Originally Posted by Bucking Bar

My insights into Douglas came from a number of friends who worked there in flight test. The Company's reluctance to spend money on engineering, only to spend a fortune on fixing the finished product can still be seen today in the 787 program (post merger with Douglas).

There is no advantage to the wing other than the tooling was already built. Douglas had hoped Chinese production would result in a huge MD8X/90 order from the Chinese, but that never happened. The Chinese kept the fuselage jigs and eventually had the Russians design a better wing for their ARJ-21.

The DC9 wing was OK for what it was designed to do, when it was designed to do it. Today it is a near textbook example of every error that could be made as it approaches trans sonic speeds. Mach airflow separation begins at about M 0.745. Drag increases exponentially beyond that point.