Showing papers by "Vaughn College of Aeronautics and Technology published in 1998"

A methodology for modelling manufacturing costs at conceptual design

Abstract: This paper describes a method for modelling costs throughout the design phase of a product's life-cycle, from conceptual to detail design. The timely provision of cost data facilitates the quantitative evaluation of designs through a cost function. This approach to design evaluation has the advantages of allowing management to make more accurate bid estimates, encouraging designers to design to cost and reducing the amount of design rework, hence reducing the product's time to market and controlling product cost. The cost modelling strategy adopted incorporates the use of knowledge-based and case-based approaches. Cost estimation is automated by linking design knowledge, required for predicting design features from incomplete design descriptions, to production knowledge. The link between the two knowledge paradigms is achieved through the blackboard framework of problem solving, which incorporates both case-based and rule-based reasoning. The method described is aimed at innovative design activity.

Impact damage in composite aircraft structures-experimental testing and numerical simulation

Abstract: This paper describes a strategy for predicting internal damage in a laminated composite structure, when subjected to low-velocity impact. The aim was to obtain a better understanding of and cure for the notorious reduction in strength of aircraft compression panels when they suffered barely visible impact damage (BVID). A finite element model is presented which incorporates the non-linear behaviour due to gross deformation, interlaminar delamination and in-plane fibre and matrix failure. The strategy is validated by impact tests for a wide range of carbon/epoxy composite structures ranging from small stiff plates to realistic aircraft compression panels. It is demonstrated that the finite element model is capable of predicting impact damage in laminated composite structures and thus could be used as a design tool.

Factors affecting the operational success of strategic airline alliances

Abstract: With increased liberalisation in major air transport markets, the intensity of competition has increased amongst air carriers. Airlines have responded to the competitive pressures in many ways, one of which has been the formation of alliances. These alliances are linkages between the firms at various operational levels. They go beyond the common interlining agreement to encompass certain marketing and cost-reducing features. However, the question is how the success of these alliances can be ensured? While companies' culture compatibility is important and much has been written in that area, this paper focuses on factors that affect operational success of airline alliances. The operational success is measured by the change in the level of partners' inter-hub traffic due to formation of the alliance. This research has developed a methodology which could be used as a management tool to measure alliances' operational success before embarking on such agreements. The analysis of recent major alliances covering 52 inter-hub routes suggests that the main factors ensuring the alliances' operational success are: the partners' network size and their compatibility, the frequency of service between the hubs of the partners, the flight connection time at the hub and the level of competition on their network.

Nonclassical symmetry reductions of the three-dimensional incompressible Navier-Stokes equations

Abstract: The nonclassical reduction method as pioneered by Bluman and Cole ( J. Meth. Mech. 18 1025-42) is used to examine symmetries of the full three-dimensional, unsteady, incompressible Navier-Stokes equations of fluid mechanics. The procedure, when applied to a system of partial differential equations, yields reduced sets of equations with one fewer independent variables. We find eight possibilities for reducing the Navier-Stokes equations in the three spatial and one temporal dimensions to sets of partial differential equations in three independent variables. Some of these reductions are derivable using the Lie-group method of classical symmetries but the remainder are genuinely nonclassical. Further investigations of one of our eight forms shows how it is possible to derive novel exact solutions of the Navier-Stokes equations by the nonclassical method.

The effect of skewing on the vorticity produced by an airjet vortex generator

Abstract: The vorticity production by a single vortex generator jet in a turbulent boundary layer at high speed and zero pressure gradient was studied by analysing surface-flow patterns. The investigation involved a range of jet mass flow rates and skew angles while the freestream Mach number and jet pitch angle were held constant. A qualitative analysis of the skin friction patterns demonstrated the effective role of the skew angle as a bifurcation parameter. The vortex production is classified into three main regimes as the skew angle increases from zero (fully downstream) to 180° (fully upstream). Better understanding of the physical mechanism behind the transition from the first regime to the second is crucial in the design of the airjet vortex generator.

Electronically tunable microstrip patch antennas

Abstract: This paper presents the performance of a varactor loaded, probe-fed microstrip patch antenna An effective impedance bandwidth of 50% is achieved centred around a frequency of 220 GHz The simple transmission line model is used to predict the resonant frequency, and practical results obtained showed a good agreement between the predicted and measured values

Non-linear Flight Dynamics at High Angles of Attack

Abstract: The methods of non-linear dynamics are applied to the longitudinal motion of a vectored thrust aircraft, in particular the behaviour at high angles-of-attack. The model contains analytic non-linear aerodynamic coefficients based on Nasa windtunnel tests on the F-18 high alpha research vehicle (Harv). The equilibrium surfaces are plotted against thrust magnitude and thrust deflection and are used to explain the behaviour. When the aircraft is forced with small thrust deflections whilst in poststall equilibrium, chaotic motion is observed at certain frequencies. At other frequencies, several limiting states coexist, e.g. a chaotic attractor and a limit cycle, or two limit cycles. The steady state behaviour then depends on the initial conditions

Surface suction on aerofoil aerodynamic characteristics at transonic speeds

Abstract: This paper presents a numerical study of the effects of an active flow control through surface suction on shock boundary layer interactions over transonic aerofoils. Two different aerofoils were studied. Firstly, for the purpose of validation, an NACA64A010 aerofoil with a trailing edge flap was investigated and the numerical results were compared with experimental data with and without suction for surface pressure distributions and lift and drag coefficients. Grid sensitivity has also been studied regarding the numerical accuracy. The second geometry was an RAE9647 aerofoil, which was designed for superior aerodynamic performance when applied to a helicopter rotor blade. An active surface was used to prevent or alleviate shock-induced separation. The suction strength and location were varied to determine the effect on aerodynamic performance and to provide an effective means of suppressing undesirable flow features. In both cases, increases in both lift and drag were observed when surface suction was app...

The Minimization of Combat Aircraft Life Cycle Costs Through Conceptual Design Optimization

Abstract: In an effort to permit the procurement of more costeffective military equipment, a method has been developed to perform conceptual studies on combat aircraft, resulting in designs optimized for minimum Life Cycle Cost (LCC). Consequently, the design loop can be considered as being closed, allowing the automated production of a consistent set of cost and performance data for different aircraft solutions. The design engineer can thus make informed, unbiased, design decisions, leading to a more efficient use of shrinking defense budgets. The models and the optimization tool are described, and results of their implementation are presented.

Computational Prediction of Pitch Damping for Supersonic Blunt Cones

Abstract: Conclusions Observations clearly demonstrate thatthe PSIhas had the desired effect on the TIDEmeasurements: Low-energy ions that would otherwise be unobservable are seen. Equally clear is that the PSI modie es the sheath structure around the POLAR spacecraft in ways that also affect measurements made by other instruments, such as the PWI and the EFI. This implies that it will also have quantitative consequencesfortheTIDEobservations.TheEFIobservationssuggest that the TIDE core ion measurements will not be signie cantly affected unless ion energies are much less than 5 eV. Core electrons are more affected by the PSI sheath, and at lower oute ow speeds the ions will also be ine uenced, requiring a better understanding of the sheath. A physical model has been presented that explains qualitatively the origin of the anisotropy found in observations with the PSI operating. This model can be used to guide the development of a detailed and accurate numerical model, which in turn can be used to develop modie cations to the analysis to compensate for the PSI effects. The best understanding of the PSI sheath will come from synoptic operations of the PSI and dedicated analysis of the complete POLAR plasma data set.