Quoted:
Kryptonian muscle tissue when super-charged with solar-energy, can generate a powerful gravity field. These fields in combination with Superman's personal bioelectric field give him the ability to negate gravity, allowing him to fly.
When in flight, he's fully suspended by this energy, almost completely repelling earth's gravimetric influence over him. He becomes his own center of gravity, and no longer has to physically leverage against the gravity of whatever planetary body he's on, or any object.
By emitting a jet of rapidly moving particle/electron interaction by-products, Superman is capable of Mach speeds in excess of Mach 10 in atmosphere. He can fly to the moon in minutes, but faster than that outside of atmospheric interference.
His control of his flight is perfect and he can perform aerobatic feats such as hovering, flying backwards and even lifting great weights while flying.
Not bad, a little off on the propulsion theory though.
The Kryptonese, living on a planet with 17.97 g forces developed a localized telekinetic field to support their bodies under the high gravitic forces. Their bodies processed the relatively weak solar energies of their red sun and still required conventional food for sustenance.
A Kryptonese, continuously living under a yellow sun on a planet with gravity like Earth's absorbs and retains the greater amounts of radiant energy and can use it for various purposes. The basic telekinetic field they naturally generate is much more intense, allowing such a being great structural integrity and an active force field that can repel harmful vectors like bullets, flame, cold, and certain nuclear energies. The Kryptonese can extend this field to large masses in close proximity, such as airplanes, ships, and buildings so that they can lift and move them without tearing them apart.
Using this telekinetic field to warp space/time, in small amounts they can move at near lightspeed and even perceive events in what is now popularly referred to as "bullet-time", allowing them to move amongst a crowd, without so much as messing up a woman's hair in passing. Free of a planet's gravitic field, a Kryptonese could make FTL speeds.
Other examples of harnessing this telekinetic manipulation of gravity are; generating gravitic lenses both for telescopic effect and microscopic abilities; sensitivity to ultra and subsonic frequencies in various decibel levels; a specific type of both bioluminescence and waste heat disposal displayed as "heat vision"; another hybrid effect of bioluminescence in the x-ray spectrum known as "X-ray vision"; an exotic example of thermodynamic manipulation at a cryogenic level known as "super breath".