A clutch for a lift fan comprises at least one output shaft lug key positioned in a keyway of at least two output clutch plates and extending axially from one to the other of the two output clutch plates. The output shaft lug key couples the rotation of the output clutch plates to the rotation an output shaft and allows axial movement of the two output clutch plates relative the output shaft lug key. The width of an inner surface of the output shaft lug key varies along the axial length as a function of the proximity to a home axial position of each of the output clutch plates when in the disengaged position.

A rotation transmission disc includes: an outer circumferential portion on which a load acts when rotation is transmitted; a center opening portion formed inside the outer circumferential portion; and a plurality of attachment holes for attachment of the rotation transmission disc 1 to a rotating element. A first crosspiece portions are formed in each of ranges of divided angles formed by two adjacent attachment holes with respect to a center of the rotation transmission disc. The first crosspiece portion extends from a load point, which is an intersection between a straight line extending in a radial direction to internally divide the divided angles at a predetermined angular ratio and a load radius position of the outer circumferential portion, to one of the attachment holes forming the divided angles. The second crosspiece portion extends from the load point to the other attachment hole of the attachment holes forming the divided angles.