NACA cowling
The idea that the NACA cowling produced thrust through the [[Meredith effect]] is fallacious—although in theory the expansion of the air as it was heated by the engine could create some thrust by exiting at high speed, in practice this required a cowling designed and shaped to achieve the high speed exit of air required (which the NACA cowling was not), and in any case, at 1930s airspeeds, the effect was negligible.