Rated Engine Thrust
Rated engine thrust refers to the maximum amount of thrust an engine is designed to produce, typically under specific environmental conditions (like temperature and altitude), and is a crucial factor in aircraft performance and safety. This thrust value, often expressed in pounds (lb) or newtons (N), is a key piece of engine identification data and is used for takeoff and climb calculations.
Here's a more detailed explanation
What it is
Maximum Thrust
Rated thrust represents the highest thrust an engine can generate under specific conditions.
Engine Identification
It's a critical piece of data for identifying and understanding an engine's capabilities.
Measured in Pounds or Newtons
Thrust is a force, and is measured in pounds (lb) or newtons (N).
Flat-Rated Temperature
Engines are often "flat-rated" by the manufacturer, meaning they are designed to produce their rated thrust up to a specific ambient temperature (often expressed as an ISA+xx° value).
FADEC (Full Authority Digital Engine Control)
The FADEC system manages engine operation, including adjusting fuel flow and limiting rotational speed to ensure the engine doesn't exceed its limits, including the flat-rated temperature.
How it relates to aircraft performance
Takeoff and Climb
Rated thrust is essential for achieving adequate acceleration and climb performance during takeoff and climb.
Drag and Thrust
The amount of thrust required to overcome drag and maintain steady, level flight depends on the aircraft's drag characteristics.
Maximum Level Flight Speed
The maximum level flight speed is achieved when the thrust required equals the maximum thrust available from the engine.
Temperature Limitations
As ambient air temperature increases above the flat-rated temperature, the engine's ability to produce its rated thrust decreases linearly until the engine becomes temperature-limited.
Reduced Thrust Takeoff
In some cases, the FADEC can be instructed to reduce the amount of thrust produced by the engine, even if the engine is capable of producing its rated thrust, for example, to reduce noise or fuel consumption.
Engine Life
Limiting thrust to the rated value, especially at lower air temperatures, helps to maximize engine service life.
Specific Thrust
Specific thrust is a way to determine the efficiency of a jet engine regardless of the size of the engine. It is calculated by dividing the thrust created by the engine by the mass flow rate of the air.
Examples
CFM56-3: This engine, designed for the Boeing 737 Classic series, has static thrust ratings from 18,500 to 23,500 lbf (82.3 to 105 kN).
GE9X: This engine, developed by GE Aviation for the Boeing 777X, is the world's most powerful commercial jet engine, with a test run reaching 134,300 pounds of thrust.
