An engineer working on one of Air Atlantique’s DC-6 Double Wasp engines.

When it was first introduced in 1933, the revolutionary Boeing 247, seen here, came without variable-pitch propellers. Shortly afterwards, as the single Douglas DC-1 was taking shape, it became clear that it would be substantially heavier than originally estimated. It would thus not be able to meet single-engine take-off requirements unless variable-pitch propellers were installed.

Douglas chose the Wright F3 model of the R-1820 Cyclone for use in its new airliner, the DC-2. The Cyclone was Wright's first really successful air-cooled high power engine and its reliability gave passengers confidence in the twin-engine (rather than tri-motor) configuration.

No less than three General Electric turbochargers were used to boost the power of the Wright TurboCompound to 3,700hp; thus making possible the Lockheed Super Constellation.

No successful radial ever had more than nine cylinders in a single row, and no successful one ever had cylinders of greater individual displacement than the Pratt & Whitney Hornet - seen here powering a Boeing Model 40B-4.

Replacing the earlier Jupiters’ cast aluminium crankcase with a forged one reduced the weight of the Jupiter VI by 7%. It was used on the DH.66 Hercules, with which Imperial Airways started its UK-India service, later extended to Australia.