main clutch. This image also shows the gearbox attached to the four-cylinder engine and clearly shows the offset between the cylinders, and the flywheel at the front of the engine which doubled as a fan. The epicyclic gear next to the clutch has a reduction ratio of 2.7:1, the other has a reduction ratio of 1.7:1. The latter is used to give 3rd gear, the former to give 2nd gear, and both together give 1st gear, all operated by a single hand lever. The fact that reverse is not provided by the gearbox, but instead by the rear axle (see below), and operated by a reversing lever separate from the gearchange lever, means the cars had as many reverse gears as they did forward gears. The use of helical planetary gears later became the main gear mechanism for automatic transmissions, the key difference from the Wilson-Pilcher design being that gear changes were made automatically and not by moving a gear change lever. Rear Axle The rear axle, like the gearbox and engine, was housed in an aluminium case. In addition to the normal function of providing a differential, it also provided the reverse gear, and contained the rear brake (foot operated). Reversing is achieved by changing which of the large bevel gears (these days known as crown wheels) engages with the drive on the end of the propshaft. Like the gearbox, all gears within the axle are helical cut. See also List of car manufacturers of the United Kingdom Bibliography G. N. Georgano: Autos. Encyclopédie complète. 1885 à nos jours. Courtille, 1975 (French) David Culshaw, Peter Horrobin: The Complete Catalogue of British Cars 1895–1975, Veloce Publishing PLC, Dorchester (1997), (English) References External links Armstrong Whitworth Defunct motor vehicle manufacturers of England Defence companies of the United Kingdom Engineering companies of the United Kingdom Vintage vehicles Companies based in Newcastle upon Tyne