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  • Airplane jet engines have gotten bigger and bigger over time - and it’s not just because


  • planes are getting bigger: the Airbus A350 is a smaller plane than the Boeing 747 but


  • has bigger engines. The reason? Bigger engines are simply more efficient, up to a point.

    引擎卻更大。 為何?更大的引擎在一定範圍內更有效率。

  • Modern jet engines actually consist of two propulsion systems working together: the jet


  • core, which provides the power and a small amount of thrust, and the fan, which is just


  • a big propellor driven by the jet core that provides most of the thrust.


  • Pure jet engines can be incredibly powerful (which is why theyre used for fighter jets),


  • but theyre also horribly inefficient because they shoot out their exhaust at super high


  • speeds, which equates to huge amounts of kinetic energy, since kinetic energy is proportional


  • to the speed squared, so accelerating exhaust to twice the speed takes 4 times the energy.


  • In exchange for power, they literally blast energy away as a bunch of hot air.


  • Of course, you do have to shoot some air out of the back of an engine to generate thrust,


  • but it doesn’t have to have lots of energy. Instead of accelerating a little bit of air


  • a lot, you can achieve your desired thrust by accelerating a lot of air a little bit


  • - you get the same momentum boost but save a ton of energy.


  • Essentially, if you make an engine too small, it has to accelerate the air so much as to


  • be a waste of energykind of like using a machine gun to propel your car. But if you


  • make the engine too big, then it starts to cause too much drag. An ideal engine is somewhere


  • in betweenrough estimation puts the ideal engine somewhere around 4 meters in diameter,


  • which is just slightly bigger than the current largest engines.


  • So you can expect jet engines to continue growing in size... but not forever.


  • I’d like to thank for supporting this video. As you may have heard, Audible

    感謝 Audible.com支持本片。你也許聽過,

  • has audiobooks of all sorts, including fiction, non-fiction and periodicals. You can try Audible

    Audible擁有各式有聲書,包含故事、非故事和期刊。 你可以免費試用Audible

  • free for 30 days by going to, and if you do so I recommend the book Ender’s


  • Game by Orson Scott Card, it was one of the pivotal sci-fi novels I read as a teenager

    Orson Scott Card寫的Ender’s Game,這是我青少年時

  • and I can’t recommend it enough. Remember, the enemy’s gate is down. And you can try

    讀過最重要的科幻小說,誠心推薦。 記住,敵人的大門已經關上。

  • Audible free for 30-days by going to

    你可以上 免費試用Audible30天。

Airplane jet engines have gotten bigger and bigger over time - and it’s not just because



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