Tech Briefs

Computer simulations and even ground hardware tests can supplement flight testing.

A program of research has addressed a methodology of scaling of flight tests of unmanned air vehicles (UAVs) intended primarily for military use in observing and/or attacking targets on the ground. The main goal of this research is to make it possible to design a model UAV that is suitable for evaluating the performance of a given real UAV or family of UAVs. This research also demonstrates the use of results of computational simulations and ground hardware experiments on models of vehicles other than UAVs to predict performances of UAVs prior to conducting flight tests.

Two Surrogate Vehicles — one much slower and one much faster than a nominal UAV — were analyzed along with the UAV in a computational simulation to study the possibility and effects of scaling of vehicle dynamics and sensor behavior.
In the development of UAVs, as in many other engineering endeavors, testing of models offers obvious advantages of economy and safety over testing of fullsize systems, provided that, for a given UAV or other system, it is possible to establish the necessary mathematical relationships for scaling of dimensions and other physical quantities. The mathematical basis for scaling in the present methodology is the Buckingham pi theorem, which was introduced by E. Buckingham in 1914 and is a key theorem in dimensional analysis. For a given physical system, the Buckingham pi theorem provides a means of computing groups of dimensionless parameters (usually represented by symbols that include the eponymous Greek letter pi) from the given physical variables, even if the form of the dynamical equation of the system is unknown. For the purpose of the theorem, two systems (e.g., a model and the system being modelled) for which the dimensionless parameters coincide are said to be similar; they are equivalent for the purpose of the equation.