X engine

An X engine is a piston engine comprising twinned V-block engines horizontally opposed to each other. Thus, the cylinders are arranged in four banks, driving a common crankshaft. Viewed head-on, this would appear as an X. X engines were often coupled engines derived from existing powerplants.

This configuration is extremely uncommon, primarily due its weight and complexity as compared to a radial engine. It was more compact (per number of cylinders) than a V-engine, however. Shorter crankshafts relative to an inline or V design also appealed to early 20th century engineers like Henry Ford, given the less developed metallurgical technology of the time.^[1]

Most examples of X engines are from the World War II era, and were designed for large military aircraft. The majority of these are X-24s based on existing V-12s. The following are examples of this engine type:

• Ford, as an X-8 prototype during the 1920s that led the way to the company's eventual Flathead V-8.^[2][3]
• Daimler-Benz DB 604, developed for the Luftwaffe’s Bomber B program. Development suspended.
• Isotta-Fraschini Zeta R.C. 24/60, developed for the Caproni F6 fighter, but never fully completed before Italy’s surrender in 1943.
• Rolls-Royce Vulture, based on two Peregrines and the powerplant of the ill-fated Avro Manchester bomber and the Hawker Tornado fighter.
• Rolls-Royce Exe, an air-cooled sleeve valve prototype engine.
• Napier Cub, a water-cooled X-16 engine of the 1920s, which powered the prototype Blackburn Cubaroo torpedo bomber.
• Honda is said to have experimented with an X-32 engine configuration in the 1960s for their Formula One racing efforts, but abandoned the design as being too complex and unreliable.

References

v t e Reciprocating engines and configurations Type Bourke Deltic Orbital Piston Pistonless (Wankel) Radial Rotary Split cycle Stelzer Tschudi Stroke cycles Two-stroke Four-stroke Six-stroke Configurations and number of cylinders Single cylinder Single Split-single Inline / straight I2 I3 I4 I5 I6 I7 I8 I9 I10 I12 I14 Flat F2 F4 F6 F8 F10 F12 F16 V / Vee V2 V3 V4 V5 V6 V8 V10 V12 V14 V16 V18 V20 V24 W W8 W12 W16 W18 Other inline H U Square four VR Opposed X Components Valves Cylinder head porting Corliss Intake Exhaust Multi Overhead Piston Poppet Side Sleeve Slide Rotary valve Variable valve timing Camless Desmodromic Fuel supplies Carburetor Gasoline direct injection Common rail Mechanisms Cam Camshaft Overhead camshaft Connecting rod Crank Crankshaft Scotch Yoke Swashplate Rhombic drive Linkages Peaucellier–Lipkin Watt's (parallel) Other Hemi Recuperator Turbo-compounding