The Chinese commuter airliner, the ARJ21 is using tight integration between the engine and wing to boost aerodynamic performance.

The plane has a DC-9 configuration (see picture below), and they are hoping to get a 1% increase in l/d ratios by integrating the engines airflow and with the wings.

Essentially, this means that the inlet air to the engines will boost the energy of the airflow over the wing.

It’s an interesting concept, but given the fact that if this aircraft achieves even modest success, there will be stretched variants, where the engines will be further from the wing, one wonders if this technique can still work as the gap between engine and wing grows.