The Supermarine Spitfire, the Messerschmitt Bf-109, and the Mitsubishi A6M Zero, were contemporary WW2 fighters, introduced roughly around the same period. All three enjoyed successes at their early careers, but while the Spitfire and Bf-109 remained competitive throughout the war, the A6M was left behind and was unable to compete with later Allied aircraft in the Pacific.
The lag in development led to appalling losses after the Allies abandoned low-speed combat in favour of high speed attacks. The Zero was unable to run to pursue, or to escape. Initially the kill:loss ratio was 12:1, that now was reversed!
It is untrue to say that the A6M Zero did not undergo any further development. The war had begun with the A6M2. The A6M3 shortened the wings by removing the folding wingtips and made the engine cowl smaller and more aerodynamic, and improved the Sakae 21 engine by adding a two-stage supercharger for better performance at higher altitude. These modifications improved the fighter’s ability to roll and dive and increased the maximum speed from 313 to 330 mph, without replacing the engine.
The next model, the A6M5 gave the engine individual exhaust stacks that provided extra thrust, and thicker wing skinning to allow faster diving speed without tearing the wing, increasing the speed to 350mph (diving speed now exceeded 450mph), but otherwise it simply formalized the ad-hoc modifications of the A6M3.
The improvement in performance between A6M2 and A6M3 were significant, while the A6m5 model was a more incremental improvement.
Unfortunately for the Imperial Japanese Navy Air Force, the newer Allied aircraft far outpaced the A6M5 in late 1943. An over-emphasis on low-speed turning combat and range had led to neglect in protection and engine power, and above all, high-speed maneuvers.
Could the Zero have been modified further to keep it at least competitive?
Tracing the further development of its contemporaries, the Spitfire and the Bf-109, we find that:
- Engine power for British and German fighters kept increasing. Engine development continued as the Rolls-Royce Merlin and Daimler Benz DB-601/605 were tweaked to higher power, exceeding 1500hp and eventually 2000hp. Power increased in leaps and bounds for the Bf-109: while it had been originally designed around a 700hp engine with its high performance gained from exceptional aerodynamics, the late war Bf-109K had a Daimler-Benz DB-605 engine roaring away at 2000hp.
- Both aircraft began the war emphasizing low speed turning combat, just like the A6M. Despite having top speed of over 300 mph, most early war turning dogfights took place at only 150-200 mph. The Spitfire’s large elliptical wings reduced the tendency to stall when turning steeply at low speed. The Bf-109 had smaller wings which made slow speed turns more prone to stalling, but it had a trick up its sleeve: automatic leading edge slats that popped out and enabled turning at high angles. But later in the war, ever-increasing engine power and the change to high-speed tactics made these low-speed features superfluous. The Zero relied on its large wing area like the Spitfire, and its very light weight, to excel at turning at low speed.
The ability of the Spitfire and Bf-109 to evolve kept them competitive.
What more could have been done to keep the Zero more competitive, if not a war-winner then at least not cannon fodder? It needed to make the transition from low speed turning combat to high speed fighting.
For a start, it needed a new engine. The Sakae-21 engine built by Nakajima was extremely reliable, but low-powered at 1100hp. The Zero had originally been designed for the Mitsubishi Kinsei engine which started with equal power with the Sakae, but later mark Kinsei-62 had been successfully tweaked to 1500hp by 1943.
The Kinsei-powered Zero was an aircraft that almost came into being, except for interference by Navy officers. The designers at Mitsubishi had been overruled at the Zero’s introduction in 1940 and ordered to fit the fighter with the inferior Zuisei engine, then with rival Nakajima’s Sakae. The Navy also overruled the now-tweaked 1500hp Kinsei-62 for the A6M5 upgrade in 1943 due to the necessity of retooling the aircraft factories to produce a different engine mount; pilots would pay very dearly for the stubbornness of the Navy admirals.
A more powerful engine would give the Zero pilot more options for pursuit and escape, and more extreme vertical maneuvers which the Zero already excelled at in addition to its low speed maneuverability. Had the Zero been equipped with the Kinsei in 1940 as intended by its designer, the upgrade would have involved tweaking its engine rather than outright replacement involving redesigning its engine mounts, cowl and plumbing.
The reduction in wing size was a step in the right direction, improving the roll performance and increasing its speed. There was still one very large handicap: at high speed, the ailerons became unusable. The pressure exerted by the airstream on the ailerons was too much for human muscle to overcome; controls were operated directly by the pilot with cables or rods connected directly to the control stick and rudder pedals. Very few aircraft had power assisted controls. The Zero’s large ailerons gave it excellent turning characteristics at low speed but were impossible to operate at high speed. At high speed, the Zero could loop up or dive but was unable to roll sideways: rolling was the prelude to turning. It made the fighter too predictable in high speed combat.
Jiro Horikoshi, the Zero’s designer, had originally installed servo tabs on the ailerons to assist high speed roll. A servo tab is a small flap hinged to the trailing edge of the aileron. It requires less force to operate against the high speed airstream due to its small size, and it uses the force generated by the airstream to help move the aileron in the opposite direction the tab is moved. This did indeed free up the ailerons at high speed, but it encouraged the Zero pilots to make extremely aggressive high speed turns that overstressed the wings. Horikoshi was forced to remove them.
The Zero would need strengthened wings as well as servo tabs in order to perform high speed roll and turn. In the meantime, pilots would have to change their style of flying, making the famously steep turns only at low speed, and to roll and make shallower turns at high speed.