Laythe Plane (now with Flight Data questions)

[numerobis]

My "jets compendium" died with the purge, but would answer many of your questions. Otherwise, you can read the comments in my KSP-scripts

The fuel flow depends on altitude because Isp depends on altitude (well, on air pressure), and in KSP, engines maintain thrust but change fuel flow as the Isp changes. Same as a rocket, though the jet Isp is a curve, not just a line.

The most efficient way to do very long distances in a jet is to climb as fast as possible to high altitudes, then speed up to orbital speed. Do a suborbital hop and you'll have cleared a large fraction of the planet's circumference, depending how high you let apoapsis get to.

The basic jet is more fuel efficient at low speed and high air pressure (near 1 bar). Generally you won't spend much time in those conditions, so it's not usually useful efficiency.