White light interferometer for measuring radial growth in components experiencing rotating stresses

An apparatus, comprising:

• a fan having a plurality of blades made of a non-metallic structure rotating about a rotation axis of the fan;
• a fixed structure surrounding the fan and having an inner surface separated from the blades by a clearance;
• a position detector for determining when a tip of a blade of the fan rotates past a hole defined in the fixed structure and generating an actuation signal responsive to rotation of the tip of the blade of the fan past the hole defined in the fixed structure;
• and
• white light interferometer circuitry, initiated responsive to the actuation signal, for reflecting a white light beam off of the tip of the blade of the fan to determine the clearance between the tip of the blade of the fan and the inner surface of the fixed structure, wherein the actuation signal actuates the white light interferometer circuitry to reflect the white light beam off of the tip of the blade of the fan through the hole defined in the fixed structure.

A method for measuring clearances between a rotating structure within a fixed surrounding structure, comprising:

• determining when at least one portion of the rotating structure rotates past a hole defined in the fixed surrounding structure using a position detector;
• generating an actuation signal responsive to rotation of the at least one portion of the rotating structure past the hole defined in the fixed surrounding structure using the position detector;
• reflecting a white light beam off of at least one portion of the rotating structure through the hole defined in the fixed surrounding structure using white light interferometer circuitry responsive to the actuation signal;
• and
• determining a clearance between the at least one portion of the rotating structure and an inner surface of the fixed surrounding structure using the white light interferometer circuitry.