Abstract:

ESDU 93032 illustrates the application to a real situation of the ESDU data on drag due to cavities, grooves, steps, ridges and control gaps, and the drag magnification factor applied to them to account for the effects of a non-uniform pressure distribution. An aileron, a leading-edge slat, a spoiler, a trailing-edge flap, a typical fuel tank access door and a main undercarriage unit door are considered. For each component the necessary information is provided: graphs of flow data (Mach number, velocity, temperature and density) and a detailed sketch showing all dimensions and sealing arrangement. Two cases are treated for each component: an ideal state with airtight seals and no avoidable surface mismatches, and a situation with poor sealing or surface mismatches. The comparison between results for the two cases illustrates the penalties from poor sealing or fits, and the possible effects of in-service deterioration. Detailed calculations are given for one feature of each excrescence, and the complete drag calculation is summarised in tabular form. The major contributions to the drag of each component are discussed and methods of reducing them are considered. The results from all the examples are finally reviewed to indicate the basic principles in design for low excrescence drag, and, to show their relative importance, the contribution of each component is expressed as a fraction of a plausible total excrescence drag for the wing.