Showing papers by "Vaughn College of Aeronautics and Technology published in 1999"

Observation of the Halo of the Edge-On Galaxy IC 5249

Abstract: Optical photometry and H I synthesis observations of the southern edge-on Sc/Sd galaxy IC 5249 are reported. The rotation curve rises linearly out to a radius of 7 kpc and then appears to flatten out at ~100 km s-1. The H I mass out to 24.5 kpc is ~6 × 109 M⊙, or 10% of the total mass out to this radius. The color, central surface brightness, scale height, and scale length of the disk of IC 5249 are R - I ≈ 0.4, μ = 20.6 ± 0.1RC mag arcsec-2, 600 ± 40 pc, and 11 ± 2 kpc, respectively. Additional light to that predicted by an exponential disk is present at distances greater than 3 kpc from the disk. At 5 kpc the surface brightness is 27–28RC mag arcsec-2. The measured distribution of surface brightness is used to constrain the abundance of low-mass main-sequence stars in the halo of the galaxy. A halo made up entirely of main-sequence stars heavier than 0.13 M⊙ is excluded. We also find that less than 20% of the halo can be composed of main-sequence stars heavier than 0.30 M⊙. Further observations are required to determine the rotation curve of IC 5249 to large radii and to determine precisely the abundance of low-mass main-sequence stars in the halo of the galaxy.

The influence of bend–twist coupling on the shear buckling response of thin laminated composite plates

Abstract: The finite strip method of analysis has been used in this paper to examine the effect of bend–twist coupling on the shear buckling behaviour of laminated composite constructions. The distorted nodal lines of the shear buckling mode and its complex deformation state in general are readily accounted for in the analysis procedure through the multi-term nature of the finite strip buckling displacement field and the appropriate level of structural modelling. The degree of bend–twist coupling in the laminated composite plates is varied by changing the level of anisotropy in the plies and by altering the lay-up configuration of the plies in the laminated stack. Symmetric laminates of a balanced and unbalanced nature are given consideration. It is shown that, for a given degree of anisotropy in the plies of a laminate and for a given laminate thickness, the stacking sequence of the plies significantly alters the degree of bend–twist coupling. The shear buckling performance of composite plates having the same dimensions and being made from the same material are therefore shown in the paper to be quite different. The preclusion of the bend–twist coupling coefficients in the solution procedure of the finite strip method allows the shear buckling orthotropic solution to be determined. Comparisons between the coupled and orthotropic solutions are shown in the paper to be markedly different.

Stakeholders in a hybrid market: the example of air business passenger travel

Abstract: Selects European business air travel as an example of a market that displays both industrial and consumer characteristics, and subsequently defines it as having a hybrid nature. Adopts a stakeholder approach to overcome the problems of the identification and analytical complexity associated with the decision‐making unit in this hybrid market. Collects data on three stakeholder groupings in a survey of 827 business travellers. Identifies the nature of the decision‐making process and the influence that each of the stakeholder groupings has in the purchase decision. Indicates that marketing strategies in the business air travel market could prove more successful through addressing multiple stakeholder groups involved in the purchase decision process. Suggests that the stakeholder model may provide a practical research approach to other hybrid markets where the DMU approach is difficult, particularly where there are many purchasing units.

Optimisation of air-jet vortex generators with respect to system design parameters

Abstract: A simple technique is proposed that allows the definition of the geometry and characteristics of an air-jet vortex generator to be defined, using the system requirements in practical design. Typically, the aircraft designer is concerned with the mass flow-rate and air pressure requirements of any pneumatic system for inclusion to an airframe. These parameters are not congruent with those for air-jet vortex generator aerodynamic design, and therefore, some tool is required to bridge the gap. Such a tool is proposed, based on empirical methods for the prediction of air-jet vortex generator behaviour. The technique allows the comparison of the vortex strength, and the system inputs (the jet mass flow-rate and the air-jet plenum pressure) for the air-jet, for a range of jet nozzle diameters and jet velocity ratios. Through this comparison, the optimum air-jet design can be reached for a given system input.

Incorporation of manufacturing information into an MDO environment

Abstract: The Paper describes a metal and composite recurrent cost model of a large civil aircraft wing structure for a multidisciplinary design, analysis and optimisation (MDO) environment. The work was part of a recent European MDO project (BE95-2056) which investigated methods for the integration of structures, aerodynamics, dynamics and manufacturing cost at the preliminary design stage. The paper discusses the cost modelling approach, which is based on parametric and process cost model methods, and the integration of the cost models into an MDO process. Results for the cost models are shown. A framework has been successfully developed which allows the incorporation of manufacturing cost models into an MDO environment. It allows a designer to evaluate cost changes with respect to specific design changes such as rib pitch, stringer pitch, wing area and wing sweep.

The design of a real-time engineering flight simulator for the rapid prototyping of avionics systems and flight control systems

Abstract: This paper describes the design of a real-time flight simulator, which is based on a modular architecture of PCs coupled by Ethernet. The simulator is required to provide a rapid prototyping environment to support the design and evaluation of avionics systems and flight control systems. Methods are described to ensure real-time implementation of the equations of motions using a standard PC and the provision of real-time graphics to simulate aircraft displays using SVGA. The paper includes analysis of the performance of the flight modelling methods and the simulation of aircraft displays. The paper concludes that high fidelity flight models and aircraft displays can be implemented using standard PC platforms and Ethernet cards, if attention is given to the design of the simulator architecture. The resultant simulator provides a rapid prototyping environment, standardising on the packet format and low-level packet protocols of Ethernet,

Massively separated flows due to transverse sonic jet in laminar hypersonic stream

Abstract: A numerical simulation of flow interactions due to a transverse sonic jet ejected from a two-dimensional slot into a hypersonic stream is carried out to examine the capability of Navier–Stokes solutions in predicting a massively separated flow upstream of the jet exit. Grid sensitivity has been studied using gradually refined meshes to address the numerical accuracy of the discretised solution of the governing equations. Comparison has been made with published experimental data regarding the separation and reattachment points and the pressure distribution in the separated region. Flow field visualisation provides further insight into the interaction region and reveals a small clockwise vortex immediately ahead of the jet exit, which is found to be responsible for the second peak in the surface pressure distribution.

Remarks on diffusionless combustion

Abstract: Classical studies of the dynamics of compressible media incorporate the possibility of exothermic actions in the field via the use of model combustion waves treated as discontinuous, and hence quasi–steady, phenomena. The latter are familiar under their broad titles of plane detonation waves, which travel at supersonic speeds, and deflagrations, which travel subsonically. Such deflagrations are not like conventional premixed flames insofar as laminar heat conduction and mass diffusion have no part to play in them; it is convenient to categorize these combustion waves as diffusionless. With the inclusion of adiabatic shock waves and contact discontinuities, a whole range of formally unsteady phenomena can be analysed with the aid of these discontinuous combustion–wave models. Such skeletal theoretical ideas can be instructive, but they do suffer from a serious difficulty since they do not relate speeds of propagation of the combustion waves to the local environments that they inhabit, and it is necessary to call on empirical evidence to close the theory. The present paper shows that these difficulties can be overcome by adopting an asymptotic parameter–perturbation approach to the construction of a self–contained rational theory of diffusionless combustion. It is demonstrated that asymptotic ideas are intrinsic to the classical studies of gas dynamics. Then logical pursuit of asymptotic thinking helps to consolidate the theory into a complete and consistent form, banishes the need for empiricism and sheds light on the physics of compressible reacting flows. The latter is exemplified here with an examination of the ephemeral character of weak detonations and their role in the birth of strong detonation waves.

Drinking and flying : A structural model

Abstract: BACKGROUND: Under a recent revision of the European Joint Aviation Authorities operations regulations it has been prohibited to act as a crew member of an aircraft with a BAC of greater than 0.02%. METHODS: This survey of UK Civil Aviation Authority pilots suggests that over 50% of respondents may have flown an aircraft with a BAC of greater than this prescribed amount. RESULTS: Professional pilots were found to be heavier drinkers than private pilots and were also more likely to infringe the 0.02% BAC rule. CONCLUSION: Analysis of the data using path analysis suggests that professional pilots may be more prone to offending as a result of training in a "drinking culture" and as a response to commercial pressures in the industry. Language: en

Unsteady flow around helicopter rotor blade sections in forward flight

Abstract: The aerodynamic performance of aerofoils performing unsteady motions is important for the design of helicopter rotors. In this respect the study of aerofoils undergoing in-plane oscillations (translation along the horizontal axis) provides useful insight into the flow physics associated with the advancing blade in forward flight. In this paper a numerical method is developed in which the unsteady thin layer Navier-Stokes equations are solved for aerofoils performing rigid body motions. The method has been applied to the calculation of the flowfield around a NACA 0012 aerofoil performing in-plane motions representative of high-speed forward flight. Comparison of computed pressure data with experimental measurements is generally found to be good. The quantitative differences observed between computations and experiment are thought to have arisen mainly as a consequence of the low aspect ratio of the model rotor employed in the windtunnel tests.

Aspects of solid propellant combustion

Abstract: Internal ballistics describes the combustion of solid propellant within a closed combustion chamber. This is achieved by modelling a mixture of incompressible solid particles and compressible reactive gases with averaged equations of two–phase flow. The combustion of the solid is described with interaction terms that define the rate of mass, momentum and energy exchange from solid into gas. This work concentrates on modelling ignition and the initial stages of combustion, proposing the concept of ‘gaseous ignition’ by including time–scales of chemical reaction in the gas–phase. These non–equilibrium effects are placed firmly within the context of internal ballistics by making direct comparisons between experimental pressure–time histories. In particular, excellent agreement can be achieved between numerical simulations and experimental work by assuming a two–stage reaction process during which the rate of chemical energy release will significantly differ from a single exothermic reaction.

On the design of command and stability augmentation systems for advanced technology aeroplanes

Abstract: There exists an enormous wealth of published material describing the application of so called, 'modern control methods' to the design of fliglat control systems for piloted aeroplanes. It is also evident, with the exception of a very small number of recent applications, that there is a conspicuous lack of enthusiasm on the part of the airframe manufacturers to adopt this design technology, especially for the design of command and stability augmentation systems for piloted aeroplanes. It is possible to speculate on the reasons for this apparent lack of interest, but to do so might well result in a misplaced condemnation of modern control methods. Since evidence exists to suggest that some modern control system design strategies have overlooked important flight dynamics considerations, the discussion is turned around here by drawing attention to some of the more important considerations in command and stability augmentation system design. The object is, therefore, to inform the designer, of whatever persuas...

Experimental evaluation of multivariable rotor control schemes

Abstract: The performance and robustness of a classical multivariable controller and one H∞ compensator are assessed on a model rotor rig. Both control schemes are subjected to sinusoidal and step input tests in the pitch and roll axes under a range of operating conditions and configurations. A brief description of the characteristics of the rotor mathematical model is provided, followed by a summary of the design assessment criteria. Following a description of the two control law design techniques, the performance of each controller is verified on the mathematical model prior to evaluation on the rotor rig. In absolute terms, there is a poor correlation between the simulated and experimental values of the design assessment criteria for both controllers. However, in relative terms, the H∞ control law achieves higher levels of damping and lower cross-couplings than the classical scheme although the measured improvements are not as substantial as predicted. In experimental frequency response tests at increasing advance ratios and various rotorspeeds, the H∞ scheme again consistently achieves the lowest levels of cross-coupling. In summary, the results show that although there are practical performance and robustness benefits to be gained by employing more complex control algorithms, model uncertainty will substantially reduce the predicted benefits.

Operating in the north atlantic mnps airspace.

Abstract: This paper considers the issue of operating aircraft through the North Atlantic's Minimum Navigation Performance Specification (MNPS) airspace. Noting that aircraft constantly strive for reduced fuel burn and uplift, it describes how flight operators and pilots conduct safe, efficient flights through the region. Reference is made to mechanisms of the North Atlantic MNPS airspace in terms of its Organized Track Structure and other routes that exist. These different structures emphasize the level of flexibility available. Flight planning procedures and requirements necessary to obtain oceanic Air Traffic Control (ATC) clearances are mentioned, as is an account of how communication and position reporting procedures operate to apply the Mach Number technique. Other aspects of MNPS operations such as ETOPS operational restrictions, meteorological effects, the employment of Reduced Vertical Separation Minima and planned regional changes aim to provide an overview of the MNPS system's current and future air traffic management.

Cone cavity flow at M = 8.2 with injection of air and helium

Abstract: An experimental investigation of cone cavity flow at M = 8.2 with injection of air and helium has been performed in the Cranfield University gun tunnel. The cone used had a 10° semi-angle and incorporated an annular cavity. The boundary layer ahead of the cavity was laminar. The study concentrated on the effects of increasing the mass injected into the cavity. With no injection the external flow bridged the cavity. A shock wave and a pressure peak occurred at the rear face corner. By injecting gas, this pressure peak was decreased in intensity and a shock wave was formed at the front face corner. As the mass injected was increased, the shocks initially formed at the front and rear face corners were shifted upstream from their initial positions and boundary layer separation occurred ahead of the cavity. For the highest mass flow rate injected, the pressure peak at the rear face corner was very small. The cavity flow was never more than mildly unsteady