H engine

AnH engineis apiston enginecomprising two separateflat 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 theNapier Daggerand its derivatives. The name was also applied to engines of the same basic layout, but rotated through 90 degrees—most famously theNapier Sabreseries. A variation on the "H" theme were theFairey Prince (H-16)&Fairey P.24 Monarch,where the two engines retained separate drives, drivingContra-rotating propellersthrough separate concentric shafts. Although successful, they only existed in prototype form.

Animation of an H engine

For the EMD V12/V16 "H-Engine", seeEMD 265.

The H engine is a relatively rare layout, with its main use being in aircraft engines during the 1930s and 1940s. The 1966Lotus 43Formula One car used aBRM16-cylinder H engine, and an 8-cylinder H engine was used for powerboat racing in the 1970s.

Design

The benefits of an H engine are the ability to share common parts with the flat engine upon which it is based, and the goodengine balancewhich results in less vibration (which is difficult to achieve in many other types of four-cylinder engines).

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.

TheU enginelayout uses a similar concept, placing twostraight enginesside-by-side.

History

Aircraft engines

Napier SabreH-24 engine (starboard side)

• Lycoming,US
  • Lycoming H-2470H-24 "hyper engine"(1930s) 2,300 hp (1,700 kW)
• Fairey Aviation,UK
  • Fairey Prince (H-16)(1939) – 1,500 hp (1,100 kW)
  • Fairey Monarch(1939) – H-24 2,240 hp (1,670 kW)
• 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 340 hp (250 kW)
  • Napier Dagger(1934) – H-24, air-cooled vertical, 16.85 litres 890 hp (660 kW), a development of the Rapier
  • Napier Sabre(1938) – H-24, water-cooled horizontal sleeve valves, 36.7 litres 3,500 hp (2,600 kW).
• Pratt & Whitney,US
  • XH-2240- H-24, liquid-cooled,
  • XH-2600- H-24, liquid-cooled,
  • XH-3130- H-24, liquid-cooled,
  • XH-3730- H-24, liquid-cooled,
• Rolls-Royce Eagle(1944) – H-24, 46.2 litres, 3,200 hp (2,400 kW).

Formula One racing engines

TheBritish Racing Motors(BRM) H-16 Formula One engine won the 1966 US Grand Prix in aLotus 43driven by Jim Clark.It was also used by the unsuccessful 1966BRM P83car driven by Graham Hill and Jackie Stewart. As a racing-car engine it was hampered by a highcenter 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.

• 
  BRMH-16 engine (64-valve version)

Motorcycle engines

Brough Superior H-4 motorcycle engine

TheBrough Superior Golden Dreammotorcycle, first shown in 1938.A 1,000 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.

Woolerbuilt a motorcycle prototype with a similar configuration to the Brough Superior Golden Dream and exhibited it at theBritish International Motor ShowatEarls Court Exhibition Centrein 1948 and again in 1951. This was replaced by aflat-four enginedprototype at the 1953 show.

Powerboat racing engines

German firm Konig, who specialised in racing outboard motors,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 itsflat-fourandflat-sixengines as "H4" and "H6" respectively. The letter "H" in this case refers to "horizontally-opposed", an alternative term forflat engines;these engines can also be said to look like a "H" or conjoined "H" s, albeit from the top and in schematic form.

TheSaab H engineis astraight-fourengine produced from 1981 to 2009. The letter "H" represents "high compression".