Following on from the first in the series "Approaching the Speed of Sound", this picks up with a model aircraft in a wind tunnel and proceeds to demonstrate how air density can affect the speed of the plane. This is especially risky in the "transonic" range where stability is largely compromised. Using colour illustrations, we are presented with bow waves and shock waves, and a simple explanation is provided as to the distinctions between subsonic, transonic and ultimately supersonic airflows and how that impacts on the ability of the plane to move quickly, with out excessive turbulence. It hel...