The source document is especially helpful. The overwing engine configuration is unusual because it has been an industry-accepted fact that flow interference (sp

The source document is especially helpful. The overwing engine configuration is unusual because it has been an industry-accepted fact that flow interference (specifically, the conversion of the flow from laminar to turbulent) from the wing as the angle of attack increased beyond a few degrees — which happens during take-off, climb, and landing with wing-aerodynamic braking — would have significant-to-catastrophic effects on the engine's intake. Honda says they managed to find a sweet spot amidst the interference, using computational analysis and wind-tunnel testing. Computational analysis of turbulent flows is much more difficult than laminar flows, and wind-tunnel testing has been traditionally favoured over computational analysis for this reason. Honda also says they made their own airfoil and made the upper-skin extra smooth to keep the flow more laminar between the wing and the engine. This is impressive engineering. EDIT: Just noticed, the document claims the wing had to be made of metal instead of composites " to maintain the contour required for laminar flow".