Free turbine

[code0]

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

[jc2065]

No, not all TPs are free turbines. Look them up on Wikipedia. Otherwise this would be a very long reply.

[Perrin]

Here we go let me start this off, the number one and best for me was the RR Dart.

Keep them up boys
Peter :ok:

[bigoil]

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

[Capot]

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....)

[MarkerInbound]

I'd be willing to say most models of TPs are not free turbine. I have no idea if the number of PT6s built outweighs the number of Darts, T56s, Garretts, et al.

[dixi188]

Then there's the RR Tyne!

Two spool but not free turbine.

[glum]

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 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?

[ZFT]

I would suggest that the Proteus was the first civil free turbine

[blackhand]

If the power turbine isn't connected to the compressor, what is it connected to?It would be connected by a shaft to the......power gear train and thence to the propellor or drive shaft.If the compressor isn't connected to a turbine, what is powering it? I'm pretty sure it is connected to a turbine, just not the "power" turbine. I suggest you may want to buy a good reference book, one I like is Rolls Royce the turbine engine

[glum]

Ah, thanks for the info. :ok:

[bigoil]

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.

[blackhand]

On the PT6 the compressor is (air coupled) to the power turbine, hence the term freeThe compressor is not coupled to the power turbine in any way, hence the term free turbine

[sevenstrokeroll]

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

[blackhand]

free turbine is sort of like the automatic automobiletransmission of the world
fixed shaft turbine is like manual transmission Your analagy is correct on start up but is more like fluid coupling drive than a transmission. Direct drive is direct drive no transmission

[Bye]

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

[AdamFrisch]

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.