The A6M2 had 1x 38 USgal fuselage tank (that weighed 22 lbs), plus 2x 51 USgal wing tank (that weighed 24 lbs each) for a total fuel load of 141 USgal. The tanks were non-SS and were welded aluminum with anti-slosh baffles. They were not integral to the structure (ie they were not a "wet wing" type) and they were designed to be replaceable.
The most common type of SSFT used on UK aircraft (Hurricane, Spitfire, Mosquito, Lancaster to name a few) for most of the war, was the CIMA type (manufactured by FPT and others). It was a .5" thick multi-ply laminate applied over the outside of a metal tank, weighing about .96 lbs/ft2.
The A6M2 fuel tanks were approximately the following size (I looked for accurate dimensions but did not find any, so I approximated from the cut-aways and blueprints I did find.)
The 38.0 USgal tank was about 1.36' x 1.5' x 2.5' which equals a volume of 5.1 ft^3 and a wall square footage of 21.8 ft^2
Each 51.5 USgal tank was about 1.00' x 2.2' x 3.2' which equals a volume of 6.9 ft^3 and a wall square footage of 24.9 ft^2
NOTE that 1 ft^3 = 7.48 USgal by volume
1 x 38.0 USgal 21.8 ft2 x .96 = 21 lbs added weight
1 x 51.5 USgal 24.9 ft2 x .96 = 24 lbs added weight
1 x 51.5 USgal 24.9 ft2 x .96 = 24 lbs added weight
The .5" thickness would also reduce the dimensions of the metal structure and the volume of the tank by an amount proportionate to the square footage of the tank walls, so:
1 x 38.0 USgal = 5.1 ft3 - 21.8 ft2 x .5" x 12"^2 / 12"^3 = 0.91 ft^3 yielding a reduction in volume of 6.8 USgal
1 x 51.5 USgal = 6.9 ft3 - 24.9 ft2 x .5" x 12"^2 / 12"^3 = 1.04 ft^3 yielding a reduction in volume of 7.8 USgal
1 x 51.5 USgal = 6.9 ft3 - 24.9 ft2 x .5" x 12"^2 / 12"^3 = 1.04 ft^3 yielding a reduction in volume of 7.8 USgal
The increase in weight due to the SSFT materials would be about 69 lbs and the decrease in fuel load would be 22.4 USgal.
Fitting the same amount of armor as the 1941 Spitfire carried would add about 150 lbs.
Adding a more capable radio such as the TR.1133 would add another 30 lbs or so.
Increase in weight due to the SSFT, armour, and radio, would be 69 + 150 + 30 = 249 lbs.
Decrease in weight due to reduction in fuel load would be 22.4 USgal x 6 lb/gal = 135 lbs.
Net change in TOGW would be 249 - 135 = +114 lbs.
So the increased TOGW would be 5335 + 249 - 135 = 5449 lbs, while the wing loading at combat weight would only increase by about 1.03 lb/ft^2.
Decrease in range would be significant, at a bit over 22.4 / 141 = 16% or about 200 miles, leaving a range of 1000 miles at 250 mph TAS/200 IAS (max economic cruise at 15,000 ft), with enough fuel for 20 minutes of combat (max power) and 30 minutes reserve (at best economic cruise).
In addition to the above weight increases you would probably have to strengthen the underlying metal structure of the fuel tanks. I do not know how much weight this would add to the above calculations, but I doubt it would be more than 50-60 lbs (That is just a guestimate on my part, as I am not familiar with the structure required to withstand the forces imposed on the tank by the impact and penetration of the projectiles).
The A6M3 had a TOGW of ~5500 lbs and according to the US, Australian, and UK tests, it was still ridiculously more maneuverable than the Allied fighters at low-medium speeds so I figure the same mods could be done to the A6M3 with little loss in combat effectiveness.
(I am doing this late at night so let me know if I made any errors.
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edit: The above 1000 mile range is predicated on the maximum range not being limited by the internal fuel load. The fuel load at TOGW would be 141 - 22.4 = 118.6 USgal internal plus the normal 87 USgal DT, for a total fuel load of 118.6 + 87 = ~205 USgal.
2nd edit: tyrodtom pointed out that I made an error in my original calculations by incorporating a multiplier of .5 in the added weight of the SSFT calculations. I have corrected the above calculations and all subsequent calculations/values in my later posts. Thank you tyrodtom.
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