Leeham News and Analysis
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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.
Bjorn’s Corner: Faster aircraft development. Part 29. AI and the Program Plan.
By Bjorn Fehrm and Henry Tam.
February 27, 2026, ©. Leeham News: Last week, we looked at the development timeline for Part 25 airliner programs to reach Entry Into Service (EIS) after launch, Figure 1.
We can see that development times have doubled from the 1960s to the 1980s, compared with development since the year 2000.
The main change is the complexity of the aircraft, both in terms of highly optimized structures using new materials and avionics/flight control systems with many software code lines that require extensive verification.
We concluded that modern toolchains, with the capability to produce so-called Digital Twins, helped avoid further slip in development times, but they could not reduce them. The question then remains, can the employment of AI change this?
Figure 1. The development times for airliners over the years. Source: Leeham Co.
Bjorn’s Corner: Faster aircraft development. Part 28. Development times.
By Bjorn Fehrm and Henry Tam
February 20, 2026, ©. Leeham News: We have, since August 2025, gone through an FAA CFR 14 Part 25 development project of an airliner in the 200-seat class. The aim was to identify the activities required for such a project and the regulatory actions needed to achieve Type Certification (TC) and Production Certification (OC) for the aircraft.
The program followed the time plan in Figure 1, which indicated that it would take about seven years from the start of conceptual design to deliver the first aircraft and enter service (EIS). At each phase, we assessed whether modern support techniques, such as AI, could help with development and certification and whether they would accelerate the program plan.
Figure 1. A typical Program Plan for a smooth-running Part 25 airliner development. Source: Leeham Co.
We now summarize the findings and incorporate additional modern support, such as Digital Twin support, to assess the overall impact of today’s technologies on the program plan timeline in Figure 1. Read more
Bjorn’s Corner: Faster aircraft development. Part 27. Where Speed-Up gets Tough.
By Bjorn Fehrm and Henry Tam.
February 13, 2026, ©. Leeham News: We are summarizing how modern tools, processes, and AI can help reduce the time required to develop a clean-sheet 200-seat replacement for the Airbus A321neo and the Boeing 737 MAX 10.
We discussed some ideas in the last article on how current AI can support development. We could see it helping reduce the time spent on templating documents and on designing and verifying simple parts, such as mounting brackets for pipes and cables.
To address the more challenging parts where AI struggles to assist, we need to understand why development programs now take longer than in the past and what can be done to shorten the timeline.