After the drone is launched, its rotor will rotate at a very high speed, drawing in air and relying on the reaction force received from it to fly. Although some of these rotors (or air propellers) are only made of thin plastic and do not look sharp, once they enter the state of high-speed rotation, even a thin plastic sheet will become extremely sharp and can cut through skin easily.
According to current statistics of drone rotor injury accidents, human eyes, neck and fingers are the most vulnerable parts of drones, even mini-aircrafts, if they hit a human body. Vulnerable parts can also cause serious injury.
The damage dealt by drones depends on the size of the drone. Larger drones with larger rotors can do some pretty serious damage, and in the worst case, they can even cut through the human body; smaller drones do less damage, of course, but enough to rip through skin and do the necessary damage. Stitch the wound.
How dangerous are drone rotors? How can we avoid this risk? And see below.
How fast are drone rotors?
The speed of the UAV rotor is related to the size of the rotor. Generally speaking, the larger the size of the UAV rotor, the lower the speed, so that the final speed of the rotor blades (final speed = rotor speed × rotor radius) can be kept within reasonable limits.
After launching the drone, its rotor will gradually accelerate from fast to slow. As the speed increases, the UAV rotor will draw more and more air to the bottom of the rotor, and the air will give the rotor a reaction so that the UAV can take off.
During flight, the maximum speed of a typical UAV is about 80-110 km/h, while the speed of a large UAV can reach about 200 km/h. The speed of the UAV main rotor plays a decisive role in the flight speed, stability and maneuverability of the UAV.
Generally speaking, the average rotor speed of a typical drone is between 8000 and 9000 RPM. If we take 9000 revolutions per minute as an example, then this is equivalent to 150 revolutions of the rotor per second. At this speed, ordinary plastic can also be turned into a sharp blade for human flesh and blood.
Injuries caused by drone rotors are not uncommon. Injuries caused by misuse can often be seen in the news. Of course, more often than not, misused drones cause no harm to ground personnel. trees or buildings, etc.). With the increase in the number of drones, the frequency of injury accidents at this time is also increasing year by year.
Big drones with big rotors are more dangerous because those rotors are made of hard materials like carbon fiber. Although the speed of this rotor will be slightly reduced due to the larger radius of the rotor, so the speed of its tip is generally higher. . And such drones tend to have more powerful engines that can cause serious injury. Just like the volunteer from Chongqing, whose head was directly cut by the rotor.
How to make sure that the drone rotor does not harm people?In fact, most drone rotor accidents and injuries can be prevented by taking extra safety precautions in the first place. With the rise of drones for aerial photography and the growing voice of urban aviation in the future, we will face more and more security conflicts between helicopters and people. How to make drones as safe as possible is a problem that should be addressed. pay attention., and should be included in the schedule of the UAV manufacturer.
The rotor guard is a great tool for smaller drones. While many people buy rotor guards to protect the rotor from impact damage, rotor guards have proven to be very useful in protecting people from small rotors.
For medium to large drones, it may be better to use a ducted rotor design. There are many types of air ducts, including air ducts and propellers. Ducted propellers have a long history, and they appeared very early in airships, propeller-driven aircraft, helicopter tail rotors, and even hovercraft. In recent years, with the development of the concept of urban aviation, rotor technology has been widely used in the design of urban aviation aircraft.
Vented rotors have many advantages. For example, compared to propellers of the same size, the thrust efficiency of channeled rotors can be greatly improved; Implemented to provide vector thrust.
What is most relevant to the topic of our article is that the rotor air duct in the channel can provide good protection, enough to prevent ground personnel from being cut by accidental contact with a high-speed spinning rotor, as well as to protect the rotor from light impact damage solid items.
Of course, this does not mean that there is no harm in channeling. The channel design will bring additional empty weight, and the design of the gap between the air duct and the rotor tip is also highly demanding. Compared with an open propeller, the vibration level of the channel rotor needs to be controlled in a smaller range inside. In addition, when flying at high speed, the air duct can also create a lot of additional drag, affecting forward flight efficiency. But that's another topic.
The above two points are related to the hardware aspect. In order for the UAV rotor not to harm people, it is not only a hardware problem, but also a software problem, especially the integration of artificial intelligence technology. According to the current level of artificial intelligence, drones that need to fly in crowded areas should at least have technologies such as active crowd detection on the ground, active crowd avoidance, and ensuring that the flight altitude is far from the crowd.
Secondly, these UAVs must add a rotor "emergency brake" function, combined with an artificial intelligence active recognition system, to ensure that in case of a risk of human injury, an active "emergency brake" is implemented, so in order to avoid possible further accidents, a large risk.
If we take into account the development of smart materials technology in the future, there will be more opportunities to ensure the safety of drones. For example, through the development of intelligent materials with variable stiffness, the rotor blades will actively reduce the stiffness upon impact with the human body to reduce harm to humanbody, this may also be a research direction in the future.
In short, the advent of drones has changed the way we live and has increased the efficiency of our work and production. In the future, there will be larger application scenarios and a wider market. But at the same time, drone safety should be included as a main metric in the development process of drone manufacturers to reduce the frequency of such accidents.