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Blended Wing Body Airliners Require Different Engine Designs
The higher optimal cruise altitude of BWB aircraft means they need engines with less thrust lapse at high altitudes.
Apr. 17, 2026 at 7:20am
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Visualizing the unique aerodynamic and engine performance challenges of blended wing body aircraft designs.Stanford TodayIn the latest installment of his series on blended wing body (BWB) airliners, aviation analyst Bjorn Fehrm explains how the unique aerodynamics of BWB designs require a different approach to engine selection compared to traditional tube-and-wing aircraft. The higher optimal cruise altitude of BWB planes means they need engines with less thrust lapse at high altitudes, which is an area traditionally served by business jet engines rather than commercial airliner powerplants.
Why it matters
As aircraft manufacturers continue to explore more efficient BWB designs, understanding the unique engine requirements will be crucial to developing viable commercial airliners that can compete with traditional configurations. The tradeoffs between engine bypass ratio, thrust lapse, and optimal cruise altitude are key factors that will shape the future of large commercial aircraft design.
The details
Fehrm's analysis shows that the dominance of air friction drag over induced drag in BWB designs results in a 10,000 foot higher optimal cruise altitude compared to an equivalent-capacity tube-and-wing airliner. This higher altitude means BWB engines experience greater thrust lapse, which reduces the available thrust for climb and cruise. To minimize this issue, Fehrm says the BWB-focused JetZero company has chosen to use an older Pratt & Whitney PW2040 engine with a lower bypass ratio of 5.5, rather than the higher bypass ratio engines used in modern airliners. However, this comes at the cost of reduced fuel efficiency. If JetZero needs to upgrade to a more modern engine, the current industry trend towards even higher bypass ratios of 15 may not be suitable for their BWB design.
- Fehrm's analysis was published on April 17, 2026.
The players
Bjorn Fehrm
An aviation analyst who has written a series of articles examining the potential benefits and challenges of blended wing body airliner designs.
JetZero
An aircraft manufacturer that is developing a 250-seat blended wing body airliner called the Z4, which Fehrm has analyzed in his articles.
Pratt & Whitney
An aircraft engine manufacturer whose PW2040 engine, with a bypass ratio of 5.5, has been selected by JetZero for their BWB Z4 aircraft.
The takeaway
As aircraft designers continue to explore more fuel-efficient blended wing body configurations, understanding the unique engine requirements will be critical. The higher optimal cruise altitude of BWB planes means they need engines that can maintain thrust at altitudes above 40,000 feet, which is an area traditionally served by business jet engines rather than commercial airliners. Balancing engine bypass ratio, thrust lapse, and cruise performance will be a key challenge in bringing viable BWB airliners to market.
