Unique counter-rotating design to help mitigate technical risk of integrating engines on to airlifter

Airbus Military has chosen a unique "handed" propeller concept for the A400M airlifter in a bid to mitigate some of the technical risk associated with integrating what will be the West's most powerful turboshaft engines on to the airframe.

Also known within Airbus as the "down between the engines", or DBE, configuration, describing the downward sweep of the blades between each pair of wing-mounted, 10,700shp (8,000kW) engines - the design will ensure a symmetrical airflow over each wing and allow a simpler flap system and smaller horizontal stabiliser and fin, according to the manufacturer. It will also reduce vibration and noise levels in the cargo bay and allow air-drops to be performed more effectively.

The downside is that while the turbomachinery in all four engines will be identical, two engines will require additional gearbox components, a larger oil system and a mirror-image propeller design, increasing support costs.

Airbus Military commercial director Richard Thompson says "concerns had always existed"about rotating all four 5.33m (17.5ft) - diameter propellers in the same direction, after Lockheed Martin hit propwash problems in the C-130J development programme. He adds that adopting the handed approach meant "we had to do a lot of trade-off studies, which we had the resources to do only after launch.

"This is the most effective solution. It is a risk-reduction measure which has been confirmed by windtunnel tests to be the right direction. The impact on cost is marginal in terms of 30-year life-cycle costs."

Production of parts for the first EuroProp International (EPI) TP400-D6 turboprop has begun and first run is scheduled for August next year at MTU Aero Engines' Ludwigsfelde final assembly site. Series production is due to get under way in late-2007 or early 2008.

The engine programme will effectively require two certifications - one for each gearbox/propeller configuration - separated by around three months, says R-R Deutschland TP400 programme director Dr Christian Poensgen. It is expected that the first flight of the A400M, due in October 2007, will be performed with only one of the two engine/gearbox-propeller configurations certificated.

Source: Flight International