Drag
The ventral fin on the first of the probe equipped R1s was definitely made of wood. This was the R1 that had the pipework (bowser hose) coming down through the flight deck and into the floor just forward of the Nav's bench. The pipework also came out of the fuselage under the wing and reentered a few feet further back using two right angles and more bowser hose. I think that was 664, that had the first fit. Subsequent aircraft had a more professional fit with a fibreglass ventral fin and also the additional fins on the horizontal stabilisers. The first aircraft did not have those.
Anyway, back to the Herc!
S-D