Jane-DoH,
The original geodetic arframes, Wellington, Watwick etc; were all covered in fabric and as has already been said the fabric would start to pant at higher speeds.
The early Vicker Vikings had a conventional fuselage of stressed skin, but the wings were fabric covered. They then came out with a modification (Mod 508???) where the fabric was removed and sheet metal riveted on. The later ones and the Vallettas all had sheet metal over the same structure but from the factory.
Speedbird48