Medium size quad with GTF engines?

[divinehover]

Would there be any viability in building a medium quad (A340-300 size) with GTF engines? Could these engines with up to 35000lbs thrust offer an advantage over a twin with bigger 'old style' fans?

[twistedenginestarter]

The direction is more building a medium twin with GTF engines. That's what Rolls Royce is aiming at with Ultrafan.

[riff_raff]

If you're going to do a clean sheet design to replace the A340-300 the economics greatly favor a twin engine configuration. That's what Airbus chose for the A340-300 replacement - the A350-800.

If you are only considering retrofit of the existing CFM56-5C3 engine with a geared fan engine of similar thrust that is already under development, such as the PW1133G, as a minimum it would require new nacelles/pylons. And would likely require taller landing gear, since the fan of the PW1133G is about 20 inches larger in diameter than the CFM56-5C3 fan.

In reality, the cost to re-engine the A340-300 would not likely be viable given the relatively small number of this aircraft model in service. However, the much greater bypass ratio (12.5:1 vs 5.5:1) and overall pressure ratio (50:1 vs 33:1) of the new PW1133G vs the legacy CFM56-5C3 would definitely result in significantly lower fuel consumption.

Interesting question from a technical perspective, but ultimately the decision is driven mostly by economic factors.

[megan]

What might have been the driver for the Japanese going with 4 versus the Boeing P-8 with two? The Japanese developed the engine specifically for the aircraft.

[riff_raff]

Military versus commercial. The P-8 is a derivative of the commercial 737. The P-1 is a military aircraft. Like most countries, the Japanese government readily subsidizes domestic companies like IHI for aerospace/defense related projects like dedicated engines for the P-1.

Consider the Honda business jet project. Honda and IHI tried to develop their own clean-sheet engine design. But eventually partnered with GE for the production and certification work.

[Frequent Traveller]

When developped, the "TA11" to be dubbed later A340 was presented to prospects with full engine commonality with A320 Series ... when built, the powerplants differed, but the sales pitch caught the attention of Asset Traders. An A340 NEO revival (GTF or Leap) is what you raise here ... ? The question boils down in essence to six counts :


1. quadri range vs ETOPS330 twin range
2. quadri take-off performance vs twin take-off performance
3. dry engine weight of NEO x 4 vs ditto of eg Trent XWB x 2
4. engine-induced drag of NEO x 4 vs ditto of eg Trent XWB x 2
5. fuel consumption of NEO x 4 vs ditto of eg Trent XWB x 2
6. engine maintenance & spares costs of NEO x 4 vs ditto of eg Trent XWB x 2


So to answer your question in some detail is not done in a snap of fingers ...

[plhought]

There's already a 'medium-ish' airplane with Quad GTFs - it's called a 146 😉

[riff_raff]

That's an interesting point about the AVCO-Lycoming geared fan engines used on the BAe 146. Besides the use of four engines when most other comparable commercial jet aircraft used only two, the BAe 146 also had a high wing. However, the 146 was designed for specific applications that favored using four engines and a high wing. Later there was a proposal to develop a twin engine derivative of the aircraft, but it was not built.

The most ubiquitous geared turbofan engine is probably the Garrett TFE731. There were some Dassault Falcon 20 jets that had their GE CF700 turbofan engines replaced with TFE731 geared fan engines. So there is some precedent for this type of engine retrofit. There was also the Lockheed JetStar that used four TFE731 geared fan engines.