If gravity pulls everything down, why don’t airplanes fall like stones?

Krishna: Like everything else on Earth, airplanes are subject to gravity, which pulls them downwards. In order to fly against gravity, planes develop a force that counters gravity.

Airplanes don't fall like stones because of lift, a force that counteracts gravity . Lift is generated by the shape of the wings, which causes air to move faster over the top than the bottom, creating a pressure difference that lifts the airplane upward. Airplane wings are specifically designed to create lift. The curved shape of the wings forces air to travel faster over the upper surface than the lower surface.

Image source: Shutterstock

This difference in air speed results in lower air pressure above the wing and higher pressure below. The difference in pressure creates a force that pushes the airplane upwards, countering gravity.

For an airplane to stay aloft, the lift generated by its wings must be equal to or greater than the force of gravity and drag.

The faster an airplane travels the more lift is generated. Inclining the wing to the wind also produces more deflection and more lift. The wings of an airplane have adjustable flaps that can be extended or retracted. When extended, the flaps increase the deflection of the air and provide greater lift for takeoff and landing. (1)

In addition to lift, airplanes use thrust, which is typically generated by engines, to move forward and counteract drag (air resistance). Shape is important in overcoming drag. The nose of a plane is rounded so it can push through the air more easily. The front edge of each wing is rounded too.

These are the forces of flight

Image credit: http://grc.nasa.gov

An airplane does not fall because the forces acting upon it are balanced. Specifically, the engine provides thrust to propel the plane forward, overcoming drag, and the wings create lift by deflecting air downwards, generating an equal and opposite upward force that counteracts gravity. When lift and thrust are stronger than weight and drag, the plane remains aloft.

Anything that disturbs this balance causes the plane to crash.

In aircraft, a stall is a critical aerodynamic condition where the airflow over the wings separates, leading to a rapid decrease in lift. This happens when the angle of attack (the angle at which the wing meets the airflow) exceeds the critical angle, causing the airflow to break away from the wing surface.

A stall, a sudden loss of lift due to the airflow over the wings becoming turbulent, is a critical flight condition that can lead to a loss of control and potentially a crash. It's caused by exceeding the critical angle of attack, the angle at which the wings lose lift.

When an aircraft stalls, the airflow over the wings becomes disrupted, leading to a significant decrease in lift. Flight controls become less responsive, and the pilot may experience buffeting, which is the turbulent air hitting the tail of the aircraft. If the aircraft remains stalled, it can enter a spin, a more severe and difficult-to-recover-from condition.

Pilots are trained to recognize and recover from stalls by lowering the nose to reduce the angle of attack and increase airspeed. The most significant risk is the lack of altitude for recovery. If the aircraft stalls at a low altitude, the pilot may not have enough time or space to recover before hitting the ground. Modern aircraft are equipped with advanced systems and warning lights to alert pilots and help them manage stalls.

While a stall itself isn't inherently dangerous, a lack of altitude for recovery can be.

A stall is a dangerous situation where the aircraft loses lift and control. While pilots are trained to recover from stalls, a lack of altitude or improper recovery can lead to a crash.

That is when a plane falls like an ordinary stone pulled down by gravity.

Image source: Shutterstock

Footnotes:

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