Your calculations are correct, but you've baked a few other assumptions into them. - Fuel has no structural strength. Batteries are rigid and can double as par

Your calculations are correct, but you've baked a few other assumptions into them. - Fuel has no structural strength. Batteries are rigid and can double as parts of the airframe, saving weight. - Combustion engines are complex and expensive. This precludes mounting a dozen tiny engines on a plane and integrating them at just the right spots. Electric fans are cheaper and easier to integrate into the airframe, reducing drag. This also helps with engine-out capability. If you have two engines and one fails, you've lost half your thrust. If you have 36 engines and one fails, you've lost 3% of your thrust. - Air becomes less dense with altitude. This reduces drag, but it also reduces the power of combustion engines. Electric aircraft don't need oxygen, so their power remains the same at altitude. There are losses due to the fan having to rotate more to move the same mass of air, but in general, electric aircraft become more efficient at altitude. - Electric fans respond much faster to throttle inputs and are easier to gimbal than combustion propellors or jets. This allows designs with reduced or even eliminated control surfaces. The lack of rudder and elevator reduces drag, allowing for greater range. That last trick might sound insane for human-rated aircraft, but there are already flying prototypes that use this approach.[1][2] 1. https://www.youtube.com/watch?v=5ukmS9ZJm40 https://www.youtube.com/watch?v=5ukmS9ZJm40 2. https://www.youtube.com/watch?v=ZH7DSFRCqDQ https://www.youtube.com/watch?v=ZH7DSFRCqDQ