The Radial Engine

 How the radial aircraft engine works. 

In the early days, automobile engines were modified for use in flying machines. The designs are:

Inline, as in most car engines today – and in older aircraft engines (think DH Gipsy Major);
Vee engines, such as pioneered by the Ford V-8 – and the Rolls-Royce Merlin; and
Horizontally-opposed auto engines, think Porsche – and the modern Continental aero engines.
Radial engines were not used in automobiles, although there were land and marine applications.

The radial engine is a reciprocating type, internal combustion engine configuration in which the
cylinders ‘radiate’ outward from a central crankcase like the spokes of a wheel. The radial configuration was very commonly used for aircraft engines before turbine engines became predominant.

For an excellent visual presentation, see:
Part 1
Part 2

For the complete article see the attached pdf.