Υπερηχητικοί μαγνητοϋδροδυναμικοί (MHD) κινητήρες Aurora

Παράρτημα 1: MHD

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Το μυστικό της υπersonic πτήσης

Όσο πιο γρήγορα πετάει ένα αεροπλάνο, τόσο πιο ψηλά πρέπει να ανεβαίνει και να πετάει σε υψόμετρο κρουαζιέρας. Δεν είναι δυνατόν να πετάει σε επίπεδο εδάφους σε υψηλό αριθμό Mach, αποκλειστικά λόγω των μηχανικών περιορισμών που οφείλονται στην υψηλή πίεση. Πέραν του Mach 3-3,5, η πτήση είναι δυνατή με turbojet κινητήρες (εικόνα πάνω αριστερά). Σε υψηλότερους αριθμούς Mach, αυτές οι περιστροφικές μηχανές δεν μπορούν να χρησιμοποιηθούν. Μπορεί τότε να γίνει η μετάβαση σε statoreactor (δεξιά). Μέχρι το Mach 6,5, μπορούν να χρησιμοποιηθούν scramjets (supersonic combustion ramjets) (κάτω). Το leading edge ψύχεται μέσω κυκλοφορίας υγρού υδρογόνου και οξυγόνου. Το μίγμα καίγεται σε ένα δακτυλοειδές θάλαμο καύσης σε υπersonic ταχύτητα.

Πέραν του Mach 6,5, φαίνεται δύσκολο να επιτευχθεί μεγαλύτερη ταχύτητα, λόγω της πολύ υψηλής θερμοκρασίας (που προκαλείται από την αναπρόσπιση του αέρα μέσω ενός ισχυρού shock wave). Πριν από μερικά χρόνια, οι Ρώσοι αποκάλυψαν ότι είχαν ένα πρόγραμμα called "Ajax", σχεδιασμένο για πολύ υψηλούς αριθμούς Mach. Στη συνέχεια, βρίσκουμε δύο εικόνες που λήφθηκαν σε ένα υπersonic wind tunnel, δείχνοντας δοκιμές του Ajax. Παρατηρούμε ότι ο γενικός σχεδιασμός μοιάζει με τα σχέδια που υποτίθεται ότι αντιπροσωπεύουν το "Aurora" ή το "Aurora project". Όπως φαίνεται, το άνω μέρος αυτών των μοντέλων είναι επίπεδο.

Ajax με statoreactors

Ο Fraidstadt, ο σχεδιαστής του Ajax, παρείχε μια ενδιαφέρουσα και surprising πληροφορία. Αυτή η μηχανή προοριζόταν να πετάει σε υπersonic ταχύτητες με... conventional turbo-reactors. Επιπλέον, η πτήση ήταν δυνατή αν το MHD σύστημα λειτουργούσε. Το Ajax δεν ολοκληρώθηκε ποτέ, λόγω έλλειψης χρημάτων στη Ρωσία. Το Aurora ήταν το "αμερικανικό Ajax", βασισμένο στις ίδιες έννοιες. Ξεκινώντας από αυτό, δεν ήταν δύσκολο, μέσω συζητήσεων με αμερικανούς ερευνητές που συμμετείχαν στο πρόγραμμα Aurora, να ανακαλυφθεί το μυστικό μιας τέτοιας ιπτάμενης μηχανής. Ο αναγνώστης θα το ανακαλύψει στη σειρά εικόνων που ακολουθεί.

Στην πρώτη εικόνα, βρίσκουμε τον γενικό σχεδιασμό του "wall convertor", που εφευρέθηκε σε πολλά μέρη στο τέλος της δεκαετίας του '60. Εγώ personally experienced wall convertors στο εργαστήριό μου στη δεκαετία του '70. Ένα σύνολο γραμμικών ηλεκτρικών αγωγών δημιουργεί μια αρκετά peculiar μαγνητική γεωμετρία πεδίου, shown on the right, "spatially periodic". Αυτό ζευγαρώνεται με ένα σύνολο γραμμικών ηλεκτροδίων. Αν αποφασίσουμε να χρησιμοποιήσουμε αυτόν τον wall MHD convertor ως wall MHD accelerator, one injects electric power. Τότε είναι easy to see that the device produces a Lorentz force field parallel to the wall (acting, for example, in the boundary layer).

Από την άλλη πλευρά, μπορούμε να το χρησιμοποιήσουμε ως wall MHD generator. Τότε η Velocity V, combined to the magnetic field B, παράγει ένα induced electric field E = V × B. Σε υψηλό υψόμετρο, η πυκνότητα του αέρα είναι αρκετά χαμηλή και η ηλεκτρική αγωγιμότητα καλύτερη από ό,τι σε επίπεδο εδάφους. Η μηχανή μπορεί να παράγει electric power. At the same time, η Lorentz force slows down the air. Η πυκνότητά της μπορεί να αυξη sufficiently 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 that 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.

Αυτό είναι απλώς μια 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-temperature plasma physics, a field that was completely abandoned in Europe at the beginning of the seventies. Two-temperature plasmas, combined with 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 turboreactors. Then it climbs at supersonic regime. When it flies high enough, its MHD system is operated. Lower air inlets 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 2,000,000 feet, conventional rockets provide additional thrust, so that the airplane becomes a low altitude orbiter (its range becomes... infinite). It becomes a perfect spyplane, able to take very good pictures of the ground. If desired, the machine may turn like the "Silver Surfer". It is a "pilotable orbiter". Completely surrounded by plasma, it is fully stealth.

It has no thermal shield. Its re-entry is 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. It enters the atmosphere like a "MHD glider".

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

Civilian applications.

Presently, Aurora is an orbiter spyplane. It can take off from a base located in the US and turn around the Earth in four hours. Its mission duration is shorter than the time of a night, so that it is very rarely observed and photographed. 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 inject space modules on orbit, it would provide a much smaller cost per kilo. But the USA prefer to devote such smart plane to military purposes.

A secret long-range hypersonic bomber.

Everybody knows the B2-bomber. Twenty-two are based at Whiteman, Missouri. Official authorities say that their unit cost should be 2 billion dollars. When a specialist looks at the machine closely, he cannot understand why the cost is so high. Moreover, it is supposed to be... subsonic. The US Air Force says that this bomber can operate from the US at huge distances: 30,000 miles and go back home immediately. Of course, this implies several refuelings 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 the B-52 could be composed of 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 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, as the Mojave desert is very, very dry. The three elliptic spots correspond to lamps attached to the landing gear. We think that these white bars correspond to MHD controlled inlets 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 better stability when landing. A good specialist in fluid mechanics can guess why it is designed this way. But the upper part is different. The "real B2" has a thick wing, as its four (conventional) motors are housed inside. Before their inlets, we find the MHD wall generator, which slows down the air enough to make hypersonic flight possible in very rarefied air and high altitude (200,000 feet) with... conventional turboreactors. Velocity: 6,000 knots.

The "real B2" is more sophisticated than the spyplane Aurora. It is not designed to be satellite-based. 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 at any point. The strength of the discharge modifies the local value of the speed of sound. The geometry of the two high-voltage discharges, at 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, as it is no longer necessary. As shown in the figure, the modern hypersonic US bomber is very flat, very stealth.

It can take off from an airport based in the USA, fly to Kabul, and be back in a single night.

The hypersonic bomber represents also the future of civil transport, able to take people from New York to Tokyo in two hours.

The US possesses hypersonic stealth drones with similar air intakes. Naive people still believe they are designed to be subsonic.

Annex 1 (MHD) Previous page Annex 2 (other weapons) Annex 3 (MHD torpedo)