Morphing wings at LARCASE at ÉTS

The study of morphing wings is not new to our laboratory (LARCASE). Indeed, the LARCASE team has already explored research and development paths for morphing wing technologies. This research was conducted in the frame of two major projects funded at the governmental level by the Consortium for Research and Innovation in Aerospace in Quebec (CRIAQ) and the Natural Sciences and Engineering Research Council of Canada (NSERC). These projects were carried out within the framework of agreements signed between university and industry partners. Each of these projects has led to the design and manufacture of prototypes and their tests in the National Research Council – Institute for Aerospace Research (NRC-IAR) wind tunnel, and to publications in scientific journals. These projects, entitled CRIAQ 7.1 and CRIAQ MDO 505 (where MDO stands for Multidisciplinary Design Optimization), were realized in collaboration with Bombardier, Thales, the NRC-IAR and École Polytechnique in Canada. In addition, the CRIAQ MDO 505 international project was realized in collaboration with Italian partners such as Alenia, the Italian Center for Aerospace Research (CIRA), University of Naples – Frederico II. These two major projects carried out under the leadership of LARCASE aimed at morphing the upper surface of the wing in order to improve its aerodynamic performance.

The first project was called CRIAQ 7.1 (Popov, Grigorie, Botez, Mamou, & Mebarki, 2010). In this project, the morphing of the upper surface was done using Smart Material Actuators (SMA). The deformation obtained made it possible to delay the transition of the flow on the wing. In this project, an ideal rectangular wing was used, thus, no existing structural constraints for a real wing were considered. This concept has been validated using wind tunnel tests.

The second CRIAQ project was called CRIAQ MDO 505 (Koreanschi, et al., 2016). In this project, the goal was to design and validate a wing with an aileron, that was able to delay along the wing chord the flow transition from the laminar regime to the turbulent regime. For this aim, the wing was provided with four-point actuators in order for it to be able to morph. This wing was equipped with an aileron of a real Bombardier regional aircraft and presented the structural constraints. Experimental results have shown that this system composed of wing and aileron could produce the delay of the flow transition. However, irregular deformation of the wing and aileron surface appeared. Between the four-point actuators, the surface morphed did not had a quadradic form because of the structural constraint of the wing.

Another project was realized on a wing with the airfoil of an ATR42 (Regional Transport Aircraft). In this project, the upper surface of the wing was modified by using two oval bars. As they turned, the surface was pushed outwards (Sugar Gabor, Koreanschi, & Botez, 2012). This system therefore made it possible to morph the surface towards the outside but not towards the inside. Thus, aerodynamic performance gain of lift coefficient and drag coefficient was limited.

These morphing projects made it possible to optimize the laminar flow on the upper surface of the wing, but they were limited in order to modify the aerodynamic coefficients of lift and drag for the improvement of their performances. These morphing systems can not replace the control surfaces of the wing. From these three projects, we can conclude that in order to significantly improve the aerodynamic coefficients of lift and drag of a wing, the morphing f the upper surface only was not enough. Thus, in the research proposed here, we will focus on the design and experimental validation of different types of morphing wing systems.

The different types of morphing wing 

Wing aspect ratio 

The aerodynamic coefficients improvement was made possible by modifying the span of the wing by using telescopic spars. A morphing prototype has been tested in the wind tunnel (Blondeau, Richerson, & Pines, 2003). The results analysis indicated that this morphing system made it possible to improve the lift and drag coefficients, however, this improvement was countered by the perturbation on the flow generated by the model. It was therefore necessary to obtain a significant increase in wingspan before perceiving a gain on the aerodynamic performance of the morphing wing. Following experimental tests, a 5 in extension in the span increase the drag coefficient of the wing while a 7 in extension in the span reduce it. This type of morphing was more effective in reducing the drag coefficient for angles of attack between 0° and 5°. From the structural point of view, this type of mechanism has been complex; there were three nested cylinders which involved a complex manufacturing and handling.

Morphing of the camber 

The most promising type of morphing to meet our objectives will be the “morphing of the camber” of the airfoil (Sanders, Eastep, & Forster, 2003). Indeed, by modifying the camber of the airfoil, one could for example convert a NACA0012 airfoil into a NACA4412 airfoil, which would bring a significant increase in the lift coefficient of the wing, and a small drag coefficient increase. The National Advisory Committee for Aeronautics (NACA) airfoil, whose name includes two digits and a two-digit number, respect the following rule:

1. The first digit denotes the airfoil maximum camber as a percentage of chord;
2. The second digit gives the position of this maximum camber in ten percentage (10%) of chord;
3. The third number (last two digits) represents the thickness of the airfoil in % of the chord .

Two types of deformations, combined together, make it possible to achieve this objective of deformation of the camber; the two types include the deformation of the leading edge and the deformation of the trailing edge (Gandhi & Anusonti-Inthra, 2008). However, a problem often encountered during the morphing of the shape of the airfoil is the appearance of waves on the wing surface due to interactions between the actuating system and the wing structure (Peel, Mejia, Narvaez, Thompson, & Lingala, 2009).

Another difficulty encountered in the development of morphing wing mechanism for UAS is the weight of the mechanism, and its size. The gains in aerodynamic coefficients (lift, drag) can therefore be canceled out by the additional weight of the mechanism. We must therefore be able to develop a mechanism that would improve the aerodynamic performances of the morphing wing without increasing its weight. Several morphing mechanisms have been studied in our project to achieve this objective.

Morphing wing using SMA 

SMAs ( (Elzey, Sofla, & Wadley, 2005), (Elzey, Sofla, & Wadley, 2003) and (Berton, 2006)) are materials that can change their size under the action of an electrical current and thus morph the surface of a wing. They have the advantage of being light enough, however they consume a lot of energy to work, thus, the energy saving goal is not respected (Fischer, Terriault, & Brailovski, 2012). Another method considered the acting on the surface directly by used of piezoelectric materials (Moosavian, Chae, Pankonien, Lee, & Inman, 2017), (Wang, Bartley-Cho, Martin, & Hallam, 2001). However, these materials required large electrical consumption.