Assuming that a new, huge passenger airplane was just built, now comes the time to do an actual testing. Even if millions of dollars are spent on designing a plane made from shiny titanium metal and it is tested down the runaway to check if it really flies, calculations can go wrong.
For instance, the plane takes off and after twenty seconds, drops and falls on a city filled with 5 million individuals. This is probably not the most efficient way to test something this risky. That is why airplane designers test such things on the ground first with the use of scale models in wind tunnels. Here is a closer view on the way they work.
Based on Science
To build airplanes that will fly fast, efficiently and economically, designers should see to it that air flows smoothly above their wings and beyond their tube-shaped bodies. This is the science of aerodynamics. The moment a plane is already in the air, it would be difficult to know about the air that moves past it (but an expert test pilot will know the cause of any problems).
In case there is something wrong with its design, the plane will not fly at all. For this reason, modern airplanes and spacecrafts are tested on the ground in a wind tunnel, which is a pipe-like structure, whereby air blasts at very high speeds.
The logic behind the wind tunnel is plain and simple: when a plane can’t be moved through the air, perhaps the air can be moved past the plane. From a scientific viewpoint, it is just the same. When the plane drags (causing air resistance) as it soars across the sky, the air will drag in the same exact way as it is fired past a stationary plane model on the ground.
Nothing can stop anyone from creating a humongous wind tunnel as well as testing a life-size model of it and certainly, NASA, the space agency of the US, has such structures. However, it is often a lot cheaper to use a smaller scale plane model in a smaller wind tunnel as well.
The Way a Wind Tunnel Functions
A wind tunnel looks quite like a big pipe that wraps around itself round and round that has a fan at the center. When the fan is turned on, air blows around the pipe in a circle. It is best to include a small door to get in plus a test room in the middle and presto, a wind tunnel is created.
Essentially, it is quite more sophisticated than that. Rather than having a uniform shape all around, the pipe is narrower in some places and wider in others. The air needs to speed up to go through narrow pipes. When the pipe is narrower, air has to go faster.
Similar to a bicycle pump, when air is forced out through the narrow nozzle it speeds up. It is also similar to a wind valley, in a way that wind blows a lot stronger, focused by the hills on any side.
A wind tunnel that has narrow sections makes it easy to boost speed, which is something most needed. Testing a supersonic airplane requires wind speeds that are five times faster than a hurricane. When it comes to testing a Space Shuttle, this requires wind that is blown ten times faster. Some kind of wind!