Editing H engine

{{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.

== Design ==
{{refimprove section|small=yes|date=November 2019}}
The benefits of an H engine are the ability to share common parts with the flat engine upon which it is based, and the good [[engine balance]] which results in less vibration (which is difficult to achieve in many other types of four-cylinder engines).<ref>{{cite book| last= Willoughby| first=Vic | title= Classic motor cycles| year= 1989| publisher = Ivy Leaf| isbn= 0-86363-005-7}}</ref>

However, H engines are relatively heavy and have a high centre of gravity. The latter is not only due to the second crankshaft being located near the top of the engine, but also the engine must be high enough off the ground to allow clearance underneath for the exhaust pipes{{cn|date=December 2019}}.

The [[U engine]] layout uses a similar concept, placing two [[straight engine]]s side-by-side.

== History ==

===Aircraft engines===
[[File:CASM - Napier Sabre - 030906.jpg|thumb|[[Napier Sabre]] H-24 engine (starboard side)]]
*[[Lycoming Engines|Lycoming]], US
**[[Lycoming H-2470]] H-24 "[[hyper engine]]" (1930s) {{cvt|2300|hp}}
*[[Fairey Aviation]], UK
**[[Fairey Prince (H-16)]] (1939) – {{cvt|1500|hp}}
**[[Fairey Monarch]] (1939) – H-24 {{cvt|2240|hp}}
*[[Klöckner-Humboldt-Deutz DZ 710|Klöckner-Humboldt-Deutz DZ 720]] – H-32, 102.9 litres diesel
*[[D. Napier & Son]], UK.
**[[Napier Rapier]] (1929) – H-16 air-cooled vertical, 8.83 litres {{cvt|340|hp}}
**[[Napier Dagger]] (1934) – H-24, air-cooled vertical, 16.85 litres {{cvt|890|hp}}, a development of the Rapier
**[[Napier Sabre]] (1938) – H-24, water-cooled horizontal sleeve valves, 36.7 litres {{cvt|3500|hp}}.
*[[Pratt & Whitney]], US
**[[Pratt & Whitney X-1800|XH-2240]] - H-24, liquid-cooled,
**[[Pratt & Whitney X-1800|XH-2600]] - H-24, liquid-cooled,
**[[Pratt & Whitney XH-3130|XH-3130]] - H-24, liquid-cooled,
**[[Pratt & Whitney XH-3130|XH-3730]] - H-24, liquid-cooled,
*[[Rolls-Royce Eagle (1944)|Rolls-Royce Eagle]] (1944) – H-24, 46.2 litres, {{cvt|3200|hp}}.

=== Formula One racing engines ===
The [[British Racing Motors]] (BRM) H-16 Formula One engine won the 1966 US Grand Prix in a [[Lotus 43]] driven by Jim Clark.<ref>{{cite web|url=http://members.madasafish.com/~d_hodgkinson/brm-e-H16.htm |title=BRM engines H16 |publisher=Members.madasafish.com |access-date=2010-09-12}}</ref> It was also used by the unsuccessful 1966 [[BRM P83]] car driven by Graham Hill and Jackie Stewart. As a racing-car engine it was hampered by a high [[center of gravity]], and it was heavy and complex, with gear-driven twin overhead cams for each of four cylinder heads, two gear-coupled crankshafts, and mechanical fuel injection.<ref>{{cite journal |journal= Model Cars |issue= July 1967 |last1=Taylor |first1=Roger |title=Lotus 43 & B.R.M. 83 |page= 327 |url=http://vsrnonline.com/Mags/MC/Vol4/V4N7/MC_V4N7_p327.jpg |archive-url=https://web.archive.org/web/20160326130659/http://vsrnonline.com/mags/mc/Vol4/V4N7/MC_V4N7_p327.jpg |archive-date=26 March 2016 |url-status=dead}}</ref><ref>{{cite journal |journal= Model Cars |issue= July 1967 |last1=Taylor |first1=Roger |title=Lotus 43 & B.R.M. 83 |url=http://www.vsrnonline.com/mags/mc/Vol4/V4N7/MC_V4N7_p328.jpg |page= 328 |archive-url=https://web.archive.org/web/20160304185506/http://www.vsrnonline.com/mags/mc/Vol4/V4N7/MC_V4N7_p328.jpg |archive-date=4 March 2016 |url-status=dead}}</ref>

<gallery mode="packed" heights="200px" style="text-align:left">
File: BRM H16 engine.jpg |[[British Racing Motors|BRM]] H-16 engine (64-valve version)
</gallery>

=== Motorcycle engines ===
[[File:Brough Superior Golden Dream (close up).JPG|thumb|Brough Superior H-4 motorcycle engine]]
The [[Brough Superior Golden Dream]] motorcycle, first shown in 1938.<ref>{{cite book|last=Wilson|first=Hugo|title=The Encyclopedia of the Motorcycle|chapter-url=https://archive.org/details/encyclopediaofmo00wils_1|chapter-url-access=registration|year=1995|publisher=Dorling Kindersley|location=London|isbn=0-7513-0206-6|pages=[https://archive.org/details/encyclopediaofmo00wils_1/page/34 34–35]|chapter=Brough Superior Dream}}</ref> A 1,000&nbsp;cc H-4 design and a few units were produced in early 1939. Any development planned was interrupted by World War II and subsequent years of austerity.

[[Wooler (motorcycles)|Wooler]] built a motorcycle prototype with a similar configuration to the Brough Superior Golden Dream and exhibited it at the [[British International Motor Show]] at [[Earls Court Exhibition Centre]] in 1948 and again in 1951. This was replaced by a [[flat-four engine]]d prototype at the 1953 show.

=== Powerboat racing engines ===
{{refimprove section|small=yes|date=November 2019}}
German firm Konig, who specialised in racing outboard motors,<ref>{{cite web |title=Quincy vs Konig |url=http://www.quincylooperracing.us/gpage8.html |website=www.quincylooperracing.us |access-date=16 November 2019}}</ref> built a few 1000cc  H-8s in the 1970s, which were basically two of their VC500 flat fours mounted one above the other, with the direction of rotation reversed on one of them. Each half of the engine was a water cooled 2-stroke with rotating disc valve driven by a toothed belt via two 45/90 degree pulleys, plus two siamesed expansion chamber exhausts, fed by two single choke carbs. Both cylinders at each end of each engine fired at the same time, hence the siamesed exhausts for each pair.

== Other engines named "H" ==
Subaru has marketed its [[flat-four engine|flat-four]] and [[flat-six engine|flat-six]] engines as "H4" and "H6" respectively. The letter "H" in this case refers to "horizontally-opposed", an alternative term for [[flat engine]]s; these engines can also be said to look like a "H" or conjoined "H"s, albeit from the top and in schematic form.

The [[Saab H engine]] is a [[Straight-four engine|straight-four]] engine produced from 1981 to 2009. The letter "H" represents "high compression".

== References ==
{{commonscat|H engines}}
{{reflist}}

{{Piston engine configurations}}
[[Category:Piston engine configurations]]
[[Category:Engines by cylinder layout]]