There are four forces of flight -drag, thrust, weight and lift. All four play an important role in how planes fly.
Drag
As the airplane moves through the air, there is an aerodynamic force present. The air resists the motion of the aircraft and the resistance force is called drag. Drag is directed along and opposed to the flight direction. There are many factors that affect the magnitude of the drag force including the shape of the aircraft, the "stickiness" of the air, and the velocity of the aircraft. We collect all of the individual components' drags and combine them into a single aircraft drag magnitude. Drag acts through the aircraft center of pressure. The drag of the air makes it hard for the plane to move quickly. Another name for drag is air resistance. A streamlined shape slips smoothly through the air.
Thrust
To overcome drag, airplanes use a propulsion system to generate a force called thrust. The direction of the thrust force depends on how the engines are attached to the aircraft.
On some aircraft, such as the Harrier, the thrust direction can be varied to help the airplane take off in a very short distance. The magnitude of the thrust depends on many factors associated with the propulsion system including the type of engine, the number of engines, and the throttle setting.
For jet engines, it is often confusing to remember that aircraft thrust is a reaction to the hot gas rushing out of the nozzle. The hot gas goes out the back, but the thrust pushes towards the front. Action <--> reaction is explained by Newton's Third Law of Motion.
Lift
As the aircraft moves forward into a stream of air, the wing deflects the air. Some of the air moves to flow above the wing while some of the air moves to flow below the wing.
The wing is curved to help the air that flows above the wing move more quickly than the air that was able to flow below the non-curved bottom of the wing. This curve is called an aero-foil wing.
The air that is moving more quickly above the curved wing starts to put less pressure on the wing while it adjusts to its new stream. Meanwhile, the air that is moving at a consistent speed below the wing maintains its rate of pressure. This quick differential produces lift. The higher air pressure pushes the wing upward into the space where the air pressure is lower.The distribution of lift around the aircraft is important for solving the control problem. Aerodynamic surfaces are used to control the aircraft in roll, pitch, and yaw.
Weight
The motion of the airplane through the air depends on the relative strength and direction of the forces shown above. If the forces are balanced, the aircraft cruises at constant velocity. If the forces are unbalanced, the aircraft accelerates in the direction of the largest force.
On some aircraft, such as the Harrier, the thrust direction can be varied to help the airplane take off in a very short distance. The magnitude of the thrust depends on many factors associated with the propulsion system including the type of engine, the number of engines, and the throttle setting.
For jet engines, it is often confusing to remember that aircraft thrust is a reaction to the hot gas rushing out of the nozzle. The hot gas goes out the back, but the thrust pushes towards the front. Action <--> reaction is explained by Newton's Third Law of Motion.
Lift
As the aircraft moves forward into a stream of air, the wing deflects the air. Some of the air moves to flow above the wing while some of the air moves to flow below the wing.
The wing is curved to help the air that flows above the wing move more quickly than the air that was able to flow below the non-curved bottom of the wing. This curve is called an aero-foil wing.
The air that is moving more quickly above the curved wing starts to put less pressure on the wing while it adjusts to its new stream. Meanwhile, the air that is moving at a consistent speed below the wing maintains its rate of pressure. This quick differential produces lift. The higher air pressure pushes the wing upward into the space where the air pressure is lower.The distribution of lift around the aircraft is important for solving the control problem. Aerodynamic surfaces are used to control the aircraft in roll, pitch, and yaw.
Weight
Weight is a force that is always directed toward the center of the earth. The magnitude of the weight depends on the mass of all the airplane parts, plus the amount of fuel, plus any payload on board (people, baggage, freight, etc.). The weight is distributed throughout the airplane. But we can often think of it as collected and acting through a single point called the center of gravity. In flight, the airplane rotates about the center of gravity.
The motion of the airplane through the air depends on the relative strength and direction of the forces shown above. If the forces are balanced, the aircraft cruises at constant velocity. If the forces are unbalanced, the aircraft accelerates in the direction of the largest force.
No comments:
Post a Comment