http://gizmodo.com/why-is-the-first-ever-production-aircraft-in-a-modern-w-1776209810

Otto Lilienthal was the first human to develop and create a
production aircraft, going on to make over 2,000 well-documented gliding
flights. But now, 125 years on, a model of his creation is inside a modern wind
tunnel.

Lilienthal studied how birds fly in fine detail before making the first flight
using his patented hang glider in 1891. Now, researchers at the German Aerospace
Center, DLR, have put a replica of the world’s first production aircraft inside
the Large Low Speed wind tunnel at the DNW facility in Marknesse, the
Netherlands, to study his approach. “125 years ago, aviation pioneer Lilienthal
flew for the first time with his glider,” they explained when I asked them about
the spectacular experiment on Twitter. “We want to find out why and how it
worked.”