Quasi-analytical Modelling and Optimisation Techniques for Transport Aircraft Design

Abstract: The research work presented here focuses on the subject oftransport aircraft design at the pre-design or conceptuallevel. The primary topics addressed are: (1) generation of avast array of new quasi-analytical expressions to permit aconceptual treatment of commercial and business transportaircraft with adequate sensitivity for more advanced tradestudies; (2) review and adoption of a method to predictstability and control characteristics (using the Mitchellmethod); (3) a study of the relative merits between variousmethods in facilitating an expedient and robust constrainedmulti-objective optimisation result within the context oftraditional conceptual design problems (Genetic Algorithms andNelder-Mead Simplex search); (4) creation of a software packageas a new and unique conceptual tool that permits the generationof design proposals in an accurate yet expeditious manner; and,(5) practical demonstration of the new conceptual designsoftware package by undertaking some actual aircraft designproposals.The design problem is addressed using mostly closed formsolutions but transcendental expressions with much simplifiednumerical scheme algorithms have also been adopted for sake ofaccuracy. Various new models have been proposed for atmosphericproperties, geometry, gas-turbine engine performance, low-speedand high-speed aerodynamic characteristics, minimum controlspeed limited balanced field estimation, asymmetric flight,and, en route performance characteristics including definitionof operationally permissible speed schedules and flighttechniques for payload-range/fixed sector profiles optimised interms of maximum specific air range, minimum fuel, minimumtime, minimum direct operating cost and maximum profit/returnon investment. The work was extended further to include issuesrelating to the impact of vehicular attributes to pricing themarket is willing toabsorb. Useful information regarding howthese individual computational elements of the methodology maybe integrated for the purpose of constructing coherent modularsub-spaces and formulation of a basic inter-disciplinarycoupling is also presented. The mathematical foundationsderived in this work have lead to an array of tangibleconclusions that aid the conceptual designer via implicitguidelines to achieve truly balanced design concepts.In an explicit demonstration of methodology effectivenessand relative simplicity, a software package called QCARD orQuick Conceptual Aircraft Research and Development was createdin the MATLAB environment. The new software system wasdeveloped to assist the designer in predicting, visualising andoptimising conceptual aircraft designs in a much moreinteractive and far-reaching manner than what is afforded withcontemporary applications whilst emphasising speed and economyof effort.The methodology and software was employed for a 19 passengerturbofan commuter transport design using the cost effectiveWilliams International FJ44-2 engines. To complement this, afuselage stretch version of the baseline vehicle designed toaccommodate 31-34 passengers was also undertaken utilising agrowth version of the original FJ44 power plant. The minimumgoal for both of these concepts was to afford unparalleledcomfort through speed and spaciousness with a competitive edgeagainst turboprops in terms of economics and field performance.The final design effort involved proposal of a Trans-Atlantichigh-performance executive transport employing anunconventional Twin Oblique Lifting Surfaces, or, TOLSconfiguration. The intent here was to produce a new super-largebusiness jet able to operate up to low supersonic speeds withfield performance, en route fuel burn efficiency and costcomparable to that of contemporary business aircraft for thismarket segment.Keywords: aircraft, conceptual, design, specifications,atmosphere, geometry, weight, aerodyanmics, propulsion,operational performance, stability and control, constrainedmulti-objective optimisation, computer aided design, regional,business, high-transonic, low-supersonic.