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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

An analysis of the impact of cabin floor angle restrictions on L/D for a typical supersonic transport

High floor angles at cruise have been identified as a significant problem facing airline and public acceptance of a supersonic transport. In order to explore the relationship between cruise performances and floor angle, four related wing-fuselage design and integration studies have been conducted. The studies were: (1) a fuselage camber study in which perturbations in the fuselage camber distribution were examined with a baseline wing, (2) a wing optimization study in which wings were optimized for minimum drag at C sub L's less than the design C sub L. These wings were optimized as wing planform camber surfaces alone and evaluated with a baseline fuselage, (3) a second wing optimization study in which wings were optimized for minimum drag at C sub L's less than the design C sub L but for this study the wings were optimized in the presence of the baseline fuselage, and (4) a third wing optimization study in which wings were optimized for minmum drag subject to C sub M constraints designed to produce more positive C sub MO's, thereby reducing trim drag. The studies indicated that it was not possible to both improve the aircraft cruise L/D and substantially reduce the cruise floor angle. The studies did indicate that the cruise floor angle could be reduced by reducing the fuselage incidence relative to the wing, but the reduction in floor angle was accompanied by a substantial reduction in L/D.

Radkey, R. L.↗
NASA NTRS1976

An evaluation of the method for determining the Whitham F-function using distributions of downwash and sidewash angles

The method of computing the Whitham F function using distributions of downwash and sidewash angles was evaluated with two different models. F functions which were calculated for a half angle cone cylinder at M infinites = 2.01, using theoretically and experimentally derived flow angles, show that the method is sensitive to small inaccuracies in the measured flow angles. An oblique wing transport model was tested at 0 deg angle of attack at M infinitely = 2.01. In this test, two different probes were used at two different distances from the model. The pressure signature derived from the F function was extrapolated and compared to the pressure signature measured at the distance of 0.87 body lengths with the static pressure probe. The agreement between the two pressure signatures was poor due to the many inaccuracies involved in using a probe designed to measure flow angularity.

Mendoza, J. P.↗
NASA NTRS1975

Resonance-line transfer with partial redistribution. VII Angle-dependent redistribution

A method is presented for treating radiative transfer in resonance lines, allowing for the full angle and frequency dependence of redistribution in the scattering process, as seen in the laboratory frame. The case of an equivalent-two-level-atom source function is considered; the problem to be treated is then linear in the radiation field. We apply this method to the Ca II lines in the solar atmosphere, using a redistribution function which takes into account a mixture of coherence in the atom's frame, with Doppler redistribution in the laboratory frame (for atoms which have not suffered an elastic collision), and of complete redistribution in the laboratory frame (for atoms that are collisionally perturbed during the emission process). Both the angle-averaged approximation and the full angle-dependent solution were obtained, and were compared to assess, differentially, the effects of angular redistribution upon the computed line profile and its center-to-limb behavior. For the Ca II line in a homogeneous solar chromosphere the angle-dependent effects are found to be negligible, indicating that one may use angle-averaged redistribution functions when studying partial redistribution effects in line profiles.

Milkey, R. W.↗
NASA NTRS1975

Effect of combined roll rate and sideslip angle on aircraft flight stability

The combined destabilizing effects of roll rate and sideslip angle are studied for a high angle-of-attack flight condition using a linear simulation of the coupled motions of a Space Shuttle-like configuration. Variations in the eigenvalues for a flight condition nominally identified by an angle of attack of 33.29 deg and a Mach number of 4.9 are examined with illustrations of the separate effects of body-axis roll rate and yaw rate, stability-axis roll rate, dynamic pressure, and sideslip angle. It is shown that the stability of the free motion of the vehicle is sensitive to roll rate and that this sensitivity is enhanced by nonzero sideslip angle. The results suggest that fully coupled linearized equations can be of value both for the study of Space Shuttle stability and for a better understanding of post-stall gyrations, incipient spin, and departure prevention for high-performance aircraft.

Stengel, R. F.↗
NASA NTRS1976

Side forces on a tangent ogive forebody with a fineness ratio of 2.5 at high angles of attack and low speed

A wind tunnel study to determine the subsonic aerodynamic characteristics, at high angles of attack, of a tangent ogive forebody with a fineness ratio of 2.5, is reported. Static longitudinal and lateral-directional stability data were obtained at Reynolds numbers ranging from 0.4 x 1 million to 3.7 x 1 million (based on base diameter) at a Mach number of 0.25. Angle of attack was varied from 36 deg to 88 deg at zero sideslip. It was found that at low Reynolds numbers the forebody does not have a side force att high angles of attack; however, at Reynolds numbers above about 2 x 1 million, a side force occurs in the angle of attack range from 45 deg to 80 deg. The maximum side force is as large as the maximum normal force. The maximum normal force coefficient varies between 1.0 and 2.0 over the Reynolds number range tested and occurs at angles of attack near 65 deg.

Keener, E. R.↗
NASA NTRS1977

Euler angles, quaternions, and transformation matrices for space shuttle analysis

Relationships between the Euler angles and the transformation matrix, the quaternion and the transformation matrix, and the Euler angles and the quaternion are analyzed, and equations developed are applied directly to current space shuttle problems. The twelve three-axis Euler transformation matrices as functions of the Euler angles, the equations for the quaternion as a function of the Euler angles, and the Euler angles as a function of the transformation matrix elements are included along with a group of utility subroutines to accomplish the Euler matrix, quaternion matrix, and Euler quaternion relationships.

Henderson, D. M.↗
NASA NTRS1977

Shuttle Program. Euler angles, quaternions, and transformation matrices working relationships

A brief mathematical development of the relationship between the Euler angles and the transformation matrix, the quaternion and the transformation matrix, and the Euler angles and the quaternion is presented. The analysis and equations presented apply directly to current space shuttle problems. The twelve three-axis Euler transformation matrices are given as functions of the Euler angles, the equations for the quaternion as a funtion of the Euler angles, and the Euler angles as a function of the transformation matrix elements.

Henderson, D. M.↗
NASA NTRS1979

Cold-air performance of free power turbine designed for 112-kilowatt automotive gas-turbine engine. 2: Effects of variable stator-vane-chord setting angle on turbine performance

The cold-air performance of an axial-flow power turbine with a variable stator designed for a 112-kW automotive gas-turbine engine was determined at speeds from 30 to 110 percent of design and at pressure ratios from 1.11 to 2.67. Performance is presented in terms of equivalent mass flow, torque, power, and efficiency for stator-vane-chord setting angles of 26 degs, 30 degs, 35 degs (design), 40 degs, 45 degs, and 50 degs. Turbine braking performance at a nominal stator setting angle of 107 degs is also presented. Turbine efficiency increased with increasing stator setting angle. A 10-point efficiency increase was obtained by opening the stator from the design setting angle of 35 degs to a setting angle of 45 degs.

Mclallin, K. L.↗
NASA NTRS1981

Effect of sweep angles on aerodynamic performance of double arrow wing - An analytical study

Hybrid wing planforms are studied for adoption on supersonic transport and fighter aircraft. The free vortex sheet method is used to determine effects of the leading-edge sweep angles on the aerodynamic performance of a double arrow wing with a strake. Results show lift and drag increase with the increase of the inboard and outboard leading-edge sweep angles. However, the lift-to-drag ratio is little influenced by the changes in these sweep angles. Spanwise surface pressure distributions on the aft region are influenced by the inboard sweep angle while the outboard sweep angle has no effect on these pressures. Finally, the experimental data and predicted results are compared to show good agreement.

Reddy, C. S.↗
NASA NTRS1981

Canopy reflectance as influenced by solar illumination angle

The interaction of the solar illumination angle and row azimuth angle of the measured reflectance factor (RF) of soybean canopies was investigated. Diurnal changes of nearly 140% were observed in the red wavelength region when canopies covered 64% of the soil. The amount of shadow observed was a function of the plant geometry and row width. As soil cover approached 100%, the diurnal changes diminished. A function tht describes the solar illumination angle with respect to the row azimuth explained most of the diurnal variation in the measured RF. Variation in near infrared response was much less and did not appear to be as strongly related to Sun-row angle interactions. The near infrared/red ratio was highly sensitive to Sun angle-row direction interactions, whereas the greenness function, utilizing all four spectral bands, was not.

Bauer, M. E.↗
NASA NTRS1982

Rates of solar angles for two-axis concentrators

The Sun's position by the azimuth and elevation angles and its rate of change at any time of day are determined to design 2 axis tracking mechanisms of solar concentrators. The Sun's angles and their rates for selected months of the year (March, June, September and December) and for seven selected atitudes (0, + or - 30, + or - 60, + or - 90) covering both the northern and southern hemispheres were studied. The development of the angle and angle rate analytical expressions for any month, hour of day, and latitude provides the solar concentrator designer with a quantitative determination of the limiting Sun's position and angle rates for an accurate automatic tracking mechanism.

Yung, C. S.↗
NASA NTRS1982

Bifurcation analysis of nonlinear stability of aircraft at high angles of attack

The problem of stability of steady flight of an aircraft flying at high angles of attack subject to finite-amplitude disturbances in pitch is studied using bifurcation theory, taking account of the interactions between the pitching motion and the unsteady flow. The aerodynamic responses to large-amplitude slow oscillations of the aircraft are obtained from that of infinitesimal amplitude case. Increasing the angle of attack past some critical angle for which the damping vanishes, the steady flight becomes unstable and Hopf bifurcation sets in, resulting in a periodic motion. A simple criterion in terms of the aerodynamic coefficients is given for determining the stability of the bifurcating period motion. For supersonic/hypersonic flat plate airfoils the bifurcating periodic motion is found to be unstable. This implies that when the angle of attack is increased past that of neutral damping, there will be drastic changes of the motion of the aircraft from its steady flight condition at the critical angle, including, e.g. hysteresis.

Hui, W. H.↗
NASA NTRS1983

High-angle-of-attack stability characteristics of a 3-surface fighter configuration

A wind tunnel investigation was conducted to study the low speed, high angle of attack stability characteristics of a three surface fighter concept based on the F-15 configuration. Static force data were measured over angle of attack and side-slip ranges of 0 to 85 and -10 and 10 deg, respectively. A force oscillation technique was used to obtain dynamic derivatives at angles of attack from 0 to 60 deg. The tests were conducted for several canard deflections and with the canards removed to investigate the effects of the close coupled canard on the high angle of attack stability characteristics of the configuration. A fuselage strake was developed which significantly improved static lateral directional stability characteristics at high angles of attack while also increasing the maximum lift of the configuration.

Grafton, S. B.↗
NASA NTRS1981

Some experiments on Yaw stability of wind turbines with various coning angles

A horizontal axis wind turbine was constructed to study the effect of coning angle on the yawing moments produced. Coning angles of 0 deg, +10 deg and -10 deg were studied in the upwind and downwind cases. Moment and rotational frequency of the blades at each yaw angle setting were taken. It was found that as the coning angle increased from -10 deg to +10 deg in either the upwind or downwind case the stability decreased. The downwind case was slightly more stable for all coning angles than was the upwind case. It is found that all the previous cases were stable for high rotation speeds, but at lower rotation speeds, they were all unstable and could not self start unless held in the wind.

Bundas, D.↗
NASA NTRS1983

Large-scale wind-tunnel investigation of a close-coupled canard-delta-wing fighter model through high angles of attack

Data obtained through very high angles of attack from a large-scale, subsonic wind-tunnel test of a close-coupled canard-delta-wing fighter model are analyzed. The canard delays wing leading-edge vortex breakdown, even for angles of attack at which the canard is completely stalled. A vortex-lattice method was applied which gave good predictions of lift and pitching moment up to an angle of attack of about 20 deg, where vortex-breakdown effects on performance become significant. Pitch-control inputs generally retain full effectiveness up to the angle of attack of maximum lift, beyond which, effectiveness drops off rapidly. A high-angle-of-attack prediction method gives good estimates of lift and drag for the completely stalled aircraft. Roll asymmetry observed at zero sideslip is apparently caused by an asymmetry in the model support structure.

Stoll, F.↗
NASA NTRS1983

The effects of solar incidence angle over digital processing of LANDSAT data

A technique to extract the topography modulation component from digital data is described. The enhancement process is based on the fact that the pixel contains two types of information: (1) reflectance variation due to the target; (2) reflectance variation due to the topography. In order to enhance the signal variation due to topography, the technique recommends the extraction from original LANDSAT data of the component resulting from target reflectance. Considering that the role of topographic modulation over the pixel information will vary with solar incidence angle, the results of this technique of digital processing will differ from one season to another, mainly in highly dissected topography. In this context, the effects of solar incidence angle over the topographic modulation technique were evaluated. Two sets of MSS/LANDSAT data, with solar elevation angles varying from 22 to 41 deg were selected to implement the digital processing at the Image-100 System. A secondary watershed (Rio Bocaina) draining into Rio Paraiba do Sul (Sao Paulo State) was selected as a test site. The results showed that the technique used was more appropriate to MSS data acquired under higher Sun elevation angles. Topographic modulation components applied to low Sun elevation angles lessens rather than enhances topography.

Parada, N. D. J.↗
NASA NTRS1983

Noise of the SR-6 propeller model at 2 deg and 4 deg angles of attack

The noise generated by supersonic-tip-speed propellers creates a cabin noise problem for future airplanes powered by these propellers. Noise of a number of propeller models were measured in the NASA Lewis 8- by 6-Foot Wind Tunnel with flow parallel to the propeller axis. In flight, as a result of the induced upwash from the airplane wing, the propeller is at an angle of attack with respect to the incoming flow. Therefore, the 10-blade SR-6 propeller was operated at angle of attack to determine its noise behavior. Higher blade passage tones were observed for the propeller operating at angle of attack in a 0.6 axial Mach number flow. The noise increase was not symmetrical, with one wall of the wind tunnel showing a larger noise increase than the other wall. No noise increase was observed at angle of attack in a 0.8 axial Mach number flow. For this propeller the dominance of thickness noise, which does not increase with angle of attack, explains the lack of noise increase at the higher 0.8 Mach number.

Dittmar, J. H.↗
NASA NTRS1984

Evaluation of a flow direction probe and a pitot-static probe on the F-14 airplane at high angles of attack and sideslip

The measurement performance of a hemispherical flow-angularity probe and a fuselage-mounted pitot-static probe was evaluated at high flow angles as part of a test program on an F-14 airplane. These evaluations were performed using a calibrated pitot-static noseboom equipped with vanes for reference flow direction measurements, and another probe incorporating vanes but mounted on a pod under the fuselage nose. Data are presented for angles of attack up to 63, angles of sideslip from -22 deg to 22 deg, and for Mach numbers from approximately 0.3 to 1.3. During maneuvering flight, the hemispherical flow-angularity probe exhibited flow angle errors that exceeded 2 deg. Pressure measurements with the pitot-static probe resulted in very inaccurate data above a Mach number of 0.87 and exhibited large sensitivities with flow angle.

Larson, T. J.↗