Editing Radial engine (section)

===Multi-row radials===
[[File:Pratt & Whitney R-4360 Wasp Major 1.jpg|thumb|The [[Pratt & Whitney R-4360 Wasp Major|Wasp Major]], a four-row radial]]
Originally radial engines had one row of cylinders, but as engine sizes increased it became necessary to add extra rows.  The first radial-configuration engine known to use a twin-row design was the 160&nbsp;hp Gnôme "Double Lambda" rotary engine of 1912, designed as a 14-cylinder twin-row version of the firm's 80&nbsp;hp [[Gnome Lambda|Lambda]] single-row seven-cylinder rotary, however reliability and cooling problems limited its success.

Two-row designs began to appear in large numbers during the 1930s, when aircraft size and weight grew to the point where single-row engines of the required power were simply too large to be practical. Two-row designs often had cooling problems with the rear bank of cylinders, but a variety of baffles and fins were introduced that largely eliminated these problems. The downside was a relatively large frontal area that had to be left open to provide enough airflow, which increased drag. This led to significant arguments in the industry in the late 1930s about the possibility of using radials for high-speed aircraft like modern fighters.{{Citation needed|date=October 2014}}

The solution was introduced with the BMW 801 14-cylinder twin-row radial. [[Kurt Tank]] designed a new cooling system for this engine that used a high-speed fan to blow compressed air into channels that carry air to the middle of the banks, where a series of baffles directed the air over all of the cylinders. This allowed the cowling to be tightly fitted around the engine, reducing drag, while still providing (after a number of experiments and modifications) enough cooling air to the rear. This basic concept was soon copied by many other manufacturers, and many late-WWII aircraft returned to the radial design as newer and much larger designs began to be introduced.{{Citation needed|date=October 2014}} Examples include the [[Bristol Centaurus]] in the [[Hawker Sea Fury]], and the [[Shvetsov ASh-82]] in the [[Lavochkin La-7]].{{Citation needed|date=October 2014}}

For even greater power, adding further rows was not considered viable due to the difficulty of providing the required airflow to the rear banks. Larger engines were designed, mostly using water cooling although this greatly increased complexity and eliminated some of the advantages of the radial air-cooled design. One example of this concept is the [[BMW 803]], which never entered service.{{Citation needed|date=October 2014}}

A major study{{which|date=October 2014}} into the airflow around radials using [[wind tunnel]]s and other systems was carried out in the US, and demonstrated that ample airflow was available with careful design. This led to the [[Pratt & Whitney R-4360|R-4360]], which has 28 cylinders arranged in a 4 row ''[[corncob]]'' configuration. The R-4360 saw service on large American aircraft in the post-[[World War II]] period. The US and [[Soviet Union]] continued experiments with larger radials, but the UK abandoned such designs in favour of newer versions of the Centaurus and rapid movement to the use of [[turboprop]]s such as the [[Armstrong Siddeley Python]] and [[Bristol Proteus]], which easily produced more power than radials without the weight or complexity.{{Citation needed|date=October 2014}}

Large radials continued to be built for other uses, although they are no longer common. An example is the 5-ton [[Zvezda M503]] diesel engine with 42 cylinders in 6 rows of 7, displacing {{convert|143.6|L|cuin}} and producing {{convert|3942|hp|kW|abbr=on}}. Three of these were used on the fast [[Osa class missile boat]]s.{{Citation needed|date=October 2014}} Another one was the [[Lycoming XR-7755]] which was the largest piston aircraft engine ever built in the United States with 36 cylinders totaling about 7,750 in<sup>3</sup> (127 L) of displacement and a power output of 5,000 horsepower (3,700 kilowatts).