Leeham News and Analysis
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Leeham News and Analysis
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- Strike slows Boeing’s march toward improving safety culture October 7, 2024
- Aerospace supply chain still ailing; Sustainable Aviation Fuel isn’t the answer to go green October 4, 2024
- Bjorn’s Corner: New engine development. Part 27. Long developments October 4, 2024
- Longshoreman strike adds to Airbus, Boeing woes October 1, 2024
Bjorn’s Corner: New engine development. Part 24. New versus old, GTF versus V2500
By Bjorn Fehrm
September 13, 2024, ©. Leeham News: We do an article series about engine development and why it has longer timelines than airframe development. It also carries larger risks of product maturity problems when it enters service than the airframe of an airliner.
We have covered the engine’s different parts and their technology challenges. We now look at some examples of recent developments with problems and put them in a historical perspective.
The V2500 and the Geared Turbofan, GTF
V2500
The V2500 was developed 40 years ago and entered service on the Airbus A320 in 1988 as an alternative to CFM’s CFM56. The V2500 was a Joint venture between Rolls-Royce (Fan, High compressor), Pratt & Whitney (Combustor, High turbine), Japan Aero Engine Corporation (Booster), and MTU (Low turbine).
The five partners (thus the V) created a company in 1983 called International Aero Engines, IAE, to manage the engine project and sell and support the engine.
The first version of the engine, V2500-A1, was certified and entered service on the A320 in 1988. The -A1 version was limited to 25,000lb of thrust; therefore, a version with increased massflow and thrust was developed, the V2500-A5, with up to 32,000lb thrust for the A321.
The V2500 had several issues in the early versions, including blade root problems in the high compressor, cracking in the high turbine parts, and high nozzle guide vane deterioration. It took the -A5 version and many years of service to mature the V2500 into a reliable engine.
GTF
IAE looked at making a geared version of the V2500 called the SuperFan, which was proposed in 1986 as the main engine for Airbus’ A340. Deeper studies showed the critical component, the Pratt & Whitney fan gearbox, did not have a TRL (development maturity) level where a possible failure could be detected at least a week in advance, which was deemed unacceptable to airlines.
Although the SuperFan was canceled, PW continued gearbox research and developed technology to detect possible failure months in advance. After 40 years of research, development, and tests, the Geared Turbofan (GTF) entered service on the A320neo in 2016.
The long development and testing of the fan gearbox in the GTF paid off. No failure has occurred due to a design problem (two gearboxes have failed due to a manufacturing fault). While the gearbox enjoyed a 40-year development and test period, the rest of the GTF engine did not. Pratt & Whitney had not developed a new commercial engine since the V2500 (if one disregards the failed PW6000 project), and the new GTF core was not tested enough when it entered service in January 2016 on the A320neo.
The list of in-service problems is long;
- Engine seal stability and wear. A new type of aero-cushion seal in the core had to be changed to a classical carbon seal.
- Rotor bow. As engines are shut down, heat accumulates at the top of the engine, bowing the engine’s main rotor. This causes the compressor blades to scrape the stators at the next engine start. The fix was ventilation revving of the engine during shutdown and restart, resulting in long engine start times.
- Combustor burn-through. The GTF combustor liners were eaten up, especially in polluted environments. The combustor is currently in the fourth revision, which shall fix the burn-through problems.
- Knife edge seal problems, which was fixed with a new seal design.
Pratt & Whitney has also been affected by a serious manufacturing defect. The powder metal used to fabricate the discs in Pratt & Whitney engines has been contaminated, resulting in a fatigue fracture risk for the disc. The recall and change of engine discs before the fatigue risk can manifest has caused major disruption for GTF users.
This is not a design issue, and it is not attributable to the GTF engine. But it shows the high stakes involved in engine development and manufacture. The tiniest quality lapse in the very complex manufacture of an engine’s high-tech parts has major availability and economic consequences for airline customers and the engine OEM.
Conclusion
The V2500 development followed a classical timeline: launch in 1983, certification and use by 1988, and a five-year development timeline. This resulted in an engine that needed almost a decade to mature into a highly reliable and durable part of an airliner.
The GTF has had four decades of gearbox development with several test engine projects. This part of the engine has been solid, but the rest has not. The GTF launched in 2008, with the first customer, the PW1200G for the Mitsubishi Regional Jet. The PW1100g for the A32oneo was launched in 2010, with the first flight in 2012 and entry into service in 2016.
A six-year development period for a new engine is too short. It doesn’t give room for a maturity flight test program, which is needed for today’s advanced engines, which are delivered at high production ramp rates to demanding airline customers. Any issue in the engine affects many in-operation airliners, and the taking off wing of engines to change a failed part gets disruptive and expensive.
We will write more about the need for an engine maturity testing phase in a later Corner and give examples of how this has successfully changed the reliability and durability of a new engine. Planning with maturity testing of engines before they enter service will prolong the engine development program by up to 30%, making engine development programs take more time than airframe programs.
Another issue on GTF: sand deposit into HPT blades leading a blade life reduced by half . No solution given for the time being as far as i know, CFM already provided improvement with a new blade and IPS.
Rotor bow was an issue on the V2500 too. It shouldn’t have been such a problem on engines that came afterwards.
One of the advantages of a triple spool design is that you can (must) put a bearing between the IP and HP compressors, a twin spool has to have a bearing at the front of the HP compressor. This allows a slightly narrower and lighter, yet stiffer, shafts. This leads to lots of benefits, tighter blade clearances, a narrower core, slower degradation.
There are other drawbacks however. Weight, lubrication and air sealing.
Think you forgot Fiat Avio as one of the 5 initial partners, hence the V in V2500. There was a side mounted version of the A5, the D5 used by the MD-90.
Often it is the housings thermal deformation after shut down and its bearing position shifting causing the rotor induced vibrations called rotor bow. The rotor does not bend. The RR designed shroudless fan on the V2500 and 2 stage HPT giving it a small performance edge and its popularity on the A321ceo. Had Sully flown a V2500 A320 the IFSD would probably never happened thanks to its RR fan blades and CFMI never seen the need for new engines that they did and started the A320neo family with new engines with wide chord fan blades.
Historical footnote…there is also an E5 in production today as the powerplant for the C390
Every drawing that I’ve seen says Japanese Aero Engine Corp had responsibility for the fan.
It’s then a misunderstanding. The fan uses the Rolls-Royce hollow titanium technology and their wide-chord areo and mechanical design. It’s a strong part of the V25000 technology. JAEC did not have this technology.
Yes. JAEC does the low pressure compressor stage but not the adjacent front fan.
Even after RR exited IAE it continued to make parts such as the fan and HPC as a subcontractor in RR Germany, Fiat Avio had the same arrangement when it left the consortium a bit earlier.
The original base engine as the RJ500 was between RR and JAEC
Very interesting article and discussion. Gives a lot of insight into the development of propulsion.
Agreed. Its the in depth tech stuff I am most interested in.
Trying to get relevant information in a cohesive form is difficult to impossible from general reading, Bjorn presents it right up front.
Wasn’t this supposed to be on the then 7j7 too?
@williams
IAE (and the V2500 by extension) was the market entree for single aisle for RR and PW for anything above 22K thrust (I think). That’s why the PW6000 came out indefinitely of the V2500 (only on the A318).
When it came time to bid on the MRJ, both PW and RR bid independently. PW won. It was around this time that PW and RR did not come to terms on continuing IAE in its existing form. They each went their separate ways and RR lost out on the neo. IAE still exists but it is now a PW led entity.
Thank you.
I read the then Boeing 727 replacement, the 7j7 was being engineered to accept the GTF engine or Superfan along with propfan. Boeing was hedging its bets on engines.
Would have been interesting to see what effect the SuperFan would have had on A340 sales
@Williams
The A340 could have done better if it was dual powerplant installation with a higher thrust requirement. The original version especially was underpowered. There was a running joke that only way the A340 could take off was due to the curvature of the earth.
Thats a misunderstanding of how much airliner takeoff power is needed.
A twin needs to continue take-off even if one engine fails- so massively overpowered.
Same rule with a quad means one engine fail is that 3 can continue take-off.
Its the twins that are inefficient in this area as each engine is too big for a normal use, but in reality the actual thrust setting on a twin take-off is much lower than maximum for maintenance reasons. The name of the game is fuel consumption and maintenance not ‘fast takeoffs’
The A340 did come in a twin engine version , just that its was called the A330. After the A340 stopped being sold the A330 max weight grew considerably to allow the long haul flights – often over water- that the earlier A340 could do.
@Duke
I guess my only response is that the early versions of the A340 were powered by CFM56 with 31-34k of thrust and the replacement Trent were 55-62k of thrust. The original versions were sufficiently powered; the subsequent versions more than made up that perception of power deficiency net of the increased MTOW.
A more accurate statement would be to say to say the power to weight ratio was not impressive. Climb time to altitude and cruising speed lagged though the engines were efficient.
Dual powerplant. A beefed-up A330.
I remember the A340 quad is better ads in ATW, and AW by Airbus. They rode that horse hard until it died.
MRJ was the launch customer for Pratt & its partners for a GTF back in 2008, but it had been under development for some time as it was revealed at Paris 2007
https://aviationweek.com/mitsubishi-pratt-whitney-launch-mrj-geared-turbofan-0
The RR exit from IAE came in 2011, unrelated to the GTF , they were concentrating on big fan engines and their development costs and well before had not joined the GTF consortium MTU, JAE, Fiat Avio
Mitsubishi Aero engines is small partner both with Pratt GFT and RR large aero engines. So the linkup up with P&W on the GTF was inevitable
@Duke
I don’t think we are disagreeing. In reality the process of next gen engines was a in work for a few years from 2007-2011. The companies had different ideas of go-to-market architecture with RR going with a conventional design. By mid 2011 they were out of the running. They ultimately exited IAE later that year as there would have been a clunky transition from a V2500 to a PW1100 sales strategy otherwise. Both sides announced that they would partner in the future on a new engine, but that quickly died off. Yes RR focused on big engines, but only after they were eliminated on the neo.
RR was only a part of V2500, so it could have continued that work . The engine still needed a front fan and other modules. Avio did the gear box to P&W specifications as a sub contractor
RR needed the $1.5 bill from its partners buyout.
The sales strategy hasnt changed as IAE is still the marketing company behind the PW1100, remember its still built with risk sharing partners as before , but MTU has a bigger involvement including a final assembly line in Germany.
The RR twin spool traditional series continues with tech upgrades as the Pearl line but only for business jets . I couldnt find any reference to similar offered to MRJ.
I do not believe it is correct that the PW1000 is Marketed by IAE.
How the IAE consortium splits out I have not looked at in any depth, just that RR dropped out and PW continued.
RR did not need the 1.5 billion, that was prior to the various debacles on its Trent engines.
It was an odd move as RR had no presence in SA anymore and no plans for that.
Continuing to work in the IAE would have been a good presence and I believe PW would have been happy to risk sharing partners on the GTF.
Now they do have all the same partners sans RR, but PW runs the program its not a combined board of some kind. The other members may be risk sharing partners as well keeping their respective areas as they had on the V2500.
Bjorn has confirmed what I had thought, it was a pretty good engine and over time achieved good returns though like the CFM-56, people forget there were dips in how it all played out.
Its a shame the C390 is not 4 engine bird, it would be nice to have more volume production of that engine.
Certainly an interesting choice over CFM as GE had the engines on the E1 series. Possibly the V2500 has some characteristics that make it better for that application?
Still when the E2 came out they went with the GTF. Possibly as PW had a size range that extended across the E2 to the MAX/NEO that CFM was no offering.
@TW
The PW1100 is technically sold through amodified version of IAE. It is marketed as a PW product, but the consortium that sold the V2500 is the more or less the same less RR. They all have ownership stakes in the engine. The PW1500 is done differently yet. All of this is a nit perhaps. All engine programs have risk partners of some flavor or another. It is too expensive and risky to ever see an investment 100% by one OEM.
As for the C390, you were never going wrong with either the V2500 or CFM56. Whether one engine had a longer TOW advantage or not was mildly interesting. The utilization on the C390 is a fraction of the commercial installation.
As for the E2, the GTF dislpaced the CF34. GE/CFM has no modern engine in that thrust category, and they were never going to develop one just for the E2…not enough volume. They still do have a trickle of sales on the E175-E1, which was to be replaced with its own E2 as a GTF (the stillborn 17K version). Embraer is still on the clock to make a final E175 decision in 2025 I believe.
The sub-25K commercial market exists in the same graveyard that a 40-55K thrust sits in…no real market or only enough to justify one OEM.
As the tech matures, reliability will improve. But we should not be surprised if airlines evaluate the next-gen “green” tech critically.
Airlines will take greenwashing and older reliable tech any day.
Regarding the V2500, it reminds me of an old saying: “an elephant is a mouse designed by a committee”. With the GTF, apparently that elephant is STILL in the room…
I understand that RR REALLY wanted to stay in NB, but couldn’t make the numbers work on the neo. The reason for this was that they believed (because Boeing told them) that Boeing would offer an all new NB to compete against the neo (at the time, the MAX was barely a plan C, let alone a plan B) – as a result, the neo would be a 5 year plane, before it was obsolesced, and no engine OEM can make money on a 5 year production run. This all changed in 2012, when a courtesy call from American Airlines to Boeing informed them of AA’s imminent order for 500 neos. Suddenly Boeing ditched the all new NB and hurriedly brought in the MAX (and AA bought ~250 each of the MAX and the neo). At that moment, the neo went from being a 5 year plane to a 20 year plane, but it was too late for RR as they had already exited.