Mitsubishi A6M Zero (1941): range by subtraction

· THE STORY

A fighter with nothing to spare

When the Zero arrived over Pearl Harbor and then over every Allied airfield from Malaya to Darwin, nobody had a fighter that could stay with it in a turn, and nobody believed a fighter could fly the distances it flew. It could escort bombers 1,000 km to Guadalcanal and 1,000 km back, on an engine of only 950 hp. The trick was weight: no armour and no self-sealing fuel tanks on the A6M2 (later Zeros added some of both), a spar of a new aluminium alloy, and an empty weight under 1,700 kg. It was superbly built and deliberately unprotected, and once Allied pilots learned to dive, shoot and leave rather than turn, its lack of protection became the thing that killed it.

533 km/hTop speed (A6M2)3,100 kmMax range with tank

· WHY IT MATTERED

Power-to-weight by subtraction

Jiro Horikoshi’s team was asked for speed, range, agility and two cannon on 950 hp, and decided it was possible only if every unnecessary gram went. The spar used Sumitomo’s Extra Super Duralumin, an aluminium-zinc alloy that the rest of the world would later call 7075. Nothing protected the pilot or the fuel. The result had a wing loading of 107 kg/m² loaded, roughly a third less than a loaded Bf 109 E and far below the later G, which is why it turned inside everything.

GO DEEPERRange by subtraction →

· WHY IT MATTERED

Range that fooled a war

With a 330-litre drop tank and a lean, slow cruise technique its pilots were drilled in, a Zero could fly about 3,100 km: a maximum, still-air figure with the drop tank, not a combat radius. Allied commanders in 1942 concluded there must be several times as many Zeros as actually existed, because they kept appearing where no fighter could possibly be.

· WHY IT MATTERED

Beaten by tactics, then by numbers

Above about 400 km/h the Zero’s ailerons went heavy and its roll slowed. American pilots learned not to dogfight it: dive on it, fire, keep going, or pair up in the Thach weave so that whichever Zero followed one aircraft flew into the other’s guns. From 1943 the F6F Hellcat had twice the power and armour, and the Zero had lost its trained pilots.

· THE ENGINE

The Sakae: 950 hp, air-cooled, and light

A radial engine has no radiator, no coolant and no water jackets, and the Sakae’s quoted dry weight was about 530 kg for its 950 hp. It was never a powerful engine: the Merlin of the same year made 1,030 hp and the Sakae was overtaken by everything by 1943. But it was reliable and it was enough, because the aircraft around it weighed so little. The later Sakae 21 added a second supercharger speed and 180 hp, at the price of range.

Nakajima Sakae 12 · 14-cylinder two-row radial · 27.9 L · single-speed supercharger · 950 hp at 4,200 m; Sakae 21 two-speed, 1,130 hp

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· WEAPONS AND SPECIALITY

Two cannon with seven seconds of ammunition

The two 20 mm cannon in the wings hit hard, about 2.3 kg a second with the machine guns, but their drums held sixty rounds each, seven and a half seconds of firing, and their shells left the muzzle at about 600 m/s, slower than the 7.7 mm bullets, so they dropped faster and were harder to aim at range. After that the Zero was down to two rifle-calibre guns over the engine. Experienced pilots saved the cannon for a certain kill; inexperienced ones emptied them in the first pass.

· TRY IT

The range equation, and what armour would have cost

The lab’s range tab runs the Zero through the Breguet range equation: 518 litres inside, 330 in the drop tank, a lean cruise. Then add the 100 kg of armour and the self-sealing tanks it did not have, and watch how much of the flight to Guadalcanal disappears.

Readout

Still-air range3,100 km

Radius with a fight1,440 km

Guadalcanalin reach

Breguet with the A6M2’s fuel, L/D and cruise consumption; the fight is charged as a fixed slice of range. A planning sum, not a sortie.

· THE LAB

Power, guns and range: the same three models for all ten

Power against altitude from the type of supercharger, weight of fire against the other nine, and Breguet range with the armour and drop-tank trades. Simplified models, each scaled to this aircraft’s published figures, so the shapes are honest and the third decimal is not.

Still-air range 3,100 km with 0 kg of extra weight, 611 kg of fuel on board.

Readout

Still-air range3,100 km

Half the still-air range1,550 km

Fuel on board611 kg

Fuel fraction20 %

Mitsubishi A6M Zero: Breguet with cruise L/D 13.5, scaled so that the published 3,100 km comes out with the drop tank, as the speed tab is scaled to the published speed. Still air, no reserve, no climb, no combat: half of it is not a combat radius.