Earlier this week, Boeing released some of the confirmed design details for its re-engined 737 MAX narrow-body program. The new series of aircraft is expected to retain significant commonality with its predecessor, the Boeing 737NG program, however unlike Airbus' competing A320neo re-engine program, there are tangible changes being made between the 737NG and 737MAX due to the increased engine diameter and weight.
"The 737 MAX is on-track to deliver substantial fuel-savings to customers starting in 2017," said Beverly Wyse, vice president and general manager, 737 program. "We've made several design decisions that support the performance targets for the MAX and evolve the Next-Generation 737's design within the scope of the 737 MAX program."
The major design decisions and changes are as follow:
- Aft body aerodynamic improvements - The tail cone will be extended and the section above the elevator will be thickened to improve steadiness of air flow, thereby eliminating the need for vortex generators on the tail.
- Engine installation - The new CFM LEAP-1B engines will be integrated with the wing similar to the aerodynamic lines on the Boeing 787 Dreamliner, and on a more pronounced manner than the 737NG's aerodynamic lines. A new pylon and strut, as well as an 8 inch nose gear extension will allow the 737 MAX to maintain similar ground clearance to the 737NG despite the integration of the larger LEAP engine, which is planned to have a fan diameter of 68.4 inches versus the roughly 61 inch diameter of the CFM56 family of engines that power the 737NG.
- Flight control and system updates - The flight controls will include fly-by-wire spoilers (the Airbus A320 "classic" is primarily a fly-by-wire aircraft, while the 737NG eschews the use of such computers). "The MAX also will feature an electronic bleed air system, allowing for increased optimisation of the cabin pressurisation and ice protection systems."
- Additional changes include, "strengthening the main landing gear, wing and fuselage to accommodate the increase in loads due to the larger engines."
The rationale for the aerodynamic and flight control changes are that they are relatively simple, and reduce the 737MAX's drag, thereby decreasing the aircraft's block fuel burn.
Meanwhile the changes on engine installation and structural strength arise because the 737MAX needs a larger engine fan diameter to accrue the maximum reduction in specific fuel consumption (sfc) from the newest generation of engines.
Doubts remain on the 737 MAX, CFM LEAP Engine Despite this continuous progress on the part of the 737MAX, there remain several doubts about its position relative to its biggest competitor, the Airbus A320neo. From a pure numbers perspective, the A320neo has outsold the 737MAX by roughly 1.5 times (please note that we are counting Boeing's "commitments" for the 737MAX as sales because they will in all likelihood become sales) overall. But even more impressive has been its ability to win former 737NG customers. To date (by our count), Airbus has won over 3 customers for the A320neo that had previously only operated 737NGs, whereas in comparison, Boeing has made no such deals.
This interesting dichotomy has sparked speculation in the industry over the 737MAX's actual positioning relative to the A320neo. Conventional wisdom says that because the Airbus aircraft is able to take advantage of a much larger fan on the engine (up to 81 inches versus 68), its specific fuel consumption (sfc), and by extension (in this fuel environment) operating costs, will be tangibly lower than those of the 737MAX. In real terms however, there is a trade off between more effecient sfc and the additional weight of a larger and heavier engine, with the extra weight from the latter offsetting the gains of increasing fan diameter ( simple physics; a larger fan yields more propulsive efficiency). Thus there is a certain "sweet spot" in engine size, where the net effect on block fuel burn (ultimately the most important measure) turns negative; i.e a point above which, increasing fan diameter adds so much weight that the sfc improvement is more than offset. Where this sweet spot lies only time and years of service for these engines can tell, but at the moment, it appears that this puts Boeing at a competitive disadvantage.
Which is why my colleague over at Aspire Aviation
pointed out that:
While Boeing and CFM have spent months refining the configuration of the Leap-1B engine since the 737 MAX’s launch in August 2011, given Pratt & Whitney’s experience and work done on the similarly-sized PW1524G engine with a fan size of 73 inches powering the Bombardier CSeries, the world’s third-largest engine-maker could easily design a downscaled PW1524G with a 71 inches (180.3 cm) fan sizes indicated by Aspire Aviation‘s sources at Chicago-based airframer that fit the 737 MAX with minimal investment and programme risk. In addition, the downscaled PurePower engine could easily incorporate any lessons learned and improvements from the post-EIS (entry into service) flight hours amassed on the PW1524G under Bombardier CSeries’ wings that makes the downscaled PurePower engine on the 737 MAX more fuel efficient.
From a performance standpoint, a 71 inches downscaled PW1524G engine could feasibly provide a 15% reduction in engine specific fuel consumption (SFC), which lost around 1% SFC saving due to a smaller engine fan from 73 inches to 71 inches, not taking into account the reduced weight and drag that are compensated on the aircraft’s block fuel burn separately. In comparison, the CFM Leap-1B will contribute a 12% lower engine SFC towards the 737 MAX’s 11% lower fuel burn per seat than the 737-800.
The potential for a geared turbofan (GTF) on the 737MAX is very intriguing, especially when one considers that the GTF is projected to offer significant maintenance cost reductions versus the LEAP.
It has become clear in recent weeks, that the pure performance of the LEAP is not up to snuff vis a vis the PW-1000G even on the Airbus A320neo, where Pratt & Whitney's product holds a commanding 60-40 market share. Some
reports place that figure as high as 4% advantage to the GTF, but we feel that that is a little bit on the high side. Remember, existing operators of CFM powered A320s are likely to choose the LEAP-X on the A320neo for commonality purposes, but even the combination of commonality and favorable pricing cannot usually outweigh a 4% long term deficit in performance. But even if the performance is 2-2.5% worse (our best estimate for a "worst case scenario"), this is still a serious problem for Boeing, as the LEAP-1B used on its MAX will be less optimized than the LEAP-X for the A320neo.
On the other hand, part of the allure of a 737MAX would be commonality with the current generation of CFM engines, but if Boeing keeps offering the CFM option, then allowing P&W in on the MAX race is a relatively low-risk proposition, especially if it would equalize the fuel burn improvement on the MAX models with that of the Airbus' A320neo family.
Regardless, things are not all bad for Boeing's cash cow 737 program. Even as 737MAX development costs are likely to double those of the A320neo, Boeing will still maintain its heavy edge in profit margin. Plus, even in its current form, the 737MAX could win many more orders thanks to greater availability and heavy optimization of the base 737 MAX 8. For example, the consensus of our sources now indicate that the United Airlines order for 200+ narrowbody aircraft that will be announced next month is leaning towards Boeing over Airbus and the competing Bomabardier C-Series. Major players like Turkish Airlines, and many of the Chinese carriers have yet to place orders for the next generation of aircraft as well.
And at this point, there is no turning back for Boeing; the MAX will likely be the backbone of their narrowbody offering at least into the 2020s.
“Our intention is that we will build the MAX until the market doesn’t want to buy any more and we don’t know when that’s going to be. I wouldn’t predict 2025 or 2035, at some point, either something better will come along or the marketplace will decide they won’t continue to take it. We’ll make it until it runs out of gas and that could be a long, long time,” Boeing Commercial Airplanes (BCA) senior vice president (SVP) of marketing Mike Bair said.
