How do planes stay in the air?

From the outside it looks impossible, but flight rests on a few simple rules of physics. Knowing them makes the aircraft feel more familiar.

Four forces

Four forces act on a flying aircraft at every moment: weight pulls it down, lift pushes it up, thrust carries it forward, and drag is the air's resistance. In cruise these forces are in balance, which is why the aircraft glides along at a steady speed in a straight line.

How does the wing use the air?

A wing's cross-section is curved on top, flatter underneath, and meets the air at a slight angle. Air flowing over the wing speeds up and its pressure drops, while the air beneath pushes the wing up. The wing also turns air downward; pushing air down, it is pushed up in return. Lift comes from both.

What do the engines do?

Engines don't lift the aircraft, they push it forward. As it moves forward, air flows over the wings and creates lift. So what keeps the plane up is its speed, and the engines provide that speed.

At takeoff and landing

The aircraft is slower at takeoff and landing. So flaps extend from the wing's trailing and leading edges: the wing gets bigger and more curved, making enough lift at low speed. The whine you hear after takeoff is the flaps slowly retracting.

What you feel

Being pressed into your seat in the climb, a light floating feeling in descent, and leaning in turns all come from these forces changing. They're all ordinary parts of flight. The flying course in SafeSkies explains them through a captain's eyes, in short lessons.