Low spool starter system for gas turbine engine

1. A gas turbine engine comprising:

a first compressor;

a second compressor;

a starter generator coupled to the first compressor; and

a ramp/roller clutch that centrifugally disengages above a threshold rotational speed to selectively couple the first compressor and the second compressor, the ramp/roller clutch comprising:

an actuation arm;

a spring biasing the actuation arm to engage the ramp/roller clutch and to couple the first and second compressors below the threshold rotational speed; and

a flyweight coupled to the actuation arm, wherein centrifugal loading imposed on the actuation arm and the flyweight by the first compressor rotating above the threshold rotational speed automatically disengages the clutch and decouples the first compressor and the second compressor.

2. The gas turbine engine of claim 1 wherein the ramp/roller clutch comprises:

a clutch shaft coupled to the first compressor and the ramp/roller clutch so as to rotate with the first compressor; and

a stub shaft coupled to the second compressor and releasably engaged with the ramp/roller clutch so as to selectively rotate with the first compressor.

3. The gas turbine engine of claim 1 wherein the first compressor comprises a low pressure compressor and the second compressor comprises a high pressure compressor.

4. The gas turbine engine of claim 1 and further comprising:

a low pressure turbine coupled to the low pressure compressor;

a high pressure turbine coupled to the high pressure compressor; and

a propulsor module disposed aft of the low pressure turbine and the high pressure turbine.

5. The gas turbine engine of claim 4 wherein the propulsor module comprises:

a power turbine coupled to a power shaft.

6. The gas turbine engine of claim 5 and further comprising:

a propeller system coupled to the power shaft.

7. The gas turbine engine of claim 6 and further comprising:

a gear system coupling the propeller system to the power shaft.

8. The gas turbine engine of claim 1 wherein the starter generator is disposed coaxially upstream of the first compressor.

9. A gas turbine engine comprising:

a low pressure spool comprising:

a first compressor;

a first turbine; and

a first shaft connecting the first compressor and the first turbine;

a high pressure spool nested between the first compressor and the first turbine, the high pressure spool comprising:

a second compressor;

a second turbine; and

a second shaft coaxial with the first shaft and connecting the second compressor and the second turbine; and

a clutch coupled to the first shaft and engagable with the second shaft, the clutch comprising:

a ramp/roller interface;

an actuation arm;

a spring-actuated lock comprising a spring biasing the actuation arm to engage the clutch and to couple the first and second shafts below a threshold rotational speed; and

a flyweight-actuated release comprising a flyweight coupled to the actuation arm, wherein centrifugal loading imposed on the actuation arm and the flyweight by the first compressor rotating above the threshold rotational speed automatically disengages the clutch and decouples the first and second shafts.

10. The gas turbine engine of claim 9 and further comprising:

a starter generator coupled to the low pressure spool.

11. The gas turbine engine of claim 10 wherein the starter generator is disposed coaxially upstream of the first compressor.

12. The gas turbine engine of claim 9 and further comprising:

a power turbine configured to receive gas from the first turbine and the second turbine.

13. The gas turbine engine of claim 9 and further comprising a turboprop driven by gas from the low pressure spool and the high pressure spool.

14. The gas turbine engine of claim 9 wherein the low pressure spool and the high pressure spool are configured as a two-spool core.

15. A method for starting a gas turbine engine, the method comprising:

engaging a low pressure compressor with a high pressure compressor utilizing a clutch, wherein the clutch comprises:

a ramp/roller interface;

an actuation cage;

an actuation arm coupled to the actuation cage;

a lock mechanism comprising a spring biasing the actuation arm and the actuation cage into an engaged position of the clutch; and

a flyweight actuation mechanism;

rotating the low pressure compressor and the high pressure compressor utilizing a starter generator coupled to the low pressure compressor;

igniting the gas turbine engine;

rotating the high pressure compressor above a threshold rotational speed to disengage the clutch using the flyweight actuation mechanism to allow the high pressure compressor to rotate independently of the low pressure compressor, wherein the flyweight actuation mechanism comprises a flyweight coupled to the actuation arm, and wherein above the threshold rotational speed, centrifugal forces acting on the flyweight and the actuation arm cause the actuation arm to compress the spring and to urge the actuation cage into a disengaged position of the clutch to automatically disengage the clutch; and

powering a turboprop propulsor module with the gas turbine engine, wherein the turboprop propulsor module comprises:

a power turbine;

a gear system connected to the power turbine; and

a propeller system connected to the gear system.