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This doesn't sound right: aren't unstable airframes controlled by computers the norm now? If that is the case, a software fix is the answer. If unstable airfra

This doesn't sound right: aren't unstable airframes controlled by computers the norm now? If that is the case, a software fix is the answer. If unstable airframes are not the norm, then the question we need to be asking is how the regulatory regime let an unstable airframe into service.

neuronic 8y ago
If you want to fly from Germany to the Canarian Islands for 50 EUR round trip then you're going to end up with unstable airframes. The 737 MAX is in part unstable due to repositioned engines. They are larger and thus significantly more fuel efficient, however they would not keep enough ground clearance if they were positioned the same way as on the 737-NG. MCAS corrects for the repositioning, otherwise the plane may start to climb which in turn could lead to a stall.
- jlangenauer 8y ago
  > If you want to fly from Germany to the Canarian Islands for 50 EUR round trip then you're going to end up with unstable airframes. How does B follow from A? That's quite the non-sequitur.
  - neuronic 8y ago
    B follows from A because in part A makes B economically possible. Reductions in fuel consumption factor greatly into ticket prices. It's easy to reduce services (luggage, refreshments, leg space) but reducing fuel consumption is entirely up to the aircraft manufacturers.
    - usrusr 8y ago
      But you don't need instability to get fuel economy, all you need is an airframe that actually matches the current engines instead of a relic from the 1960ies that was designed for tiny inefficient low-bypass engines. A plane designed for the new engines could be perfectly benign without sacrificing efficiency. Even a more properly adapted 737 that had the changes required to solve the problems aerodynamically instead could be fuel efficient.
      - neuronic 8y ago
        Oh that's true, except a new airframe leads to new everything, including certifications and training for pilots. Those do not come free.
      - inferiorhuman 8y ago
        Things that lead to instability can help, look at Boeing's MD-11. The horizontal stabilizer was made smaller than the DC-10 for fuel efficiency but resulted in a plane that was a handful to land safely.
- ricardobeat 8y ago
  Manager at Boeing? You might not realize it but that’s most likely the mindset that resulted in all this tragedy.
  - neuronic 8y ago
    No, just bad at expressing myself. I wasn't trying to defend Boeing's management and reasoning. In fact, I am very much against low costs flights like that and would rather see less planes in the air, as long as they burn fossil fuels.
- salawat 8y ago
  I can think of many ways that achieve the same goal. Yes, most require re-cert, as they should. Trying to make an old tool do things it wasn't meant to do (see: Internet w.r.t security, 737 MAX w.r.t. engine placement) has a compounding effect that very rarely works out as well as a clean slate design with the right compromises in mind. This is an example of a tragedy of the commons. Market forces found a solution to a problem (for one actor) that externalized long term costs for the sake of sealing a short-term deal, that in the end, was not guaranteed to stick around.
lm28469 8y ago
afaik unstable airframes are the norm for some military/experimental planes (fighter jets for example) to allow more manoeuvrability. It's definitely not something you want (or need) on a commercial airplane, it adds a ton of complexity and you're not going to do a high G turn or a cobra manoeuvre with a 737. https://www.boldmethod.com/learn-to-fly/aerodynamics/3-types-of-static-and-dynamic-stability-in-aircraft/ https://www.boldmethod.com/learn-to-fly/aerodynamics/3-types...

neuronic 8y ago

If you want to fly from Germany to the Canarian Islands for 50 EUR round trip then you're going to end up with unstable airframes. The 737 MAX is in part unstable due to repositioned engines. They are larger and thus significantly more fuel efficient, however they would not keep enough ground clearance if they were positioned the same way as on the 737-NG. MCAS corrects for the repositioning, otherwise the plane may start to climb which in turn could lead to a stall.

jlangenauer 8y ago
> If you want to fly from Germany to the Canarian Islands for 50 EUR round trip then you're going to end up with unstable airframes. How does B follow from A? That's quite the non-sequitur.
- neuronic 8y ago
  B follows from A because in part A makes B economically possible. Reductions in fuel consumption factor greatly into ticket prices. It's easy to reduce services (luggage, refreshments, leg space) but reducing fuel consumption is entirely up to the aircraft manufacturers.
  - usrusr 8y ago
    But you don't need instability to get fuel economy, all you need is an airframe that actually matches the current engines instead of a relic from the 1960ies that was designed for tiny inefficient low-bypass engines. A plane designed for the new engines could be perfectly benign without sacrificing efficiency. Even a more properly adapted 737 that had the changes required to solve the problems aerodynamically instead could be fuel efficient.
    - neuronic 8y ago
      Oh that's true, except a new airframe leads to new everything, including certifications and training for pilots. Those do not come free.
    - inferiorhuman 8y ago
      Things that lead to instability can help, look at Boeing's MD-11. The horizontal stabilizer was made smaller than the DC-10 for fuel efficiency but resulted in a plane that was a handful to land safely.
ricardobeat 8y ago
Manager at Boeing? You might not realize it but that’s most likely the mindset that resulted in all this tragedy.
- neuronic 8y ago
  No, just bad at expressing myself. I wasn't trying to defend Boeing's management and reasoning. In fact, I am very much against low costs flights like that and would rather see less planes in the air, as long as they burn fossil fuels.
salawat 8y ago
I can think of many ways that achieve the same goal. Yes, most require re-cert, as they should. Trying to make an old tool do things it wasn't meant to do (see: Internet w.r.t security, 737 MAX w.r.t. engine placement) has a compounding effect that very rarely works out as well as a clean slate design with the right compromises in mind. This is an example of a tragedy of the commons. Market forces found a solution to a problem (for one actor) that externalized long term costs for the sake of sealing a short-term deal, that in the end, was not guaranteed to stick around.

lm28469 8y ago

afaik unstable airframes are the norm for some military/experimental planes (fighter jets for example) to allow more manoeuvrability. It's definitely not something you want (or need) on a commercial airplane, it adds a ton of complexity and you're not going to do a high G turn or a cobra manoeuvre with a 737. https://www.boldmethod.com/learn-to-fly/aerodynamics/3-types-of-static-and-dynamic-stability-in-aircraft/ https://www.boldmethod.com/learn-to-fly/aerodynamics/3-types...