Wind-tunnel investigation of a flush airdata system at Mach numbers from 0.7 to 1.4

Flush pressure orifices installed on the nose section of a 1/7-scale model of the F-14 airplane were evaluated for use as a flush airdata system (FADS). Wing-tunnel tests were conducted in the 11- by 11-ft Unitary Wind Tunnel at NASA Ames Research Center. A full-scale FADS of the same configuration was previously tested using an F-14 aircraft at the Dryden Flight Research Facility of NASA Ames Research Center (Ames-Dryden). These tests, which were published, are part of a NASA program to assess accuracies of FADS for use on aircraft. The test program also provides data to validate algorithms for the shuttle entry airdata system developed at the NASA Langley Research Center. The wind-tunnel test Mach numbers were 0.73, 0.90, 1.05, 1.20, and 1.39. Angles of attack were varied in 2 deg increments from -4 deg to 20 deg. Sideslip angles were varied in 4 deg increments from -8 deg to 8 deg. Airdata parameters were evaluated for determination of free-stream values of stagnation pressure, static pressure, angle of attack, angle of sideslip, and Mach number. These parameters are, in most cases, the same as the parameters investigated in the flight test program. The basic FADS wind-tunnel data are presented in tabular form. A discussion of the more accurate parameters is included

Qualitative evaluation of a flush air data system at transonic speeds and high angles of attack

Flight tests were performed on an F-14 aircraft to evaluate the use of flush pressure orifices on the nose section for obtaining air data at transonic speeds over a large range of flow angles. This program was part of a flight test and wind tunnel program to assess the accuracies of such systems for general use on aircraft. It also provided data to validate algorithms developed for the shuttle entry air data system designed at NASA Langley. Data were obtained for Mach numbers between 0.60 and 1.60, for angles of attack up to 26.0 deg, and for sideslip angles up to 11.0 deg. With careful calibration, a flush air data system with all flush orifices can provide accurate air data information over a large range of flow angles. Several orificies on the nose cap were found to be suitable for determination of stagnation pressure. Other orifices on the nose section aft of the nose cap were shown to be suitable for determination of static pressure. Pairs of orifices on the nose cap provided the most sensitive measurements for determining angles of attack and sideslip, although orifices located farther aft on the nose section could also be used

High-frequency performance of Schottky source/drain silicon pMOS devices

A radio-frequency performance of 85-nm gate-length p-type Schottky barrier (SB) with PtSi source/drain materials is investigated. The impact of silicidation annealing temperature on the high-frequency behavior of SB MOSFETs is analyzed using an extrinsic small-signal equivalent circuit. It is demonstrated that the current drive and the gate transconductance strongly depend on the silicidation anneal temperature, whereas the unity-gain cutoff frequency of the measured devices remains nearly unchanged

Digital program for calculating static pressure position error

A computer program written to calculate the static pressure position error of airspeed systems contains five separate methods for determining position error, of which the user may select from one to five at a time. The program uses data from both the test aircraft and the ground-based radar to calculate the error. In addition, some of the methods require rawinsonde data or an atmospheric analysis, or both. The program output lists the corrections to Mach number, altitude, and static pressure that are due to position error. Reference values such as angle of attack, angle of sideslip, indicated Mach number, indicated pressure altitude, stagnation pressure, and total temperature are also listed

High-angle-of-attack pneumatic lag and upwash corrections for a hemispherical flow direction sensor

As part of the NASA F-14 high angle of attack flight test program, a nose mounted hemispherical flow direction sensor was calibrated against a fuselage mounted movable vane flow angle sensor. Significant discrepancies were found to exist in the angle of attack measurements. A two fold approach taken to resolve these discrepancies during subsonic flight is described. First, the sensing integrity of the isolated hemispherical sensor is established by wind tunnel data extending to an angle of attack of 60 deg. Second, two probable causes for the discrepancies, pneumatic lag and upwash, are examined. Methods of identifying and compensating for lag and upwash are presented. The wind tunnel data verify that the isolated hemispherical sensor is sufficiently accurate for static conditions with angles of attack up to 60 deg and angles of sideslip up to 30 deg. Analysis of flight data for two high angle of attack maneuvers establishes that pneumatic lag and upwash are highly correlated with the discrepancies between the hemispherical and vane type sensor measurements

Preliminary results from a subsonic high angle-of-attack flush airdata sensing (HI-FADS) system: Design, calibration, and flight test evaluation

A nonintrusive high angle-of-attack flush airdata sensing (HI-FADS) system was installed and flight-tested on the F-18 high alpha research flight vehicle. The system is a matrix of 25 pressure orifices in concentric circles on the nose of the vehicle. The orifices determine angles of attack and sideslip, Mach number, and pressure altitude. Pressure was transmitted from the orifices to an electronically scanned pressure module by lines of pneumatic tubing. The HI-FADS system was calibrated and demonstrated using dutch roll flight maneuvers covering large Mach, angle-of-attack, and sideslip ranges. Reference airdata for system calibration were generated by a minimum variance estimation technique blending measurements from two wingtip airdata booms with inertial velocities, aircraft angular rates and attitudes, precision radar tracking, and meteorological analyses. The pressure orifice calibration was based on identifying empirical adjustments to modified Newtonian flow on a hemisphere. Calibration results are presented. Flight test results used all 25 orifices or used a subset of 9 orifices. Under moderate maneuvering conditions, the HI-FADS system gave excellent results over the entire subsonic Mach number range up to 55 deg angle of attack. The internal pneumatic frequency response of the system is accurate to beyond 10 Hz. Aerodynamic lags in the aircraft flow field caused some performance degradation during heavy maneuvering

Spectroscopy of Globular Clusters out to Large Radius in the Sombrero Galaxy

We present new velocities for 62 globular clusters in M104 (NGC 4594, the Sombrero Galaxy), 56 from 2dF on the AAT and 6 from Hydra on WIYN. Combined with previous data, we have a total sample of 108 M104 globular cluster velocities, extending to 20 arcmin radius (~60 kpc), along with BVR photometry for each of these. We use this wide-field dataset to study the globular cluster kinematics and dark matter content of M104 out to 10 arcmin radius (30 kpc). We find no rotation in the globular cluster system. The edge-on nature of M104 makes it unlikely that there is strong rotation which is face-on and hence unobserved; thus, the absence of rotation over our large radial range appears to be an intrinsic feature of the globular cluster system in M104. We discuss ways to explain this low rotation, including the possibility that angular momentum has been transferred to even larger radii through galaxy mergers. The cluster velocity dispersion is ~230 km/s within several arcmin of the galaxy center, and drops to ~150 km/s at ~10 arcmin radius. We derive the mass profile of M104 using our velocity dispersion profile, together with the Jeans equation under the assumptions of spherical symmetry and isotropy, and find excellent agreement with the mass inferred from the stellar and gas rotation curve within 3 arcmin radius. The M/L_V increases from ~4 near the galaxy center to ~17 at 7 arcmin radius (~20 kpc, or 4 R_e), thus giving strong support for the presence of a dark matter halo in M104. More globular cluster velocities at larger radii are needed to further study the low rotation in the globular cluster system, and to see if the dark matter halo in M104 extends beyond a radius of 30 kpc.Comment: 40 pages, 7 figures, accepted for publication in Ap

A photometric and spectroscopic study of dwarf and giant galaxies in the Coma cluster - V. Dependence of the spectroscopic properties on location in the cluster

We investigate the radial dependence of the spectroscopic properties, in particular the Mg2, and H beta spectroscopic indices, in a sample of galaxies spanning a wide range of absolute luminosity in the Coma cluster. After allowing for the magnitude dependence of these indices, we find a significant gradient in Mg2, in the sense that galaxies in the core of the cluster have stronger Mg2. We find only weak gradients in and H beta. Using the model grids presented in an earlier paper in this series, we attribute the Mg2 gradient to changes in metal abundance. One possible mechanism to create this abundance gradient is pressure confinement by the intracluster medium of material from Supernova driven winds early in the history of the galaxies.Comment: 12 pages, 11 figures, accepted by Ap. J. (main journal

Ages of S0 and elliptical galaxies in the Coma cluster

The ages of stellar populations in 52 elliptical and S0 galaxies in the Coma cluster are investigated using a new spectroscopic sample. More than 40% of the S0s are found to have experienced recent star formation in their central regions during the last ~5 Gyrs, while such activity is absent in the ellipticals. Galaxies in this sample have absolute magnitudes in the range -20.5 < M_B < -17.5, and the fraction of S0 galaxies with recent star formation is higher at fainter luminosities. The observed luminosity range of S0 galaxies with signs of recent star formation activity is consistent with them being the descendants of typical star-forming spirals at intermediate redshift whose star formation has been halted as a consequence of the dense environment.Comment: 18 pages, ApJ in pres