Martin K. Sekula

Analysis of a Multi-Flap Control System for a Swashplateless Rotor

An analytical study was conducted examining the feasibility of a swashplateless rotor controlled through two trailing edge flaps (TEF), where the cyclic and collective controls were provided by separate TEFs. This analysis included a parametric study examining the impact of various design parameters on TEF deflections. Blade pitch bearing stiffness; blade pitch index; and flap chord, span, location, and control function of the inboard and outboard flaps were systematically varied on a utility-class rotorcraft trimmed in steady level flight. Gradient-based optimizations minimizing flap deflections were performed to identify singleand two-TEF swashplateless rotor designs. Steady, forward and turning flight analyses suggest that a two-TEF swashplateless rotor where the outboard flap provides cyclic control and inboard flap provides collective control can reduce TEF deflection requirements without a significant impact on power, compared to a single-TEF swashplateless rotor design.

Optimization of an Active Twist Rotor Blade Planform for Improved Active Response and Forward Flight Performance

Abstract A study was conducted to identify the optimum blade tip planform for a model-scale active twist rotor. The analysis identified blade tip design traits which simultaneously reduce rotor power of an unactuated rotor while leveraging aeromechanical couplings to tailor the active response of the blade. Optimizing the blade tip planform for minimum rotor power in forward flight provided a 5 percent improvement in performance compared to a rectangular blade tip, but reduced the vibration control authority of active twist actuation by 75 percent. Optimizing for maximum blade twist response increased the vibration control authority by 50 percent compared to the rectangular blade tip, with little effect on performance. Combined response and power optimization resulted in a blade tip design which provided similar vibration control authority to the rectangular blade tip, but with a 3.4 percent improvement in rotor performance in forward flight. Background Active rotors have been studied as a potential solution to a diverse range of problems plaguing rotary-wing vehicles. Numerous analytical and experimental studies have provided encouraging results indicating that vibration, noise, performance, as well as other issues may be successfully addressed through the use of trailing edge flaps, gurney flaps, active twist, and other active control concepts [1-11]. Some of these studies have also exposed potential limitations of active concepts – the inability of current state-of-the-art actuators to meet the control requirements necessary to fully achieve the potential benefits [11]. Volumetric constraints and the challenges of operating in a rotating environment have led to a considerable effort being dedicated to maximizing actuator control authority through mechanical amplification and optimization of actuators, control surfaces, and structures [12-16]. The current approach to address the aforementioned control authority problem begins with viewing the problem from a different perspective. Instead of redesigning an actuator, control surface, etc., to improve its deflections or its application force to provide more control authority over a problem (vibration, noise, etc.), this study examines how a rotor blade tip can be designed to improve the blade response to an actuator input and thereby achieve the required control authority without more stringent actuator requirements. Previous work on active-twist rotor designs have examined the effect of various structural parameters on blade response and rotor power [17, 18]. Optimization of the blade structure and actuator positioning has also been performed [12, 13]. Finally, a limited, but more pertinent, parametric study examining the effect of blade tip sweep, taper, and anhedral on rotor vibration, performance, and response has been conducted previously [19]. The present work will expand on these results by performing an optimization study of a more complex blade tip planform than considered previously. While there have been multiple blade planform optimization studies conducted previously, they have examined the aerodynamic design in an effort to improve performance, reduce noise, reduce vibration, or some combination of these goals [20-23]. None have specifically dealt with active control improvements. The ultimate goal of this study is to develop a proof of concept for employing the blade tip design to improve the control authority of an active rotor – in this case study, an active twist rotor – and with this proof of concept identify limitations of the general approach and areas for further research and development.