Date: Sun Mar 28 1993 22:07:26 Subj: Ufo Problem: Sonic Booms (also: A +quot;real+quot; Uf

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Date: Sun Mar 28 1993 22:07:26 From: Don Allen Subj: Ufo Problem: Sonic Booms (also: A "real" Ufo?) * Forwarded from "Sci.Skeptic" * Originally by Loren I. Petrich * Originally dated 19 Mar 1993, 14:40 From: lip@s1.gov (Loren I. Petrich) Date: 18 Mar 93 19:20:28 GMT Organization: LLNL Message-ID: <1oai1s$b02@s1.gov> Newsgroups: sci.skeptic One of the problems with the extraterrestrial spaceship hypothesis is that many of them supposedly travel at supersonic speeds through our atmosphere and if that is the case, then why don't they produce sonic booms? Here, UFOlogy collides with a well-established result of the hydrodynamics of compressible fluids. A practically universal result of supersonic flow is the formation of shock fronts, which are what make sonic booms. This is apparent from observations, experiments, computer simulations, and simplified analytic developments. In effect: Direction of motion: /\ || || /@@\ / @@ \ / /\ \ / / \ \ / / \ \ / \ / \ I did my thesis project on a computer simulation of accretion of interstellar gas (or something similar) onto a black hole. Whenever the hole moved faster than the gas's speed of sound, a shock front formed. And this was without any direct contact; all that the gas "saw" was the hole's gravitational field. Similar shocks appeared for purely Newtonian calculations of accretion, onto (say) protoplanets or white dwarfs. Analytic developments? Try linearizing the equations for fluid behavior to get the behavior far away from the object, and take the stationary (no time variation) case. For subsonic flow, the equations are elliptic, like Poisson's equation, implying no shocks, while for supersonic flow, the equations are hyperbolic, like a wave equation, implying that a shock will propagate from the object. Thus, shockless supersonic travel represents an Extraordinary Claim, which demands extraordinary evidence, which no UFO case to date has provided, as far as I am aware. In every clear case so far, there are alternate explanations at least more plausible (see the works of Menzel, Klass, and Sheaffer). And if you want to consider "real" UFOlogy, consider the March 1993 issue of _Popular Science_, which discussed a supposed secret Mach 6 airplane nicknamed "Aurora" that has produced several sonic booms and that has even been sighted on occasion. The sonic booms are, of course, what a supersonic aircraft is expected to produce. The article also went into detail into what the aircraft would be expected to be like. Like the SR-71 and the underside of the Space shuttle, it would be black, to radiate away the heat generated by the friction of its fast travels. It would look much like the "Stealth" fighter, with stubby wings, pointed nose, and a streamlined body. Air intakes would be underneath, and the contours of the plane would help compress the air and absorb some of the thrust from the exhaust. Its fuel would be liquid methane, whose boiling would absorb some of the heat, and the engine would be a rocket/ramjet. At low speeds, rocket engines would be lowered into the ramjet engines, and a mixture of methane and air compressed by a turbocharger would be burned. Liquid oxygen would be added for extra thrust. As the plane's speed increase beyond Mach 2.5, first the liquid oxygen would be shut off, and then the rocket engines would be pulled upward, letting the engines run as pure ramjets. There were discussions of other projects in that article, like a subsonic delta-wing spy plane nicknamed the "Manta", a big airplane with a flat space on top, presumably for piggybacking another airplane (to get into orbit?), and an external-combustion hypersonic airplane nicknamed the "Pumpkin Seed"; at a big enough Mach number, its turbojets would be turned off and fuel supplied to be burned outside (!). The flame would be kept next to the plane by the shock wave produced by its travel, so it transmits some of its thrust to the plane's body. It has supposedly been seen as a rapidly moving bright light in the night sky. The article discusses such things as Pentagon budgeting for secret projects, and mentions the curiosity of the Air Force retiring its SR-71 fleet not too long ago, despite there being no necessity of doing so. These aircraft might be called Unidentified Flying Objects, but they are almost certainly not extraterrestrial spaceships. Have the advocates of the extraterrestrial spaceship hypothesis shown this kind of rigor? Not that I'm aware of. /Loren Petrich, the Master Blaster /lip@s1.gov

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