[caldrail]

Hi caldrail,
watch this... I just read about the "Meredith Effect" in a german flying magazin, which was on a P-51 in 1944 in Florida.
Actually the test was made on D-Modell, which has a combined water and oil cooler system underneath the fuselage.
The hot air which comes out of that sytem compenseds the restitance from that large cooler into thrust.
Meredith, an english airplane constructor givin the name.

i knew someone would think of this. No, it doesn't. Any real increase in speed regarding the P51 radiator is due to the amount of air allowed through it. It really is all about drag. The laws of physics tell us you can't get something for nothing, so 'ram-air' effects will not produce thrust. You can't go faster by moving forward - changes in momentum still require additional impetus and energy.

Now whereas the amount of heat generated by a large V12 aero-engine is considerable, the airflow across a radiator is designed to carry that heat away, not to derive thrust from it, and in any case, since the airflow is pretty much one way, any expansion due to heat obtained is not actually impacting on the aeroplane but the airflow pushing it out the back, thus there is no significant thrust obtained, nor for that matter is the heat generated by the P51's engine sufficient to produce any thrust at all - the whole idea is cool the system down, not let it get hot, and temperature gain of air flowing through the radiator does not rise as much as might be imagined.