Boeing continues to optimise 737 MAX
During the first-quarter, Chicago-based airframer Boeing continues to rack up orders and commitments for its re-engined 737 MAX aircraft, garnering 301 firm orders, including 100 737 MAX 8s from Oslo-based low-cost carrier (LCC) Norwegian Air Shuttle (NAS) and 201 737 MAX 9s from Indonesia-based LCC Lion Air in the three months ending 31st March. Its transatlantic arch-rival Airbus, in contrast, received 143 firm orders for the re-engined A320neo (new engine option) aircraft, including 35 from Kuwaiti aircraft lessor ALAFCO, 45 from US ultra low-cost carrier Spirit Airlines, 33 from Avianca-Taca and 30 from Mexican low-cost carrier (LCC) Volaris, in addition to the Norwegian’s memorandum of understanding (MOU) for 100 A320neos.
Meanwhile, the world’s second-largest aircraft manufacturer is edging closer to the conclusion of the final phase of wind-tunnel testing on the re-engined 737 MAX, where QinetiQ in Farnborough, United Kingdom, will assess the re-engined narrowbody aircraft’s low-speed performance along with the company’s facility in Seattle to evaluate the aircraft’s high-speed performance, laying the foundation for the aircraft’s mid-2013 firm configuration milestone.
“Wind tunnel testing is on the critical design path of the programme. Based on previous work in the wind tunnel, we are confident this final phase of testing will substantiate our predictions of the aerodynamic performance of the airplane,” Boeing Commercial Airplanes (BCA) 737 MAX chief project engineer and deputy programme manager Michael Teal said.
“This final phase of wind tunnel testing confirms that we are on track to complete our design goals and deliver the 737 MAX to customers beginning in 2017,” Teal said.
One of the primary objectives behind the final phase of the wind-tunnel testing is to “update the model to incorporate the minor changes we’re making for the MAX and the larger engine nacelles. These initial test runs will give our engineers a baseline of the current airplane’s performance that they can compare with the MAX’s optimised design,” Boeing Commercial Airplanes (BCA) vice president (VP) of marketing Randy Tinseth said.
And as the next-generation narrowbody engines featuring advanced engine core technologies form the centrepiece of the upgrade from the existing single-aisle airplanes, which delivers the bulk of the 737 MAX and A320neo’s fuel-burn savings, the economics of engines, or “enginomics”, are likely to continue to be the prime focus of these aircraft programmes as they developments advance and progress.
During the quarter, Boeing and General Electric (GE) settled on a 68.4 inches (173.7 centimetres) engine fan size for the 737 MAX, from the previous fan sizes of 68 inches (172.7 cm) and the widely reported 68.75 inches (174.6 cm).
“It’s nailed down. We’ve finished all the installation studies, and for all practical purposes, it’s done. It’s going to be a very unique installation for the 737 MAX. We’re going to take full advantage of the integration we do with Boeing and with Spirit to make sure the overall engine-airplane combination is incredibly efficient from an integrated propulsion system and the engine is really optimised for this airplane.” General Electric (GE) Aviation chief executive David Joyce told Bloomberg.
As the final phase of the wind-tunnel testing is still ongoing at press time and the firm configuration is still a year away, Aspire Aviation‘s sources at the Chicago-based aircraft manufacturer cautioned that the eventual engine fan size will remain fluid before settling on the most optimised one.
Indeed, Boeing acknowledged to Aviation Week that future changes in engine fan size are possible and Aviation Week quoted 737 MAX programme official as saying that the company is studying a fan size as large as 69 inches (175 cm).
“However, as detailed design work continues and we incorporate wind-tunnel testing results, we’ll continue to work with CFM to refine the engine [including fan size] as we work towards final configuration in 2013,” the company was quoted as saying.
Engine fan size matters since each inch increase in the fan size generally leads to a 0.5% reduction in engine specific fuel consumption (SFC), notwithstanding the penalty on the aircraft’s overall block fuel burn due to increased drag and added weight. However, it is a delicate balance between engine fan size, drag and weight that is often a complicated trade-off, as a large engine fan size also inevitably leads to an increase in drag and weight, and Boeing said the “sweet spot” is around 68 inches.
For the 737 MAX, not only does the engine fan size affect the re-engined aircraft’s overall fuel burn performance, it also has an implication on the modifications required to accommodate the bigger and heavier engine.
For instance, the squash-bottomed 68.4-inch CFM Leap-1B engine that sits in a much forward position than the existing CFM56-7BE engine on the next-generation 737 will shift the centre of gravity (CG) of the re-engined aircraft forward, of which one possible solution is to adopt the 787-styled trailing edge variable camber (TEVC) that redistributes engineering load inward and also moves the centre of lift forward, thus alleviating the situation of a forward centre of gravity (CG). Though the adoption of a TEVC will nonetheless carry a drag penalty that negates the benefits of a weight saving and a forward centre of lift, thus making such an adoption complicated.
Instead, the primary focus is reducing the weight of the engine. In doing so, not only could the block fuel burn penalty brought by a heavier engine be reduced, it could also minimise the extent to which the structural reinforcements need to take place, thus achieving a cumulative effect in reducing the overall weight, fuel burn of the 737 MAX.
Given the fact that the CFM Leap-1B engine will incorporate a resin transfer moulding (RTM) composite blades and fan case, as well as the ceramic matrix composite (CMC) that will contribute 1% of saving in engine specific fuel consumption (SFC) but which may not mature in time for application for the 737 MAX’s late-2017 entry into service (EIS), achieving further significant weight saving on the already efficient CFM Leap-1B engine is difficult, albeit not impossible.
According to Boeing, the 68.4 inches CFM Leap-1B engine will contribute 12% of the block fuel burn reduction and another 1% from aft-body aerodynamic improvement, which is negated by a 2% fuel burn penalty due to increased drag and weight, thus achieving an overall 11% block fuel burn reduction per seat than the 737-800 on a typical 500 nautical miles (nm) in a 2-class 162-seat configuration. In comparison, Boeing says the 150-seat A320neo will only be 12% more fuel efficient per seat than the existing A320 on a 500 nm sector, with 13.5% and 3% reduction in block fuel burn contributed by a larger, more fuel-efficient engine and the adoption of blended winglets, respectively, which is offset by 3.5% and 1% fuel burn penalty owing to increased weight and the removal of wingtip fence, respectively.
Airbus refutes these claims, saying the 150-seat A320neo (new engine option) will be 7% more fuel efficient per seat than a 157-seat 737 MAX 8 on a 800 nautical miles (nm) mission, whereas Boeing says a 162-seat 737 MAX 8 is 5% more fuel efficient per seat than a 150-seat A320neo, in addition a 7% all-in operating cost advantage (“Boeing 737 MAX sees a bright year ahead“, 20th Dec, 11).
Another less likely, yet a feasible but more controversial solution, is to feature the Pratt & Whitney (P&W) PurePower geared turbofan (GTF) engine on the 737 MAX, an industry talk that was rampant at the International Society of Transport Aircraft Trading (ISTAT) conference in March.
In doing so, not only are the structural reinforcement and modification required on the 737 MAX minimised, it will also further boost the market appeal of the 737 MAX to airlines around the world.
First and foremost, adding an engine option of the Pratt & Whitney (P&W) PurePower engine provides a hedge to Boeing for these engines with decidedly and fundamentally different architectures. The Pratt & Whitney (P&W) PurePower geared turbofan (GTF) relies on a gearbox that allows the engine fan to run at a speed 3 times lower than the speed the low pressure turbine (LPT) spins and consists of 7 moving parts and no life-limited parts (LLPs).
As a result, this maximises the engine’s propulsive efficiency while eliminating 20%, or 7 stages of life-limited parts (LLPs) in the engine, leading to a 20% lower maintenance cost than the CFM56-5B engine.
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.
This will increase the 11% fuel burn reduction per seat of the 737 MAX by an additional 2% with little extra modifications already required to accommodate the CFM Leap-1B engine, similar to the situation on the A320neo (new engine option), where the 81 inches PW1100G-JM engine will provide a 16% lower specific fuel consumption (SFC) than the CFM56-5B engine, while the 78 inches CFM Leap-1A engine provides a 15% lower SFC, albeit both of them are being rated equal by Airbus.
Furthermore, airlines will view the option of two engines favourably, primarily because of the lower price tag resulted from a fierce engine competition. What is more, some airlines have hedged their engine strategies by splitting the orders between the A320neo (new engine option) and 737 MAX which are also due to the inability of airframers delivering such a large quantity of fuel-efficient single-aisle jets within a short timeframe, such as American Airlines (AA), Norwegian Air Shuttle (NAS), etc, offering an option of 2 engines will further improve the standing and widen the lead of the 737 MAX.
“There’s not a team on the MAX considering otherwise,” Boeing spokeswoman Lauren Penning emphasised to the Puget Sound Business Journal.
Despite Boeing continues to downplay the addition of an extra engine option on the 737 MAX, it ultimately comes down to a cost and benefit analysis, with the improved standing in the marketplace from airlines’ and lessors’ perspectives against a fiercer engine competition between CFM and Pratt & Whitney (P&W), of which Boeing has a traditionally good relationship with CFM International’s parent General Electric (GE).
But given these engines’ vastly different architectures and upgrade paths, of which the CFM Leap engine is advancing materials technology and thermal efficiency while the Pratt & Whitney (P&W) will utilise on an increase in the gear ratio possibly to 5-to-1 from 3-to-1, running the engine core hotter should ceramic matrix composite (CMC) mature over time and become cheaper to make the PurePower engine more fuel efficient (“Special Report: The engine battle heats up“, 10th May, 11), hedging between them with a choice of two engine options seems wise.
After all, the CFM Leap-1B still holds the advantageous position of the installed base even after the addition of a Pratt & Whitney (P&W) PurePower engine option, given the large number of CFM engines on today’s industry workhorse 737 fleet, and if adding an engine option improves the 737 MAX’s market share and boosts its competitiveness, why not?
Air Lease Corporation (ALC) chief executive Steven Udvar-Hazy concurred, but said “I don’t think Boeing’s going to do it”.
“I’ve had long talks with [Boeing Commercial Airplanes (BCA) chief executive Jim Albaugh] and guys over there, where I showed them the dual engine has helped Airbus gain market share with the A320neo family, because they had two choices and airlines were able to leverage that to get better deals. I just don’t think Boeing is able to do that. I think they’re kind of stuck in this situation because of the airframe,” Udvar-Hazy was quoted as saying.
Improved payload/range performance
Regardless of how the engine issue evolves on the Boeing 737 MAX, the 737 MAX family aircraft nevertheless hold an advantage over the A320neo (new engine option) on an all-in operating cost basis, albeit at a reduced level, and the CFM Leap-1B engine will be a highly-efficient engine, which Aspire Aviation‘s sources say have made progress in clawing back the rumoured 2%-3% shortfall in engine specific fuel consumption (SFC).
“Compared to Airbus A320neo, which is the European firm’s latest single-aisle plane, the 737 MAX is 10% lighter and 5% more fuel efficient. Its maintenance costs 7% less. The 737 MAX will have the lowest operating costs in the single-aisle segment with a 7% advantage per seat over our future competition, the A320neo,” Boeing vice president (VP) of marketing Randy Tinseth said.
Moreover, the 737 MAX will have a slightly better payload/range performance than the A320neo (new engine option), if not equal.
“We’re going to make some minor structural enhancements to the 737 MAX, so we can have a slightly higher maximum take-off weights so we can slightly increase the range of the airplane as well,” Tinseth said on the Pacific Northwest Aerospace Alliance (PNAA) conference in early February.
According to Aspire Aviation‘s multiple sources at Boeing, the 737 MAX 8 and MAX 9 will see a 3,175 kilogrammes (7,000 lbs) increase in maximum take-off weight (MTOW) from the winglet-equipped 737-800’s 79 tonnes (174,200 lbs) to MAX 8’s 82.2 tonnes (181,200 lbs) and from winglet-equipped 737-900ER’s 85.1 tonnes (187,700 lbs) to MAX 9’s 88.3 tonnes (194,700 lbs). The smaller MAX 7 sibling will see a 2,268 kg (5,000 lbs) increase in its MTOW from winglet-equipped 737-700’s 69.4 tonnes (153,000 lbs) to 71.7 tonnes (158,000 lbs).
In comparison, Airbus said the maximum take-off weight (MTOW) of the A320neo (new engine option) will increase by 1 tonne (2,205 lbs) to 79 tonnes (174,165 lbs) from A320 weight variant WV015’s 78 tonnes (171,961 lbs), the A320 weight variant featuring the highest MTOW.
In terms of range, the range of the 737 MAX 8 will be 6,426 km (3,470 nm), an increase of 405 nm with 162 passengers. The MAX 7 and MAX 9’s ranges will be 3,800 nm with 126 passengers and 3,430 nm with 180 passengers, respectively.
The existing CFM56-5B-powered A320 has a range of roughly 3,000 nm with 150 passengers at a payload of around 13,800 kg and Airbus has said the new engine option will either add 950 km (510 nm) to range, or 2 tonnes (4,400 lbs) in additional payload. The CFM56-5B-powered A319 has a range of roughly 3,200 nm with 124 passengers at a payload of around 11,000 kg. The CFM56-5B-powered A321 has a range of roughly 3,000 nm with 185 passengers at a payload of around 17,000 kg, according to payload/range graphics on Airbus’ aircraft characteristics documents.
On an apple-to-apple basis with the same payload on both 737 MAX 8 and A320neo at 13,800 kg and all increase in payload is used to boost range, the 737 MAX 8 will have the 737-800’s range at a payload of 13,800 kg of approximately 3,240 nautical miles (nm), plus the addition of 405 nm due to the re-engining. Simply put, the 737 MAX 8 will have a range of approximately 3,645 nm, more than the A320neo’s approximately 3,510 nm.
Similarly using the aforementioned Airbus document and Boeing’s chart, the A321neo will have a range of approximately 3,510 nm whereas the 737 MAX 9 will have a range of 3,430 nm. The A319neo will have a range of approximately 3,710 nm versus the 737 MAX 7’s range of 3,800 nm.
Therefore, the 737 MAX 7 and MAX 8 are slightly better in range than the A319neo and A320neo, respectively, whereas the 737 MAX 9 will be slightly inferior to the A321neo in range.
In addition, Boeing is actively evaluating more weight-reduction and drag reduction initiatives in order to make the 737 MAX more aerodynamically and more fuel efficient, and it looks increasingly likely that this year’s continuous lower energy emissions noise (CLEEN) programme, scheduled to take place this late third-quarter on board an American Airlines (AA) Boeing 737-800 in collaboration with the US Federal Aviation Administration (FAA), will be a springboard for testing these initiatives, especially the drag reduction ones.
For example, Aviation Week reported the 737 MAX will feature an improved trailing edge from the CLEEN programme, incorporating the “mini-split flap” technology, a re-rigged outboard flap and drooped aileron, whereas Aspire Aviation‘s sources at the Chicago-based airframer say the test results of the variable area fan nozzle (VAFN) will also be watched closely on whether it delivers the promised 2% fuel burn saving.
The variable area fan nozzles (VAFN) system relies on a FADEC (Full Authority Digital Engine Control) to protect the fan against fluttering in the open position and could possibly cut 2% of fuel burn. The VAFN could also reduce noise in the intermediate position during climb.
The 737 MAX will also feature a reshaped pressure-relief port cavity, a 787-styled tail cone that incorporates a relofted design with the elimination of vortex generators, and a new design of the inlet door of the 737 MAX’s auxiliary power unit (APU) that features a “retractable intake door” found on other Boeing airplanes instead of the existing NACA APU inlet door design on the next-generation 737.
Re-engined airplanes not a long-term solution?
The founder and chief executive of Air Lease Corporation (ALC), Steven Udvar Hazy, the godfather of the aircraft-leasing industry, suggested the notion that the 737 MAX is “not a long-term solution” and while the 737 has “been a great bus for the industry, but at some point Boeing’s going to have to deal with it. Right now, I think the focus has been getting the [787-10X] launched and firming the competitive response to the A350 with its 777X”.
Hazy also commented that the 737 MAX still holds “a distinct advantage” against the A320neo (new engine option) despite a 10,000 lbs weight growth in the 737 MAX’s weight.
First of all, Aspire Aviation‘s multiple sources at Boeing confirmed that the 10,000 lbs weight growth figure is “inaccurate” and “way off mark”, and that the increase in the 737 MAX’s manufacturers’ empty weight (MEW) is currently between 2.0 tonnes (4,500 lbs) and 2.5 tonnes (5,500 lbs), whereas the MEW of the A320neo (new engine option) has increased by 1.7 tonnes (3,748 lbs) on the CFM Leap-1A-powered A320neo and 1.8 tonnes (3,968 lbs) on the PW1100G-JM-powered version.
Despite the weight growth, the 737 MAX variants nonetheless hold the weight advantage in being lighter than the A320neo (new engine option) variants. The 737-900ER with winglet has an operating empty weight (OEW) of 44.7 tonnes (98,495 lbs) whereas the CFM-powered version and International Aero Engines (IAE) V2500-powered version of the A321 have an OEW of 46.9 tonnes (103,300 lbs) and 47 tonnes (103,527 lbs), respectively.
Meanwhile, the business case of re-engined aircraft such as the Boeing 737 MAX, A320neo (new engine option) and the re-engined E-Jet remains sound, as airlines’ demand for fuel efficient aircraft ever grows in light of skyrocketing jet kerosene prices.
Most importantly, the game-changing small twin-aisle that airlines and lessors are looking for, simply will not be available until 2025 or so. The key enabler of such a game-changing small twin-aisle aircraft that features containerised cargo system, fast turnaround times and significant reductions in cash operating costs (COC), the 2nd or 3rd-generation composites with out-of-autoclave (OoA) technology, such as Australia’s Quickstep that trims the curing time by a dramatic 43%, a higher delamination resistance and a higher fibre-matrix adhesion achieved through “lower initial resin viscosity”, is emerging and will require time to mature and find its way into wider aerospace applications, as are nanotechnologies such as the carbon nanotubes reinforced polymer (CNRP) on the Lockheed Martin F-35 Lightning II Joint Strike Fighter (JSF) that promise to be 17% stronger and yet 30% lighter than the carbon fibre reinforced polymer (CFRP) found on 50% of the 787 Dreamliner by weight.
And as Boeing invests its financial and engineering resources into the double-stretched 787-10X and the potentially game-changing 777X late this year (“Boeing develops 777X to challenge Airbus A350“, 9th Feb, 12), an incremental upgrade of the single-aisle product, the 737 MAX, is the proper strategy going forward before the 3rd-generation composite technologies mature and enable the launch of a game-changing small twin-aisle aircraft that replaces the 757 and complements the existing 737 MAX aircraft family, not necessarily “killing” the 737 MAX or its Airbus counterparts altogether.
“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.
As for this decade, Boeing’s priorities will be making the 737 MAX as best as possible, launch the 777X and 787-10X, while ramping up production by 40% across its product lines within the next few years, that would pretty much make Boeing’s plates full.
In particular, Boeing simply cannot afford to repeat its past mistake of a unsatisfactory programme execution on the 737 MAX, along with the 777X and 787-10X, and especially so when Boeing officials have indicated they want to advance the 737 MAX’s entry into service (EIS) date.
“There’s a decent chance they can actually beat that target,” 737 MAX launch customer Southwest Airlines chief executive Gary Kelly told the Dow Jones Newswires.
Last but not least, the sales prospect of the 737 MAX remains bullish and Boeing expects to receive 200 737 MAX orders from China this year to satisfy the world’s second-largest aviation market’s burgeoning air travel demand, and the strong underlying demand for re-engined aircraft, combined with a strong backlog, should insulate or minimise any risks should this upward industry cycle be halted by any unforeseen events in this volatile global economy. Though one thing is sure against this backdrop of a volatile global economy and this especially cyclical aerospace sector: the contentious debate on each airplane’s merits will continue unabated, both in good times and the bad.
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