What is harder to fly or drive

Despite the heavy weight: why can airplanes fly?

They weigh hundreds of tons. And yet they take off. What exactly is it that makes planes fly? The secret is a principle that, conversely, you often come across at traffic lights.

The largest aircraft in the world (Antonov An-225) weighs 285 tons - without a load, and the fastest (Lockheed SR-71A Blackbird) reached around 3,500 km / h: Airplanes are capable of amazing things. This includes flying itself. How is that actually possible?

Put simply, it is the interaction of four physical forces that allows an aircraft to fly - provided that the relationship between these forces works:

• The propulsion (it moves the aircraft forward)
• The resistance (it brakes the plane)
• The buoyancy (it works upwards)
• Gravity (it works downwards)

Why is an airplane taking off?

As the aircraft propels, air flows past its wings. When this air is directed downwards, a counterforce is created at the same time. This force acts in the opposite direction, i.e. upwards: a dynamic lift is created.

The physical principles for this are that Second and the Third Newton's law. It is said:
"The change in movement is proportional to the action of the moving force and takes place in the direction of the straight line in which that force acts." And: "If two bodies act on each other, a force acts on each of the bodies. The forces are equally large and directed in opposite directions."

But only when the lift is stronger than gravity does the plane rise. The more throttle the pilot gives, the more air passes through the wings. So increasing the pace is one way of gaining altitude.

But how is the air diverted?

In addition to the propulsion of the aircraft, there are two other conditions for it to rise into the air:

• A suitable profile of its wings (i.e. their shape in cross section). Among other things, the wing should generate little drag - because it makes flying more difficult.
• The angle of attack must fit. This is the angle at which the wings stand to the incoming air and divert this air downwards.

These two properties, together with the speed, also determine how much air is diverted downwards. In this respect, the weight of an aircraft is not a problem - as long as the interplay of speed, wing profile and angle of attack counteract this.

At least with some aircraft there is an additional effect that goes back to the Swiss mathematician Daniel Bernoulli (1700–1782). This effect occurs on the wings of the aircraft. If you look closely at the wings, you can see that they are slightly curved at the top. As a result, the air flows faster above the wing than on its underside. This creates an overpressure at the bottom and a negative pressure at the top - the wings (and thus the aircraft) are sucked upwards.

The reverse of lift is downforce

Rear wing of a racing car: It reverses the principle of the wing. Due to its inclination, flowing air is diverted upwards, the opposing force pushes the car downwards onto the asphalt. (Source: Mario Aurich / imago images)

Incidentally, you can always come across a reversal of this effect at the traffic lights, namely on the rear wing of the car in front of you. This wing is basically shaped like an upside-down wing: it is slightly bent up at the rear. In this way it redirects the air flowing past upwards and the opposing force acts downwards. That is why we speak of downforce here. It helps keep cars firmly on the ground at very high speeds.