Tucked away in a corner of the Humboldt University's campus at Adlershof is a strange collection of sci-fi-like structures. So sci-fi, in fact, that parts of them were among the settings for the 2005 film Æon Flux. Of course, as you might have guessed from the university campus setting, they're actually part of science history rather than science fiction.
Right from the days of Otto Lilienthal Berlin played an important role in the history of aerodynamic research. As gliding gave way to powered aeroplanes, Berlin gained a new airfield dedicated to the new aircraft in 1909, out here at what was then known as Motorflugplatz Adlershof-Johannisthal (later just Flugplatz Johannisthal, with Flugplatz translating nicely as 'airfield' and Motorflugplatz perhaps best translating as 'airfield for powered flight').
In April 1912, the Deutsche Versuchsanstalt für Luftfahrt (German Research Institute for Aviation) was established on the south side of the airfield. As the nature of experiments became more and more advanced, the site began to become populated with esoteric buildings to house the test facilities, the ones we're looking at here being the work of architects Hermann Brenner and Werner Deutschmann.
Now, four key structures are preserved as protected monuments and the area has been named the Aerodynamischer Park (aerodynamic park) in reference to the aerodynamic research which went on inside them.
The first of the structures you'll come to if you've walked up along Rudower Chaussee from Adlershof S-Bahn and turned onto Newtonstraße will be the Großer Windkanal (large wind tunnel).
Built between 1932 and 1934, the Windkanal was constructed using the Zeiss-Dywidag System - a thin shell reinforced concrete building process that had originally been developed for building lightweight planetarium domes. The thickness of the tunnel's walls is, as a result, only around 8cm thick.
The wind tunnel is folded into a rectangular space and the diameter gradually increases along its length, from 8.5 to 12m. An 8.5m fan would have been at the narrower end, driven by a 2000kW electric motor, generating wind speeds of over 200km/h (124mph). Aircraft parts were placed in a measuring chamber, in the path of the stream generated by the fan, to test their aerodynamic performance.
On the side of the Großer Windkanal is a small piece of graffiti, protected by a glass panel. In fairly large, capital cyrillic letters, it says "Проверено. Мин нет" - Checked. No Mines. This is a relic from the days when the Soviet army were beginning to capture Berlin in the final days of World War II in Germany. Important buildings were sometimes booby trapped, both to injure the forces capturing the facility and to render it useless to them afterwards. The hand painted note on the Windkanal assures Soviet soldiers it's safe to go inside.
The Soviets took extensive amounts of war reparations from their sector and the facilities at Adlershof were no exception. All of the equipment was taken to the Soviet Union to be used in aerodynamic research there, leaving only the structures behind in Adlershof.
The Trudelturm was built between 1934 and 1936, to research a type of stall phenomenon in aircraft known as a spin. In a spin, one wing stalls (that is, loses lift due to a too high angle of attack) more than the other, leading the aircraft to rotate as it falls, spinning out of control. Research into the phenomenon was vital, both to help improve aircraft designs to make them more resistant to and more recoverable from spins and to help improve understanding of how to bring aircraft out of a spin once they'd entered one.
The Trudelturm was essentially a wind tunnel turned on its end. A fan at the bottom blew air upwards and aircraft models could be placed into the resulting stream of air and allowed to enter a spin. The air speed could be adjusted to match the fall rate of the model, so that it would remain suspended at a point in front of an observation platform, allowing it to be filmed by high speed cameras to enable detailed observations of the model's behaviour.
A similar facility still in operation today is NASA's 20 Foot Vertical Spin Tunnel, which was opened in 1941. You can watch a video of a model being tested in it on YouTube which ought to give you an idea of what went on inside the Trudelturm.
The Schallgedämpfter Motorenprüfstand (soundproofed engine test bed) was built between 1933 and 1935. It was used for testing aircraft engines - in particular, the propellers, which were often pushed to the point of disintegration in efforts to find their true limits. Propellers of up to 5m in diameter could be tested within the safe confines of the soundproofed building, which proved resistant not just to noise but also the bits of propellers which occasionally came flying off into the walls when the parts being tested reached breaking point.
The construction of the main part of the building is actually similar to the Großer Windkanal (the temporary scaffolding in the picture hides its shape slightly), with the outside walls only around 8cm thick. Soundproofing was achieved by the clever direction of airflows around the inside of the building, along with the use of sound damping materials. A ventilation system driven by a 500kW electric motor helped prevent the tested engines from overheating.
It now serves as a meeting point for the university's students, centered around a student-run café.
The Motorenhöhenprüfstand (engine altitude test bed) was used to test how engines would perform at different altitudes. It allowed engines to be run under differing air pressures and temperatures. The information gleaned from this testing could be used to inform estimates of fuel consumption, and lubrication and cooling requirements. It was built between 1932 and 1936.
It now houses laboratories and offices belonging to the university.
Dotted around in the grass of the Aerodynamic Park are these odd UFO-like objects. Every now and then, they'll start making UFO-like noises too. They are in fact an art installation called AIR BORNE, created by Stefan Krüskemper, with sound by Karlheinz Essl. It uses sounds from the Deutsches Rundfunkarchiv (German Radio Archive) which have been processed using software programmed by Essl, to form a composition of what he and Krüskemper call 'remembrance images'. According to the project's website, because of both the distance between the ellipsoids (that is, the UFO-like objects) and the amount of silence between the sounds, hearing the entire composition would take many years. If you plan on staying to listen to the whole thing, it may be worth making a sizeable donation to the student café up front so they don't kick you out for hogging the chairs and taking all their coffee.