J. T. Gallagher

Bio: J. T. Gallagher is an academic researcher from Northrop Corporation. The author has contributed to research in topics: Flight simulator & Wing loading. The author has an hindex of 3, co-authored 4 publications receiving 46 citations.

Pressure Distribution on a Rectangular Wing with a Jet Exhausting Normally into an Airstream

Abstract: The interaction between a jet exhausting normally from a lifting surface into a uniform airstream is explored theoretically and experimentally. A theoretical model of the flow is discussed in which the entrainment of the mainstream fluid by the j et is accounted for directly, without recourse to an empirical equation for the jet centerline. Making use of the observation that the jet deforms from a circular cross section into an elliptical cross section as it progresses downstream, the continuity and momentum equations are solved to provide the jet path. The velocity field induced by the jet is then determined by replacing the jet by a sink-doublet distribution. The distribution of sinks represents the entrainment effect of the jet, and the doublet distribution represents the blockage effect of the jet. Lifting surface theory is used to predict the loading on the adjacent lifting surface. The theory does account for the three-dimensionality of the problem, and there is good agreement between theory and the results of an experiment conducted on a 10% thick straight wing at AR = 3.

A Model-Following Variable Stability System for the NASA ARC X-14B

Abstract: A description is presented of the basic design concept, hardware design, ground and inflight acceptance testing of a Variable Stability System (VSS) installed on the NASA ARC X-14B, a twin-engine, single-seated VTOL airplane. The variable stability system was of the model-following type and provided variability in the three rotational degrees of freedom. A general-purpose airborne digital computer was used as the model residence and was an integral part of the hybrid model-following flight control system. The initial system design was achieved using optimal control techniques and the ASP computer program. Single-degree-of-freedom simulations were used to introduce nonlinear characteristics to the synthesis process, and these were extended to a sixdegree-of-freedom simulation for final system synthesis and analysis. The digital computer software acceptance testing involved emulation of the system on the IBM 360 and extensive bench tests of the computer and data adaptor combination. Systems integration and acceptance testing was initiated in a ground test mode which was then extended to testing on a captive rig and culminated in flight acceptance testing in the hover flight mode. It is demonstrated that the system was capable of model-following to the NASA specifications. The major advantages of the digital computer were the reprogramming capability, reliability of operation, and the light weight and low volume of the installation which were critical in this application. The digital computer hardware and software performance was extremely satisfactory in the hybrid flight control operation, while the analog portion of the system took considerable time for alignment and adjustment.

Investigation of the application of direct translational control to VTOL aircraft.

Abstract: The possibility of employing a mixed translation and attitude control system through a single cockpit stick has been investigated for low-speed flight control of VTOL aircraft. In this way it would be possible to command more directly low-speed longitudinal and lateral translations and to reduce the amount of installed thrust required for attitude control of VTOL aircraft. The maneuvering translation concept is not to be confused in the longitudinal plane with the more gross thrust vectoring requirement necessary for transition to wing-borne flight. In the current study, combined control schemes were evaluated on the longitudinal axis of a simulated VTOL aircraft during performance of a multiaxis IFR (instrument flight rules) hover task. With pilot opinion as a measure, some combinations of attitude and translational controls were found to be more satisfactory than attitude controls alone. Systems receiving the best ratings were 1) fully stabilized airframe provided with direct translation acceleration control and 2) stick steering control of attitude with open-loop shaping of the translational control to give pseudo-velocity control. Acceptable translational controls seem particularly well suited to IFR hover tasks, since they allow control movements to be minimized. There were definite indications that the larger control movements associated with VFR (visual flight rules) flight, where the pilot is less inhibited by the instrument scanning process, would result in mismatching of the attitude and translation controls.

Requirements on Simulators Used in Handling Qualities Research

Abstract: A methodology has been developed for driving the visual display and motion systems of a large-amplitude and rotational 3-axis flight simulators to minimize the impact of the constraints of pilot subjectivity and task dependence. In explaining the drive technique, a simple model of the sensing mechanisms of the vestibular system is used. However, a way has not been found yet to take advantage of the vestibular system description to establish the dynamic performance required of the elements in the motion and visual display system. The success of the drive scheme depends on subjective observations of test pilots which allow filters used in the drives to be properly set in terms of gain and break frequency; the filter characteristics also are task-dependent. Experiments conducted on the simulators provide some assurance that the drive technique works within these constraints. The first of a series of experiments being conducted on the large-amplitude, 3-axis simulator to develop a rationale for motion and visual display drives for moving base simulators is discussed in which a comprehensive simulation of the Cornell T-33 inflight simulator has been mechanized. Flight experiments have been repeated on the simulator. Results of this work suggest that a mix of simulators be used to study the problems associated with fighter-bomber mission effectiveness and handling qualities.

Theory of Manual Vehicular Control

Abstract: The analytical basis of manual vehicular control theory is a combination of feedback systems analysis and mathematical models for human operators engaged in control tasks. Simplified representations for the operator-system combination are provided by the 'crossover model', which is described in detail. The system dynamics and average performance of the crossover model system are developed. With these as bases, case studies are presented to illustrate the types of result which can be obtained from application of the operator-vehicle control theory. Two aircraft control examples illustrate the use of the theory and its empirical correlates to estimate operator dynamic characteristics, system performance, pilot ratings, pilot commentary, design implications, and some experimental guidelines. A driver automobile example is presented to illustrate the use of the theory in structuring the key guidance and control features of the driver's visual field. A comprehensive bibliography of operator-vehicle system analysis applications is also provided.

Energy climbs, energy turns, and asymptotic expansions

Abstract: Asymptotic expansions and energy methods applied to three dimensional aircraft maneuvers involving energy climbs and turns

Prediction of a Three-Dimensional Circular Turbulent Jet in Crossflow

Abstract: A quasi-three-di mensional integral method is used to solve the problem of the isothermal incompressible turbulent jet. The jet is submerged and is circular at its origin. The mathematical model is based on two integral momentum equations, one written for a direction parallel to the jet centerline and the other for a direction perpendicular to the centerline. For their solution, the entrainment rate into the jet is determined as the linear combination of a modified straight jet entrainment and the entrainment into a vortex pair. The family of velocity profiles required for the integration of the momentum equations is three-dimensional. The profiles are determined along the jet centerline on the basis of the distorted jet cross sections, thus being nonsimilar. The mathematical model is numerically solved, yielding the internal jet flowfield. Results are compared to experiments with different injection velocity to crossflow velocity ratios and with different injection angles. Agreement between theory and experiment is found to be satisfactory in some cases and good in others.

Interaction of jet in hypersonic cross stream

Abstract: A jet stream issuing normally from both sharp- and blunt-nose ogive-cylinder configurations into a hypersonic flow was investigated by a side-by-side experimental and numerical simulation. At a hypersonic Mach number of 12, strong interaction between jet-induced and bow shock wave systems, the jet plume trajectory, and the separated-flow surface shear pattern were highlighted for basic understanding. After the numerical solution was verified with the experimental data, the flowfield topology was reconstructed. Several unique features of this inviscid-viscous interaction phenomenon of shock-wave formation, vortical flow structure, and jet plume were delineated.

Enhancement of Impingement Cooling in a High Cross Flow Channel Using Shaped Impingement Cooling Holes

Abstract: Impingement systems are common place in many turbine cooling applications Generally these systems consist of a target plate that is cooled by the impingement of multiple orthogonal jets While it is possible to achieve high target surface heat transfer with this configuration, the associated pressure drop is generally high and the cooling efficiency low Furthermore, especially in large impingement arrays, the build-up of cross flow from upstream jets can be significant and result in deflection of downstream impingement jets reducing the resultant heat transfer coefficient distribution This paper presents a computational and experimental investigation into the use of shaped elliptical or elongated circular impingement holes designed to improve the penetration of the impinging jet across the coolant passage This is of particular interest where there is significant cross flow Literature review and computational investigations are used to determine the optimum aspect ratio of the impingement jet The improved heat transfer performance of the modified design is then tested in an experimental rig with varying degrees of cross flow at engine representative conditions In all cases a 16% increase in the Nusselt number on the impingement target surface in the downstream half of the cooling passage was achieved Under the first 4 impingement holes Nusselt number enhancement of enhancement of 28–77% was achieved provided no additional cross flow was present in the passage When appropriately aligned, a significant reduction in the stress concentration factor caused by the addition of a hole can be achieved using this designCopyright © 2006 by ASME