Boeing 737MAX

Boeing's first industry trial balloon, confirms airline and industry officials, contains two notional cross sections: a six-abreast single aisle and a seven-abreast twin-aisle with a container-sized lower cargo hold sized smaller than the 767.

"There's a wide open area in terms of what could be the cross section and that's clearly a big conversation we are having internally and also with the airlines," say Bair without going into specifics.

Additionally, an unducted fan engine, while providing significant fuel burn improvement, would require a 14 to 16ft diameter fan that makes it "hard to even conjure up a solution on what to do with blade out...and when you lose a blade all kinds of bad things happen and we have yet to figure out a solution for it. And quite frankly, can't conjure up a solution for it.

The risk of losing a blade, adds Bair, is low enough that its acceptable however "every time a blade comes off a propeller airplane the airplane is lost and we just won't do that. Having a single thread failure that can cause an airplane to be lost, we just won't do it. So we just don't see that as a solvable problem."

Bair concedes "These are going to be conventional looking engines and they're going to be conventional looking airplanes. Tube and wing has been around for a long time for lots of really good reasons. It's very very efficient way to fly stuff around, especially people."

"So the other thing that happened is since we picked the materials set on the '87', the aluminum folks did not go to sleep, so there are more choices now than when we made the decision on the '87', so we have to methodically go through that and what that might mean."

One consideration Bair considers "overblown" is the impact of ramp rash - or accidental impacts from ground handling - on a composite airframe. Compared to a long-range jetliner, a narrowbody aircraft in a high cycle environment spends more time exposed on the ramp in the course of a day, increasing the chance of potential damage.

"People's initial reaction to composites were based on their experience with things like flaps and composite movable edges which are honeycomb laminates and they're delicate. They can get damaged and they're difficult to repair, the built up laminates that we've done on the '87' are actually harder to damage than aluminum, and we have dropped stuff on these things more often than you can imagine. So they're harder to damage than aluminum...in some ways they're easier to repair than aluminum. "

Yet at the same time, Bair says, all the skin thicknesses on the 787 are sized to absorb an impact, either by hail or baggage carts: "Which means if that's how thick it has to be on a big airplane it needs to be that thick on a little airplane. So there's sort of diminishing returns in terms of efficiency."

Once the question of 'what the market wants' is answered and materials have been selected, Boeing must get under the skin and on to the wing of its new aircraft to define what technologies can meet the performance the market demands. Among those items on the table are an advanced bleed architecture pneumatic system, fly-by-light flight control system, adaptive wings and the latest developments from three major engine makers, only two of which will like be offered on the new jet.

The question when developing a new jetliner comes down to what levers does Boeing pull to deliver 10% improved cash operating costs and a 20% improvement in fuel burn over the 737 Next Generation. As a point of comparison, of the 20% improvement in fuel burn promised by the 787, ±8% comes from the engines, ±3% from the systems, ±3% from the structures and ±3% from aerodynamic efficiency.

From a pure cash perspective on short-to-medium haul missions, the cost of fuel tends to be only 25% of the costs verses 50% on a long-range mission, requiring Boeing to find other ways to reduce the overall non-fuel operating cost of the aircraft. However, that share is likely to climb as the price of oil steadily increases.

Mike Bair, vice president of Advanced 737 Product Development, says Boeing is working closely with CFM, Rolls-Royce and Pratt & Whitney to identify the airframer's engine options for a new jet.

"All three of them have given us what they think they can do for an engine that comes into service in [2019 or 2020], and it's better than what they could do for a [2015 or 2016 entry into service]," he says, an allusion to improved performance compare to the Bombardier CS300 and Airbus A320neo.

Bair also says it's Boeing preference to move away from the exclusivity agreements currently arranged with CFM International on the 737 Next Generation, providing a choice of two engines on the new aircraft.

"Our sort of fundamental assumption is that we would provide a choice," though Bair adds "If there's reasons you have an opportunity where a sole source makes sense, then you evaluate it."

Citing the experience early on in the development of the 737 Next Generation, "we were interested in having the [International Aero Engines] V2500 on the airplane. They were unwilling to do something about their fan," he says.

One industry official believes that one spot is likely reserved for the CFM Leap-X, the incumbent engine supplier on today's 737, with the second slot in competition between the Pratt & Whitney PW1000G geared turbofan and Rolls-Royce Advance2 and Advance3 engines.

Aside from fuel burn improvements, Bair says "we have opportunities on all fronts" to improve the maintenance cost of the aircraft by driving up reliability and asset utilization. In a general sense, the material choices that Boeing makes, as well as the aircraft configuration and cross section will guide maintainability and daily utilization.

How fast is too fast? How far is too far?

While much of Boeing's mission is to answer big question about the new aircraft, two characteristics hold more clarity than others, says Bair, who believes the speed and range of the new jet will be defined around the existing air traffic system and trans-continental route structures.

Bair says a cruise speed of .79 or .80 Mach - the same as today's 737 - will be used as a foundation, and big change may wreak havoc.

"You really honk up air traffic control if you throw an either vastly faster or vastly slower in those systems," he says.

As for legs of the new jet, Bair says: "Range is a little less of a mystery for us. [Trans-continental] is a pretty good capability for this size of airplane. I keep telling everyone that we say trans-con, and that sounds very US-centric, but almost every continent in the world is about the same size, so what works here, kinda works everywhere else, with the exception of Europe, which is smaller."

Based on Bair's assessment, trans-continental could place the range of the new jets anywhere from 2,700nm to 3,500nm, in line with and potentially slightly farther than today's 737s.

"If you go much beyond transcon and you put another 500 miles on the airplane, you just get wet," he says of the destination options outside of the trans-continental range circle. "So that doesn't do you any good. So more than transcon ends up being a lot more and a lot more tends to be really expensive, so the range looks pretty straight forward."

Does the 757 need replacing?

Weighing on Bair's mind is the product that sits just above today's 737, the now-out-of-production 757. The replacement of the narrowbody 757 falls squarely in Bair's mandate to identify the future of the sub-787 market.

Conceived in the midst of another fuel crisis, the 757 is able to accommodate 201 passengers in two classes and has expanded its range with the help of winglets and greater fuel capacity to 4,000nm, allowing long stage length operations from smaller markets connecting large hubs on both sides of the Atlantic.

"It's a complicated set of dynamics," he concedes, adding that the 1050 757-200s and -300 delivered between 1983 and 2004 qualifies the jet as a "niche product."

Though he acknowledges demand in the segment with both the 737-900ER and A321, though Bair asks: "Is the '57' attractive because it's bigger or is it attractive because it flies further? And If it flies further, how big is that demand? And is that economic penalty worth it? That one is less obvious to me. That penalty is a large number."

Under The Skin

Under the yet-to-be-determined skin of the aircraft, Boeing is beginning to evaluate new technologies for the potential systems architectures to significantly improve aircraft efficiency.

The first major leap, confirms industry and airline sources, is the potential offering of the first commercial implementation of a fly-by-light flight control system.

Though Bair acknowledges: "I don't know whether or not we're going to be ready to do something like that."

While the actuators at either end of the system are fundamentally unchanged, the system replaces copper signal wiring with fiber optic cable for increased data transmission.

"Everybody's enamored with using fiber optics because of high bandwidth," adding "some of the newer protocols for putting digital data on copper are getting better too, so it's obviously something that will be on the table and understand and try to figure out what the right trade is."

Gulfstream Aerospace flight tested fly-by-light controls during two flights in March and September 2008 with a G-V business aircraft, equipped with spoilers actuated with signals solely from fiber optic transmission.

The business jet maker says "The [cable] harness, which carries flight-control signals on optical fiber, performs an electrical-optical conversion at each avionics system endpoint, combining multiple signals onto a common optical backbone that spans the aircraft."

The system is intended to provide significant weight savings by replacing metallic wire bundles with - in the case of Gulfstream - just four fiber-optic wires.

Questions of scalability extended beyond the 787's material selection as Boeing works to determine if its more-electric architecture can be adapted to a smaller new aircraft. Industry officials confirm Boeing is examining an advanced pneumatic bleed air system. What exactly defines the system as advanced is yet unclear, though Bair sees challenges around scaling down the more-electric architecture.

"The whole more-electric architecture takes more room inside the airplane," says Bair, adding that it "takes less room around the pylon, but takes more inside the airplane."

The new jet, a physically smaller package, means less room inside the aircraft for items such as electric motor controllers, motor powered air condition packs. As a result, the electrical system will either be all-neumatic, all-electric or a combination of both.



Additionally, as part of the Continuous Lower Energy, Emissions and Noise (CLEEN) program Boeing and the Federal Aviation Administration will share a $25 million contract to test new environmentally friendly technologies designed to reduce aviation's environmental footprint, designed to be eventually employed on existing or all-new aircraft.

"There will be some stuff that we may see come out of that." says Bair. "I don't think it's going to be an earth shattering sort of revelation. There could be some interesting learnings that come off of that and the timing is about right on being able to incorporate them."

According to a public Boeing/FAA presentation, the airframer plans to flight test adaptive trailing edge (ATE) technology over two and a half months on its 737 'ecoDemonstrator' as early as August or September 2012.

ATE is meant to evaluate whether "tailoring wing performance" can "reduce noise and and fuel burn at different flight regimes."

The system, says Boeing, is meant to "utilize small devices on the airfoil trailing edges to alter sectional aerodynamic performance."

Different implementation, such as gurney flaps, a divergent trailing edge, mini plain flap (MPF) and mini split flap (MSF) designs are expected to be evaluated.

Additionally, Boeing will use a 777 or 787 to flight test a ceramic matrix composite exhaust nozzle as early as August/September 2013 as a way of further reducing engine noise and enabling hotter more efficient engines.