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The Meredith Effect was used on some aircraft to provide more thrust by channeling air through the radiator such that the air is expanded, heated and then compressed through a constriction, generating thrust. How much thrust could such an installment generate? How much net thrust, after accounting for drag, does such an installation generate?

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    $\begingroup$ the thrust contribution depends a lot on speed. At Mach 0.7 it provides thrust, at Mach 0.3 it causes drag. $\endgroup$
    – Peter Kämpf
    Apr 4, 2015 at 15:35
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    $\begingroup$ @PeterKämpf could it be that the propeller is actually acting as sort of a compressor, and the (piston) engine as a heat source to create a crude jet thrust mechanism? Or is ram effect enough at higher speeds? I have read there is actually lower pressure behind pro hubs, but could that have been changed to help cool the engine? $\endgroup$
    – Robert DiGiovanni
    Dec 5, 2023 at 20:10
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    $\begingroup$ @RobertDiGiovanni The pressure increase of the propeller disk is very short-lived and instantly converted into speed. Only in a shrouded prop would a pressure increase be possible. The radiator intake indeed uses ram pressure (and there you have a duct coming behind, so the pressure can be maintained. The radiator acts as a throttle, so the exit is semi-blocked. Then the pressurized air is heated and free to escape, so it picks up speed to maintain mass flow at an expanded volume). $\endgroup$
    – Peter Kämpf
    Dec 6, 2023 at 8:12
  • $\begingroup$ Well, the shroud would be the engine cowling. It would be a great study to see on what scale and speed it would have to be to make it practical. Dedicated radiator fans are actually common in automobiles. $\endgroup$
    – Robert DiGiovanni
    Dec 6, 2023 at 11:15

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Here they give a calculation for the thrust generated by a Meredith effect cooler. They do this for the P51 Mustang. It is also mentioned that in Aeroplane Monthly, May 1999 (not accessible to me), the designer Atwood claims that the Meredith effects cooler generates 300 lbs (~1334N) of force.

They perform some calculations based on geometry obtained from Gruenhagen's "Mustang. The story of the P51 fighter", 1969. These calculations also lead to a number around 300 lbs (it calculates 270 lbs of thrust). However, the calculations do not include the effects of the heating of the air whilst passing through the cooler (which is -according to me- a vital component of how these coolers generate thrust).

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