Why does the Boeing 747 have a hump?

When Boeing launched the 747 in 1966, the industry took it for granted that the future of passenger transport was supersonic. Boeing itself was working on the 2707, and many at the company believed the subsonic giant would end its days as a cargo plane once supersonic jets took over passenger routes. That's why the design was conceived from the start to carry large containers and pallets through the nose, with a door that hinges upward. That idea came from the CX-HLS military competition, which Boeing lost to the Lockheed C-5 Galaxy, but whose lessons on front-loading cargo were carried over to the civilian project.

If the nose opens, the cockpit can't occupy it. Joe Sutter and his team placed it on a second level, above the main deck, and to give that cockpit an acceptable aerodynamic shape they extended it backward with a fairing that slopes gently down to the fuselage. The result is the unmistakable silhouette. The solution had an additional advantage: the full-width, circular-section fuselage remained clear along its entire length, which proved decisive for the twin-aisle passenger business.

On the early 747-100s the space behind the cockpit was small and was used as a first-class lounge, with a spiral staircase. Airlines soon asked for more seats, and on the 747-300 Boeing stretched the hump by about 7 m to fit up to 69 passengers. The 747-400 kept that extended deck, and the 747-8 lengthened it again. The hinged nose, meanwhile, lived on in the 747F freighters, where it still serves its original purpose: loading long pieces that don't fit through a side door.