Turbofan Question

[1969912 0]

On big turbofan engines in use on airliners, is the fan driven by the main engine shaft (through a gearbox?), or does it have its own turbine disk (with the compressor stages driven by a separate turbine)?

"Once we got to the point where twenty/something's needed a place on the corner that changed the oil in their cars we were doomed . . ."
-NickDG

[GrabGrass 0]

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On big turbofan engines in use on airliners, is the fan driven by the main engine shaft (through a gearbox?), or does it have its own turbine disk (with the compressor stages driven by a separate turbine)?

Yes.

~ "Pack Fast, Pull Low... and Date Your Riggers WIFE!" ~

[1969912 0]

That was helpful!

"Once we got to the point where twenty/something's needed a place on the corner that changed the oil in their cars we were doomed . . ."
-NickDG

[airtwardo 7]

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That was helpful!

http://ctr-sgi1.stanford.edu/CITS/ge90.html

Looks like a straight shaft to me...

~ If you choke a Smurf, what color does it turn? ~

[1969912 0]

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That was helpful!

http://ctr-sgi1.stanford.edu/CITS/ge90.html

Looks like a straight shaft to me...

Maybe with its own turbine, otherwise the fan blade tip speeds would be incredibly high if the fan was rotating at the same speed as the compressor section. Any idea how fast the fan section spins?

"Once we got to the point where twenty/something's needed a place on the corner that changed the oil in their cars we were doomed . . ."
-NickDG

[airtwardo 7]

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Any idea how fast the fan section spins?

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Yes.

~ If you choke a Smurf, what color does it turn? ~

[NewGuy2005 53]

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Any idea how fast the fan section spins?

Fairly quick, if I'm not mistaken. It "fans" better, the faster it goes, you see.

[1969912 0]

Blows

"Once we got to the point where twenty/something's needed a place on the corner that changed the oil in their cars we were doomed . . ."
-NickDG

[airtwardo 7]

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Blows

http://www.turbokart.com/about_ge90.htm

Actually on the GE 90 it turns pretty slow...like 2500 rpm.

~ If you choke a Smurf, what color does it turn? ~

[2fat2fly 0]

Think Suck, Bang, Blow

I am not the man. But the man knows my name...and he's worried

[VectorBoy 0]

Those engines are actually two concentric but counter rotating shafts. Think of a spool within a spool. The big fan on the front is attached to the very last stages of the turbine.

I don't have the links but GE has some very cool audio visual clips of their products.

[1969912 0]

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Blows

http://www.turbokart.com/about_ge90.htm

Actually on the GE 90 it turns pretty slow...like 2500 rpm.

Thanks. Looks like the fan is driven through a concentric shaft arrangement by its own turbine. Based on the numbers from the page you cited, fan blade tip speed is ~1400 f/s, but in reality it is probably just subsonic.

The pressure ratio is amazing. Air is compressed to ove 600 psi to feed the burners!

"Once we got to the point where twenty/something's needed a place on the corner that changed the oil in their cars we were doomed . . ."
-NickDG

[2fat2fly 0]

http://www.aircraftenginedesign.com/custom.html4.html

I am not the man. But the man knows my name...and he's worried

[1969912 0]

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Those engines are actually two concentric but counter rotating shafts. Think of a spool within a spool. The big fan on the front is attached to the very last stages of the turbine.

I don't have the links but GE has some very cool audio visual clips of their products.

Are they counter rotating to counteract gyroscopic forces, or is it due to design of the gas flow in the tubines, i.e. using opposite rotation to act kind of like stator blades?

"Once we got to the point where twenty/something's needed a place on the corner that changed the oil in their cars we were doomed . . ."
-NickDG

[2fat2fly 0]

Go forward, learn
http://www.erau.edu/db/degrees/ap_program/ap_cert.html

I am not the man. But the man knows my name...and he's worried

[airtwardo 7]

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Think Suck, Bang, Blow

It's suck, bang, squish, blow...as opposed to the -suck squish BANG blow in a 'real' (round) airplane engine!

~ If you choke a Smurf, what color does it turn? ~

[htrammel 0]

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Think Suck, Bang, Blow

It's suck, bang, squish, blow...as opposed to the -suck squish BANG blow in a 'real' (round) airplane engine!

Nope. It still gets the squish (or squeeze) before it gets the bang.
LPC - HPC - Combustor - HPT - LPT

Also to the OP: If your profile is correct and you are in Washington, I highly recommend a pilgrimage to the museum at Boeing field (KBFI). Lots of info and just plain neat stuff there. If you ever get to the Hartford, CT area look me up and I'll get you a little tour of Pratt and Whitney. They know a thing or two about engines.

[akarunway 1]

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On big turbofan engines in use on airliners, is the fan driven by the main engine shaft (through a gearbox?), or does it have its own turbine disk (with the compressor stages driven by a separate turbine)?

This might help>http://www.grc.nasa.gov/WWW/K-12/airplane/aturbf.html

I hold it true, whate'er befall;
I feel it, when I sorrow most;
'Tis better to have loved and lost
Than never to have loved at all.

[1969912 0]

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Also to the OP: If your profile is correct and you are in Washington, I highly recommend a pilgrimage to the museum at Boeing field (KBFI). Lots of info and just plain neat stuff there. If you ever get to the Hartford, CT area look me up and I'll get you a little tour of Pratt and Whitney. They know a thing or two about engines. Smile

Yep, been to the museum, and thanks for the offer!

"Once we got to the point where twenty/something's needed a place on the corner that changed the oil in their cars we were doomed . . ."
-NickDG

[2fat2fly 0]

You in Hartford? i think I'll be up for AOPA

I am not the man. But the man knows my name...and he's worried

[billvon 3,126]

> On big turbofan engines in use on airliners, is the fan driven by the main
>engine shaft (through a gearbox?), or does it have its own turbine disk
>(with the compressor stages driven by a separate turbine)?

Most turbofans have two power turbine stages. One drives the compressor, the other drives the fan. No gearing there. Most turbofans have gearing for power takeoff to run ancillary devices like generators and pumps.

Turboshaft/turboprop aircraft have a gearbox that reduces RPM to a speed that's usable with prop engines (2000RPM or so.) Some (like the PT6 line) have a separate turbine to run the compressor and the output shaft; some (like the Garretts) have a single turbine.

[1969912 0]

So on a turbofan, what limits the RPM's of the fan? Do they have movable vanes in the tubine section or is the whole thing just designed such that the fan cannot over-rev?

"Once we got to the point where twenty/something's needed a place on the corner that changed the oil in their cars we were doomed . . ."
-NickDG

[airtwardo 7]

http://en.wikipedia.org/wiki/Compressor_stall

~ If you choke a Smurf, what color does it turn? ~

[htrammel 0]

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You in Hartford? i think I'll be up for AOPA

Lemme know. We'll have a beverage.