Abstract: In a rotor assembly, first and second annular discs are axially spaced apart on a rotatable shaft so as to be rotatable with the shaft. A plurality of rotor blades are located between the discs and are angularly spaced around the axis of the shaft, and means urges the discs against the blades so that a root portion of each blade is trapped between the discs with the remainder of the blade projecting from the discs. Each root portion is shaped so as to be non-complementary with the portions of the discs between which it is trapped, and each disc is shaped so as to present to each root portion first and second surfaces which, when the shaft is rotated in use, engage respective spaced regions of the root portion so that the root portion is held against axial movement relative to the shaft and against movement radially outwardly relative to the axis of the shaft.