Control architecture sizing is a main challenge of blended-wing–body design. This aircraft configuration typically features redundant elevons located at the trailing edge of the wing, acting simultaneously on pitch and roll axes. Consequently, a proper sizing requires one to consider coupled longitudinal and lateral criteria. Moreover, significant hinge moments due to large control surface areas, combined with high deflection rates in order to safely control the longitudinal instability, may result in excessive power consumption and actuator mass penalty. Therefore, it is highly desirable at the preliminary design level to minimize control surface areas, while ensuring adequate closed-loop handling qualities, with limited deflections and deflection rates. The problem of integrated design of control surface sizes and flight control laws for an unstable blended-wing–body aircraft is addressed here. The latest tools for H∞ nonsmooth optimization of structured controllers are used to optimize in a single step the gains for both longitudinal and lateral control laws, as well as a control allocation module, while minimizing the control surface span. The following constraints are ensured: maximal deflection angles and rates for 1) pilot longitudinal pull up, 2) pilot bank angle order, and 3) longitudinal turbulence. Using this coupled approach, significant gains in terms of the outer elevon’s span as compared to the initial layout are demonstrated, whereas closed-loop handling quality constraints are guaranteed.

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Multicontrol Surface Optimization for Blended Wing–Body Under Handling Quality Constraints

The impact of control allocation on trim drag of blended wing body aircraft

Hybrid wing–body configurations are currently an active field of research as potential candidates to meet NASA Environmentally Responsible Aviation N+2 goals. One characteristic of these configurations is the presence of a large number of redundant flight control surfaces. However, the design process and decision rationale for a given control surface layout is rarely discussed in the open literature. This work investigated tradeoffs between drag, control authority, actuator weight, and actuation power requirements as a function of the number and spacing of elevons. The actuators were sized based on hinge moments computed during nominal and failed control flight conditions. These effects were propagated upward to estimate changes to fuel burn, a system-level metric important to the Environmentally Responsible Aviation program, via the Breguet range equation. A model of the NASA N2A-EXTE hybrid wing–body configuration concept was used to demonstrate these tradeoffs. The study concluded that adjacent elevons...

Method for Evaluating Electrically Actuated Hybrid Wing–Body Control Surface Layouts

Hybrid wing–body configurations, such as the N2A-EXTE, have the potential to meet NASA Environmentally Responsible Aviation N+2 goals. These configurations have redundant elevons typically spanning the entire trailing edge of the wing, for which the large areas result in the generation of large hinge moments. To ensure aircraft stability with a reduced static margin, high control surface deflection rates may also be required. The combination of large actuation loads and rates results in significant actuation power requirements, which affect both fuel burn and the sizing of the actuation subsystem. In the early design phases, there is significant uncertainty regarding the magnitude of the actuation power, which may depend on the vehicle’s static margin, the design and designated roles of the redundant control surfaces, actuator design parameters, and the intensity of encountered atmospheric turbulence. The objective of this paper is to present a methodical approach for assessing this uncertainty and relati...

Multidisciplinary Approach to Assessing Actuation Power of a Hybrid Wing–Body

Next generation of civil transport aircraft is likely to be a radical change in overall configuration compared to traditional tube-and-wing design. From a handling qualities perspective, current trend in modern airliners is to evolve towards more and more unstable aircraft, both from longitudinal and lateral-directional point of view. As a consequence future aircraft may not be controllable by human operator without stabilizing control laws. It then becomes necessary to consider flight control systems contribution early in the design phase for control surfaces, empennages and actuators sizing, as opposed to traditional way of working dealing only with open-loop criteria for preliminary sizing. Instead of an iterative process of sizing and control laws synthesis, we propose to concurrently optimize control surfaces, actuators and flight control laws taking into account longitudinal and lateral instability as well as industrial structure for controllers, for unstable configurations such as Blended Wing-Body (BWB). This “co-design” procedure enables sizing of physical aircraft parameters taking into account benefits from feedback stabilization for counteracting external disturbance such as atmospheric turbulence, thus leading to safer and more optimal aircraft configurations.

Andreas Wildschek

Papers

Flight Dynamics and Control Related Challenges for Design of a Commercial Blended Wing Body Aircraft