Airbus Enhances Safety for Boom and Drogue Refueling

 - December 11, 2020, 6:10 AM
Airbus conducted the first fully automatic air-to-air refueling of a fighter in early 2020, using a Republic of Singapore Air Force A330 MRTT refueling a Portuguese air force F-16. (Photo: Airbus)

Airbus has developed a new system for its A330 Multi Role Tanker Transport (MRTT) that enhances safety for receivers using the aircraft’s wing-mounted and fuselage hose-drogue units (HDUs). The system comprises a sensor that monitors the length of hose that is deployed from the HDU, and a circular LED light array. In the wing pods the array is mounted in the rear tip of the pod, easily visible to the receiver pilot.

One of the challenges for the pilot of probe and drogue refueling is maintaining the aircraft at a similar speed as the tanker during contact, and therefore the separation between the two. Inevitably the receiver moves forward and aft by small amounts relative to the tanker while in contact, the HDU taking up slack in the hose or paying it out in compensation.

However, if the movement becomes too great there are undesirable effects. If the receiver lags behind too much the hose reaches its full extension and disconnects. If the receiver is overtaking it can become dangerously close to the tanker. The LED array acts as a “traffic light” array, showing green if the receiver is within the optimum separation “window”. As the outer edges of the window are approached the LED display changes to yellow to warn the pilot. If the window is exceeded the lights turn red to warn of impending disconnect or danger. The system has been trialed using F/A-18 Hornet receivers from the Spanish air force, and pilots have universally praised the system and its enhancement to safety.

In the meantime, Airbus is planning to certify its automatic air-to-air refueling (A3R) boom tanking system next year, with the Republic of Singapore Air Force as the first customer for the system. Developed as part of the Smart MRTT program, the A3R system uses algorithms in the tanker’s external vision system to accurately plot the location of the receiver, and to then automatically “fly” the refueling boom into the correct position for the boom to be extended to connect with the receiver’s receptacle, and then disconnect at the end of the process. The accuracy of boom positioning is reported to be in the order of “a couple of centimeters”.

While fully automatic refueling has obvious applications to the replenishment of unmanned air vehicles, including the Remote Carriers proposed for the FCAS project, it also significantly enhances safety, with the air refueling operator remaining fully in the loop to monitor the operation and override it if necessary. The eventual aim is to progress A3R technology to a fully autonomous level.

Airbus began flight-testing A3R in March 2017 using the company’s own A310 MRTT testbed and an F-16 receiver. This was followed by tests in June 2018 with a large receiver, a KC-30A of the Royal Australian Air Force. In February, Singapore agreed to collaborate with Airbus on the Smart MRTT, and one of the air force’s A330 MRTTs has been used for trials. In the spring the aircraft conducted a 45-hour campaign and successfully performed 120 dry contacts with a Portuguese F-16 receiver across the whole refueling envelope.