Actively Controlled Flap
The Actively Controlled Flap (ACF) is a closed-loop flow control device, which is installed at the outboard portion of the blade with a primary role of altering its aerodynamics so that vibration and/or noise reduction can be achieved.
The Actively Controlled Flaps are generally 15% of a chord length and are located between 65~85% radius of the blade, as it has been identified by Dr. Daniel Feszty in 2004 and Dr. V. Kloeppel and B. Enenkl in 2005.
The Actively Controlled Flap is a success technology of an active control systems aiming to reduce vibration and/or noise in helicopters, and it received great attention form the rotorcraft industry.
The SRS’ Actively Controlled Flap underwent an evolution process eliminating tens of parts and receiving a new 3rd Generation design. The new design simplifies its installation on the blade and improves performance in comparison to its predecessors. The unique new concept has no moving parts and is externally mounted, thus allowing easy maintenance and replacement.
The desired actuation frequency shall be of at least (N+1) per revolution, where N stands for number of blades, which was computationally identified by Daniel Feszty in 2004, Greg Davis in 2005 and Fatma Demet Ulker in 2011.
The desired flap deflection amplitude should be as large as possible, but what is commonly achievable nowadays is rather in the range of 4-6 degrees.
The new 3rd Generation ACF was assembled and tested in static setting and showed 6 degrees deflection at 90 Hz and 4 degrees of deflection at 133 Hz