Wind-Tunnel Assessment of the Concept of Active Flaps on a Helicopter Rotor Model

In December 2005 was tested in ONERA S1 Modane large wind-tunnel a Mach-scaled four-bladed helicopter rotor model, each blade featuring a trailing edge active flap. This test was part of a research project launched in 1998, called DTP RPA (Développement Technique Probatoire Rotor à Pale Active) or ABC (Active Blade Concept) project, in cooperation between ONERA, Eurocopter, DLR and Eurocopter Deutschland. The main objective of this wind-tunnel test was to demonstrate for a large flight domain the interest of such an active device to decrease the vibratory level generated by a helicopter main rotor. As an off-side aspect, the acoustic characterization of such a rotor could be documented. The rotor model was highly instrumented in order to allow a thorough analysis of the physical phenomena involved in the aeroelastic behavior of a flap-equipped rotor. After a description of the rotor model, of the flap control system and of the wind-tunnel test arrangement, an analysis of the experimental results related to aerodynamics, aero-acoustics and dynamics of the active flap concept is presented in details.