Tunnel-in-the-Sky Display for Segment-Wise Measurement of Helicopter Noise in Repetitive Approaches

Abstract

Noise emission is a limiting factor for helicopter operations. Additional to new helicopter designs, optimized flight procedures can reduce the noise level perceived on the ground. The advantage is that optimized procedures can make approaches with already existing helicopter types quieter with no engineering effort. The German Aerospace Center (DLR) has gained experience in optimizing noise abatement procedures during projects such as PAVE and Friendcopter. This research is continued under the funding of JTI Clean Sky GRC5. DLR’s computational chain SELENE is used for optimizing helicopter approaches. The outcome of this tool is a three-dimensional approach path with prescribed velocity profile. Noise critical flight parameters such as pitch angle and rotor torque can also be optimized. In order to measure the noise footprint of an approach usually a large area along the approach direction is equipped with microphones. In order to reduce the operational effort of setting up and monitoring the equipment, a different measurement method was selected for the current flight test campaign. Fewer microphones are placed in a smaller area, preferably inside the controlled area of an airport. In order to measure the full length of the optimized procedure, the helicopter flies the approach multiple times with shifted landing points. For this measurement method the pilot must fly the same procedure repeatedly with high accuracy while following the noise critical target parameters. It is of utmost importance to provide the pilot with appropriate guidance to fulfil this task. For this purpose a tunnel-in-the-sky guidance display was developed for usage in DLR’s research helicopter ACT/FHS of type EC135. It allows the pilot to intuitively understand the geometrical evolvement of the flight path. At the same time the overlaid primary flight display gives information about target airspeed, pitch angle and rotor torque. The display as well as the measurement method have been tested in first flight trials where a reference procedure has been evaluated. They have proven their applicability and will be used for future noise abatement flight test campaigns.