Modern helicopters are equipped with rotor blades with exposed linkages, swashplates, and mechanical components. While such rotor blades have proved to be highly reliable, they are the leading cause to generate noise and vibration. In addition, the drag due to exposed linkages and hinges affects the helicopter performance. To overcome these issues and improve flight quality, researchers have worked on various techniques. One promising way to mitigate noise and vibration and replace the conventional control mechanism of the rotor blade is to use a trailing edge flap. Additionally, having a morphing trailing edge flap brings the opportunity to enhance rotor performance with even better flow quality over the rotor blade surface and is potentially lightweight. Consequently, the actuation of amorphing flap at higher frequencies helps tomitigate noise and vibration. However, morphing solutions are generally hard to implement even for fixed-wing aircraft because of the conflicting requirements of flexibility, strength, and weight. For rotorcraft, the concept to the physical realization of morphing solutions is even more challenging due to the complex loading environments, smaller blade volumes, and centrifugal forces. This is the first issue that the author tries to address with the present dissertation, i.e., to design, develop and do a feasibility study of an active trailing edge camber morphing system for rotorcraft....@en

This paper presents an overview of the design and validation of a novel passive camber morphing system for rotorcraft. The passive system works for a variable speed rotor where a potential increase in pilot control authority and power reduction is possible. In the proposed concept, the rotor speed is varied by 10% to change the apparent centrifugal force which is used to morph a trailing edge flap by a mechanical system. In this context, the important design parameters in relation to the passive morphing concept are introduced, after which the working principle of the concept is explained. The design and development of the test demonstrator, experiments in a whirl tower setup, and test findings are also presented. The results indicate that a passive trailing edge morphing concept is feasible and has the potential to be used in a variable speed rotor to achieve the desired performance benefits.@en

This paper discusses the development and whirl tower testing of an active translation induced camber morphing system for rotorcraft. The system deploys the morphing flap based on the amplitude and type of the input signal. As a case study, a demonstrator is developed and tested primarily under the centrifugal force generated by a whirl tower setup. The actuation system consists of amplified piezoelectric actuators, while the morphing skin is made out of carbon fiber prepreg composite material. The response of the morphing skin and the actuators is measured and compared to the numerical studies used to design the morphing demonstrator. Results indicate that the response of the active system, including the actuators and the flexible skin, matches well to those predicted during the numerical studies. The outcome of these studies shows that the system has the potential to be used for the primary control of the rotorcraft if operated at 1/revolution or for mitigating noise and vibration if operated at 2/revolution or higher frequencies. Subsequently, the concept can be integrated into a Mach-scaled rotor blade which can be tested under both aerodynamic and centrifugal loads to further assess its performance.

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This paper presents an overview of the preliminary design process and findings aimed at morphing of trailing edge (TE) control surfaces for rotorcraft. A design methodology for a camber morphing control surface is presented, although twist can also be induced by applying differential camber of the morphing section span. The concept investigated relies on utilizing conventional aircraft structures and materials for morphing purposes; thus, in essence, has the potential to fulfil the conflicting requirements of lightweight, flexibility and strength at the same time. Based on this concept, the preliminary design work shows that an active trailing edge camber morphing mechanism can be designed after careful considerations of design and actuation requirements. The numerical results presented also indicate that such a morphing scheme increases the 2D aerodynamic efficiency.@en

Rotor morphing has been investigated in the past for improvement of rotor performance, either for reduction of rotor power demand or for vibratory load alleviation. The present study investigates the application of camber morphing for improvement of rotor performance in hover and vertical flight conditions, with a particular focus on the combination of camber morphing systems and variable RPM rotors. Camber morphing utilizes a smooth flap at the trailing edge of the rotor blade to modify the camber of blade airfoil sections without excessive drag penalties. Two different camber morphing systems will be investigated in this study, namely the active and passive systems. Passive camber morphing, which combines camber morphing with the variable speed rotor concept is the unique aspect of camber morphing which will be the primary focus of this study. The active system can be actuated at frequencies higher than 1/rev of the rotor and requires external power input for functioning. The passive system can be controlled only by varying the RPM of the rotor and requires no additional energy input. Therefore, the passive system is expected to show larger net performance benefits. Variable RPM rotors in themselves show potential towards the reduction of rotor power demand but are largely ineffective for low-speed applications. The combination of camber morphing and the variable speed rotor shows larger performance benefits than those obtained from the two technologies independent of each other. The two technologies, when combined in passive camber morphing, can remedy each other's deficiencies and improve the overall rotor performance. The use of camber morphing shows more benefit for operating points at or near the edge of the flight envelope since the rotor blade sections encounter high average angles of attack for these operating points. Vertical climb and hover at high altitude are examples of flight conditions investigated. Overall, passive camber morphing shows a larger performance benefit as compared to the active system.

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