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Digital Resource Guide
Using a model aircraft, describe the four forces that act on an aircraft in flight.
There are four forces that act on an aircraft in flight. These forces are what keep the airplane in the air, make it move, and control its flight. They are:
Lift
What it is
Lift is the force that pushes the airplane up.
How it works
Lift is generated by the wings of the airplane. The shape of the wings (called an airfoil) is designed so that air moves faster over the top of the wing and slower underneath it. This creates a pressure difference—lower pressure on top of the wing and higher pressure underneath. This difference in pressure lifts the airplane into the sky, fighting gravity.
Think of it like this: When air moves faster over the top of the wing, it’s like the wing is “sucking” the airplane upward!
Drag
What it is
Drag is the force that pushes the airplane backwards and slows it down.
How it works
Drag is like air resistance. As the airplane moves through the air, the air pushes against it, trying to slow it down. The faster the airplane goes, the more drag there is. Airplanes are designed to be streamlined (with smooth shapes) to reduce drag, but it’s always there. Drag acts opposite to the direction of thrust.
Think of it like this: Drag is like trying to run through water—it’s harder to move, right? The faster the plane goes, the more drag it faces, and that’s why the engines have to work hard to overcome it.
Thrust
What it is
Thrust is the force that pushes the airplane forward.
How it works
Thrust is created by the engines (whether that’s a jet engine, turbofan, or propeller engine). The engines push the airplane forward by expelling air (or gas) at high speed out the back. Just like a rocket, the action of pushing air out the back creates an opposite reaction—pushing the airplane forward.
Think of it like this: If you’ve ever blown air out of a balloon and watched it fly around the room, the engine is doing something similar—using fast-moving exhaust to push the plane forward.
Weight (Gravity)
What it is
Weight is the force that pulls the airplane down toward the Earth.
How it works
Weight is the force of gravity acting on the airplane’s mass. The bigger the airplane (or the more stuff it carries), the greater its weight. To keep the plane flying, lift needs to be equal to or greater than the weight of the airplane. If the plane’s weight is too much for the lift, it will fall to the ground.
Think of it like this: Gravity is always trying to pull the airplane down to the Earth, but lift is fighting to keep it up!
Equilibrium
So, what happens when these forces are balanced – or, “in equilibrium”?
- Lift and weight are vertical forces, and thrust and drag are horizontal forces.
- When the airplane is cruising, these forces are in balance: Lift equals weight, and thrust equals drag. This allows the airplane to fly steadily at a constant altitude and speed.
- When the pilot wants to climb or descend, they adjust the throttle (thrust) or pitch the plane to change the balance of forces.
In short:
- Lift pushes the plane up (created by the wings).
- Weight (gravity) pulls the plane down.
- Thrust pushes the plane forward (created by the engines).
- Drag slows the plane down (resistance from the air).
Check out this video to see the four forces in action!
Key Takeaway
To fly smoothly, a pilot has to manage and balance all these forces! It’s like a tug-of-war between them all.
Key Takeaway
To fly smoothly, a pilot has to manage and balance all these forces! It’s like a tug-of-war between them all.
