Preliminary Assessment of Morphing Winglet and Flap Tabs Influence on the Aeroelastic Stability of Next Generation Regional Aircraft

Abstract

Future aircraft wing technology is rapidly moving toward flexible and morphing wing concepts capable to enhance aircraft wing performance in off-design conditions and to reduce operative maneuver and gust loads. However, due to the reduced stiffness, increased mass, and increased degree of freedom (DOF), such mechanical systems require advanced aeroelastic assessments since the early design phases; this appears crucial to properly drive the design of the underlying mechanisms since the conceptual phase by mitigating their impact on the whole aircraft aeroelastic stability. Preliminary investigations have shown that the combined use of adaptive flap tabs and morphing winglets significantly improves aircraft aerodynamic performance in climb and cruise conditions by the order of 6%. Additionally, by adapting span-wise lift distributions to reduce gust solicitations and alleviate wing root bending moment at critical flight conditions, significant weight savings can also be achieved. Within the scope of Clean Sky 2 Airgreen 2 project, flutter and divergence characteristics of a morphing wing design integrating adaptive winglets and flap tabs are discussed. Multi-parametric flutter analyses are carried out in compliance with CS-25 airworthiness requirements (paragraph 25.629, parts (a), (b), (c) and (d)) to investigate static and dynamic aeroelastic stability behavior of the aircraft. The proposed kinematic systems are characterized by movable surfaces, each with its own domain authority, sustained by a structural skeleton and completely integrated with EMA-based actuation systems. For that purpose, a sensitivity analysis was performed taking into account variations of the stiffness and inertial properties of the referred architectures. Such layouts were reduced to a stick-equivalent model which properties were evaluated through MSC-NASTRAN-based computations. The proprietary code SANDY 4.0 was used to generate the aero-structural model and to solve the aeroelastic stability equations by means of theoretical modes association in frequency domain. Analyses showed the presence of critical modal coupling mechanisms in nominal operative conditions as well as in case of system malfunctioning or failure. Design solutions to assure clearance from instabilities were then investigated. Trade-off flutter and divergence analyses were finally carried out to assess the robustness of the morphing architectures in terms of movable parts layout, mass balancing and actuators damping.

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

“…Within the framework of the Clean Sky 2 REG IADP, the design of a fault-tolerant adaptive winglet concept was addressed to enhance the wing’s aerodynamic performance in off-design conditions and reduce maneuver loads of a turboprop regional aircraft. The integrated design of the adaptive winglet is detailed in [ 32 , 33 , 34 ]. The adaptive winglet incorporates two “finger-like” mechanisms, shown in Figure 5 , allowing shape adaptation of two movable surfaces (upper and lower tabs), each controlled by an independent electromechanical chain, and embedded into its main body [ 27 , 35 , 36 ].…”

Recent developments in the aeroelasticity of morphing aircraft

“…The MLA controller reduced the structural loads even though it resulted in a reduction in the ailerons' roll effectiveness. Noviello et al [101] investigated the influence of the combined use of morphing winglets and adaptive flap tabs on the aeroelastic stability of a regional aircraft. The combined use of morphing winglets and adaptive flap tabs improved the aerodynamic performance in climb and cruise conditions by 6%.…”

“…Another reason is that most of the morphing concepts studied in literature are at the proof of concept stage and an aeroelastic model of the full aircraft is not vital at such a low maturity stage. Examples of studies that considered the full aircraft include the work done by Castrichini et al [105][106][107], Fonte et al [100], and Noviello et al [101].…”

Aeroelastic Assessments and Functional Hazard Analysis of a Regional Aircraft Equipped with Morphing Winglets

“…This means that any loss of the system function could potentially result in "catastrophic" events for the aircraft. Flutter is surely the most important risk and requires dedicated assessments since the preliminary design stages [21]. As a result, its probability of occurrence must be proved below the threshold value of <10 −9 per flight hour.…”

“…For the purpose of performing quick trade-off analyses on the whole aircraft equipped with the adaptive winglets, the structural model of the reference aircraft, already presented in [21], was combined with a stick-beam model of the adaptive winglet. Starting from a complete finite element model of the winglet, shown in Figure 11, the equivalent stick-beam model was generated by firstly computing the position of the elastic axis and then by assuming a reasonable stiffness distribution along the winglet span.…”