Originally Posted by
Flash2001
I've been told that the "radiator", actually a convector, of the P51 aircraft made a net contribution to the force moving the aircraft forward. That is to say that the thrust exceeded the drag.
I have seen that claim also, although the reading I have done suggests that realizing a net thrust may be a little bit of an overstatement. Yes, the designers did pay a lot of attention to exploiting the Meridith effect, and yes, when the cooling exhaust was considered separately, there was thrust present. The articles I have seen which go into the subject with a lot of technical detail all seem to suggest that the exhaust thrust never exceeded the intake drag and the form drag of the radiator fairing. I have seen some sources claim that the thrust was 90% of the total drag.
In support of that, I would point out that some racers of modifies P-51's have replaced the stock radiator with a boil-off cooling system, in order to reduce the frontal area and intake drag of the stock cooling system. This isn't absolute proof of anything, but it's certainly an indication that the racers in question believed that the cooling system was not a source of net thrust.