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# Ramscoop Airship

Use the large frontal area to maximise remass
 (0) [vote for, against]

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.

 — Selky, Nov 27 2018

Inner propeller airship Inner_20propeller_20airship
Sort of what I have in mind, but not for the same reasons. [Selky, Nov 27 2018]

Coanda Effect https://en.wikipedi.../Coand%C4%83_effect
Intriguing [8th of 7, Nov 30 2018]

 // by burning a small quantity of fuel to heat it

I would recommend helium for the lifting gas.
 — not_morrison_rm, Nov 27 2018

 The overall propulsor efficiency, which relates the energy required to overcome the aircraft drag to the rate of supply of fuel energy, is the product of the thermal efficiency and the propulsive efficiency. Your arrangement will have an excellent propulsive efficiency but a thermal efficiency of approximately zero.

A turboprop by contrast has an excellent thermal efficiency (due to all the internal compression of the working fluid) and achieves a modest propulsive efficiency by using a propeller to accelerate a large mass of air by a fairly small amount.
 — EnochLives, Nov 27 2018

^ Root?
 — not_morrison_rm, Nov 27 2018

 // ^ Root? //

 — EnochLives, Nov 27 2018

Never was a fan of Genesis, just prog-rockers.
 — not_morrison_rm, Nov 27 2018

You could use the sun to heat air traveling through a black tunnel exposed by transparent panels instead of burning fuel. Although 'Jefferies Tube' propulsion is not a new idea and was first prototyped in the 60's in something called the Jefferson Airplane.
 — bigsleep, Nov 27 2018

 Yeah, right.

 Something like a Dyson "air multiplier" using multiple high-pressure jets around the inner circumference of an inflated duct, combined with an airfoil shape, might have potential. And don't neglect the possibilities of the Coanda effect to generate some extra lift.