Method and system to promote ice shedding from rotor blades of an aircraft engine

1. A method of operating an aircraft engine having a bladed rotor coupled thereto during an icing condition, the method comprising:

controlling the aircraft engine to alternatingly achieve an ice accretion rotational speed of the bladed rotor at which ice accretion on blades of the bladed rotor occurs, and a reduced rotational speed of the bladed rotor to promote ice shedding from the blades of the bladed rotor, the reduced rotational speed being lower than the ice accretion rotational speed.

2. The method of claim 1 , wherein a first time period at which the aircraft engine is controlled to achieve the ice accretion rotational speed of the bladed rotor is longer than a second time period at which the aircraft engine is controlled to achieve the reduced rotational speed of the bladed rotor.

3. The method of claim 2 , wherein the first time period is more than ten times longer than the second time period.

4. The method of claim 1 , wherein a frequency of alternatingly achieving the ice accretion rotational speed of the bladed rotor and the reduced rotational speed of the bladed rotor is based on a severity of ice accumulation on the bladed rotor.

5. The method of claim 1 , wherein alternatingly achieving the first ice accretion rotational speed and the reduced rotational speed includes:

monotonically decreasing the bladed rotor's rotational speed from the ice accretion rotational speed to the reduced rotational speed; and

monotonically increasing the bladed rotor's rotational speed from the reduced rotational speed to the ice accretion rotational speed.

6. The method of claim 1 , wherein the reduced rotational speed is between 95% and 97% of the ice accretion rotational speed.

7. The method of claim 1 , wherein:

the aircraft engine is a first aircraft engine;

the bladed rotor is a first bladed rotor;

the ice accretion rotational speed is a first ice accretion rotational speed;

the reduced rotational speed is a first reduced rotational speed;

the method includes operating a second aircraft engine having a second bladed rotor coupled thereto by controlling the second aircraft engine to alternatingly achieve a second ice accretion rotational speed of the second bladed rotor at which ice accretion on blades of the second bladed rotor occurs, and a second reduced rotational speed of the second bladed rotor to promote ice shedding from the blades of the second bladed rotor, the second reduced rotational speed being lower than the second ice accretion rotational speed,

wherein:

alternatingly achieving the first ice accretion rotational speed and the first reduced rotational speed of the first bladed rotor is out-of-phase with alternatingly achieving the second ice accretion rotational speed and the second reduced rotational speed of the second bladed rotor; and

the first and second aircraft engines are mounted to a same aircraft.

8. The method of claim 7 , wherein:

the first and second ice accretion rotational speeds are substantially equal; and

the first and second reduced rotational speeds are substantially equal.

9. The method of claim 7 , wherein when the second bladed rotor is rotating at the second reduced rotational speed, the first bladed rotor is rotating at the first ice accretion rotational speed.

10. The method of claim 7 , wherein when the first bladed rotor is rotating at the first reduced rotational speed, the second bladed rotor is rotating at the second ice accretion rotational speed.

11. The method of claim 7 , comprising operating each of the first and second aircraft engines at a substantially same nominal rotational speed of the first and second bladed rotors before operating the second aircraft engine to alternatingly achieve the second ice accretion rotational speed and the second reduced rotational speed of the second bladed rotor, and also before operating the first aircraft engine to alternatingly achieve the first ice accretion rotational speed and the first reduced rotational speed of the first bladed rotor, wherein:

the first and second ice accretion rotational speeds are higher than the nominal rotational speed; and

the first and second reduced rotational speeds are lower than the nominal rotational speed.

12. The method of claim 1 , wherein the bladed rotor is a fan and the aircraft engine is a turbofan engine.

13. A method of operating an aircraft engine having a bladed rotor coupled thereto during an icing condition, the method comprising:

operating the aircraft engine to achieve a rotational speed of the bladed rotor at which ice accretion on blades of the bladed rotor occurs;

promoting ice to shed from the blades of the bladed rotor by operating the aircraft engine to reduce the rotational speed of the bladed rotor; and

after promoting ice shedding from the blades of the bladed rotor, operating the aircraft engine to increase the rotational speed of the bladed rotor.

14. The method of claim 13 , wherein promoting ice shedding from blades of the bladed rotor includes reducing the rotational speed of the bladed rotor by between 3% and 5%.

15. The method of claim 13 , wherein:

the aircraft engine is a first aircraft engine;

the bladed rotor is a first bladed rotor;

the method includes:

operating a second aircraft engine to achieve a rotational speed of a second bladed rotor of the second aircraft engine at which ice accretion on blades of the second bladed rotor occurs;

promoting ice to shed from the blades of the second bladed rotor by operating the second aircraft engine to reduce the rotational speed of the second bladed rotor; and

after promoting ice shedding from the blades of the second bladed rotor, operating the second aircraft engine to increase the rotational speed of the second bladed rotor; and

the first and second aircraft engines are mounted to a same aircraft.

16. The method of claim 15 , wherein promoting ice to shed from the blades of the first bladed rotor and promoting ice to shed from the blades of the second bladed rotor are performed at different times.

17. The method of claim 13 , wherein the bladed rotor is a fan and the aircraft engine is a turbofan engine.

18. A system to promote ice shedding from blades of a bladed rotor of an aircraft engine, the system comprising:

one or more data processors operatively coupled to control a rotational speed of the bladed rotor; and

non-transitory machine-readable memory storing instructions executable by the one or more data processors and configured to cause the one or more data processors to:

generate an output causing the bladed rotor to alternatingly achieve an ice accretion rotational speed of the bladed rotor at which ice accretion on blades of the bladed rotor occurs, and a reduced rotational speed of the bladed rotor to promote ice shedding from the blades of the bladed rotor, the reduced rotational speed being lower than the ice accretion rotational speed.

19. The system of claim 18 , wherein:

the non-transitory machine-readable memory stores instructions executable by the one or more data processors and configured to cause the one or more data processors to cause the bladed rotor to alternatingly achieve the ice accretion rotational speed for a first time period and the reduced rotational speed for a second time period; and

the first time period is longer than the second time period.

20. The system of claim 19 , wherein:

the first time period is ten or more times longer than the second time period; and

the reduced rotational speed is between 95% and 97% of the ice accretion rotational speed.