15.16 - Turbo-Prop Engines Flashcards
What are the 2 forms of turbo prop gas turbine engine?
- Single-shaft
- Free-Turbine
How is the turbo-prop coupled with the gas turbine engine so as to allow both to travel at their optimum speed?
In a Single-shaft turbo prop engine, the turbo-prop is coupled to reduction gears from the same shaft that contains the compressors and the turbines.
In a Free turbine turbo prop engine, the turbo-prop is coupled to a turbine stage whose shaft is independent from the one used to drive the compressor.
What are the benefits of using a free turbine? (2)
A free turbine propeller can go to it’s feather position upon engine shutdown as it is not coupled to the gas generator turbine.
The turbo-prop or propeller is can run at it’s optimum speed as can the turbine engine without being problematic for each other as they are not coupled to the same shaft.
The planet and spider gears are part of what turboprop device?
also called Epicyclical type
Reduction Gear System
concentric with drive shaft and compact
What device prevents the turbo-prop propeller from going excessively over speed?
Overspeed governor which is mounted on the reduction gearbox, is a backup to the propeller governor and releases oil from the propeller moving the blades to a higher pitch angle, reducing RPM. This system is needed when propeller RPM exceeds 100%
On a twin engine turboprop, how are engine rpm and prop rpm typically controlled?
A power lever enables fuel control for a specific amount of power from the engine. The fuel control and the propeller governor together establish the correct combination of RPM, fuel flow, and propeller blade angle to provide the desired power.
In flight both engine RPM and prop RPM are governed automatically known as the alpha range.
On ground, prop RPM is not controlled automatically but by the position of the power lever position, this is called the beta range.
Describe a coupled turbine?
A turboprop engine in which the propeller reduction gears are driven by the same shaft which drives the compressor for the gas generator
Describe a free turbine / power turbine?
A gas turbine engine with a turbine stage on a shaft independent of the shaft used to drive the compressor
What type of combustion chambers are normally found on modern turboprop engines?
Annular reverse flow
What type of reduction gears are used for propellers?
- Parallel spur gear type
- The epicyclical type (Planetary gear train)
Where is ‘‘Alpha mode’’ used?
For Flight, the propeller blade angle and fuel flow for any given power setting are governed automatically according to a predetermined schedule. This is known as the ‘‘Alpha range’’
Where is ‘‘Beta mode’’ used?
Below the ‘‘flight idle’’ power lever position, the coordinated RPM blade angle schedule becomes incapable of handling the engine efficiently.
Here the ground handling range. referred to as the beta range is encountered.
In the beta range of the throttle quadrant, the propeller blade angle is not governed by the propeller governor, but is controlled by the power lever position.
The beta range is used for ground operations inclusive of slowing the aircraft after landing
In what direction is a propeller feathered?
The “feathered” position is the highest pitch angle obtainable. [Figure 14-8] The feathered position produces no forward thrust.
Propeller arms are turned 90 deg.
What equipment is needed to un-feather a propeller?
Propeller unfeathering will automatically occur with the propeller beta valve regulating the blade angle.
A ground start is accomplished with the power lever placed into flight idle position.
How is a propeller prevented from over-speeding?
Overspeed governor which releases oil from the propeller wheneber the propeller RPM exceeds a preset limit above 100%
Releasing the oil shows the blades to move to a higher pitch angle, which reduces the RPM
Define On-speed condition?
In theory, when the governor is at onspeed condition the metering valve is closed; not allowing pump oil to pass to or from the propeller and
