[baybal2]

> What would you expect given all the things you have mentioned? Twice as much fuel?

Pretty much. Most 4 engine airplanes can fly with just 2, or 1. Take off thrust is few times the cruise thrust an all jet airplanes. In flight, the engines needed to achieve the take off thrust are dead drag, and dead weight.

This is why one of crazy ideas for very early large jet planes was to have parachutable, jettisonable engines, or having RATO on civilian planes.

[wahern]

I've heard the opposite: that the large, high-thrust engines needed on twin-engine wide bodies for takeoff and ETOPS certification can have greater aerodynamic and performance losses at cruise, as well as higher maintenance costs, than the smaller engines on four-engine wide bodies. And in the specific case of the A380, having four engines did not put them at a fuel economy disadvantage, notwithstanding the widely held belief that it did.

A greater difference in fuel economy, however, comes from the generation of the engine. The A380 is no longer cost efficient not because it has 4 engines, but because those 4 engines are 1.5 generations behind modern engines.[1] Airbus and Emirates killed the A380 mere months after Rolls Royce firmly shut the door on developing an engine upgrade, and the whole multi-year saga hinged the entire time on Rolls Royce's vacillations. (Of course, Rolls Royce wouldn't invest in the engine because the market was too small, and they were also struggling with other issues that required their time & capital, but those are different matters.)

[1] Likewise, the 747 was less efficient than the 777 partly because the 777 was equipped with a newer generation of engines. But this difference was never factored into the calculus that gave rise to the belief that two engines were inherently more efficient than four, regardless of context.

[souprock]

Speaking as a passenger, the right solution is CATOBAR. Passenger airports should install linear motor catapults that can get a 500-ton aircraft up to Mach 0.85 in about 10 seconds. (it can support the plane, allowing launch with already-retracted gear) They should also install arrester cables, or something better, such as a moving platform that could handle both tasks.

[baybal2]

A much cheaper solution is just having really long runways.

[souprock]

That doesn't really work for Monaco, Vatican City, or Gibraltar. War is not cheap.

There is no reasonable way to expand London City Airport. Bulldozing London's financial industry to make more room for runways would mean bulldozing the primary customers.

Also, as a passenger, I just want CATOBAR.