Let’s go back to the example of the 747. Most variants of this plane have a fuel capacity somewhere around 200,000 liters, which is really a lot of fuel. With a density of about 0.8 kilogram per liter, this gives it a fuel mass of 160,000 kilograms. The specific energy of jet fuel is around 12,600 watt-hours per kilogram. This means that with 1 kilogram of fuel, you could get a power of 1 watt for 1 hour—assuming you can use all of the energy, which you can’t.
Let’s say that the overall efficiency of the plane is 35 percent (which is the same as saying each jet engine is
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