Mysterious Zero-sen!!!

The Zero-sen is the most thoroughly documented Japanese airplane yet there are still some quite surprising, small, less known details and information.

Here we present photos of one of the least known Zero-sen subtypes.

Asahi Shinbun, July 25, 1943. Photo taken by reporter Hashimoto. Note that this Zero has A6M2 wings, A6M3 cowling, A6M5 long barrelled 20mm wing cannons and early drop tank. Note also the absence of a radio mast.

While the initially very successful A6M2 Model 21 type was dominating the skies early in the Pacific War, Mitsubishi was already striving to improve performance. Various modifications resulted in the A6M3 Model 32 with different cowling and shortened wings. The most important difference with the previous model was the new Sakae 21 1,130hp engine instead of the Sakae 12 of 940hp. Unfortunately the new A6M3 was not particularly successful and production was terminated after 343 units were delivered. 

(Illustrations by "Fuku-san", HERE)

A6M2 Model 21

A6M3 Model 32

While the A6M3 proved to be a failure, the new engine turned out to be rather promising so an interim model keeping the A6M3 cowling and engine but with A6M2 wings started to be produced. Some were with the shortened wing cannon similar to the A6M2 but some had a longer barrel version of the 20mm Type 99 cannon. 560 units were produced of this interim type which was superseded by the new A6M5 Model 52, the first flight of which was in June 1943 and was officially accepted two months later.  

  A6M3 Model 22

Very early A6M5s were externally similar to the A6M3 Model 22.

A6M5 model 52 (early production model)

A6M5 Model 52

This Zero ready for take-off from a Rabaul airfield has all the characteristics of the A6M3 Model 22 but also 30kg bombs under the wings.

Chris Cowx excellently summarised the differences between the various models. Thank you Chris:

A6M2 model 21: Sakae 12 engine, forward firewall, full 12m wings with folding tips, no trim tabs on ailerons, collector exhaust, more angular cowling. 

A6M3 model 32: Sakae 21 engine, rear firewall with changes to fuel and oil capacities, collector exhaust, rounded cowling, squared off 11m wings without folding tips. Some had longer barrelled cannons. 

A6M3 model 22: as per model 32 but with full 12m wings with rounded folding wingtips. Extra fuel tankage in outer wing panels. Some had longer barrelled cannons. 

A6M5 model 52(early): shorter, sturdier 11m wing with thicker skin and rounded tips, Sakae 21 engine with collector exhaust, cowling and firewall location as per A6M3 models. All had longer barrelled cannons.

Pat Donahue contributed more interesting information. Thank you Pat:

The late model 21 and model 22 had BALANCE TABS mounted on the ailerons to lower control forces. These were actuated by control arms in the aileron/flap gap and can be seen in photos as an angular rod extending out of the aileron/flap gap to the tabs on the ailerons. See photo below. These a/c did not have any external fixed trim tabs on the ailerons. I might add that the late 21/22 wing also had some structural changes in the wing to allow for a different flutter speed due to the balance tab installation, these are not really visible for small scale modeling purposes. Lastly the model 22 had an additional fuel tank mounted in the wing which I believe was carried over on the model 52 and later a/c. 

When full flaps were selected to prevent overbalance of the ailerons (ie. over sensitivity to aileron input) the rods were retracted by an eccentric cam attached to the flaps. (The new Tamiya kit has these rods molded in the correct retracted position for a flaps down model) 

ALL other A6M models had an external fixed (ground adjustable only) trim tab attached to the trailing edge of the ailerons.