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At least 757 records · Page 42

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NASA NTRS1973

Supersonic aerodynamic characteristics of hypersonic low-wave-drag elliptical body-tail combinations as affected by changes in stabilizer configuration

An investigation has been made at Mach numbers from 1.50 to 4.63 to determine systematically the effects of the addition and position of outboard stabilizers and vertical- and vee-tail configurations on the performance and stability characteristics of a low-wave-drag elliptical body. The basic body shape was a zero-lift hypersonic minimum-wave-drag body as determined for the geometric constraints of length and volume. The elliptical cross section had an axis ratio of 2 (major axis horizontal) and an equivalent fineness ratio of 6.14. Base-mounted outboard stabilizers were at various dihedral angles from 90 deg to minus 90 deg with and without a single center-line vertical tail or a vee-tail. The angle of attack was varied from about minus 6 to 27 deg at sideslip angles of 0 and 5 deg and a constant Reynolds number of 4.58 x one million (based on body length).

Spencer, B., Jr.↗

NASA NTRS1972

The BMW analytic aerodynamic drag method for the Vinti satellite theory

In order to retain separability in the Vinti theory of earth satellite motion when a non conservative force such as air drag is considered, a set of variational equations for the orbital elements are introduced, and expressed as functions of the transverse, radial, and normal components of the nonconservative forces acting on the system. In particular, the atmospheric density profile is written as a fitted exponential function of the eccentric anomaly, which reproduces tabular values of static model atmospheric densities at all altitudes to within ninety-eight percent and simultaneously reduces the variational equations to indefinite integrals with closed form evaluations, whose limits are in terms of the eccentric anomaly. The values of the limits for any arbitrary time interval are obtained from the Vinti program. Results of the BMW (Bonavito, Mistretta, Watson) theory for the case of the intense air drag satellites San Marco-2 and Air Force Cannonball are given. These results indicate that the satellite ephemerides produced by the BMW theory in conjunction with the Vinti program are of very high accuracy. In addition, since the program is entirely analytic, several months of ephemerides can be obtained within a few seconds of computer time.

Watson, J. S.↗

NASA NTRS1972

Observed effects of earth-reflected radiation and hydrogen drag on the orbital accelerations of balloon satellites.

From March through May 1967, the high-altitude balloon satellites Pageos (1966 56A) and Dash 2 (1963 30D) were both in continuous sunlight orbits. Observed variations in the orbital accelerations of both satellites are found to be due primarily to a combination of the perturbing effects of earth albedo radiation and atmospheric drag. An equation based on diffuse Lambertian reflection of sunlight from the earth predicts quite well the observed trend of orbital accelerations for both satellites due to the force of earth albedo radiation. After correcting for this effect, the remaining orbital energy changes are found to be consistent with atmospheric drag perturbations, making it possible to deduce mean exospheric densities above 2300 km. The results indicate that hydrogen concentrations during the observation period were about three times greater than that given by the U.S. Standard Atmosphere Supplements (1966).

Prior, E. J.↗

NASA NTRS1973

Drag and stability characteristics of high-speed parachutes in the transonic range.

The results of wind tunnel tests of three parachute configurations in the wake of a cone-cylinder are presented. The tests were conducted to extend the drag and stability characteristics of selected parachutes through the transonic speed range. The configurations studied were the hemisflo ribbon, the cross, and the disk-gap-band types. The results are presented as the variation of the parachute drag coefficient with Mach number. General stability characteristics of the parachutes are discussed. The results are then correlated with some published subsonic and supersonic data.

Alexander, W. C.↗

NASA NTRS1973

Earth radiation pressure and the determination of density from atmospheric drag.

The effect of earth radiation pressure relative to that of atmospheric drag increases with height through the lower thermosphere. While it can be entirely neglected as a correction in the determination of density at lower heights, it becomes significant somewhat below 1000 km and rapidly becomes comparable in magnitude to drag above 1000 km. The effects of earth radiation pressure on the orbit of the balloon satellite 1963 30D were calculated during two series of intervals when the orbit was entirely in sunlight. The first of these was when the perigee was very high so that hydrogen was expected to be the dominant atmospheric constituent. The second was when the perigee was lower and helium was expected to be the dominant constituent. Two sets of calculations were performed, one using a constant mean model and the other using a seasonal-latitudinal model, based on reported Tiros VII data, for the albedo and infrared radiation.

Slowey, J. W.↗

NASA NTRS1973

A study of the diurnal variation in the thermosphere as derived by satellite drag.

Results of an analysis performed on 29,574 densities derived from the drag of ten satellites to determine the amplitude and shape of the diurnal-variation curve for the thermosphere. Although a considerable amount of smoothing is inherent in the drag method, it seemed useful to determine whether any change in the shape of the diurnal-variation curve with height, latitude, and solar activity could be detected. None was detected: the curve remains remarkably stable, symmetric, with a maximum at 1420 hr LST and a minimum at 0220 hr LST. A systematic variation of the temperature range with height is observed when static models are used to derive it.

Jacchia, L. G.↗

NASA NTRS1973

Drag characteristics of circular cylinders in a laminar boundary layer at supersonic free-stream velocities

Drag measurements were obtained with circular cylinders attached to a flat-plate surface with their longitudinal axes perpendicular to the plate surface. When more than one cylinder was tested, they were alined in a spanwise row perpendicular to the free-stream velocity vector. The drag measurements were obtained through a range of Mach numbers from 2.3 to 4.6, cylinder heights ranging from approximately 0.4 to 3 times the undisturbed laminar boundary-layer thickness, and cylinder height-to-diameter ratios of 1.0 and approximately 2. Included in the paper is a complete presentation in figure form of the experimental results and a discussion of the more significant findings. An attempt is made to select the most appropriate parameters for correlating the experimental results and, where possible, these results are compared with theoretical calculations.

Stallings, R. L., Jr.↗

NASA NTRS1974

On the theory of compliant wall drag reduction in turbulent boundary layers

A theoretical model has been developed which can explain how the motion of a compliant wall reduces turbulent skin friction drag. Available experimental evidence at low speeds has been used to infer that a compliant surface selectively removes energy from the upper frequency range of the energy containing eddies and through resulting surface motions can produce locally negative Reynolds stresses at the wall. The theory establishes a preliminary amplitude and frequency criterion as the basis for designing effective drag reducing compliant surfaces.

Ash, R. L.↗

NASA NTRS1974

Use of a pitot-static probe for determining wing section drag in flight at Mach numbers from 0.5 to approximately 1.0

The use of a pitot-static probe to determine wing section drag at speeds from Mach 0.5 to approximately 1.0 was evaluated in flight. The probe unit is described and operational problems are discussed. Typical wake profiles and wing section drag coefficients are presented. The data indicate that the pitot-static probe gave reliable results up to speeds of approximately 1.0.

Montoya, L. C.↗

NASA NTRS1974

Bonded composite to metal scarf joint performance in an aircraft landing gear drag strut

The structural performance of a boron-epoxy reinforced titanium drag strut, which contains a bonded scarf joint and was designed to the criteria of the Boeing 747 transport, was evaluated. An experimental and analytical investigation was conducted. The strut was exposed to two lifetimes of spectrum loading and was statically loaded to the tensile and compressive design ultimate loads. Throughout the test program no evidence of any damage in the drag strut was detected by strain gage measurements, ultrasonic inspection, or visual observation. An analytical study of the bonded joint was made using the NASA structural analysis computer program NASTRAN. A comparison of the strains predicted by the NASTRAN computer program with the experimentally determined values shows excellent agreement. The NASTRAN computer program is a viable tool for studying, in detail, the stresses and strains induced in a bonded joint.

Howell, W. E.↗

NASA NTRS1974

Boundary-layer transition and displacement thickness effects on zero-lift drag of a series of power-law bodies at Mach 6

Wave and skin-friction drag have been numerically calculated for a series of power-law bodies at a Mach number of 6 and Reynolds numbers, based on body length, from 1.5 million to 9.5 million. Pressure distributions were computed on the nose by the inverse method and on the body by the method of characteristics. These pressure distributions and the measured locations of boundary-layer transition were used in a nonsimilar-boundary-layer program to determine viscous effects. A coupled iterative approach between the boundary-layer and pressure-distribution programs was used to account for boundary-layer displacement-thickness effects. The calculated-drag coefficients compared well with previously obtained experimental data.

Ashby, G. C., Jr.↗

NASA NTRS1973

A study of the diurnal variation in the thermosphere as derived by satellite drag

An analysis was performed on 29,574 densities derived from the drag of 10 satellites to determine simultaneously the parameters of the solar-activity effect in the thermosphere on the one hand, and the amplitude and shape of the diurnal-variation curve on the other. This paper reports on the study of the diurnal variation only. Although a considerable amount of smoothing is inherent in the drag method, it seemed useful to see whether any change could be detected in the shape of the diurnal-variation curve with height, latitude and solar activity. None was detected; the curve remains remarkably stable, symmetric, with a maximum at 14 hr 20 min L.S.T. and a minimum at 2 hr 20 min L.S.T. A systematic variation of the temperature range with height is observed when static models are used to derive it.

Jacchia, L. G.↗

NASA NTRS1974

Inviscid drag at transonic speeds

A systematic asymptotic expansion procedure is introduced into the Euler equations to obtain the transonic, small-disturbance potential equation and corresponding relation for the drag. The relation consists of an integral around any contour enclosing the body and an integral along all shocks contained within the contour. Interpretations are given for the origin of the pressure drag due to shock waves, lift, and wind-tunnel boundaries. Numerical procedures are discussed for evaluating these quantities from finite-difference relaxation calculations. Computed results are included for various contours, and results are compared with some experimental data.

Murman, E. M.↗

NASA NTRS1972

Sweep effect on the drag of rows of perpendicular circular cylinders in a laminar boundary layer at supersonic free-stream velocities

Drag measurements were obtained for circular cylinders attached perpendicularly to a flat-plate surface. Measurements were obtained for a single cylinder and for rows of cylinders. The cylinders were alined at various sweep angles relative to the free-stream velocity vector and at spacings appropriate for roughness elements used as boundary layer trips. The drag measurements were obtained for Mach numbers of 3.95 and 4.60, ratios of cylinder height to an undisturbed laminar boundary layer displacement thickness of approximately 1.0 to 3.0, a cylinder height-to-diameter ratio of approximately 2, and sweep angles up to 60. A complete presentation of the experimental results is given. A discussion of the more significant findings, including the most appropriate parameters for correlating the experimental results, is presented.

Lamb, M.↗

NASA NTRS1974

Aerodynamic drag reduction tests on a full-scale tractor-trailer combination with several add-on devices

Aerodynamic drag tests were performed on a conventional cab-over-engine tractor with a 45-foot trailer and five commercially available or potentially available add-on devices using the coast-down method. The tests ranged in velocity from approximately 30 miles per hour to 65 miles per hour and included some flow visualization. A smooth, level runway at Edwards Air Force Base was used for the tests, and deceleration measurements were taken with both accelerometers and stopwatches. An evaluation of the drag reduction results obtained with each of the five add-on devices is presented.

Montoya, L. C.↗

NASA NTRS1975

Drag and stability characteristics of a variety of reefed and unreefed parachute configurations at Mach 1.80 with an empirical correlation for supersonic Mach numbers

An investigation was conducted at Mach 1.80 in the Langley 4-foot supersonic pressure tunnel to determine the effects of variation in reefing ratio and geometric porosity on the drag and stability characteristics of four basic canopy types deployed in the wake of a cone-cylinder forebody. The basic designs included cross, hemisflo, disk-gap-band, and extended-skirt canopies; however, modular cross and standard flat canopies and a ballute were also investigated. An empirical correlation was determined which provides a fair estimation of the drag coefficients in transonic and supersonic flow for parachutes of specified geometric porosity and reefing ratio.

Couch, L. M.↗

NASA NTRS1975

The effect of Reynolds number on boattail drag

An investigation has been conducted in the Langley pilot transonic cryogenic tunnel to determine the effects of varying Reynolds number on boattail drag at subsonic speeds. Six boattailed cone-cylinder nacelle models were tested with the jet exhaust simulated by a cylindrical sting. Reynolds number was varied from about 2.6 million to 132 million by changing model length and unit Reynolds number. Boattail pressure coefficient distributions show that increasing Reynolds number tends to make the pressure coefficients in the expansion region more negative and the pressure coefficients in the recompression region more positive. These two effects were compensating and as a result there was little or no effect of Reynolds number on the pressure drag of the isolated boattails.

Reubush, D. E.↗

NASA NTRS1975

An analytic method to account for drag in the Vinti satellite theory

A quadrature algorithm is presented which employs analytical expressions for the variations of satellite orbital elements caused by air drag. The Hamiltonian is formally preserved and the Jacobi constants of the motion are advanced with time through the variational equations. The atmospheric density profile is written as a fitted exponential function of the eccentric anomaly, which adheres to tabulated data at all altitudes and simultaneously reduces the variational equations to definite integrals with closed form evaluations, whose limits are in terms of the eccentric anomaly. Results are given for two intense air drag satellites and indicate that the satellite ephemerides produced by this method in conjunction with the Vinti program are of very high accuracy.

Watson, J. S.↗