Just curious how the A350 reduces drag/fuel burn by extending the flaps ever so slightly during cruise. Everything I've read about extending flaps says that extending them pushes the centre of pressure rearwards. This causes a pitching down moment, which means you need to increase the AoA, but this affects drag and fuel burn negatively (a pitch up command increases the down force from the tailplane which has the result of increasing the effective weight of the plane, which requires an even higher AoA to compensate, which also increases the induced drag).
Here's how it works as per the (A350 Flight Deck and Systems Briefing for Pilots)
Differential Flap Setting and Variable Camber
The Differential Flap Setting and Variable Camber enable to optimize the loads and drag on the wings.
Small flaps deflections (4° maximum) either symmetrically or asymmetrically, enable to automatically:
- Optimize the wing camber to reduce wing loads and drag
- Perform an optimized Lateral Trim function.