Gas turbine engine turbine temperature split

The method of claim 20, wherein the low to high pressure turbine temperature change ratio is in the range from 1.10 to 1.25.

The method according to claim 20, wherein the engine comprises more than two turbines, and wherein the highest pressure turbine of the engine is selected as the second turbine and the lowest pressure turbine of the engine is selected as the first turbine.

The method according to claim 20, wherein a specific thrust of the engine at cruise conditions, defined as net engine thrust divided by mass flow rate through the engine, is in the range from 50 to 100 Nkg−1s.

The method according to claim 20, wherein a fan tip loading at cruise conditions is defined as dH/Utip2, where dH is the enthalpy rise across the fan and Utip is the (translational) velocity of the fan tip is in the range from 0.25 to 0.4.

The method according to claim 20, wherein cruise conditions means the conditions at mid-cruise of an aircraft to which the engine is attached, mid-cruise being the midpoint between top of climb and start of decent.

The method according to claim 20, wherein the forward speed of the gas turbine engine at the cruise conditions is in the range of from Mn 0.75 to Mn 0.85.

The method according to claim 20, wherein the cruise conditions correspond to atmospheric conditions at an altitude that is in the range of from 10500 m to 11600 m.

The method according to claim 20, wherein the cruise conditions correspond to:

• (i) atmospheric conditions defined by the International Standard Atmosphere at an altitude of 10668 m and a forward Mach Number of 0.85;
• or
• (ii). atmospheric conditions defined by the International Standard Atmosphere at an altitude of 11582 m and a forward Mach Number of 0.8

The method according to claim 20, wherein either:

• (i) the engine comprises a total of two turbines and the first turbine entrance temperature is substantially equal to the second turbine exit temperature or
• (ii) the engine comprises more than two turbines and the high pressure turbine temperature change provides a measure of the temperature change across all turbines except the lowest pressure turbine.

The method according to claim 20, wherein the Overall Pressure Ratio (OPR) at cruise is greater than 40 and lower than 80.

The method according to claim 20, wherein the fan has a fan tip radius and:

• (i) the fan tip radius is in the range from 110 cm to 150 cm;
• or
• (ii) the fan tip radius is in the range from 155 cm to 200 cm.

The method according to claim 20, further comprising a gearbox that receives an input from the first core shaft and outputs drive to the fan so as to drive the fan at a lower rotational speed than the first core shaft, and wherein the gearbox has a gear ratio in the range of from 3.2 to 5.

The method according to claim 20, wherein the first (low pressure) turbine comprises at least four rotor stages.