[edoloughlin]

such airframes induce more drag and burn more fuel

As a curious bystander, I assumed using fly by wire tech to achieve stability would involve using control surfaces, which increase drag by their nature. How would an airframe that's naturally stable and doesn't require control inputs burn more fuel?

[AWildC182]

It's more about preventing a stall with a swept wing which is needed to achieve high mach numbers.

That said, an easy (but different) case to visualize is a traditional tailplane. The center of gravity on an airplane is in front of the wing so it wants to pitch down slowly. The tail pushes DOWN in the back to keep the nose up. Nose heavy planes are stable and forgiving but you induce drag because the wing needs to supply some lift just to counteract the tail which is producing negative lift. If you move the CG backward, you get less stability because the airplane wants to pitch up/down more violently with a control input but you have less negative lift from the tail.

[zaroth]

That’s a great explanation, even if it is oversimplifying.

We don’t build planes with training wheels anymore because the performance cost was too high. Planes are still the safest way to travel even without the training wheels.

I don’t think 737 MAX 8 pushes the envelope too far. I think they screwed up on re-training the disengage, and they may have screwed up on redundancy by only using a single AoA sensor, but I also am guessing the latest crash has absolutely nothing to do with trim.

[cmurf]

There are two alpha vanes on 737s, including the MAX 8, that measure angle of attack. Also we don't know the exact source of the error (in the Lion Air case; in the Egyptian Airlines case we don't know at all). The vane itself could be the source or some other part of the system.

[kakaorka]

I think you mean the Ethiopian airlines case, not Egyptian.

[cmurf]

Yep! Thanks for the correction.

[rocqua]

So the stable airframes we know are stable because a dynamic aerodynamic force opposes a static one.

Makes sense then, that those opposing aerodynamic forces induce drag.