Otto Lilienthal is considered to have been the very first aviator, but until now there had been no final proof that his designs were actually airworthy. Now, for the first time, there is video footage of flights performed by a historically accurate replica of the world's first biplane glider, which was designed by Otto Lilienthal. Markus Raffel, who works at the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) in Göttingen, made the flights in California in late July 2019. Raffel built upon the scientific research carried out by DLR to mark the 125th anniversary of the first human flight in 2016, which included testing a replica of Lilienthal’s monoplane glider, including in a wind tunnel. On 18 September 2019, the biplane glider, which was constructed by the Otto Lilienthal Museum in Anklam, was handed over to the museum on permanent loan.
The biplane glider was constructed from authentic materials (willow rods, hemp rope, sailcloth and steel wire) in accordance with Lilienthal's preserved plans and the results of material analyses performed on surviving gliders. Over the course of a year, the biplane was subjected to towing tests using a winch. The flight characteristics determined as a result were used to adjust the rope lengths using turnbuckles, which Lilienthal developed specially for this purpose. The flight tests took place between 21 and 30 July 2019 near the town of Monterey on California’s Pacific coast, which has consistently favourable wind conditions.
"It steered very well from the first take-off, and was forgiving in flight," says Raffel, who piloted the plane. “A slight tendency to turn to the left had to be countered by a lateral weight transfer during the first flight, but over the subsequent days we were able to rectify this by more careful adjustment of the vertical stabiliser and the upper wing struts."
The flights typically lasted 10 to 14 seconds and were limited to distances of about 100 metres due to the surf. The wind came from the west/southwest with very constant speeds of between five and seven metres per second (18 to 25 kilometres per hour). For safety reasons, the flight altitude was restricted to three to four metres above the ground. "The 'Big Biplane' is even safer and better at flying in difficult wind conditions than Lilienthal's famous monoplane glider."
Andreas Dillmann, Head of the DLR Institute of Aerodynamics and Flow Technology at the site in Göttingen, led the preliminary studies. "Markus Raffel has succeeded in making the first well-documented flights in a replica of a Lilienthal glider." The wind tunnel studies performed by DLR had confirmed that the glider had good flight characteristics in theory: "But only a flight test could show that it is actually possible – today, as it was then."
In the same way as 123 years ago, the glider was handed over to a US-American flying enthusiast. Back then, it was flown by Robert W. Wood, who became a renowned physicist and later recalled his meeting with Lilienthal in 1896. Just as before, this summer, a second pilot was able to fly the glider as soon as it had been adjusted for him, with little need for instruction.
On this occasion it was flown by the US stuntman and hang-glider flying instructor Andrew Beem. At 25 kilograms lighter than Markus Raffel and with 25 years' experience of flying hang-gliders, Beem's flights exceeded all expectations. After just a few flights, he was able to take off elegantly, steer, and land with precision.
After Otto Lilienthal's death on 10 August 1896 upon crashing his monoplane glider, his aircraft came under suspicion outside Germany of lacking flight stability and controllability. To mark the 125th anniversary of human flight, which dates back to Lilienthal's first flights in 1981, DLR had the monoplane – which is essentially the lower part of the Big Biplane – tested in the large German-Dutch Wind Tunnel. The results confirmed its good flight characteristics, which paved the way for Markus Raffel to fly the monoplane (Normal Glider) for the first time on the coast of California in 2018. These were the first properly documented flights using the Normal Glider since Lilienthal’s death.
Lilienthal's achievements were recognised and built upon by practically all of the subsequent aviation pioneers, as Bernd Lukasch explains. Lukasch is the Director of the Otto Lilienthal Museum in Anklam, which constructed the glider replica on behalf of DLR. The aircraft owes its success to three achievements – Lilienthal solved the scientific mystery of lift, created a patentable product and taught himself to fly. "The latter feat was recreated and commemorated by Markus Raffel to sensational effect."
Note to editors:
broadcast-quality TV footage can be requested from Jens Wucherpfennig.