8,660 research outputs found
A compilation and analysis of typical approach and landing data for a simulator study of an externally blown flap STOL aircraft
A piloted simulation study has been made of typical landing approaches with an externally blown flap STOL aircraft to ascertain a realistic dispersion of parameter values at both the flare window and touchdown. The study was performed on a fixed-base simulator using standard cockpit instrumentation. Six levels of stability and control augmentation were tested during a total of 60 approaches (10 at each level). A detached supplement containing computer printouts of the flare-window and touchdown conditions for all 60 runs has been prepared
Fixed-base simulator investigation of lightweight vehicles for lunar escape to orbit with kinesthetic attitude control and simplified manual guidance
Piloted simulator investigation of lightweight vehicles for emergency lunar escape to orbit with kinesthetic attitude control and simplified manual guidanc
Energy efficient transport technology: Program summary and bibliography
The Energy Efficient Transport (EET) Program began in 1976 as an element of the NASA Aircraft Energy Efficiency (ACEE) Program. The EET Program and the results of various applications of advanced aerodynamics and active controls technology (ACT) as applicable to future subsonic transport aircraft are discussed. Advanced aerodynamics research areas included high aspect ratio supercritical wings, winglets, advanced high lift devices, natural laminar flow airfoils, hybrid laminar flow control, nacelle aerodynamic and inertial loads, propulsion/airframe integration (e.g., long duct nacelles) and wing and empennage surface coatings. In depth analytical/trade studies, numerous wind tunnel tests, and several flight tests were conducted. Improved computational methodology was also developed. The active control functions considered were maneuver load control, gust load alleviation, flutter mode control, angle of attack limiting, and pitch augmented stability. Current and advanced active control laws were synthesized and alternative control system architectures were developed and analyzed. Integrated application and fly by wire implementation of the active control functions were design requirements in one major subprogram. Additional EET research included interdisciplinary technology applications, integrated energy management, handling qualities investigations, reliability calculations, and economic evaluations related to fuel savings and cost of ownership of the selected improvements
Development of a simulator for studying simplified lunar escape systems
Design and development of lunar escape system simulator for investigation of lunar escape problems and simplified manual guidance and control for lunar escape vehicle
Description and flight tests of an oculometer
A remote sensing oculometer was successfully operated during flight tests with a NASA experimental Twin Otter aircraft at the Langley Research Center. Although the oculometer was designed primarily for the laboratory, it was able to track the pilot's eye-point-of-regard (lookpoint) consistently and unobtrusively in the flight environment. The instantaneous position of the lookpoint was determined to within approximately 1 deg. Data were recorded on both analog and video tape. The video data consisted of continuous scenes of the aircraft's instrument display and a superimposed white dot (simulating the lookpoint) dwelling on an instrument or moving from instrument to instrument as the pilot monitored the display information during landing approaches
Preliminary flight tests of an oculometer
A remote sensing oculometer has been successfully operated during flight tests. This device was able to track the pilot's eye-point-of-regard (lookpoint) consistently and unobtrusively in the flight environment. The instantaneous position of the lookpoint was determined to within approximately 1 degree. Data were recorded on both analog and video tape. The video data consisted of continuous scenes of the aircraft's instrument display and a superimposed white dot (simulating the lookpoint) dwelling or moving from instrument to instrument as the pilot monitored the display information during landing approaches
The Stability of an Isotropic Cosmological Singularity in Higher-Order Gravity
We study the stability of the isotropic vacuum Friedmann universe in gravity
theories with higher-order curvature terms of the form
added to the Einstein-Hilbert Lagrangian of general relativity on approach to
an initial cosmological singularity. Earlier, we had shown that, when ,
a special isotropic vacuum solution exists which behaves like the
radiation-dominated Friedmann universe and is stable to anisotropic and small
inhomogeneous perturbations of scalar, vector and tensor type. This is
completely different to the situation that holds in general relativity, where
an isotropic initial cosmological singularity is unstable in vacuum and under a
wide range of non-vacuum conditions. We show that when , although a
special isotropic vacuum solution found by Clifton and Barrow always exists, it
is no longer stable when the initial singularity is approached. We find the
particular stability conditions under the influence of tensor, vector, and
scalar perturbations for general for both solution branches. On approach to
the initial singularity, the isotropic vacuum solution with scale factor
is found to be stable to tensor perturbations for and stable to vector perturbations for , but is
unstable as otherwise. The solution with scale factor
is not relevant to the case of an initial singularity for
and is unstable as for all for each type of perturbation.Comment: 25 page
Random background charges and Coulomb blockade in one-dimensional tunnel junction arrays
We have numerically studied the behavior of one dimensional tunnel junction
arrays when random background charges are included using the ``orthodox''
theory of single electron tunneling. Random background charge distributions are
verified in both amplitude and density. The use of a uniform array as a
transistor is discussed both with and without random background charges. An
analytic expression for the gain near zero gate voltage in a uniform array with
no background charges is derived. The gate modulation with background charges
present is simulated.Comment: 10 pages, 7 figure
Thermal Rounding of the Charge Density Wave Depinning Transition
The rounding of the charge density wave depinning transition by thermal noise
is examined. Hops by localized modes over small barriers trigger
``avalanches'', resulting in a creep velocity much larger than that expected
from comparing thermal energies with typical barriers. For a field equal to the
depinning field, the creep velocity is predicted to have a {\em
power-law} dependence on the temperature ; numerical computations confirm
this result. The predicted order of magnitude of the thermal rounding of the
depinning transition is consistent with rounding seen in experiment.Comment: 12 pages + 3 Postscript figure
Statistical Topography of Glassy Interfaces
Statistical topography of two-dimensional interfaces in the presence of
quenched disorder is studied utilizing combinatorial optimization algorithms.
Finite-size scaling is used to measure geometrical exponents associated with
contour loops and fully packed loops. We find that contour-loop exponents
depend on the type of disorder (periodic ``vs'' non-periodic) and they satisfy
scaling relations characteristic of self-affine rough surfaces. Fully packed
loops on the other hand are unaffected by disorder with geometrical exponents
that take on their pure values.Comment: 4 pages, REVTEX, 4 figures included. Further information can be
obtained from [email protected]
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