Here is an interesting video from the German Aerospace Center (DLR) released in 2021. The Germans built a replica of Lilienthal's final glider from original plans using original materials. In a classic build-up approach, they test it in a wind tunnel, do a tethered flight in the wind tunnel, a tethered flight behind a car, a winch-drawn flight, and finally a free flight down a dune at the beach. Structural engineers should be sure NOT to watch the motions of the tail--they're scary.
You can see the actual hill that Otto Lilienthal built for his glider on Google Maps. The hill is now a monument to Otto Lilienthal. You can use Street View to get a better view of some of the area. If the link doesn't work for you, search Google Maps for "Lilienthal Park Berlin". The hill is no longer suitable for glider flying because of all the trees around it.
- Russ Erb