry, but design-point performance levels tend to be underestimated unless vortex forces are included. Illustrative examples of the use of these methods in the design of efficient low-speed flap systems are included.

Carlson, Harry W.↗

NASA NTRS1990

The effects of structural flap-lag and pitch-lag coupling on soft inplane hingeless rotor stability in hover

A 1.62-m-diameter rotor model was tested in hover to examine the effects of structural flap-lag and pitch-lag coupling on isolated rotor blade lead-lag stability. Flap-lag coupling was introduced by inclining the principal axes of the blade structure up to 60 degrees. Pitch-lag coupling was obtained either alone or in combination with flap-lag coupling through the use of skewed flexural hinges. The principal results confirm the predictions of theory, and show that both structural flap-lag and pitch-lag coupling when used separately are beneficial to blade stability. Moreover, when the couplings are combined, the lead-lag damping is significantly greater than it would be if the individual contributions were superimposed. Pitch-flap coupling is shown to have only a minor effect on blade lead-lag damping. Differences between theory and experiment observed at zero blade pitch and flexure angles during the initial testing were determined in a second test to be caused by stand flexibility. Other differences between theory and experiment warrant further investigation.

Bousman, William G.↗

NASA NTRS1991

Unsteady vortex-dominated flow around wings with oscillating leading-edge flaps

Unsteady vortex-dominated flow around delta wings with oscillating leading-edge flaps represents an important classs of problems for supermaneuverability and flow control of advanced aircraft. The problem is solved using time accurate integration of the unsteady, compressible, thin-layer Navier-Stokes equations in conjunction with the unsteady, linearized, Navier-displacement equations. Starting with an initial configuration of the wing and its flaps, the Navier-Stokes equations are solved on an initial structured grid for the steady flow. The forced oscillation of the flaps is then applied, and the problem is solved accurately in time. The Navier-displacement equations are solved for the grid deformation and the Navier-Stokes equations are solved for the flowfield. Symmetric and anti-symmetric flaps oscillations are presented to study the effect of the flaps oscillation on the leading-edge vortical flow.

Kandil, Osama A.↗

NASA NTRS1991

Study of external dynamic flap loads on a 6 percent B-1B model

The origin of dynamic pressure loads on external divergent engine nozzle flaps of the B-1B aircraft was investigated in the NASA/LaRC 16 foot transonic tunnel using a 6 percent full span model with powered engine nacelles. External flap dynamic loads and afterbody drag associated with flap removal were measured using this model. Both dry and max. A/B power nozzles were evaluated in this study. As a result of this study, the principal mechanisms responsible for high dynamic external flap loads were determined along with performance penalty associated with flap removal.

Seiner, John M.↗

NASA NTRS1992

Computational evaluation of an airfoil with a Gurney flap

A 2D numerical investigation was performed to determine the effect of a Gurney flap on a NACA 4412 airfoil. A Gurney flap is a flat plate on the order of 1 to 3 percent of the airfoil chord length, oriented perpendicular to the airfoil chord line and located at the trailing edge of the airfoil. An incompressible Navier Stokes code, INS2D, was used to calculate the flow field about the airfoil. The fully turbulent results were obtained using the Baldwin-Barth one-equation turbulence model. Gurney flap sizes of 0.5 , 1, 1.25, 1.5, 2, and 3 percent of the airfoil chord were studied. Computational results were compared with experimental results where possible. The numerical solutions show that the Gurney flap increases airfoil lift coefficient with only a slight increase in drag coefficient. Use of a 1.5 percent chord Gurney flap increases the maximum lift coefficient by approximately 0.3 and decreases the angle of attack for a given lift coefficient by more than 3 deg. The numerical solutions exhibit detailed flow structures at the trialing edge and provide a possible explanation for the increased aerodynamic performance.

Jang, Cory S.↗

NASA NTRS1932

The aerodynamic characteristics of a model wing having a split flap deflected downward and moved to the rear

Tests were made on a model wing with three different sized split trailing-edged flaps, in the NACA 7 by 10 foot wind tunnel. The flaps were formed of the lower rear portion of the wing and were rotated downward about axes at their front edges. The lift, drag, and center of pressure were measured with the axis in its original position and also with it moved back in even steps to the trailing edge of the main wing, giving in effect an increase in area. The split flaps when deflected about their original axis locations gave slightly higher maximum lift coefficients than conventional trailing-edge flaps, and the lift coefficients were increased still further by moving the axes toward the rear. The highest value of C(sub L max), which was obtained with the largest flap hinged at 90 per cent of the chord from the leading edge, was 2.52 as compared with 1.27 for the basic wing.

Weick, Fred E↗

NASA NTRS1933

Aerodynamic tests of a low aspect ratio tapered wing with various flaps, for use on tailless airplanes

Wind tunnel tests were made of a model wing having an aspect ratio of 3 and a tapered plan form with a straight trailing edge. The model had the Clark Y airfoil section throughout it's entire span and had no washout, depending on a trailing-edge flap for longitudinal balance and control. The flap had a constant chord and was divided into four equal portions along the span. The tests were made with the entire flap deflected to obtain longitudinal control and balance, and also with the inner portions deflected alone, and with the outer portions deflected alone. It was found that the simple wing with no washout or change of basic section along the span has aerodynamic characteristics well suited for use on tailless airplanes. A higher lift coefficient was obtained with the full-span flap deflected as a unit to give longitudinal balance than was obtained with either the inner or the outer portions of the flap deflected.

Weick, Fred E↗

NASA NTRS1936

Notes on the technique of landing airplanes equipped with wing flaps

The proper landing of airplanes equipped with flaps, although probably no more difficult than landing without them, requires a different technique. The effects of flaps on the aerodynamics characteristics of a wing are given and, with the aid of figures and diagrams, a detailed comparison of the glide and landing of an airplane with and without flaps is made. The dangers attending improper execution and the importance of such factors as air speed fuselage attitude, glide-path angle, and control manipulation, upon all of which a pilot bases his judgement, are emphasized. Of most importance in connection with the use of flaps are: the maintenance of a sufficient margin of speed above the stall; a decisive use of the controls at the proper time; more cautious use of power during the approach glide; and, above all, the willingness to accept the steep nose-down attitude necessary in the glide resulting from the use of flaps.

Gough, Melvin N↗