Application
Morphing wings are desired in aircraft applications due to their advantages compared with fixed wings, including being able to responsively adapt to aerodynamic drag. Researchers from California State University at San Bernardino have developed two approaches for obtaining control surfaces (aerodynamic devices that allow pilots to adjust the flight attitude of an aircraft) on morphing wings using microfiber composite (MFC) actuators. The authors explored the effectiveness of using two bonding approaches: a flap approach in which the MFC actuator was bonded to each side of a metal substrate and a direct bonding approach in which MFC actuators were directly bonded to the Kevlar wing using Master Bond EP31.
Key Parameters and Requirements
For the direct bonding approach, the authors bonded the MFC actuator as close to the trailing edge as possible while simultaneously avoiding knotted areas in the air bladder of the wing. The actuator was bonded to the airfoil using Master Bond EP31. According to the authors, EP31 was chosen because of its high shear strength of 20 kN, which helped reduce compliance problems that would have otherwise reduced the actuator’s performance. After cleaning the surface of the actuator and the airfoil with acetone, the adhesive was cured for 28 hours at room temperature.
Results
The bonding reliability was assessed by repeatedly applying sinusoidal voltage signals to the actuator over a frequency range of < 1 Hz to > 1 kHz. After visually inspecting the bond, the authors found no visible signs of debonding. Furthermore, when using the direct bonding approach, the authors conducted bonding reliability tests for several days and successfully reproduced their experimental results several times. The authors noted tha > 90% of the actuator formed a strong bond with the wing, and this bonding percentage could be further increased by increasing the temperature during bonding. After successfully bonding the MFC actuators to the wings, the authors compared the two bonding approaches. Their results showed that, although the flap approach produced greater displacements, it also made the wing less flexible. By directly bonding the MFC actuator to a metal substrate and then attaching it to the trailing edge of the wing (similar to traditional wing flaps), the authors were able to maintain the flexibility of the wing but observed problems with tension loading at higher wing pressures. As noted by the authors, EP31 played a key role in ensuring the reliability of the direct bonding approach.