Highly Instrumented BO105 and EC135-FHS Aeroacoustic Flight Tests Including Maneuver Flights

Aeroacoustic flight tests have been performed on the two highly instrumented DLR helicopters, the BO105 and the EC135-FHS, in order to generate a noise data base for noise abatement flight procedure design and optimization. The instrumentation of the helicopters covered all the noise relevant flight parameters including freestream velocity probes at the tip of nose booms. On the BO105 the pressure of a main rotor blade was measured using 79 sensors and another blade was equipped with 11 strain gauges for flapping motion measurement. The noise was measured on ground using 43 microphones operated using a new wireless acoustic measurement system and distributed on an 800 m diameter disk. Instantaneous noise directivities from maneuver flights could as well be measured as steady flights directivities. The tests comprised steady flights at various velocities and aerodynamic slopes, up to 20 deg in tailwind descent flight. A series of maneuver flights was also measured: turns, turn roll-in, turn roll-out, begin and end of descent… About 350 flights were performed including some entire landing and take-off procedures. Preliminary acoustic results comparing left and right turns and steep descent flights of both helicopters are provided.