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I asked similar question about angle of attack (both 737 max and AF447) - can't they just look at a glass of water to see they are at wrong angle. But with pla

I asked similar question about angle of attack (both 737 max and AF447) - can't they just look at a glass of water to see they are at wrong angle. But with planes it doesn't work that way - everything is relative to the air outside, not the ground. With good tailwind you still have to go with your cruising speed relative to the tailwind. Your ground speed will be insane. The opposite is with headwind.

rvnx 7y ago
Maybe a gyroscope + glass of water ?
- XMPPwocky 7y ago
  No. Angle of attack behaves in some very non-obvious ways- For example, if you maintain the same attitude, but decrease thrust so that your forward airspeed drops, and you begin descending... your angle of attack increases, despite the aircraft not actually rotating. Why? When you start descending, the air below now seems to be "coming up at you"- you go from ---> (=== to 7 (=== / / if that ASCII art helps at all (equals signs being the wing) Now consider how roll, yaw, and crosswinds affect this- as the AoA becomes variable across the wing...
- t0mas88 7y ago
  Doesn't work. The stall is about the angle at which the airflow meets the wing. The gyroscope (with or without glass of water) will tell you the attitude of the plane, but nothing about the direction from which the air meets the wing. You can stall in a nose down attitude if you're descending fast, the air comes from "below" and you try to pull out ift the dive thereby increasing the angle at which the air meets the wing. All the while your nose is still pointing below the horizon.
aaronmdjones 7y ago
As other comments have mentioned, a glass of water tells you nothing about the conditions outside the plane, which are the ones that matter. But also, it is sometimes useless at telling you about the conditions inside the plane too. If you're rolling and yawing at the same time (known as a coordinated turn), the water in the glass will stay level (relative to the bottom of the glass), and the glass will not slide along its surface, even in a 20 degree bank.
- FabHK 7y ago
  But if you’re in straight and level unaccelerated flight, and the wind outside has no vertical component, the glass of water would allow you to deduce your angle of attack (namely, the angle of the water plus the angle of incidence, if I’m not mistaken). Of course, that doesn’t help you at all during dynamic or unusual situations.
ants_a 7y ago
Here is a good illustration why looking at a glass of water will not work: https://www.youtube.com/watch?v=V9pvG_ZSnCc https://www.youtube.com/watch?v=V9pvG_ZSnCc

rvnx 7y ago

Maybe a gyroscope + glass of water ?

XMPPwocky 7y ago
No. Angle of attack behaves in some very non-obvious ways- For example, if you maintain the same attitude, but decrease thrust so that your forward airspeed drops, and you begin descending... your angle of attack increases, despite the aircraft not actually rotating. Why? When you start descending, the air below now seems to be "coming up at you"- you go from ---> (=== to 7 (=== / / if that ASCII art helps at all (equals signs being the wing) Now consider how roll, yaw, and crosswinds affect this- as the AoA becomes variable across the wing...
t0mas88 7y ago
Doesn't work. The stall is about the angle at which the airflow meets the wing. The gyroscope (with or without glass of water) will tell you the attitude of the plane, but nothing about the direction from which the air meets the wing. You can stall in a nose down attitude if you're descending fast, the air comes from "below" and you try to pull out ift the dive thereby increasing the angle at which the air meets the wing. All the while your nose is still pointing below the horizon.

aaronmdjones 7y ago

As other comments have mentioned, a glass of water tells you nothing about the conditions outside the plane, which are the ones that matter. But also, it is sometimes useless at telling you about the conditions inside the plane too. If you're rolling and yawing at the same time (known as a coordinated turn), the water in the glass will stay level (relative to the bottom of the glass), and the glass will not slide along its surface, even in a 20 degree bank.

FabHK 7y ago
But if you’re in straight and level unaccelerated flight, and the wind outside has no vertical component, the glass of water would allow you to deduce your angle of attack (namely, the angle of the water plus the angle of incidence, if I’m not mistaken). Of course, that doesn’t help you at all during dynamic or unusual situations.

ants_a 7y ago

Here is a good illustration why looking at a glass of water will not work: https://www.youtube.com/watch?v=V9pvG_ZSnCc https://www.youtube.com/watch?v=V9pvG_ZSnCc