Hi Nashwan,
>Yes, but the FR XIV had a warning about stability anyway.
In fact, it's a pity you didn't start reading at (a) rather than (b)

I considered (a) to be closely related to (b). What was the reason for the reduced stability of the F. R. XIV in your opinion?
>The Spit IX and XVI could take a 75 gallon rear tank. Again the manual says by special order only, but later in the manual it says no aerobatics with more than 30 gallons in the rear tank, whereas the RAF manual for the Mustang says no aerobatics with any fuel in the rear tank.
That's a world of difference to the extremely cautious words about the Spitfire XIV, and one reason more to take the warnings about the latter very seriously.
It's still somewhat confusing, considering that the Griffon-engined Seafires reportedly cured the Seafire's stability problems (to some degree) by moving the centre of gravity foward. The Spitfire IX/XIV comparison seems to imply the opposite direction.
(The USAAF P-51D/K manual mentions an absolute 40 gallon limit for aerobatics, though implying that straight and level flying would be better with any fuel in the rear tank.)
>Mustang pilots would presumably be trained to fly with the extra tank, but as it was rarely used on the Spit, I doubt many Spit pilots were.
I'm sure you're right - the USAAF P-51 manual actually mentions the necessity of familiarization with flight with a full rear tank.
Regards,
Henning (HoHun)