enginehistory.org

[dpennings]

Prof. Hugo Junkers invented the "Düsenkühler" (Jet cooler) in 1915 and used it on his early aircrafts. The arrangement was quite similar to that of the P51. I found his Patent (AT000000078422B, Google doesn't find it) which describes this principle and also contains variable inlet and exhaust geometry. No doubt, that this cooler could create a Meredith effect and give forward thrust, but Junkers was unaware of it. He described it as reducing drag, but not as giving forward thrust. Junkers was Professor for Thermodynamics, so he could have done the (relative) simple calculations for that design which would have lead him to the Meredith Effect (which would have become the "Junkers Effect").

It's a bit strange that he used this design only in his very early aircrafts, maybe because he felt it was unsafe to pump the hot water downwards, so that in case the cooling water pump failed, there would be no more circulation. Engines of this time often relied on the thermosiphon effect. The ventilation of the engine bay might have also played a roll, it’s easier to archive with the “car arrangement” where the cooling air flows around the engine after it left the cooler. On the other hand, many early WW1 planes used terrible ineffective coolers with no cowling at all, his Düsenkühler would have reduced drag and sheltered the cooler to some degree against bullets.

[rinkol]

The early liquid cooled engines used water at atmospheric pressure as a coolant. Later engines with pressurized coolant systems and ethylene glycol based coolants were ale to run at considerably higher temperatures. This allowed the size of the radiator to be reduced and increased the gain possible from the Merredith Effect.