During World War II, the most mass-produced fighter aircraft, including the German Bf-109, British Spitfire, and American P-51 Mustang, predominantly used inline engines over the simpler radial engines for several key reasons.
First, inline engines offered better aerodynamics. The narrow, streamlined shape of an inline engine allowed aircraft designers to build slimmer fuselages, reducing drag and improving speed. This was crucial during dogfights, where high speeds and maneuverability were essential for survival. In contrast, radial engines, with their wide, bulky design, created more drag, which limited the aircraft's overall performance in terms of speed and agility.
Second, inline engines provided better center-of-gravity control. The engine's placement within the fuselage, closer to the aircraft’s center, helped balance the plane, making it more stable in flight. Radial engines, often mounted further forward, could affect the aircraft's handling and balance, especially at higher speeds or during tight maneuvers. Inline engines allowed for a more favorable distribution of weight, contributing to smoother handling.
Additionally, inline engines generally produced more power for their size and weight compared to radial engines. This made them more efficient in terms of fuel consumption and overall power output, critical factors for long-range missions. Fighters like the P-51 Mustang, for example, benefited from the powerful Rolls-Royce Merlin inline engine, which not only delivered excellent performance but also allowed the aircraft to escort bombers over long distances.
While radial engines were simpler to maintain and more reliable in harsh conditions (such as in the Pacific Theater), the need for speed, maneuverability, and longer range in European air combat made inline engines the preferred choice for these iconic WWII fighters.