Ramscoop Airship

The impulse generated by an engine is based on the total momentum sent out the back, which is proportional to the velocity and mass of whatever you're ejecting; whilst the energy consumed is proportional to the mass and the *square* of the velocity. Hence, an engine that puts out a large amount of mass at low velocity consumes less energy than one that puts out a small amount of mass at high velocity, for the same impulse.

Airships have a large frontal surface area. I propose that the front of the airship should constitute a scoop, which would funnel large amounts of air through a central tube. This air would then be accelerated out the back, possibly by burning a small quantity of fuel to heat it (see: Air augmented rocket), providing substantially more thrust than a traditional propeller design could achieve.