Do birds fly in IMC?

RJM62 said:
In addition, even if the bird managed to become fully inverted while flapping, I think they'd realize it from the exertion required to flap their wings.

Consider that the natural tendency of the wings based solely on CG and aerodynamics (that is, without active input from the bird) would be to move upwards to whatever maximum dihedral the attachment joints allow. The lift from the wings is exerted upwards, and the weight of the body exerted downward. Flapping "down" to place the wings into anhedral, therefore, would require much more muscular force that flapping "up," which is assisted by aerodynamics and gravity.

If the bird were inverted, however, in additional to whatever inertial means it has to sense positional instability, the bird would also experience a situation where the sensory feedback from wing flapping was reversed. The aerodynamic and gravitational forces would now favor anhedral (with respect to the bird's body), and muscular force would be required to move the wing through neutral to positive dihedral. Surely the bird would sense this and correct for it.
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Why would the exertion be any different when pulling 1 g while inverted (or in a spiral vs upright? I keep hearing about how a bird could "feel" the difference between different flight attitudes but we all know that humans can't do this and the physics are the same for birds.

The notion that a bird could recover or at least maintain stability by assuming a high dihedral configuration does seem plausible but IMO only if you consider the "lift" generated by high drag (i.e. parachute mode). As long as the bird's wings are generating most of their lift in the conventional sense it seems to me that there would be sufficient "control authority" to roll and if the bird rolled without a visual (or internal inertial) reference it sure seems like they could inadvertently get into a spiral dive or worse.

I wonder if there are any true experts in this area who've experimented with some birds in flight with their eyes covered. OTOH if the results are what I'd expect the SPCA might object.
 
gismo said:
Why would the exertion be any different when pulling 1 g while inverted (or in a spiral vs upright? I keep hearing about how a bird could "feel" the difference between different flight attitudes but we all know that humans can't do this and the physics are the same for birds.

The notion that a bird could recover or at least maintain stability by assuming a high dihedral configuration does seem plausible but IMO only if you consider the "lift" generated by high drag (i.e. parachute mode). As long as the bird's wings are generating most of their lift in the conventional sense it seems to me that there would be sufficient "control authority" to roll and if the bird rolled without a visual (or internal inertial) reference it sure seems like they could inadvertently get into a spiral dive or worse.

I wonder if there are any true experts in this area who've experimented with some birds in flight with their eyes covered. OTOH if the results are what I'd expect the SPCA might object.
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I'm no bird expert, true or otherwise. But it seems pretty clear that if a bird is upside-down, then the forces of gravity and aerodynamics are tending to push its wings into anhedral (with respect to its body) as opposed to dihedral, as they usually would. So now all of the sudden the bird is having to exert much greater muscular force to put its wings into dihedral with respect to its body -- something that air and gravity usually assist with.

Surely they can sense that. Any animal with movable limbs has neuromuscular feedback to detect limb position and external forces acting on the limb. In the case of a bird's wing, I suspect that force feedback must be especially exquisite.

-Rich
 
Physics includes more than just gravity.

A very strong contributor to pilot disorientation is all the fictitious forces. The net force is not straight down. There are few better ways to cause vertigo than to excite the Coriolis force. Such as, a vigorous head motion during a significant turn about a different axis.

Properly executed coordinated turns always have net forces pointed to the floor, even in a 60 deg bank. Flying inverted does not require forces to the ceiling, unless it is flying inverted straight and level. No one ever does that by accident. Flying inverted in an overhead loop may very well have forces pointed to the floor throughout the maneuver.

Saying a bird can always know which way is down by feel is entirely equivalent to saying a plumb bob always points down. Try it in your aircraft. It doesn't work in steep turns or skidding turns. It doesn't work when nosing over, or when "pulling G's."
 
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RJM62 said:
I'm no bird expert, true or otherwise. But it seems pretty clear that if a bird is upside-down, then the forces of gravity and aerodynamics are tending to push its wings into anhedral (with respect to its body) as opposed to dihedral, as they usually would. So now all of the sudden the bird is having to exert much greater muscular force to put its wings into dihedral with respect to its body -- something that air and gravity usually assist with.

Surely they can sense that. Any animal with movable limbs has neuromuscular feedback to detect limb position and external forces acting on the limb. In the case of a bird's wing, I suspect that force feedback must be especially exquisite.

-Rich
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Go watch the Bob Hoover video where he does a roll while pouring some coffee or tea or something. Notice how you can be upside down and not be able to feel it. Notice how the coffee pours "UP" while they're upside down. If you couldn't see out the windshield it would just appear he was pouring coffee.

You can do a roll, you can do numerous things in an airplane, while maintaining 1G to where it feels as if nothing has changed but in reality your attitude is nowhere near straight and level.

The above effect is what causes us to lose control quickly when we try to fly based on feel.

 
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jesse said:
Go watch the Bob Hoover video where he does a roll while pouring some coffee or tea or something. Notice how you can be upside down and not be able to feel it. Notice how the coffee pours "UP" while they're upside down. If you couldn't see out the windshield it would just appear he was pouring coffee.

You can do a roll, you can do numerous things in an airplane, while maintaining 1G to where it feels as if nothing has changed but in reality your attitude is nowhere near straight and level.

The above effect is what causes us to lose control quickly when we try to fly based on feel.

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I was just posting the same thing about Bob Hoover and then said what's the use? :dunno:

Anyway, yeah, acceleration and gravity are locally equivalent. A plumb bob will tell you if you're in an uncoordinated turn. It won't tell you which way is down.
 
jesse said:
Go watch the Bob Hoover video where he does a roll while pouring some coffee or tea or something. Notice how you can be upside down and not be able to feel it. Notice how the coffee pours "UP" while they're upside down. If you couldn't see out the windshield it would just appear he was pouring coffee.

You can do a roll, you can do numerous things in an airplane, while maintaining 1G to where it feels as if nothing has changed but in reality your attitude is nowhere near straight and level.

The above effect is what causes us to lose control quickly when we try to fly based on feel.

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I get that, Jesse. But don't you think the bird would feel the difference in the direction of the torsion forces on the joint corresponding to the wing root?

Hoover's perfectly-executed roll aligned the centrifugal force so it "pushed" the tea into the cup, much as when you swing a bucket of water over your head, so effectively he maintained 1G throughout the roll. But that didn't change the forces of the air against the airframe or the stresses they created.

But an airplane can't feel those stresses on its body. I believe that a bird must be able to feel them. So even it's maintaining 1G and there's no vestibular sensation (or whatever the bird equivalent is), won't its "shoulder" hurt from the torsion force exerted by its own being opposite to what's normal?

Please see the attached picture, which may help explain what I'm talking about.

-Rich
 

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RJM62 said:
I get that, Jesse. But don't you think the bird would feel the difference in the direction of the torsion forces on the joint corresponding to the wing root?

Hoover's perfectly-executed roll aligned the centrifugal force so it "pushed" the tea into the cup, much as when you swing a bucket of water over your head, so effectively he maintained 1G throughout the roll. But that didn't change the forces of the air against the airframe or the stresses they created.

But an airplane can't feel those stresses on its body. I believe that a bird must be able to feel them. So even it's maintaining 1G and there's no vestibular sensation (or whatever the bird equivalent is), won't its "shoulder" hurt from the torsion force exerted by its own being opposite to what's normal?

Please see the attached picture, which may help explain what I'm talking about.

-Rich
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The forces would be the same. That's the point Rich. There is nothing different for the bird to feel in this particular scenario. This will lead the bird to take the wrong corrective action which will then create greater G forces and more loss of control.
 
So how do we fly IMC partial panel? If we can determine our attitude based on rate of turn, rate of climb and airspeed why shouldn't a bird be able to?
 
Skylane81E said:
So how do we fly IMC partial panel? If we can determine our attitude based on rate of turn, rate of climb and airspeed why shouldn't a bird be able to?
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The rate of turn indicator is an electrically driven gyroscope a bird would have no access to.

The equivalent would be flying partial panel with no vacuum AND no electrical system.
 
MAKG1 said:
The rate of turn indicator is an electrically driven gyroscope a bird would have no access to.

The equivalent would be flying partial panel with no vacuum AND no electrical system.
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Compass works too
 
A brainless shuttle-cock always automatically stabilizes in any phase of flight. The bird's body weight is in both its position and CG functions, analogous to the weight end of the shuttle-cock. If spatially disoriented in IMC, simple proprioceptive muscle feed back from the wings will tell them and the bird momentarily assumes with its wings, the high dihedral geometry analogous to the vanes of the shuttle-cock, until oriented and then resumes powered flapping.

This in flight reconfiguration may take place as often as every few seconds and Chick-a-dees routinely fly like this, even in daylight. Also, air and ground speeds of bird flight are substantially lower than in aircraft, translating to an increased measure of control.
 
Anyone know of any research regarding this? Googling it comes up with this thread. lol
 
Dave Krall CFII said:
A brainless shuttle-cock always automatically stabilizes in any phase of flight. The bird's body weight is in both its position and CG functions, analogous to the weight end of the shuttle-cock. If spatially disoriented in IMC, simple proprioceptive muscle feed back from the wings will tell them and the bird momentarily assumes with its wings, the high dihedral geometry analogous to the vanes of the shuttle-cock, until oriented and then resumes powered flapping.

This in flight reconfiguration may take place as often as every few seconds and Chick-a-dees routinely fly like this, even in daylight. Also, air and ground speeds of bird flight are substantially lower than in aircraft, translating to an increased measure of control.
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A brainless shuttle-cock always orients itself into the relative wind, and as it has no lift or thrust in the end that leads it to point down
 
Skylane81E said:
A brainless shuttle-cock always orients itself into the relative wind, and as it has no lift or thrust in the end that leads it to point down
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More accurately, it orients its flight path as a function of both its kinetic energy and relative wind, combined ultimately with gravitational forces.

Both shuttle-cock and bird flight in increasing severity of turbulence, will reach a threshold where it is no longer possible, same as in our aircraft.
 
Skylane81E said:
A brainless shuttle-cock always orients itself into the relative wind, and as it has no lift or thrust in the end that leads it to point down
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Which means all a bird has to do, is put it's wings in a severe dihedral and exert no force, and it will turn into a shuttle-cock. Body of the bird = weighted end, wings = the netted cone.

To put what Rich is saying a different way, the difference between birds and airplanes, is the wings are providing the lift AND the thrust. The downward motion in normal flight is always going to offer greater resistance than the upward motion due to gravity. If the bird inverts the downward motion suddenly becomes much easier, and the bird will go, "hey, wait a minute, not correct sensory input, I'm upside down." Because of that the bird will always know which way the Earth is, because thrust and lift are developed by the same motion. A bird would immediately know if it is disoriented due to this. If a bird propelled itself by perpetually farting, and the wings were fixed like in an airplane, I could see it getting disoriented.

Imagine skydiving, and strapping some wings to your arms. You start to fall belly down, flap your arms like a bird and you will feel much more resistance when your arms move toward each other, than when they go out. Roll over onto your back, and the sensation is flipped. That's how the bird knows.
 
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Ok do the article I posted above mentions 12 bird strikes in IMC (7 at night) from 91-97 so we know they are doing it. They also successfully disoriented pigeons by spinning them blindfolded.
 
EdFred said:
Which means all a bird has to do, is put it's wings in a severe dihedral and exert no force, and it will turn into a shuttle-cock. Body of the bird = weighted end, wings = the netted cone.

To put what Rich is saying a different way, the difference between birds and airplanes, is the wings are providing the lift AND the thrust. The downward motion in normal flight is always going to offer greater resistance than the upward motion due to gravity. If the bird inverts the downward motion suddenly becomes much easier, and the bird will go, "hey, wait a minute, not correct sensory input, I'm upside down." Because of that the bird will always know which way the Earth is, because thrust and lift are developed by the same motion. A bird would immediately know if it is disoriented due to this. If a bird propelled itself by perpetually farting, and the wings were fixed like in an airplane, I could see it getting disoriented.

Imagine skydiving, and strapping some wings to your arms. You start to fall belly down, flap your arms like a bird and you will feel much more resistance when your arms move toward each other, than when they go out. Roll over onto your back, and the sensation is flipped. That's how the bird knows.
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EXACTLY!

-Rich
 
EdFred said:
Sometimes, ya just gotta dumb it down. :rofl:
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I understood what Rich was trying to suggest; but his explanations were not correct. It's interesting that there doesn't appear to be much research on this.
 
jesse said:
I understood what Rich was trying to suggest; but his explanations were not correct. It's interesting that there doesn't appear to be much research on this.
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To me, it still comes down to whether the bird is able to feel the difference in the way the air exerts pressure on its wings and body at different attitudes. The vestibular system can be fooled, but I submit that birds, by their nature, must be very sensitive and able to correctly interpret the direct forces of air against their flight surfaces.

I agree, though, I would love to see some research on this. I find it pretty fascinating.

-Rich
 
RJM62 said:
To me, it still comes down to whether the bird is able to feel the difference in the way the air exerts pressure on its wings and body at different attitudes. The vestibular system can be fooled, but I submit that birds, by their nature, must be very sensitive and able to correctly interpret the direct forces of air against their flight surfaces.

I agree, though, I would love to see some research on this. I find it pretty fascinating.

-Rich
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I don't think the vestibular system would really come into play. I think the determination would be how much force is being exerted for the flapping motion. Even if I was spun and tumbled in the plane before I jumped while blindfolded in my above scenario, I would still be able to tell whether more force was being exerted when my arms moved inward or outward. That alone tells me which way down is, even if my brain is acting wonky.

If you spun and tumbled a bird before releasing it, the ability to fly in a straight line or level would be hard, just as when you spin around quickly 20-30-40 times and then try to walk a straight line.
 
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EdFred said:
If you spun and tumbled a bird before releasing it, the ability to fly in a straight line or level would be hard, just as when you spin around quickly 20-30-40 times and then try to walk a straight line.
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And they do have difficulty.
 
EdFred said:
I don't think the vestibular system would really come into play. I think the determination would be how much force is being exerted for the flapping motion. Even if I was spun and tumbled in the plane before I jumped while blindfolded in my above scenario, I would still be able to tell whether more force was being exerted when my arms moved inward or outward. That alone tells me which way down is, even if my brain is acting wonky.

If you spun and tumbled a bird before releasing it, the ability to fly in a straight line or level would be hard, just as when you spin around quickly 20-30-40 times and then try to walk a straight line.
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That's what I think, as well. But as I sit here watching through the window at everything from finches to raptors flying by, I've noticed that birds also seem to do subtle things with their feathers that more or less correspond to what airplane engineers do with spoilers, vortex generators, and so forth. On airplanes, these things were designed by successive generations of very smart people who'd studied an awful lot of math and physics, and had spent a lot of time in wind tunnels trying to understand things like Bernoulli's principle, Newton's law, other finer points of fluid dynamics, and so forth.

Birds, on the other hand, seem to grasp it all after an hour or two of self-training, without the benefit of even a BSAE, much less a wind tunnel.

I've watched fledglings before their first flights. After orienting themselves into the wind, they just sort of play with the air for a while -- kind of like most of us used to do by sticking our palms out the window of a moving car, forming an airfoil, and feeling the changes as we varied the camber and the AoA of the airfoils we formed with our hands.

Young birds do pretty much the same thing, feeling the effect of the air flowing over them as they move their wings and tails, and the feathers on their wings and tails, through their operational ranges, before finally leaping off into the wind. They actually have to learn the effects of the air moving across their bodies before they attempt actual flight. It's kind of like a self-taught lab course in aerodynamics.

To me, this suggests that in addition to basic proprioception and the ability to understand and use muscular exertion feedback to establish basic situational awareness and for attitude control, they also possess a keen ability to detect and manipulate the actual airflow over their bodies, which they use for fine control.

I've noticed, for example, that kestrels can transition to a hover in high winds by spreading out the feathers on the trailing edges of their wings, and applying down elevator with their tails. While they're hovering, they seem to be using the feathers at the trailing edge of their wings and tails more so than the wings and tails themselves, which suggests a very keen awareness of the airflow over even over the individual feathers, and knowledge of how to manipulate that airflow.

-Rich
 
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EdFred said:
I don't think the vestibular system would really come into play. I think the determination would be how much force is being exerted for the flapping motion. Even if I was spun and tumbled in the plane before I jumped while blindfolded in my above scenario, I would still be able to tell whether more force was being exerted when my arms moved inward or outward. That alone tells me which way down is, even if my brain is acting wonky.
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Once again, "down" is a local thing. To anything flying whether organic or aluminum, if the flying is coordinated (e.g. not sliding sideways) "down" will be toward the airplane or bird's belly regardless of whether that belly is closest to the ground or sky. And that local "down" is the direction that the wings will feel the most opposition in force.
 
gismo said:
Once again, "down" is a local thing. To anything flying whether organic or aluminum, if the flying is coordinated (e.g. not sliding sideways) "down" will be toward the airplane or bird's belly regardless of whether that belly is closest to the ground or sky. And that local "down" is the direction that the wings will feel the most opposition in force.
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If thrust was not being provided by the wings, then yes. But it's a completely different setup for a bird since the wings provide the thrust and the lift.
 
gismo said:
Once again, "down" is a local thing. To anything flying whether organic or aluminum, if the flying is coordinated (e.g. not sliding sideways) "down" will be toward the airplane or bird's belly regardless of whether that belly is closest to the ground or sky. And that local "down" is the direction that the wings will feel the most opposition in force.
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But the organic version flaps to produce lift and thrust. And in the process of flapping, in inverted flight it's going to notice that gravity is now assisting the down stroke and opposing the up stroke -- exactly the opposite of normal -- even if the bird's flight remains coordinated. And a bird's wing is not monolithic, so it would feel this effect in more than one joint.

Also, birds don't flap constantly. Most birds stop flapping and glide briefly (perhaps for this very reason -- to get a read on their attitude -- or perhaps to rest, or perhaps just because it's fun) even in normal flight. While gliding, the weight of their bodies at the wing attachment joints would alert them to attitude changes unless they were in a coordinated maneuver, which would bring centrifugal force into play.

To me, this suggests that any time a bird wants to get a read on its attitude, all it really has to do is stop flapping (to remove thrust and the Newtonian aspect of lift) and alter its wings' dihedral to check that everything feels normal. Even if it's riding an updraft or a thermal, it should be able to sense in its wing joints by ordinary proprioception whether the vertical aspect of lift and the force of gravity are opposed.

In straight and level flight, which the bird surely knows how to configure itself for, W always opposes L. If W and L are aligned, the bird is upside-down. If W and L are at some other angle than 0 degrees or 180 degrees, they are in a roll. The only time this would not be true would be if centrifugal force came into play in a coordinated maneuver, but the coordination would be broken if the bird stopped flapping, thus revoking all thrust as well as Newtonian lift.

Consider this: When I'm flying an airplane, if I suddenly throttle back, I can immediately feel that change in at least three places: My vestibular system senses it, my ass rises slightly with respect to the aircraft's seat, and my shoulders get a little tighter against the seat belt. In a WSC, I also feel the change in the control bar as the wing attempts to decrease pitch.

Now, if my wings were attached to my shoulders like a bird's are, I'd feel those changes much more acutely, as well as other changes that I can't feel as a human because the aircraft's wing is not physically attached to my body by bone, muscle, and sinew. I would be able to feel the changes in lift, thrust, and even drag as the airflow over and through my feathers changed. We know that birds can use their feathers to make these fine changes. Is it a stretch to think that they can feel the forces in their feathers -- that they have some proprioceptive sense in their skin where the feathers attach -- as well?

At a minimum, if I were flying inverted (or at any other orientation other than level), and if my wings were attached to my shoulders, when I suddenly throttled back (stopped flapping), I would feel the changes in my shoulders. Even in a coordinated maneuver, throttling back would break the coordination, modify the element of centrifugal force (thus also restoring vestibular sensation in the process), and change the angles of all the aerodynamic forces, as well as the physical sensation of those forces that my wings were transferring through my shoulders. And if I had feathers, I'd be able to feel the changes in the air playing over and through them.

As an aside, I think I may enroll in a TAD course. I took one back in the late 1970's as part of the Airframe curriculum, but it didn't get into anything particularly advanced. I think it would be quite enjoyable to take a more advanced one now.

-Rich
 
You keep fixating on gravity, all it is is a force of acceleration, 32ft/sec/sec, that acceleration can happen in any direction
 
A pair of sparrows are sitting on a nest under my rear deck. They're used to me farting around in the yard adjacent to the deck, so they no longer fly away when I stop to chat.

I just asked whichever one was on duty -- I can't really tell them apart, especially in the dark -- whether they can feel their orientation in flight without visual reference. The bird responded with a cocked head and one tweet. Now, the cocked head is a universal sign meaning, "That was a dumb question, dude;" and one tweet, of course, means yes. One always means yes, and two always means no. Everyone knows that.

I would submit that to be the authoritative answer -- except for one thing: There are some sparrows that live in New York City in the winter, and fly up here for the warmer months. That means that there's at least a possibility that my sparrow is a New York City sparrow -- or possibly even a Brooklyn sparrow -- in which case there would be a distinct possibility of sarcasm. If it's a Brooklyn sparrow, then the cocked head and the one tweet would mean "Yeah, right," which when translated out of Brooklynese would mean "No."

Maybe what we should do is find an ornithology forum, and post a link to this thread on their forum. Either that, or find a sparrow who's not from Brooklyn.

-Rich
 
RJM62 said:
A pair of sparrows are sitting on a nest under my rear deck. They're used to me farting around in the yard adjacent to the deck, so they no longer fly away when I stop to chat.

I just asked whichever one was on duty -- I can't really tell them apart, especially in the dark -- whether they can feel their orientation in flight without visual reference. The bird responded with a cocked head and one tweet. Now, the cocked head is a universal sign meaning, "That was a dumb question, dude;" and one tweet, of course, means yes. One always means yes, and two always means no. Everyone knows that.

I would submit that to be the authoritative answer -- except for one thing: There are some sparrows that live in New York City in the winter, and fly up here for the warmer months. That means that there's at least a possibility that my sparrow is a New York City sparrow -- or possibly even a Brooklyn sparrow -- in which case there would be a distinct possibility of sarcasm. If it's a Brooklyn sparrow, then the cocked head and the one tweet would mean "Yeah, right," which when translated out of Brooklynese would mean "No."

Maybe what we should do is find an ornithology forum, and post a link to this thread on their forum. Either that, or find a sparrow who's not from Brooklyn.

-Rich
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:rofl:

Now here is the question,

By the act of flapping is there a time where the wings are not generating any lift? If there is (and I suspect that there is) wouldn't the bird just be falling at that point, brief as it may be? If you knew when you were just falling and where the Gs were pointed at that time maybe....
 
Skylane81E said:
:rofl:

Now here is the question,

By the act of flapping is there a time where the wings are not generating any lift? If there is (and I suspect that there is) wouldn't the bird just be falling at that point, brief as it may be? If you knew when you were just falling and where the Gs were pointed at that time maybe....
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Yes, there would be, which is why they can tell which way is down.
 
Now I see an issue with my above thought...


During that time the bird would be weightless as it would be still accelerating down when lift resumed and the nominal and possibly erroneous g forces resumed.
 
Skylane81E said:
:rofl:

Now here is the question,

By the act of flapping is there a time where the wings are not generating any lift? If there is (and I suspect that there is) wouldn't the bird just be falling at that point, brief as it may be? If you knew when you were just falling and where the Gs were pointed at that time maybe....
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Well, sure. At a minimum, they'd be losing the Newtonian action, and I suppose Bernoulli's lift would be perpendicular to the plane of the wing at any point in the flap... so there would be a dramatic loss of the vertical component of lift with every upstroke... I think.

-Rich
 
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