Radial engine/cowling diameters and external/internal drag

[Pandorum]

Are there data about the diameters of radial engines or their cowlings on the WW2 fighters respectively? For drag comparison.
And is their info about how to duct internal airflow to minimize drag? Which fighters did especially well?

 

[SaparotRob]

Though not knowing anything myself, I hear the voices in my head chanting "NACA".

 

[tomo pauk]

Are there data about the diameters of radial engines or their cowlings on the WW2 fighters respectively? For drag comparison.
And is their info about how to duct internal airflow to minimize drag? Which fighters did especially well?

Getting the data about diameters of radial engines is easy. Much less so about the diameter of their cowlings.
The data about ducting designed so that the drag is reduced - not sure that I've ever read anything about that. Indeed, perhaps the NACA docs can help.

 

[Simon Thomas]

One of many NACA cowling papers:

Design of NACA Cowlings for Radial Air-Cooled Engines

"The information on the propeller-cowling-nacelle combinations, presented in Technical Reports nos. 592, 593, and 596 and in Technical Note 620, is applied to the practical design of NACA cowlings. The main emphasis is placed on the method of obtaining the dimensions of the cowling...

digital.library.unt.edu

The references listed will help you track down the rest.