Preliminary Aerostructural Optimization of a Large Business Jet

Abstract

An overview of an industrial approach to the aerostructural optimization of a large business jet is presented herein. The optimization methodology is based on the integration of aerodynamic and structural analysis codes that combine computational, analytical, and semi-empirical methods, validated in an aircraft design environment. The aerodynamics subspace is analyzed with a three-dimensional transonic small disturbance code capable of predicting the drag of a complete, trimmed aircraft within engineering accuracy. The design of the wing structure is accomplished using a quasi-analytical method that defines the layout of the ribs and geometry of the spar webs, spar caps, and skin-stringer panels, and predicts the wing flexural properties and weight distribution. In addition, the prediction of operating economics as well as the integrated en route performance is coupled into the scheme by way of fractional change functional transformations. To illustrate the automated design system capabilities, the methodology is applied to the optimization of a large business jet comprising winglets, rear-mounted engines, and a T-tail configuration. The aircraft-level design optimization goal in this instance is to minimize a cost function for a fixed range mission assuming a constant maximum takeoff weight.Nomenclature A sk = cross-sectional area of skin, in: 2 A st = cross-sectional area of stiffener, in: 2 AR = aspect ratio C crew = hourly cost of the flight (and cabin) crew, CU=h C D = total drag coefficient C fees = landing fee charge based on maximum landing weight, CU=lb C fuel = price of fuel, CU=lb C L = operating lift coefficient C mnt = time-dependent airframe and engine maintenance cost, CU=h C mnt cyc = cyclic airframe maintenance cost, CU C mnt eng = cyclic engine maintenance component that is assumed to have a functional dependency with the engine derate level, CU E = relative or absolute error f = function; substitution parameter in modified integrated range model formulation g = acceleration due to gravity, ft=s 2 H = fuel calorific value, Btu=lb k aero = control factor used to regulate the extent of coupling (congruity or otherwise) between high-speed and intermediate-speed aerodynamic efficiency k clb = constant of proportionality required to predict all-up weight at top of climb k M = empirically derived coefficient used to establish a simplified relationship between overall power plant efficiency and Mach number k res = constant of proportionality establishing linear relationship between fractional change in total reserve fuel and fractional change in zero-fuel weight L=D = lift-to-drag ratio M = Mach number R = range, nm t = time, as in block or flight time, h V = forward speed [(knots, calibrated airspeed (KCAS) or knots, indicated airspeed (KIAS)] W= weight of a given component or assembly, all-up weight, lb x, y = arbitrary independent parameters or design variables z = arbitrary dependent parameters or objective functions = exponent, flight profile correction coefficient when useful load varies but payl...

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