Jtam-A4.dvi JOURNAL OF THEORETICAL AND APPLIED MECHANICS 55, 1, pp. 307-316, Warsaw 2017 DOI: 10.15632/jtam-pl.55.1.307 PRELIMINARY DESIGN OF AN ADAPTIVE AILERON FOR THE NEXT GENERATION REGIONAL AIRCRAFT Gianluca Amendola, Ignazio Dimino, Antonio Concilio Centro Italiano Ricerche Aerospaziali, Department of Smart Structures, Capua, Caserta, Italy e-mail: g.amendola@cira.it; i.dimino@cira.it; a.concilio@cira.it Francesco Amoroso, Rosario Pecora University of Naples “Federico II”, Department of Industrial Engineering, Aerospace Division, Naples, Italy e-mail: f.amoroso@unina.it; rosario.pecora@unina.it Design ofmorphing wings at increasing TRL is common to several research programsworl- dwide. They are focused on the improvement of their performance that can be expressed in several ways, indeed: aerodynamic efficiency optimization, fuel consumption reduction, COx and NOx emission reduction and so on, or targeted to overcome the classical draw- backs related to the introduction of a novel technology such as system complexity increase and management of certification aspects. The Consortium for Research and Innovation in Aerospace in Quebec (CRIAQ) lunched projectMD0505 that can be inserted in this crow- ded frame. The target of this cooperation, involving Canadian and Italian academies and a research centre, is the development of a camber “morphing aileron” integrated on an in- novative full scale wing tip of the next generation regional aircraft. This paper focuses on the preliminary design and the numericalmodeling of its architecture.The structural layout is, at the beginning, described in detail and furthermore, a finite element (FE) model of the entire aileron architecture is assessed and used to verify the structural integrity under prescribed operational conditions. Keywords: morphing, actuation system, adaptive wing 1. Introduction Commercial aircraft wings are typically designed for cruise operations. However, different flight phases are encountered during a standard mission; efficiency is therefore seldom optimal (Bar- barino et al., 2011). The realization of lifting surfaces able to “adapt” themselves to variable operative conditions and, therefore, to match the necessity of modifying the reference configu- ration, may improve the current performance levels. A main feature that can be associated to a morphing structure is then for instance its potentiality to optimize the aircraftL/D ratio all over the flight envelope. Several Europeanprojects, such asClean Sky (2008) and Saristu (2012- -2015) were launched in recent years to develop and assess new technologies devoted to add the structural systems with new adaptation capabilities through the use of innovative, integrated devices, demonstrating their real applicability and benefits. Aiming at those same targets, the CRIAQProject was launched, with a specific focus on the wing trailing edge, specifically in the aileron region, (CRIAQ MDO-505, 2012). In fact, many studies (Monner et al., 1999; Bolonkin andGilyard, 1999), demonstrated the particular effectiveness of morphing trailing edge devices located in that area.Moreover, the aileron region constitute a very delicate wing zone for several reasons. Mainly, the aileron constitutes a primary safety critical control surface whose failure is catastrophic for the entire aircraft and in addition, it must be demonstrated that no aeroelastic instability (flutter) occurs during operations. Also the reduced available space constitutes an 308 G. Amendola et al. important aspect which makes the morphing aileron design challenging, because it results are difficult to integrate actuators and kinematic leverage. The present paper describes the design phase of a morphing aileron prototype, ready for installation and tests in a wind tunnel. The adaptive aileron device is integrated with another complementary morphing wing system, de- scribed by Kammegne et al. (2016). The present aileron is otherwise not aimed at substituting the conventional architecture but adds new functionalities to the classical design. In fact, the aileron can still rotate rigidly around its main hinge axis while it can morph (by modifying its camber).When it is not actuated, the aileronworks in the usualmanner, preserving the aircraft roll control and stability (the morphing part behaves as a rigid component). In the presented application, the system works in cruise to compensate aircraft weight variations following fuel consumption. During classical manoeuver, the aileron works classically. The morphing techno- logy can be applied also to give a better solution to the active load control on aircraft with new approaches such as active flow control (Stalewski and Sznajder, 2014), which change the flow conditions on the wing surface and, in turn, the aerodynamic loads. In the current paper, it is described how themodification of wing load distribution could be tailored to achieve wing-root bending moment alleviation as a sudden increase of aerodynamic loads occurs (gust or rapid manoeuvers). Themorphing aileron ismade of three-segmented ribs assembled into a finger-like architecture (Pecora et al., 2014), connected through longitudinal spars to guarantee a suitable torsional rigidity. The actuation system is completely integrated within the structural body. It includes distributed actuators the number of which is fixed according to their load-bearing capability, their force generation possibility, the allowable space and the stiffness requirements. In fact, the complete system must be able to deform while withstanding the external aerody- namic loads. These two requirements may be overcome by the use of load-bearing actuators. The kinematics allow a single degree of freedom per rib that is blocked by the actuator devi- ce. It has then the role to absorb the external load and move the system against that load. A mechanical chain converts the actuator torque into a controlled linear displacement in order to amplify the transferred force vs. a limited motion penalty. Linear motion guides are made of two main components: a stainless steel rail and a sliding element directly connected to the leverage, in turn linked to the actuator rotating shaft by means of a fork-shaped crank. The vertical force needed tomove the trailing edge results by the contact between the slider and the rail. The complete system is made of commercial elements: actuators, kinematics, linear guides and all the other devices are in fact available on the market. The implemented architecture is a slight modification of the so-called quick-return mechanism (Amendola et al., 2016). In this paper, the aileron structure is sized with respect to the designated load chosen among themost critical operative ones. The working principle of the actuation system is described in detail and preliminary results of a finite element simulation are shown. Static and buckling analyses do not show any particular criticality; in other words, no plasticization arises under the limit loads, herein selected. 2. Morphing aileron: structural layout and evaluation of loads Themorphing aileron consists of segmented adaptive ribs based on finger-like segments enabling aileron cambermorphinguponactuation.Each rib (Fig. 1) is assumed tobe segmented into three consecutive blocks (B1,B2,B3) connected to each other bymeans of hinges located on the airfoil camber line (A,B). Block B1 is rigidly connected to the rest of the wing structure through a torsion tube enabling aileron rotation for roll control. BlocksB2andB3 are free to rotate around the hinges on the camber line, thus physically turning the camber line into an articulated chain of consecutive segments. A linking rod elements (L) hinged on not adjacent blocks forces the camber line segments to rotate according to specific gear ratios. Preliminary design of an adaptive aileron... 309 Fig. 1. Morphing rib architecture: (a) blocks and links, (b) hinges The ribs kinematic is transferred to the overall aileron structure by means of a multi-box arrangement (Fig. 2) where the skin is hidden for clarity. Fig. 2. Morphing aileron structure: multi-box arrangement Referring toFig. 3, the internal structural components are depicted, and it is also shown that the aileron is divided into one actuated and one passive segment. The internal kinematic chain actuates the first two bays while the last are considered slaved during themorphingmovement. The referenceCartesian systemS0 (Fig. 4)hasbeenusedas thedatumfor the load evaluation addressed by this paper; the following conceptual definition applies to S0: • Origin (O) at the intersection point between the Test Article (T/A) leading edge and the root rib plane; • X-axis onto root rib plane, parallel to the chord of the T/A airfoil @ the root section and aft oriented; • Y -axis normal to the root rib plane and oriented towards the T/A tip; • Z-axis perpendicular toXOY plane and oriented upwards. The rotation angle γ of block B2 with respect to block B1 is determined in order to appro- ximate target shapes bymeans of the articulated one-DOFmechanism described in Fig. 1. The angle γ is represented in Fig. 5. It ismeasured respect to the unmorphed chord direction and it corresponds to rigid rotation of the plain control surface comprised between−5◦ and+5◦. TheVLMmethod has been adop- ted to evaluate aerodynamic pressure distribution along the aileron in correspondence to each 310 G. Amendola et al. Fig. 3. CAD of the morphing aileron with an internal view to the actuation system Fig. 4. CAD of the Test Article with the reference system used for aerodynamic loads Fig. 5. Morphing aileron deflection angle γ in morphed down andmorphed up Preliminary design of an adaptive aileron... 311 consideredflight attitude (namely thewingangle of attack, flight altitude and speed) andaileron geometrical configuration. 3D flat-panelsmesh is generated in correspondence to the outer wing segment. For each flight attitude and aileron shape, the lifting pressure (Pi) acting along each box (bi) is calculated according to the following equation Pi = q(P0,i+αPα,i+γPγ,i) (2.1) where: q=0.5ρV 2 ∞ is the dynamic pressure, ρ the air density andV ∞ the airspeed;α is thewing angle of attack; P0,i is the pressure arising on bi in correspondence to unit dynamic pressure at α, γ equal to zero (airfoil baseline camber effect); Pα,i is the pressure on bi due only to unit α at unit dynamic pressure (incidence effect); Pγ,i is the pressure on bi due only to unit γ at unit dynamic pressure (morphing effect). Thanks to Eq. (2.1), P0,i, Pα,i, Pγ,i are calculated only one time for all the boxes and then combined according to the flight attitude parameters (α,q) and aileron morphed shape (γ) to be investigated. The combination ofα, q, γ leading to themost significant pressure levels along aileron segments is then determined andused as the design operative condition for the structural sizing purpose. The spanwise pressure distributions on the aileron segments at the design point (α=2◦, q=4425N/m2, γ=7◦) are plotted in Fig. 6. Fig. 6. Pressure distribution along aileron span The estimated pressure distribution will be considered as the reference load for structural sizingand itwill beapplied to theaileronfinite elementmodel inorder toasses the stressanlaysis. This constitutes the foundamental step to be done before proceeding with the manufacturing process. 3. Actuation system Themain target of the actuation kinematics is to develop ameans of transforming the actuator motion to specific rotation of themorphingdevice. Itmust bedesigned towithstand the external aerodynamic loads without undergoing structural damage and at the same time to move the system to the desired morphed shape. It is based on the classical quick-return mechanism, also referred to as oscillating glyph kinematics that (Fig. 7) is widely discussed andwas validated by Amendola et al. (2016). Figure 7 shows themain structural components of theglyphkinematic system. It is composed of crank R with an actuator shaft positioned at the point O, leverage beam BL connected to 312 G. Amendola et al. Fig. 7. Oscillating glyph kinematic scheme aileron B3 rib segment. The sliding element moves along its rail subjected during operation to the vertical force F. The actuator shaft rotation is transmitted to the structure by means of the crank R and a contact force is generated by the sliding element along the linear guide. Thereby, a moment is produced that equilibrates the aerodynamic hinge moment, so that the system keeps its desired morphed shape. The mechanism is then a SDOF architecture. In the kinematic scheme, the angle β is the actuator shaft rotation whileϕ is the morphing deflection directly related to the aileron angle γ (Fig. 5). The relation between the achieved angle and the mechanical advantage (MA), expressed as a ratio between the external load and the generated momentum,may be represented as in Fig. 8. The diagram shows that the greater ribmorphing angle, the higherMAand, consequently, the actuator torque required to equilibrate the external aerodynamic moment decreases. The aileron design condition (selected as the most severe one) occurs at ϕ = 7◦ with MA = 4.2. This peculiarity may lead to significant benefits in terms of the actuator power and weight. Fig. 8. MA vs. rib morphing angle The actuator shaft rotation β may be related to the morphing angle ϕ as described by Eq. (3.1) and represented in Fig. 9 cotϕ= L Rsinβ − cotβ (3.1) It is evident that in the design range between+7◦ ofmorpheddown and−7◦ ofmorphedup, the actuator rotation is comprised among ±45◦. The actuation system kinematics with details of the linear guides and its integration on the aileron rib are shown in Fig. 10. Preliminary design of an adaptive aileron... 313 Fig. 9. Rib morphing angle vs. actuator shaft rotation Fig. 10. Integration between the actuation system and rib (left) and details of the linear guide elements (rigth) 4. FE validation In order to verify the structural robustness of the conceivedmorphing architectures as well as to estimate its dynamic behavior, a very refined finite element model (FEM) has been generated (Fig. 11). The model has been realized with solid finite TET10 elements both for structural components (ribs and spars) and actuation system leverages. All the hinges have beenmodeled bymeans of two-nodes CBUSH elements. Each node of the CBUSH has been rigidly connected to a representative set of nodes belonging to the structural item by means of RBE2 (Fig. 12) (MSC-Nastran). The materials adopted for the aileron are described in Table 1 and highlighted in Figs. 13a and 13b. The aluminum components are depicted in grey while the steel components in black. Table 1.Aileron component materials Material E ρ ν Items (isotropic) [Gpa] [kg/m3] [-] Harmonic steel 210 7850 0.3 Beamof theactuation system, linear guide features, crank and rib links Al 2024-T351 70 2768 0.33 All the other items Theaileronmodel is considered constrained in correspondence to the crank exactlywhere the actuator shaft is located in order to prevent its rotation (clamped configuration). The following analyses have been carried out: • Linear static analysis at the limit load • Buckling analysis at the limit load. 314 G. Amendola et al. Fig. 11. Details of the aileron structure mesh Fig. 12. Morphing aileron finite element model with details of the hinges Fig. 13. Aileronmaterials: complete structure (a), inner structure (b) Theglobalmagnitudeof thedisplacements exhibitedby theaileronat the limit load condition is shown. The maximum value (21.8mm) is located at the trailing edge in proximity of the 1st bay (Fig. 14). ThemaximumvonMises stresses are detected around the rib links (257MPa) and aroundhinges of the second rib (231MPa) andon theactuationbeam(467MPa), resultingbelow the yield strength of AL 2024 alloy and steel. The described results are depicted in Figs. 14-16. Preliminary design of an adaptive aileron... 315 The first buckling eigenvalue occurs at−10.391, whichmeans that the first critical load is more than 10 times of the applied pressure but in the opposite direction. The buckling deformation related to this eigenvalue involves rib connection links as shown in Fig. 16. Fig. 14. Global aileron displacement distribution Fig. 15. Global vonMises stress distribution on the ribs 5. Conclusions In this paper, the working principle of a morphing aileron actuation system is presented. The actuation mechanism is based on an oscillating glyph mechanism, combining characteristics of functionality, robustness and integrability required for adaptive structures. In particular, the study of the smartmechanical system involved functional integration of the kinematic actuation chain into a finger-like adaptive ribs architecture. The static load has been imposed to the structures and the stress results and the buckling eigenvalue have been provided. The results show that all margin of safety are positives and there are no critical points for structural safety 316 G. Amendola et al. Fig. 16. First buckling deformationmode of the aileron of the proposed morphing aileron. The next step will involve the manufacture phase where the aileron prototype will be built. Subsequently, the results herein presented will be validated by means of dedicated ground tests campaign where both static and dynamic behavior will be assessed before wind tunnel tests. References 1. 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