Engines Flashcards
Headline paragraph for our engines
2x Pratt & Whitney PT6A-67A free-turbine, reverse flow turboprop engines, flat rated to 1050 shaft horse power.
Define ‘free turbine’ and name the different engine sections
Compressor section is not physically connected to the power turbines.
Compressor turbine drives the engine compressor and accessories, dual-power turbine drives the power section and propeller.
Define ‘reverse flow’ and its benefits
Airflow changes direction 180deg through the combustion chamber. Creates a compact combustion section, reducing length and weight of the engine.
What is ITT and where is it measured from?
Interstage Turbine Temperature, measured at the T5 station, between the compressor and power sections.
What is the purpose of the integral planetary gearbox, and what is the reduction ratio from power turbine shaft to prop RPM?
To convert the high speed/low torque of the power turbine to low speed/high torque required at the propeller.
Ratio approx. 17.6:1.
What is the purpose of the compressor bleed valve?
Prevents compressor stalls and surges. At low N1s, compressor axial stages produce more compressed air than the centrifugal stage can use, so axial-stage air (P2.5) bleeds to reduce the back pressure on axial stages.
What are the signs of a stuck open/closed compressor bleed valve?
Stuck closed - below 90% N1, compressor stalls.
Stuck open - at high N1 speeds, engine producing less torque with a higher ITT.
Describe the jet-flap intake system.
The P2.5 bled air from the compressor bleed valve passes into the intake zone, providing a swirl effect on inlet air entering the compressor, thus improving low speed compressor characteristics.
How much of the inlet air mixes with fuel for combustion? What is the remainder used for?
Approx. 25% mixes, remainder used to centre the flame in the combustion can and internally cool the engine.
L/R CHIP DETECT
Magnetic chip detector in the bottom of each engine nose gearbox, alerting to a possible metal contamination within the oil supply.
