Annex 1: MHD

The secret of hypersonic flight
The faster an airplane flies the higher it must climb and cruise. It is not possible to fly at ground level at high Mach number just for mechanical constraints due to high pressure. Over Mach 3-3.5 flight is possible with turbo-reactors (below figure). At higher Mach numbers these rotating machines cannot be used any longer.


One can shift to strato-reactor (below right). At Mach number up to Mach 6.5 scramjets can be used (below). The leading edge is cooled by liquid hydrogen an oxygen circulations. The mixture burns in annular combustion chamber at supersonic velocity.

Over Mach 6.5 it seems difficult to go faster, due to the very high temperature (caused by air recompression through a strong shock wave). Some years ago the Russian revealed that they had a project called "Ajax", designed for very high Mach numbers.


Next, we find two images taken in an hypersonic wind tunnel showing Ajax tests. We see than the general design looks like the drawings of what was supposed to be "Aurora" or the "Aurora project". As we can see the upper part of such models is flat.

Ajax with statos

Fraidstadt, the designer of Ajax, gave an interesting and surprising information. This machine was supposed to fly at hypersonic velocities with... conventional turbo-reactors. In addition the flight was possible if MHD system was operated. Ajax was never finished, due to the lack of money in Russia.


Aurora was the "American Ajax", based on the same concepts. Starting from this it was not difficult, through discussions with American researchers involved in Aurora program to discover the secret of such flying machine. The reader will discover it on the next set of figures.

On the first one you find the general design of the "wall converter", invented in many places at the end of the sixties. I personally experienced wall converters in my lab in the seventies. A set of linear electrical conductors creates a quite peculiar magnetic field geometry, shown on the right, "spatially periodic".


This is couples to a set of linear electrodes. If we decide to use this wall MHD converter as a wall MHD accelerator, one injects electric power. Then it is easy to see than the device produces a Lorentz force field parallel to the wall (acting, for example, in the boundary layer).

On another hand we can use it as a wall MHD generator. Then the Velocity V, combined to the magnetic field B produces an induced electric fields E = V x B. At high altitude the density of the air is quite low and the electrical conductivity better than at ground level. The machine can produce electric power. At the same time the Lorentz force slows down the air. Its density can be raised high enough to make possible to burn a mixture air-fuel in an ordinary turbo-reactor.


The ordinary inlet (2) is closed. The air is admitted through a new inlet, located on the upper part of the airplane (4). We have figured the Mach lines, schematically. The Mach number decreases continuously from high value to subsonic regime. As the kinetic energy of the gas is partially converted into electricity its temperature remains low enough. The electric energy is used to increase the exhaust velocity in (5), using a wall MHD accelerator.


The whole implies what people now calls "MHD by-pass". Notice a conventional turbo-reactor implies some "mechanical bypass" for a part of the energy produced by the combustion of fossil fuel is transferred to the front part of the machine, at the compressor.

This is just a schematic presentation of Aurora. Flying at 200,000 feet its MHD generator works in high Hall parameter conditions, so that the transverse Hall electric field is high and can be used to create an wide electric discharge at the leading edge of the machine. This plasma cushion protects the wing against thermal effects associated to the shock wave. This phenomenon becomes to be known now.


All this implies a great knowledge in two-temperatures plasma physics, a field that was completely abandoned in Europe at the beginning of the seventies. Two-temperature plasmas, combined to high Hall parameters values experience violent Velikhov instability (which caused the complete failure of the civil programs in many countries, ended at the beginning of the seventies). This had to be solved through original solutions (plasma stabilization by magnetic confinement effect) whose description is over the scope of the present paper.

Anyway, Aurora can take off using its four turbo-reactors. Then it climbs at supersonic regime. When it flies high enough its MHD system is operated. Lower air inlet are closed and MHD inlet opened. The lift is given by the shock wave which takes place below the machine, so that Aurora is a "wave-rider" at 6000 knots.


But, as explained by American specialists, when the machine flies at 2000,000 feet conventional rockets provide additional thrust, so that the airplane becomes a low altitude orbiter (its range becomes .. infinite). It becomes a perfect spy-plane, able to take very good pictures of the ground. If desired, the machine may turn like the "silver surfer". It a "pilotable orbiter". Completely surrounded by plasma it is fully stealth.

It has no thermal shield. Its re-entry if operated in a completely different way. Aurora enters the atmosphere at small angle and dissipates its kinetic energy using a set of MHD short-circuited wall generators, so that the energy is dissipated mainly through radiative process. If enters the atmosphere like a "MHD glider".

Presently the American military try to hide those secret as long as they can. Pseudo-projects are shown to public. America is supposed to "think about hypersonic flight". In fact, US engineers master it since 12 years !



Civilian applications
Presently, Aurora is a orbiter spy-plane. It can take off from a base located in US and turns around the Earth in four hours. Its mission duration is shorter then the time of a night so that is is very rarely observed and pictures. Stealth, it is not detected by radars. Cruising alone in this portion of space it is a "battle station" for directed energy systems. It can attack both satellites and targets located on the ground.

Considered in a different way, Aurora is a better launcher than conventional rockets. If used to place space modules on orbit it would provide a much smaller cost per kilo. But USA prefer to devote such smart plane to military purposes.


A secret long-rang hypersonic bomber
Everybody knows the B2-bomber. Twenty-one are base at Witheman, Missouri. Official say that their unit cost should be 2 billions dollars. When a specialist looks to the machine closely he cannot understands cost is so high. Moreover it is supposed to be ... subsonic.


The US Air force says that this bomber can operate from US at huge distances: 30,000 miles and go back home immediately. Of course this implies several refueling and a long, very long flight time. A specialist will notice that the B2 bomber has a crew limited to two pilots. There is no cabin to take rest in, as in the old B-52, designed for long duration missions. Remember that the crew of B-52 could be composed by 6 men. Over very long missions three took care of the plane, while the three others could take place in the rest cabin.

A B2, flying near by Edwards base, was observed in October 1997. This is not a picture but a drawing made by a witness who is a journalist, specialized in aeronautics.

These lights at the leading edge cannot correspond to water condensation for the Mojave desert is very very dry. The three elliptic spots correspond to lamps attached to landing gear. We think that these white bars correspond to MHD controlled inlet at low altitude, as confirmed later by the specialists of the Edwards base.

As far as we can see the so-called B2 is not... the real one. This last has a similar design (see above). The peculiar shape of its wing has been designed to give the machine a better stability when landing. A good specialist in fluids mechanics can guess why it is designed such way. But the upper part is different. The "real B2" has a thick wing, for its four (conventional) motors take place in. Before their inlet we refined the MHD wall generator, which slows down the air enough to make possible hypersonic flight in very rarefied air and high altitude (200,000 feet) with... conventional turbo-reactors. Velocity: 6,000 knots.

The "real B2" is more sophisticated than the spy-plane Aurora. It is not designed to be sattelised. It must stand long range missions so that it has been designed to operate complete shock wave cancellation. The surface of the bomber is fully coated by MHD wall converters. Some parts work as generators, some as accelerators. The whole ensures the complete control of the flow in ant point.


The strength of the discharge modifies the local value of the velocity of the sound. The geometry of the two high voltage discharges, et the stagnation point and at the end of the profile modifies the flow, the drag and the relative width of the wing. There is no canopy, for it is non longer necessary. As shown on the figure the modern hypersonic US bomber is very flat, very stealth.

It can take off from an airport based in USA, fly to Kabul and be back in a single night. The hypersonic bomber represents also the future civil transport, able to take people from New York to Tokyo in two hours.


US own hypersonic stealth drones with similar air intake. Naive people still believe they are designed to be subsonic.


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