“Dainty as a Dragonfly and Dangerous as a Rapier”
- From Sunburst: The Rise of Japanese Naval Air Power, 1909-1941 by Mark R. Peatie
Few American fighter pilots on their own survived a turning, twisting, close-in dogfight against a capable Japanese pilot flying a Mitsubishi A6M Zero during World War II. Innovative tactics devised by U.S. Navy Commander John S. “Jimmy” Thach in 1942 returned the advantage to American pilots but the Zero remained a deadly adversary until the war ended. The Japanese official designation was Rei Shiki Sento Ki (Type 0 Fighter). Type 0 referred to the year of the emperor’s reign when production of Zero fighters began in 2600 on the imperial calendar (Julian calendar year 1940). Pilots called it the Zero even after the official codename became ‘Zeke’ in 1942. In this blog, I will explore why the Zero remained one of the world’s most maneuverable fighters to the end of the war.
Zero chief designer Jiro Horikoshi assembled a team in 1937 to design a new fighter for the Imperial Japanese Navy with two primary goals in mind: to make the aircraft as maneuverable as possible and to provide it with enough range to escort Japanese bombers all the way to distant targets in China and back. Navy leadership set these requirements based on missions against Chinese targets during the Second Sino-Japanese War that began in July of that year. When Horikoshi and his team began working on the aircraft in October, they already knew that making the fighter as lightweight as possible would benefit both maneuverability and range.
Making the Zero Lightweight
Horikoshi’s team designed lightness into the Zero’s airframe by paying close attention to many small details. As explained in a 1945 article about the Zero published in Aviation, “Nothing has been spared to keep weight down, neither excessive man-hours to manufacture complex units nor increasing maintenance difficulties for ground crews.” An example is the bracket made of sheet aluminum pierced with large lightening holes and riveted together to support the aileron control tube. Crafts persons could have made this subassembly more easily using fewer and larger metal pieces, but at the cost of increased weight. Workers cut lightening holes in many parts, and in several areas they used plywood instead of aluminum or steel as backing to reinforce the metal canopy frame and to reinforce the false spar that supported the ailerons and flaps in the wings.
For heavier solid parts of the airframe, the team used “extra super duralumin,” which was developed in 1935 by Sumitomo Metal. By alloying zinc with aluminum, metallurgists made a strong lightweight metal that resisted fatigue. Horikoshi used it to build solid pieces such as the two main wing spars that brace the wing much like the keel braces a ship. The Alcoa company began using a similar aluminum alloy in 1943 called “7075.”
Airplanes are built in subassemblies. Wings, fuselage, tail, engine, and landing gear follow separate paths around a factory before workers join them together during final assembly. The fittings that attach the wings and fuselage together are strong and heavy. To make these parts smaller and reduce their weight, Horikoshi’s team permanently joined the wings to the Zero fuselage and designed the aft fuselage including the tail to more easily mount to the forward fuselage at a point just behind the cockpit. Each wing half-mounted the guns, the landing gear, and the fuel tanks, making the wings significantly heavier than the tail. The fittings needed to join the tail could be smaller and lighter because they only had to support the weight of the tail. The gross weight of the A6M2 Zero (5,555 lb.) was 1,871 lbs less than its primary adversary in spring 1942, the Grumman F4F-4 Wildcat (7,426 lb.).
Making the Zero Maneuverable
Locating the engine close to the cockpit didn’t just save weight, it made the Zero more maneuverable as well., The centers of gravity and the aerodynamic center of lift lie at points very near the cockpit and serve as the fulcrum through which the empennage acts as a lever. Keeping the engine close to the fulcrum allowed the aft fuselage to be shorter and save a bit more weight. The elevator retained enough leverage to push the Zero into a tight turn or loop when the pilot hauled back the stick.Wing loading, the weight supported by each square foot of an aircraft’s wing in level flight, also impacts maneuverability. Less wing loading generally means quicker maneuvering because there is less inertia to overcome when the pilot moves the controls to pitch, roll, and yaw the aircraft. At 24.3 lb/ft², the A6M2 Zero had a lower wing loading than the Grumman F4F-4 Wildcat at 28.6 lb/ft². The Zero design team used an engine that made around 300 horsepower less than the Pratt & Whitney R-1840 Twin Wasp powering the F4F-4 Wildcat. Newer American fighters more than doubled the Zero’s horsepower with a commensurate increase in wing loading and performance. The American pilots refused to attack Zeros unless they held a clear advantage in height or speed. When they did attack, they made one pass and hopefully “boomed” a Zero and continued right on going past, avoiding a dogfight. Once they were out of range, they regained the altitude or speed advantage and attacked again if possible and necessary, again one pass, boom, zoom away at speed or to regain altitude above the target.
Accounts of fighter operations during the Pacific war vary on how often Zeros carried radios. All the Zeros flying during the Midway operation in June 1942 had them, but whether a Zero had a radio or not varied depending on the operational needs of a particular mission. Those Zeros not equipped with radios would have been tens of pounds lighter with a corresponding slight decrease in wing loading. The Japanese were slow to develop and use self-sealing fuel tanks but eventually did so later in the war. That they did not begin the war with self-sealing tanks and armor plate to protect the pilot was a result of several factors including an intense and pervasive focus on offensive operations driven by strategic necessity and cultural inclination. The absence of this protective equipment was less costly at the start of the war and even contributed to the Zero’s agility in combat, but American tactics and technology rapidly improved and the Japanese eventually lost many pilots flying Zeros that lacked this protection.
With the extra fuel from a droppable tank carried on the belly, a Zero could fly over 1,600 miles, more than 300 miles farther than the F4F-4 carrying two drop tanks. As the war continued, weight increases due to armor and self-sealing fuel tanks reduced the Zero’s impressive flight range. All the characteristics that comprise the aircraft design process such as structures, aerodynamics, propulsion, and accommodation, act in unison. Changes to one usually affect the other. Horikoshi’s team successfully balanced these characteristics to make the Zero as light as possible and highly maneuverable. As the war progressed, the Zero continued to operate without significant improvements, suggesting that Horikoshi’s team had already extracted all possible performance from the Zero design.
Russell Lee is a curator in the Aeronautics Department and responsible for Japanese aircraft.