Photo by NeONBRAND on Unsplash, this article is from WeChat public account:2030 Travel Lab (ID: PHD2030MRL) , author: He Peiwen, Dr. power electronic Engineering, University of Maryland graduate, now working Joby Aviation, engaged in electric passenger VTOL aircraft power supply system design and development
2019 seems to be a year of “air taxis”, people began to revisit the topic of “flying cars”, more and more traditional aircraft manufacturers and startups have begun to join the development of “flying cars” The ranks and the injection of a large amount of capital have also made this originally calm market undercurrent. With the release of various concept maps and prototypes, we can’t help but wonder, is the era of “flying” of the whole people really coming?
The road construction of the city seems to never catch up with the development of the city. Living in densely populated cities such as New York, San Francisco, Tokyo and Beijing, people are forced to endure the roads of heavy traffic during the peak hours. The data shows that in the San Francisco area only in 2018, due to traffic jams, the average annual loss was nearly 116 hours; in Paris, the figure came to 237 hours. [1]
Congested City Roads
Public rail transit is an effective way to solve urban congestion, but the development of rail transit is subject toUrban planning, geological conditions, and historical and cultural factors, as well as high construction and maintenance costs have also hindered the development of rail transit. So people’s eyes began to shift from the land to the air –
Vertical Take-off and Landing Vehicle (VTOL), or “air taxi”, seems to have become a vertical takeoff and landing flight vehicle
Uber Copter Network Aircraft
So, in the past two years, we have seen more and more companies start the development of their own vertical take-off and landing aircraft, including traditional aircraft manufacturers like Boeing, Airbus and Bell, including Joby Aviation. Start-up companies like Volocopter and Yihang. Compared with traditional helicopters, we can see that the design of the vertical take-off and landing aircraft at this stage can be said to have different characteristics, ranging from the size and position of the rotor to the way of propulsion. Today we will talk about the vision and technical challenges of the vertical take-off and landing aircraft as urban public transportation, in conjunction with Uber’s earlier White Paper on Future Urban Air Traffic [2].
Airbus CityAirbus
Joby Aviation S2
Yihang 184
First, the prospect of urban vertical takeoff and landing aircraft network
First of all, compared to traditional ground transportation, long-distance roads, tracks, erected bridges or tunnels are required. Vertical take-off and landing aircraft can use the existing helipad, the large parking lot, and even the open space on the highway. As a stop site, it greatly saves the cost of the previous infrastructure.
Secondly, ground transportation is limited by road construction. An ordinary traffic accident or road construction may cause large-scale traffic congestion and vertical take-off and landing.The aircraft is free from the constraints of the two-dimensional space on the ground, so the route planning can be more flexible and less likely to cause delays due to unexpected situations.
Therefore, the construction of the urban vertical take-off and landing aircraft network has its significance. Following the development of the Uber white paper, the first step is to use the existing infrastructure such as the helipad as the initial aircraft stop, thereby reducing the initial construction investment of the aircraft network, and then using the traditional ground transportation to complete the “last mile.” “The delivery.” In the second step, as the number of production aircraft increases, the number of passengers increases, the stops and the operation mode continue to improve, the cost of passengers taking “air taxis” will continue to decrease, and the cost of “flying” will not be The reason that hinders people from choosing to take the “air taxi”. Finally, with the development of autonomous driving technology, “air taxis” will gradually become more and more flexible from the need of driver control to unmanned driving, and passengers’ travel will become simpler and more flexible. Maybe then, “fly” “It will be as easy as it is now called a car.”
Uber Air Air Taxi [3]
With so many wonderful visions, let’s talk about the technical and policy barriers to building airplanes and building air traffic networks, as well as possible solutions.
Second, technology, policy barriers and solutions
1. Security
If you want to let the public widely accept “air taxis,” high enough security is a prerequisite. Currently, the Federal Aviation Administration’s (passenger miles)The number of deaths in the accident is less than 1.2.
This safety standard is actually no higher than driving. Therefore, if you want to build a commercial air network on a large scale, the aircraft as a vehicle must be much safer than the helicopter, and it must be safer than the ground traffic. The goal at this stage is to increase the design safety of “air taxis” to four times that of helicopters, which is “less than 0.3 deaths per 100 million passenger miles”.
“Flight Car” Flight Test [4]
According to statistics [5], most of the flight accidents were caused by the driver’s misoperation, bad weather and air traffic control. Based on these points, a more advanced assisted driving system or fully automatic driving can effectively reduce accidents caused by human error.
Mechanical failure is another important cause of aircraft crash. In the face of this problem, distributed electric propulsion 2. Noise
Noise seems to be an easy-to-understand but extremely important issue in VTOL aircraft design. No one wants to endure hundreds of planes roaring overhead every day. Therefore, in order to achieve large-scale commercial use, every “air taxi” must be quiet enough.
Reducing noise to the level of existing ground traffic noise is also a design challenge for vertical takeoff and landing aircraft. Uber’s goal is to fly a plane flying in a 250-foot (76m) air with a ground measurement noise of less than 67 decibels, which is equivalent At 7 meters away, a Toyota Prius with 35 mph (56 km/h) noise while driving, and early analysis and models The data believes that this goal can be achieved.
At the same time, because of the need to take off and land in the city, the noise control during take-off and landing is an important design requirement. The design, load capacity, duration of take-off and landing of the aircraft propeller are all factors that affect the noise of the take-off and landing. In addition, the choice of docking station directly determines the impact of aircraft take-off and landing noise on the surrounding environment. And these standards are also being established and improved.
How do you reduce the noise of the aircraft? Here again I have to mention the distributed electric propulsion system mentioned earlier. We know that traditional helicopters emit a lot of noise when flying. There are many factors that cause noise. In short, most of them come from the noise generated by the aircraft propellers passing through the air. At a certain speed, the larger the propeller, the greater the line speed of the tip. Unfortunately, the noise generated by the blade is exponential with the tip speed (depending on the shape of the blade) , if you can reduce the line speed of the tip by one-third, the noise can be reduced by 24 times! The multi-blade design can greatly reduce the length of each blade and the tip line speed while ensuring sufficient power, thus greatly reducing the noise emitted by each propeller, and the total noise generated by multiple propellers. It can be roughly understood that the linear superposition of the noise of each propeller is still much lower than the noise generated by a single propeller.
Joby S4 Rotor Aerodynamic Simulation [6]
Another important source of noise for a conventional helicopter is the engine, which emits the same noise as its propeller noise. In contrast, motors of the same power have negligible noise. Moreover, the motor structure is relatively simple and the weight is light, so each propeller can be equipped with an independent motor, thereby eliminating the complicated transmission system, improving the reliability, greatly reducing the weight of the aircraft and increasing the cruising of the aircraft. Coupled with the safety mentioned earlier, this is why all open vertical take-off and landing aircraft now choose the electric multi-rotor design without exception. The optimized design of the propeller can also effectively reduce flight noise.
3. Battery and flight performance
Because the aircraft is to be powered by electricity, it has to use the battery. Even today’s best lithium-ion batteries have far less energy density than fossil fuels. Therefore, with limited power, higher aircraft performance and flight efficiency mean longer uptime and more economic benefits. Pure rotorcraft, like the 184 of the Air China and the Air Taxi of Volocopter, can achieve high take-off and landing efficiency, but the efficiency is not high in horizontal flight, so it is more suitable for low-speed, short-haul routes.
Volocopter’s Air Taxi
and likeJoby S2 and Vahana’s A3 rotor and fixed wing design, through the change of the direction of the rotor to achieve vertical takeoff and landing to the horizontal flight, when the aircraft is in horizontal flight, the lift provided by the fixed wing can effectively improve the flight efficiency of the aircraft . So you can fly faster and farther. The price of course is the more complex body design and the corresponding weight increase. This design of “air taxis” can reach 150-200 miles per hour (240-320 km) cruising speed (partially subject to FAA speed limits) and 200 miles (320 km) The voyage is expected to achieve inter-city transportation.
Vahana’s A3
At present, the battery energy density still limits the development of “air taxis” to a certain extent, and the battery cost accounts for almost half of the aircraft manufacturing costs. However, as various manufacturers increase their investment in battery research and development and fast charge technology, this situation is expected to be alleviated.
4. Payload, Autopilot and Air Traffic Control System
The payload is directly related to the economic benefits of “air taxis”. The higher the payload, the more passengers can be carried. In the early days of the “air taxi” operation, the carpool (or the plane is more suitable) mode should be the main mode of operation, so each time it is carried The greater the number of passengers, the lower the cost of sharing and the more attractive to consumers. According to the analysis of the existing model, 2-4 people can be carried on the “air taxi” operated in the city.Passengers (including drivers) are most effective in aircraft design. Aircraft with higher loads can carry more passengers, but this also means greater take-off weight and greater noise – a factor that every aircraft manufacturer needs to weigh.
Autopilot can remove the reliance on the driver, further improve safety and indirectly increase the number of passengers that can be carried, so the development of autonomous driving technology is more attractive for “air taxis”. Compared with ground transportation, “air taxis” fly in relatively simple and empty areas, so the autonomous driving technology is correspondingly easier to achieve. At the same time, the automatic driving standards for vertical take-off and landing aircraft also need to be established.
For the air traffic network, how to effectively manage hundreds of “air taxis” flying over the city every day is also a challenge. Perfecting an efficient air traffic control system is key, while ensuring adequate flight control and data safety.
5. Certification
Although at the end, obtaining the certification of the National Aviation Administration may be the most difficult to turn over for the “air taxi” commercialization, and the most unpredictable factor. The process of certification for new commercial spacecraft may vary from country to country, but without exception. Take the Federal Aviation Administration’s FAA as an example. The entire certification process takes 3-4 years or more. From the prototype display to the design parameters, requirements and test methods of each software and hardware, the FAA needs to be reviewed and approved. Obtain software and hardware certification, control certification, and also need to obtain type certification for aircraft (Production Certificate) (production standards, models, etc.) , but also to obtain FAA’s flight certification for testing and research and development only (Operation Certificate). Each during this period