Helicopter rotor blades and drone propellers (or fan blades) both consist of several blades that, when rotating, push air to create airflow. When we feel that the wind from a drone or electric fan has become weaker, we can simply increase its rotational speed a bit, and the airflow will become stronger. So, if we notice that a helicopter is descending, would it be sufficient to just increase the rotor’s rotational speed in order for it to rise back up?

In fact, that’s not the case. Whether a helicopter is ascending or descending, it relies primarily not on adjusting the rotor’s rotational speed, but rather on adjusting the rotor’s angle of attack. When the rotor’s angle of attack increases, the velocity of the air being pushed downward by the rotor also increases, and the rotor itself experiences a greater reaction force. This force is precisely what generates the helicopter’s lift.

So, how do we control the angle of attack of a helicopter rotor? People have invented a device called the swashplate. It consists of two closely fitted circular rings. The upper disc rotates along with the helicopter rotor and is connected to the rotor via a hinged mechanism. The lower ring does not rotate, but it can move up and down and also tilt. ， Adjusted by several push-pull rods 。

When the helicopter needs to ascend, the pilot adjusts the control stick, pushing both swashplates downward. This action causes the hinge mechanism connecting to the rotor blades to increase the blade’s angle of attack, thereby generating greater lift. Conversely, when the helicopter needs to descend, the pilot pushes both swashplates upward, causing the hinge mechanism to decrease the blade’s angle of attack. As a result, the rotor produces less lift, and the helicopter begins to descend.

Thanks to the swashplate, a helicopter can generate not only upward lift but also downward thrust. When the control stick pushes both swashplates all the way up, the helicopter’s rotor blades develop a negative pitch angle. The force generated in this way is precisely the downward thrust. As a result, the helicopter begins to accelerate downward. If this downward thrust is strong enough, the helicopter can even fly upside down! This type of helicopter control is called— “Total Rectangular Control.”

Rotary-wing aircraft are a general term for aircraft that rely on rotors to generate lift. Helicopters are the most familiar type of rotary-wing aircraft. However, there are also some aircraft equipped with large rotors that take to the skies using the same principle—but they aren't classified as helicopters. So, how do these aircraft differ from helicopters?

It turns out that the rotor of a helicopter is driven by the engine, with the rotor shaft connected directly to the engine’s shaft. In contrast, the rotor of a autogyro is spun by the oncoming airflow; its rotor shaft is not connected to the engine and remains free.

　The engine of a rotorcraft is used solely to propel the aircraft forward. It typically drives a propeller that blows air backward, generating forward thrust. This thrust pushes the rotorcraft forward, and the resulting airflow causes the free-spinning rotor blades on top of the fuselage to rotate. Once the rotor reaches a certain rotational speed, it generates sufficient lift to enable the rotorcraft to take off and fly. Compared to helicopters, rotorcraft have a simpler structure, lower costs, and are relatively safer. However, they can only fly forward and cannot hover or fly backward; thus, their maneuverability does not match that of helicopters.