Depleted uranium has indeed been used in airplanes. Some models of 747 have a ton or so of depleted uranium, though I believe this practice was phased out in later models.
It's not just planes though. Some sailboats have been made with DU keels. Usually lead is used, but DU would presumably allow for a smaller (thinner?) keel.
It's not just planes though. Some sailboats have been made with DU keels. Usually lead is used, but DU would presumably allow for a smaller (thinner?) keel.