The developments in flight simulation since its inception are reviewed and the latest trends in the use of modeling and simulation for design of flying vehicles are presented. Mathematical model based system development is now universally recognized as a cost effective way to bring new design concepts into reality. The efforts made at CSIR-NAL in this regard over the years are also described in brief. The design of systems which require scenario based evaluation like the flight control system and avionics benefit from the use of a reconfigurable simulator developed concurrently with the aircraft. A reconfigurable simulator allows for rapid prototyping of the systems during the design phase in an integrated environment. Ideas for the implementation of Systems Engineering concepts in new and existing aircraft programs using mathematical models are discussed.