Airbus Industrie has begun trials of an A340 set up to fly with reduced stability margins as part of its drive to validate technology for the proposed 550-seat A3XX.

Ina recent initial trial, the natural stability of the A340 was reduced by transferring fuel between tanks so that the airliner's centre of gravity was moved aft of the point of neutral stability. The move means that less downward force needs to be applied by the horizontal tailplane to maintain the aircraft in stable flight, reducing the size, weight and drag of the surface.

One technology being considered for the A3XX is a non-mechanical back-up fly-by-wire flight control system (Flight International, 24-31 March). This would have a level of integrity such that stability margins could be reduced below those of current airliners.

Such a move would enable the area of the A3XX horizontal tailplane to be cut by 10% from 200m2 (2,150ft2), reducing trim drag by about 0.5%, says Airbus. This will save 700kg (1,500lb) and help to lower direct operating costs to 15% below those of the Boeing 747-400 - the level required for programme launch. More A340 flights are set for this month.

Source: Flight International