Design, Optimization, Testing, Verification, and Validation of the Wingtip Active Trailing Edge

Abstract

Within the scope of the SARISTU project (smart intelligent aircraft structures), a wingtip active trailing edge (WATE) is developed. Winglets are intended to improve the aircraft's efficiency aerodynamically, but simultaneously they introduce important loads into the main wing structure. These additional loads lead to heavier wing structure and can thus diminish the initial benefit. Preliminary investigations have shown that a wingtip active trailing edge can significantly reduce these loads at critical flight points (active load alleviation). Additionally, it can provide adapted winglet geometry in off-design flight conditions to further improve aerodynamic efficiency. The idea of the active winglet has been successfully treated in several theoretical studies and small-scale experiments. However, there is a big step towards bringing this concept to a real flight application. In this project, a full-scale outer wing and winglet are currently being manufactured and will be tested, both structurally and at low speed in a wind tunnel. The scope for eventual EASA CS25 certification of a civil transport aircraft with such a winglet control device will then be assessed. In particular, a 219 load alleviation system requires a minimum operational reliability to take effect on the applicable flight load envelope for structural design. Therefore, the potential failure modes are assessed, and a fault tree analysis is performed to draw key requirements for the system architecture design. In order to assess the overall system benefit, manufacturing, operation, and maintenance requirements are taken into account. The confined space inside the winglet loft-line presents a significant challenge for integration of an active control system. It is shown how small changes to the aerodynamic surface have both reduced the aerodynamic hinge moments (leading to lighter actuators) and created additional internal space for systems, whilst maintaining an equivalent overall drag level. The potential for reducing wing and winglet loads with a winglet control device is assessed. The kinematic design challenge of delivering the necessary power in a confined space is described. Actuation is accomplished by a single electromechanical actuator which is housed inside the CFRP winglet. Nomenclature ACE Actuator control electronics AS Assumption CAD Computer-aided design CFRP Carbon fibre reinforced polymer CG Centre of gravity CMM Coordinate measurement machine CNC Computerized numerical control DAL Development assurance level DAQ Data acquisition EMA Electromechanical actuator FC Failure condition FEA Finite element analysis FEM Finite element model FHA Failure hazard assessment FTA Fault tree analysis GLAS Gust load alleviation system GST Ground static testing GVT Ground vibration testing IS Integration scenario LCM Liquid composite moulding L/D Lift to drag (ratio) MARI Membrane-assisted resin infusion MCU Motor control unit MIF Multivariate mode indicator NDI Non-destructive inspection OOA Out of autoclave P Probability of occurrence of failure PSSA Preliminary system safety analysis 220 A. Wildschek et al.