External Blowing Flap Technology on the USAF McDonnell Douglas YC-15

The YC-15 will be the first aircraft to employ the externally blown flap (EBF)-powered lift system. Since the success of the aircraft to a large extent is dependent on the proper functioning of this system, considerable effort is going into its design. The present paper discusses some of the fundamental aerodynamic considerations which led to the selection of the specific flap configuration and presents resulting aerodynamic characteristics. Structural design criteria for the system and methods of analysis are covered, as are details of the flap-actuating system and structure.