Flight Mechanics Modeling of the PrandtlPlane for Conceptual and Preliminary Design

The conceptual and preliminary design of a 300-passenger box-wing aircraft configuration, designated the PrandtlPlane, is investigated. Currently there are still a number of technical issues which must be investigated thoroughly to demonstrate the feasibility of this configuration. This research study is focused on two aspects of the PrandtlPlane design, (1) the propulsion system and (2) the flight control system. A nonlinear aircraft model is created with an in-house developed flight mechanics toolbox, which is designed for its application in the conceptual and preliminary design phase. The resulting propulsion system design has two conventional turbofan engines at the tail of the aircraft. For a large version of the PrandtlPlane, it might be beneficial to consider large open-rotor systems underneath the rear wing. The volume of the wing system, which is smaller than that of conventional aircraft, poses constraints on the fuel system design. Flight control of the PrandtlPlane is quite different from the control of conventional aircraft. If control surfaces are placed on the front and rear wings, then a pure moment can be created by differential deflection of these controls. Furthermore, a combined deflection of the front and rear wing control surfaces allows the use of direct lift control. The aircraft exhibits good inherent handling qualities in the longitudinal axis. The Dutch roll mode is slightly unstable. Improvements are expected if the vertical tails of the aircraft are redesigned. Finally, a model-based inversion flight control law is presented which provides a rate command response type in all axes. An additional outer control loop is designed which provides direct lift control. The control law is tested on the nonlinear aircraft model and demonstrates the potential of the PrandtlPlane control characteristics.