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Bjorn Fehrm

@bjorn-fehrm · 8 positions · 0 changes of mind

Aeronautical engineer, former fighter pilot and airline executive, now an analyst at Leeham Company writing the weekly Bjorn's Corner on aircraft economics and design. He works from an aircraft performance model and has spent years checking the arithmetic of electric, hybrid and hydrogen aviation projects against it.

Bjorn Fehrm did not write this page.

We collected these quotes from things they published elsewhere, and every quote links to where it was said. They have no account here and have not endorsed this site. Quotes are word for word; the short line under each one is our own restatement, not their wording. Their own site. Is this you? Claim it or ask us to remove it. Or tell us what is wrong here.

  1. Our reading

    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.

    Their wordsAll 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.leehamnews.com 1st of 2 in this piece

    Interesting

  3. Our reading

    The multicopter air taxi is energy-intensive by construction, which holds its range to about twenty miles however good the batteries get.

    Their wordsThe 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.leehamnews.com 2nd of 2 in this piece

    energybatteries

    Interesting
  4. 5 months earlier

  5. Our reading

    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%.

    Their wordsthe 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.leehamnews.com 1st of 3 in this piece

    energy

    Interesting

  7. Our reading

    An airliner's empty weight is at least half its take-off weight, and no flying design has ever come in below 47%.

    Their wordsThe 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.leehamnews.com 2nd of 3 in this piece

    design

    Interesting

  9. Our reading

    Electric aircraft projects have collected airline orders for specifications that fail a weight calculation taught in the first hours of flight training.

    Their wordsThese projects have been around for years, yet no one has done this simple math.

    ↗Bjorn’s Corner: Sustainable Air Transport. Part 4. Reality checks.leehamnews.com 3rd of 3 in this piece

    Interesting
  10. 10 months earlier

  11. Our reading

    Battery-electric airliners do not work even on optimistic assumptions, and the arithmetic said so before anyone built one.

    Their wordsHaving 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 standleehamnews.com 1st of 3 in this piece

    batteries

    Interesting

  13. Our reading

    A hybrid-electric airliner ends up heavier and more complex than the aircraft it replaces and delivers no fuel saving at all.

    Their wordsNow 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 standleehamnews.com 2nd of 3 in this piece

    Interesting

  15. Our reading

    Sustainable aviation fuel cannot be scaled to the size of the fleet, because its feedstock competes with growing food.

    Their wordsThere 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 standleehamnews.com 3rd of 3 in this piece

    Interesting