Why can't airplanes move backwards by themselves?

Knowledge question

Why can a helicopter be in the air?

In nature, hummingbirds are the role models for helicopters: They can stand almost motionless in the air and even fly backwards for short distances. No other bird in the world can do this.

The hummingbirds move their wings in the shape of a figure eight and can use this flying technique to stop in the air.

Just as the hummingbird stands out among birds due to its maneuverability, the helicopter, in contrast to the airplane, can take off and land vertically, maneuver in all directions and above all hover in the air.

The helicopter is a safe means of transport that hovers down like a leaf even if the engine fails.

The helicopter has rotating blades. They act like the wings of an airplane. But the rotation of the rotor blades already generates so much lift when stationary that the helicopter ascends without moving forward.

This effect can be intensified by the adjustable angle of the blades.

During the lift, the rotor blades curved on the top divide the air flow. The air has to travel a longer distance above the leaves than below.

So that both air flows arrive at the same time, the air at the top has to flow faster. A negative pressure is created above the rotor and an overpressure is created below the rotor, which causes the helicopter to fly upwards.

With a lever, the pilot can adjust the angle of the rotor blades so that they sometimes displace more and sometimes less air. If he adjusts it so that there is more pressure on one side of the helicopter than on the other, the machine will slide to one side.

With this technique, the helicopter can fly sideways, forwards and even backwards. If the angles of the rotor blades are set so that the helicopter neither sinks to the ground nor continues to rise, it hovers in the air.