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At least 1,063 records · Page 59
All sourcesNASA NTRSDOE OSTI
NASA NTRS1996

Effects of Winglets on the Drag of a Low-Aspect-Ratio Configuration

A wind-tunnel investigation has been performed to determine the effect of winglets on the induced drag of a low-aspect-ratio wing configuration at Mach numbers between 0.30 and 0.85 and a nominal angle-of-attack range from -2 deg to 20 deg. Results of the tests at the cruise lift coefficient showed significant increases in lift-drag ratio for the winglet configuration relative to a wing-alone configuration designed for the same lift coefficient and Mach number. Further, even larger increases in lift-drag ratio were observed at lift coefficients above the design value at all Mach numbers tested. The addition of these winglets had a negligible effect on the static lateral-directional stability characteristics of the configuration. No tests were made to determine the effect of these winglets at supersonic Mach numbers, where increases in drag caused by winglets might be more significant. Computational analyses were also performed for the two configurations studied. Linear and small-disturbance formulations were used. The codes were found to give reasonable performance estimates sufficient for predicting changes of this magnitude.

Smith, Leigh Ann↗
NASA NTRS1957

Effects of Inlet Modification and Rocket-Rack Extension on the Longitudinal Trim and Low-Lift Drag of the Douglas F5D-1 Airplane as Obtained with a 0.125-Scale Rocket-Boosted Model Between Mach Numbers of 0.81 and 1.64: TED No. NACA AD 399

A flight investigation was conducted to determine the effects of inlet modification and rocket-rack extension on the longitudinal trim and low-lift drag of the Douglas F5D-1 airplane. The investigation was conducted with a 0.125-scale rocket-boosted model between Mach Numbers of 0.81 and 1.64. This paper presents the changes in trim angle of attack, trim lift coefficient, and low-lift drag caused by the modified inlets alone over a small part of the test Mach number range and by a combination of the modified inlets and extended rocket racks throughout the remainder of the test.

Hastings, Earl C., Jr.↗
NASA NTRS1975

Aerodynamic characteristics of the 10-percent-thick NASA supercritical airfoil 33 designed for a normal-force coefficient of 0.7

A 10-percent-thick supercritical airfoil based on an off-design sonic-pressure plateau criterion was developed and experimental aerodynamic characteristics measured. The airfoil had a design normal-force coefficient of 0.7 and was identified as supercritical airfoil 33. Results show the airfoil to have good drag rise characteristics over a wide range of normal-force coefficients with no measurable shock losses up to the Mach numbers at which drag divergence occurred for normal-force coefficients up to 0.7. Comparisons of experimental and theoretical characteristics were made and composite drag rise characteristics were derived for normal-force coefficients of 0.5 and 0.7 and a Reynolds number of 40 million.

Harris, C. D.↗
NASA NTRS1999

Modeling the High Speed Research Cycle 2B Longitudinal Aerodynamic Database Using Multivariate Orthogonal Functions

The data for longitudinal non-dimensional, aerodynamic coefficients in the High Speed Research Cycle 2B aerodynamic database were modeled using polynomial expressions identified with an orthogonal function modeling technique. The discrepancy between the tabular aerodynamic data and the polynomial models was tested and shown to be less than 15 percent for drag, lift, and pitching moment coefficients over the entire flight envelope. Most of this discrepancy was traced to smoothing local measurement noise and to the omission of mass case 5 data in the modeling process. A simulation check case showed that the polynomial models provided a compact and accurate representation of the nonlinear aerodynamic dependencies contained in the HSR Cycle 2B tabular aerodynamic database.

Morelli, E. A.↗
NASA NTRS1975

An analytical evaluation of airfoil sections for helicopter rotor applications

An analytical technique was used to evaluate airfoils for helicopter rotor application. This technique permits assessment of the influences of airfoil geometric variations on drag divergence Mach number at lift coefficients from near zero to near maximum lift. Analytical results presented in this paper indicate the compromises in drag divergence Mach number which result from changes in (1) thickness ratio, (2) location of maximum thickness, (3) leading-edge radius, (4) camber addition, and (5) location of maximum camber of NACA four- and five-digit-series airfoils and some 6-series airfoils of potential interest for helicopters. Examples of airfoil sections which combine several of the geometric changes favorable to both advancing and retreating section performance have been presented.

Bingham, G. J.↗
NASA NTRS1945

High-Speed Wind-Tunnel Tests of a 0.3-Scale Model of the P-47D Airplane

Presented in this report are the results of high-speed wind-tunnel tests of a 0.3-scale model of the P-47D airplane. Included are the aerodynamic characteristics of the model, pressure distributions on the wing and horizontal tail, elevator hinge moments, and tuft photographs showing the flow over the wing and horizontal tail. The results indicate that, at level-flight lift coefficients, the P-47D airplane will not exhibit a diving tendency below a Mach number of 0.78 at an altitude of 20,000 feet or below a Mach number of 0.72 at an altitude of 40,000 feet. The Mach number at which the lift, drag, and pitching-moment coefficients diverged rapidly from the low speed values is about C.15 higher than the critical Mach number. This is an unusually large margin.

William T Hamilton↗
NASA NTRS1984

Performance of large-eddy breakup devices at post-transitional Reynolds numbers

Large-eddy alteration techniques were used to modify the drag characteristics of the turbulent boundary layer. Local skin-friction coefficients were measured for single and multi-element arrays of thin plates suspended in a fully turbulent, flat plate, boundary layer at R(theta) = 3,000. Effects of these devices were measured more than 300 boundary-layer thicknesses downstream to R(theta) = 17,000. It was found that although most of the devices reduced the local skin friction immediately downstream, this reduced skin-friction region persisted for only 100-120 delta-0, after which a rapid rise in skin-friction coefficient occurred, often exceeding flat plate values. Net drag reductions were obtained only for tandem configurations and these reductions were sensitive to device spacing and height. The maximum net drag reduction reported was approximately 7 percent with a device spacing of 10 delta-0 at a height of 0.8 delta-0.

Anders, J. B.↗
NASA NTRS1988

VSAERO analysis of tip planforms for the free-tip rotor

The results of a numerical analysis of two interacting lifting surfaces separated in the spanwise direction by a narrow gap are presented. The configuration consists of a semispan wing with the last 32 percent of the span structurally separated from the inboard section. The angle of attack of the outboard section is set independently from that of the inboard section. In the present study, the three-dimensional panel code VSAERO is used to perform the analysis. Computed values of tip surface lift and pitching moment coefficients are correlated with experimental data to determine the proper approach to model the gap region between the surfaces. Pitching moment data for various tip planforms are also presented to show how the variation of tip pitching moment with angle of attack may be increased easily in incompressible flow. Calculated three-dimensional characteristics in compressible flow at Mach numbers of 0.5 and 0.7 are presented for new tip planform designs. An analysis of sectional aerodynamic center shift as a function of Mach number is also included for a representative tip planform. It is also shown that the induced drag of the tip surface is reduced for negative incidence angles relative to the inboard section. The results indicate that this local drag reduction overcomes the associated increase in wing induced drag at high wing lift coefficients.

Martin, D. M.↗
NASA NTRS1987

A quartic dispersion equation for internal gravity waves in the thermosphere

A new quartic dispersion equation in the square of the complex vertical wave number is derived by employing the 'shallow atmosphere' approximation and an ion drag approximation. These approximations allow the coefficients of the quartic equation to be given in terms of the corresponding cubic equation (which neglects the Coriolis force and the zonal ion drag component), but modified to take into account these neglected effects. Coupling between the extraordinary viscosity wave mode and the other three wave modes is highlighted and numerical solutions are compared for this quartic equation, an exact eighth order equation and the cubic equation. For the first time the validity of using the 'shallow atmosphere' approximation to describe internal gravity wave motions is demonstrated.

Hickey, M. P.↗
NASA NTRS1961

Take-off Distances of a Supersonic Transport Configuration as Affected by Airplane Rotation During the Take-off Run

The take-off distances over a 35-foot obstacle have been determined for a supersonic transport configuration characterized by a low maximum lift coefficient at a high angle of attack and by high drag due to lift. These distances were determined analytically by means of an electronic digital computer. The effects of rotation speed, rotation angle, and rotation time were determined. A few configuration changes were made to determine the effects of thrust-weight ratio, wing loading, maximum lift coefficient, and induced drag on the take-off distance. The required runway lengths based on Special Civil Air Regulation No. SR-422B were determined for various values of rotation speed and compared with those based on full engine power. Increasing or decreasing the rotation speed as much as 5 knots from the value at which the minimum take-off distance occurred increased the distance only slightly more than 1 percent for the configuration studied. Under-rotation by 1 deg to 1.5 deg increased the take-off distance by 9 to 15 percent. Increasing the time required for rotation from 3 to 5 seconds had a rather small effect on the take-off distance when the values of rotation speed were near the values which result in the shortest take-off distance. When the runway length is based on full engine power rather than on SR-422B, the rotation speed which results in the shortest required runway length is 10 knots lower and the runway length is 4.3 percent less.

Hall, Albert W.↗
NASA NTRS1975

Analysis of various descent trajectories for a hypersonic-cruise, cold-wall research airplane

The probable descent operating conditions for a hypersonic air-breathing research airplane were examined. Descents selected were cruise angle of attack, high dynamic pressure, high lift coefficient, turns, and descents with drag brakes. The descents were parametrically exercised and compared from the standpoint of cold-wall (367 K) aircraft heat load. The descent parameters compared were total heat load, peak heating rate, time to landing, time to end of heat pulse, and range. Trends in total heat load as a function of cruise Mach number, cruise dynamic pressure, angle-of-attack limitation, pull-up g-load, heading angle, and drag-brake size are presented.

Lawing, P. L.↗
NASA NTRS1977

Trimmed noncoplanar planforms with minimum vortex drag

Vortex-lattice subsonic method determines mean camber surface for trimmed noncoplanar planforms with minimum vortex drag. Multiple surfaces can be designed together to yield trimmed configuration with minimum induced drag at some specified lift coefficient. Program is applicable to isolated wings, wing-canard configuration, tandem wing, and wing-winglet configuration.

Lamar, J. E.↗
NASA NTRS1976

Effect of design factors on surface temperature and wear in disk brakes

The temperatures, friction, wear and contact conditions that occur in high energy disk brakes are studied. Surface and near surface temperatures were monitored at various locations in a caliper disk brake during drag type testing, with friction coefficient and wear rates also being determined. The recorded transient temperature distributions in the friction pads and infrared photographs of the rotor disk surface both showed that contact at the friction surface was not uniform, with contact areas constantly shifting due to nonuniform thermal expansion and wear. The effect of external cooling and of design modifications on friction, wear and temperatures was also investigated. It was found that significant decreases in surface temperature and in wear rate can be achieved without a reduction in friction either by slotting the contacting face of the brake pad or by modifying the design of the pad support to improve pad compliance. Both design changes result in more uniform contact conditions on the friction surface.

Santini, J. J.↗
NASA NTRS1976

Thermal Analysis of Axially Grooved Heat Pipes

The liquid viscous drag and the evaporator film coefficient were determined analytically for a heat pipe with axial rectangular grooves under zero-g conditions. The liquid pressure drop and the evaporator film coefficient for an axially grooved heat pipe were found to be expressed by the functions of the meniscus angle, which makes it possible to predict its performance analytically. The performance near its capillary pumping limit is influenced by the contact angle.

Kamotani, Y.↗
NASA NTRS1978

Theoretical analysis of aerodynamic characteristics of two helicopter rotor airfoils

An analytical study was conducted to predict the aerodynamic characteristics of two helicopter rotor airfoils. Documentation of the predictive process covers the development of empirical factors used in conjunction with computer programs for airfoil analysis. Tables of lift, drag, and pitching-moment coefficient for each airfoil were prepared for two dimensional, steady flow conditions at Mach numbers from 0.3 to 0.9 and Reynolds numbers of 7,700,000 to 23,000,000, respectively.

Morris, C. E. K., Jr.↗
NASA NTRS1982

A New View on Origin, Role and Manipulation of Large Scales in Turbulent Boundary Layers

The potential of passive 'manipulators' for altering the large scale turbulent structures in boundary layers was investigated. Utilizing smoke wire visualization and multisensor probes, the experiment verified that the outer scales could be suppressed by simple arrangements of parallel plates. As a result of suppressing the outer scales in turbulent layers, a decrease in the streamwise growth of the boundary layer thickness was achieved and was coupled with a 30 percent decrease in the local wall friction coefficient. After accounting for the drag on the manipulator plates, the net drag reduction reached a value of 20 percent within 55 boundary layer thicknesses downstream of the device. No evidence for the reoccurrence of the outer scales was present at this streamwise distance thereby suggesting that further reductions in the net drag are attainable. The frequency of occurrence of the wall events is simultaneously dependent on the two parameters, Re2 delta sub 2 and Re sub x. As a result of being able to independently control the inner and outer boundary layer characteristics with these manipulators, a different view of these layers emerged.

Corke, T. C.↗