A Comprehensive Survey of Individual Blade Control Emphasizing Recent Implementations

Helicopters encounter several constraints such as high vibration and noise levels, and relatively high fuel consumption in high-speed forward flight that have limited their success. Individual Blade Control (IBC) has proven to be effective in alleviating some of these deficiencies. IBC has been implemented using different approaches such as: (1) blade root actuation, (2) trailing edge flaps, (3) active piezoelectric fibers in the form of an active twist, and (4) deployable microflaps. This survey paper focuses on IBC emphasizing the most recent and promising implementations that appear to have the potential of eventually being in-stalled in a production vehicle. Thus only the last three implementations mentioned are considered in detail. The paper starts with a brief survey of the vibration and noise issues. Next, the paper summarizes important findings obtained during wind tunnel and flight tests using blade root actuation technology. These findings motivate the current research. Comments on the algorithm known as the Higher Harmonic Control (HHC) approach are made. This ap-proach works well for all actuation concepts. The HHC algorithm has been implemented in several versions either in the frequency domain or in the time domain, and it also has several variants such as relaxed and adaptive. It works well for both, vibration and noise reduction. Other possible extensions of the algorithm to performance enhancement are mentioned. The most useful results obtained in previous studies are summarized. The paper concludes with the principal lessons learned