Consideration of Tanker’s Wake Flow for Helicopter Air-to-Air Refueling

Kurzfassung

Helicopter air-to-air refueling (HAAR) is a complex maneuver, where usually both the helicopter and the tanker aircraft operate at the limits of their respective flight envelopes; the helicopter at its high-speed limit, and the fixed wing tanker at its low speed limit. To conduct refueling, the helicopter needs to approach and engage with the drogue, attached to a hose behind the outer wing. Typically, this hose is approximately 80 ft in length. In this position the open propeller engines, the high angle of attack and the deflected high lift flaps together create a distinct wake flow topology that might heavily perturb the motion of the helicopter. The paper presents results from an investigation of the tankers flowfield in this low-speed condition and its potential impact on the helicopter at positions that are important for establishing contact. Computational Fluid Dynamics (CFD) Simulations were done to consider the tanker’s wake flow. Based on the results, real-time capable wind fields were implemented within DLR’s Air Vehicle Simulator (AVES) to support pilot studies. It could be shown, that a shifted downwards position of the Helicopter in the pre-contact position would reduce the influences of the tanker’s wake flow. To consider the tanker’s wake flow within the HAAR simulation is found to be essential for an accurate model. Further investigations and pilot studies are planned to assess the difficulty for the pilots between different methods.