Editing Flat engine (section)

==Aviation use==
[[File:Puch Flugmotor Patent AT 48877 1909-11-08.png|thumb|right|Twin-boxer of [[Johann Puch]], Patent AT 48877 (1909)]]
[[File:Riedelanlasser.jpg|thumb|right|World War II-era Riedel starter motor]]

In 1902, the Pearse monoplane (which would later become one of the first aircraft to achieve flight) was powered by a flat-twin engine. Amongst the first commercially-produced aircraft to use a flat engine was the 1909 [[Santos-Dumont Demoiselle]] range of aeroplanes, which was powered by boxer-twin engines.{{Citation needed|date=March 2021}}

Several boxer-four engines have been produced specifically for light aircraft. A number of manufacturers produced boxer-six aircraft engines during the 1930s and 1940s.{{Citation needed|date=March 2021}}

During World War II, a boxer-twin engine called the "Riedel starter" was used as a starter motor/mechanical [[Auxiliary power unit#As mechanical "startup" APUs for jet engines|APU]] for the early German jet engines, such as the [[Junkers Jumo 004]] and [[BMW 003]]. Designed by [[Norbert Riedel]], these engines have a very [[Stroke ratio#Oversquare or short-stroke engine|oversquare]] stroke ratio of 2:1 so that they could fit within the intake diverter, directly forward of the turbine compressor.{{Citation needed|date=March 2021}}
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