Hyperloop UPV
The Hyperloop UPV concept is a levitating rail-free pod design. Using magnetic repulsion and air cushioning for levitation is expensive and can produce unpredictable forces. The pod is equipped with a hybrid system of permanent magnets and electromagnet units, being able to control lift, so it can hover from the top of the tube. That way, the pod doesn't need so much electricity to be lifted by itself. Propulsion is obtained through expansion of the air with a nozzle, located at the rear of the pod, achieving speeds of up to 1000 km/h. The turbine recovers energy from the flow allowing a more efficient journey. This clean tube layout is said to cut costs in up to 30% of the whole Hyperloop project (about 180m USD) and the possibility to comfortably fit more passengers.
Arthur Kantrowitz
A recent high-speed transportation option for rapid transit between populous city-pairs about apart, the Hyperloop, has the Kantrowitz limit as a fundamental design criterion. Attempting to pass a high-speed passenger-pod through a very low pressure tube runs squarely into the Kantrowitz fluid flow limit. Historically, the solutions to working within the limit have been "go fast" and "go slow". A major innovation in the Hyperloop proposal provides a novel third approach to remain below the Kantrowitz limit while still moving at high-subsonic velocities: adding a front-end inlet compressor to actively transfer high-pressure air from the front to the rear of the high-speed transport capsule, and thus bypassing much of the air that would have resulted in the dynamic shock of the choked flow. The flow in the smaller duct through the capsule is also subject to the Kantrowitz Limit, this is relieved by increasing the pressure and the density to achieve the required mass flow. In the Hyperloop alpha design of 2013, the air-inlet pump also provides a low-friction air-bearing suspension system for traveling at over .