Warrior of Scorpio by Alan Burt Akers

Once again in the grip of the Star Lords of the Constellation Scorpio, Dray Prescot finds himself torn from the battles of the Inner Sea for a mission in the air. For it is now his mission to carry his beloved Delia by airboat to that far kingdom, Vallia, from whence she had come. But the route lay across the gaunt mountains and the shadowy jungles of the Hostile Territories -- and there Dray will be plunged among stranger peoples and more fantastic challenges than even his Kregen princess has known.

Warrior of Scorpio is the third book in the epic saga of Dray Prescot of Earth and of Kregen.