Hybrid tests of contact events in air-to-air refueling

Air-to-air refueling is a vital technique for extending the range and endurance of manned or unmanned aircraft, with over 1000 refueling procedures flown per day in military operations. The hardware used for air-to-air refueling needs to be tailored to the specific aircraft and airspeeds involved, performing markedly different for permutations of tanker and receiver craft. Extensive flight testing is costly and risky to equipment and personnel, but laboratory testing is marred by unrepresentative test conditions. This Paper presents the first full-scale hybrid test of an air-to-air refueling probe and drogue contact, where physical refueling hardware in the laboratory is coupled to a numerical simulation of the remainder of the system using sensors and actuators. It is found that the forces and motion trajectories faithfully capture the characteristic drogue response dynamics in full refueling scenarios. Rigorous validation shows that the method can emulate the dominant contact-impact phenomena observed in air-to-air refueling scenarios with high repeatability, including problematic design-critical responses such as drogue tipping and hose whip. With the costs of equipping a tanker fleet standing around 500 million, the technique offers an important means of laboratory testing to inform design iterations, reducing development timescales and costs, as well as improving safety and reliability before flight testing.