Bjorn Fehrm
Aeronautical engineer and former fighter pilot; analyses aircraft design and airline economics at Leeham News.
Bjorn Fehrm did not write this page. What is this?
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Where they publish
Site Leeham News The aviation analysis site he writes for. Has a feed; the card shows only his own pieces.
His series work through an aircraft's design and economics from first principles — fuel burn, weight, range — rather than from the manufacturer's claims. Scott Hamilton and others write there too, and their items are dropped by the per-item byline filter.
Recent
- Bjorn’s Corner: Aircraft Structures Part 19. Liquid Composite Molding 18 Sept 2026 By Bjorn Fehrm • Aerospace Analyst September 18, 2026 Last week we looked at dry fiber layup methods that use a binder to tack fabrics or the tape in an AFP/ATL system to the previous ply, creating a...
- How To Measure the Range of an Airliner 17 Sept 2026 By Bjorn Fehrm • Aerospace Analyst September 17, 2026 Subscription Required Last week we looked at airliner capacity and size and found that measuring it by seats makes sense, since seats are the primary revenue driver…
Link verified 20 Sept 2026. Recent items update automatically from the channel.
Beliefs
Korrents What they believe 8 beliefs — each backed by an exact quote.
Each is a — compiled by korrents.com, not by them: the one-line wordings are korrents', the quotes are theirs.
Recent
Every aircraft propulsion system is an air pump, and accelerating a large mass of air a little is always more efficient than accelerating a little air a lot.
All propulsion systems are air pumps, and they work more efficiently if they accelerate a large mass of air to a small overspeed than vice versa.
Bjorn’s Corner: Sustainable Air Transport. Part 27. Multicopters. Said 8 Jul 2022
The multicopter air taxi is energy-intensive by construction, which holds its range to about twenty miles however good the batteries get.
The drone-like architecture of the multicopters is simple, but as the rotors are responsible for keeping the unit at a constant altitude with hover power, they represent an energy-intensive version of VTOLs. Their range is, therefore, short, typically less than 20 miles.
Bjorn’s Corner: Sustainable Air Transport. Part 27. Multicopters. Said 8 Jul 2022
Electrification transfers badly from cars to aircraft, because a car engine is under 10% efficient while a modern aero engine is already 30 to 40%.
the electric technology used for cars only has to beat energy hogs that are below 10% in efficiency, our everyday car. But to qualify for aircraft use, the technology has to equal or beat what is used today, which is at the 30% to 40% efficiency level using modern turboprop or turbofan engines.
Bjorn’s Corner: Sustainable Air Transport. Part 4. Reality checks. Said 28 Jan 2022
Show 5 more
An airliner's empty weight is at least half its take-off weight, and no flying design has ever come in below 47%.
The model output, which uses data from 74 presently flying airliner variants, from short-haul Commuters to long haul Widebodies, made with aluminum or composites, shows that the OEW fraction (OEW divided by MTOW) never go below 47%.
Bjorn’s Corner: Sustainable Air Transport. Part 4. Reality checks. Said 28 Jan 2022
Electric aircraft projects have collected airline orders for specifications that fail a weight calculation taught in the first hours of flight training.
These projects have been around for years, yet no one has done this simple math.
Bjorn’s Corner: Sustainable Air Transport. Part 4. Reality checks. Said 28 Jan 2022
Battery-electric airliners do not work even on optimistic assumptions, and the arithmetic said so before anyone built one.
Having done the sums before hitting the keys, I was a skeptic. It just didn’t work, even with optimistic assumptions around the parameters for the aircraft and its batteries.
Bjorn’s Corner: The challenges of hydrogen. Part 31. Wrap-up: Where we stand Said 2 Apr 2021
A hybrid-electric airliner ends up heavier and more complex than the aircraft it replaces and delivers no fuel saving at all.
Now you have a carbon fuel burning aircraft that is more complex and heavier than the plane that it replaces, and if you do your sums carefully, you find that there are no fuel efficiency gains and, therefore, no environmental gains.
Bjorn’s Corner: The challenges of hydrogen. Part 31. Wrap-up: Where we stand Said 2 Apr 2021
Sustainable aviation fuel cannot be scaled to the size of the fleet, because its feedstock competes with growing food.
There won’t be enough of it for the 25,000 planes flying each day, the feedstock will compete with food production.
Bjorn’s Corner: The challenges of hydrogen. Part 31. Wrap-up: Where we stand Said 2 Apr 2021
What is a korrent?
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