[pas]

How does this AoA sensor works? I'm guessing it has to sense the direction of the wind and then calculate the vector of the wings compared to that?

I've seen pictures of it ( https://aviation.stackexchange.com/questions/2317/how-does-a... ) and seems to be a simple mechanical component.

Why isn't this compounded with something that works by estimating the AoA from other factors? A few simple gravity based sensors would be able to tell the vector of the plane, and simply assuming that wind (airflow) is parallel to the ground would go a long way. Or is the vertical component of the local airflow so variable?

[inferiorhuman]

Why isn't this compounded with something that works by estimating the AoA from other factors?

Cost, probably. The 777 and 787 still only use two alpha vanes, but they calculate a synthetic angle-of-attack value as well.

[azernik]

When in flight, accelerometers only tell you what forces are being exerted by the wings and the engines, not which way is down. Consider, for example, the way the drinks in a cup don't spill when a plane turns.

[pas]

I know that an airplane can make a roll that keeps the fluid in the cup, but when usual commercial planes fly, they don't do stunts, so usually there's no centrifugal force to mimic gravity. When a big jet points its nose down or up people and fluids feel it pretty much as if they were on the ground on a slanted flat surface as one of its edge is being raised or lowered.

Sure, this would probably worth next to nothing in turbulence, but in a simple take off and landing (where MCAS is already active and depends on AoA) it might help.

And of course I might be completely ignorant of most of the relevant problems with using any kind of gyroscopic or acceleration based sensor.

[mannykannot]

I think general relativity rules out the possibility of making a gravity detector that can distinguish it from acceleration.

[tropo]

No, but cost probably does. There have been a number of satellites flown (GOCE, GRACE, SLATS) with the sort of equipment you'd need. With that equipment, simply measure the strength of gravity in multiple parts of the plane. This gets you altitude, just as GPS or air pressure would, and then you can determine the angle of the plane.

An edit as response to the followup mentioning Einstein, due to HN throttle:

Yes, yes... and it doesn't matter for this purpose, because you can measure gravity at multiple points within the aircraft and because gravity falls off with distance.

https://en.wikipedia.org/wiki/Inverse-square_law#Gravitation

We have built equipment sensitive enough to measure this difference and we have flown it in satellites.

[mannykannot]

"Einstein’s ground-breaking realization (which he called “the happiest thought of my life”) was that gravity is in reality not a force at all, but is indistinguishable from, and in fact the same thing as, acceleration, an idea he called the “principle of equivalence”.

https://www.physicsoftheuniverse.com/topics_relativity_gravi...