**2. Design of a morphing aileron**

The design of a camber morphing aileron is following detailed as a reference case study for research into the subject. The aileron main functionalities such as roll maneuver are not modified. Conversely, with augmented capabilities integrated, the morphing aileron is deployed in cruise, through a symmetric deflection, to obtain a near optimum wing geometry enabling optimal aerodynamic performance. The design approach, including underlying concepts and analytical formulations, combines design methodologies and tools required to develop such an innovative control surface.

#### **2.1. Multi-box structure design**

Inner and medium wing regions where flap systems are generally located are growingly receiving considerable attention in research. That successful development was worth to be further investigated in order to understand its applicability to the whole wing span. It does then mean to verify the applicability of those concepts to the aileron region. This region plays a fundamental role for the aircraft roll control while is subjected to the external loads. Thus, during the preliminary design phase, it is important to consider some specific critical aspects: (i) The aileron constitutes a primary control surface, which is safety critical. Failure is a catastrophic event for the aircraft; (ii) the morphing capability is added to the conventional aileron which remains free to rotate around its main hinge axis; (iii) the aileron region constitutes a delicate zone from aero-elastic point of view; (iv) morphing will introduce normal modes driving flutter instability; (v) the wing tip region is characterized by very reduced space leading to a difficult integration of actuator and kinematic. This section details the design phases of the morphing aileron, spanning from preliminary numerical verifications to wind tunnel tests. The general morphing architecture and design process resemble the same philosophy developed for the SARISTU trailing edge. The device is aimed at working in cruise to modify a limited chord segment of the aileron, so to accomplish the aircraft weight variations following fuel consumption. However, during classical maneuver, this morphing part remains rigid and the aileron works in the usual manner. Such complex adaptive system has to meet specific requirements in terms of the aerodynamic target shape, stiffness distribution, and morphing controllability. In light of these considerations, an articulated mechanism was developed, in which each component have a predominant utility, but at the same time have to cooperate with the others in withstanding loads, distributing stress and driving the architecture in a controlled way from the baseline configuration to the target shapes (morphed down and morphed up). The proposed architecture was designed according to transport regional aircraft specifications. The morphing aileron is mainly composed of: (i) five segment‐ ed rib connected by means of rotational hinges positioned on the camber line creating a kinematic chain assuring enough structural robustness and transmitting deformation; (ii) spanwise stiffening elements such as spars and stringers in a multi-box arrangements; (iii) three servo-rotary actuators which drive the mechanism; (iv) a segmented skin ("armadillolike" configuration) with silicon gap fillers to avoid discontinuities between adjacent parts and to ensure low friction sliding during morphing.

The geometrical external contour of the aileron constitutes the first step for its structural design. The rib mechanism uses therefore a three segment polygonal line to approximate the camber of the airfoil and to morph it into the desired configuration, while keeping approximately unchanged the airfoil thickness distribution. Each aileron articulated ribs (**Figure 11**) has been assumed to be segmented into three consecutive blocks (B0, B1, and B2) connected to each other by means of hinges displayed on the airfoil camber line (A and B) in a "finger-like" configuration. Moreover, non-consecutive rib plates are connected by mean of a link (L) that forces the camber line segments to rotate according to specific gear ratio and makes each rib equivalent to a single-DOF mechanism.

**Figure 11.** Morphing rib architecture: (a) blocks and links, (b) hinges.

The ribs' kinematic was transferred to the overall aileron structure by means of a multi-box arrangement (**Figure 12**). Each spanwise box of the structural arrangement is characterized by a single-cell configuration delimited along the span by homologue blocks of consecutive ribs, and along the chord by longitudinal stiffening elements (spars and/or stringers). Upon the actuation of the ribs, all the boxes are put in movement thus changing the external shape of the aileron; if the shape change of each rib is prevented by locking the actuation chain, the multi-box structure is elastically stable under the action of external aerodynamic loads. A fourbay (five-rib) layout was considered for an overall (true-scale) span of 1.5 meters. AL2024-T351 alloy was used for spars, stringers, and rib plates, while 17-4PH steel was used for ribs' links. Off-the-shelf airworthy components were properly selected for the bearing and bushings at the hinges and coupled to torsional springs to recover any potential free-play.

#### **2.2. Actuation system design**

deployed in cruise, through a symmetric deflection, to obtain a near optimum wing geometry enabling optimal aerodynamic performance. The design approach, including underlying concepts and analytical formulations, combines design methodologies and tools required to

Inner and medium wing regions where flap systems are generally located are growingly receiving considerable attention in research. That successful development was worth to be further investigated in order to understand its applicability to the whole wing span. It does then mean to verify the applicability of those concepts to the aileron region. This region plays a fundamental role for the aircraft roll control while is subjected to the external loads. Thus, during the preliminary design phase, it is important to consider some specific critical aspects: (i) The aileron constitutes a primary control surface, which is safety critical. Failure is a catastrophic event for the aircraft; (ii) the morphing capability is added to the conventional aileron which remains free to rotate around its main hinge axis; (iii) the aileron region constitutes a delicate zone from aero-elastic point of view; (iv) morphing will introduce normal modes driving flutter instability; (v) the wing tip region is characterized by very reduced space leading to a difficult integration of actuator and kinematic. This section details the design phases of the morphing aileron, spanning from preliminary numerical verifications to wind tunnel tests. The general morphing architecture and design process resemble the same philosophy developed for the SARISTU trailing edge. The device is aimed at working in cruise to modify a limited chord segment of the aileron, so to accomplish the aircraft weight variations following fuel consumption. However, during classical maneuver, this morphing part remains rigid and the aileron works in the usual manner. Such complex adaptive system has to meet specific requirements in terms of the aerodynamic target shape, stiffness distribution, and morphing controllability. In light of these considerations, an articulated mechanism was developed, in which each component have a predominant utility, but at the same time have to cooperate with the others in withstanding loads, distributing stress and driving the architecture in a controlled way from the baseline configuration to the target shapes (morphed down and morphed up). The proposed architecture was designed according to transport regional aircraft specifications. The morphing aileron is mainly composed of: (i) five segment‐ ed rib connected by means of rotational hinges positioned on the camber line creating a kinematic chain assuring enough structural robustness and transmitting deformation; (ii) spanwise stiffening elements such as spars and stringers in a multi-box arrangements; (iii) three servo-rotary actuators which drive the mechanism; (iv) a segmented skin ("armadillolike" configuration) with silicon gap fillers to avoid discontinuities between adjacent parts and

The geometrical external contour of the aileron constitutes the first step for its structural design. The rib mechanism uses therefore a three segment polygonal line to approximate the camber of the airfoil and to morph it into the desired configuration, while keeping approximately unchanged the airfoil thickness distribution. Each aileron articulated ribs (**Figure 11**) has been assumed to be segmented into three consecutive blocks (B0, B1, and B2) connected to each

develop such an innovative control surface.

to ensure low friction sliding during morphing.

**2.1. Multi-box structure design**

98 Recent Progress in Some Aircraft Technologies

The actuation system peculiarity resided in the fact that it is an un-shafted distributed servoelectromechanical arrangement deployed to achieve the aileron shape transition from the baseline configuration to a set of design target shapes in operative conditions moreover it is self-contained within the structure assuring a smooth surfaces exposed to the flow without fairing. The only kinematic mechanism that satisfies the target specifications is the oscillating glyph. The internal structure room defines the geometrical parameters which are directly related to the kinematic transmission ratio also defined as mechanical advantage (MA); furthermore, it is necessary to identify the number of actuators required to morph the aileron in particular due to small sizes near the tip, the last two bays could not be equipped with the kinematic. In **Figure 12**, it is shown that the first three ribs are drive by three individual actuators while the passive segment is slaved to the actuated one.

**Figure 12.** Internal view of the aileron with actuated and passive segment highlight.

A lightweight and compact leverage was investigated to activate the morphing aileron through EMAs. The deployment kinematics is based on a "direct-drive" actuation moving a beam rigidly connected to block B2 of **Figure 11**. The actuation beam transmits the actuation torque to the third segment of the rib, thus making it to rotate with respect to its original position. In particular, during morphing, the block B2 rotates around an instantaneous rotation centre. The instantaneous rotation center is here intended as the point in the moving plane around which all other points are rotating at a specific instant of time. As illustrated in **Figure 13(a)**, the trajectories of the points in the third block are all circles centered in this point. The determi‐ nation of point V coordinates allows for the estimation of the actuation torque needed to withstand the aerodynamic loads acting on the morphing rib structure.

**Figure 13.** Circular trajectories of sample points (E, F, and G) during morphing (left) and position of hinges A, V, and B (right).

With reference to the **Figure 14**, the rotational motion of the actuation beam is provided by the crank rotation β which moves the carriage along its guide. A force F is thus generated by the contact between the carriage and the rail. By connecting the actuator shaft to the crank hinge O and the beam to the third rib segment (B2), the actuation torque is transmitted firstly to the crank and secondly to the rib rotating around the V in order to counterbalance the external moment *Mrib*#3.

**Figure 14.** Oscillating glyph connected to the third rib segment of the morphing aileron [7].

**Figure 12.** Internal view of the aileron with actuated and passive segment highlight.

100 Recent Progress in Some Aircraft Technologies

withstand the aerodynamic loads acting on the morphing rib structure.

(right).

A lightweight and compact leverage was investigated to activate the morphing aileron through EMAs. The deployment kinematics is based on a "direct-drive" actuation moving a beam rigidly connected to block B2 of **Figure 11**. The actuation beam transmits the actuation torque to the third segment of the rib, thus making it to rotate with respect to its original position. In particular, during morphing, the block B2 rotates around an instantaneous rotation centre. The instantaneous rotation center is here intended as the point in the moving plane around which all other points are rotating at a specific instant of time. As illustrated in **Figure 13(a)**, the trajectories of the points in the third block are all circles centered in this point. The determi‐ nation of point V coordinates allows for the estimation of the actuation torque needed to

**Figure 13.** Circular trajectories of sample points (E, F, and G) during morphing (left) and position of hinges A, V, and B

The aileron shape can be, in this way, adaptively controlled to realize camber variations. The target morphing angles were derived as corresponding to a rigid rotation of a plain control surface comprised between -7° and +7°. The mechanical advantage of the mechanism (MA) can be written as follows:

$$MA = \frac{LOAD}{DRIVER} = \frac{M\_{r \text{ib } \pi 3}}{M\_{\text{av}}} = \frac{F \cdot BL}{F \cdot BR} = \frac{BL}{BR} \tag{1}$$

where the *Mrib*#3 is the external moment due to aerodynamic loads estimated with respect to the hinge V, while *Matt* is the actuation torque provided by the actuator in order to equilibrate the system. F is the force that the crank produces by means of the cursor, *BL* is the force arm, and *BR* is the crank projection along the guide. Equation (2) shows that the mechanical advantage only depends on the geometrical characteristics of the system. By combining geometrical terms, it follows:

$$\cot \varphi = \frac{L}{R \cdot \sin \beta} \cot \beta \tag{2}$$

This equation allows calculating the actuator shaft rotation (*β*) needed to achieve a given morphing angle (*ϕ*) of the rib block and hence of the entire mechanism. After estimating MA, it is possible to identify the actuation torque that actuator shall supply. Accordingly, the value of the force F shall be known in order to verify that the stress arising in the carriage moving into the rail, does not exceed design allowable. The actuation rod is then subjected to the simultaneous action of the force F and the external moment *Mrib*#3, both producing bending stress. This indicates that actuation system design requires a trade-off between the mechanical advantage and the geometrical constraints limiting the actuator shaft rotation and L/R ratio. In order to mitigate the maximum counterbalancing load acting on the guide to equilibrate the aerodynamic moment, a fork-shaped crank coupled with a double sided linear guide was preferred, as shown in **Figure 15**.

**Figure 15.** Actuation system final architecture with high rigidity linear guide.

The VLM method was adopted to evaluate aerodynamic pressure distribution along the aileron in correspondence of each considered flight attitude (namely wing angle of attack, flight altitude, and speed) and aileron geometrical configuration. The obtained loads were considered for structural sizing and validation. A linear static analysis of the isolated actuation system mechanism by means of a FE simulation was, in a first approximation, performed. The aim of the numerical simulation was to verify if the static force acting on the linear guide was below the allowable value prescribed by the producer. In the real operative condition, the linear guide, being free to move, is not subjected to stress in the direction of motion. Force is transmitted in the vertical (with respect to the guide axis) and, partially, normal direction (with respect to the guide plane). For the current application, the actuator system was sized, referring to the jamming condition, considered as the most critical. In fact, as visible in **Figure 16**, the larger extent of the constraints (additional clamps) is expected to lead to higher stresses, locally (in the contact region) and distributed (overall). The actuation beam is then simultaneously loaded with the external aerodynamic moment, the vertical static force and a horizontal component (linked to the jamming), producing a pure bending with a higher stress level rather than the free guide. This effect was simulated by means of a perfect bonding between the rail and slider. The reaction force acting on the linear guide for a given aerodynamic moment was firstly evaluated and then compared to the expected actuation torque (**Figure 17**) multiplying by the crank length.

**Figure 16.** Stress contour on the linear guide element (max stress ~400 MPa).

it is possible to identify the actuation torque that actuator shall supply. Accordingly, the value of the force F shall be known in order to verify that the stress arising in the carriage moving into the rail, does not exceed design allowable. The actuation rod is then subjected to the simultaneous action of the force F and the external moment *Mrib*#3, both producing bending stress. This indicates that actuation system design requires a trade-off between the mechanical advantage and the geometrical constraints limiting the actuator shaft rotation and L/R ratio. In order to mitigate the maximum counterbalancing load acting on the guide to equilibrate the aerodynamic moment, a fork-shaped crank coupled with a double sided linear guide was

The VLM method was adopted to evaluate aerodynamic pressure distribution along the aileron in correspondence of each considered flight attitude (namely wing angle of attack, flight altitude, and speed) and aileron geometrical configuration. The obtained loads were considered for structural sizing and validation. A linear static analysis of the isolated actuation system mechanism by means of a FE simulation was, in a first approximation, performed. The aim of the numerical simulation was to verify if the static force acting on the linear guide was below the allowable value prescribed by the producer. In the real operative condition, the linear guide, being free to move, is not subjected to stress in the direction of motion. Force is transmitted in the vertical (with respect to the guide axis) and, partially, normal direction (with respect to the guide plane). For the current application, the actuator system was sized, referring to the jamming condition, considered as the most critical. In fact, as visible in **Figure 16**, the larger extent of the constraints (additional clamps) is expected to lead to higher stresses, locally (in the contact region) and distributed (overall). The actuation beam is then simultaneously loaded with the external aerodynamic moment, the vertical static force and a horizontal component (linked to the jamming), producing a pure bending with a higher stress level rather than the free guide. This effect was simulated by means of a perfect bonding between the rail and slider. The reaction force acting on the linear guide for a given aerodynamic moment was firstly evaluated and then compared to the expected actuation torque (**Figure 17**) multiplying

preferred, as shown in **Figure 15**.

102 Recent Progress in Some Aircraft Technologies

by the crank length.

**Figure 15.** Actuation system final architecture with high rigidity linear guide.

**Figure 17.** Beam displacement contour (a, left); guide reaction loads of 177 N and 179 N (b, right).

The finite element model of the entire aileron was then carried out. The FE model is represen‐ tative of the three-dimensional drawings (CAD) of the entire aileron demonstrator. It includes main structural components such as segmented ribs and spars, actuation system leverage, and skin panels. Solid elements (CTETRA) were used for the mesh of the primary structure and the actuation leverage; meanwhile, beam elements (CBEAM) were used for modelling all the joints (fasteners, hinges, pins, and so on). FE model general data are recapped in **Table 1**.


**Table 1.** FE model characteristics.

The aileron primary structure is composed of ribs, actuation kinematic chains, spars, and skin. Aileron leading edge was not modelled for stress analysis purposes; however, it was consid‐ ered only to properly evaluate the interface loads transmitted by the aileron to the wing box. In **Figure 18**, a global view of the aileron FE model is depicted, while in **Figure 19(a)** and **(b)**, details of rib and spars meshes are shown.

**Figure 18.** Aileron FE model.

**Figure 19.** (a) Aileron rib solid mesh (CTETRA), (b) spar solid mesh (CTETRA).

Main mechanical properties of the materials adopted for the aileron components are listed in the next table (**Table 2**).


**Table 2.** Aileron components material.

All the components of the actuation system were connected to each other by means of several pins which were simulated using CBEAM elements (**Figure 20(a)** and **(b)**).

The aileron primary structure is composed of ribs, actuation kinematic chains, spars, and skin. Aileron leading edge was not modelled for stress analysis purposes; however, it was consid‐ ered only to properly evaluate the interface loads transmitted by the aileron to the wing box. In **Figure 18**, a global view of the aileron FE model is depicted, while in **Figure 19(a)** and **(b)**,

details of rib and spars meshes are shown.

104 Recent Progress in Some Aircraft Technologies

**Figure 19.** (a) Aileron rib solid mesh (CTETRA), (b) spar solid mesh (CTETRA).

Al 2024-T351 70 2768 0.33 All other items

Main mechanical properties of the materials adopted for the aileron components are listed in

**)** *v* **Items**

guide features, crank, and rib links

Steel C50 220 7850 0.3 Beam of the actuation system, linear

**Figure 18.** Aileron FE model.

the next table (**Table 2**).

**Table 2.** Aileron components material.

**Material (isotropic) E (GPa)** *ρ* **(kg/m3**

**Figure 20.** Connection pins between linear guides items (a) and detail of the local connection among the actuation kine‐ matic parts (b).

Static analysis results have been here reported with reference to the limit load and ultimate load (1.5 times the limit load). In **Figure 21**, the global magnitude of the displacements exhibited by the aileron at limit load condition is shown. The maximum value (21.8 mm) is located at the trailing edge in proximity of the first bay.

**Figure 21.** Global aileron displacement distribution at LL condition.

The stress distribution is characterized by concentrated peak around hinges and high solici‐ tation of the actuation beam which is the most loaded components. Concerning the actuation levers, it is showed the typical stress distribution in bending; stress peaks greater than 350 MPa were found close to un-chamfered notches (**Figure 22(a)**). In addition, it is depicted (**Figure 22(b)**) the elements with stress level higher than 320 MPa. In this case, showing the most stressed elements is localized in a small area around the holes of the linkage between beam and spar and in proximity of the linear guides.

**Figure 22.** Global VM stress distribution on actuation beam at LL (a) and element stress distribution above threshold values of 320 MPa (b).

#### **3. Prototyping and wind tunnel tests**

On the basis of the numerical outcomes, the executive drawings of the prototype were produced and the aileron was then manufactured. Main structural parts are machined, while linear guides and actuators are components off-the-shelf (COTS). In the subsequent pictures, the segmented rib architecture, the actuation kinematic chain, and the final manufactured prototype (after painting) are shown. The morphing aileron was then integrated in a wing box and tested in wind tunnel at NRC (National Research Council of Ottawa, Canada), in the framework of the research program CRIAQ MDO505 involving Italian and Canadian univer‐ sity and research centre cooperation [8]. The aileron deflections are shown in **Figure 26**, and the integrated wing prototype is reported in **Figure 27**. The preliminary results obtained during wind tunnel tests were computed for baseline and morphed down configurations: lift versus angle of attack (*CL − α*). (**Figure 28**); drag versus angle of attack (*CD − α*) (**Figure 29**); drag polars (*CL − CL*) (**Figure 30**). The first one shows a typical linear trend. The curve slope (*CLα*) remains unchanged and clearly by a morphing aileron deflection (from baseline to 6°), the camber increase (high *α*0*<sup>L</sup>* and the curve moves in parallel upwards. The *CD* − *α* curve trend is reported in **Figure 29** for both unmorphed and morphed down configurations. The tendency shows that the minimum drag coefficient shift on the left as the morphing deflection increase leading to high *CD*0. Finally, the drag polars are depicted in **Figure 30**. In this case, when a morphing deflection occur, the polar cross in correspondence of a pivot point for high *CL* while it moves on the right side of the Cartesian plane for low *CL*. This means that it is possible to identify an envelope curves which is the optimum one (dotted red line) (**Figures 23**–**25**).

**Figure 23.** Aileron manufacturing with detail on hinges and rib.

stressed elements is localized in a small area around the holes of the linkage between beam

**Figure 22.** Global VM stress distribution on actuation beam at LL (a) and element stress distribution above threshold

On the basis of the numerical outcomes, the executive drawings of the prototype were produced and the aileron was then manufactured. Main structural parts are machined, while linear guides and actuators are components off-the-shelf (COTS). In the subsequent pictures, the segmented rib architecture, the actuation kinematic chain, and the final manufactured prototype (after painting) are shown. The morphing aileron was then integrated in a wing box and tested in wind tunnel at NRC (National Research Council of Ottawa, Canada), in the framework of the research program CRIAQ MDO505 involving Italian and Canadian univer‐ sity and research centre cooperation [8]. The aileron deflections are shown in **Figure 26**, and the integrated wing prototype is reported in **Figure 27**. The preliminary results obtained during wind tunnel tests were computed for baseline and morphed down configurations: lift versus angle of attack (*CL − α*). (**Figure 28**); drag versus angle of attack (*CD − α*) (**Figure 29**); drag polars (*CL − CL*) (**Figure 30**). The first one shows a typical linear trend. The curve slope (*CLα*) remains unchanged and clearly by a morphing aileron deflection (from baseline to 6°), the camber increase (high *α*0*<sup>L</sup>* and the curve moves in parallel upwards. The *CD* − *α* curve trend is reported in **Figure 29** for both unmorphed and morphed down configurations. The tendency shows that the minimum drag coefficient shift on the left as the morphing deflection increase leading to high *CD*0. Finally, the drag polars are depicted in **Figure 30**. In this case, when a morphing deflection occur, the polar cross in correspondence of a pivot point for high *CL* while it moves on the right side of the Cartesian plane for low *CL*. This means that it is possible to identify an envelope curves which is the optimum one (dotted red line) (**Figures 23**–**25**).

and spar and in proximity of the linear guides.

106 Recent Progress in Some Aircraft Technologies

**3. Prototyping and wind tunnel tests**

values of 320 MPa (b).

**Figure 24.** Detail on aileron actuation system.

**Figure 25.** Photograph of the aileron prototype.

**Figure 26.** Morphing aileron at various deflections.

**Figure 27.** Complete CRIAQ wind tunnel test article including a morphing aileron [8].

**Figure 28.** Lift coefficient versus angle of attack curve.

**Figure 29.** Drag coefficient versus angle of attack curve.

**Figure 26.** Morphing aileron at various deflections.

108 Recent Progress in Some Aircraft Technologies

**Figure 28.** Lift coefficient versus angle of attack curve.

**Figure 27.** Complete CRIAQ wind tunnel test article including a morphing aileron [8].

## **4. Conclusions**

A self-contained morphing concept applied to a safety critical hinged control surface was presented in this chapter. In particular, a morphing aileron was investigated as an extension of an adaptive trailing edge in order to improve of L/D ratio and at the same time to preserve the conventional aileron functionality. The resulting morphed geometry, called "morphing aileron," ensures an augmented functionality with respect to a conventional "rigid" aileron. The device is able to rigidly rotate around main hinge axis and in addition will enable camber morphing. Being a safety critical surface, the structural design of a complete morphing aileron is rarely addressed in the literature. Such an original work provides thus evidence and arguments that contribute to the knowledge of morphing systems. Potentially suitable for static or dynamic purposes, the morphing aileron is an extension of the morphing trailing edge technology to the wing tip where small deflections could bring significant aerodynamic benefits. It has been designed for a symmetrical deflection during cruise in order to compensate A/C weight variation due to fuel burned. In such a manner, it is aimed to increase aerodynamic efficiency (reduce drag) in off design points. Additionally, the deflection of a morphing aileron it is expected to redistribute the spanwise wing distribution in order to reduce wing root bending moment. On the other hand, by increasing actuator bandwidth, it can be tailored to reduce peak stress from gust.

In order to deflect a "finger-like" rib architecture, a compact electromechanical actuation based on double-sided guides and a fork-shaped crank has been designed. Advanced finite element model in order to validate the structure at limit and ultimate loads have been carried out setting all the details necessary to produce a laboratory demonstrator. This one was assembled and tested, proving the effective functionality of the concept. Finally, wind tunnel tests assessing the aerodynamic trend of such innovative architectures have been reported. The idea herein described leads the way to further researches aimed at enhancing the TRL of the concept. To this aim, some remarks should be done on the most critical aspects of the current device. In particular, future steps may be: (i) an embedded sensing network for enhanced control in order to assure the achievement of the target aero-shapes; (ii) actual shapes evaluation and compar‐ ison with expected aero-shapes; (iii) aerodynamic benefits comparison between rigid and morphing aileron; (iv) morphing aileron-related (wing and A/C) performance benefits estimations; (v) enhanced design with topology optimization; (vi) segmented skin aerody‐ namics comparison with a tailored complaint skin technology; (vii) high-speed simulations and tests.
