Thursday, January 26, 2012

The Aerodynamics of Flight

There are 4 main forces that affect a flying object. Lift, which is created by the wings, happens when more pressure in the air is bellow an object than above it. When the wings of a plane create more pressure bellow the plane than above it the pressure forces the plane up. Lift is generated from the wings of a plane and allows the plane to fly. Some might say that the turbine, or jet engine is what allows a plane to fly but this is incorrect. The turbine is what drives the plane forward. I think about it like this, if a plane had no wings, but it did have a turbine it would just be a really fast car. Hangliding is another way to show that the wings allow the plane to fly. Hang-gliding is the act of launching oneself from a steep incline and soaring through the air by using a hang-glider which is a pair of V shaped wings under which a pilot is strapped. Hangliders have no engines but they are able to fly.

Wings are shaped like an airfoil which forces air to pass under the wing more slowely than the air that passes over the wing. The air under the wing moves slower and has more pressure. Therefore it creates an upword thrust to lift up the plane.

Thrust is the force that drives the plane forward. The thrust is generated by turbines or prepellers of a plane. Thrust is necessary to allow a plane to continue to fly. Without thrust a plane would fall to the ground. Take a hang-glider for example, since it has no thrust it cannot make 5 hour flights like airplanes with turbines can. So, it is clear that lift and thrust are the two forces that help a plane fly forward.
The two forces that do the opposite of lift and thrust are weight and drag. The weight pulls the plane down and can counteract the lift of the wings if it is too much. The gross weight is the plane's weight plus everything on board. In order for a plane to fly the lift must be greater than or equal to the gross weight. If the weight is more than the lift the plane will not be able to fly.

Drag is the force that opposes thrust. Drag happens simply because the plane exists and is moving. Drag happens because the air is resisting the sudden push that it gets from the plane. Planes constantly are pushing air out of the way and are transfering energy into that air. As a result, energy is lost and we call that drag. Thrust must be greater than or equal to drag in order for the plane to fly.

So my concern comes in in the lift and weight area. If not only wing span was longer but also the width of the wings was bigger in commercial airplanes, it would allow more seating (directly in the wings) which would increase the weight, but it would also increase the lift. I think one day commercial airplanes should have wings like a B-2 stealth bomber. 

My knowlege of math is nowhere close to being able to calculate if wings like that would create lift greater than or equal to the weight. However, when i can calculate whether this is true or not, I will write about it.

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?!