T700 Gas Turbine Engines Flashcards
What is a gas turbine engine?
A system of components that uses air as a working fluid. It extracts energy from the working fluid to drive the aircraft’s rotor system and sustain engine operation
What are the components of an engine?
Inlet, compressor, combustor, gas generating turbine assembly connected to the compressor, freewheeling power turbine assembly connected to the main rotor system, and the exhaust
How does it basically function?
incoming air must be compressed, heated through fuel/air combustion and expanded across the turbine assemblies to operate the engine
How many assemblies are in the compressor?
2; compressor rotor and compressor stator
What is the compressor rotor comprised of?
5 axial stages and 1 centrifugal stage
What is the compressor stator comprised of?
Inlet variable guide vane, two stages of variable guide vanes, 3 stages of fixed guide vanes
How does the compressor work?
Each stage of the vanes acts as a convergent/divergent duct, increasing the static pressure and temperature while decreasing velocity. Each stage is limited in the compression it can provide which is why multiple stages are needed.
How does the turbine work (GG and PT)?
GG and PT have rotor and stator axial flows. The stator vanes are called nozzles which will decrease volume and increase the velocity across the rotors which allows for energy to be converted into shaft horsepower. 75% of this energy is needed to power the engines, while the remaining goes to powering the rotor system to propel the airframe.
The engine is designed for that gas generation (Ng) varies based on load demand or aerodynamics, which maintains a constant power turbine (NP) speed directly proportional to the airframe Rotor Speed (NR)
What is creep?
An elongation of the GG blades due to high temperatures. To counteract, a portion of the compressed air is bled off at the compressor stage 3 to cool the blades
What could affect flow restriction?
Any obstacles to the gas path flow through the engine will affect engine’s prodution
What is NP Governing?
Turboshaft engines maintain a set main rotor speed through NP speed setpoint. Any reduction in NP will alert the engine to produce more power, by increasing fuel to the combustor causing TGT to rise. The rise in heat causes the GG to turn fast, causing compressor to squeeze more air into the combustor.
The opposite occurs with an increase in NP
How does air density and temperature affect engine performance?
As air temperature rises, air density decreases. The compressor must turn faster to compensate for the low density, requiring a greater amount of fuel to increase the GG rotors, increasing Ng, fuel flow, and TGT to maintain NP/NR
This can cause the engine to reach it’s mechanical or thermal limits (NG, TGT) prior to reaching the airframe transmission limit
On cold days, cooler air has a higher air density and the engine compressor can produce the same ratio at a lower NG, TGT, and fuel flow.
