US Patent 7210899 Passive clearance control

The clearance between the tips of the rotor blades and the segmented shroud of a gas turbine engine is controlled by a passive clearance control that includes a support ring made from a low thermal expansion material supporting a retainer for the blade outer air seal that is slidable relative thereto so that the segments expand circumferentially and move radially to match the rate of change slope of the rotor during expansion and contraction for all engine operations. A leaf spring between the support ring and outer air seal biases the outer air seal in the radial direction and maintains the desired radial position during steady state operation of the gas turbine engine.