Parametric design studies for propulsive fuselage aircraft concepts

Abstract

Breaking with the classical separation of airframe and power plant system, new synergy effects may be rooted in close design coupling and the approach of distributing the production of thrust along the main components of the airframe. Beside greater configurational flexibility, airframe structural relief, improved noise shielding, and, the potential for control power augmentation, distributed propulsion is particularly interesting due to the reduced propulsive power demands expected from the notion of aircraft wake filling. In previous work, the concept of a propulsor encircling the aft fuselage with intent to entrain the fuselage boundary layer was identified to be one of the most promising concepts for aircraft wake filling. In this paper, the analytical basis for the quantification of efficiency benefits connected to the propulsive fuselage concept is discussed. Appropriate control volume and consistent efficiency chain definitions are introduced. A simplified boundary layer model is derived from axisymmetric fuselage CFD simulation and used to determine the momentum deficit ingested by the fuselage propulsor. Based on a novel figure of merit for vehicular efficiency, the energy-specific air range, ESAR, the dependency of aircraft cruise efficiency on basic propulsion system and aircraft design changes is parametrically investigated. Specifically, the sensitivities of vehicular efficiency w.r.t. wing aspect ratio and flow transition characteristics, propulsor size, and aircraft design cruise Mach number are studied.