Opinion: The 40,000-Lb. Question Facing Aircraft Development

There are two large unfilled requirements in civil and military aero markets today. Both of these notional new aircraft need an engine that does not yet exist. And the path forward for a new engine in this class is far from clear.

Opportunity One is a new midmarket jetliner. As I and others have been saying for over a decade, (AW&ST March 24, 2014, p. 14), airline fleet planning is increasingly favoring midsize, midrange fragmentation machines. This has resulted in a stream of orders for the Airbus A321neo, which is not perfect for this role but is the only choice in its class.

Boeing CEO David Calhoun’s November 2022 announcement that Boeing would not launch a new jet in this class turned this stream into a flood, with 1,300 orders in 2023 alone. As the chart below shows, the A321neo is now central to the airline industry’s future. Incredibly, 58% of all Airbus jets on backlog, and 34% of all Airbus and Boeing jets on backlog, are A321neos.

New management might well change Boeing’s self-destructive position on a new aircraft in this class. Alternatively, a new market entrant, such as Embraer or JetZero, might try to enter the segment. Airbus could act first, reinforcing its position with a reengined, rewinged A322. Either way, the A321neo would be vulnerable to disruption; even the XLR version does not have the midmarket capabilities the market really wants.

The second opportunity is a new U.S. strategic military airlifter. The C-5 fleet is aging, while C-17 flight hours have exceeded expectations. An emphasis on Pacific operations only will increase both the U.S. military airlift requirement and the strain in the legacy fleet. So, the U.S. Air Force is moving forward on a new C-X program (AW&ST Nov. 7-20, 2022, p. 16). The requirement to lift outsize equipment such as tanks or helicopters means it might look a lot like the previous airlifters.

Coincidentally, both market opportunities call for an engine in the exact same thrust class. Any good midmarket jet designed to beat the A321neo would likely be somewhat more capable than Boeing’s 757, which uses 40,000-lb.-thrust engines. Any new strategic lifter also would require similarly powerful engines, assuming it is a quadjet—the C-17 and C-5 were each built with four 40,000-43,000-lb.-thrust turbofans.

Yet no new engine in that size class is being planned. Not only is nothing in development; nothing is being built. Production ended years ago on both Pratt & Whitney’s PW2000 and Rolls-Royce’s RB211-535. CFM’s Leap 1 and Pratt’s PW1000 geared turbofan families are rated below 35,000 lb. thrust, with no plans to exceed that. A 25,000-lb.-thrust gap exists between those models and the next series of production engines, which start at around 60,000 lb. thrust.

There is clearly a strong case for at least one of the three engine OEMs to invest in a new 40,000-45,000-lb.-thrust engine. But that is where things get complicated. While the consensus is that there will be at least another generation of gas turbine powerplants, no firm agreement exists on its architecture. CFM is pressing ahead with its RISE program, focused on a geared propfan. Pratt and Rolls seem to prefer a ducted engine with a gearbox.

Test results from a RISE propfan will not be known for another few years at least, with GE-Safran aiming for 20% fuel-burn reduction over today’s engines. If Pratt were to launch a larger geared turbofan, or if Rolls were to launch an engine in this class using its UltraFan technology, they could be vulnerable if RISE were to achieve its stated goals.

Or a propfan could be vulnerable if ducted engines are close in performance and score stronger customer preference. In particular, it is not clear whether the military will accept a propfan, for whatever reason. In any event, engine OEMs will be loath to launch a new engine family without clear signals from the airframers. The age of “if we build it, they will come,” as when the original CFM56 engine was launched, are probably over.

There is a positive way to view this problem. Perhaps the impressive rewards presented by these two opportunities will motivate one or more engine OEMs to press ahead with architecture-agnostic technology developments scaled for something in the 40,000-lb.-thrust class—combustors, gearboxes, etc. There would be risk, but the rewards are enticing, too.