similitude

thumb|right|280px|A full scale NASA X-43|X-43 [[wind tunnel test. The test is designed to have dynamic similitude with the real application to ensure valid results.]]

Similitude is a concept applicable to the testing of engineering models. A model is said to have similitude with the real application if the two share geometric similarity, kinematic similarity and dynamic similarity. Similarity and similitude are interchangeable in this context. The term dynamic similitude is often used as a catch-all because it implies that geometric and kinematic similitude have already been met.