5 ms·

but wouldn't the wind exert some pressure on the back of the bird? wouldn't it not generate any lift otherwise and just drop back to the ground? like sails on

but wouldn't the wind exert some pressure on the back of the bird? wouldn't it not generate any lift otherwise and just drop back to the ground? like sails on a sailboat, for the sailors it feels like there is no wind, but the sails are carrying massive pressure

dTal 3y ago
>for the sailors it feels like there is no wind, but the sails are carrying massive pressure The only way this is possible is if the sails are moving at a different airspeed than the sailors, which is only possible if 1) the sailor is running up and down the deck or 2) there is an windspeed gradient with altitude, which the sails penetrate by virtue of being tall.
mongol 3y ago
The comparison with the balloon is perhaps not entirely accurate since birds like you say, fly using lift from the wings. So they need to have some relative speed vs the air.
- lxgr 3y ago
  The point is that as long as the entire body of air the bird is flying through is moving uniformly and without acceleration, it's perceptually indistinguishable from calm air (except visually, and even that only when flying pretty low). For rotating and turbulent air, which would both not be totally unheard of in a hurricane, this probably doesn't apply though.
  - quickthrower2 3y ago
    This is probably like when you swim out at the beach, and back and find you are 20m away from where you started due to currents. But you didn’t feel it. With dead reckoning you could probably figure out.
    - lxgr 3y ago
      You can’t feel linear/unaccelerated motion, and biological organisms aren’t great at indirectly deriving it from acceleration and rotation over time the way inertial navigation systems do.
      - stouset 3y ago
        Hell, even those have a hard time doing it without experiencing drift! So they periodically re-establish a baseline using something like GPS.
- atq2119 3y ago
  It doesn't really matter in this case, but hummingbirds would like to have a word with you.
HPsquared 3y ago
A sailboat uses the speed difference between the water (basically stationary) and the wind. A bird (or sailplane) just moves along with the wind. Birds and sailplanes can however hang around areas of rising air to overcome their natural sink rate.
_moof 3y ago
When you're flying, wind is no longer the air moving over the ground, it's the ground moving under the air. It doesn't produce acceleration except for a brief moment when you leave the ground.
stouset 3y ago
If you’re in a boat in a river, your “natural” speed is the speed of the river. Same with air. You point about a sailboat and wind is confused; the pressure comes from the fact that the boat is traveling at one speed through the water and at a different speed through the air.
- natoliniak 3y ago
  ok, if the bird's natural speed is that of the ambient air, then how does it stay up? the bird is not lighter than air, so where does the upwards pressure on the bird come from? either the bird must flap its wings to stay up or there must be speed difference between the bird and the ambient air to generate lift.
  - tw04 3y ago
    If the bird’s natural speed is 7mph, and the tail wind is 7mph, the bird is still flying at 7mph airspeed, its ground speed just increases to 14mph. No different than a jet flying with or against the jet stream. https://science.howstuffworks.com/transport/flight/modern/airspeed-vs-groundspeed.htm https://science.howstuffworks.com/transport/flight/modern/ai...
    - natoliniak 3y ago
      that is my point - in order to stay up, the bird would need to either flap its wings for 700 miles non-stop (unlikely) in order to maintain velocity difference between it and the ambient air OR glide which basically means he was not traveling at the speed of ambient air, otherwise there would be no lift pressure generated on his wings and he would drop to the ground
      - hansvm 3y ago
        Ignore the storm for a moment, and ask whether a bird can fly for 7h+, either from flapping, gliding, or navigating updrafts. The answer is yes, that's trivial for many many bird species, especially those with a propensity for ocean travel. The storm then just changes the baseline ground speed.
cratermoon 3y ago
If your stall speed is 6mph and the winds are 100mph, you can fly into the wind at just above stall speed and still be doing 94mph tailfeathers-first.

dTal 3y ago

>for the sailors it feels like there is no wind, but the sails are carrying massive pressure The only way this is possible is if the sails are moving at a different airspeed than the sailors, which is only possible if 1) the sailor is running up and down the deck or 2) there is an windspeed gradient with altitude, which the sails penetrate by virtue of being tall.

mongol 3y ago

The comparison with the balloon is perhaps not entirely accurate since birds like you say, fly using lift from the wings. So they need to have some relative speed vs the air.

lxgr 3y ago
The point is that as long as the entire body of air the bird is flying through is moving uniformly and without acceleration, it's perceptually indistinguishable from calm air (except visually, and even that only when flying pretty low). For rotating and turbulent air, which would both not be totally unheard of in a hurricane, this probably doesn't apply though.
- quickthrower2 3y ago
  This is probably like when you swim out at the beach, and back and find you are 20m away from where you started due to currents. But you didn’t feel it. With dead reckoning you could probably figure out.
  - lxgr 3y ago
    You can’t feel linear/unaccelerated motion, and biological organisms aren’t great at indirectly deriving it from acceleration and rotation over time the way inertial navigation systems do.
    - stouset 3y ago
      Hell, even those have a hard time doing it without experiencing drift! So they periodically re-establish a baseline using something like GPS.
atq2119 3y ago
It doesn't really matter in this case, but hummingbirds would like to have a word with you.

HPsquared 3y ago

A sailboat uses the speed difference between the water (basically stationary) and the wind. A bird (or sailplane) just moves along with the wind. Birds and sailplanes can however hang around areas of rising air to overcome their natural sink rate.

_moof 3y ago

When you're flying, wind is no longer the air moving over the ground, it's the ground moving under the air. It doesn't produce acceleration except for a brief moment when you leave the ground.

stouset 3y ago

If you’re in a boat in a river, your “natural” speed is the speed of the river. Same with air. You point about a sailboat and wind is confused; the pressure comes from the fact that the boat is traveling at one speed through the water and at a different speed through the air.

natoliniak 3y ago
ok, if the bird's natural speed is that of the ambient air, then how does it stay up? the bird is not lighter than air, so where does the upwards pressure on the bird come from? either the bird must flap its wings to stay up or there must be speed difference between the bird and the ambient air to generate lift.
- tw04 3y ago
  If the bird’s natural speed is 7mph, and the tail wind is 7mph, the bird is still flying at 7mph airspeed, its ground speed just increases to 14mph. No different than a jet flying with or against the jet stream. https://science.howstuffworks.com/transport/flight/modern/airspeed-vs-groundspeed.htm https://science.howstuffworks.com/transport/flight/modern/ai...
  - natoliniak 3y ago
    that is my point - in order to stay up, the bird would need to either flap its wings for 700 miles non-stop (unlikely) in order to maintain velocity difference between it and the ambient air OR glide which basically means he was not traveling at the speed of ambient air, otherwise there would be no lift pressure generated on his wings and he would drop to the ground
    - hansvm 3y ago
      Ignore the storm for a moment, and ask whether a bird can fly for 7h+, either from flapping, gliding, or navigating updrafts. The answer is yes, that's trivial for many many bird species, especially those with a propensity for ocean travel. The storm then just changes the baseline ground speed.

cratermoon 3y ago

If your stall speed is 6mph and the winds are 100mph, you can fly into the wind at just above stall speed and still be doing 94mph tailfeathers-first.