Книга: H engine: Engine configuration, Cylinder (engine), Flat engine, Power- to-weight ratio, Aircraft engine, Aerodynamics, Center of mass, Straight engine, U engine, Crankshaft

An H engine (or H-block) is an engine configuration in which the cylinders are aligned so that if viewed from the front, they appear to be in a vertical or horizontal letter H. An H engine can be viewed as two flat engines, one atop or beside the other. The 'two engines' each have their own crankshaft, which are then geared together at one end for power-take-off. This leads to a worse power-to-weight ratio than simpler configurations with only one shaft. One obvious advantage of the H configuration is to allow the building of reasonably short engines with more than 12 cylinders, their compact size being useful as aircraft engines where their small size allows for better aerodynamics. On the other hand, for automotive and especially race-car applications, there is also the obvious disadvantage of a higher center of gravity, not only because one crankshaft is located atop the other, but also because the entire engine must be sandwiched between the exhaust pipes, which places the center of gravity even higher. The U engine is a similar concept, except that it uses two straight engines.