Presented at the 53rd Annual Forum of the American Helicopter Society, Virginia Beach, VA, April 29 - May 1, 1997.Beyond the Bell/Boeing 609, the next step in civil tiltrotor evolution will most likely be a larger capacity vehicle (~ 40 passenger class) similar to NASA? vision of a Short Haul Civil Tiltrotor (SHCT). This vehicle will be designed, built and operated in an era being shaped by today? increased emphasis on affordability. This paper discusses the authors?views on the subject and outlines the steps taken to develop a new methodology which will allow a true assessment of the affordability of such a SHCT. Affordability will not be defined by cost metrics alone. Instead, it will be based on the concept of value and tradeoffs between cost and mission effectiveness; measured by maintainability, reliability, safety, etc. In addition, the motivation for this shift in design philosophy and the resulting need for knowledge to be brought forward in the proposed methodology is reviewed. Furthermore, this shift in knowledge calls for a paradigm shift in the design evolution process based on the realization that decisions made during the early design phases are not deterministic in nature and should therefore be handled probabilistically. The approach taken acknowledges this need and defines a suitable probabilistic design environment. The fundamental building blocks of this method are also outlined and discussed including key concepts, tools, techniques, and the approach taken to implement this process
