LP turbine stages: Leap 1A vs PW1000G

[AeroTech]

Hi,

Leap 1A (A320neo) is fitted with 7 LP turbine stages. PW1000G (A320neo) is fitted with 3 LP turbine stages.

Why such difference for LP turbine stages?

Feedback appreciated.

[SMOC]

The 1000G.

Geared Fan - 3 stage LP compressor - 8 stage HP compressor - combustion chamber - 2 stage HP turbine - 3 stage LP turbine.


LEAP 1A.

Fan - 3 stage LP compressor - 10 stage HP compressor - combustion chamber - 2 stage HP turbine - 7 stage LP turbine.


The leap is is not a geared fan so I assume has to extract a lot of energy to spin the fan, low RPM high torque, while the Pratt will have high RPM low torque to spin the gear assembly.

The RPM of the LP shafts should be vastly different seeing the gear ratio is around 3:1 on the Pratt.

[lomapaseo]

The RPM of the LP shafts should be vastly different seeing the gear ratio is around 3:1 on the Pratt.

just where is this gear on the Pratts ?

I thought the idea was to lower the RPM of the fan and raise the rpm of the turbine to get the best efficiency and the LP goes along with the turbine

[Goldenrivett]

Hi lomapaseo,

just where is this gear on the Pratts ?

"This patented gearbox is at the heart of Pratt's PurePower turbofan. Located between the compressor and the fan,..."
Gear Up | Pratt Seeks Gold On Its $1 Billion Bet On A 'Green' Turbofan Engine | HartfordBusiness.com

[barit1]

In principle, it's no different than the prop reduction gearbox of a turboprop. Located inside the front sump area, although I believe it has its own lube system.

[fruitloop]

Been done before with the ALF 502.507 series engine.. This time there appears to be no centrifugal compressor !!

[DaveReidUK]

And before that with the TFE731, which also has a centrifugal stage.

[Turbine D]

The reason the TFE731 and ALF502.507 engines had a centrifugal compressors was to route the final stage of compressed air to the inlet of the combustor. The combustor wrapped around the outside at least part of the turbine section with the exit of the combustor making a u-turn feeding the hot gas into the HP stage 1 turbine nozzle. I think this was done to cut down on the length of the engine, probably saved a foot or more in overall length plus a weight savings.

On the Pratt "PurePower" turbofan engine, I wonder how the PW1100G will handle the shock of a fan blade out or bird ingestion, especially the gear system?

[barit1]

I wonder how the PW1100G will handle the shock of a fan blade out or bird ingestion, especially the gear system?

Likely about as well as a turboprop tossing a fan blade.

However, with the slower-turning fan, the fan blades see lower centripetal forces and can thus be lighter. So, imbalance load will be less than with a traditional direct-drive fan.

But as with all things mechanical, your mileage may vary.