Otto Lilienthal's Fliegeberg

[lethargic_man]

Most people probably think of the Wright brothers as the first to successfully pull off powered heavier-than-air flight, but the reality is more that they were the first to reach the finishing line, so to speak, without succumbing to an aviation disaster along the way.

Amongst those who were ahead of the Wright brothers in the field was the British aviation pioneer Percy Pilcher, who was planning a trial flight with a motor-driven aeroplane in 1899 when a strut broke on his hang-glider and he plunged to his death. (Some of you might have, along with me, seen a fascinating Horizon about him in 2003.)

But Pilcher in turn had his researches influenced (as did the Wright brothers) by German aviation pioneer Otto Lilienthal, who was the first to fly a heavier-than-air aircraft, after studying (and publishing a book on) the avian wing as the basis for artificial flight. Lilienthal developed eighteen different glider types, and carried out more than two thousand flights, but died when he was unable to recover his hang-glider from a stall in 1896.

Lilienthal used the rubble from a brickworks near where he lived in Lichterfelde, near (now in) Berlin, to construct a 15m high hill from which to conduct his flights, and I went for a look at it as part of a bike ride the other day.

The area was converted to a park in 1900, and the brickworks' quarry turned into a carp pond.

A monument to Lilienthal was erected in 1932 atop the hill; the bronze globe is a replacement of the original, which was melted down during the War.

Here's the view from the top.

Leicht ist es wahrlich uns Menschen nicht gemacht, frei wie der Vogel das Luftreich zu durchmessen. Aber die Sehnsucht danach lässt uns keine Ruhe; ein einziger großer Vogel, welcher über unserm Haupte seine Kreise zieht, erweckt in uns den Wunch, gleich ihm am Firmament dahinzuschweben.

It is truly not made easy for us humans to sweep, free as a bird, through the airy realm. But the desire for it leaves us no rest; a single large bird describing its circles above our heads awakes in us the wish to float along in the firmament like it.

—Otto Lilienthal, „Weshalb ist es so schwierig das Fliegen zu erfinden“, in Prometheus Nr. 261, Berlin, 1895

Comments

[hairyears]

Yes and no...

Lilienthal's gliders were important in the early history of aviation, but neither he nor anyone else who wasn't called Orville or Wilbur was ever going to get a heavier-than-air aircraft off the ground under its own power before the Wrights did.

There were three key insights and inventions made by the Wright brothers, together with a 'secret sauce' that everyone overlooks because we can't get beyond the words 'bicycle maker'.

The secret sauce is that the Wrights were very, very successful bicycle makers, who were in business at exactly the right time to pick up two technological advances: the availability of light and accurately-made steel tubing in standard sizes with consistent structural properties, and the application of Euler's mathematical theories into usable techniques of structural analysis.

They weren't bicycle 'makers', they were bicycle engineers, and everything they did flows from that source or 'sauce'.

They made their money on the racing track when engineering calculations started to win out over craftsmanship and guesswork, and they made their money selling mass-produced lightweight bicycles that were strong and light and safe, selling them on the back of the publicity of winning trophy after trophy with their racing bikes.

The Wrights got interested in flight but... As engineers, not as curious amateurs.

So they tested Lilienthal's theory of aerodynamics and his concept of an aerofoil by constructing the world's first wind tunnel, and measuring the forces of lift and drag; and, as they visited the major cities of the United States as part of the National 'tour' of bicycle racing events, the talks and lectures that they gave at local branches of the American Society of Engineers tracked their development of an accurate and practical theory of the aerofoil.

So there are the first two inventions, right there: the wind tunnel, and an accurate design framework for a working wing.

The third one - and, critically, the one that made it possible to fly safely - was the realisation that an aircraft in flight requires tri-axial control - pitch, yaw, and roll - and, as engineers, the Wrights calculated the control forces and designed a working set of control surfaces.

So they built their flying machines, right from the start, with an engineer's calulated understanding of how it could be controlled, and of the speeds they knew it should fly in order to be controllable.

If anyone else knew that before the Wright brothers, none of them wrote it down, at all, at any level of practical understanding, let alone a comprehensive calculation of control forces.

And, of course, the Wright brothers knew how strong the wing and the airframe needed to be: not by guesswork and a craftsmans eye - that isn't good enough for heavier-than-air-flight! - but by engineering: structural calculation and wind-tunnel measurements of the forces that it would experience.

This is the context behind all the comical film footage of early aviation pioneers and their collapsible contraptions; and, alas, of the lethal lack of understanding of triaxial control and the critical airflow speed required for an aerofoil to work.

Comedy, and tragedy: despite the Wrights' openness and generosity with their advances in the discipline of aeronautical engineering, all too many of their rivals died from stalls and failures of controllability that they could and should have known about.

The bit that the Wrights kept to themselves was the development of an efficient airscrew: I will leave it as an exercise to the reader, to consider the calculations required to design the first rotating pair of continuously-twisted aerofoils that operated in a spiral airflow with no part of it in 'stall'...

But they did, and they knew the thrust that it would generate, and the loads it would impose upon the airframe.

None of their rivals came close to the precision with which the Wrights had calculated that.

And so the day arrived when a petrol engine-builder told the Wrights that there was now a power plant with the power-to-weight ratio they *knew* would get a flyer off the ground.

The rest is Kittyhawk and history: and Lilienthal's advances in the theory of the aerofoil contributed to that, but he never came close enough to replicate it before his lack of understanding of triaxial controllibility resulted in his death.

[lethargic_man]

Interesting; thanks for taking the time to write all that up.