Monday, January 2, 2012

Why Do Clouds Form Around Fast Flying Jets?

Breaking the Sound Barrier

The capabilities of fighter jets these days are awesome. Breaking the sound barrier seems easily achieved for many fighter jets. However, these days the military seems to be making more stealth planes/bombers and those cannot break the sound barrier because the sonic boom would defeat their purpose. Sound travels at about 760 mph. When a plane goes that fast it causes both visual and audible effects. There is one effect that I want to focus on; that skirt of water vapor that forms around the tail end of the jet in the picture. Why does this happen? When a jet goes that fast it is pushing the air around it away and creating more pressure in certain areas around the plane.

In this picture of a bullet traveling at high speeds, you can see the bends that the bullet is causing. As the bullet travels quickly it pushes the air in front of it out of the way. Pushing the air causes more air to be around the sides of the bullet. The same happens to a jet. Since jets are so large, when they create pressure waves they are condensing a lot more air in a given place than a bullet can. So, if the air in which the plane is flying is very moist, the moisture is condensed under the pressure of the air. The plane forms enough pressure that the water condenses into a temporary cloud around the area where the pressure is high enough to condense the water. I say temporary, because the cloud is only forming because of the intense air pressure caused by the jet traveling at very high speeds. The cloud forms, dissipates and reforms which makes it look like its moving as the plane moves. As soon as the plane’s speed drops below the sound barrier it does not create enough pressure in the air to condense water so the cloud would no longer be visible.

This image depicts the pressure wave well, calling it a shock wave which is similar to a pressure wave. As you can see in the picture a cone shape forms as the plane flies. At low altitudes, the air is filled with water vapor from evaporation, humans breathing, sweating, plants giving off water and so on. In previous blog posts I explained how cars could run on water in the future. If there is water in the air, could we use that for energy? Someday, could planes run on the moisture of the air?!

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