Helicopter Rotor Boundary Layer Transition Measurement in Forward Flight Using an Infrared Camera

Boundary layer transition measurement was demonstrated using differential infrared thermography on the top side of a helicopter rotor in forward flight. The tests used a FLIR X8500xc SLS long wave infrared camera to observe the DLR EC135 test helicopter rotor. The boundary layer transition was detected for hover out of ground effect (150 ft) and for forward flight at 80 kt (1700 ft). The measured boundary layer transition positions are consistent with previous measurements of the EC135 hovering in ground effect, and with predicted boundary layer transition positions. A