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Volume 112 - Issue 1138 - December 2008

Contents

Research Article

  • Comparison between blade-element models of propellers

  • O. Gur, A. Rosen
  • Published online by Cambridge University Press:
    03 February 2016, pp. 689-704

  • Blade-element models are the most common models for the analysis of propeller aerodynamics, performance calculations and propeller design. In spite of their simplicity these models are very efficient and accurate. Blade-element models use the local induced velocities as an input thus they should be combined with another model in order to calculate these induced velocities. Various models are used for the calculation of the induced velocity, where the most popular ones include: momentum, simplified-momentum, lifting-line (prescribed and free wake), and vortex (McCormick and Theodorsen) models. The paper describes the various models, compares their results and discusses the advantages and disadvantages of each one. The results indicate that the Bladeelement/simplified-momentum model offers very good accuracy together with high efficiency. For propeller performance calculations during steady axial flight, where most of the cross-sections do not experience stall, detailed and complicated models for calculating the induced velocities do not show advantages over the simple bladeelement/simplified-momentum model,

  • Effect of amplitude and mean angle-of-attack on the boundary layer of an oscillating aerofoil

  • M. R. Soltani, A. Bakhshalipour
  • Published online by Cambridge University Press:
    03 February 2016, pp. 705-713

  • Extensive experiments were conducted to study the effect of various parameters on the surface pressure distribution and transition point of an aerofoil section used in a wind turbine blade. In this paper details of the variation of transition point on the aforementioned aerofoil are presented. The aerofoil spanned the wind-tunnel test section and was oscillated sinusoidally in pitch about the quarter chord. The imposed variables of the experiments were free stream velocity, amplitude of motion, mean angle-of-attack, and oscillation frequency.

    The spatial-temporal progressions of the leading-edge transition point and the state of the unsteady boundary-layer were measured using eight closely-spaced, hot-film sensors (HFS). The measurements show that:

    (i) Reduced frequency has a pronounced effect on the variations of the transition point.

    (ii) There exists a hysteresis loop in the dynamic transition location and its shape varies with the reduced frequency and mean angle-of-attack.

  • Dither-based compensating strategy for radome boresight error and gimbal friction

  • Y.-C. Lin, C.-L. Lin, W.-C. Shi, S.-W. Huang
  • Published online by Cambridge University Press:
    03 February 2016, pp. 715-723

  • This paper proposes an effective missile radome error compensator by incorporating a nondestructive dither on the missile guidance loop to improve tracking accuracy. The compensation strategy predicts the radome slope error by introducing the dithering techniques along with band-pass filtering mechanism. A new condition is derived to ensure the guidance and control system stability while there is in the presence of the compensation error. As an application, the design methodology is extended to deal with the gimbal friction compensation problem. Simulation study confirms efficacy of our proposed approach.

  • Solid propellants burning enhancement using foil embedding method

  • H. G. Darabkhanid, N. S. Mehdizadeh
  • Published online by Cambridge University Press:
    03 February 2016, pp. 725-732

  • The method of metal embedding is widely employed in solid propellant motors with end-burning configuration, thereby significantly improving the burning rate of the propellants. In this study, the cylindrical foil embedding method is applied to double-base solid propellant, as a new method, and the effects of the type and thickness of the foil on the burning surface, as well as the burning rate, are experimentally investigated. It is shown that by using the foil embedding method, the burning characteristics of solid propellants can be improved. Results have been compared to some available data. To the best of the author’s knowledge there are no published data available on this method.

  • Contrail avoidance in the aircraft design process

  • F. Noppel, R. Singh
  • Published online by Cambridge University Press:
    03 February 2016, pp. 733-737

  • As aviation is one of the fastest growing industrial sectors world wide, air-traffic emissions are projected to increase their stake in the contribution to global warming. According to studies, both carbon dioxide and contrails are the principal air-traffic pollutants, whereas the impact from contrails in terms of radiative forcing is possibly larger than that of all other air-traffic pollutants combined. New regulations with the objective of mitigating contrail occurrences might cause a change in the design requirements of aircraft. In light of this, a method considering contrail formation during the aircraft design process is presented in this paper. Aircraft performance and optimisation is carried out with NASA’s flight optimisation system. Combining historical meteorological data with air-traffic data enables an assessment regarding contrail formation. As an example, a particular aircraft type in terms of range, speed and payload is optimised for minimum block fuel consumption considering different altitudes. The change in contrail formation in terms of contrail-km formed is calculated. The results suggest that if aircraft of the considered class were designed for higher altitudes, contrail occurrences would diminish slightly at a non-negligible fuel burn penalty.

Book Reviews

Other

Front matter

  • AER volume 112 issue 1138 Cover and Front matter

  • Published online by Cambridge University Press:
    03 February 2016, pp. f1-f3
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Back matter

  • AER volume 112 issue 1138 Cover and Back matter

  • Published online by Cambridge University Press:
    30 March 2016, pp. b1-b5
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