Summarize an article about Aviation Pioneer Otto Lilienthal in less than 50 words.
Otto Lilienthal, an aviation pioneer born in Germany in 1848, built and flew unpowered gliders to demonstrate the concept of heavier-than-air flight. His research methods were used to develop the world's first manned aircraft. Lilienthal studied bird flight and built winged vehicles, while also working as an engineer and patenting devices in various fields. He earned 25 patents, four of which were aviation-related.