The full story is more involved and more beautiful . The first paragraph (and it’s sub links) are enough if you don’t have the time to read the full article.
Turbofan - Wikipedia
George
Great article that, thanks. Fascinating comparing the specs of the actual manufactured engines....
Thanks a lot George.On a non-geared turbofan engine, the fan is driven by a rotating shaft(*)
On a geared turbofan engine the driving shaft enters a reduction gearbox, the output of which drives the fan with a reduced angular velocity ω. The exercise aims to make fan blades function at subsonic tangential velocity (v= ω *r) along their full length, now that fan diameters becomes larger and larger. This old article explains it better than me (put fan blade in place of propeller blade).
Popular Science - Βιβλία Google
(*)Hans, I guess your question has to do with where does the driving shaft connects to at the other end, yes?
The other end is a turbine disk, the blades of which are hit by the exhaust gases of a constantly burning mixture of air and kerosene, thus turbine disk rotates and drives the shaft that rotates the fan disk.
The full story is more involved and more beautiful . The first paragraph (and it’s sub links) are enough if you don’t have the time to read the full article.
Turbofan - Wikipedia
George
Now I know a lot more. I thought the turbine blades are what you see from the outside, but they turn out to be the fan.
The Turbine is the motor inside driving the Fan which is pushing the air.
The magazine from 1943 was hilarious. Interesting article on propeller blades, but also building instructions for a Triode Oscillator, an Old Dutch Settle, a DIY Wooden Baby Walker and so on.
Nice to see how the world progressed in the past 80 years.
Still a few questions, what about the torque problem that propeller engines have for a turbo fan engine, and what about variable pitch to accommodate the different demand for taking off and cruising for this type of engine ?
And how to reverse the engine after landing to assist the brakes.
Hans
For jets, the rear of the engine cowling is split. For reverse thrust the split cowling opens tilting back at the same time forming a reflector to redirect engine output gases forward.
That’s an interesting question and one of the most difficult to be answered properly by me.
If all you want is a simple bipolar answer, here is this poor version: Turbofan induces much less of the ‘torque problem’ than propeller propulsion
This you call as ‘torque problem’ is a combination of many effects, some (two) having to do with rotational masses [mechanical masses (*) and masses of air] and a few more (four) having to do with aerodynamic effects [spiral propwash, asymmetric loading (p-factor), torque, and gyroscopic effects] and none of them are simple.
Some of all these effects apply equally on fans and on propellers, some are specific to one or the other.
For certain, on twin turbofan aircrafts, L and R fan disks and engine cores rotate in the same direction.
For propellers, do not assume that all twin engine propeller planes cater for the issue. Most don’t. Both engines and both propellers turn in the same direction. Only on a few airplanes L propellers rotate opposite to the R (some through reverse rotating reciprocating engines, other through reversing gearboxes).
For the case of flying an airplane, a pilot is trained to fly a specific airplane and corrects by rudder pedal and or ailerons the tendency of each plane to turn left (or right) or feel heavy on one side.
None. Only the thrust lever position changes increasing and decreasing fuel flow on the fuel nozzles. This alters the core and fan rotation velocity which affects velocity and mass flow of air thrown back and consequently engine thrust.
Engine rotation does not reverse. They operate deflector panels to deflect the fan air stream or the outlet gas stream or both toward the front (thrust reversal ) as Mark wrote.
George
(*) I know only of two turbine engines (P&W PT6, RR Pegasus) that have part of their rotating masses (HP turbine) turn CW and part (LP turbine) rotating CCW but there may be some others too.
Attachments
Thanks Bill.
These need to have high clearance from ground. For to make commercial debut, either the landing gears have to become twice as long as they are today with the engines attached to common ‘low wing’ configuration, or the planes have to be redesigned to have their wings above the fuselage (‘high wing’), or the engines be installed at the rear of the fuselage asking for a ‘T tail’ empennage .
It seems that Russians have the longest operating experience with profans and the design expertise for high powered engines of this kind.
Propfan - Wikipedia
https://www.faa.gov/about/office_or...orts/media/Open_Rotor_Public_Final_Report.pdf
You may have wandered (I did) why GE hasn’t yet jumped on the train of geared turbofans. Now I know why
(from when they had adapted a GE F404 core to build GE C36):“Key feature of system is unique direct turbine drive eliminating need for gearbox to transmit power to propeller blades.”
Load turbine was a seven stage module. Each stage was a pair of rotors rotating in opposite direction to each other; there were no stators (except from the inlet and outlet guide vanes of the module) . Alternate rotos were directly coupled to counterrotating fan blades. The counter-rotating turbine ran at half the rpm of a conventional turbine,so it did not require a reduction gearbox to drive the ductless fan
General Electric GE36 - Wikipedia
https://ia601206.us.archive.org/12/...19900000732/NASA_NTRS_Archive_19900000732.pdf
George
Contrarotating turbine...I can't think what could possibly go wrong thereYou may have wandered (I did) why GE hasn’t yet jumped on the train of geared turbofans. Now I know why
“Key feature of system is unique direct turbine drive eliminating need for gearbox to transmit power to propeller blades.”
$1.3bn of somebodies money spent! Way to make a small fortune in aerospace is to start with a much bigger fortune! I can see why the Trent engine development bankrupt RR and why the A380 has wiped out their profits for some years to come (and a few other problems they have had).
BTW George, not like you to double post!
Everyone knows Richard Thompson's original, maybe haven't heard Greg Brown outside the US:
YouTube
All good health and fortune,
Chris
I seem to remember Rolls-Royce trying carbon fiber fan blades, but it didn’t turn out well. Looks like GE got the jump on them.
As an aside, when I was in Asia, one of my expat friends was the service and maintenance manager for P&W and another had a similar role at Boeing who were selling loads of planes to the Chinese.
As an aside, when I was in Asia, one of my expat friends was the service and maintenance manager for P&W and another had a similar role at Boeing who were selling loads of planes to the Chinese.
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