In the stock game the F4F-3 Wildcat has endurance of 330 (minutes). Combined with its cruising speed of 155mph this gives the Wildcat a transfer range of 852,5 miles (14,2 hexes), extended range of 284,1 miles (4,73 hexes) and normal range of 213 miles (3,55 hexes). Thus we have hex ranges of 14/4/3 for the F4F-3 in the game.
However, in real life, the F4F-3 used two 54gal drop tanks for ferry (=transfer) missions, giving it a transfer range of 1,690 miles (28 hexes). Normal max range with internal fuel was 845 miles (14 hexes), close to the 852,5 miles in the game (ranges depend on sources used).
The question is now, which ranges are correct for the game?
The game engine always uses the transfer range as basis for range calculations. Extended range is 1/3 of maximum range, normal range 1/4.
Using a transfer range of 1,690 miles as basis for the calculation would result in ranges of 28 hexes (maximum transfer range, 1,690 miles), 9 hexes (extended range, 563 miles) and 7 hexes (normal range 422,5 miles).
A vast difference. I used the F4F-3 as example because it makes a extreme difference (considering that the F4F-4 had a ferry range of only 1,250 miles with drop tanks, I'm not sure if my 1,690 miles for the F4F-3 is a correct figure; when using 1,250 miles as basis for a calculation for the F4F-4 it would give it ranges of 20/6/5)
Drop tanks work in the game, but simply by adding their "effect" as additional endurance to a given plane type when calculating maximum range. They're basically chrome, one can simply enter an endurance value in the editor.