Theoretically speaking, when the inner part of the tube is in the condition of absolute vacuum, the aerodynamic drag for the levitation train inside the tube will be zero.

Shen and Yan discussed the possibility, strategy, and the technical proposal for developing the ETT in China. In view of this fact, the evacuated tube transportation (ETT) was proposed to reduce the aerodynamic drag and improve the speed of the maglev train. The train speed is much lower than the airplane speed because airplanes flight in a circumstance of rarefied gas in the high altitude. At a speed range between 400 and 500 km/h, the aerodynamic drag accounts for 80 %–90 % of the total drag including the aerodynamic drag, the eddy resistance force, and the braking force. Whatever the trains are levitated or not, the aerodynamic drag is the dominate part of drag when it runs at a high speed in the atmosphere near the earth’s surface. At high speeds, however, the aerodynamic drag is too large to be neglected. When the trains run at low speeds, this drag is not evident. Even with these three methods, the velocity of trains could not be improved remarkably because of the aerodynamic drag. There are three types of levitation technologies: electromagnetic suspension (EMS), electrodynamic suspension (EDS), hybrid electromagnetic suspension (HEMS). The trains can be levitated above the rail to avoid such friction with the technology of magnetic levitation. When the trains are running at a low speed, most of the energy is consumed by friction. The speed of traditional trains is limited because of the dynamic friction between the wheels of the train and the fixed rail on the ground. Thus, the pressure, the velocity, and the blockage ratio are viewed as the three important factors that contribute to the energy loss in the evacuated tube transportation. The two results show the approximately same relationship between the aerodynamic drag on the maglev and the other factors such as the pressure in the tube, the velocity of the maglev and the blockage ratio. Then the damped speed was recorded and used to calculate the experimental drag. When the vehicle reached an expected speed, the LIM was stopped. With regard to this system a high temperature superconducting magnetic levitation vehicle was motivated by a linear induction motor (LIM) fixed on the permanent magnetic guideway. In order to study the relationships between the aerodynamic drag of maglev and other factors in the evacuated tube, the formula of aerodynamic drag was deduced based on the basic equations of aerodynamics and then the calculated result was confirmed at a low speed on an experimental system developed by Superconductivity and New Energy R&D Center of South Jiaotong University.

Aerodynamic aspect ratio calculator