10 Questions
What does N1, or %N1, denote in a jet engine?
The rotation rate of the low-speed rotor
What is the corrected N1 calculated by dividing?
%N1 by the total temperature ratio raised to some power
What type of engine uses %N1 as the primary thrust setting parameter?
General Electric and CFMI engines
What is engine stall also known as?
Compressor stall
What is surge in a jet engine?
A condition of unsteady airflow through the engine
What can cause a flameout in a jet engine?
Unsteady airflow through the engine
What is bleed in a jet engine?
Extraction of compressed air from the engine
In a two-spool engine, what does N2 denote?
The rotation rate of the high-speed rotor
What does %RN1 represent?
The corrected N1
What is the relationship between gauge N1 and corrected N1 dependent on?
The engine type
Study Notes
Thrust Equation
- Net thrust (Fnet) equation: mass flow rates and velocities.
- Force equation: F = w * g * (V2 – V1), relating force, gas flow, gravity, and initial/final gas velocities.
Factors Affecting Thrust
- Air density, a function of temperature and pressure altitude, is a significant component affecting thrust
- Other factors include engine design limitations, such as pressure differential across the engine case, turbine inlet temperature, and fan speed
Thrust Settings and Ratings
- Maximum Takeoff Thrust: the highest thrust level available from an engine, certified and time-limited to a maximum of 5 minutes (extendable to 10 minutes for one-engine inoperative takeoff)
- Go-Around Thrust: a certified rating
- Maximum Continuous Thrust (MCT): a certified rating
- Maximum Climb Thrust (MCLT) and Maximum Cruise Thrust (MCRT): not certified ratings
Engine Parameters
- Engine Pressure Ratio (EPR): the ratio of the total pressure at the exhaust to the total pressure in front of the fan
- Percent of Fan Reference RPM (%N1): the percentage of the reference rotation speed of the fan
Common Jet Engine Terms
- Corrected N1 (or Referred N1): N1 divided by the total temperature ratio raised to some power
- N2 and N3: the rotation rates of the medium-speed and high-speed rotors of a three-spool engine
- Engine Stall (compressor stall): a condition characterized by stalled airflow over the compressor blades
- Surge: a condition of unsteady airflow through an engine due to abnormal flow conditions
- Flameout: a condition in which the combustion chambers lose their ignition
- Bleed: the extraction of compressed air from the engine
Learn about the thrust equation in jet engines, derived from Newton's second law of motion. Understand the variables involved and how they affect the thrust of a jet engine.
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