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At least 883 records · Page 49
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Geodetic Precession Vs. Frame Dragging

Report discusses precession of freely falling or orbiting gyroscope with respect to geodetic precession and frame-dragged precession, predicted by metric theories of gravitation. Geodetic precession caused by motion of gyroscope in gravitational field of massive body; frame-dragged precession caused by gravitomagnetic interaction, which is magnetic-like effect caused by motion of massive body. Both effects small. Relevant to investigations in orbital mechanics, navigation, and general relativity.

Krisher, Timothy P.↗
NASA NTRS1991

Trim drag reduction concepts for horizontal takeoff single-stage-to-Orbit vehicles

The results of a study to investigate concepts for minimizing trim drag of horizontal takeoff single-stage-to-orbit (SSTO) vehicles are presented. A generic hypersonic airbreathing conical configuration was used as the subject aircraft. The investigation indicates that extreme forward migration of the aerodynamic center as the vehicle accelerates to orbital velocities causes severe aerodynamic instability and trim moments that must be counteracted. Adequate stability can be provided by active control of elevons and rudder, but use of elevons to produce trim moments results in excessive trim drag and fuel consumption. To alleviate this problem, two solution concepts are examined. Active control of the center of gravity (COG) location to track the aerodynamic center decreases trim moment requirements, reduces elevon deflections, and leads to significant fuel savings. Active control of the direction of the thrust vector produces required trim moments, reduces elevon deflections, and also results in significant fuel savings. It is concluded that the combination of active flight control to provide stabilization, (COG) position control to minimize trim moment requirements, and thrust vectoring to generate required trim moments has the potential to significantly reduce fuel consumption during ascent to orbit of horizontal takeoff SSTO vehicles.

Shaughnessy, John D.↗
NASA NTRS1993

An improved far field drag calculation method for nonlinear CFD codes

An improved method to calculate drag based on far field conditions is presented and demonstrated. The method is illustrated using two CFD codes, PARC and CFL3D, and examining their ability to preserve lift and drag coefficients along grid line defined integration paths. The flow fields were generated by solving the Euler equations for a NACA 0012 airfoil at a free stream Mach number of 0.8 and angle of attack of 1.25 degrees. In comparison to force coefficients obtained by surface pressure integration, neither code acceptably preserved both force coefficients throughout the near and far fields. An investigation into the relationship between numerical prediction error and calculated force coefficients revealed a direct connection between solution mass conservation error and force coefficients error. A method to correct the predicted force coefficients based on integrated mass conservation error is described and demonstrated. The corrected force coefficients for both codes are shown to be more accurate than the uncorrected values. The correction method is applicable to both two and three dimensions and is independent of the algorithm used to generate the flow field.

Sirbaugh, James R.↗
NASA NTRS1993

Base drag prediction on missile configurations

New wind tunnel data have been taken, and a new empirical model has been developed for predicting base drag on missile configurations. The new wind tunnel data were taken at NASA-Langley in the Unitary Wind Tunnel at Mach numbers from 2.0 to 4.5, angles of attack to 16 deg, fin control deflections up to 20 deg, fin thickness/chord of 0.05 to 0.15, and fin locations from 'flush with the base' to two chord-lengths upstream of the base. The empirical model uses these data along with previous wind tunnel data, estimating base drag as a function of all these variables as well as boat-tail and power-on/power-off effects. The new model yields improved accuracy, compared to wind tunnel data. The new model also is more robust due to inclusion of additional variables. On the other hand, additional wind tunnel data are needed to validate or modify the current empirical model in areas where data are not available.

Moore, F. G.↗
NASA NTRS1993

Identification of integrated airframe-propulsion effects on an F-15 aircraft for application to drag minimization

The application of an adaptive real-time measurement-based performance optimization technique is being explored for a future flight research program. The key technical challenge of the approach is parameter identification, which uses a perturbation-search technique to identify changes in performance caused by forced oscillations of the controls. The controls on the NASA F-15 highly integrated digital electronic control (HIDEC) aircraft were perturbed using inlet cowl rotation steps at various subsonic and supersonic flight conditions to determine the effect on aircraft performance. The feasibility of the perturbation-search technique for identifying integrated airframe-propulsion system performance effects was successfully shown through flight experiments and postflight data analysis. Aircraft response and control data were analyzed postflight to identify gradients and to determine the minimum drag point. Changes in longitudinal acceleration as small as 0.004 g were measured, and absolute resolution was estimated to be 0.002 g or approximately 50 lbf of drag. Two techniques for identifying performance gradients were compared: a least-squares estimation algorithm and a modified maximum likelihood estimator algorithm. A complementary filter algorithm was used with the least squares estimator.

Schkolnik, Gerald S.↗
NASA NTRS1993

Effect of lift-to-drag ratio in pilot rating of the HL-20 landing task

A man-in-the-loop simulation study of the handling qualities of the HL-20 lifting-body vehicle was made in a fixed-base simulation cockpit at NASA Langley Research Center. The purpose of the study was to identify and substantiate opportunities for improving the original design of the vehicle from a handling qualities and landing performance perspective. Using preliminary wind-tunnel data, a subsonic aerodynamic model of the HL-20 was developed. This model was adequate to simulate the last 75-90 s of the approach and landing. A simple flight-control system was designed and implemented. Using this aerodynamic model as a baseline, visual approaches and landings were made at several vehicle lift-to-drag ratios. Pilots rated the handling characteristics of each configuration using a conventional numerical pilot-rating scale. Results from the study showed a high degree of correlation between the lift-to-drag ratio and pilot rating. Level 1 pilot ratings were obtained when the L/D ratio was approximately 3.8 or higher.

Jackson, E. B.↗
NASA NTRS1928

The Drag of a J-5 Radial Air-Cooled Engine

This note describes tests of the drag due to a Wright "Whirlwind" (J-5) radial air-cooled engine mounted on a cabin type airplane. The tests were made in the 20-foot Propeller Research Tunnel of the National Advisory Committee for Aeronautics. The drag was obtained with three different types of exhaust stacks: Short individual stacks, a circular cross section collector ring, and a streamline cross section collector ring.

Weick, Fred E↗
NASA NTRS1931

The Effect of Slots and Flaps on the Lift and Drag of the Mcdonnell Airplanes Determined in Flight

This note contains the results of flight test conducted by the National Advisory Committee for Aeronautics on a low-wing monoplane equipped with leading-edge slots extending over the entire wing and flaps extending only to the ailerons, to find their effect on the lift and drag characteristics of the airplane. Curves are given showing the lift and drag characteristics of the airplane for the following conditions of the slots and flaps neutral; slots closed and flaps down; and slots open and flaps down. In addition, the high and low speed in level flight and the climbing characteristics are given. The results show that the slots used alone increase the maximum lift coefficient 54 per cent; the flaps alone increase it 38 per cent; and the slots and flaps in combination decrease the landing speed from 60 to 43 m.p.h.; increase the speed range of the airplane 40 per cent; and increase the glide angle at landing speed 4.2 degrees.

Soule, Hartley A↗
NASA NTRS1933

The Drag of Streamline Wires

Preliminary results are given of drag tests of streamline wires. Full-size wires were tested over a wide range of speeds in the N.A.C.A. high speed tunnel. The results are thus directly applicable to full-scale problems and include any compressibility effects encountered at the higher speeds. The results show how protuberances may be employed on conventional streamline wires to reduce the drag, and also show how the conventional wires compare with others having sections more like strut or symmetrical airfoil sections. Because the new wire sections developed are markedly superior aerodynamically to conventional wires, it is recommended that some of them be tested in service in order to investigate their relative susceptibility to vibration and to fatigue failure.

Jacobs, Eastman N↗
NASA NTRS1939

Comparison of Profile-drag and Boundary-layer Measurements Obtained in Flight and in the Full-scale Wind Tunnel

The effect of the existing turbulence in the full scale tunnel was determined from measurements of the profile drag of an N-22 section by the momentum method under corresponding conditions in flight and the tunnel. The transition-point location on the upper surface of the air-foil was also determined from velocity surveys in the boundary layer. The measurements were made at section lift coefficients from 0.480 to 0.635 with a range of Reynolds Numbers from 4,600,000 to 3,900,000. The results show that the end of transition occurs at approximately the same point on the airfoil in flight and in the tunnel. The transition region was somewhat broader in the tunnel and started farther forward than in flight. The laminar profiles in the tunnel had some characteristics of transition profiles in the tunnel and had a much steeper slope near the surface than did the laminar profiles obtained in flight. These differences, however, caused an increase of only 0.0001 in the profile-drag coefficients, as determined by the momentum method.

Goett, Harry J↗
NASA NTRS1955

Reduction of Profile Drag at Supersonic Velocities by the Use of Airfoil Sections Having a Blunt Trailing Edge

A preliminary theoretical and experimental investigation has been made on the aerodynamic characteristics of blunt-trailing-edge airfoils at supersonic velocities. The theoretical considerations indicate that properly designed airfoils with moderately blunt trailing edges can have less profile drag, greater lift-curve slope, and high maximum lift-drag ratio than conventional sections. These predictions have been substantiated by experimental measurements on airfoils of 10-percent-thickness ratio at Mach numbers of 1.5 and 2.0, and at Reynolds numbers between 0.2 and 1.2 million.

Chapman, Dean R↗
NASA NTRS1956

Theoretical wave drag of shrouded airfoils and bodies

Formulas for the wave drag of shrouded symmetrical airfoils and shrouded bodies of revolution of arbitrary shape are derived by means of linearized theory. In the case of the airfoils, the shroud consists of flat plates and for the bodies of revolution the shroud is a cylindrical shell. The results obtained hold for a Mach number range dependent on the geometry of the configuration. Expressions are also given for determining a class of body shapes for which the wave drag is theoretically zero.

Byrd, Paul F↗
NASA NTRS1956

Drag Interference Between a Pointed Cylindrical Body and Triangular Wings of Various Aspect Ratios at Mach Numbers of 1.50 and 2.02

The drag of a body alone, six triangular wings of various aspect ratios, and the combinations were measured at Mach numbers of 1.50 and 2.02 at a Reynolds number of 5.5 million (based on the body length). The experimental drag-interference results were in accordance with calculations based on NACA RM A9E19, 1949, with skin-friction effects taken into account, the interference effect being principally the result of fixing transition on the body by adding a wing.

BODIES↗
NASA NTRS1956

Investigation of Vertical Drag and Periodic Airloads Acting on Flat Panels in a Rotor Slipstream

Tests have been conducted on the Langley helicopter test tower to determine the vertical drag and pressure distributions on flat panels mounted below a helicopter rotor. Calculations of the vertical drag by use of a strip-analysis procedure outlined in the paper and the assumption of a fully contracted wake agreed well with the experimental results over the range from 0.2 to 0.64 rotor radius beneath the plane of zero flapping. The pressure increase caused by the passage of the blade over the panel is a maximum at about the 0.8 radius spanwise station. At this station, the pressure decreases from 10 times the disk loading per blade at 0.05 radius beneath the rotor plane of zero flapping to one-half of the disk loading per blade at 0.64 radius beneath the plane of zero flapping.

LOADS - ROTATING WINGS↗
NASA NTRS1951

Results of Flight Tests to Determine Drag of Parabolic and Cone-cylinder Bodies of Very Large Fineness Ratios at Supersonic Speeds

Results of a free-flight investigation at supersonic speeds to determine zero-lift drag of a series of bodies of revolution are presented. Configurations tested included two parabolic bodies with fineness ratios of 17.78 and 24.5 and two 8 degree cone-cylinder bodies with fineness ratios of 17.2 and 21.2. Results of previous tests of similar parabolic bodies but with lower fineness ratios are included in this paper for comparison. All bodies for which data are presented in this paper had a base-to-maximum-diameter ratio of 0.437. Calculated drag coefficients are shown for all bodies for which data are presented. (author)

Welsh, Clement J↗
NASA NTRS1954

Experimental investigation at Mach numbers 1.88, 3.16, and 3.83 of pressure drag of wedge diverters simulating boundary-layer-removal systems for side inlets

The pressure drag coefficients for a number of simulated wedge diverter boundary-layer-removal systems for side inlets were obtained at Mach numbers of 1.88m 3.16, and 3.83. Wedge included angle, wedge height, and wedge axial position relative to the splitter plate were independently varied for unswept and swept splitter plate configurations immersed in the turbulent boundary layer of a flat plate. Friction and total drag coefficients for several configurations were also obtained at Mach number 3.16

Piercy, Thomas G↗
NASA NTRS1958

Jet Effects on the Base Drag of a Cylindrical Afterbody with Extended Nozzles

A wind-tunnel investigation to determine the effects of both single and twin jets on base drag of a cylindrical body has been conducted at Mach numbers from 0.6 to 1.4. The plane of the jet exit was varied with respect to that of the afterbody. Jet total-pressure ratio ranged up to 20. Significant improvements in base drag were obtained by extending the plane of the jet exits beyond the afterbody base and by venting the base cavity to the external stream.

Nelson, William J↗
NASA NTRS1952

Preliminary Free-flight Investigation of the Zero-lift Drag Penalties of Several Missile Nose Shapes for Infrared Seeking Devices

The results of a preliminary investigation to develop a nose shape suitable for housing an infrared seeker are presented. The zero-lift drag characteristics of a missile-like body with various unconventional nose shapes were obtained through a range of Mach numbers from 0.8 to 1.8 and Reynolds numbers, based on body length, from 20 x10 to the 6th power to 70 x 10 to the 6th power, respectively, by using rocket-propelled free-flight models. Results of the test indicate that at supersonic speeds about 70 percent of the drag penalty incurred by using spherical-tip nose shapes may be eliminated by using nose shapes which will still allow the seeker to function.

Piland, Robert O↗