Structural Design of a Multifunctional Morphing Fowler Flap for a Twin-Prop Regional Aircraft

Abstract

In the framework of Clean Sky 2 Airgreen 2 (REG-IADP) European research project, a novel multifunctional morphing flap technology was investigated to improve the aerodynamic performances of the next Turboprop regional aircraft (90 passengers) along its flight mission. The proposed true-scale device (5 meters span with a mean chord of 0.6 meters) is conceived to replace and enhance conventional Fowler flap with new functionalities. Three different functions were enabled: overall airfoil camber morphing up to +30° (mode 1), +10°/−10° (upwards/downwards) deflections of the flap tip segment (mode 2), flap tip “segmented” twist of ±5° along the outer flap span (mode 3). Morphing mode 1 is supposed to be activated during take-off and landing only to enhance aircraft high-lift performances and steeper initial climb and descent. Thanks to this function, more airfoil shapes are available at each flap setting and therefore a dramatic simplification of the flap deployment system may be implemented. Morphing modes 2 and 3 are enabled in cruise and off-design flight conditions to improve wing aerodynamic efficiency. The novel structural concept of the three-modal morphing Fowler flap (3MMF) was designed according to the challenges posed by real wing installation issues. The proposed concept consists of a multi-box arrangement activated by segmented ribs with embedded inner mechanisms to realize the transition from the baseline configuration to different target aero-shapes while withstanding the aerodynamic loads. Lightweight and compact actuating leverages driven by electromechanical motors were properly synthesized to comply with stringent requirements for real aircraft implementation: minimum actuating torque, minimum number of motors, reduced weight, and available design space. The methodology for the kinematic design of the inner mechanisms is based on a building block approach where the instant center analysis tool is used to preliminary select the locations of the hinges’ leverages. The final geometry of the inner mechanisms is optimized to maximize the mechanical advantage as well as to provide the kinematic performances required by the three different morphing modes. The load-path was evaluated, and the cross-sectional size of leverages was subsequently optimized. Finally, actuating torques predicted by instant center analysis were compared to the calculated values from finite element analysis. The structural sizing process of the multi-box arrangement was carried out considering elementary methods, and results were compared with finite element simulations.

A Preliminary Technology Readiness Assessment of Morphing Technology Applied to Case Studies

“…The adaptive flap was developed within the framework of the CleanSky and CleanSky2 programs, [ 30 ]. The device is characterized by a multi-box arrangement with shape-morphing capabilities enabled by robotic (finger-like) ribs driven by electro-mechanical actuators.…”

“…Starting from the reference aero-loads related to the most severe working conditions expected in service, [ 30 ], the morphing flap device was designed according to an articulated engineering process compliant with CS-25 requirements and industrial standards [ 30 , 31 ]. To properly monitor the process, three revision gates were placed at the end of the conceptual, preliminary, and advanced design phases (critical concept review, preliminary design review, and critical design review).…”

“…To properly monitor the process, three revision gates were placed at the end of the conceptual, preliminary, and advanced design phases (critical concept review, preliminary design review, and critical design review). The goodness of the adopted structural solutions as well as of the actuation and control strategy were successfully proved by means of full-scale static, functionality, and dynamic tests, Figure 4 , [ 30 ]. Relying upon the outcomes of the dynamic tests, a thorough assessment of the flap impacts on aircraft aeroelastic stability was also addressed, showing the absence of any flap-induced flutters also in case of flap malfunctions (jamming) and/or free plays, [ 31 ].…”

Adaptive Structures and Biomimetic Robots – A Perspective

“…Herein the movement is enabled by inner moveable articulations, shown in Figure 4, consisting of rigid blocks that are allowed to rotate in relation to each other to change the wing camber. The optimization process of such a complex device involves parametric kinematic analyses considering leverage components' number, shape, and position as functions of the mechanical advantage to be achieved by the overall mechanism, [12].…”