Evaluating Next Generation Airliner Contenders: Part 1

Some urge Boeing to take the plunge “now” to launch a new airplane program. Institutional knowledge is slipping away, they say. Boeing hasn’t launched a new airplane since December 2003 (the 787). The 737 Max is selling at a poor second to the Airbus A320neo family. Boeing continues to lose market share. On the other hand, Airbus is in no hurry to launch a new airplane program—or so it says. It can’t keep up with current demand.

Against this backdrop, Leeham News and Analysis, which is now part of the AIN Media Group, has evaluated 13 next-generation airliner contenders. This is our take on prospects for these possibilities, starting with concepts 1-5 from the list below. Concepts 6-13 will be assessed in the Wednesday edition of AIN’s Dubai Airshow News.

1. Airbus A220-500
2. Boeing’s transonic truss-braced wing
3. Boom Overture supersonic transport aircraft
4. Blended wing bodies
5. Boeing's concept for a hybrid aircraft
6. Airbus ZeroE hydrogen-powered mainline jet
7. Boeing's New Midsize Airplane
8. Boeing’s New Light Twin
9. Comac C929 
10. Leeham’s light twin concept
11. CFM-powered Open Fan single-aisle airplane
12. Re-engined Boeing 787
13. Re-engined Airbus A350

1. Airbus A220-500

Don’t expect an A220-500 this decade. Proceeding with a stretched model 500 is largely dependent on Airbus turning this into a profitable program. Bombardier was losing money on its C Series before it sold the program to Airbus, which renamed it the A220. Airbus is still losing money on it. At one point, Bombardier estimated it would break even with 1,200 deliveries. So far, Airbus has sold 904 A220s and delivered 418.

Achieving a production rate of 14 airplanes per month is also key to achieving profitability. The Covid-19 pandemic, Pratt & Whitney's GTF engine problems, and supply chain issues combined to delay achieving this rate. Currently, Airbus produces an estimated six units per month and aims to hit 14 per month next year. This requires a major increase that seems unlikely. Any move to launch a stretched A220-500 before hitting this rate and turning a profit is off the table, according to people with direct knowledge of the program.

Bombardier had its conceptual CS500 design on the shelf when Airbus bought the program in 2017. Now unofficially called the A220-500, this is a stretched CS300/A220-300. The debate within Airbus is whether the -500 is a “simple stretch,” trading range for more passengers, or a stretch with a new wing and more powerful engines.

The sensible change is to retain the existing wing, increase engine thrust by approximately 5%, which is feasible, and modify the wing with larger winglets. This would reduce the range from an honest (airliner rules) 3,200 nm to 2,900 nm. This is still enough for east-to-west transcontinental U.S. flights, but not enough for a diagonal transcontinental flight from Miami to Seattle.

Airbus now appears to be leaning toward this simple stretch. Airlines with the A220-300 in their fleets that want the stretch model appear to be more interested in the added capacity than a model that retains the current range of more than 3,200 nm. Keeping this range requires more powerful engines and a new wing. Both are costly.

2. Boeing Transonic Truss-braced Wing

The transonic truss-braced wing (TTBW)—at least at Boeing—is already dead. Former Boeing CEO David Calhoun was enamored with the TTBW, which features a super-thin wing with a span so great that it requires supporting trusses to reduce induced drag (weight-related drag) on the aircraft. With advanced engines, Calhoun touted up to 30% better efficiency.

Calhoun's successor, Kelly Ortberg, killed further expenditures on this aircraft. Instead, Boeing will focus on a slender conventional wing that was at the heart of the TTBW’s design, this time without the complication of trusses.

The reason for the changes is that Boeing has to focus on getting the projects it's working on out the door. Boeing focused on completing the long-overdue certification of the 737 Max 7, 737 Max 10, and 777X this year.

The 737-7 and 777X seem on track. It’s unclear how far along the Max 10 certification requirements are and whether it will be certified this year.

That doesn’t mean Boeing’s Product Development (PD) department isn’t working on other ideas. Design of a new-build 787 freighter has paused and now appears to be a 2030 project rather than in 2028. But LNA understands that PD is studying other new aircraft. This is hardly earthshaking. Studies routinely take years to evolve.

Boeing studied the New Midsize Airplane (NMA) from 2012 to 2019, when the second Max fatal accident caused all work on this to be suspended. This was superseded by the TTBW program, which has now been killed.

Boeing recently issued a Request for Information for a 30,000-pound-thrust category engine for a new single-aisle airplane. But this doesn’t mean Boeing is planning for one; it just wants to update its understanding of the new technologies in this field.

The 737 Max remains unprofitable at the current production rate, and Boeing needs its cash flow, profits, and return on investment before proceeding with a replacement aircraft.

3. Boom Overture

Despite all the hype, the market LNA talks to remains highly skeptical of the aircraft and of Boom.

So far, U.S. law still prohibits supersonic flying over land. President Donald Trump, via an executive order, directed the FAA to rescind this restriction. But Congressional action is needed to do so, and there are contingencies in the executive order that also must be met. There are mission-related challenges, as well as airframe and engine-related ones.

The company was founded in 2014, and it still doesn’t have a demonstrator airplane that resembles the final design. CEO Blake Scholl now expects the first Overture flight in 2027 and service entry in 2030, both of which are unrealistic, as there are no engines for such prototypes or for serial-production aircraft.

While a supersonic airframe is a major development and production undertaking that does not support the optimistic timing predictions by Boom, the real problem lies with the engines.

GE Aerospace, Pratt & Whitney, and Rolls-Royce passed on developing an engine for Overture, and for good reasons. Supersonic engines are designed with a different technology tradeoff than the present high-bypass turbofans used in our jet airliners.

If you want to fly faster than the typical airliner—Mach 0.85—you need a lower-bypass-ratio engine. This is why the fast business jets that fly up to Mach 0.92 have bypass ratios that are half of the airliner engines.

If you want to fly really fast—Concorde speed, Mach 2.2—you need a bypass ratio of zero to be efficient. It’s why the Concorde engines were straight jets. Choose your speed in between, like Boom Overture’s Mach 1.7, and your bypass ratio should be in between. But a turbofan with a bypass ratio of around three is noisy. The engines covered by the 2027 ICAO noise and emissions regulations have bypass ratios exceeding 3.

Therefore, an engine for the Overture must be a clean-sheet, variable-bypass-ratio design with low noise at takeoff and landing that's efficient at Mach 1.7. Such engines are at the research stage for military fighter applications. The airliner engine manufacturers have done no work on such engines.

Boom cobbled together three companies to design and build its own engine of this type. The experienced engine makers GE and Safran announced a new technology engine, CFM Revolutionary Innovation for Sustainable Engines (RISE), in 2021, after a 14-year development. Boom says its engine work will be available for test flights in two years.

Billions of dollars are needed for the airframe and engine developments that Boom doesn’t have; hence, LNA doesn’t give Boom a chance of success.

4. Blended wing bodies

Several companies propose a blended-wing-body (BWB) airliner, a concept that has been around for decades. JetZero appears to be the leading contender to bring a BWB to market first. Another start-up, Natilus, also touts a BWB design.

JetAero appears much better funded than Natilus. However, even the former’s funding is now under threat. A key element was a $235 million contract from the U.S. Air Force for a concurrent BWB refueling tanker study. Funding was contingent on JetZero obtaining private funding, which would release federal money.

Natilus’ funding is unknown. What is known is that they, or any new entrant, need billions of dollars to design, produce, and bring to market a new airplane.

JetZero publicly acknowledged it needs $7 billion to $10 billion. The company says it can keep costs down by using “off the shelf” systems and components, modifying them for its 250- to 300-passenger Z4 aircraft. For example, it’s using a flight control system originally designed for Gulfstream’s corporate jets; landing gear from the out-of-production McDonnell Douglas MD-11 and Boeing 757; and the out-of-production Pratt & Whitney PW2040 engine. While this might be acceptable for a functional demonstrator, it will not be acceptable for a certifiable prototype or a serial production aircraft.

The engine may be especially problematic. In 2017, the global agency International Civil Aviation Organization (ICAO) adopted emission and noise standards that have been validated by governments across the globe. Anything that doesn’t meet these standards can’t be produced after 2027.

The PW2040 requires major upgrading to comply. Pratt & Whitney dodged a question by LNA about whether the 1970s technology engine can be upgraded to comply with emission standards. “We continue to be engaged with JetZero as the future of the technology and platform evolve,” a spokesman said.

So, LNA asked engine experts and an OEM at the Paris Air Show in June if the required upgrade is feasible.

Broadly speaking the responses could be characterized as follows: “In theory, yes, it can be done. In practice, it would be hard and costly. The limiting factors, which, if change were necessary, would push the costs sky high, are the dimensions, proportions, and features of the casings and discs. In other words, if you don’t change these, then you are limited in what you can do with the aero features of the compressors, combustion, and turbine in order to achieve your design goals,” was a representative response. It is not simply a case of putting 3D aero, new materials, latest technology combustor design, etc., into the existing envelope of the engine.”

The cost might be prohibitive. The true market potential is also a question.

JetZero wants to have a full-size demonstrator BWB flying in 2027 and entry into service of the Z4 in the early 2030s. LNA believes these dates are highly ambitious, given the lack of money, certification hurdles, technical challenges, and other issues.

5. The GE, NASA, and Boeing hybrid

The project began as a GE project to develop a hybrid electric powertrain. In 2021, NASA joined, and a year later, Aurora Flight Sciences, Boeing’s alternative propulsion subsidiary, was chosen to integrate the hybrid powerplant into a Saab 340 twin turboprop.

The GE project aimed to develop a megawatt-class electric hybrid system for use in airliners. The large electric motor was a major development, but it requires a range of equally challenging peripherals to function effectively.

When an electric motor in the megawatt class (1,340 shp) is used in an aircraft, you need to run the motor and its systems at the highest possible voltage to reduce the currents flowing around the system.

The practical upper limit, where arching and other issues can be avoided, is around 1,000 volts. If the hybrid system is designed to operate at 1,000 volts, the current flowing through the system at full electric-motor power remains 1,000 amps per side of the aircraft, which is very high.

The challenge is not only designing the motor for such voltages and currents, but also the surrounding electronics, including electric contactors, cabling, a solid-state motor inverter (which converts the battery power into alternating current for the motor), and the battery management system.

GE's long-term development of an airplane hybrid system received development support from NASA in 2021. Boeing joined the project when its Aurora Flight Sciences subsidiary was chosen as the system integrator for the GE-owned SAAB 340, Figure 2.

While a megawatt electrical motor with systems is high power in the electric motor world, it’s not high power in the airliner engine space. The Saab 340 GE CT7-9 engines develop 1.3 megawatts, and the Swedish aircraft is a 30-seater. By comparison, the 170-seat Airbus A320neo or Boeing 737 Max has two engines that develop 15 megawatts each.

In car hybrids, the electric motor drives the car up to a speed at which the thermal engine kicks in. It’s not the case for aircraft. You can taxi on the ground using the electric motor in a parallel hybrid, such as the GE one, but for takeoff and climb, the thermal engine needs to bear the brunt of the required power.

The problem for aircraft hybrids is not the hybrid system and its motor; it’s the energy source needed to feed the motor, the battery. If we use the megawatt motors of the Saab 340 for takeoff and climb in a typical mission, we will need a battery that lasts at least 20 minutes. Based on technology available this side of 2030, the battery systems would weigh around 3 tonnes, and potentially around 2.5 tonnes in the next decade.

The three tonnes of batteries and probably a further one tonne of motors, gearboxes, and electronics for the hybrid system indicate why the hybrids being considered today are mild hybrids, where the electric motor, its system, and battery load the aircraft with less additional weight. The mild hybrid will boost the plane's thermal engines rather than complement or replace them.

Aircraft engines have a generator on their auxiliary gearboxes, together with hydraulic and fuel pumps. It’s easy and convenient to turn this generator into a motor/generator and to use it for engine boost during takeoff. It will reduce the extra weight of the motor, especially the battery, which is the component that is the primary culprit in hybrid systems for aircraft.

The system components developed by GE shall be seen in this context, where these can be used in a mild hybrid in the next-generation engine, such as the CFM RISE.

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