HHC or IBC anywhere near production?

[Reely340]

I stumbled over the concepts of Higher Harmonic Control (HHC) and the even more sophisticated Individual Blade Control (IBC). HHC seems to superimpose a well triggered, synchronous "rattling" on the swashplate at frequencies of 2/rev or higher (on the stationary side of the swashplate) , and IBC does the same on the revolving side, essentially changing blade pitch link length, individually for each blade, multiple times per rev.

The goal is (external) noise and vibration reduction.

I find the idea of rocking the swashplate at such high frequencies - even if only for +/-1° angle of attack - rather scary, given the forces the swashplate's bearing must withstand due to inertia of blades around their pitch axis. Actuating the individual pitch links sounds even more interesting, considering that fact that they ride around the mast a couple hundred times per second.

Apparently the Germans tortured a good ol' BO105, with promising results: http://ftp.rta.nato.int/public/PubFullText/RTO/MP/RTO-MP-051/MP-051-PSF-30.pdf


Is any of these concepts aready deployed on a production helicopter, yet?

[riff_raff]

I find the idea of rocking the swashplate at such high frequencies - even if only for +/-1° angle of attack - rather scary, given the forces the swashplate's bearing must withstand due to inertia of blades around their pitch axis.I have seen a couple different IBC concepts with the capability for HHC that have been tested on rotor stands, however none of them involved rocking the swashplate at high frequencies. I've seen small displacement, high-frequency linear EHA devices that replaced the pitch link between the swash plate and blade, such as this concept tested by NASA (http://rotorcraft.arc.nasa.gov/publications/files/Jacklin_AHSF02.pdf), which is intended for HHC function only. I have also seen a more recent concept from ZF for a rotary EMA device mounted directly to the hub, which provided both IBC and HHC functions, but I can't find a link for it.

Here's a interesting presentation from ZF (http://www.mp.haw-hamburg.de/pers/Scholz/dglr/hh/text_2004_10_28_Hubschrauber.pdf) covering some of the linear EHA concepts they developed for high-frequency blade control on existing rotorcraft such as CH-53 and UH-60.