Originally Posted by
NutLoose
The P51 with clever ducting actually produced thrust from the big radiator bulge on the undersde, not a lot, but more than enough to offset it's drag.
That sort of depends on who you believe. While it's often claimed that the Mustang radiator had a net thrust gain, most knowledgeable analysis I've seen suggest that - at best - it was thrust/drag neutral and under most conditions it created some net drag (although not much). That being said it was a brilliant design that minimized the drag penalty of the cooling system.
Minimizing the frontal area (and resultant drag) of a big radial engine was non-trivial, but there were several highly successful designs that did that and gave the resultant fighter aircraft impressive top speed.
To name just a few:
F6F Hellcat
F4U Corsair
P-47 Thunderbolt
Japanese A6M Zero