The "RONAP" Aeroacoustic Flight Tests with a Highly Instrumented BO 105 Helicopter

Within the joint DLR/ONERA Research Concept 2 "The Quiet Rotorcraft", a very comprehensive flight test, called RONAP (Rotorcraft Operational Noise Abatement Procedure), with a fully instrumented BO 105 helicopter was conducted at Cochstedt Airport (Germany), in October 2001, with the objective to generate a high quality aerodynamic and acoustic database for (1) the design of low noise flight procedures, for (2) the validation of aerodynamic and acoustic prediction codes and for (3) the verification of the equivalence of scaled model rotor wind tunnel and full scale flight test results. DLR provided its experimental BO 105, equipped with pressure instrumented main and tail rotors (respectively 88 and 32 sensors), a nose boom mounted 7-hole probe, a DGPS system and a complex data acquisition system to synchronously measure, digitize and store the aerodynamic blade surface pressures of main and tail rotors, the operational, attitude and flight path data. Synchronized by GPS time, the flyover noise was simultaneously acquired by two extended microphone chains (600 m wide), each consisting of 11 ground microphones (operated by DLR and ONERA, respectively). The test matrix covered numerous steady flight conditions focused on descent with variation of airspeed (20 to 117 knots) and of descent angle (1.5° to 15°), but also included climb and level flight conditions and a number of transient, acclerated (maneuver) and decelerating flight procedures. The paper presents the test equipment, site, procedures and matrix. It provides typical sample results especially on the 6-degree descent flight. It addresses preliminary results on the wind effects on the difference between the geometric glide slope and the aerodynamic glide slope, and on the effect of the glide slope (up to 15 degrees) on noise level contours, at two speeds.