On this page
Before anyone could fly an aeroplane, someone had to find out how wings behave and then prove it by flying. Otto Lilienthal did both. His measurements and his glides between 1891 and 1896 gave later inventors data and confidence. This post covers who he was, what he measured, how he flew, a worked example on glide ratio and power, common mistakes, and what you can take from his way of working.
Who was Otto Lilienthal?
The Otto-Lilienthal-Museum in Anklam, his home town, gives his birth there on 23 May 1848. At grammar school he studied mathematics under the astronomer Gustav Spörer. He trained at the technical school in Potsdam and then at the Royal Technical Academy in Berlin from 1867 to 1870. His first experiments on flight date from 1867. He worked all his life with his brother Gustav.
He earned his living as an engineer. The museum says his first patent, in 1877, was for a mining machine, the first of 25 patents, four of them in aviation. In 1883 he founded a company in Berlin making boilers and steam engines, and in 1890 he introduced a 25% profit-sharing scheme for its workers.
What did Lilienthal measure?
The National Air and Space Museum says that in the 1870s he tested wing shapes and gathered air-pressure data using a whirling arm and in the natural wind, producing "the best and most complete body of aerodynamic data of the day". He established that a curved wing section generates lift better than a flat surface. In 1889 he published the results as Der Vogelflug als Grundlage der Fliegekunst (Birdflight as the Basis of Aviation). The Anklam museum adds that an English translation appeared in 1911.
How did he fly?
Lilienthal did not stop at the data. The museum's timeline records jumps and flights of about 80 feet near Potsdam in 1891, glides of up to about 800 feet in the Rhinow Hills in 1893, and an artificial hill, the Fliegeberg, built near his home in Lichterfelde, Berlin. In 1894 he began making his "Normal Glider" in series. In 1895 visitors included S. P. Langley of the Smithsonian and the Russian aerodynamicist N. J. Zhukovsky.
The National Air and Space Museum says he made close to 2,000 brief flights in 16 different designs. Most were monoplanes with a tail at the rear, and he controlled them by shifting his body weight forward, back and sideways. The museum's own glider, built in 1894, is made of wood, cotton and hemp cord, and its wings fold for storage.
On 9 August 1896 he crashed after failing to steer a Normal Glider through a gust of rising warm air, the Anklam museum says, and died in Berlin the next day. The Anklam museum's introduction to Lilienthal says his research and flights inspired the Wright brothers, whose story our post on the Wrights' first flight picks up.
Worked example: glide ratio and the power a hill supplies
Sample numbers: glider and pilot together have a mass of 100 kg. On one glide they lose 20 m of height while covering 150 m horizontally, at a steady airspeed of 10 m/s. Take g = 9.8 m/s².
Glide ratio. Horizontal distance / height lost = 150 / 20 = 7.5.
Glide angle. tan θ = 20 / 150 = 0.133, so θ = 7.6°.
Why this equals lift over drag. In a steady glide the forces balance. Along the flight path, drag D = mg sin θ. At right angles to it, lift L = mg cos θ. So L/D = 1/tan θ = 7.5. A better wing gives a flatter glide.
Sink rate. The vertical part of the velocity is v sin θ = 10 × sin 7.6° = 1.32 m/s.
Power from gravity. Potential energy is lost at mg × sink rate = 100 × 9.8 × 1.32 = about 1,300 W.
So in this example, staying in the air at 10 m/s costs about 1.3 kW, and the hill pays for it by giving up height. To fly level, an engine would have to supply at least that much power, more once propeller losses are counted. That is the gap between gliding and powered flight.
What mistakes do students make with problems like this?
Using the path length for the glide ratio. The ratio uses horizontal distance. At small angles the difference is small but not zero.
Using the full speed for the power. Gravity's power is mg times the vertical component of velocity only.
Treating lift as vertical. Lift is at right angles to the flight path, which is tilted in a glide.
Mixing units. Convert km/h to m/s before multiplying.
The JEE (Main) 2026 syllabus covers equilibrium of concurrent forces in Unit 3 and power in Unit 4, which is all this example uses. Wing theory itself is beyond the syllabus. Our post on George Cayley and lift and drag shows where the idea of splitting the air's force came from.
If you want to see how angle and forces change together, the Fermi Simulation Lab has interactive simulations for ideas that are easier to see than read.
What can a student take from Lilienthal's way of working?
Measure before you build. Years of whirling-arm tests came before his first glide.
Progress in small steps. From 80-foot hops to 800-foot glides took two years of practice.
Publish what you find. His book let others start from his data instead of from nothing.
Next step: work out the glide ratio, angle and power for a glider that loses 15 m over 180 m at 12 m/s.
