How much weight did the Spitfire I or II gain with added armor

[pinsog]

How much weight did the Spitfire Mark I or Mark II gain when they added pilot armor, bullet proof windshield and self sealing fuel tank?

 

[Shortround6]

Roughly 240lbs or a bit less.

Spitfire K. 9793 weighed 5935lbs gross on trials in July of 1939 with a 2pitch metal propeller.
Spitfire N. 3171 weighed 6050lbs gross on trials in March of 1940 with a Rotal propeller., Bullet proof windscreen and armour on fuel tank. but no back armor for pilot.
Spitfire P. 7280 weighed 6172lbs gross on trials in May of 1940. The back armor for the pilot weighed 73lbs.

I believe (but could be wrong) that on the early SPitifires only the upper tank was treated with selfsealing material. and a heavy gauge aluminium sheet was palced over the top ot the tank?

I would also note that the "service load" (does not include fuel or oil) increased from 657lbs on the MK Is to 735lbs on the MK II.

 

[pinsog]

Were British self sealing fuel tanks as effective as US tanks? Were they lighter simply because they only had 1 73 gallon fuel tank vs say a P40 that had 3 separate tanks of 140-160 gallons?

 

[fubar57]

From "Spitfire" by Alfred Price...

 

[tomo pauk]

Were British self sealing fuel tanks as effective as US tanks? Were they lighter simply because they only had 1 73 gallon fuel tank vs say a P40 that had 3 separate tanks of 140-160 gallons?

The early-mid war Spitfires (I to VI, plus the IX and XVI) carried 100 US gals of fuel. Part of the P-40s' weight figures probably stemmed from a 5-spar wing, where the Spitfire was with 1 main + 1 auxiliary spar; another part was from USA having the lateral G limit requirement (+1.5G IIRC) that did not existed on the UK specs. Not much of the 5-spar stiffenes was used up operationally (apart from testing with 2 x 225 gal ferry tanks), the only visible benefit was that P-40 rolled much better at high speeds. Wing itself weighted a bit over 1000 lbs on the P-40s, up to the P-40C at least.
The P-40 (no suffix) in 1940 weighted just above 6800 lbs ready for take off, but without fuel in the rear tank. Later versions quickly gained weight, though.