Shape
The inlet cone is shaped so that the shock wave that forms on its apex is directed to the lip of the intake; this allows the engine to operate properly in supersonic flight. As speed increases, the shock wave becomes increasingly more oblique (the cone gets narrower). As a result, some inlet cones (for example, on the SR-71) are designed to move axially to maintain the shock-on-lip and allow efficient operation over a wider range of flight speeds. On MiG-21 this movement also makes the opening between the intake (diffusor) lip and the cone smaller, preventing the inside of the intake section from bursting open from dynamic air overpressure at the aircraft's highest speeds above Mach 2.
Read more about this topic: Inlet Cone
Famous quotes containing the word shape:
“Man’s own youth is the world’s youth; at least he feels as if it were, and imagines that the earth’s granite substance is something not yet hardened, and which he can mould into whatever shape he likes.”
—Nathaniel Hawthorne (1804–1864)
“The work of the world is common as mud.
Botched, it smears the hands, crumbles to dust.
But the thing worth doing well done
has a shape that satisfies, clean and evident.
...
The pitcher cries for water to carry
and a person for work that is real.”
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“Somebody once said that I am incapable of drawing a man, but that I draw abstract things like despair, disillusion, despondency, sorrow, lapse of memory, exile, and that these things are sometimes in a shape that might be called Man or Woman.”
—James Thurber (1894–1961)