A general discussion covering the basic considerations regarding ultra high bypass (UHB) or turboprop propulsion systems and their installation is given. This is followed by a description of the analytical methods used to analyze isolated propellers and complete installed aircraft configurations. Experience with these methods and verification with ground test data have developed confidence in their use. Future verification of the concepts and methods will occur during a Douglas MD-80 demonstrator flight test program to be conducted in 1987. The design experience and verified analytical methods have been used to conduct a number of detailed commercial and military design studies. The results of these are presented indicating significant gross weight and fuel-burn advantages for UHB-powered aircraft concepts.