The ERATO Programme: Wind Tunnel Results and Proof of Design for an Aeroacoustically Ouptimized Rotor

The bilateral ERATO project between ONERA and DLR had the ambitious goal to design, build, and test a quiet model rotor which is fifty percent less noisy in specific descent and level flight conditions than a reference rotor of current technology (the 7AD ONERA-EC rotor), for a helicopter of the 4 to 6 ton class with the constraints of minimum power and vibration level penalties. this cooperative research effort resulted in a novel aeroacoustically optimized rotor blade design, which was built with extensive pressure and strain gauge instrumentation. Both the ERATO and the 7AD rotor have been tested in the S1 Modane-Avrieux (S1MA) wind tunnel (acoustically lined closed test section) at high-speed and in the DNW (open jet anechoic test section) at moderate and low speed to prove compliance with the objectives and to verify the design methodology employed. The results of both test campaigns together with a preliminary analysis, are presented and the noise reduction potential at improved performance of the ERATO rotor in comparison to the reference rotor is demonstrated.The novel quiet rotor features acoustic gains up to 7 dBA at descent flight and up to 13 dBA at high speed level flight. Furthermore, significant rotor performance gains (up to 12%) were found for high speed level flight, but limited to moderate blade loadings. In summary, the high quality experimental results globally verify the quiet rotor design methodology applied.