I have been working with the Westland Whirlwind for a couple of "what if" missions in 1941. One of the things I've done, besides correcting the engine data and weight, was to correct the fuel load to correct the wing tank load, (300 liters per tank) and then added the thirty gallon fuel tank that would have been included with a redesign, and then added drop tanks (44 gallons each) to the payloads.
I've made sure that the .air file includes the drop tanks and relevant info, and that they are sequential. But apparently, the corresponding information must also be included in the .cfg file, because the aircraft.cfg includes the fuel tank data.
LeftMain=0.000, -3.000, -0.667, 79.252, 0.000
RightMain=0.000, 3.000, -0.667, 79.252, 0.000