Leeham News and Analysis
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Bjorn’s Corner: Blended Wing Body Airliners. Part 6
By Bjorn Fehrm
April 17, 2026, ©. Leeham News: We have started a series of articles on the Blended Wing Body (BWB) as a potentially more efficient design for passenger-carrying airliners than the classical Tube-And-Wing (TAW) configuration.
In the fifth article last week, we discussed how the drag characteristics of the BWB are different from a classical Tube-And-Wing airliner. The dominance of air-friction drag over induced drag results in a 10,000ft higher optimal cruise altitude compared with an equal-capacity TAW.
We compared JetZero’s Z4 project to a 250-seat variant of Boeing’s NMA that we have analyzed several times with our Aircraft Performance and Cost Model, APCM. Both aircraft use modern composite structures, aerodynamics, and systems, resulting in similar overall weights and drag.
Figure 1. The JetZero Z4 BWB. Source: JetZero.
The difference is how the drag is partitioned between the wetted area caused drag (air friction drag) and drag due to weight (induced drag). The difference between drag and optimal cruise altitudes has consequences for engine choice. Here is how.
Bjorn’s Corner: Blended Wing Body Airliners. Part 5
By Bjorn Fehrm
April 10, 2026, ©. Leeham News: We have started a series of articles on the Blended Wing Body (BWB) as a potentially more efficient design for passenger-carrying airliners than the classical Tube-And-Wing (TAW) configuration.
In last week’s article, we discussed how the wingspan is an important factor in an airliner’s takeoff performance. The induced drag is about 85-90% of the drag at the critical V2 point after rotation, where regulations require that a twin-engined airliner be able to fly on one engine with a climb rate of 2.4%.
We now go through the entire mission for a BWB airliner and compare its drag characteristics with those of a classical Tube-And-Wing (TAW) design.
Figure 1. The JetZero Z4 BWB. Source: JetZero.
Bjorn’s Corner: Blended Wing Body Airliners. Part 4
By Bjorn Fehrm
April 3, 2026, ©. Leeham News: We have started a series of articles on the Blended Wing Body (BWB) as a potentially more efficient design for passenger-carrying airliners than the classical Tube And Wing (TAW) configuration.
In the third article last week, we saw that the large wing surface area of a Blended Wing Body does not come from cruise-phase requirements; it comes from the lift needed in the landing phase, where BWBs lack flaps to increase wing lift. It needs a large wing area to compensate.
Now we will see that the wingspan is not sized by cruise requirements but by takeoff requirements.
Figure 1. The JetZero Z4 BWB. Source: JetZero.
Bjorn’s Corner: Blended Wing Body Airliners. Part 3.
By Bjorn Fehrm
March 27, 2026, ©. Leeham News: We have started a series of articles about the Blended WingBody (BWB) as a potentially more efficient passenger-carrying airliner design than the classical Tube And Wing (TAW) configuration.
In the second article last week, we saw that the aircraft skin surface area, which creates the dominant skin friction drag, was smaller than that of the same capacity Boeing 767 for the 250-seat JetZero Z4, but not for the 165-seat Ascent1000, compared with the Boeing 737 MAX 8.
Both the Z4 and the Ascent1000 had a larger wingspan than the 767 and 737-8, but this is comparing future concepts with older aircraft. The Ascent1000 has folding wingtips to fit in the 36m gate, which a TAW replacement for the MAX 8 would also have. The Z4 and the 767 must use widebody gates.
Figure 1. The JetZero Z4 BWB. Source: JetZero.
Why do the BWBs have such large wetted areas when they lack a fuselage and empennage? It’s because they lack a tailplane! Why does a lack of a tailplane force a larger BWB wing?
The state of alternative propulsion aircraft? Part 9.
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By Bjorn Fehrm
March 26, 2026, © Leeham News: In our series on the state of alternative propulsion projects, we are looking at different hydrogen-fueled propulsion systems.
Hydrogen can be processed chemically in a fuel cell to produce electrical power, which is then coupled to an electrical propulsion system, such as in hybrids or battery-electric aircraft. The advantage is that the system eliminates inefficient batteries that kill these systems.
Figure 1. The 100-seat fuel cell airliner is now Airbus’ ZEROe alternative. Source: Airbus.
The other alternative is to burn hydrogen in a gas turbine’s combustor. The advantage is that we keep the high power-to-mass ratio of a gas turbine, but with a heavier, more complicated fuel system, and use a lighter fuel than Jet Fuel/SAF.
We first dive deeper into the fuel cell-based variant.
The state of alternative propulsion aircraft? Part 8.
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By Bjorn Fehrm
March 19, 2026, © Leeham News: In our series on the state of alternative propulsion projects, we have analysed electric hybrid projects and found that these do not make for an operationally acceptable airliner. They are more expensive in production, thus in purchase, and their operational costs are not lower than the aircraft they shall replace.
Projects analyze hybrids after realizing that battery-electric airliners are too limited in range. But soon, the problem areas of hybrids become clear. The studies then swing to hydrogen propulsion systems.
Figure 1. The Airbus ZEROe hydrogen-fueled concepts for a future airliner. Source: Airbus.
These have new technical challenges but produce aircraft with operationally acceptable range. We now examine the various concepts for hydrogen-fueled propulsion and outline their challenges and capabilities.
Bjorn’s Corner: The Blended Wing Body, BWB, Airliner. Part 1.
By Bjorn Fehrm
March 13, 2026, ©. Leeham News: The flying wing has been researched for almost 100 years. During the Second World War, the Horten Brothers developed as flying wing military aircraft in Germany with mixed success. The Northrop company then flew several flying wing prototypes after the war, finding these to have severe stability issues at higher angles of attack.
With the advent of Fly-By-Wire, this could be mastered, and the flying wing’s inherent low radar cross-section is used in the B-2 and B-21 US Air Force bombers.
A flying wing is not suitable for use as an air transport passenger aircraft, as passengers would feel as if they were being transported in a coffin within the wing. An evolution of the flying wing is the Blended Wing Body (BWB, Figure 1), which moves the center section forward to form a blended fuselage that houses the payload.
Figure 1. The JetZero Z4 BWB in United’s colors. Source: JetZero.
As the search for lower fuel consumption and emissions intensified, the search for a more efficient way to transport passengers has led to increased interest in the BWB concept since the early 1990s, primarily from NASA and the US aircraft industry.
The proliferation of composite primary structures since 2000 has helped address the structural problems of a BWB. This has created a renewed interest in BWBs, both for military and commercial applications.
The state of alternative propulsion aircraft? Part 7.
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By Bjorn Fehrm
March 12, 2026, © Leeham News: In our series on the state of alternative propulsion projects, we are analysing where the electric hybrid projects are and how parallel hybrids work and perform.
Figure 1. The Pratt & Whitney Parallel Hybrid DH8-100 test aircraft, presently under preparation. Source: Pratt & Whitney
We summarized the status last week and compared it to the serial hybrids that we analyzed before Christmas. Serial hybrids are motivated in special cases, but in general, they make an aircraft more expensive to produce and operate.
For those who react, “But hybrid work very well for cars”?, let’s summarize: The car thermal engines are energy hogs, and you brake away all the acceleration energy at the next stoplight. Hybrids reduce this waste by recovering energy during braking. Aircraft and aircraft engines are wonders of efficiency by comparison, and there are no energy-recovery phases in an airliner mission.
We now use our Aircraft Performance and Cost Model (APCM) to go deeper into the parallel hybrid. Can it avoid the negative verdict of the serial hybrid?
Bjorn’s Corner: Faster aircraft development. Part 30. Wrap-up.
By Bjorn Fehrm and Henry Tam
March 6, 2026, ©. Leeham News: We started the series on developing a new airliner in the 14 CFR Part 25 class (i.e., not a commuter-class aircraft) on August 1st 2025. The objective was to write a series about such development with people I knew that has “been there, done that”?
Here is how the series started:
Four years ago, I did a series on aircraft development with Henry Tam and Andrew Telesca, both part of the canceled Mitsubishi SpaceJet program. The series was about the arduous task of developing and producing a certified aircraft for the FAA Part 23 standard and its EASA equivalent. The idea was to better describe what’s ahead for the many upstarts that wanted to develop green aircraft and VTOLs. Now we will do a series about recent ideas on how the long development times for large airliners can be shortened. New projects talks about cutting the development time by one-third. Is this realistic?
The state of alternative propulsion aircraft? Part 6.
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By Bjorn Fehrm
March 5, 2026, © Leeham News: Before Christmas, we started a series examining the status of alternative propulsion projects. We finished on December 18 by looking at Series Hybrids, often as battery-electric aircraft with range extenders (Figure 1).
The range extender is the natural next step when a project realizes that a pure battery-electric aircraft won’t be able to fly the missions the market is asking for.
Figure 1. The Heart Aerospace Battery-Rlectric ES-30 with dual range extending turbo-generators in the back. Source: Heart Aerospace.
After a while, analysing the range extender, the drawbacks become increasingly obvious. Charging the battery system in flight or directly feeding the electric propulsion system from a turbogenerator is inefficient. The losses along the path from the gas turbine through a generator, an inverter, and then to a motor that drives a propeller or fan are much higher than when the gas turbine drives the propeller directly.
A series hybrid can’t compete on operational economics with the aircraft it shall replace (for example, the Cessna Caravan or the SAAB 340). Projects then turn to parallel hybrids, the subject of today’s article.