Device for monitoring clearance between rotor blades and a housing

In a turbojet engine having a housing and at least one rotor blade wheel rotatable with respect to the housing and having a plurality of rotor blades radially extending from its periphery, the improved device for maintaining a clearance around the rotor blade tips as they undergo centrifugal and thermal expansion and contraction, comprising:

• (a) continuous inner annular wall having thermal characteristics substantially the same as the rotor blade wheel and rotor blades, and disposed about the rotor wheel at a predetermined minimum distance from the tips of the rotor blades, the annular wall comprising:
• (i) a plurality of first segments having a relatively thin radial dimension and a relatively low thermal inertia, and inner wall of each of the first segments being exposed to the gas passing across rotor blades;
• and,
• (ii) a plurality of second segments, each second segment interposed between and rigidly affixed to adjacent first segments such that peripheral expansion of contraction of the first and second segments causes radial expansion of contraction of the continuous inner annular wall to maintain the predetermined distance from the rotor blade tips, the second segments having a larger radial dimention and a higher thermal inertia than the first segments;
• and
• (b) attaching means to attach at least some of the second segments to the housing so as to permit the annular wall to radially expand to contract with respect to the housing.