Anyone with a driver’s license can drive a 99A tank, so how is driving a helicopter any different?

When a helicopter flies low overhead, many people may wonder how to drive a helicopter, and whether it is similar to driving a car. The media reported that if you have a driver's license, you can drive a 99A tank, so what is it like to drive a helicopter? Today we will discuss this question.
Driving a manual transmission car is relatively complicated. During driving, both hands are responsible for controlling the steering wheel, the right hand is also responsible for shifting gears, the left foot controls the clutch, and the right foot controls the accelerator and brake. Driving a helicopter also requires the use of both hands and feet. The following takes a single-rotor helicopter with a tail rotor as an example to analyze how to control the flight of a helicopter. First, you need to understand the structure of a helicopter, as shown in Figure 1.

Figure 1 Schematic diagram of helicopter structure (Source: Expert data map)

Simply put, the helicopter engine generates power, the blades generate lift, the hub controls the rotor, and the tail rotor controls the direction of the nose. To fly a helicopter, you need to use the cyclic pitch lever, collective throttle lever, and pedals in the cockpit. The cyclic pitch lever controls the horizontal movement of the helicopter, the collective pitch lever controls the takeoff and landing of the helicopter, and the pedals control the heading of the helicopter. For ease of understanding, the following analysis is conducted according to the control mechanisms.

Figure 2 Schematic diagram of simple helicopter control (Source: Expert data map)

Question 1: How to control the flight direction of a helicopter?

The helicopter's forward, backward, left or right flight is controlled by the cyclic pitch lever. The cyclic pitch lever, also known as the joystick, is pushed forward to make the helicopter fly forward, and pushed backward to make it fly backward, and the same is true for left and right. The lift of the helicopter comes from the rotating rotor. When the rotor rotates, it forms a rotating cone with the bottom facing up. When the helicopter is hovering at a low altitude, the upward pull of the rotating cone is balanced with the helicopter's gravity. Push the stick forward, the cone tilts forward, and the rotor pull produces two components in the vertical and horizontal directions. The horizontal component is the pull of the helicopter forward.

Figure 3 Schematic diagram of helicopter forward flight and hovering force analysis (Source: Expert data map)

The action of the cyclic pitch lever will cause a series of very complex mechanical link interactions. As shown in Figures 4 and 5, the pitch lever drives the fixed ring below the automatic tilt mechanism to tilt along with the pitch lever through the hydraulic cylinder, and then drives the dynamic ring above the automatic tilt mechanism to tilt synchronously. The dynamic ring of the automatic tilt mechanism drives the blades to flap through the pitch lever, and the blade angle of attack changes periodically, and finally the entire rotor tilts, and the direction of the rotor pull changes synchronously with the cyclic pitch lever, driving the helicopter to fly.

Figure 4 The rotor component connected to the cyclic pitch rod (Source: Expert data map)

Question 2: How does a helicopter control takeoff and landing?

The height change of the helicopter is controlled by the collective pitch lever. By raising and lowering the collective pitch lever, the helicopter's flight altitude can be controlled to rise and fall. The collective pitch lever ultimately changes the total pitch of all blades, referred to as the collective pitch. When the collective pitch lever is raised, the hydraulic cylinder drives the fixed ring of the automatic tilt mechanism to rise as a whole, and then the dynamic ring rises with it, pushing the variable pitch lever to increase the angle of attack of all blades, increasing the lift of the blades, and naturally increasing the pulling force of the entire rotor, and the rotor drives the helicopter to rise. When the collective pitch lever is raised, there is also a steel cable that will synchronously control the fuel regulator to increase the fuel injection, so that the engine output power is adapted to the power demand of the rotor to increase the collective pitch.

Figure 5 Schematic diagram of the control process of the operating mechanism (Source: Expert data map)

The working process of lowering the collective pitch lever is the opposite of that of raising the collective pitch lever. One thing needs to be explained here in particular. When the collective pitch lever is raised or lowered to synchronously control the throttle to increase or decrease, the collective pitch of the rotor is changed, but the rotor speed will not be greatly changed. The rotor speed remains relatively stable, which is different from driving a car.

Question 3: How does a helicopter adjust its heading?

The previous section explains how a helicopter can fly in a straight line and how it can change altitude. Now let's analyze how a helicopter can turn. A helicopter changes its heading by using two pedals. Pressing the left pedal turns the helicopter to the left, and pressing the right pedal turns the helicopter to the right. As shown in Figure 5, the pedals are connected to the tail rotor and can control the pitch of the tail rotor.
The tail rotor of a helicopter is mainly used to overcome the reaction torque generated by the rotation of the main rotor. Do not underestimate the tail rotor. Once it fails, the nose of the helicopter will rotate in the opposite direction of the rotation of the main rotor, which can easily cause a flight accident. When one side of the pedal is pressed, the angle of the tail rotor blades is changed, resulting in a change in the tail rotor pitch. The balance between the reaction torque of the main rotor and the torque of the tail rotor is broken, and the helicopter will turn left or right, and the direction of the nose will naturally change accordingly.

Figure 6 Schematic diagram of the relationship between tail rotor thrust change and helicopter heading (Source: Expert data map)

The above introduces the operation of the cyclic pitch lever, collective pitch lever, pedals and other mechanisms. In the actual flight process, the pilot needs to coordinate the use of the control mechanism to keep the helicopter in a stable flight state. For example, when the helicopter is flying forward, the cyclic pitch lever is pushed forward. After the rotor pull force is tilted, it will not only accelerate the helicopter, but also generate a downward pitch moment around the center of gravity of the helicopter, causing the fuselage to tilt downward. In other words, the helicopter must lower its head to accelerate forward. When the downward pitch angle reaches the requirement, the pilot must pull back the lever in time to balance the pitch moment, otherwise the helicopter will keep pitching down and lose control. In addition, when the helicopter accelerates forward, the pull on the rotor is asymmetric, which will cause the fuselage to tilt. A helicopter with a right-handed rotor will tilt to the right, and a helicopter with a left-handed rotor will tilt to the left. The greater the acceleration, the greater the tilt angle. Therefore, when the pilot pushes the stick forward, he must also press the stick to the left or right to maintain a balanced state.

If the influence of complex airflow is added, it will be more difficult to keep the helicopter stable, and the helicopter pilot needs to constantly adjust the control mechanism to maintain dynamic balance. It can be seen that flying a helicopter is much more complicated than driving a car. Do you have the urge to learn how to fly a helicopter?

Introduction to the Science Popularization Team: The 597.9 Highland Science and Technology Innovation Team is a young science and technology innovation team dedicated to modern warfare research, combat theory innovation, military science popularization, and professional military theory consulting. The team is composed of several doctors in military science, who have extensive experience in military, college, and scientific research institutions, have fruitful academic research results, and have a rigorous and realistic attitude towards scholarship and a pioneering spirit of innovation. The fundamental purpose of the team is to "spread scientific and technological knowledge, promote the fighting spirit, and help strengthen the country and the army."

Produced by: Popular Science China Military Technology Frontier

Author: Lu Ying (military expert)

Planning: Jin He

Scientific review: Liang Chunhui (military expert)

Producer: Guangming Online Science Department