<P> Lycoming manufactures a popular series of flat - four aircraft engines ranging up to 360 cu in (5.9 L), as used in many smaller Cessnas and other general aviation aircraft . Similar engines are produced by Continental Motors, Franklin Engine Company, and others . Retired aircraft engines power many shallow draft boats in the Florida Everglades . </P> <P> The OS Engines company in Japan has made miniature, air - cooled flat - four engines in 40 cc and 52 cc sizes for radio - controlled aircraft hobby use, with the 52 cc "FF - 320" engine currently in production . </P> <P> Homebuilt aircraft builders often favour flat four engines because of their smoothness and suitability for air - cooling . For some years modified Volkswagen and Subaru flat - fours were popular . In recent times, flat - fours manufactured specifically for kit planes have been successful; such motors include the Rotax 912, the Jabiru 2200 and the D - Motor LF26 . </P>

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