Airbus patented multi-fan engines, placed directly on the hull of the plane to save space and decrease aerodynamic resistance.
In order to increase the efficiency of propulsion engines applied with a larger diameter. However, you cannot do this without end, because they are placed under the wings of machines where space is very limited. Because Airbus came up with the idea of creating a multi-fan engine, in which the rotation of one will be powered the others. In this way, increase their productivity, and the size will not have much significance, since the whole construction will be attached to the fuselage and not as hitherto to the wings.
Quantity at the expense of the several units
However, this is only one of the concept. The other assumes similar and longitudinal structures located under the wings. Airbus believes that the multi-fan engine is currently the only way to increase the efficiency of the drive units.