Session: 01-02-03: Adaptive and Multifunctional Structures

Paper Number: 121566

121566 - Adaptive-Stiffness Characteristics of Pneumatic Rotary Actuators for Folding Wingtips 

High aspect ratio wings improve the aircraft's efficiency by reducing its induced drag. However, increased span is accompanied by increased wing root bending moment, reduced aircraft maneuverability, and violations of airport conformity. A recent trend is to face the challenges of high aspect ratio wings by using folding wingtip devices. The Boeing 777X, first flown in 2020, can fold its wingtips upward on ground to comply with the airport's space limitations. Beyond that, Airbus is investigating a free-flapping wingtip device that can be unlocked in flight to enable passive load alleviation. The capabilities of free-flapping wingtips have been demonstrated by Airbus in flight tests in 2019 and 2020 on the AlbatrossOne and will be further investigated on a larger scale with the extra high performance wing demonstrator. Further improvement in the aircraft's efficiency and performance would be possible with a multifunctional wingtip actuator that allows for active adjustment of the wingtip's cant angle and hinge stiffness. Such an actively actuated wingtip hinge featuring adaptive stiffness enables additional functionalities such as advanced flight control, mission adaptability, and enhanced load alleviation.

While previous research of the authors investigated a pressure-actuated morphing structure consisting of several pressurized polygonal cells to enable adaptive stiffness and active deflection, this paper presents a more simplified actuator design. This simplified design of actuated adaptive wingtips is based on a commercially available pneumatic rotary actuator with two antagonistic pneumatic cylinders connected by a gearwheel. The authors identify the operating envelope of the pneumatic actuator by applying a set of input pressures and actuator moments on a custom-made pneumatic test stand. The stiffness characteristics of the wingtip hinge can be obtained from the actuator's working graph using a regression model.

The experimental characterization proves the adaptive-stiffness properties required for multifunctional wingtip actuators for use on highly efficient high aspect ratio aircraft. By implementing a closed-loop control, the wingtip stiffness can be set independently of the actuator's deflection or moment. A wingtip device with such characteristics allows switching between a relatively stiff cruise configuration and an almost free-flapping load alleviation configuration without affecting the wing shape. In addition, the combination of actuator moment and actuator stiffness eliminates the need for a wingtip locking mechanism, as passive load alleviation is always provided due to the nature of the wingtip device. Therefore, there is no need for gust detection when operating the actuator in passive mode. Besides the passive load alleviation mode, active adjustment of the actuator stiffness to the flight mission and weather conditions transforms the folding wingtips into multifunctional actuated adaptive wingtips. The next step is to scale up the presented actuator device to achieve the load-bearing capacity required for implementation on an aircraft like a Cessna Citation, which is the basis of Airbus' extra high performance wing demonstrator.

Presenting Author: Patrick Meyer Technische Universität Braunschweig

Presenting Author Biography: Patrick Meyer is a research associate and doctoral student at the Institute of Mechanics and Adaptronics at the Technische Universität Braunschweig in Germany. His research focuses on shape morphing aircraft structures and on the design of compliant mechanisms. His current research interest is on folding wingtips. During his studies, he worked as an intern and working student at the German Aerospace Center on the design of natural laminar flow wings, at Airbus Operations GmbH in the single-aisle structural assembly department, and at Volkswagen AG on the development of new vehicle concepts. He completed his master's degree in aerospace engineering at the Technical University of Braunschweig in 2017 with distinction.