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Vicroy, Dan D.

Publications and source records attributed to Vicroy, Dan D..

43 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Assessment of microburst models for downdraft estimation

The effectiveness of three microburst models in estimating the downdraft from horizontal velocity measurements is assessed. The development of the models and their characteristics are discussed. The simplest model, a linear one, works well for altitudes below 200 m and near the microburst core. A ring-vortex model and an empirical model give the best overall results. The former is the most complex, requiring four variables to define it. The empirical model uses three variables.

Vicroy, Dan D.↗
NASA NTRS1990

Guidance concepts for time-based flight operations

Airport congestion and the associated delays are severe in today's airspace system and are expected to increase. NASA and the FAA is investigating various methods of alleviating this problem through new technology and operational procedures. One concept for improving airspace productivity is time-based control of aircraft. Research to date has focused primarily on the development of time-based flight management systems and Air Traffic Control operational procedures. Flight operations may, however, require special onboard guidance in order to satisfy the Air Traffic Control imposed time constraints. The results are presented of a simulation study aimed at evaluating several time-based guidance concepts in terms of tracking performance, pilot workload, and subjective preference. The guidance concepts tested varied in complexity from simple digital time-error feedback to an advanced time-referenced-energy guidance scheme.

Vicroy, Dan D.↗
NASA NTRS1990

The aerodynamic effect of heavy rain on airplane performance

The National Aeronautics and Space Administration has been conducting a series of tests to determine the effect of heavy rain on airfoil aerodynamics. The results of these tests have shown that heavy rain can significantly increase drag as well as decrease lift and stall angle of attack. This paper describes a recent effort to use the heavy rain airfoil data to determine the aerodynamic effect on a conventional twin-jet transport. The paper reports on the method used to model the heavy rain aerodynamic effect and the resulting performance degradation. The heavy rain performance effect is presented in terms of the diminished climb performance associated with increasing rain rates. The effect of heavy rain on the airplane's ability to escape a performance-limiting wind shear is illustrated through a numerical simulation of a wet microburst encounter. The results of this paper accentuate the need for further testing to determine scaling relationships and flow mechanics, and the full configuration three-dimensional effects of heavy rain.

Vicroy, Dan D.↗
NASA NTRS1988

Influence of wind shear on the aerodynamic characteristics of airplanes

The aerodynamic effect of shear flow through a series of sensitivity studies of the wind velocity gradients and wing planform geometry parameters is investigated and characterized. The wind shear effect is computed using a modified vortex-lattice computer program and characterized through the formulation of wind shear aerodynamic coefficients. The magnitudes if the aerodynamic effects are demonstrated by computation of the resultant change in the aerodynamics of a conventional wing and horizontal stability configuration on a fixed flight path through a simulated microburst. The results indicate that as much as 20 percent of the control authority of the airplane may be required to counteract the wind-shear-induced forces and moments in the microburst environment.

Vicroy, Dan D.↗
NASA NTRS1988

Investigation of the influence of wind shear on the aerodynamic characteristics of aircraft using a vortex-lattice method

The objective was to investigate and characterize the aerodynamic effect of shear flow through a series of sensitivity studies of the wind velocity gradients and wing planform geometry parameters. The wind shear effect was computed using a modified vortex-lattice computer program and characterized through the formulation of wind shear aerodynamic coefficients. The magnitude of the aerodynamic effect was demonstrated by computing the resultant change in the aerodynamics of a conventional wing and tail combination on a fixed flight path through a simulated microburst. The results of the study indicate that a significant amount of the control authority of an airplane may be required to counteract the wind shear induced forces and moments in the microburst environment.

Vicroy, Dan D.↗
NASA NTRS1988

The effect of spatial wind gradients on airplane aerodynamics

An account is given of the results of recent studies of the effect of a spatially sheared wind field on airplane aerodynamics; the wind shear was computed by a modified vortex-lattice computer program, and characterized through the formulation of wind shear aerodynamic coefficients. The magnitude of the aerodynamic effect was demonstrated by computing the change in conventional wing/tail configuration aerodynamics for a fixed flight path through a simulated microburst. A substantial portion of the control authority of the aircraft may be required to counteract the wind shear-induced forces and moments in the microburst environment; both aperiodic and oscillatory instabilities may be generated by shear-dependent dynamic modes.

Vicroy, Dan D.↗