Do birds fly in IMC?

I hit a bird IMC at night once in a CRJ. I had thought they stay out of clouds too. There was a solid layer though and maybe he got caught above it?
 
The Canadian Geese and Mallards winter here. They not only fly in IMC, they do so at night!

:yes:
 
Humans and birds all have internal gyros. It's just that ours are not good enough to stay upright in IMC. I'd venture that the birds' are, especially when fused with information from their internal accelerometers, magnetometers and vector airspeed sensors.
 
All I know is that on numerous occasions, when I'm out fishing early in the morning on my little lake, and it's 100' OVC (deep overcast)...

...that's when it's the best fishing after all...especially if it's near the full or new moon...

...I'll be sitting there in my canoe, minding my own business, enjoying my coffee, the tranquility, the scenery and the flitter of my fly popping along the water's surface when...

....of a sudden...

...a flock of ducks or geese, in formation, will descend out of the scud and make a perfect formation landing on the water.

MY reaction is always WTF? How do they do that?

Or on occasion, they'll see me, go missed, and presumably fly back to the FAM VOR and hold until I'm done fishing.

:)
 
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pericynthion said:
Humans and birds all have internal gyros. It's just that ours are not good enough to stay upright in IMC. I'd venture that the birds' are, especially when fused with information from their internal accelerometers, magnetometers and vector airspeed sensors.
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I don't know about birds, but humans have accelerometers, not gyros. VERY different. You can't keep an aircraft upright with only an accelerometer., even if it's perfect. The attitude solutions become multivalued. You can make 1G to the floor in a coordinated bank by nosing over.
 
We have accelerometers, certainly. We also have gyros - just not very good ones. They're rate gyros and they saturate.

The gyros in our aircraft panels (either vacuum or MEMS) aren't that good either, but in combination with accelerometers and a valid dynamics model of the aircraft, they work to get a usable attitude solution. In an electronic PFD, those accels and the dynamics model are explicit (and it typically uses magnetometer, GPS and air data as well); in the mechanical AH the accel and dynamic model are implicit in the erecting mechanism (snerk)
 
timwinters said:
All I know is that on numerous occasions, when I'm out fishing early in the morning on my little lake, and it's 100' OC (deep overcast)...

...that's when it's the best fishing after all...especially if it's near the full or new moon...

...I'll be sitting there in my canoe, minding my own business, enjoying my coffee, the tranquility, the scenery and the flitter of my fly popping along the water's surface when...

....of a sudden...

...a flock of ducks or geese, in formation, will descend out of the scud and make a perfect formation landing on the water.

MY reaction is always WTF? How do they do that?

Or on occasion, they'll see me, go missed, and presumably fly back to the FAM VOR and hold until I'm done fishing.

:)
Click to expand...


My guess would be they are flying just high enough to see the ground. From you position from the canoe you not able to determine where they were before you saw them so I'm not accepting 'descend out of the scud' at face value.
 
MAKG1 said:
I don't know about birds, but humans have accelerometers, not gyros. VERY different. You can't keep an aircraft upright with only an accelerometer., even if it's perfect. The attitude solutions become multivalued. You can make 1G to the floor in a coordinated bank by nosing over.
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I think it likely that birds can utilize neuromuscular feedback from the wing and tail joints to determine attitude, as well.

Also, the attachment and design of most birds' wings wouldn't seem to lend themselves well to prolonged inverted flight. In fact, I wouldn't be surprised if most birds are aerodynamically self-righting.

There are some exceptions, such as kestrels and eagles. Their dihedral in soaring configuration is close to neutral, and they seem pretty comfortable flying inverted. But most birds use deeper dihedral when soaring, which combined with their CGs, would tend to right them if inverted.

-Rich
 
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Captain said:
My guess would be they are flying just high enough to see the ground. From you position from the canoe you not able to determine where they were before you saw them so I'm not accepting 'descend out of the scud' at face value.
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I thought you were going to say that they used Google Maps. :D

-Rich
 
pericynthion said:
We have accelerometers, certainly. We also have gyros - just not very good ones. They're rate gyros and they saturate.
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No. Semicircular canals are NOT gyros, rate or otherwise. They are rotational accelerometers. That's why they disorient people.

A rate gyro (like an RLG) can detect constant rotation. Your semicircular canals can't.
 
RJM62 said:
I thought you were going to say that they used Google Maps. :D

-Rich
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I was trying to make a joke to the effect of 'everyone knows bird brains don't trust Google' but there's no way I can see to make it not come off mean.

:D
 
Captain said:
My guess would be they are flying just high enough to see the ground. From you position from the canoe you not able to determine where they were before you saw them so I'm not accepting 'descend out of the scud' at face value.
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Well, except that my honey hole is in a small valley. And when it's 100' OVC on the water, there's terrain obscuration in every direction except due south.

And...

I can hear them coming.

And...

It ain't always from the south.
 
I don't know what scientific research has revealed about all this, but I think birds, being born with wings, have a natural advantage in marginal conditions and maybe can do OK in IMC when necessary. I've seen ducks, geese and gulls flying in some pretty crummy weather with great confidence. Their eyes,and the amount of brainpower devoted to seeing stuff and navigating by pilotage, probably makes them very, very good "ground contact" flyers. Back in the old days before gyros, flying in what we now call IMC was called "ground contact" flying... if you could see the ground, you were good to go (and barring traffic, wires, and airspaces, this is still true, if somewhat risky).

I have read accounts of pre-WWII training in biplanes where flying through clouds was encouraged, provided the pilot could discern where the sun was and knew where it ought to be, relative to the horizon, based on the time of day. If humans can pull that sort of thing off, for birds it must be a cinch.

But they definitely know when it's too gusty, or the precip is too heavy. Every IFR pilot should know that if the ducks are walking, they should think twice about taking off. :D
 
MAKG1 said:
No. Semicircular canals are NOT gyros, rate or otherwise. They are rotational accelerometers. That's why they disorient people.

A rate gyro (like an RLG) can detect constant rotation. Your semicircular canals can't.
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There's no such thing as a "rotational accelerometer" - or alternatively, that's one definition of a certain kind of gyro. Semicircular canals can be seen as rate gyroscopes coupled to (imperfect, saturable) high-pass filters.

I'm not trying to say that it's possible to fly blind with the sensors we've got.
 
Last time I was out we were headed back in due to bad weather on the horizon. We spotted a Hawk departing the pattern towards the weather. I am a believer. :)
 
pericynthion said:
There's no such thing as a "rotational accelerometer" - or alternatively, that's one definition of a certain kind of gyro. Semicircular canals can be seen as rate gyroscopes coupled to (imperfect, saturable) high-pass filters.

I'm not trying to say that it's possible to fly blind with the sensors we've got.
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That's a really weird form of saturation you're dealing with there. They detect accelerations. Conventional saturation would be that rates above a certain value are detected incorrectly.

And of course you can have rotational accelerometers. Just like linear ones, just arranged in a circle....you could do that with damped springs (like a conventional accelerometer with at least two springs), or with a damping fluid acting against an elastic boundary.

A rate gyro detects rates. Your ears don't. If you put yourself in a coordinated constant turn, you won't feel like you're turning, once the transient dies out. And all accelerometers have transients, related to the damping coefficient.
 
RJM62 said:
I think it likely that birds can utilize neuromuscular feedback from the wing and tail joints to determine attitude, as well.

Also, the attachment and design of most birds' wings wouldn't seem to lend themselves well to prolonged inverted flight. In fact, I wouldn't be surprised if most birds are aerodynamically self-righting.

There are some exceptions, such as kestrels and eagles. Their dihedral in soaring configuration is close to neutral, and they seem pretty comfortable flying inverted. But most birds use deeper dihedral when soaring, which combined with their CGs, would tend to right them if inverted.

-Rich
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Notice the factory didn't equip any of them with a vertical fin. Engineering determined it was unnecessary.
 
Jaybird180 said:
Notice the factory didn't equip any of them with a vertical fin. Engineering determined it was unnecessary.
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The directional stability provided by an airplane's vertical stabilizer is unnecessary given the exquisite control birds have over their wings, which provides for control of lift, thrust, and drag in exactly the amounts needed to maintain stable flight. A vertical stabilizer would also have costs in terms of drag, weight, and the ability to execute deliberately abrupt maneuvers, while providing no survival advantage whatsoever.

-Rich
 
I have frequently encountered seabirds and geese in nearly zero zero at low level, (500ft or less), and ingested a pelican into an engine in heavy haze and twilight at about 800 ft. The pelican was in formation, how we missed the others I do not know.
 
RJM62 said:
The directional stability provided by an airplane's vertical stabilizer is unnecessary given the exquisite control birds have over their wings, which provides for control of lift, thrust, and drag in exactly the amounts needed to maintain stable flight. A vertical stabilizer would also have costs in terms of drag, weight, and the ability to execute deliberately abrupt maneuvers, while providing no survival advantage whatsoever.

-Rich
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and tail. Watch a birds tail while they are manuvering.
 
pericynthion said:
There's no such thing as a "rotational accelerometer" - or alternatively, that's one definition of a certain kind of gyro. Semicircular canals can be seen as rate gyroscopes coupled to (imperfect, saturable) high-pass filters.
Click to expand...

I disagree. First there is such a thing as a rotary accelerometer (more accurately called an "angular accelerometer" and that is closer to the behavior of your inner ear. A rate gyro provides a continuous indication of turning motion, an angular accelerometer's output goes to zero when rotated at a constant speed. MEMS based AHRS use rate gyros coupled with linear accelerometers and other external inputs and physics models to determine attitude but that additional input is only required because the long term stability of the MEMS devices available today is insufficient (they don't output a zero indication when there's no rotation). A RLG is a "perfect" rate gyro and can provide accurate attitude information without external help.

Technically, a "perfect" angular accelerometer could do so as well but it's sensing is one order further removed from attitude. Attitude is equal to integrated turn rate and turn rate is equal to integrated angular acceleration but each level of integration magnifies any noise or error infinitely given enough time.

I think it's safe to assume that without rotating masses or photons, birds cannot accurately sense attitude without visual references and even if they had vibrating rate sensors (organically feasible but nonexistent AFaIK) they'd need GPS or airspeed data to "compute" attitude. It is certainly possible if not likely that some or all birds can sense magnetic direction and if true they might well be able to maintain spatial orientation without visual references just like we can in an airplane using nothing but the magnetic compass. Of course they'd also experience "magnetic dip" unless their magnetic sensing was three dimensional so they might have trouble flying IMC when headed north in the northern hemisphere.

It might also be that some are aerodynamically "spin resistant" and it seems likely that they are capable of limiting g-force so if/when they lose control in IMC they probably are able to recover once they catch sight of the ground.
 
If you haven't wached the entire BBC series EarthFlight then you probably have no clue what birds do and go through just to survive. It can only be described as spectacularly incredible. You won't believe it's real but ti is and all in super high def.

Hell, I think I'm gonna watch it again
 
gismo said:
I disagree. First there is such a thing as a rotary accelerometer (more accurately called an "angular accelerometer" and that is closer to the behavior of your inner ear. A rate gyro provides a continuous indication of turning motion, an angular accelerometer's output goes to zero when rotated at a constant speed. MEMS based AHRS use rate gyros coupled with linear accelerometers and other external inputs and physics models to determine attitude but that additional input is only required because the long term stability of the MEMS devices available today is insufficient (they don't output a zero indication when there's no rotation). A RLG is a "perfect" rate gyro and can provide accurate attitude information without external help.

Technically, a "perfect" angular accelerometer could do so as well but it's sensing is one order further removed from attitude. Attitude is equal to integrated turn rate and turn rate is equal to integrated angular acceleration but each level of integration magnifies any noise or error infinitely given enough time.

I think it's safe to assume that without rotating masses or photons, birds cannot accurately sense attitude without visual references and even if they had vibrating rate sensors (organically feasible but nonexistent AFaIK) they'd need GPS or airspeed data to "compute" attitude. It is certainly possible if not likely that some or all birds can sense magnetic direction and if true they might well be able to maintain spatial orientation without visual references just like we can in an airplane using nothing but the magnetic compass. Of course they'd also experience "magnetic dip" unless their magnetic sensing was three dimensional so they might have trouble flying IMC when headed north in the northern hemisphere.

It might also be that some are aerodynamically "spin resistant" and it seems likely that they are capable of limiting g-force so if/when they lose control in IMC they probably are able to recover once they catch sight of the ground.
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The birds needn't even catch sight of ground at all to recover their attitude in IMC, similar to a bad-mitten bird tossed haphazardly into the wind, it will come back down weighted end first, even with some wobble.

Like the way pigeons sometimes lay their wings back at ~45degree angle to descend without increasing forward airspeed, the body naturally is below the wings. Combined with magnetic direction sensing via magnetite, they're good to go IMC.

Even every flap of their wings must be a mini attitude indication to them, with greater turbulence being more challenging as it creates its own variable G-forces for them to temporarily deal with, separate from constant gravity.
 
Dave Krall CFII said:
The birds needn't even catch sight of ground at all to recover their attitude in IMC, similar to a bad-mitten bird tossed haphazardly into the wind, it will come back down weighted end first, even with some wobble.

Like the way pigeons sometimes lay their wings back at ~45degree angle to descend without increasing forward airspeed, the body naturally is below the wings. Combined with magnetic direction sensing via magnetite, they're good to go IMC.

Even every flap of their wings must be a mini attitude indication to them, with greater turbulence being more challenging as it creates its own variable G-forces for them to temporarily deal with, separate from constant gravity.
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That's basically what I was thinking. Aerodynamically, they're self-righting due to their wing attachment and CG; plus they have whatever directional sense(s) they've been endowed with, and neuromuscular feedback, to enable them to detect the changes, correct for them, and resume course.

Or so it would seem to me, not being a particular expert on birds, but believing that whether by evolution or divine endowment, creatures born with functional wings would also possess such capabilities as are needed to make the best use of them.

-Rich
 
Dave Krall CFII said:
The birds needn't even catch sight of ground at all to recover their attitude in IMC, similar to a bad-mitten bird tossed haphazardly into the wind, it will come back down weighted end first, even with some wobble.

Like the way pigeons sometimes lay their wings back at ~45degree angle to descend without increasing forward airspeed, the body naturally is below the wings. Combined with magnetic direction sensing via magnetite, they're good to go IMC.

Even every flap of their wings must be a mini attitude indication to them, with greater turbulence being more challenging as it creates its own variable G-forces for them to temporarily deal with, separate from constant gravity.
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If a bird can "activate" a parachute like mode and the resulting descent rate is survivable that seems like a sufficient explanation for how they can live through an IMC encounter. But I don't think it comes close to supporting the notion that they can remain upright while flying (i.e. creating most of their lift by virtue of airflow over their wings) without a visual reference.

As to the idea that flapping wings somehow creates the ability to sense attitude I'd have to say that's feasible but probably not realistic for anything larger than a hummingbird since the gyroscopic effect of a vibrating mass requires a fairly rapid vibration rate to produce a measurable indication and even then it's only a rate sensor.
 
gismo said:
If a bird can "activate" a parachute like mode and the resulting descent rate is survivable that seems like a sufficient explanation for how they can live through an IMC encounter. But I don't think it comes close to supporting the notion that they can remain upright while flying (i.e. creating most of their lift by virtue of airflow over their wings) without a visual reference.

As to the idea that flapping wings somehow creates the ability to sense attitude I'd have to say that's feasible but probably not realistic for anything larger than a hummingbird since the gyroscopic effect of a vibrating mass requires a fairly rapid vibration rate to produce a measurable indication and even then it's only a rate sensor.
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Flying birds' weights and wing flap frequencies are not factors in their IMC attitude.

Gross attitude adjustment contingent upon wing flapping forces happens virtually automatically, due to forces of the wings lift being transmitted to the birds' bodies above their body CG because of the location of their 2 wing root articulations, creating a simple plumb-bob effect while in flight.
 
Dave Krall CFII said:
Flying birds' weights and wing flap frequencies are not factors in their IMC attitude.

Gross attitude adjustment contingent upon wing flapping forces happens virtually automatically, due to forces of the wings lift being transmitted to the birds' bodies above their body CG because of the location of their 2 wing root articulations, creating a simple plumb-bob effect while in flight.
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A Cessna 182 has a CG well below the wings but won't keep you right side up in IMC. I will readily admit I know very little about bird aerodynamics but if a bird is capable of rolling when the average dihedral of their wings is as high as it can go while maintaining altitude then I'm pretty sure they could roll over if they didn't have some way to determine what right side up is besides how their wings feel. Just like an airplane, their wings would "feel" the same thing while upside down if they were pulling 1g towards the ground.
 
tonycondon said:
A british study recently put GPS devices on pigeons and found that they migrate using the simplest method available. Basically they follow roads, towns. Easy landmarks. Pilotage! It even found some birds going around a roundabout several times before deciding what road to follow out of it.

Of course they were expecting them to naturally fly point to point by some advanced magnetic seeking device in their brains or something too.

Ill see if i can dig up the link.
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This does sound a little hard to swallow. Pigeons were certainly around long before roads.
 
gismo said:
A Cessna 182 has a CG well below the wings but won't keep you right side up in IMC. I will readily admit I know very little about bird aerodynamics but if a bird is capable of rolling when the average dihedral of their wings is as high as it can go while maintaining altitude then I'm pretty sure they could roll over if they didn't have some way to determine what right side up is besides how their wings feel. Just like an airplane, their wings would "feel" the same thing while upside down if they were pulling 1g towards the ground.
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Partially copy the bird's technique of quickly variable wing dihedral by installing wings with about 45 degrees dihedral and the C182 will self right the same way even with fixed wings, very similar to the bad mitten shuttle cock example.
 
Dave Krall CFII said:
Partially copy the bird's technique of quickly variable wing dihedral by installing wings with about 45 degrees dihedral and the C182 will self right the same way even with fixed wings, very similar to the bad mitten shuttle cock example.
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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.

-Rich
 
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Uh Oh....
Looks like this thread needs to be referred to.....
 

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