The U.S. Air Force is seeking turbofan engine concepts in the 35,000-50,000-lb.-thrust range to power a variety of commercial and military aircraft projects, including a new type of commercial airliner, a military variant of a blended wing body (BWB) airlifted or tanker, and a reengineering program for the Boeing C-17 fleet.
The U.S. Air Force late February proposal is part of a larger initiative to use government cash to seed investments in future commercial technologies, lowering the cost of subsequent military derivatives.
At the same time, the U.S. Air Force proposed engine investment, if carried out, can resuscitate a long-dormant section of the turbofan propulsion industry, filling a gap between the narrowbody and widebody classes. The requested thrust range would revitalize the “middle of the market” segment established by the out-of-production Boeing 757 and meet the demand for a developing niche of airliners between 220 and 270 passengers.
The U.S. Air Force Operational Energy Office advises that development expenses and initial manufacture be shared with an industrial partner. Still, it also allows for other forms of project finance. “Unique or unconventional methods of project financing are encouraged,” according to Airlift Efficiency’s “commercial solutions opening” on February 27.
The method could be similar to that used by the Operational Energy Office and JetZero Inc., a startup developing a 250-seat airplane with a BWB design. In 2023, the government planned to invest $235 million in JetZero over four years, with the goal of building and flying a full-scale demonstrator by 2027. The arrangement connects regular annual payments to JetZero’s ability to privately raise specific amounts of extra capital.
JetZero intends to power the demonstration with 43,000-pound-thrust Pratt & Whitney PW2040 engines, the commercial equivalent of the C-17’s F117 powerplants. Meanwhile, the new Airlift Efficiency project would provide a more extensive thrust range and a new or modified engine for JetZero’s next-generation commercial aircraft family.
However, the U.S. Air Force call for proposals has an urgent delivery timetable, which may limit the level of propulsion technology development. One of the Air Force’s high-level requirements is for an entrance into service date no later than 2030, with the caveat that responses might specify a projected delivery date if it falls outside that time frame. The Air Force solicitation also accepts solutions based on an existing commercial engine.
The U.S. Air Force predicts strong market demand once production begins. Responses should contain the proposer’s intention to supply at least 40 engines per month by 2035 and 80 engines per month by 2037, including spares. A monthly production output of this size would allow for 480 twin-engine aircraft deliveries per year in less than 12 years.
If the commercial market grows successfully, the Air Force aims to capitalize on the demand for the engine to update its aging fleet of large airlifters and tankers. The Air Force’s 221 C-17 transports are between 11 and 32 years old.
“As the C-17 will remain a mainstay of the Air Force’s strategic airlift capabilities for at least the next three decades, a re-engine or technology upgrade for the current F117 (PW2040) engines could provide value,” the Air Force’s announcement about the project states.
The Air Force’s participation in JetZero demonstrates that it is also open to updating its air mobility fleet with BWB technology. Such a layout must overcome several obstacles, including flight controls, passenger experience, and the effects of pressurizing a non-circular airframe. If such issues can be resolved, the benefits of combining the fuselage and high-aspect-ratio wing into a continuous aerodynamic shape might be enormous, including a potential 40-50% reduction in fuel consumption compared to current airliners.
It’s unclear how the Air Force will proceed with the project. A commercial solutions opportunity gives the Office of Operational Energy a quick path to executing an Other Transaction agreement, which is a type of contract. However, the Air Force’s funding levels for the program are not yet public.
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