A321 NEO PW1100 case crack on DEP from Brussels.
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C'mon guys, it's a straightforward Epicyclic sun & planet gear train, been used for all sorts of uses for about 100 years or more. For Pratt & Whitney, the good old PT6 turboprop, like most turboprops, had its reduction gearing using the same concept, though that had three intermediate carrier gears instead of five.
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HPT, HPC and FAN all turn anticlockwise viewed from the front. LPT and LPC turn the opposite way.
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This has nothing to do with the main gearbox driving the fan, the crack is in the auxiliary gearbox.
A simple case crack is unlikely, something inside probably cut loose and gave it a whack.
A simple case crack is unlikely, something inside probably cut loose and gave it a whack.
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not according to the PW operating instructions, the AMP, the MTM and the FCOM all of which I have open in front of me
Planetary gearboxes are commonly used for very high torque applications since it distributes the loads through multiple gears and hence lessens the loads on the individual gears. Planetary gear boxes were common on the early automobiles for that reason - the metallurgy at the time had difficulty making the gears strong enough for a conventional gearbox to last (IIRC the Ford Model T used a planetary gear box). As the metallurgy improved, planetary gearboxes fell out of favor due to their greater complexity and manufacturing costs.
Hoppy - "planetary gear-set" is a rather generic term - commonly used regardless of whether the 'planet' gears are fixed or rotating.
Just curious - is the fan gearbox (regardless of what it's called) readily visible/accessible on the PW1100 series engines? Or is it pretty much covered up and hidden?
It looks like it's pretty well impossible to see the fan gearbox in situ in an assembled engine.
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There will be an amount of oil in the gearbox but the front and rear faces of the alloy casing have mounts for the various systems driven by the gears.
These would include Fuel Systems, Oil Pump, Hydraulic Systems and ElectricalPower Generator.
Some of these can be reasonably heavy hence load bearing.
However, compared to the extremely highly stressed engine components the alloy gearbox casings would have low stresses.
It is possible that at the end of the manufacturing process the casing would be heat treated to normalise the stresses.
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Agreed - likely an internal failure caused the case crack. There were a couple events early on with the GEnx-1B (787) where an internal gear failure actually punched a hole in the gearbox (yes, the design was changed to address it).
Planetary gearboxes are commonly used for very high torque applications since it distributes the loads through multiple gears and hence lessens the loads on the individual gears. Planetary gear boxes were common on the early automobiles for that reason - the metallurgy at the time had difficulty making the gears strong enough for a conventional gearbox to last (IIRC the Ford Model T used a planetary gear box). As the metallurgy improved, planetary gearboxes fell out of favor due to their greater complexity and manufacturing costs.
Hoppy - "planetary gear-set" is a rather generic term - commonly used regardless of whether the 'planet' gears are fixed or rotating.
Just curious - is the fan gearbox (regardless of what it's called) readily visible/accessible on the PW1100 series engines? Or is it pretty much covered up and hidden?
Planetary gearboxes are commonly used for very high torque applications since it distributes the loads through multiple gears and hence lessens the loads on the individual gears. Planetary gear boxes were common on the early automobiles for that reason - the metallurgy at the time had difficulty making the gears strong enough for a conventional gearbox to last (IIRC the Ford Model T used a planetary gear box). As the metallurgy improved, planetary gearboxes fell out of favor due to their greater complexity and manufacturing costs.
Hoppy - "planetary gear-set" is a rather generic term - commonly used regardless of whether the 'planet' gears are fixed or rotating.
Just curious - is the fan gearbox (regardless of what it's called) readily visible/accessible on the PW1100 series engines? Or is it pretty much covered up and hidden?
By doing so the poster is incorrectly describing the way the gearing works as planets orbit the sun gear whereas stars do not.
I only corrected the poster as he incorrectly described the gear system while glibly saying "C'mon guys, it's a straightforward Epicyclic sun & planet gear train".
There is a difference between calling it a "planetary gear-set" and referring to the star gears as planets.
By doing so the poster is incorrectly describing the way the gearing works as planets orbit the sun gear whereas stars do not.
I only corrected the poster as he incorrectly described the gear system while glibly saying "C'mon guys, it's a straightforward Epicyclic sun & planet gear train".
By doing so the poster is incorrectly describing the way the gearing works as planets orbit the sun gear whereas stars do not.
I only corrected the poster as he incorrectly described the gear system while glibly saying "C'mon guys, it's a straightforward Epicyclic sun & planet gear train".
I'd favour this one (my emphases):
"An epicylic gear is a planetary gear arrangement consisting of one or more planet (epicyclic) gears meshed and rotating round a central sun gear. The planet gears are also meshed and rotate within an internal ring gear. The planet gears are fixed to a planet carrier-crank arm designed to rotate on the same centre as the sun gear. Only one planet-carrier/crank arm is used in a single epicyclic gear train. This complicated arrangement has a number of modes of operation depending on which members are locked."
The three possible modes of operation are then described as:
Planetary arrangement: The ring gear is fixed
Star arrangement: The planetary arm is fixed
Sun arrangement: The sun gear is fixed
Epicyclic Gears
So it looks like we're all correct.
Again, not particularly familiar with the PW1100, but Pratt routinely uses a PMA to power the FADEC. FADEC power is separate from the aircraft Generator so that the FADEC will remain powered (and able to control the engine) regardless of whatever failures might affect the aircraft electrical power system.
