Mechanism and method to engage/disengage a sprag clutch based on coefficients of thermal expansion

A method of engaging and disengaging a clutch, the method comprising:

• inputting a rotation force to the clutch, the clutch comprising:
• an inner race;
• an outer race;
• a radial cavity between the inner and outer races;
• a plurality of sprags disposed in the radial cavity between the inner and outer races, wherein the sprags have a different coefficient of thermal expansion (CTE) from the inner race, the outer race, or both the inner and outer races;
• a sprag cage positioned to retain each of the sprags at a uniform spacing within the radial cavity;
• operating the clutch at a first temperature, wherein the clutch is disengaged when the clutch operates at the first temperature;
• and
• operating the clutch at a second temperature, wherein the clutch is engaged at the second temperature.

An aircraft having a clutch comprising:

• at least one engine affixed to the aircraft and operably coupled to a drivetrain;
• the clutch coupling the at least one engine to the drivetrain, the clutch further comprising:
• an inner race;
• an outer race;
• a radial cavity between the inner and outer races;
• a plurality of sprags disposed in the radial cavity between the inner and outer races, wherein the sprags have a different coefficient of thermal expansion (CTE) from the inner race, the outer race, and/or both the inner and outer races;
• and
• a sprag cage positioned to retain the sprags at a uniform spacing within the radial cavity;
• wherein when the clutch is at a first temperature a gap exists between the sprags and the inner race, between the sprags and the outer race, or between the sprags and both races, and the clutch is disengaged;
• and
• wherein when the clutch is at a second temperature the sprags are in contact with both the races, and the clutch is engaged.