Editing H engine (section)

{{Short description|Inline engine with four banks driving two crankshafts}}
{{For|the EMD V12/V16 "H-Engine"|EMD 265}}
[[File:H-engine.gif|thumb|Animation of an H engine]]

An '''H engine''' is a [[piston engine]] comprising two separate [[flat engine|flat engines]] (complete with separate crankshafts), most often geared to a common output shaft. The name "H engine" is due to the engine blocks resembling a letter "H" when viewed from the front. The most successful "H" engine in this form was the [[Napier Dagger]] and its derivatives. The name was also applied to engines of the same basic layout, but rotated through 90 degrees—most famously the [[Napier Sabre]] series. A variation on the "H" theme were the [[Fairey Prince (H-16)]] & [[Fairey Monarch|Fairey P.24 Monarch]], where the two engines retained separate drives, driving [[Contra-rotating propellers]] through separate concentric shafts. Although successful, they only existed in prototype form.

The H engine is a relatively rare layout, with its main use being in aircraft engines during the 1930s and 1940s. The 1966 [[Lotus 43]] Formula One car used a [[BRM]] 16-cylinder H engine, and an 8-cylinder H engine was used for powerboat racing in the 1970s.