908. An Aerodynamic Model Applicable to the Synthesis of Conventional Fixed Wing Aircraft

Paper

Abstract

In the preliminary design stage of modern day aircraft the ability to determine the tradeoffs in large matrix of design or system variables, from the standpoint of mission , gross weight , or cost effectiveness , is mandatory. An effective tool used at the Lockheed-California Company to affect such tradeoffs is the ASSET (Advanced Systems Synthesis and Evaluation Technique) computer program.
This ASSET computer program is comprised of many computer models or subroutines such as configuration generation, weights, aerodynamics, propulsion, and cost. Following input of the desired configuration variables, these subroutines combine together to perform and cost the matrix of desired aircraft.
The aerodynamics model of ASSET defines the component lift and drag of each configuration variable and sums these components into the total flaps up airplane lift and drag. The sources of drag considered by the model include friction, profile, compressibility, wave induced protuberance and drag of external stores. The model uses configuration data defining aircraft component size and shape and prediction techniques to generate the matrix of parametric aerodynamic data as, a function of Mach number, altitude and lift coefficient. The steps required to produce the parametric drag data include:
(1) generating component friction drag buildups for a Mach number-altitude matrix;
(2) determining the zero – lift transonic drag rise and supersonic wave drag for the wing;
(3) generating component zero – lift pressure drag buildups for a range of Mach numbers;
(4) determining the parabolic induced drag factor over the speed regime;
(5) computing induced drag increments due to drag divergence for a matrix of lift coefficients and transonic Mach numbers.
Experience gained through design application demonstrates that the model is flexible enough to accommodate a wide variety of fixed-wing aircraft configurations. The drag data provided by the model are applicable in the subsonic through supersonic flight regime for the moderate lift coefficients usually encountered over the mission profile and the accuracy is consistent with the requirements of the conceptual design phase.