The key to an aircraft's supersonic speed or fuel efficiency, is its aerodynamics or how smoothly the wind flows over its wings and around its body. However, what may look super-efficient on computer models, may not work so well in real life. Therefore, before any new aircraft takes to the skies, manufacturers test prototypes or even the actual aircraft, inside giant man-made wind tunnels.

The advantage to this is that it tests the aircrafts in real-life like conditions, giving the manufacturer accurate feedback about how well the design works. However, since most manufacturers want to guard their creations, wind tunnels throughout the world, are closely guarded accessible, to only a few authorized personnel. Recently however, a few lucky journalists were allowed to enter and experience what goes on inside Europe's largest air tunnels. What they saw, was quite stunning.

Nestled amongst the hills and valleys of Mondane in Eastern France, the four man-made steel tubes sport a diameter of 24-meters and are fitted with giant propellers that weigh about one ton each. These giant fans can move at astonishing speeds of 230 revolutions a minute - emitting enough wind to test any aircraft to its limit. The object to be tested, be it a prototype or the full-size aircraft, is first fastened to the tunnel so that it will not blow away.

When the air is blown around it sometimes at hypersonic speeds to test things like spacecrafts or supersonic aircrafts, it will simulate how the object will react when it faces similar wind patterns during a real flight. Smoke or dye is sometimes filtered in, so that the air can be observed as it moves. Special instruments also monitor the resilience of the aircraft by measuring the impact of the wind, as it breezes past the aircraft.

While each simulation lasts for just a few seconds, it provides invaluable feedback for aircraft manufacturers - One that could either declare the aircraft ready for take-off or, send the engineers scrambling back to the drawing board.

Testing aircraft in this manner is not a new idea. In fact, the first of the four tunnels placed here was uprooted from Austria in 1945. They picked the current site, because of the quality of the air and more importantly, its proximity to dams, which provide the power for the giant propellers - For believe it or not, the four testing tunnels alone consume about one-thousandths of France's total electric capacity.

Resources: dailymail.com, NASA.gov, wired.com