Geared gas turbine engine with oil deaerator and air removal

1. A gas turbine engine comprising:

a fan drive turbine for driving a gear reduction, said gear reduction for driving a fan rotor; and

a lubrication system for supplying oil to said gear reduction, the lubrication system including a lubricant pump supplying an air/oil mixture to an inlet of a deaerator, said deaerator including a separator for:

separating oil and air,

delivering separated air to an air outlet, and

delivering separated oil back into an oil tank,

wherein said separated oil is first delivered into a pipe outwardly of the oil tank, and then into a location beneath a minimum oil level in the oil tank,

wherein air within the oil tank moves outwardly through an air exit into the deaerator, the air exit from the oil tank to pass around a deflector to remove oil that may still be mixed with the air, and the deflector extends outward from said deaerator into the oil tank;

an inlet velocity of the air/oil mixture to the deaerator is less than or equal to 14 feet/second; and

wherein a bypass duct is defined outwardly of said fan rotor by a housing, and said fan rotor delivering air into said bypass duct and into a compressor section, a bypass ratio is defined as the volume of air delivered into the bypass duct divided by the volume of air delivered to the compressor section, said bypass ratio is greater than 10.0, a gear ratio defined by said gear reduction being greater than 2.3, said fan rotor carrying fan blades, and a fan pressure ratio is defined as a pressure ratio across one of the said fan blades alone, with said fan pressure ratio being less than or equal to 1.45.

2. The gas turbine engine as set forth in claim 1 , wherein the deaerator has an air outlet, and an exit guide extending into the deaerator from the air outlet, and the deaerator inlet delivering the air/oil mixture about the exit guide, and against a wall of the deaerator such that air and oil are separated.

3. The gas turbine engine as set forth in claim 2 , wherein the separated oil enters the oil tank through a diffusor.

4. The gas turbine engine as set forth in claim 3 , wherein an exit velocity from the deaerator of the separated air is less than or equal to 14 feet/second.

5. The gas turbine engine as set forth in claim 4 , wherein said pipe includes a pipe outlet at least 2 inches (5.08 centimeters) below the minimum oil level but above an inlet to an oil supply pipe within the tank.

6. The gas turbine engine as set forth in claim 5 , wherein a dwell time of oil in the tank as removed by said oil pump, on average, is five seconds or less.

7. The gas turbine engine as set forth in claim 6 , wherein said oil tank holds greater than or equal to 25 and less than or equal to 35 quarts of oil.

8. The gas turbine engine as set forth in claim 7 , wherein said gear reduction includes a sun gear for driving intermediate gears and there being oil baffles located circumferentially between said intermediate gears.

9. The gas turbine engine as set forth in claim 8 , wherein an oil capture gutter surrounds said gear reduction.

10. The gas turbine engine as set forth in claim 7 , wherein said engine is rated greater than or equal to 15,000 and less than or equal to 35,000 lbs in rated thrust at take-off.

11. The gas turbine engine as set forth in claim 1 , wherein said oil tank holds greater than or equal to 35 and less than or equal to 50 quarts of oil.

12. The gas turbine engine as set forth in claim 11 , wherein said oil tank is associated with an engine having greater than or equal to 35,000 and less than or equal to 100,000 lbs in rated thrust at take-off.

13. The gas turbine engine as set forth in claim 1 , wherein an oil capture gutter surrounds said gear reduction.

14. The gas turbine engine as set forth in claim 1 , wherein the air exit includes a baffle extending away from an end of the deaerator, and toward the air outlet.

15. A method of designing a gas turbine engine comprising:

providing a fan drive turbine for driving a gear reduction, said gear reduction for driving a fan rotor; and

providing a lubrication system for supplying oil to said gear reduction, with an oil tank, the lubrication system including a lubricant pump; and

supplying an air/oil mixture to an inlet of a deaerator, said deaerator including a separator for:

separating oil and air,

delivering separated air to an air outlet, and

delivering separated oil back into an oil tank,

wherein said separated oil is first delivered into a pipe outwardly of the oil tank, and then into a location beneath a minimum oil level in the oil tank,

wherein air within the oil tank moves outwardly through an air exit into the deaerator, the air exit from the oil tank to pass around a deflector to remove oil that may still be mixed with the air, and the deflector extends outward from said deaerator into the oil tank, and

an inlet velocity of the air/oil mixture to the deaerator is less than or equal to 14 feet/second; and

wherein a bypass duct is defined outwardly of said fan rotor by a housing, and said fan rotor delivering air into said bypass duct and into a compressor section, a bypass ratio is defined as the volume of air delivered into the bypass duct divided by the volume of air delivered to the compressor section, said bypass ratio is greater than 10.0, a gear ratio defined by said gear reduction being greater than 2.3, said fan rotor carrying fan blades, and a fan pressure ratio is defined as a pressure ratio across one of the said fan blades alone, with said fan pressure ratio being less than or equal to 1.45.

16. The method as set forth in claim 15 , wherein the deaerator has an air outlet, and an exit guide extending into the deaerator from the air outlet, and the deaerator inlet delivering the air/oil mixture about the exit guide, and against a wall of the deaerator such that air and oil are separated.

17. The method as set forth in claim 16 , wherein the separated oil enters the oil tank through a diffusor.

18. The method as set forth in claim 17 , wherein an exit velocity from the deaerator of the separated air is less than or equal to 14 feet/second.

19. The method as set forth in claim 18 , wherein said pipe includes a pipe outlet at least 2 inches (5.08 centimeters) below the minimum oil level but above an inlet to an oil supply pipe within the tank.

20. The method as set forth in claim 19 , wherein a dwell time of oil in the tank as removed by said oil pump, on average, is five seconds or less.

21. The method as set forth in claim 20 , wherein said oil tank holds greater than or equal to 25 and less than or equal to 35 quarts of oil.

22. The method as set forth in claim 21 , wherein said gear reduction includes a sun gear for driving intermediate gears and there being oil baffles located circumferentially between said intermediate gears.

23. The method as set forth in claim 22 , wherein an oil capture gutter surrounds said gear reduction.

24. The method as set forth in claim 21 , wherein said engine is rated greater than or equal to 15,000 and less than or equal to 35,000 lbs in rated thrust at take-off.

25. The method as set forth in claim 15 , wherein said oil tank holds greater than or equal to 35 and less than or equal to 50 quarts of oil.

26. The method as set forth in claim 25 , wherein said oil tank is associated with an engine having greater than or equal to 35,000 and less than or equal to 100,000 lbs in rated thrust at take-off.

27. The method as set forth in claim 15 , wherein an oil capture gutter surrounds said gear reduction.

28. The method as set forth in claim 15 , wherein the air exit includes a baffle extending away from an end of the deaerator, and toward the air outlet.