Free turbine
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Free turbine
Greeting to all!
quick question! Are all turbo props are "free turbine" engines? anything wrong you mention that word for every turbo prop?
Thanks in advance
Code0
quick question! Are all turbo props are "free turbine" engines? anything wrong you mention that word for every turbo prop?
Thanks in advance
Code0
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Not a long explination at all
The PT6 is a free turbine meaning the power turbine is not connected to the compressor,,, other turbines have a shaft between the power turbines and the compressor turbines.. end of story
The PT6 is a free turbine meaning the power turbine is not connected to the compressor,,, other turbines have a shaft between the power turbines and the compressor turbines.. end of story
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Pratt & Whitney PT6 (various) and Garrett AirResearch TPE 331 are 2 engines of quite similar size and output; Beech used one or the other in different versions of the Kingair.
PT6 is free, TPE 331 is fixed shaft.
(Until the bull-gear disintegrates unexpectedly, but that's another story....)
PT6 is free, TPE 331 is fixed shaft.
(Until the bull-gear disintegrates unexpectedly, but that's another story....)
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The PT6 is a free turbine meaning the power turbine is not connected to the compressor,,, other turbines have a shaft between the power turbines and the compressor turbines.. end of story
If the compressor isn't connected to a turbine, what is powering it?
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If the power turbine isn't connected to the compressor, what is it connected to?
If the compressor isn't connected to a turbine, what is powering it?
Last edited by blackhand; 5th Nov 2012 at 10:31.
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On the PT6 the compressor is (air coupled) to the power turbine, hence the term free. You can turn the prop which spins the power turbine but the compressor doesn't turn. Or you can motor the engine with the starter and hold the prop.
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On the PT6 the compressor is (air coupled) to the power turbine, hence the term free
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ok, its like this
free turbine is sort of like the automatic automobiletransmission of the world
fixed shaft turbine is like manual transmission
fixed shaft is more responsive and a tiny bit more efficient
free turbine is a bit simpler
I have about one hour of free turbine time (king air)
I have thousands of hours of fixed shaft turbine.
I'll take the fixed shaft anyday. however one has to remember to shut the engines down correctly or a minor problemhappens with starting
fixed shaft turbine is like manual transmission
fixed shaft is more responsive and a tiny bit more efficient
free turbine is a bit simpler
I have about one hour of free turbine time (king air)
I have thousands of hours of fixed shaft turbine.
I'll take the fixed shaft anyday. however one has to remember to shut the engines down correctly or a minor problemhappens with starting
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free turbine is sort of like the automatic automobiletransmission of the world
fixed shaft turbine is like manual transmission
fixed shaft turbine is like manual transmission
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Think of it this way.
the engine is like a normal jet engine with lots of hot gas coming out the back which would normally push the aircraft along, this engine works happily on its own, using a proportion of the energy extracted by the turbine to drive the compressor, about 10,000 HP on a large high bypass engine, and the rest is chucked out the back to create thrust. So now we stick another turbine in the gas flow to convert the fast moving gas's energy into torque to drive something that needs torque as opposed to thrust to make it work.
There will probably be a bit of thrust left over, as its hard to convert all of the thrust to torque, so we point the exhaust backwards for a bit of a push.
obviously a simplistic explanation and hope it helps you to understand the concept.
GB
the engine is like a normal jet engine with lots of hot gas coming out the back which would normally push the aircraft along, this engine works happily on its own, using a proportion of the energy extracted by the turbine to drive the compressor, about 10,000 HP on a large high bypass engine, and the rest is chucked out the back to create thrust. So now we stick another turbine in the gas flow to convert the fast moving gas's energy into torque to drive something that needs torque as opposed to thrust to make it work.
There will probably be a bit of thrust left over, as its hard to convert all of the thrust to torque, so we point the exhaust backwards for a bit of a push.
obviously a simplistic explanation and hope it helps you to understand the concept.
GB
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There are operational differences as well.
1. A prop strike in a PT6 is less involved than in a TPE331 for instance, as it's not connected to everything else as it is in the Garrett.
2. On the other hand, the TPE331 is certified to run on pretty much anything you'll feed it, including the occasional Avgas, Diesel, Mogas run as the turbine stage is less delicate. Not something you can do with a PT6. More bush, if you wish.
3. Garrets are slightly more efficient (burn less fuel) and they have higher TBO's (5400hrs on most of them).
4. On the other hand, the Garretts need a lot more electric power to get started as they have to spin the prop before they light up. This is also why they're susceptible to hot starts if the battery is weak, as it won't push enough cold air through the core.
1. A prop strike in a PT6 is less involved than in a TPE331 for instance, as it's not connected to everything else as it is in the Garrett.
2. On the other hand, the TPE331 is certified to run on pretty much anything you'll feed it, including the occasional Avgas, Diesel, Mogas run as the turbine stage is less delicate. Not something you can do with a PT6. More bush, if you wish.
3. Garrets are slightly more efficient (burn less fuel) and they have higher TBO's (5400hrs on most of them).
4. On the other hand, the Garretts need a lot more electric power to get started as they have to spin the prop before they light up. This is also why they're susceptible to hot starts if the battery is weak, as it won't push enough cold air through the core.
Last edited by AdamFrisch; 18th Nov 2012 at 23:00.
