A semiempirical method is described that was applied to predict the preflight drag of the A310 and the A300-600 for takeoff, one-engine conditions. The first part of the present paper is concerned with wind-tunnel models and tests basically designed to obtain aerodynamic performances at low speeds, i.e., drag and maximum lift. In addition, special measurements with turbine-powered simulators (TPS) are described which were performed to investigate the effect of installed engines on second-segment climb drag. The correction of tunnel results to full-scale aircraft data is the subject of the next part. A simple scaling rule is shown covering the effect of Reynolds number on lift, pitching moment, and drag. The quality of this rule is demonstrated by a comparison of scaled results with corresponding model data obtained in a pressurized wind tunnel. The third part of the paper compares flight test results with corresponding; predictions for several takeoff configurations. It is demonstrated that with the model/test philosophy and the scaling method described, the predictions agree with the flight test data within a range of ±1% of overall drag.