Blade tip clearance systems

1. A blade tip clearance system comprising:

a first control ring having a first coefficient of thermal expansion and a first thermal response rate;

a second control ring located radially outward of and operatively connected to the first control ring, the second control ring having a second coefficient of thermal expansion that is different from the first coefficient of thermal expansion and a second thermal response rate that is different from the first thermal response rate;

a carrier that radially centers the first and the second control rings; and

a support connected to the carrier to center the carrier relative to the case

wherein thermal expansion and contraction of the first and the second control rings are configured to control a radial position of the blade tip clearance system relative to a rotating blade component;

wherein the support comprises a support spline slot, the carrier comprises a carrier spline tab, and the support spline slot is slidably engaged to the carrier spline tab; and

wherein the first control ring comprises a spline tab, and the support spline slot is slidably engaged to the spline tab of the first control ring.

2. A blade tip clearance system as recited in claim 1 , wherein the coefficient of thermal expansion of the first control ring is lower than that of the second control ring.

3. A blade tip clearance system as recited in claim 2 , wherein the rate of thermal response of the first control ring is higher than that of the second control ring.

4. A blade tip clearance system as recited in claim 3 , wherein the first control ring is a hollow structure including through holes to allow airflow therethrough.

5. A blade tip clearance system as recited in claim 4 , wherein the first control ring includes interior fins to increase heat exchanger therethrough.

6. A blade tip clearance system as recited in claim 3 , wherein the second control ring is a full-hoop continuous ring.

7. A blade tip clearance system as recited in claim 1 , further comprising seals forward and aft of the second control ring.

8. A blade tip clearance system as recited in claim 1 , further comprising flat feather seals at least one wall of the carrier surrounding the second control ring to thermally isolate the second control ring.

9. A blade tip clearance system as recited in claim 1 , wherein the second control ring is a segmented ring with a split at a circumferential location configured to minimize radial gaps between the second control ring and the carrier.

10. A blade tip clearance system as recited in claim 1 , wherein the carrier is a segmented structure with a forward and an aft section.

11. A blade tip clearance system as recited in claim 1 , further comprising a blade outer air seal operatively connected to and radially inward of the first control ring that seals secondary flow air from the rotating blade component and forms an outer shroud for the rotating blade component.

12. A blade tip clearance system as recited in claim 1 , further comprising at least one spring interposed between the first and the second control rings.

13. A blade tip clearance system comprising:

a first control ring disposed in a case and having a first coefficient of thermal expansion and a first thermal response rate;

a second control ring located radially outward of and operatively connected to the first control ring, the second control ring having a second coefficient of thermal expansion that is different from the first coefficient of thermal expansion and a second thermal response rate that is different from the first thermal response rate;

a carrier that radially centers the first and the second control rings; and

a support connected to the carrier to center the carrier relative to the case;

wherein thermal expansion and contraction of the first and the second control rings are configured to control a radial position of the blade tip clearance system relative to a rotating blade component;

wherein the support comprises a support spline slot, the carrier comprises a carrier spline tab, and the support spline slot is slidably engaged to the carrier spline tab; and

wherein the second control ring comprises a spline tab, and the support spline slot is slidably engaged to the spline tab of the second control ring.

14. A gas turbine engine comprising:

a rotating structure including a plurality of rotating blades with radially outward tips;

a blade tip clearance system located in a case adjacent to the radially outward tips comprising:

a carrier;

a blade outer air seal in communication with the carrier, the blade outer air seal including a radially inward seal face adjacent to the radially outward tips of the rotating blades;

an inner control ring configured to be radially centered with respect to the carrier, the inner control ring having a first coefficient of thermal expansion and a first thermal response rate;

an outer control ring configured to be radially centered with respect to the carrier, the outer control ring having a second coefficient of thermal expansion and a second thermal response rate; and

a support connected to the carrier to center the carrier relative to the case;

wherein thermal expansion and contraction of the inner and the outer control rings maintains a clearance between the radially inward seal face of the blade outer air seal and the radially outward tips of the rotating blades;

wherein both the inner control ring and the outer control ring are radially translatable relative to the carrier during operation of the blade tip clearance system;

wherein the support comprises a support spline slot, the carrier comprises a carrier spline tab, and the support spline slot is slidably engaged to the carrier spline tab; and

wherein the outer control ring comprises a spline tab, and the support spline slot is slidably engaged to the spline tab of the outer control ring.

15. A gas turbine engine as recited in claim 14 , wherein the outer control ring is separated from the inner control ring by a portion of the carrier.