Engine pylons?
 

Hi,



I just read where an airline that’s having issues with the PW powered Neo A320s are getting rid of them. They’re new airplanes that are heading to the scrap yard because they’re worth more as parts. It’s not the first time I’ve heard this story.



Now I understand that there are some system differences between PW, GE and RR, but what in the design of the pylon is leading to such incompatibility between different engines for the same plane?



What’s the reason the pylon (and whatever few downstream engine-specific components) aren’t designed so that you can switch engine manufacturers?

It's more than just the pylons; my understanding is that there's a lot of software, wiring, and other systems differences throughout the aircraft. You already said that...

The 787 was supposed to be built so that you could swap engine manufacturers easily (I think there were even jokes about different engines on each wing?), but that basically went out the window when Boeing started having integration problems and the program was delayed.

There are a surprising number of engine-specific portions of the engine/aircraft interface - and modern FADEC engines are deeply integrated into the aircraft systems. Stuff that is very expensive to change if you want to swap to a different engine type.
As Someone Somewhere notes, making the 787 engines 'plug and play' was an initial design objective, the deeper they got into it, the more difficult it became, and eventually the whole idea was quietly dropped. I once asked one of my friends on the 787 program what exactly the problems were that were so difficult to solve - he didn't really answer except to say there were 'a lot'.
When Boeing introduced the CF6-80C2 engine on the 767, the FADEC version wasn't ready, so deliveries were started with the "PMC" (supervisory electronic control vs. full authority electronic control with FADEC). A couple operators wanted the ability to upgrade to FADEC once it was available, so we tried to design in 'provision' to allow future conversion to the FADEC version. In spite of those 'provisions' - it turned out the costs to convert a PMC 767 into a FADEC 767 was going to be well north of a million dollars per aircraft (and that didn't include a similar number for converting the engines). As a result, I'm reasonably sure no PMC powered 767 was ever converted to FADEC - it just wasn't cost effective. And remember, that was the same engine type, just a different engine control system.

Years ago, when aircraft were basically analog and engine control was via cables and hydromechanical controls, re-engining with new, lower fuel burn and/or quieter engines made sense. DC-8, KC-135, and 727s were all successfully re-engined.
But I'm unaware of any successful program to do that sort of re-engine with highly integrated FADEC engines.

No first hand knowledge, but I was told by people 'who should know' that Pratt lost their shirt when they had Douglas install JT9D engines on the DC-10 (originally designed for GE CF6). Northwest refused to buy the DC-10 with GE engines (at the time, the CEO of Northwest allegedly said 'I wouldn't by a light bulb from GE) and was able convince Douglas and Pratt that installing JT9D engines would be a good investment. It wasn't - it cost a rather large fortune, didn't work very well, and I believe Northwest ended up being the only customer.

Didn't Eastern swap it's PW engines for RR on their 757 fleet?
I remember reading this a long time ago but can't remember the specifics.

Eastern had RR engines from day one on their 757s, they did modify them to a higher thrust, more efficient version with a different, extended cowling a few years later as did BA, the other launch customer

Thanks for the insight guys!

ISTR that BA had the same powerplant on the 747-436 and the 767-236. RB211-524

The RB211-524 engine was indeed common between the 767 and the 747-400 installation - in general the only change needed was to 'rerate' the engine (simple replacement of the rating plug on the fuel control, not so simple paperwork trail).
But that was not uncommon. Both the CF6-80C2 FADEC and the PW4000/94" were common between the 767 and 747-400 - again with the proviso that you needed to change the rating plugs.

When you have a common engine, it's easy to make the engine/aircraft interface common between two airframes.
However it's a much different story when you have a common airframe and want to fit dissimilar engines.

BTW silton - that's my recollection as well. Both the initial Eastern and BA 757s had the RB211-535C engines - Rolls later introduced the RB211-535E4 engine in response to the Pratt PW2000. The 535E4 incorporated wide-cord blades and had a big fuel burn improvement relative to the 535C engine. Again, keeping the engine/aircraft interface consistent was relatively easy given it was a design requirement for the 535E4 engine and the interface differences between the 535C and E4 variants was minor.

BA kept the original 535C engines on their 757s that were delivered with them. G-BIK* and G-BMR* series aircraft.

BA’s later G-BPE* and G-CPE* aircraft delivered from 1989 had the E4 engines. But BA never converted an aircraft, and continued to take delivery of the C engines long after the E4 was available.

Eastern converted all their C powered 757s. As did Monarch. The only airlines to do so as I recall. Air Europe never changed engines on their few early C powered 757s.

Very interesting, thanks for that

The shorter cowling on the C engine was very different and quite noticeable compared to the E4s more elongated design

I flew the later variant and was extremely impressed, an incredibly smooth and extremely powerful engine I never had the slightest problem with in eleven years operating the -200 and -300 series 757

So 10 posts in, and we've yet to see an example of an in-service airliner being re-engined with one from another manufacturer. That should tell us something. :O

Yes, there have been re-engining programmes in the past, but mostly military where other considerations apply (or don't).

The DC-8 and 727 both had it happen at some scale.

Different scenario, but the first B777-200 (WA001) was re-engined before it was delivered to Cathay Pacific. The aircraft originally had PW4000 engines and was re-engined with the RR Trent 800 and new pylons to match the other B777-200s in Cathay's fleet.