A follower on TikTok sent us the following question:
What is the first thing you learn in ground school?
Mary Allen, Austin, Texas
The very first lesson I had covered the essential parts of an airplane, the four forces of lift, aircraft controls, pre-flight inspection procedures, and a general introduction to the concepts of flying. My first lesson came the same day as my discovery flight.
The four forces of flight are lift, drag, thrust, and weight. Lift acts upwards, drag opposes forward motion, thrust pushes the aircraft forward, and weight pulls it downwards due to gravity.
Explanation:
Lift: The upward force generated by the wings of an aircraft as air flows over them, allowing it to stay airborne.
Drag: The force that opposes the aircraft’s forward motion caused by air resistance.
Thrust: The forward force the aircraft’s engine produces, propelling it through the air.
Weight: The downward force exerted on the aircraft due to gravity.
Key point: For an aircraft to fly, the lift force must be greater than the weight, and the thrust must be greater than the drag.
When are the Four Forces Equal?
In straight and level flight with a constant airspeed
In a steady-state climb (constant airspeed and constant rate of climb)
In a steady-state descent (constant airspeed and constant rate of descent)
When are the Four Forces not Equal?
When you begin to climb or begin a descent
When you level off from a climb or descent (a changing vertical speed or rate of climb/descent)
Anytime there is acceleration in a vertical or horizontal direction
When you are changing airspeed
Remember:
Thrust opposes drag, and lift opposes weight.
For an airplane to fly, thrust must overcome drag, and lift must overcome weight.
In unaccelerated flight, all forces are in balance (or equal). Even if the airplane is climbing or descending, all forces are equal. The only thing that makes the forces unequal to each other is acceleration.
FlightInsight on YouTube has a great video (below) that describes these four forces.
George Cayley is credited with officially identifying the four forces of flight in 1799.
