Historically, many engines could be fit on different frames such as the RB211 and the CF6. Why isn't the RR Trent 1000 an option on the B748 just like the GEnx is?

Finally, is it possible to fit a B748 GEnx-2B to a B788? According to GE, albeit having identical core and similar materials the -2B features a smaller fan, de-staged booster and low-pressure turbine. Also, the takeoff thrust is de-rated. I guess it's not possible then?

Cheers,

346fetish

346fetish wrote:

Historically, many engines could be fit on different frames such as the RB211 and the CF6. Why isn't the RR Trent 1000 an option on the B748 just like the GEnx is?

Finally, is it possible to fit a B748 GEnx-2B to a B788? According to GE, albeit having identical core and similar materials the -2B features a smaller fan, de-staged booster and low-pressure turbine. Also, the takeoff thrust is de-rated. I guess it's not possible then?

Cheers,

346fetish

Both of these questions come back to the same point - there is a significant architecture difference in the engines built for the 787 compared to those on the 747 (and pretty much every other airliner), in that the engines on the 787 do not take off bleed air for running pressurisation, and instead must deliver a higher amount of electrical power from the generator. As a result the engines on the 747-8 aren't a straight swap from the 787, but needed some amount of work. Presumably the expected sale numbers meant it did it did not make sense to offer two engine options since neither manufacturer would be able to make a decent return on it. It also means you couldn't simply take an engine off a 747-8 and bolt it on the a 787-8.

V/F

The main reason is economics. It costs money to (a) make a given engine work on a given airframe and (b) prove to the authorities that it works well enough to go into airline service. If you can't make back the money plus a profit margin, you just don't do it. In turn some times the engine provider negotiates an exclusive deal so it's more likely it can make money selling their engines for the airliner. IIRC GE has an exclusive deal with Boeing, so no RR on 747-8.

It's also by no means a hard-and-fast rule that multiple engines could be provided for a given type - beyond any contractual exclusivity arrangements, as VirginFlyer notes there can be major differences in architecture between types that make certain engines unsuitable, and even if they are suitable the engine-airframe combination needs to be tested and certified. No customer interest? No financial rationale to seek certification.

The 737 NG, for example, has only ever been offered with a modified version of the CFM56 (given the 737's original design doesn't really allow for engines much larger than the original Pratt and Whitney JT8D), while the 757 was originally offered with the RB211 before Pratt came on-board with the PW2037. GE also indicated that they would offer the CF6-32 but eventually withdrew due to limited customer interest.

Even within the 747 family, for which engines from all three manufacturers were available, the RB211 was never certified on the 747-400ER and Pratt only got the PW4000 onto the options list some time after the model was first offered.

And of course there's the RB211 being the only choice on the L-1011, much as Lockheed may have wished they'd not walked that road...

346fetish wrote:

Historically, many engines could be fit on different frames such as the RB211 and the CF6. Why isn't the RR Trent 1000 an option on the B748 just like the GEnx is?

Finally, is it possible to fit a B748 GEnx-2B to a B788? According to GE, albeit having identical core and similar materials the -2B features a smaller fan, de-staged booster and low-pressure turbine. Also, the takeoff thrust is de-rated. I guess it's not possible then?

Cheers,

346fetish

GEnxB has bleed air, GEnx A does not as the 787 is bleed airless (well almost , at least for the cabin and wing but not the nacelle). Also why the original Mk1 A350 XWB had GEnxB engines. Trent 1000 does not have bleed air, as its only for the 787. I suppose theres a chance you could put a Trent 7000 (Trent 700 with 1000 and XWB tech and with bleed air) on a 747.
Also theres the issue of cruise thrust, while Take Off thrust for some engines may be similar cruise thrust may be significanty different which is important if you are going from 2 to 4 engines.

XAM2175 wrote:

It's also by no means a hard-and-fast rule that multiple engines could be provided for a given type - beyond any contractual exclusivity arrangements, as VirginFlyer notes there can be major differences in architecture between types that make certain engines unsuitable, and even if they are suitable the engine-airframe combination needs to be tested and certified. No customer interest? No financial rationale to seek certification.

The 737 NG, for example, has only ever been offered with a modified version of the CFM56 (given the 737's original design doesn't really allow for engines much larger than the original Pratt and Whitney JT8D), while the 757 was originally offered with the RB211 before Pratt came on-board with the PW2037. GE also indicated that they would offer the CF6-32 but eventually withdrew due to limited customer interest.

Even within the 747 family, for which engines from all three manufacturers were available, the RB211 was never certified on the 747-400ER and Pratt only got the PW4000 onto the options list some time after the model was first offered.

And of course there's the RB211 being the only choice on the L-1011, much as Lockheed may have wished they'd not walked that road...

Northwest Airlines was the launch customer for the the 747-400 and their aircraft only came with Pratt& Whitney engines or more to the point "power plants."}
Luthansa order there 7847-400s with General Electric engine as they did NOT like Pratt & Whitney power plants.
Pratt & Whitney Power Plants on the early 747 classics were very troublesome.

I don't know if Boeing and GE signed an exclusive on the 748 as they did on the heavy 777s, but either way, RR is probably happy they didn't try to join the party. Reportedly, BA was miffed that there was no RR option, and cited that as one reason not to buy.

trex8 wrote:

I suppose theres a chance you could put a Trent 7000 (Trent 700 with 1000 and XWB tech and with bleed air) on a 747.

Afaik the Trent 7000 is a Trent1000TEN with full bleed and less installed electric power. ( gearbox(es), generators.)
Same fan, same engine sfc ( beyond some microscopic differences for bleed use ) A different nacelle though. no chevrons.
That should improve "outer" sfc slightly.