Question on Spitfire XIV Range with 90gal Tank

[cfulbright]

The Spitfire LF.IX has a range without tank of 195 miles and with 90gal tank of 353 miles.

The Spitfire XIV has a range without tank of 197 miles and with 90gal tank of 313 miles.

Why is that?

Cary

[Denniss]

more internal fuel on the XIV so DT less effective

[cfulbright]

Dennis,

I don't understand. I would think the same amount of additional fuel would provide roughly the same amount of additional range.

Is it related to the higher cruising and max speeds of the Spitfire XIV compared to the Spitfire LF.IX?

Cary

[Denniss]

Standard range and amount of internal fuel are taken into account for range gains from DTs. Basically Miles per Pound of internal Fuel is applied to the amount of fuel in the DT for calculation of range extension (some substractions for draggy external mount though).
LF IX has about 25% less internal fuel than XIV but achieves a similar standard range. Thus a DT probably adds ~20% more range on the LF IX than on the XIV