Principles of Flight

Newton's third law is often thought of as a lot of action reaction. This is a jet engine bay. When the engines mounted in here, it creates one heck of an action coming right at you. The obvious reaction is it forces the airplane that way. That makes sense, but I was a jet engine work? Just like a balloon flies away when you let go of it, air comes in here, goes way back into the engine, is heated up, goes faster, comes around the back with a lot of force. That's how a jet works.

With al of that force, or action, there has to be an opposite reaction. The reaction makes the airplane move forward, just like the rocket sled you saw earlier. But this time the aircraft has wings, which provide lift, forcing it into the air. In fact, there are four forces- actions and reactions- working every time an airplane flies. The thrust of the engine is one of the forces making aircraft move forward. But there's an opposing force the thrust and it's called drag. Drag is the resistance of the atmosphere on the aircraft, what you feel when you stick your hand out the window of the car while you're driving down the freeway. When the drag equals the thrust and the aircraft is no longer accelerating but remains the same speed since the forces are equal. If thrust is added and becomes greater than the drag the plane will accelerate. As a plane speed increases, the drag also increases until the thrust and drag are equal again. There are two other forces as well. Lift is the force provided by the wings as air passes over the airfoil. The opposing force is, of course, weight. It may seem strange but lift always equals weight otherwise the aircraft couldn’t stay in the air. As you can see Newton's laws are really quite simple but a good understanding of them is essential to the development and flight of aircraft. It’s even more important if you are going to test the airplane. I’m teaming up with some of the best pilots and engineers at the Dryden Flight Research Center, NASA’s home of experimental flight test, and together we're going to show you the fun side of flight testing Newton’s Laws. And speaking of fun, we're out of here.