One way to increase the efficiency of a high-bypass jet engine is to turn the fan into an open rotor, a bit like returning to propellers, but using two rings of stubby counter-rotating blades.

ECONOMIST: A new way to build a greener jet engine

It seems that global preseason tours, driven by the need to boast revenue and satisfy the growing demand of an international fan base, shows no sign of ending soon even if jet-lagged players maybe a growing sight on the opening day of the European season.

CNN: Preseason football goes global

Whereas in the 1960s, jet engines were long and slim, today they have a vast opening at the front containing a giant fan.

ECONOMIST: A new way to build a greener jet engine