[zerebubuth]

From the data on the Wikipedia page for the Boeing 747, it looks like the empty weight is around half the maximum take-off weight. Passenger and cargo aircraft seem to usually turn around quite quickly and spend only a small amount of time on the ground. In which case around half of the energy required on take off is just to lift the airframe back to the same altitude it landed from.

Perhaps if aircraft could use some sort of funicular system so that one aircraft taking off could get a "boost" from one slowing down to land?

Or planes could land on giant inflatable runways at 30,000ft, with the passengers and cargo taking a lift down to ground level?

[sokoloff]

I would think that most of that energy is used to transport the 747 1/3 of the way around the earth, overcoming induced and parasitic drag for 8+ hours.

From a straight lifting standpoint, lifting 910K pounds to 37K feet takes about 45 billion joules, which is the energy content in about 320 gallons (~2200 pounds) of jet fuel (if consumed perfectly efficiently).

A 747 burns about 1 gallon of fuel per second, meaning the straight lifting fuel consumed represents about 5 minutes or 1% of the fuel consumption on the flight.