Low profile embedded blade tip clearance probe assembly

1. A low profile embedded blade tip clearance (BTC) probe, comprising:

a housing defining a cavity therewithin;

a lower insulator disposed within the cavity;

a sensor element disposed within the cavity;

an upper insulator disposed within the cavity;

a cap wherein the cap fills a remainder of the cavity; and

a hard lead in electronic communication with the sensor element and the housing,

wherein the upper insulator comprises a first alignment hole and a clearance cutout, and

wherein the cap comprises disk having an upper surface and a lower surface, a second alignment hole through the upper surface and the lower surface, and a hemispherical clearance cutout proximate the lower surface, wherein the lower surface is in contact with the upper insulator.

2. The low profile embedded BTC probe of claim 1 , wherein the housing further comprises a top surface, a bottom surface, a step, and a first bore, wherein the cavity extends from the top surface to the step, wherein the first bore extends from the step through the bottom surface, wherein the cavity comprises a first diameter and the first bore comprises a second diameter wherein the second diameter is less than the first diameter.

3. The low profile embedded BTC probe of claim 2 , wherein the lower insulator further comprises a first flange, a cylindrical extrusion, and a second bore comprising a third diameter wherein the third diameter is less than the second diameter, wherein the first flange is in contact with the step and wherein the cylindrical extrusion is disposed within the first bore.

4. The low profile embedded BTC probe of claim 3 , wherein the sensor element comprises a cylinder having a base and second flange opposite the base, wherein the second flange is in contact with the first flange and the cylinder is disposed within the second bore.

5. The low profile embedded BTC probe of claim 4 , wherein an internal stress is locked within the low profile embedded BTC probe in response to coupling the cap to the housing.

6. The low profile embedded BTC probe of claim 5 , wherein the housing comprises a first coefficient of thermal expansion (CTE), the sensor element comprises a second CTE, the cap comprises a third CTE, the upper insulator and the lower insulator comprise a fourth CTE, and wherein the first CTE, the second CTE, the third CTE, and the fourth CTE are selected such that an average of the second CTE, the third CTE, and the fourth CTE is greater than the first CTE.

7. The low profile embedded BTC probe of claim 6 , wherein a difference between a combined axial growth, comprising an axial growth along an axis of the sensor element, an axial growth along an axis of the upper insulator, and an axial growth along an axis of the lower insulator in response to a temperature, and at least one of an axial growth of the housing along the axis of the sensor element in response to the temperature or an axial growth of the cap along the axis of the sensor element in response to the temperature is between about 0.00001 inches and 0.0004 inches where about in this context means±0.000001 inches.

8. A gas turbine engine comprising:

a fan section comprising:

a fan having a blade having a tip;

a fan case having an inner aerodynamic surface and a rub strip;

the blade proximate the inner aerodynamic surface; and

a low profile embedded blade tip clearance (BTC) probe, comprising:

a housing having a cavity disposed radially outward of a blade;

a lower insulator disposed within the cavity;

a sensor element disposed within the cavity;

an upper insulator disposed within the cavity;

a cap wherein the cap fills a remainder of the cavity; and

a hard lead in electronic communication with the sensor element and the housing,

wherein the upper insulator comprises a first alignment hole and a clearance cutout,

wherein the cap comprises disk having an upper surface and a lower surface, a second alignment hole through the upper surface and the lower surface, and a hemispherical clearance cutout proximate the lower surface, wherein the lower surface is in contact with the upper insulator.

9. The gas turbine engine of claim 8 , wherein the housing further comprises a top surface, a bottom surface, a step, and a first bore, wherein the cavity extends from the top surface to the step, wherein the first bore extends from the step through the bottom surface, wherein the cavity comprises a first diameter and the first bore comprises a second diameter wherein the second diameter is less than the first diameter.

10. The gas turbine engine of claim 9 , wherein the lower insulator further comprises a first flange, a cylindrical extrusion, and a second bore comprising a third diameter wherein the third diameter is less than the second diameter, wherein the first flange is in contact with the step and wherein the cylindrical extrusion is disposed within the first bore.

11. The gas turbine engine of claim 10 , wherein the sensor element comprises a cylinder having a base and second flange opposite the base, wherein the second flange is in contact with the first flange and the cylinder is disposed within the second bore.

12. The gas turbine engine of claim 11 , wherein an internal stress is locked within the low profile embedded BTC probe in response to coupling the cap to the housing.

13. The gas turbine engine of claim 12 , wherein the housing comprises a first coefficient of thermal expansion (CTE), the sensor element comprises a second CTE, the cap comprises a third CTE, the upper insulator and the lower insulator comprise a fourth CTE, and wherein the first CTE, the second CTE, the third CTE, and the fourth CTE are selected such that an average of the second CTE, the third CTE, and the fourth CTE is greater than the first CTE.

14. The gas turbine engine of claim 13 , wherein a difference between a combined axial growth, comprising an axial growth along an axis of the sensor element, an axial growth along an axis of the upper insulator, and an axial growth along an axis of the lower insulator in response to a temperature, and at least one of an axial growth of the housing along the axis of the sensor element in response to the temperature or an axial growth of the cap along the axis of the sensor element in response to the temperature is between about 0.00001 inches and 0.0004 inches where about in this context means±0.000001 inches.

15. A method of manufacturing a low profile embedded blade tip clearance (BTC) probe, the method comprising:

forming a housing having a first coefficient of thermal expansion (CTE), a cavity, and a neck, inserting a hard lead comprising a hard shield and a lead wire into the neck, and coupling the hard lead to the neck about the hard shield;

bending the lead wire toward a sidewall of the cavity and inserting a lower insulator having a fourth CTE into the cavity past the lead wire, wherein the lower insulator comprises a bore;

coupling an alignment fixture having an alignment pin to the housing and inserting the alignment pin into the cavity;

inserting a sensor element having a second CTE into the cavity past the lead wire and into the bore of the lower insulator and aligning the sensor element with the alignment pin;

coupling the lead wire to the sensor element;

aligning an upper insulator having the fourth CTE and comprising a clearance cutout with the alignment pin;

inserting the upper insulator into the cavity;

aligning a cap having a third CTE with the alignment pin and filling a remainder of the cavity with the cap; and

coupling the cap to the housing while a compressive force F is applied to the cap.

16. The method of claim 15 , further comprising determining the compressive force F in response to a difference between at least one of the first CTE, the second CTE, the third CTE, and/or the fourth CTE; and selecting the first CTE, the second CTE, the third CTE, and the fourth CTE such that an average of the second CTE, the third CTE, and the fourth CTE is greater than the first CTE.