Prerequisite Knowledge:
None
At any point in flight, it can be said that there are four basic forces acting on an aircraft. Understanding how these forces are created and how they affect the aircraft is essential to comprehending all other aspects of flight.
None
At any point in flight, it can be said that there are four basic forces acting on an aircraft. Understanding how these forces are created and how they affect the aircraft is essential to comprehending all other aspects of flight.
- Weight/Gravity: Is the force that acts vertically, pulling the aircraft towards the ground.
- Lift: Acts vertically, although this pulls the aircraft up, and keeps it in the air. Lift is primarily generated by an aircraft's wings, and is discussed in more detail in the lift/drag (advanced) article.
- Drag: One of the horizontal forces, drag is caused by several things, and it is what resists the motion of the aircraft. Drag is discussed in more detail in the lift/drag (advanced) article.
- Thrust: Thrust is generated by the engines, and is what pulls the aircraft through the air. For more information on how engines work, and how thrust is produced, see the engines category.
Equilibrium:
When discussing the motion of an aircraft, equilibrium is term that gets thrown around a lot. Equilibrium refers to a state where all the forces are in balance, and everything cancels out. To better understand equilibrium, you should consult Newton's first and second law's of motion.
An object in motion will remain in the same motion unless an unbalanced and external force acts upon it.
According to Newton's second law of motion, in order for there to be acceleration, there must be a net force. The net force is the sum of all of the forces acting on an object.
When an aircraft is moving in level flight at a constant speed, all of the four forces are balanced, which means the net force is zero (therefore no acceleration). If an aircraft is speeding up, there has to be a net force forwards, accelerating it in that direction. Likewise, if an aircraft is slowing down, the force pulling it backwards would be greater than the force pushing it forwards, creating a net backwards force that slows the plane down. Remember, acceleration is the change in motion. Just because the net force is zero doesn't mean the object is stationary; when the net force is zero, the object can still be in motion, but it's motion is not changing (no acceleration).
As another example, take into account an aircraft that is in level flight , transitioning into a climb. In level flight, the force of lift and weight are balanced (it is in equilibrium). As the pilot pulls back on the controls, the plane rotates upwards into a climb. The wings generate more lift, meaning the lift force is greater than the weight. This unbalanced force means there is a net force upwards, pulling the plane up. The pilot eventually releases the controls, and as the plane stops rotating, it goes back into equilibrium. The plane is climbing, but it is still in equilibrium since there is no acceleration (change in motion).
When an aircraft is moving in level flight at a constant speed, all of the four forces are balanced, which means the net force is zero (therefore no acceleration). If an aircraft is speeding up, there has to be a net force forwards, accelerating it in that direction. Likewise, if an aircraft is slowing down, the force pulling it backwards would be greater than the force pushing it forwards, creating a net backwards force that slows the plane down. Remember, acceleration is the change in motion. Just because the net force is zero doesn't mean the object is stationary; when the net force is zero, the object can still be in motion, but it's motion is not changing (no acceleration).
As another example, take into account an aircraft that is in level flight , transitioning into a climb. In level flight, the force of lift and weight are balanced (it is in equilibrium). As the pilot pulls back on the controls, the plane rotates upwards into a climb. The wings generate more lift, meaning the lift force is greater than the weight. This unbalanced force means there is a net force upwards, pulling the plane up. The pilot eventually releases the controls, and as the plane stops rotating, it goes back into equilibrium. The plane is climbing, but it is still in equilibrium since there is no acceleration (change in motion).
As the plane levels out, the pilot pushes forward on the controls, whic makes the wings generate less lift. The weight is greater than the lift force, and as a result there is an unbalanced force downwards. This causes the aircraft to rotate downwards.
That's it for basic aerodynamics! The next article covers advanced lift concepts.
That's it for basic aerodynamics! The next article covers advanced lift concepts.