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 a inline or V design also appealed to early 20th century engineers like Henry Ford, given the less developed metallurgical technology of the time.
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.
- 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.
- ↑ "Henry Ford's Weird Old Engines", Popular Science: pp. 64–67, August 1960, http://books.google.ca/books?id=xSUDAAAAMBAJ&pg=PA64
- ↑ Hemmings.com. "Hemmings Auto Blogs » Blog Archive » SIA Flashback - Experimental Ford Engines". Blog.hemmings.com. http://blog.hemmings.com/index.php/2008/01/27/sia-flashback-experimental-ford-engines/. Retrieved 2011-12-06.
- ↑ "Eli Apolzon and daughter Ruth Family Page * * * Austin, Texas - Henry Ford's X-8 engine and how it will be used to raise dollars for Autistic and other Special Needs children". Lutheransonline.com. 2011-05-10. http://www.lutheransonline.com/servlet/lo_ProcServ/dbpage=page&mode=display&gid=00032000001081239920917940&pg=00032000001086276828588714. Retrieved 2011-12-06.