Whirl Tower Demonstration of an SMA Blade Twist System

Abstract

This paper focuses on the development and demonstration of a novel blade morphing system within a whirl tower facility. The scope is to investigate the behavior of the proposed architecture under representative loads, demonstrating its capability to alter the blade original shape in operation under centrifugal, aerodynamic, and internal forces. The morphing concept was developed inside the European project “Shape Adaptive Blades for Rotorcraft Efficiency”, SABRE, and consists of a shape memory alloy system able to change the original twist law and, in this way, enhance rotor performance at certain specific regimes, such as hover and vertical flight. These phases, indeed, are generally penalized with respect to other more extended flight regimes (cruise). The work starts with an overview of the research in the field of morphing, with specific reference to the researches envisaging rotary wing demonstrations. Then, an overview of the morphing twist concept is provided, with particular attention paid to those features particularly suited for the whirl tower representative test environment. The laboratory characterization and commissioning operations are illustrated. Then, the task of the installation of the prototype on the whirl tower facility is described together with the testing modality adopted. Finally, the results of the test campaign are illustrated and critically discussed, providing the reader with insights and possible future steps to be taken in further research. The impact on the morphing capability of the following different parameters was investigated: the number of the prototype segments switched on, the speed and thus the centrifugal actions, and the angles of attack. The stiffening effect due to centrifugal actions was quantified through the measurement of the actual twist and the internal deformation. The link between speed, angle of attack at root, and twist and flap angles was also tracked, building a database useful for the comprehension of the phenomenon, and for the assessment of numerical predictive models. The achieved results highlighted the capability of the system to produce a twist angle matching the target of 8° per blade radius; this figure is related to a potential power saving of 10% in hover and vertical flight and an improvement of about 1% on the over-all efficiency of the rotorcraft.

Development and Prospect of Smart Materials and Structures for Aerospace Sensing Systems and Applications

“…Balzarek et al [ 84 ] attempted to integrate SMA actuators into the helicopter’s wings to form an elastic skin for better hover flight capabilities. On this basis, Ameduri et al [ 85 ] systematically studied the influence of different parameters on the adaptive deformation ability of rotating wings and established a database that can be used to predict model behavior in subsequent related studies. In addition to this, Courchesne et al [ 86 ] studied the aeroelastic characteristics of applying SMA directly to the skin of deformed wings.…”

SMA blade twist system: from the requirements to the demonstration in relevant environment

“…The DMUs produced in the previous task were used to realize two demonstrators, one made of 4 cells for the WT plant of the Univ of Bristol and the other one made of 3 cells for the WhT facility of the DLR [14] [17]. In Fig.…”

“…The impact on the aerodynamic performance was observed in terms of LoD that, at 25 m/s, for the fully twisted configuration, arose up to about 65, well over the reference (21): this confirmed the aerodynamic effectiveness of the additional twist, this way in support of the expectation of power reduction. The tests in the WhT facility were executed for AoA between -8 and +8 deg and at two speeds, 95 and 120 rpm [17]; this latter value, about 3.6 times lower than the nominal speed (44 rad/s), chosen for meeting the WhT safety requirement and corresponding to 1/5 of the centrifugal action, restricts the validity of the tests to short blade segments close to the root. However, it is worth note that stiffener solutions, integrated with SMA elements with larger authority, may withstand nominal working conditions assuring the same twist actuation.…”

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

“…The activities related to this device were carried out within the SABRE project, and involved extensive test campaigns on three different system breadboards based on consolidated knowledge of SMA-based actuators [ 40 , 42 , 43 ] and [ 44 , 45 , 46 ]. In detail, a wide FEM analysis, [ 42 ], and mechanical characterization of shape memory alloys-based systems were conducted in suited configurations, [ 44 ].…”

“…The activities related to this device were carried out within the SABRE project, and involved extensive test campaigns on three different system breadboards based on consolidated knowledge of SMA-based actuators [ 40 , 42 , 43 ] and [ 44 , 45 , 46 ]. In detail, a wide FEM analysis, [ 42 ], and mechanical characterization of shape memory alloys-based systems were conducted in suited configurations, [ 44 ]. The latest experiments aimed at evaluating the system performance in a relevant environment, installed on a surrogate of the hosting platform, and implementing due modifications for refining its design.…”