lighter-than-aircraft

...However, it does not include things that fly through space such as spaceships and space rockets. They are divided into lighter-than-air aircraft and heavier-than-air aircraft. The former are made by filling a bag with helium or hydrogen gas, which is lighter than air, or by heating the air in the bag with a burner or other device to make it lighter than the surrounding air, making the specific gravity of the entire aircraft lighter than the specific gravity of the air, and using buoyancy to float. They are divided into airships and balloons depending on whether they have a power source for navigation. ...

*Some of the terminology that refers to "lighter-than-aircraft" is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…ただし宇宙船，宇宙ロケットのように宇宙空間を飛ぶものは含めない。空気より軽い軽航空機lighter‐than‐aircraftと空気より重い重航空機heavier‐than‐aircraftとに分けられる。前者は空気より軽いヘリウムや水素のガスを袋に詰めたり，あるいは袋の中の空気をバーナーなどで熱して周囲の空気より軽くすることにより，機体全体の比重を空気の比重より軽くし，浮力を利用して浮くもので，航行のための動力の有無によって飛行船と気球に分けられる。…

※「lighter-than-aircraft」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報