A vortex lattice method application in aerodynamic analysis and design of light aircraft

Abstract

In initial stages of aircraft aerodynamic design, it is common practice to apply fairly simple but reliable computer packages, that enable engineers to perform a large number of test runs in a reasonably short time. This paper is mainly focused on the tests done by such software, based on 3D vortex-lattice method, with an aim to verb its capabilities to give results that properly coincide with the existing airplane's data. For software reliability tests, the popular domestic Utva-75 light aircraft has been selected, for which a wide scope of wind tunnel test results exist. Since the applied computational model is based on inviscid flow concept, effectiveness of the flaps and control surfaces, deflected to angles larger than 5 degrees, are inherently overestimated. In order to compensate for the omitted boundary layer influence and separation effects, a set of calibration options has been properly applied, the non-linear calibration diagrams for their effectiveness and circulation influence have been derived and very good agreements with wind tunnel data have been achieved. The actual aim of defining software calibration functions is to enable efficient prediction and optimization of the large number of aerodynamic characteristics for a new airplane of the same category, during the first stages of its conceptual analysis.