Abstract: An air jet helicopter rotor and air distribution system of the semi-rigid type, having tension straps, in which the hub is connected to a rotatable mast shaft by a teetering hinge; the mast shaft is supported by a thrust bearing; and the rotors, the hub and an upper rotatable plenum chamber which surrounds the mast shaft and from which compressed air is distributed to each rotor through flexible ducts all rotate with the mast shaft. Below and adjoining the rotatable plenum chamber and also surrounding the mast shaft is a stationary plenum chamber which is mounted atop the thrust bearing housing and which transports compressed air from a source within the helicopter into the rotatable plenum chamber. Self-centering, self-aligning air seals at the adjoinments of the plenum chambers and the stationary plenum chamber and the mast shaft allow for flexing throughout the system as well as the usual flapping and rocking movements of the rotor blades.