The advent of powered balloons, called dirigible balloons, and later of rigid hulls allowing a great increase in size, began to change the way these words were used. Huge powered aerostats, characterized by a rigid outer framework and separate aerodynamic skin surrounding the gas bags, were produced, the Zeppelins being the largest and most famous. There were still no fixed-wing aircraft or non-rigid balloons large enough to be called airships, so "airship" came to be synonymous with these aircraft.
The emergence of powered balloons, termed dirigible balloons, and subsequently of rigid hulls permitting a significant increase in size, started to alter the way these terms were employed. Enormous powered aerostats, distinguished by a rigid external structure and a separate aerodynamic covering enveloping the gas bags, were created, with the Zeppelins being the largest and most renowned. There were still no fixed-wing aircraft or non-rigid balloons substantial enough to be referred to as airships, so "airship" came to be synonymous with these aircraft.