Thrust efficient turbofan engine

1. A turbofan engine comprising:

a gas generator section for generating a gas stream flow with higher energy per unit mass flow than that contained in ambient air;

a power turbine converting the gas stream flow into shaft power, the power turbine rotating at a first rotational speed;

a first speed reduction device driven by the power turbine;

a second speed reduction device driven by the power turbine, wherein the power turbine section includes an inner shaft supporting a first plurality of airfoils rotatable in a first direction and a drum including a second plurality of airfoils and driven by the second speed reduction device in a direction opposite the first plurality of airfoils; and

a propulsor section including a fan driven by the power turbine through the first speed reduction device at a second speed lower than the first rotational speed for generating propulsive thrust as a mass flow rate of air through a bypass flow path, wherein an Engine Unit Thrust Parameter (“EUTP”) defined as net engine thrust divided by a product of the mass flow rate of air through the bypass flow path, a tip diameter of the fan and the first rotational speed of the power turbine is less than about 0.15 at a take-off condition.

2. The turbofan engine as recited in claim 1 , wherein the EUTP at one of a climb condition and a cruise condition is less than about 0.10.

3. The turbofan engine as recited in claim 1 , wherein the EUTP at one of a climb condition and a cruise condition is less than about 0.08.

4. The turbofan engine as recited in claim 1 , wherein the tip diameter of the fan is between about 50 inches and about 160 inches.

5. The turbofan engine as recited in claim 1 , wherein the mass flow generated by the propulsor section is between about 625 lbm/sec and about 80,000 lbm/sec.

6. The turbofan engine as recited in claim 1 , wherein the first relative rotational speed of the power turbine is between about 6200 rpm and about 12,500 rpm.

7. The turbofan engine as recited in claim 1 , wherein the propulsive thrust generated by the turbofan engine is between about 16,000 lbf and about 120,000 lbf.

8. The turbofan engine as recited in claim 7 , wherein the gas generator defines an overall pressure ratio of between about 40 and about 80.

9. A turbofan engine comprising:

a gas generator section for generating a gas stream flow with higher energy per unit mass flow than that contained in ambient air;

a power turbine converting the gas stream flow into shaft power, the power turbine rotating at a first rotational speed;

a first speed reduction device driven by the power turbine;

a second speed reduction device driven by the power turbine, wherein the power turbine section includes an inner shaft supporting a first plurality of airfoils rotatable in a first direction and a drum including a second plurality of airfoils and driven by the second speed reduction device in a direction opposite the first plurality of airfoils; and

a propulsor section including a fan driven by the power turbine through the speed reduction device at a second speed lower than the first rotational speed for generating propulsive thrust as a mass flow rate of air through a bypass flow path, wherein an Engine Unit Thrust Parameter (“EUTP”) defined as net engine thrust divided by a product of the mass flow rate of air through the bypass flow path, a tip diameter of the fan and the first rotational speed of the power turbine is less than about 0.10 at one of a climb condition and a cruise condition.

10. The turbofan engine as recited in claim 9 , wherein the EUTP at one of the climb condition and the cruise condition is less than about 0.08.

11. The turbofan engine as recited in claim 9 , wherein the EUTP at a take-off condition is less than about 0.15.

12. The turbofan engine as recited in claim 9 , wherein the tip diameter of the fan is between about 50 inches and about 160 inches.

13. The turbofan engine as recited in claim 9 , wherein the mass flow generated by the propulsor section is between about 625 lbm/sec and about 80,000 lbm/sec.

14. The turbofan engine as recited in claim 1 , wherein the first relative rotational speed of the power turbine is between about 6200 rpm and about 12,500 rpm.

15. The turbofan engine as recited in claim 9 , wherein the propulsive thrust generated by the turbofan engine is between about 16,000 lbf and about 120,000 lbf.

16. The turbofan engine as recited in claim 9 , wherein the gas generator defines an overall pressure ratio of between about 40 and about 80.

17. A turbofan engine comprising:

a gas generator section for generating a high energy gas stream, the gas generating section including a compressor section, combustor section and a first turbine;

a second turbine converting the high energy gas stream flow into shaft power, the second turbine rotating at a first speed and including less than or equal to about six (6) stages;

a first geared architecture driven by the second turbine;

a second speed geared architecture driven by the second turbine, wherein the second turbine section includes an inner shaft supporting a first plurality of airfoils rotatable in a first direction and a drum including a second plurality of airfoils and driven by the second geared architecture in a direction opposite the first plurality of airfoils; and

a propulsor section driven by the second turbine through the geared architecture at a second speed lower than the first speed, the propulsor section including a fan with a pressure ratio across the fan section less than about 1.45, the propulsor section generating propulsive thrust as a mass flow rate of air through a bypass flow path from the shaft power, wherein an Engine Unit Thrust Parameter (“EUTP”) defined as net engine thrust divided by a product of a mass flow rate of air through the bypass flow path, a tip diameter of the fan and the first rotational speed of the second turbine is less than about 0.15 at a take-off condition.

18. The turbofan engine as recited in claim 17 , wherein the EUTP at one of a climb condition and a cruise condition is less than about 0.10.

19. The turbofan engine as recited in claim 17 , wherein the EUTP at the take-off condition is less than about 0.08.

20. The gas turbofan engine as recited in claim 17 , wherein the fan section defines a bypass airflow having a bypass ratio greater than about ten (10).

21. The turbofan engine as recited in claim 17 , wherein the tip diameter of the fan is between about 50 inches and about 160 inches.

22. The turbofan engine as recited in claim 17 , wherein the mass flow generated by the propulsor section is between about 625 lbm/sec and about 80,000 lbm/sec.

23. The turbofan engine as recited in claim 17 , wherein the first relative speed of the second turbine is between about 6200 rpm and about 12,500 rpm.

24. The turbofan engine as recited in claim 17 , wherein the second turbine comprises a low pressure turbine with 3 to 6 stages.

25. The turbofan engine as recited in claim 1 , wherein the first rotational speed of the power turbine comprises a combination of the speed of the first plurality of turbine blades rotating in the first direction and a speed of the second plurality of blades rotating in the direction opposite the first direction.

26. The turbofan engine as recited in claim 9 , wherein the first rotational speed of the power turbine comprises a combination of the speed of the first plurality of turbine blades rotating in the first direction and a speed of the second plurality of blades rotating in the direction opposite the first direction.

27. The turbofan engine as recited in claim 17 , wherein the first rotational speed of the second turbine comprises a combination of the speed of the first plurality of turbine blades rotating in the first direction and a speed of the second plurality of blades rotating in the direction opposite the first direction.