The reduction gearbox allows the fan to be driven directly from the IPT with both at optimal RPM. So LPT (running at a lower, fan optimised RPM) is no longer required. It's still essentially a three shaft engine it's just recovering the fan drive energy mechanically, directly from the core, instead of via LPT
As I understand it, by running each stage closer to optimal RPM, the gearbox allows high OPR over fewer, smaller diameter stages, so the core is more efficient, has less parts and is lighter. However the forces on each compressor blade are much greater because the pressure ratio of each individual stage is then higher.
This puts RR in a very good position to develop an efficient large GTF because triple spool core architecture shares similar characteristics (i.e. less stages, high pressure ratio per stage.) so their previous experience with blade materials/cooling/geometry etc. will be applicable.
I think P&W did well to develop their GTF and it's certainly been a commercial success. But they will need to work on the core to scale it up. RR have the advantage with core tech but they are still working on the fan and gearbox. So essentially the two manufacturers are pursuing the same goal from opposite directions.
Last edited by Sonikt; 24th Apr 2021 at 00:52.