An Airbus R&D programme launched to try and solve some of the issues linked to refuelling helicopters from the A400M should achieve its flight test phase before the end of this year. The R&D programme was launched after it emerged that the fuel hose needed to be longer. Because the helicopter pilots cannot see the A400M’s tail while they are refuelling they were uncomfortable not only with the proximity of their rotor blades to the aircraft but also how buffetted they were in the strong turbulence behind the A400M.
As a result the fuel hose will be extended from 80ft to 120ft. “However, this extra length causes oscillations in the hose,” explained Miguel Ángel Morell, Airbus Head of Engineering, at a media briefing in Munich today. “That means we have to make the hose thinner,” he said. This is because the overall mass of the hose has to remain the same so if it is 1/3 longer it has to be proportionately thinner so that the drum it rolls around can hold it all once it is drawn back into the aircraft body. That also means that the amount of fuel able to flow through the hose will be lower and that it will therefore take longer to refuel an aircraft than with the thicker hose.
So, why were these considerations not thought of when the aircraft was being designed? According to Morell the change is being made at the request of helicopter pilots because in theory there is enough room between the A400M’s tail and helicopter rotors for safe refuelling. With the original design, commercially available fuel hoses could be used and these are manufactured to a maximum length of 95ft. “This means the new hose will have to be made specifically,” Morell added. And presumably that will make it more expensive.
The R&D programme is in two phases, the first consisting of advanced simulation and modelling to check hose stability and hose response behaviour, and the second of wind tunnel testing. The latter has been undertaken at the French Onera laboratory facilities and the aerodynamic assessment of the data generated is on-going.
Once the R&D programme is completed a flight test programme will follow to fully validate the results. Morell said the “target is to proceed with a flight test proximity testing before the end of 2016.“