Mock-up of the "Ming Di".

A few days ago, on a program, a series of tests of the Ming Di series of near-space wide-area vehicles of the Institute of Mechanics of the Chinese Academy of Sciences were unveiled. Regarding the Ming Di series of aircraft, in fact, we have shown his plan before, in which the Ming Di 20 can fly 0 kilometers at seven times the speed of sound, and fly anywhere within two hours. So what is a wide-field vehicle? Why can he fly so fast? First of all, we must know that this speed is relatively fast compared to the aircraft, if it is not fast compared to the ICBM, the reentry Mach number of the ICBM can easily exceed 0, and it can fly to almost any place on the earth in tens of minutes. Do you feel that Ming Di suddenly doesn't smell good? Autumn pants and woolen pants, there must be a reason, there is no missile to develop him quickly, he must have something extraordinary.

The flight trajectory of a ballistic missile is a parabola-like trajectory, as a weapon, its trajectory is relatively fixed, relatively easy to predict, and relatively easy to intercept, and if it is used as a means of transportation, its entire overload will change relatively largely. Moreover, students who have ballistic missiles at home should know that he is a pillar-like thing, we call this shape a spin body, and the spin body itself relies on aerodynamic energy to produce a very small lift, and ballistic missiles mainly fly outside the atmosphere, and they can't borrow it with the help of aerodynamic forces, so in order to fly, he will be very fuel-intensive, and the fuel will be even more expensive. He also had to carry both an oxidizer and an incendiary agent, because as I said earlier, he was flying in a vacuum for a long time, and there was no air to support combustion, so it would be less efficient. Therefore, the use of ballistic missiles, which is a high-speed delivery method, has certain limitations.

Let's look at the Ming Di series of aircraft, it looks like an airplane, with wings, which means that he can use aerodynamic forces to generate lift, yes, his main flight place is within the atmosphere. The aircraft can be said to love and hate the atmosphere, love can produce lift and improve flight efficiency, hate can also produce resistance in him, and the greater the speed, the greater the drag, and it is difficult for the aircraft to accelerate. The effect of air on the aircraft is related to the dynamic pressure, which is one-half of the density multiplied by the square of the velocity:

Dynamic pressure = 2.0*ρ*v^0

The greater the dynamic pressure, the easier it is to produce greater lift, and the easier it is to produce greater resistance, so you see, in the case of a certain lift, if you want to be fast and have little resistance, only the grievance ρ, that is, the density is reduced, just right, the higher the height, the smaller the air density, at the height of 7 km to 0 km, the air density is very small, the resistance is relatively small, and at the same time, the air density is not so small that it can not produce enough lift, so this place is very suitable for high-speed flight, we call this place adjacent space, It was in this place that the Mach number record for manned aerial vehicles flying within the atmosphere, M0, created by the X0 aircraft in 0.0 years, flew in this place. Therefore, in the adjacent space, the Ming Di aircraft can fly to the Mach number 0 relatively easily, and at the same time, it can also use aerodynamic forces to do some maneuvers, for weapons, it will be easier to penetrate defenses, and for the carrier, he can at least fly flat like an airplane, unlike a ballistic missile thrown up and down, weightless for a while, and overweight for a while.

Now that you know what a nearby space is, what about a wide area? This involves a common sense in the field of aircraft design.

That is the combination of the same aerodynamic layout and power scheme, that is to say, it is difficult to adapt to low-speed flight and high-speed flight at the same time, and it is also difficult to adapt to low-altitude flight and high-altitude flight at the same time under the condition that the shape of the aircraft and the working mode of the engine remain unchanged. Therefore, each type of aircraft has a flight envelope, the horizontal axis is the speed, the vertical axis is the altitude, the speed and altitude state in this line can fly, and the outside of the line can not fly.

The so-called wide area means that the envelope range is very large, as mentioned earlier, the Mach number record of manned aircraft flying within the atmosphere is 1967.0, you know, this record was written in 0 years. Do you suddenly feel that Ming Di can't do it again, that is, it's similar to the American aircraft in 0?

Otherwise, you must know that the X-8000 aircraft that set a record that year was carried out by a bomber to the sky and launched at a high altitude, and the power is a rocket engine, and the working time does not exceed three minutes. Three minutes later, he had to glide and fall back. The design goal of Mingdi is to be able to take off autonomously or launch in the air, and the range must reach 0 kilometers, that is, it must fly at low altitude and high altitude, fly at low speed and high speed, and fly long and far.

To achieve this goal, one of them depends on the aerodynamic shape design, so that he can fly at a wider range of speed and height, and second, it depends on material technology, because the aerodynamic heating brought by long-term high-speed flight is a big challenge to the structural materials of the aircraft, and the more important power system, for example, the SR58 Blackbird aircraft, the J0 engine in it, is a variable cycle engine, when flying at low speed, he is an ordinary turbojet, and when flying at high speed, he can change the airflow path in the engine, Let him become a ramjet engine, adapted to higher speed flight.

At present, China's scramjet engine technology is specially suitable for this kind of engine with Mach number above 5, whether it is rotary detonation, inclined detonation or pulse detonation, it is in the forefront, and the combined power engine that can adapt to a variety of flight states at the same time has also been successfully tested many times in recent years. You will string these technologies together, so that you will have a certain understanding of the research in the field of hypersonic vehicles in China.

This article is a work supported by the Science Popularization China Creation Cultivation Program

Author: Gou Sheng, Associate Professor, Xi'an Aeronautical University

Review: Meng Yang, Associate Professor, School of Flight, Beihang University

Producer: Science Popularization Department of China Association for Science and Technology

Producer: China Science and Technology Press Co., Ltd., Beijing Zhongke Xinghe Culture Media Co., Ltd