13 ATPL Training Gas Turbine Engines #13 Performance

Summary

This video explains the performance of gas turbine engines, focusing on key factors such as thrust, fuel consumption, and engine power. It explores how thrust is derived from accelerating air, and how different engine types (turbojet, turboprop, turbofan) measure and manage power output. The impact of altitude, temperature, and airspeed on engine efficiency and thrust is examined, as well as the role of specific fuel consumption (SFC). Additionally, the video delves into engine power settings for different flight phases and explains how environmental conditions affect engine performance, including how temperature and altitude influence thrust and fuel efficiency.

Takeaways

• 😀 The performance of a gas turbine engine is calculated using specific symbols that represent pressures and temperatures at various locations within the engine.
• 😀 Thrust is generated by accelerating air backwards, following Newton's third law: for every action, there is an equal and opposite reaction.
• 😀 Thrust can be calculated using the mass flow of air, inlet velocity, and exit velocity, with additional pressure thrust in the case of a turbojet engine.
• 😀 Engine power is measured in various ways depending on the type of engine: thrust for turbojets, shaft horsepower (SHP) for turboprops, and torque for certain engines.
• 😀 Thrust Equivalent Horsepower (TEHP) combines shaft horsepower and jet thrust in turboprop engines, which suffer from power loss with increasing altitude.
• 😀 Specific Fuel Consumption (SFC) is a critical metric for engine efficiency, representing the ratio of fuel consumption to thrust or shaft horsepower.
• 😀 Thrust in turbojets is proportional to engine RPM, but for twin-spool engines, the relationship between RPM and thrust is non-linear, with optimal efficiency at higher RPMs.
• 😀 At high bypass ratio turbofan engines, idle power settings are typically lower but increase during flight due to the windmilling effect caused by forward airspeed.
• 😀 As altitude increases, air density decreases, leading to reduced engine thrust. However, this is partly compensated by the decrease in air temperature at higher altitudes.
• 😀 Engine performance and fuel consumption are affected by ambient temperature conditions, with lower temperatures (below ISA) requiring more fuel to maintain RPM due to denser air.

Q & A

What is the main purpose of the symbols used in the gas turbine engine diagram?

The symbols represent pressures and temperatures at various locations within the engine, and they help calculate the performance level of the engine. These symbols may vary slightly depending on the type of engine.

How is thrust generated by a gas turbine engine?

Thrust is generated by accelerating a mass of air backward, which creates a reaction force in accordance with Newton's third law: for every action, there is an equal and opposite reaction.

What is the relationship between thrust and mass flow rate in a turbojet engine?

Thrust is proportional to both the mass flow rate of air through the engine and the acceleration imparted to that air. These factors are influenced by altitude, temperature, and airspeed.

How is the power output of a turboprop engine measured?

The power output of a turboprop engine is measured in shaft horsepower (shp), which is produced at the propeller shaft. The engine's torque is proportional to this shaft horsepower.

What does Thrust Equivalent Horsepower (TEHP) represent?

Thrust Equivalent Horsepower (TEHP) is the unit of power used to describe the power output of turboprop and some turboshaft engines, which combines shaft horsepower and any jet thrust produced.

How does altitude affect the performance of a gas turbine engine?

As altitude increases, air pressure and temperature decrease, which leads to a decrease in engine thrust due to the lower air density. However, the reduction in temperature partially compensates for this loss by maintaining air density.

What is Specific Fuel Consumption (SFC) and why is it important?

Specific Fuel Consumption (SFC) is the ratio of fuel used per hour per pound of thrust or shaft horsepower. It is a critical metric for determining an engine's efficiency in converting fuel into power.

What is the impact of temperature on engine thrust and fuel consumption?

On hot days, the lower air density reduces thrust, but the engine requires less fuel to maintain RPM. Conversely, on colder days, the increased air density boosts thrust, but the engine needs more fuel to maintain RPM.

What is the role of the power limiter in a gas turbine engine?

The power limiter prevents the engine from exceeding a set maximum pressure by limiting the fuel flow, ensuring that the compressor's output does not surpass a safe limit, which helps protect the engine.

How does aircraft speed affect engine thrust?

As the aircraft speed increases, the engine intake pressure increases due to the ram effect, which increases the mass flow through the engine and the exit velocity. This results in a complex interaction between shaft horsepower and jet thrust, affecting the total thrust.