Hybrid Control

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The SHARCS blade with three independent control systems.

Smart Rotor Systems Inc. (SRS) presents the first in the world commercial, novel and patented “Smart Hybrid Active Rotor Control System (SHARCS)” for reduction of vibration and noise in helicopters. The unique benefit of this Hybrid Control concept is its ability to reduce both vibration and noise simultaneously by employing two independent SRS control systems: the Active Pitch Link (APL) together with either the Actively Controlled Flap (ACF), Active Twist Rotor (ATR) and/or Actively Controlled Tip (ACT).

The major advantage of any actively controlled system is its adaptability, i.e. its ability to control vibration (or noise) at various flight regimes. This is accomplished by adaptively changing the actuation schedule of control systems as the flight regime changes. Dr. V. Kloeppel* showed in 2005 that actuation schedule is different for reduction of different types of vibration (i.e. Blade Vortex Interaction (BVI) vibration, cabin vibrations, rotor imbalance vibrations) as well as noise (i.e. BVI noise). This study shows that  with one single system (such as the Actively Controlled Flap), one cannot control two phenomena at the same time. For example, cabin vibrations and BVI noise could not be reduced at the same time. What worse: in many cases not just that one cannot control two phenomena at the same time, but when one phenomena is reduced, the other becomes deteriorated, e.g. when vibration is reduced, noise increases up and vice versa, as was shown by D. Roth** in 2007 and F. K. Straub*** in 2009. This could seriously question the value of adding a control system to a helicopter.

The proposed hybrid control concept aims to address this shortcoming. It builds on that theorem of control theory that in order to meet two control objectives one needs to employ two independent control systems. Therefore, the basic idea of “hybrid control” is to use two or more independent control systems on a single rotor blade. Thus, when one is optimized to reduce vibration, the other one can be optimized to reduce noise or yet another mode of vibration (such as cabin vibration or rotor imbalance). Thus, the hybrid control concept promises to achieve simultaneous reduction of vibration and noise.

A specific aspect of the hybrid control concept, proposed by the Co-founders of SRS, is that it is based on combining not just two flow control systems (i.e. any two of the ACF, ATR, ACT) but a flow control and a structural control system, where structural control means “stiffness control” of the blade root – Active Pitch Link. Furthermore, hybrid control concept promises to improve the efficiency of Flow Control devices by adaptively lowering the torsional stiffness of the blade with the aid of a Structural Control device.

Smart Rotor Systems Inc., in collaboration with Carleton University’s Rotorcraft Research Group, is currently integrating active control systems (APL, ACF & ACT) into a scaled composite rotorcraft blade. Whirl Tower testing of a fully integrated – with active control systems – scaled composite rotorcraft blade is planned to take place in May of 2012 at SRS’s Whirl Tower Test Facility.

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* Kloeppel, V. and Enenkl, B. (2005). Rotor blade control by active helicopter servo flaps. International Forum on Aeroeleasticty and Structural Dynamics, Munich, Germany. Paper no. IF-158.

** Roth, D., Enenkl, B., and Dieterich, O. (2007). Active rotor control by flaps for vibration reduction-full scale demonstrator and first flight test results. Proceedings of the 32nd European Rotorcraft Forum, Maastricht, The Netherlands. pp. 801-814.

*** Straub, F. K., Anand, V. R., Birchette, T. S., and Lau, B. H. (2009). Smart rotor development and wind tunnel test. Proceedings of the 35th European Rotorcraft Forum, Hamburg, Germany. pp. 413-430.

 

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