Circling for rodents?

[Andy Durbin]

"Bill Daniels" > wrote in message news:<aa4Fc.11095$7t3.8707@attbi_s51>...
>
> Most hawks circling low are looking for rodents, not lift.
>
> Bill Daniels


But many times I have shared thermals with Hawks at high altitude.
How did they get there if not by working thermals at low altitude? I
have never been in a thermal with a Red Tailed Hawk that didn't seem
to be trying to optimize climb rate. Turkey Vultures are a different
story. They seem to be happy with any sloppy thermal technique as
long as they maintain altitude.


Andy

[Sid Wood]

Gulls will circle in sink just to lure the unsuspecting soaring pilot.

"Andy Durbin" > wrote in message
om...
> "Bill Daniels" > wrote in message
news:<aa4Fc.11095$7t3.8707@attbi_s51>...
> >
> > Most hawks circling low are looking for rodents, not lift.
> >
> > Bill Daniels
>
>
> But many times I have shared thermals with Hawks at high altitude.
> How did they get there if not by working thermals at low altitude? I
> have never been in a thermal with a Red Tailed Hawk that didn't seem
> to be trying to optimize climb rate. Turkey Vultures are a different
> story. They seem to be happy with any sloppy thermal technique as
> long as they maintain altitude.
>
>
> Andy

[Herbert Kilian]

(Andy Durbin) wrote in message >...
> "Bill Daniels" > wrote in message news:<aa4Fc.11095$7t3.8707@attbi_s51>...
> >
> > Most hawks circling low are looking for rodents, not lift.
> >
> > Bill Daniels
>
>
> But many times I have shared thermals with Hawks at high altitude.
> How did they get there if not by working thermals at low altitude? I
> have never been in a thermal with a Red Tailed Hawk that didn't seem
> to be trying to optimize climb rate. Turkey Vultures are a different
> story. They seem to be happy with any sloppy thermal technique as
> long as they maintain altitude.
>
>
> Andy

Andy,
My theory is that all the large and small raptors mostly go soaring
for the fun of it, just as we do. On occasion they thermal and run
while migrating like the large groups of Broad-Wings (50-100) observed
in September along the Appalachian ridges. I believe that after
catching their prey for the day most of the hawks we encounter just
enjoy the soaring conditions. Some years back I was flying the
cooling tower thermal of a nuclear power plant in NC when I noticed 4
or 5 buzzards circling above at around 5,500'. They got closer to the
well-developed base of the Cu above and then all disappeared
continuing their circle. I watched the bottom of the cloud until I
reached it and never did see them again. Relating the story to Karl
Striedieck he didn't seem surprised and explained that it is quite
normal for them to climb to the top of lift in the cloud and then cut
out to the side. I did not follow them.
They do have a couple millions of years of experience on us.
Herb, J7

[BTIZ]

you must be sharing thermals with the ones going out for dinner... cross
country

BT

"Andy Durbin" > wrote in message
om...
> "Bill Daniels" > wrote in message
news:<aa4Fc.11095$7t3.8707@attbi_s51>...
> >
> > Most hawks circling low are looking for rodents, not lift.
> >
> > Bill Daniels
>
>
> But many times I have shared thermals with Hawks at high altitude.
> How did they get there if not by working thermals at low altitude? I
> have never been in a thermal with a Red Tailed Hawk that didn't seem
> to be trying to optimize climb rate. Turkey Vultures are a different
> story. They seem to be happy with any sloppy thermal technique as
> long as they maintain altitude.
>
>
> Andy

[Uri Saovray]

Does anyone have an idea of how the birds know where to thermal? Do
they have a vario? Where is it? Where is its capacity?
Assuming they breath while thermalling, then I doubt they use their
lungs as capacity... or maybe they stop and sense the air coming out
their noses.
Just wondering...

Uri 4XGJC

(Andy Durbin) wrote in message
>...
> "Bill Daniels" > wrote in message news:<aa4Fc.11095$7t3.8707@attbi_s51>...
> >
> > Most hawks circling low are looking for rodents, not lift.
> >
> > Bill Daniels
>
>
> But many times I have shared thermals with Hawks at high altitude.
> How did they get there if not by working thermals at low altitude? I
> have never been in a thermal with a Red Tailed Hawk that didn't seem
> to be trying to optimize climb rate. Turkey Vultures are a different
> story. They seem to be happy with any sloppy thermal technique as
> long as they maintain altitude.
>
>
> Andy

[Derrick Steed]

It's a well known fact that birds bones are very light and filled with
holes, just like we have sinuses in our head bones. I've pondered how birds
might sense rate of climb many times and I now hold the view that they sense
it via the cavities in their bones - this would provide them with a very
sensitive variometer, the capacity being automatically incorporated so to
speak.

I'm also convinced that birds soar for pleasure as well as because they
might have to (e.g. Pelicans soar when they are migrating and follow similar
climb/glide patterns to us).

I once observed a seagull from the restaurant at the top of the OMPI
building in Geneva - a seagull was already soaring near the ITU building
when suddenly another shot past the window in a fast glide headed straight
for a point below the other seagull, when it got there it pulled up into the
climb underneath the other gull turning in the same direction. Obviously
his/her CSI (Chief Seagull Instructor) had made the point about proper
thermal entry.

Rgds,

Derrick Steed
>Does anyone have an idea of how the birds know where to thermal? Do
>they have a vario? Where is it? Where is its capacity?
>Assuming they breath while thermalling, then I doubt they use their
>lungs as capacity... or maybe they stop and sense the air coming out
>their noses.
>Just wondering...
>
>Uri 4XGJC
>
> (Andy Durbin) wrote in
message
>news:...
>> "Bill Daniels" wrote in message news:...
>> >
>> > Most hawks circling low are looking for rodents, not lift.
>> >
>> > Bill Daniels
>>
>>
>> But many times I have shared thermals with Hawks at high altitude.
>> How did they get there if not by working thermals at low altitude? I
>> have never been in a thermal with a Red Tailed Hawk that didn't seem
>> to be trying to optimize climb rate. Turkey Vultures are a different
>> story. They seem to be happy with any sloppy thermal technique as
>> long as they maintain altitude.
>>
>>
>> Andy
>
>>

[BTIZ]

did you ever feel the aileron twitch.. and instinctively know that the
thermal was to your left or right? with most soaring birds (raptors).. those
fingertip feathers tend to move freely.. sensing every movement of the air..
watch one some time..

as for locating thermals?? some believe they can "see the heat".. ever watch
heat rise of pavement.. that "shimmering" as the heat rises.. perhaps our
raptor friends have better vision than we give them credit for

BT


"Uri Saovray" > wrote in message
m...
> Does anyone have an idea of how the birds know where to thermal? Do
> they have a vario? Where is it? Where is its capacity?
> Assuming they breath while thermalling, then I doubt they use their
> lungs as capacity... or maybe they stop and sense the air coming out
> their noses.
> Just wondering...
>
> Uri 4XGJC
>
> (Andy Durbin) wrote in message
> >...
> > "Bill Daniels" > wrote in message
news:<aa4Fc.11095$7t3.8707@attbi_s51>...
> > >
> > > Most hawks circling low are looking for rodents, not lift.
> > >
> > > Bill Daniels
> >
> >
> > But many times I have shared thermals with Hawks at high altitude.
> > How did they get there if not by working thermals at low altitude? I
> > have never been in a thermal with a Red Tailed Hawk that didn't seem
> > to be trying to optimize climb rate. Turkey Vultures are a different
> > story. They seem to be happy with any sloppy thermal technique as
> > long as they maintain altitude.
> >
> >
> > Andy

[Jim Skydell]

> It's a well known fact that birds bones are very light and filled with
> holes, just like we have sinuses in our head bones. I've pondered how birds
> might sense rate of climb many times and I now hold the view that they sense
> it via the cavities in their bones - this would provide them with a very
> sensitive variometer, the capacity being automatically incorporated so to
> speak.

Some work was done in the early 70's on this. Whatever a bird's "vario" is, it resides in
their ear. Cutting the 8th cranial nerves (which connect the ear to the brain)
extinguished their ability to sense altitude. This work was done in pigeons, (not soaring
birds, who would be expected to have an even better "vario"). Further work (done in a
pressure chamber) indicated that even a pigeon can sense an ambient pressure change
equivalent to climbing 2 feet.
>
> I'm also convinced that birds soar for pleasure as well as because they
> might have to (e.g. Pelicans soar when they are migrating and follow similar
> climb/glide patterns to us).

Other research done in the 70's was carried out by a glider pilot in Africa. He wanted to
figure out where all the buzzards went during the middle of the afternoon (all would
disappear every day). They thermaled up, out of sight from the ground. Either for
pleasure,or to cool off?

[Vaughn]

"Jim Skydell" > wrote in message
...
> Other research done in the 70's was carried out by a glider pilot in Africa.
He wanted to
> figure out where all the buzzards went during the middle of the afternoon (all
would
> disappear every day). They thermaled up, out of sight from the ground. Either
for
> pleasure,or to cool off?

Or simply because it takes little energy and makes them temporarily safe
from all ground-bound predators?

Vaughn

[Martin Gregorie]

On 4 Jul 2004 14:20:05 GMT, Derrick Steed
> wrote:

>I once observed a seagull from the restaurant at the top of the OMPI
>building in Geneva - a seagull was already soaring near the ITU building
>when suddenly another shot past the window in a fast glide headed straight
>for a point below the other seagull, when it got there it pulled up into the
>climb underneath the other gull turning in the same direction. Obviously
>his/her CSI (Chief Seagull Instructor) had made the point about proper
>thermal entry.
>
I've noticed that gulls joining a thermal will almost always circle
the same way as the birds or gliders already in it. I've had them join
me when I was the sole occupant of the thermal and they have always
respected my turn direction. I wish I could say the same about the
small raptors around Cambridgeshire - they often join going the wrong
way and keep a pretty poor lookout too.

Judging from what I've seen from the ground kites and vultures have
better thermalling manners than their smaller relatives. That said,
back in the late '70s I remember seeing a stationary thermal in Jaipur
over the local abattoir that was stuffed with several hundred Indian
vultures. They were flapping up to join at 100 ft or so and riding it
to at least 1000 ft before peeling off in a skein that crossed the
city to another thermal - a magical sight. I wasn't a glider pilot
then, but I remember that a few were turning the wrong way. Sadly, I'm
told that this sight has now vanished from Indian skies. 95% of the
vultures have been killed by a now-common veterinary medicine and the
farmers are learning the hard way just how much cleaning up the
vultures did for them.

--
martin@ : Martin Gregorie
gregorie : Harlow, UK
demon :
co : Zappa fan & glider pilot
uk :

[Frostowits]

Pardon this input from an uninformed intruder to this subject, but why couldn't
birds simply sense how strong the lift is by the amount of stress it puts on
their "airframe". When I pump iron, I'm all too aware of the amount of effort
required. Surely birds can do the same.

Ted Frost
Soaring Society of Boulder

[Martin Gregorie]

On 04 Jul 2004 18:48:04 GMT, (Frostowits)
wrote:

>Pardon this input from an uninformed intruder to this subject, but why couldn't
>birds simply sense how strong the lift is by the amount of stress it puts on
>their "airframe". When I pump iron, I'm all too aware of the amount of effort
>required. Surely birds can do the same.
>
Some seem to do just that. Kites in particular. I used to watch them a
lot in India and discovered that you can tell how strong the lift is
by looking at them - the stronger it is the more dihedral they use. If
its really strong they just bomb round with a steep V-form and their
tip feathers closed. Weaker lift gets more care and attention, less
dihedral and more open tip feathers. When they're really scratching
their wings are flat or even a little anhedralled and the tip feathers
are fully spread and up to give tip dihedral. They initiate a turn
with a big dab of negative in the inner tip and then control the turn
on tail tilt - the outer tail tip is raised, so you can tell that
they fly like we do with down force on the tail. Kites are easy to
read because they often work low altitude lift where you can see
exactly what they are doing and have big, long tails that are easy to
observe.

I wondered about how vultures fly but they were so seldom low enough
to really watch that I couldn't work out very much. Also, with much
shorter tails than kites its difficult to see whether they use tail
tilt at all or which way its applied.

The above is about all I know about soaring birds: I'm no
ornithologist or naturalist. My background is chemistry, competitive
free flight model flying and, latterly, soaring.

I've heard a number of theories about how birds detect thermals
including that they hear them. I'd well believe that, with a nerve on
each feather, they must *really* feel the air and all its
micro-turbulence. Maybe they can hear it too. However, that tells
something about how they work 'normal' thermals but not a lot about
how they can find and work the very weak, smooth lift you get early
and late in the day. We know that migratory birds have a excellent
directional sense so why shouldn't a soaring bird have a built-in
vario too? I'd love to know how it works.

If you haven't read it, find a copy of Philip Wills' "On Being A
Bird". There's a chapter about flying with vultures in South Africa
and how he worked just how vultures operate - altitudes, spacing, food
finding strategy etc. The whole book is a good read too.

--
martin@ : Martin Gregorie
gregorie : Harlow, UK
demon :
co : Zappa fan & glider pilot
uk :

[Derrick Steed]

>Martin Gregorie wrote:
>
>I've noticed that gulls joining a thermal will almost always circle
>the same way as the birds or gliders already in it. I've had them join
>me when I was the sole occupant of the thermal and they have always
>respected my turn direction. I wish I could say the same about the
>small raptors around Cambridgeshire - they often join going the wrong
>way and keep a pretty poor lookout too.
>
>--

I've found the same with buzzards, I had one in the same thermal with me
once and I was catching him up - when I got to his(her?) level eventually
our circles almost coincided and I watched as his/her flight path headed
towards my upper wing expecting the raptor to break off well before being
clouted by the wing. To my intense alarm (I suppose I was being a bit
unwary) the bird was only a few yards away from my wing when it was
literally startled by the approaching wing of my glider folded its wings,
did a back flip and just missed the imminent collision.

I'm a bit more wary now.

Rgds,

Derrick Steed

[Derrick Steed]

>Pardon this input from an uninformed intruder to this subject, but why
couldn't
>birds simply sense how strong the lift is by the amount of stress it puts
on
>their "airframe". When I pump iron, I'm all too aware of the amount of
effort
>required. Surely birds can do the same.
>
>Ted Frost
>Soaring Society of Boulder
>
The stress would only change when acceleration was present (as in entering a
thermal, we use our bums for for that - transitting from an area of intense
sink to and area of lesser sink: e.g. no thermal). In a steady climb the
stress wouldn't change and would be the same as in normal turning flight. I
suspect that Martin's observation about the birds choosing a more extreme
dihedral has more to do with lack of effort than sensing the lift intensity
- a high dihedral result and a high value of lateral stability, but poor
efficiency of the wing.

Rgds,

Derrick Steed

[Andy Blackburn]

Stress, or G-loading, is a measure of acceleration.
As such it allows birds (or pilots!) to sense changes
in the rate of climb, but not the climb rate itself
(which we all know is a velocity, not an acceleration).
I would imagine that birds can use these changes in
acceleration to help find the center of a small thermal
in some cases, but it might be less helpful in larger,
more uniform bands of lift where the ability to integrate
the cumulative acceleration effects over time is more
difficult.

A falconer at the Parowan regionals last week told
us that soaring birds have sensory organs that are
able to measure the pressure differential between the
outside air and inside their hollow bones. I have not
been able to confirm this, but it would seem to make
sense - think of the bones as capacity bottles.

Any bird experts out there?

9B



At 19:48 04 July 2004, Martin Gregorie wrote:
>On 04 Jul 2004 18:48:04 GMT,
>(Frostowits)
>wrote:
>
>>Pardon this input from an uninformed intruder to this
>>subject, but why couldn't
>>birds simply sense how strong the lift is by the amount
>>of stress it puts on
>>their 'airframe'. When I pump iron, I'm all too aware
>>of the amount of effort
>>required. Surely birds can do the same.
>>
>Some seem to do just that. Kites in particular. I used
>to watch them a
>lot in India and discovered that you can tell how strong
>the lift is
>by looking at them - the stronger it is the more dihedral
>they use. If
>its really strong they just bomb round with a steep
>V-form and their
>tip feathers closed. Weaker lift gets more care and
>attention, less
>dihedral and more open tip feathers. When they're really
>scratching
>their wings are flat or even a little anhedralled and
>the tip feathers
>are fully spread and up to give tip dihedral. They
>initiate a turn
>with a big dab of negative in the inner tip and then
>control the turn
>on tail tilt - the outer tail tip is raised, so you
>can tell that
>they fly like we do with down force on the tail. Kites
>are easy to
>read because they often work low altitude lift where
>you can see
>exactly what they are doing and have big, long tails
>that are easy to
>observe.
>
>I wondered about how vultures fly but they were so
>seldom low enough
>to really watch that I couldn't work out very much.
>Also, with much
>shorter tails than kites its difficult to see whether
>they use tail
>tilt at all or which way its applied.
>
>The above is about all I know about soaring birds:
>I'm no
>ornithologist or naturalist. My background is chemistry,
>competitive
>free flight model flying and, latterly, soaring.
>
>I've heard a number of theories about how birds detect
>thermals
>including that they hear them. I'd well believe that,
>with a nerve on
>each feather, they must *really* feel the air and all
>its
>micro-turbulence. Maybe they can hear it too. However,
>that tells
>something about how they work 'normal' thermals but
>not a lot about
>how they can find and work the very weak, smooth lift
>you get early
>and late in the day. We know that migratory birds have
>a excellent
>directional sense so why shouldn't a soaring bird have
>a built-in
>vario too? I'd love to know how it works.
>
>If you haven't read it, find a copy of Philip Wills'
>'On Being A
>Bird'. There's a chapter about flying with vultures
>in South Africa
>and how he worked just how vultures operate - altitudes,
>spacing, food
>finding strategy etc. The whole book is a good read
>too.
>
>--
>martin@ : Martin Gregorie
>gregorie : Harlow, UK
>demon :
>co : Zappa fan & glider pilot
>uk :
>
>

[Uri Saovray]

Yes, but could you hear their varios beep?

Derrick Steed > wrote in message >...
> It's a well known fact that birds bones are very light and filled with
> holes, just like we have sinuses in our head bones. I've pondered how birds
> might sense rate of climb many times and I now hold the view that they sense
> it via the cavities in their bones - this would provide them with a very
> sensitive variometer, the capacity being automatically incorporated so to
> speak.
>
> I'm also convinced that birds soar for pleasure as well as because they
> might have to (e.g. Pelicans soar when they are migrating and follow similar
> climb/glide patterns to us).
>
> I once observed a seagull from the restaurant at the top of the OMPI
> building in Geneva - a seagull was already soaring near the ITU building
> when suddenly another shot past the window in a fast glide headed straight
> for a point below the other seagull, when it got there it pulled up into the
> climb underneath the other gull turning in the same direction. Obviously
> his/her CSI (Chief Seagull Instructor) had made the point about proper
> thermal entry.
>
> Rgds,
>
> Derrick Steed
> >Does anyone have an idea of how the birds know where to thermal? Do
> >they have a vario? Where is it? Where is its capacity?
> >Assuming they breath while thermalling, then I doubt they use their
> >lungs as capacity... or maybe they stop and sense the air coming out
> >their noses.
> >Just wondering...
> >
> >Uri 4XGJC
> >
> > (Andy Durbin) wrote in
> message
> >news:...
> >> "Bill Daniels" wrote in message news:...
> >> >
> >> > Most hawks circling low are looking for rodents, not lift.
> >> >
> >> > Bill Daniels
> >>
> >>
> >> But many times I have shared thermals with Hawks at high altitude.
> >> How did they get there if not by working thermals at low altitude? I
> >> have never been in a thermal with a Red Tailed Hawk that didn't seem
> >> to be trying to optimize climb rate. Turkey Vultures are a different
> >> story. They seem to be happy with any sloppy thermal technique as
> >> long as they maintain altitude.
> >>
> >>
> >> Andy
>
> >>

[Martin Gregorie]

On 4 Jul 2004 20:39:04 GMT, Andy Blackburn
> wrote:

>Any bird experts out there?
>
While still in India I met a German lass who was an ornithologist and
in India do a PhD on vultures. Naturally, I asked her about their
flight performance. She just looked at me like I was a dinosaur: she
knew nothing and cared less about their flight performance or
operating methods. All she was interested in was stuff like population
densities, diet and their behaviour when not flying. I found her
attitude most odd.

That was 25 years ago so things, hopefully, might have improved in
ornithological circles.

So, pick your bird expert carefully before asking about how birds fly.

BTW, a good book about flight in general (literally from insects to
747s) is 'The Simple Science Of Flight' by Henk Tennekes. It won't
tell you how raptors find lift but has a good analysis of how flying
creatures size and weight affect their way of making a living and vice
versa. Besides, any book on flight that can sensibly show everything
from a Monarch Butterfly to a 747-400 on the same graph can't be all
bad!



--
martin@ : Martin Gregorie
gregorie : Harlow, UK
demon :
co : Zappa fan & glider pilot
uk :

[Marian Aldenhövel]

Hi,

> Does anyone have an idea of how the birds know where to thermal? Do
> they have a vario? Where is it?

How about simple inertia?

They may sense the vertical acceleration. Humans do so too,
but they cannot integrate the information well over time. Varios
fix that fault just like attitude indicators fix the problem of
spatial orientation.

birds propably have evolved to work more exactly in this aspect.

Ciao, MM
--
Marian Aldenhövel, Rosenhain 23, 53123 Bonn.
Fon +49 228 624013, Fax +49 228 624031.
http://www.marian-aldenhoevel.de
"Wie trennt man drei Schlampen von zwei Säufern? Cockpittüre zu!"

[Peter Harvey]

I'm no bird expert, but did 20 years competing hang
gliding around the world, before really getting into
gliding.
Hang gliders mixed with (soaring) birds far more than
sailplanes. Probably a performance thing.

The birds seem to do different things depending upon
the task at hand.
IE: want to gain height quick - they'll be in the best
core or thermal within the vicinity. Want to go somewhere-
they'll be heading towards the next thermal that optimises
their route. Want to 'hang out' they'll be in any old
lift.
I witnessed the whole USA hang gliding team joining
a flock of circling Orubu in Brazil. They all landed
next to the dead cow.
Larger raptors can be more territorial and therefore
don't have the same choice on area, thus might put
up with inferior lift.
Storks just seem to follow the leader.
Swifts and Swallows are almost always in good cores,
but I haven't a clue how they transit between thermals
so quickly.

The soaring birds not only find the best cores, but
seem to very quickly know where the next thermal is.
Many times I've watched their transiting direction
- always dead straight - and altered my course to intercept
or get ahead. It usually works.

When we fly a lot, we pick up those extra sensory inputs
- the micro turbulence, the twitch of the wing - it
gives us huge amounts of info if we're open to it.
By the end of the soaring season, I've sometimes just
known where the core was by feel - which way to turn,
etc. I don't know how - just intuitive. Birds fly all
the time, so should be totally tuned in.
Lastly, I'm sure they plot sink. We tend to focus on
lift, whereas, of course, it's just a part of the equation.
If you know where the sink is, then happy days, avoid
it!
Pete Harvey

>A falconer at the Parowan regionals last week told
>us that soaring birds have sensory organs that are
>able to measure the pressure differential between the
>outside air and inside their hollow bones. I have not
>been able to confirm this, but it would seem to make
>sense - think of the bones as capacity bottles.
>
>Any bird experts out there?

[tango4]

Vultures are amazing *pilots*. The ones around the Magalies gliding club in
SA are known to range as far as the Kruger National Park, over 200 km away.
I've flown with them at cloudbase as high as 14 000', had them formate on a
wingtip and once over the shoulder of a Blanik, peering into the rear
cockpit from less than a metre away.

Flying in the Drakensburg one can often end up with 30 or more birds in a
big thermal or fly in formation with a group of them along the cliff faces.

Ian





"Martin Gregorie" > wrote in message
...
> On 04 Jul 2004 18:48:04 GMT, (Frostowits)
> wrote:
>
> >Pardon this input from an uninformed intruder to this subject, but why
couldn't
> >birds simply sense how strong the lift is by the amount of stress it puts
on
> >their "airframe". When I pump iron, I'm all too aware of the amount of
effort
> >required. Surely birds can do the same.
> >
> Some seem to do just that. Kites in particular. I used to watch them a
> lot in India and discovered that you can tell how strong the lift is
> by looking at them - the stronger it is the more dihedral they use. If
> its really strong they just bomb round with a steep V-form and their
> tip feathers closed. Weaker lift gets more care and attention, less
> dihedral and more open tip feathers. When they're really scratching
> their wings are flat or even a little anhedralled and the tip feathers
> are fully spread and up to give tip dihedral. They initiate a turn
> with a big dab of negative in the inner tip and then control the turn
> on tail tilt - the outer tail tip is raised, so you can tell that
> they fly like we do with down force on the tail. Kites are easy to
> read because they often work low altitude lift where you can see
> exactly what they are doing and have big, long tails that are easy to
> observe.
>
> I wondered about how vultures fly but they were so seldom low enough
> to really watch that I couldn't work out very much. Also, with much
> shorter tails than kites its difficult to see whether they use tail
> tilt at all or which way its applied.
>
> The above is about all I know about soaring birds: I'm no
> ornithologist or naturalist. My background is chemistry, competitive
> free flight model flying and, latterly, soaring.
>
> I've heard a number of theories about how birds detect thermals
> including that they hear them. I'd well believe that, with a nerve on
> each feather, they must *really* feel the air and all its
> micro-turbulence. Maybe they can hear it too. However, that tells
> something about how they work 'normal' thermals but not a lot about
> how they can find and work the very weak, smooth lift you get early
> and late in the day. We know that migratory birds have a excellent
> directional sense so why shouldn't a soaring bird have a built-in
> vario too? I'd love to know how it works.
>
> If you haven't read it, find a copy of Philip Wills' "On Being A
> Bird". There's a chapter about flying with vultures in South Africa
> and how he worked just how vultures operate - altitudes, spacing, food
> finding strategy etc. The whole book is a good read too.
>
> --
> martin@ : Martin Gregorie
> gregorie : Harlow, UK
> demon :
> co : Zappa fan & glider pilot
> uk :
>

[Derrick Steed]

Uri Saovray wrote:
>Yes, but could you hear their varios beep?
>

Don't be silly, have you ever seen a bird carrying batteries?

Rgds,

Derrick Steed

[Derrick Steed]

Take a look at Darryl Stinton's book "The design of the aeroplane" - there
is a captioned picture in the front of it showing a gull (an Albatross, I
think) soaring a cliff in front of the camera. The caption points out
aerodynamic function of various parts of the birds anatomy in a most
enlightening manner! I don't have the book in my possession right now (I
loaned it to the CFI of a local club, I should get it back I suppose) or I
would post the picture and it's caption.

Rgds,

Derrick Steed
>On 4 Jul 2004 20:39:04 GMT, Andy Blackburn
>wrote:
>
>Any bird experts out there?
>
>While still in India I met a German lass who was an ornithologist and
>in India do a PhD on vultures. Naturally, I asked her about their
>flight performance. She just looked at me like I was a dinosaur: she
>knew nothing and cared less about their flight performance or
>operating methods. All she was interested in was stuff like population
>densities, diet and their behaviour when not flying. I found her
>attitude most odd.
>
>That was 25 years ago so things, hopefully, might have improved in
>ornithological circles.
>
>So, pick your bird expert carefully before asking about how birds fly.
>
>BTW, a good book about flight in general (literally from insects to
>747s) is 'The Simple Science Of Flight' by Henk Tennekes. It won't
>tell you how raptors find lift but has a good analysis of how flying
>creatures size and weight affect their way of making a living and vice
>versa. Besides, any book on flight that can sensibly show everything
>from a Monarch Butterfly to a 747-400 on the same graph can't be all
>bad!
>

[Gary Evans]

Our understanding of the reason/s for a bird’s excellent
soaring ability continues to be severely hampered by
the lack of progress in establishing verbal communications.
Perhaps a species that can fly through a thicket and
sleep on a branch do not consider it worth their time.



At 20:54 04 July 2004, Andy Blackburn wrote:
>Stress, or G-loading, is a measure of acceleration.
>As such it allows birds (or pilots!) to sense changes
>in the rate of climb, but not the climb rate itself
>(which we all know is a velocity, not an acceleration).
>I would imagine that birds can use these changes in
>acceleration to help find the center of a small thermal
>in some cases, but it might be less helpful in larger,
>more uniform bands of lift where the ability to integrate
>the cumulative acceleration effects over time is more
>difficult.
>
>A falconer at the Parowan regionals last week told
>us that soaring birds have sensory organs that are
>able to measure the pressure differential between the
>outside air and inside their hollow bones. I have not
>been able to confirm this, but it would seem to make
>sense - think of the bones as capacity bottles.
>
>Any bird experts out there?
>
>9B
>
>
>
>At 19:48 04 July 2004, Martin Gregorie wrote:
>>On 04 Jul 2004 18:48:04 GMT,
>>(Frostowits)
>>wrote:
>>
>>>Pardon this input from an uninformed intruder to this
>>>subject, but why couldn't
>>>birds simply sense how strong the lift is by the amount
>>>of stress it puts on
>>>their 'airframe'. When I pump iron, I'm all too aware
>>>of the amount of effort
>>>required. Surely birds can do the same.
>>>
>>Some seem to do just that. Kites in particular. I used
>>to watch them a
>>lot in India and discovered that you can tell how strong
>>the lift is
>>by looking at them - the stronger it is the more dihedral
>>they use. If
>>its really strong they just bomb round with a steep
>>V-form and their
>>tip feathers closed. Weaker lift gets more care and
>>attention, less
>>dihedral and more open tip feathers. When they're really
>>scratching
>>their wings are flat or even a little anhedralled and
>>the tip feathers
>>are fully spread and up to give tip dihedral. They
>>initiate a turn
>>with a big dab of negative in the inner tip and then
>>control the turn
>>on tail tilt - the outer tail tip is raised, so you
>>can tell that
>>they fly like we do with down force on the tail. Kites
>>are easy to
>>read because they often work low altitude lift where
>>you can see
>>exactly what they are doing and have big, long tails
>>that are easy to
>>observe.
>>
>>I wondered about how vultures fly but they were so
>>seldom low enough
>>to really watch that I couldn't work out very much.
>>Also, with much
>>shorter tails than kites its difficult to see whether
>>they use tail
>>tilt at all or which way its applied.
>>
>>The above is about all I know about soaring birds:
>>I'm no
>>ornithologist or naturalist. My background is chemistry,
>>competitive
>>free flight model flying and, latterly, soaring.
>>
>>I've heard a number of theories about how birds detect
>>thermals
>>including that they hear them. I'd well believe that,
>>with a nerve on
>>each feather, they must *really* feel the air and all
>>its
>>micro-turbulence. Maybe they can hear it too. However,
>>that tells
>>something about how they work 'normal' thermals but
>>not a lot about
>>how they can find and work the very weak, smooth lift
>>you get early
>>and late in the day. We know that migratory birds have
>>a excellent
>>directional sense so why shouldn't a soaring bird have
>>a built-in
>>vario too? I'd love to know how it works.
>>
>>If you haven't read it, find a copy of Philip Wills'
>>'On Being A
>>Bird'. There's a chapter about flying with vultures
>>in South Africa
>>and how he worked just how vultures operate - altitudes,
>>spacing, food
>>finding strategy etc. The whole book is a good read
>>too.
>>
>>--
>>martin@ : Martin Gregorie
>>gregorie : Harlow, UK
>>demon :
>>co : Zappa fan & glider pilot
>>uk :
>>
>>
>
>
>
>

[Gill Couto]

Darwin would say the ones that didn't thermal too well didn't
survive, didn't reproduce, and simply missed out on some good
airtime for generations to follow. The birds that acquired the
insight to locate updrafts gained the same advantage we seek: xc
distance. Soaring birds are usually larger than others, maybe good
thermaling skills means better meals. They still need to survive
winters with fewer, weaker thermals by other means.

gill
www.gillcouto.com


Uri Saovray wrote:
> Does anyone have an idea of how the birds know where to thermal? Do
> they have a vario? Where is it? Where is its capacity?
> Assuming they breath while thermalling, then I doubt they use their
> lungs as capacity... or maybe they stop and sense the air coming out
> their noses.
> Just wondering...
>
> Uri 4XGJC

[Silent Flyer]

> >
> > I'm also convinced that birds soar for pleasure as well as because they
> > might have to

Earlier this year sitting in my garden on a hot windless day, I watched a
Buzzard pick up a thermal over a small local wood and climb until it was a
speck in the sky. It then closed its wings and dived at great speed until it
was about fifty feet above the ground, pulled out and then proceeded to
climb again. It repeated the climb, dive, climb manoeuvre three times before
I went indoors. Surely that could not have been for anything other than
pleasure ?

DB

[Don Johnstone]

More likely it was stooping for prey which moved to
cover or perhaps a mating display. (Showing off, nothing
new there then :-))

Most birds of prey (owls excepted) use thermals as
a source of free energy to be able to observe prey.
Captive birds of prey will not fly if they are 'not
hungry', in need of food and if they eat and become
over a certain weight flight becomes difficult or even
impossible for them. (Anyone know the maximum all up
weight of a swallow)

At 09:12 05 July 2004, Silent Flyer wrote:
>
>> >
>> > I'm also convinced that birds soar for pleasure as
>>>well as because they
>> > might have to
>
>Earlier this year sitting in my garden on a hot windless
>day, I watched a
>Buzzard pick up a thermal over a small local wood and
>climb until it was a
>speck in the sky. It then closed its wings and dived
>at great speed until it
>was about fifty feet above the ground, pulled out and
>then proceeded to
>climb again. It repeated the climb, dive, climb manoeuvre
>three times before
>I went indoors. Surely that could not have been for
>anything other than
>pleasure ?
>
>DB
>
>
>

[J.M. Farrington]

"Don Johnstone" wrote in
> More likely it was stooping for prey which moved to
> cover or perhaps a mating display. (Showing off, nothing
> new there then :-))
>
As Buzzards are carrion eaters I doubt if it was chasing it very far.

John

[Don Johnstone]

Sorry to be pedantic, but not exclusively, Buzzards
can and do take live coneys and rats, I have witnessed
them doing so. Are you sure you are not confusing them
with Kites which are almost exclusively carrion eaters.


At 12:36 05 July 2004, J.M. Farrington wrote:
>
>'Don Johnstone' wrote in
>> More likely it was stooping for prey which moved to
>> cover or perhaps a mating display. (Showing off, nothing
>> new there then :-))
>>
>As Buzzards are carrion eaters I doubt if it was chasing
>it very far.
>
>John
>
>
>

[Marcel Duenner]

"Silent Flyer" ]> wrote in message >...
> > >
> > > I'm also convinced that birds soar for pleasure as well as because they
> > > might have to
>
> Earlier this year sitting in my garden on a hot windless day, I watched a
> Buzzard pick up a thermal over a small local wood and climb until it was a
> speck in the sky. It then closed its wings and dived at great speed until it
> was about fifty feet above the ground, pulled out and then proceeded to
> climb again. It repeated the climb, dive, climb manoeuvre three times before
> I went indoors. Surely that could not have been for anything other than
> pleasure ?
>
> DB

Definitely not. I have watched similar behaviour many times. One
particular time I was climbing under an nice fat cu where three
buzzards were climbing in to the cloud out of sight and then diving
out of it about five seconds later, over and over again.

Marcel
-------------
Why walk when you can soar?

[Bob]

> impossible for them. (Anyone know the maximum all up
> weight of a swallow)

Would that be an African or European swallow?

[Mike Lindsay]

In article >, Uri Saovray
> writes
>Does anyone have an idea of how the birds know where to thermal? Do
>they have a vario? Where is it? Where is its capacity?
>Assuming they breath while thermalling, then I doubt they use their
>lungs as capacity... or maybe they stop and sense the air coming out
>their noses.
>Just wondering...
>
>Uri 4XGJC
>
Its a long time since I did any comparative anatomy, but I believe many
birds have air filled cavities in some of their bones.

While on the subject of birds using thermals, the German expedition to
the Andes (1937) decided to bring some raptors birds back to Germany,
the idea being they would find thermals for them. During the voyage back
they were of course kept in cages and fed by the crew. And everyone
else.

When the ship docked in Bremen, the birds had got so heavy they couldn't
get airborne.

From a biography of Hanna Reich.
--
Mike Lindsay

[Mark James Boyd]

Can birds sense pressure changes? Maybe they have bio-varios.
I've noticed they seem to chirp, even on gloomy mornings,
when I have noticed pressure rising on the
altimeter or baro. It wouldn't surprise me if
this was true, but I haven't heard of any studies...

So I'm guessing maybe they know they are
climbing from vario alone...

In article >,
Derrick Steed > wrote:
>>Pardon this input from an uninformed intruder to this subject, but why
>couldn't
>>birds simply sense how strong the lift is by the amount of stress it puts
>on
>>their "airframe". When I pump iron, I'm all too aware of the amount of
>effort
>>required. Surely birds can do the same.
>>
>>Ted Frost
>>Soaring Society of Boulder
>>
>The stress would only change when acceleration was present (as in entering a
>thermal, we use our bums for for that - transitting from an area of intense
>sink to and area of lesser sink: e.g. no thermal). In a steady climb the
>stress wouldn't change and would be the same as in normal turning flight. I
>suspect that Martin's observation about the birds choosing a more extreme
>dihedral has more to do with lack of effort than sensing the lift intensity
>- a high dihedral result and a high value of lateral stability, but poor
>efficiency of the wing.
>
>Rgds,
>
>Derrick Steed
>
>
>
>


--

------------+
Mark Boyd
Avenal, California, USA

[Uri Saovray]

So, if the experiment had them sense the altitude in a pressure
chamber, and if whatever they use for thermalling is the same as
sensing altitude, this precludes all the "G-force" and vertical
accelerometers theories mentioned here: you can fool a vario in a
stationary pressure chamber, but not an accelerometer ...
Going back to the ears: do birds' ears connect to the nasal cavity and
from there to the lungs, like our own ears? If so - could they "hold
their breath" for a short while and sense the air escaping or rushing
in to their lungs through any orifice in the ear? Even without a hole
in their ear, maybe they can sense the increasing or decreasing
pressure on their eardrums (much like we can feal air pressure when we
"pump" our ears)? I would think the lung capacity is much larger than
the total volume of the bone "hollows".
I guess more information on bird anatomy is needed here.

Uri - 4XGJC

Jim Skydell > wrote in message >...
> > It's a well known fact that birds bones are very light and filled with
> > holes, just like we have sinuses in our head bones. I've pondered how birds
> > might sense rate of climb many times and I now hold the view that they sense
> > it via the cavities in their bones - this would provide them with a very
> > sensitive variometer, the capacity being automatically incorporated so to
> > speak.
>
> Some work was done in the early 70's on this. Whatever a bird's "vario" is, it resides in
> their ear. Cutting the 8th cranial nerves (which connect the ear to the brain)
> extinguished their ability to sense altitude. This work was done in pigeons, (not soaring
> birds, who would be expected to have an even better "vario"). Further work (done in a
> pressure chamber) indicated that even a pigeon can sense an ambient pressure change
> equivalent to climbing 2 feet.
> >
> > I'm also convinced that birds soar for pleasure as well as because they
> > might have to (e.g. Pelicans soar when they are migrating and follow similar
> > climb/glide patterns to us).
>
> Other research done in the 70's was carried out by a glider pilot in Africa. He wanted to
> figure out where all the buzzards went during the middle of the afternoon (all would
> disappear every day). They thermaled up, out of sight from the ground. Either for
> pleasure,or to cool off?

[Derrick Steed]

Uri Saovray wrote:
>So, if the experiment had them sense the altitude in a pressure
>chamber, and if whatever they use for thermalling is the same as
>sensing altitude, this precludes all the "G-force" and vertical
>accelerometers theories mentioned here: you can fool a vario in a
>stationary pressure chamber, but not an accelerometer ...
>
But you CAN fool an accelerometer in a uniformly ascending mass of air, but
not a vario...

Rgds,

Derrick Steed

[Marian Aldenhövel]

Hi,

> But you CAN fool an accelerometer in a uniformly ascending mass of air, but
> not a vario...

How? You have to enter that mass of air at some point and there you
will record the acceleration.

Ciao, MM
--
Marian Aldenhövel, Rosenhain 23, 53123 Bonn.
Fon +49 228 624013, Fax +49 228 624031.
http://www.marian-aldenhoevel.de
"Wie trennt man drei Schlampen von zwei Säufern? Cockpittüre zu!"

[Lorry Charchian]

Derrick Steed > wrote in message >...
> Uri Saovray wrote:
> >So, if the experiment had them sense the altitude in a pressure
> >chamber, and if whatever they use for thermalling is the same as
> >sensing altitude, this precludes all the "G-force" and vertical
> >accelerometers theories mentioned here: you can fool a vario in a
> >stationary pressure chamber, but not an accelerometer ...
> >
> But you CAN fool an accelerometer in a uniformly ascending mass of air, but
> not a vario...
>
> Rgds,
>
> Derrick Steed

I have just started to read this thread and became interested in the
various theories on how birds sense thermals. I would like to quote
from Phillip Wills well known book "On Being A Bird" where he contends
that soaring birds hear thermals. He goes on to say that "the birds
ear drum is anchored from the opposite side (from that of man) so is
streched by decreasing pressure, thus in all likehood giving him a
sensation when he climbs." For those interested this is from page 29
Paragraph 3. If you haven't read this book, shame on you!

Lorry Charchian (LJ)

[Derrick Steed]

Rgds,
I did say "uniformly ascending mass of air", I didn't say how one got there. For the given condition it's just a statement of Newton's first law.

If you've done any relativity, you'll know that the twins paradox in special relativity suffers from the same problem.

Derrick Steed
Hi,

>> But you CAN fool an accelerometer in a uniformly ascending mass of air, but
>> not a vario...
>
>How? You have to enter that mass of air at some point and there you
>will record the acceleration.
>
>Ciao, MM
>--
>Marian Aldenhövel, Rosenhain 23, 53123 Bonn.
>Fon +49 228 624013, Fax +49 228 624031.
>http://www.marian-aldenhoevel.de <http://www.marian-aldenhoevel.de>
>"Wie trennt man drei Schlampen von zwei Säufern? Cockpittüre zu!"

[Bill Gribble]

Bob > writes
>> impossible for them. (Anyone know the maximum all up
>> weight of a swallow)
>
>Would that be an African or European swallow?

Albatross! Get your fresh albatross here!

Hmm... Perhaps it's too early in the morning for such abstract,
serpentine humour :P

[Marian Aldenhövel]

Hi,

> I did say "uniformly ascending mass of air", I didn't say how one got there.

All right. If you put an accelerometer in an ascending mass of air and
then, when it moves with that mass of air, read it, it will show zero.
I concede that :-).

But that is the same thing as saying a vario will read zero when the
pressure around it is not changing.

I cannot quite understand how that relates to "fooling" an
accelerometer. There is no way to get it from lying on the ground
to moving with the uniformly ascending mass of air without it showing
a non-zero value at some point in time.

So, if birds can be made to believe that they are changing altitude by
putting them in a pressure chamber and changing ambient pressure, then
I think accelerometers as sensors are indeed ruled out. At least as
singular source of input.

In these experiments how does one know that the bird thinks it is
climbing or descending? If you put a human into the same chamber it
will likely notice a change in pressure, even if not as small a
change as the bird. But we are rarely able to tell which way, much
less relate the relative change in pressure to absolute change in
altitude.

Designing an experiment where one can make sure the bird translates
pressure change to altitude seems hard to me.

Ciao, MM
--
Marian Aldenhövel, Rosenhain 23, 53123 Bonn.
Fon +49 228 624013, Fax +49 228 624031.
http://www.marian-aldenhoevel.de
"Wie trennt man drei Schlampen von zwei Säufern? Cockpittüre zu!"

[Don Johnstone]

At 09:36 06 July 2004, Marian_Aldenhövel wrote: (snip)

>will likely notice a change in pressure, even if not
>as small a
>change as the bird. But we are rarely able to tell
>which way, much
>less relate the relative change in pressure to absolute
>change in
>altitude.

We can detect which way the pressure is changing but
the rate of change has to be large for us to do it.
( Hold nose on way down and blow to push the eardrum
out as pressure increases and hold nose and swallow
when climbing, and before someone says that is not
a good thing to do I know. Birds appear much more sensitive
to the change in pressure.
>
>Designing an experiment where one can make sure the
>bird translates
>pressure change to altitude seems hard to me.

I don't think anyone was saying that birds use the
pressure change to measure altitude, as an altimeter,
but they do appear to use it as we do a vario. I don't
think birds worry whether they are at the correct flight
level or above transition altitude even. A vario works
by measuring small changes in air pressure.

>Ciao, MM
>--
>Marian Aldenhövel, Rosenhain 23, 53123 Bonn.
>Fon +49 228 624013, Fax +49 228 624031.
>http://www.marian-aldenhoevel.de
>'Wie trennt man drei Schlampen von zwei Säufern? Cockpittüre
>zu!'
>

[CV]

Martin Gregorie wrote:
> On 04 Jul 2004 18:48:04 GMT, (Frostowits)
> wrote:
>>Pardon this input from an uninformed intruder to this subject, but why couldn't
>>birds simply sense how strong the lift is by the amount of stress it puts on
>>their "airframe". When I pump iron, I'm all too aware of the amount of effort
>>required. Surely birds can do the same.

Well, the stress only occurs briefly on entry into the thermal,
when you have upward acceleration. Once established in the climb,
assuming it is more or less smooth, you no longer have acceleration
nor any acceleration generated stress forces so you need some other
means of knowing whether you are still climbing, such as rate of
pressure change, which is what the vario measures.

cheers CV

[Jim Vincent]

>assuming it is more or less smooth, you no longer have acceleration
>nor any acceleration generated stress forces so you need some other
>means of knowing whether you are still climbing, such as rate of
>pressure change, which is what the vario measures

If the rate of climb is not changing, then there is no acceleration. If the
climb rate reduces, than there will be an acceleration in the negative (down)
direction. The rate of change of velocity is the acceleration:
dV/dt=acceleration.

Jim Vincent
N483SZ

[Bill Daniels]

It's pretty well established that soaring birds have extremely good
eyesight. I think they just see the ground moving away when they are
climbing. Thermals also have a lot of stuff in them like insects and seeds.
The birds are probably able to see these rising at a considerable distance

There's a lot of visual cues while thermalling. If you are trying to thermal
near a mountain peak it's easy to see the glider rise at the onset of lift.
The varios will signal lift two or three seconds later.

BTW, that story about the USA hang glider team chasing buzzards and landing
next to a dead cow is really funny.

Bill Daniels



"Derrick Steed" > wrote in message
...
> It's a well known fact that birds bones are very light and filled with
> holes, just like we have sinuses in our head bones. I've pondered how
birds
> might sense rate of climb many times and I now hold the view that they
sense
> it via the cavities in their bones - this would provide them with a very
> sensitive variometer, the capacity being automatically incorporated so to
> speak.
>
> I'm also convinced that birds soar for pleasure as well as because they
> might have to (e.g. Pelicans soar when they are migrating and follow
similar
> climb/glide patterns to us).
>
> I once observed a seagull from the restaurant at the top of the OMPI
> building in Geneva - a seagull was already soaring near the ITU building
> when suddenly another shot past the window in a fast glide headed straight
> for a point below the other seagull, when it got there it pulled up into
the
> climb underneath the other gull turning in the same direction. Obviously
> his/her CSI (Chief Seagull Instructor) had made the point about proper
> thermal entry.
>
> Rgds,
>
> Derrick Steed
> >Does anyone have an idea of how the birds know where to thermal? Do
> >they have a vario? Where is it? Where is its capacity?
> >Assuming they breath while thermalling, then I doubt they use their
> >lungs as capacity... or maybe they stop and sense the air coming out
> >their noses.
> >Just wondering...
> >
> >Uri 4XGJC
> >
> > (Andy Durbin) wrote
in
> message
> >news:...
> >> "Bill Daniels" wrote in message news:...
> >> >
> >> > Most hawks circling low are looking for rodents, not lift.
> >> >
> >> > Bill Daniels
> >>
> >>
> >> But many times I have shared thermals with Hawks at high altitude.
> >> How did they get there if not by working thermals at low altitude? I
> >> have never been in a thermal with a Red Tailed Hawk that didn't seem
> >> to be trying to optimize climb rate. Turkey Vultures are a different
> >> story. They seem to be happy with any sloppy thermal technique as
> >> long as they maintain altitude.
> >>
> >>
> >> Andy
> >
> >>
>
>
>
>
>
>

[Graeme Cant]

CV wrote:
>
> Well, the stress only occurs briefly on entry into the thermal,
> when you have upward acceleration. Once established in the climb,
> assuming it is more or less smooth, you no longer have acceleration
> nor any acceleration generated stress forces so you need some other
> means of knowing whether you are still climbing, such as rate of
> pressure change, which is what the vario measures.

Why wouldn't they just _see_ that they are getting higher? The vast
majority of birds operate at altitudes where looking at the ground tells
ME whether I'm climbing or descending accurately enough for all
practical purposes and birds have far better vision than I do. Altitude
measurement by eye would be fine without ATC radar second-guessing you.

I think Martin is probably correct. Humans have a very sensitive g
meter in our leg and body muscles. I suspect that birds have even better
ones in their wing root muscles ('proprio-sensors' from a hazy Biology
101). I would have thought inbuilt stress gauges combined with accurate
vision provided a perfectly possible and very probable set of flight
sensors. Birds probably also have a built in AoA sensor in the tail
muscles which gives control load feedback. AoA may also come from
feedback from feather control muscles, especiallly the pinions. I'd
guess these are integrated with the g sensors.

The visual bit for altitude is quite secondary, I'd guess. Steady state
lift is a theoretical concept, not reality. Lift is constantly varying
and a sensitive stress gauge would always be detecting some change.

When it comes to birds, you have to start with the idea that their
flight system is probably more fundamental than our balance and walking.
I suspect that a bird's flight control system is completely integrated
at a quite deep level. I would guess that the muscle movements to
centre lift are almost directly connected to the muscle feedback that
detects a decrease or increase in lift - and that feedback probably
comes from several different sources.

I think the birds fly like us. By the seat of their pants, visually.

cheers, GC
>
> cheers CV
>

[Martin Gregorie]

On Wed, 07 Jul 2004 23:03:26 +1000, Graeme Cant >
wrote:

>When it comes to birds, you have to start with the idea that their
>flight system is probably more fundamental than our balance and walking.
> I suspect that a bird's flight control system is completely integrated
>at a quite deep level. I would guess that the muscle movements to
>centre lift are almost directly connected to the muscle feedback that
>detects a decrease or increase in lift - and that feedback probably
>comes from several different sources.
>
That's certainly true. We have to learn to stand up and walk as babies
while a colt, for instance, can stand and walk within minutes of
birth. A bird can fly well enough to gain height and steer once it has
fledged and its muscles are developed, so that puts its flight system
closer to a horse's ability to walk than to ours, i.e. at a more
instinctive level.

I'm not saying that they don't learn to fly better or that all birds
are created equal - you only have to watch a flock of gulls soaring a
cliff in light conditions to see that some birds fly much better than
others.

>I think the birds fly like us. By the seat of their pants, visually.
>
Agreed. I just can't imagine having all the information they must get
while flying just flowing in from every nerve. I think I'm envious.

On raptor vision and the story about buzzards climbing to cloud base:
I find it hard to believe that's hunting behaviour and subscribe to
the mating display and/or joy of flight theories:

- I saw an eagle travelling xc in Hungary last year. It went to cloud
base under one cloud and set off dead straight so it was obvious where
it thought it would get its next climb half-way there it evidently ran
into lift and, just like we would, thought "This is good - lets have a
circle". It looked to be a lumpy, multi-cored patch patch and it
evidently really got into finding the strongest bit before really
tightening up and coring it. Doubtless it was thinking "Yes! Got it!"
as it climbed. It eventually left on its original course. I'd rate
this as soaring for fun: the bird was very high to start with and just
plain didn't need the climb.

- Philip Wills observation that the African vultures didn't hunt above
2500 AGL and that they were spaced about a half mile apart (both
distances are the same for metric speakers), so this marked about the
limit of fully acute vision for vultures makes a lot of sense to me.
I'd expect the same to apply to eagles, etc and suspect that the their
acute vision limit is a lot less than 5000 ft cloud base of the story.
Needless to say, they can't hunt from above cloud base in a Cu!
Kestrels hover preferentially at 50-100 feet and when I've seen
harriers and buzzards hunting they've usually been under 500 ft.


--
martin@ : Martin Gregorie
gregorie : Harlow, UK
demon :
co : Zappa fan & glider pilot
uk :

[CV]

Bill Daniels wrote:
> It's pretty well established that soaring birds have extremely good
> eyesight. I think they just see the ground moving away when they are
> climbing.

Good eyesight is one thing, precision at judging distance another,
the latter basically dependent on how far apart your eyes are.

No way can they judge their climb rate based on seeing the ground
moving away.

Thermals also have a lot of stuff in them like insects and seeds.
> The birds are probably able to see these rising at a considerable distance

That could be, and other visual cues as well.

CV

[Bill Daniels]

C'mon, now. Binocular depth perception ends for humans at about 20 feet and
is only really useful up to arms length, yet we can still judge distance
well. Since the bird is moving, they can use dynamic field depth perception
that has nothing to do with interocular distance.

Close one eye and move your head back and forth or up and down. You will
see what I mean. Birds and other small animals are observed to move their
heads constantly to better judge distances.

Ever ride one of those glass elevators (lifts) on the outside of a tall
building? Did you notice how powerful the impression of climbing is?

I still claim that they can see themselves rise away from the ground.
Excellent vision and the experience to use it to the fullest is the likely
explanation. It's the simplest explanation and requires no internal vario.

Bill Daniels


"CV" > wrote in message
...
> Bill Daniels wrote:
> > It's pretty well established that soaring birds have extremely good
> > eyesight. I think they just see the ground moving away when they are
> > climbing.
>
> Good eyesight is one thing, precision at judging distance another,
> the latter basically dependent on how far apart your eyes are.
>
> No way can they judge their climb rate based on seeing the ground
> moving away.
>
> Thermals also have a lot of stuff in them like insects and seeds.
> > The birds are probably able to see these rising at a considerable
distance
>
> That could be, and other visual cues as well.
>
> CV
>

[CV]

Graeme Cant wrote:
> majority of birds operate at altitudes where looking at the ground tells
> ME whether I'm climbing or descending accurately enough for all
> practical purposes

Well, supposing you are flying at 1000 ft and hit a 2 knot
thermal. The distance to the ground would be changing at a
rate of 0,3 per cent per second. It is a little hard to
believe that anyone can detect that by eyesight alone.

Sure, after a while you'll be able to tell you are higher,
when everything is smaller, but that's not quick enough
to help you stay in the thermal.

CV

[CV]

Jim Vincent wrote:

>>assuming it is more or less smooth, you no longer have acceleration
>>nor any acceleration generated stress forces so you need some other
>>means of knowing whether you are still climbing, such as rate of
>>pressure change, which is what the vario measures
>
> If the rate of climb is not changing, then there is no acceleration. If the
> climb rate reduces, than there will be an acceleration in the negative (down)
> direction. The rate of change of velocity is the acceleration:
> dV/dt=acceleration.

That is not much use to us humans though. We have very poor
ability to "integrate" the sense of acceleration over time,
which is very convincingly demonstrated by how quickly we
become disoriented in IMC.

If birds happened to have a higher developed sense for this
than humans, then that could be part of the explanation but
I wouldn't bet on it.

CV

[Ray Payne]

Come on you lot! cant you remember your first flights in gliders without
elec varios? birds do what we all did in the 70s listen, you always hear the
rush close to the centres

[CV]

Graeme Cant wrote:

> I think Martin is probably correct. Humans have a very sensitive g
> meter in our leg and body muscles. I suspect that birds have even better
> ones in their wing root muscles ('proprio-sensors' from a hazy Biology
> 101). I would have thought inbuilt stress gauges combined with accurate
> vision provided a perfectly possible and very probable set of flight
> sensors. Birds probably also have a built in AoA sensor in the tail
> muscles which gives control load feedback. AoA may also come from
> feedback from feather control muscles, especiallly the pinions. I'd
> guess these are integrated with the g sensors.

I think you are on the right tracks here btw. Rather than
just sensing g-forces it might be more important to sense
the difference in force on your left and right respectively,
just like when we are gliding a gust lifting one wing
can give us a hint of where the lift is.

With multiple (g-loads and AoA) sensitivities at various
points of both wings birds may be able to get a "feeling"
for where the edges of the thermal are and center it based
on that.

CV

[Mike Lindsay]

In article >, CV
> writes
>Jim Vincent wrote:
>
>>>assuming it is more or less smooth, you no longer have acceleration
>>>nor any acceleration generated stress forces so you need some other
>>>means of knowing whether you are still climbing, such as rate of
>>>pressure change, which is what the vario measures
>>
>> If the rate of climb is not changing, then there is no acceleration. If the
>> climb rate reduces, than there will be an acceleration in the negative (down)
>> direction. The rate of change of velocity is the acceleration:
>> dV/dt=acceleration.
>
>That is not much use to us humans though. We have very poor
>ability to "integrate" the sense of acceleration over time,
>which is very convincingly demonstrated by how quickly we
>become disoriented in IMC.
>
I can see this thread developing into a discussion of how a non gyro
equipped bird manages to fly in cloud.

Presumably by integrating all the information it's getting from muscle
tension in wing muscles, airspeed from pressure on feathers, and sense
organs in the lining of bone cavities?

--
Mike Lindsay

[Eric Greenwell]

Mike Lindsay wrote:

>
> I can see this thread developing into a discussion of how a non gyro
> equipped bird manages to fly in cloud.
>
> Presumably by integrating all the information it's getting from muscle
> tension in wing muscles, airspeed from pressure on feathers, and sense
> organs in the lining of bone cavities?

Or by discerning sun direction by the brightest area in the cloud?

--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

[Robert Ehrlich]

Martin Gregorie wrote:
>
> On 04 Jul 2004 18:48:04 GMT, (Frostowits)
> wrote:
>
> >Pardon this input from an uninformed intruder to this subject, but why couldn't
> >birds simply sense how strong the lift is by the amount of stress it puts on
> >their "airframe". When I pump iron, I'm all too aware of the amount of effort
> >required. Surely birds can do the same.
> >
> Some seem to do just that.

This doesn't work, as well as the earlier mentionnned feeling of vertical
accelaration. This is because both only give just a "differential"
information, i.e. not the rate of climb, but the change in the rate of
climb. The real rate of climb can only been obtained from this information
by a (mental) integration, but every such value in any domain obtained
by integration from a raw differential input suffers a major deficiency:
errors accumulate in time during this process so that if no other
absolute information is available to determine the correct value at
regular time intervals, the integrated value becomes meaningless.
We all know that the feeling of accelaration is a good hint for
a thermal, but we also check the vario to be sure it is not due
to a high sink becoming very quickly a lower sink not deserving
any circling. And while circling we check with the vario that
the lift is not very slowly vanishing, at a rate at which no
acceleration perception would warn us, and leave the thermal if this
happens.


> ... They initiate a turn
> with a big dab of negative in the inner tip and then control the turn
> on tail tilt - the outer tail tip is raised, so you can tell that
> they fly like we do with down force on the tail.
> ...

A raised tail (or elevator) doesn't mean there is a down force on it.
On our gliders the opposite would rather be true : modern gliders are
tuned so that that there is a zero force on the tail near the best glide
angle of attack, in order to minimize the (induced ) drag due to this
force, and as the airfoils used are unstable, at higher angles of attack
we should have an upward force and a downward force at lower angles
of attack, but the elevator is raised for higher angles of attack
and lowered for lower ones. This is not a contradiction, it just means
than without the move of the elevator, the upward or downward force
on the tail plane would even be higher, so bringing back the angle
of attack to its previous value, i.e. the tail plane fulfils its
stabilizing duty.

[Robert Ehrlich]

Mike Lindsay wrote:
> ...
> Presumably by integrating all the information it's getting from muscle
> tension in wing muscles, airspeed from pressure on feathers, and sense
> organs in the lining of bone cavities?
>

No, integration can't work in the long term because of the
accumulation of errors along time. This is how inertial navigation
systems work, but the integration process is carried with a precision
that no brain can meet, and they need absolute attitude information
from gyros, and nevertheless need recalibration after some time. I
think without the gyros, i.e. obtaining attitude also by integration
of rotational accelerations, the precision would be lost after a few
minutes.

[Martin Gregorie]

On Thu, 08 Jul 2004 17:37:11 +0000, Robert Ehrlich
> wrote:

>A raised tail (or elevator) doesn't mean there is a down force on it.
>
I didn't say "a raised elevator". I was talking about a tail surface
that is tilted laterally in relation to the wing and said "a raised
tip" to describe the direction of tail tilt. Please do me the courtesy
of reading what I wrote before sounding off about it.

If you watch kites for a while its quite obvious that they use a lot
of tail tilt to control a turn once its initiated. A kite maintains
the turn with tail tilt and its always the outer tip that's highest.
That shows there is a down-load on its tail - the tilt generates an
outward component from the down force which in turn keeps the turn
going. If the tail was generating no lift the tail tilt would have no
effect and if it was generating positive lift the inner tip would have
to be raised to maintain the turn, but neither of these are seen
amongst kites.

Tail tilt is a basic part of the Free Flight Model Trim 101 semester:
Trimming models Without Auto-surfaces. The techniques for controlling
glide circle with tail tilt are only applicable to fixed-surface Free
Flight models and are totally inappropriate to any other type of
man-made aircraft, model or full-size. I'd not expect anybody who
hasn't flown free flight models to be aware its implications.

>On our gliders the opposite would rather be true : modern gliders are
>tuned so that that there is a zero force on the tail near the best glide
>angle of attack, in order to minimize the (induced ) drag due to this
>force, and as the airfoils used are unstable, at higher angles of attack
>we should have an upward force and a downward force at lower angles
>of attack, but the elevator is raised for higher angles of attack
>and lowered for lower ones. This is not a contradiction, it just means
>than without the move of the elevator, the upward or downward force
>on the tail plane would even be higher, so bringing back the angle
>of attack to its previous value, i.e. the tail plane fulfils its
>stabilizing duty.
>
All that's quite true but irrelevant to the subject of tail tilt and
its relationship to trimmed tail loads.

--
martin@ : Martin Gregorie
gregorie : Harlow, UK
demon :
co : Zappa fan & glider pilot
uk :

[Martin Gregorie]

On Thu, 08 Jul 2004 19:51:39 +0100, Martin Gregorie
> wrote:

Correcting myself: I wrote:

>The techniques for controlling
>glide circle with tail tilt are only applicable to fixed-surface Free
>Flight models and are totally inappropriate to any other type of
>man-made aircraft, model or full-size.
>
Almost but not entirely correct. Some of the MacCready man-powered
aircraft used foreplane tilt for turning - they were canards, so this
is exactly equivalent to tail tilt. IIRC Gossamer Condor used this
control method and I'm not sure about Gossamer Albatross.

--
martin@ : Martin Gregorie
gregorie : Harlow, UK
demon :
co : Zappa fan & glider pilot
uk :

[Mike Lindsay]

In article >, Robert Ehrlich
> writes
>Mike Lindsay wrote:
>> ...
>> Presumably by integrating all the information it's getting from muscle
>> tension in wing muscles, airspeed from pressure on feathers, and sense
>> organs in the lining of bone cavities?
>>

That's the problem with language.

I suspect you are taking 'integration' to mean the mathematical process.
I meant to convey the idea that the bird gets all this information
together, and the result is that the bird can cloud fly without a visual
input.

--
Mike Lindsay

[Graeme Cant]

Robert Ehrlich wrote:
> Mike Lindsay wrote:
>>...
>>Presumably by integrating all the information it's getting from muscle
>>tension in wing muscles, airspeed from pressure on feathers, and sense
>>organs in the lining of bone cavities?
>>
>
> No, integration can't work in the long term because of the
> accumulation of errors along time.

No Robert. I didn't mean 'integration' and I don't think Mike meant
'integration'. We meant integration. :)

Our integration is not the mathematical opposite of differentiation.
We're simply saying it takes data from all its information sources to
decide what's happening. It doesn't look at each one separately like we
shift from ASI to horizon to vario to altimeter to compass picking up
separate bits of information. With a bird it's all one. It's integrated.

This is how inertial navigation
> systems work, but the integration process is carried with a precision
> that no brain can meet, and they need absolute attitude information
> from gyros, and nevertheless need recalibration after some time. I
> think without the gyros, i.e. obtaining attitude also by integration
> of rotational accelerations, the precision would be lost after a few
> minutes.

Bird fight is not like our flight where what we're doing is totally
alien and has to be (mostly) a conscious process. Birds fly quite
UNconsciously. What they see is "integrated" with what they feel in
their muscles. There is no separate process for "I am entering a
thermal" which is different from "I am in a steady climb". It's all one.

They measure altitude with their eyes as Bill Daniels said. They
'recalibrate' their gyros continuously by looking around. They're not
much better at raw data IMC than we are and lose their 'calibration'
quite quickly in cloud.

Many of the ideas are interesting but I'm with Occam's Razor. Birds fly
like we walk - by looking around to 'calibrate' the inner ear balance
mechanism and feedback from muscles. I can't see a real need for any
other unique mechanism.

.... until we get to intercontinental migration.

GC

[ventus45]

And so could we, if we installed strain gauges along the spars, say at 5
foot intervals, and connected them up to a minicomputer which read them, add
an accelerometer, a standard netto vario setup, a gps, and some fancy
software, and we should be able to create a computer display that will be
able to produce a PPI "map" display of a thermal as we turn, gradually
building up the data, plotting "lift" like contour lines on a map, so we
could soon see where the "core" was, and centre accordingly. A good
research/thesis project for some bright spark at university. Any takers ?

[Mike Lindsay]

In article <40ee83d7@
>Bird fight is not like our flight where what we're doing is totally
>alien and has to be (mostly) a conscious process. Birds fly quite
>UNconsciously. What they see is "integrated" with what they feel in
>their muscles. There is no separate process for "I am entering a
>thermal" which is different from "I am in a steady climb". It's all one.
>
>They measure altitude with their eyes as Bill Daniels said. They
>'recalibrate' their gyros continuously by looking around. They're not
>much better at raw data IMC than we are and lose their 'calibration'
>quite quickly in cloud.
>
Are you sure about this? I have seen birds flying in cloud quite
successfully.

>Many of the ideas are interesting but I'm with Occam's Razor. Birds fly
>like we walk - by looking around to 'calibrate' the inner ear balance
>mechanism and feedback from muscles. I can't see a real need for any
>other unique mechanism.
>
>... until we get to intercontinental migration.
>
>GC
>

--
Mike Lindsay

[Robert Ehrlich]

Graeme Cant wrote:
>
> Robert Ehrlich wrote:
> > Mike Lindsay wrote:
> >>...
> >>Presumably by integrating all the information it's getting from muscle
> >>tension in wing muscles, airspeed from pressure on feathers, and sense
> >>organs in the lining of bone cavities?
> >>
> >
> > No, integration can't work in the long term because of the
> > accumulation of errors along time.
>
> No Robert. I didn't mean 'integration' and I don't think Mike meant
> 'integration'. We meant integration. :)
>
> Our integration is not the mathematical opposite of differentiation.
> We're simply saying it takes data from all its information sources to
> decide what's happening. It doesn't look at each one separately like we
> shift from ASI to horizon to vario to altimeter to compass picking up
> separate bits of information. With a bird it's all one. It's integrated.
>
> This is how inertial navigation
> > systems work, but the integration process is carried with a precision
> > that no brain can meet, and they need absolute attitude information
> > from gyros, and nevertheless need recalibration after some time. I
> > think without the gyros, i.e. obtaining attitude also by integration
> > of rotational accelerations, the precision would be lost after a few
> > minutes.
>
> Bird fight is not like our flight where what we're doing is totally
> alien and has to be (mostly) a conscious process. Birds fly quite
> UNconsciously. What they see is "integrated" with what they feel in
> their muscles. There is no separate process for "I am entering a
> thermal" which is different from "I am in a steady climb". It's all one.
>
> They measure altitude with their eyes as Bill Daniels said. They
> 'recalibrate' their gyros continuously by looking around. They're not
> much better at raw data IMC than we are and lose their 'calibration'
> quite quickly in cloud.
>
> Many of the ideas are interesting but I'm with Occam's Razor. Birds fly
> like we walk - by looking around to 'calibrate' the inner ear balance
> mechanism and feedback from muscles. I can't see a real need for any
> other unique mechanism.
>
> ... until we get to intercontinental migration.
>
> GC

OK, you may call as you like the process of determining climb rate from
acceleration or muscle tension or any other differential information,
it will nevertheless be a mathematical integration, or an equivalent
process, but as the result is unique starting from a known state, any
equivalent process is the same process.

None of the mechanism mentionned in the previous post (acceleration,
muscle tension, ground watching), except the use of a pressure sensor,
can explain how birds feel they are climbing, and as a matter of fact
someone said in a previous post that the evidence of such a sensor
in the birds has been proved and also that loosing this specific
information makes them unable to climb.

[Robert Ehrlich]

Martin Gregorie wrote:
>
> On Thu, 08 Jul 2004 17:37:11 +0000, Robert Ehrlich
> > wrote:
>
> >A raised tail (or elevator) doesn't mean there is a down force on it.
> >
> I didn't say "a raised elevator". I was talking about a tail surface
> that is tilted laterally in relation to the wing and said "a raised
> tip" to describe the direction of tail tilt. Please do me the courtesy
> of reading what I wrote before sounding off about it.
>

I read what you wrote and my remark was not about the "raised tip"
or the tilt, but about "so you can tell that they fly like we do
with down force on the tail". Sorry if you misunderstood me, or
if I misunderstood you, remember English is not my native language.

[Robert Ehrlich]

Bill Daniels wrote:
>
> C'mon, now. Binocular depth perception ends for humans at about 20 feet and
> is only really useful up to arms length, yet we can still judge distance
> well. Since the bird is moving, they can use dynamic field depth perception
> that has nothing to do with interocular distance.
>
> Close one eye and move your head back and forth or up and down. You will
> see what I mean. Birds and other small animals are observed to move their
> heads constantly to better judge distances.
>
> Ever ride one of those glass elevators (lifts) on the outside of a tall
> building? Did you notice how powerful the impression of climbing is?
>
> I still claim that they can see themselves rise away from the ground.
> Excellent vision and the experience to use it to the fullest is the likely
> explanation. It's the simplest explanation and requires no internal vario.
>

I can't believe that, except for very low heights. The elevator experience
you mention mention is for such heights, or at least when something (the
building itself) is very near.

The best processing system (e.g. the bird's brain) cannot infer anything
from missing or non significative input. In the case of climbing, the only
information on which you say they rely is the change in the apparent size
of ground features. I didn't do the computation, but I bet that the change
during one full turn is below the optical resolution of a bird's eye. In
this domain, we are better equiped than they are, our eyes are larger.
Nevertheless we can't decide if a glider or a bird is climbing when watching
them from below just by watching the change of their size during a short
time, except when they are very low. However I agree that after watching
a bird for a long time, as it changed from a beautiful thing with discernable
separate feathers at the tips to a vanishing little point in the sky, I can
say that it was climbing.

[Andy Blackburn]

WinPilot and Mobile SeeYou already do this to a very
great extent by plotting out the flight path with climb
rate indicated on the moving map display. I have used
this to return to thermals going in and out of turnpoints
to good effect. They are not fast enough to really
be helpful in coring except over many turns, and even
then it's hard to stay oriented between the glider,
the display and the ground reference. WP Pro also has
a 'climb optimizer' that assumes your are flying in
a more-or-less circular path - it works pretty well
in my experience and can help the pilot divert attention
to other tasks while climbing.

I'm not sure you really need the strain guages to do
this as you already can measure rate of climb directly,
either through differential altitude readings from
the GPS, or more precisely through the TE pressure
system. I believe the CAI 302 also has an accelerometer
built in, so if you want to use acceleration you can
get it directly rather than having to derive it from
wing strain.

9B

At 14:48 09 July 2004, Ventus45 wrote:
>And so could we, if we installed strain gauges along
>the spars, say at 5
>foot intervals, and connected them up to a minicomputer
>which read them, add
>an accelerometer, a standard netto vario setup, a gps,
>and some fancy
>software, and we should be able to create a computer
>display that will be
>able to produce a PPI 'map' display of a thermal as
>we turn, gradually
>building up the data, plotting 'lift' like contour
>lines on a map, so we
>could soon see where the 'core' was, and centre accordingly.
> A good
>research/thesis project for some bright spark at university.
> Any takers ?
>
>
>

[Martin Gregorie]

On Fri, 09 Jul 2004 17:10:49 +0000, Robert Ehrlich
> wrote:

>Martin Gregorie wrote:
>>
>> On Thu, 08 Jul 2004 17:37:11 +0000, Robert Ehrlich
>> > wrote:
>>
>> >A raised tail (or elevator) doesn't mean there is a down force on it.
>> >
>> I didn't say "a raised elevator". I was talking about a tail surface
>> that is tilted laterally in relation to the wing and said "a raised
>> tip" to describe the direction of tail tilt. Please do me the courtesy
>> of reading what I wrote before sounding off about it.
>>
>
>I read what you wrote and my remark was not about the "raised tip"
>or the tilt, but about "so you can tell that they fly like we do
>with down force on the tail". Sorry if you misunderstood me, or
>if I misunderstood you, remember English is not my native language.

Fair enough and I was forgetting the native language difference.

We agree too on gliders minimising down-force, but it is still there -
otherwise the folks who've flown and survived with the tail bolt
missing (much earlier thread this year) would be unlikely to have
survived the experience with an intact glider, but I digress.

I was meaning to point out two things: (1) you can deduce the flight
load on a bird's tail by watching how it uses tail tilt to control a
turn and (2) the kite family have down-force on their tail and a fair
amount of it or the tilt would be ineffective.

I'd like to hear about similar observations of other species for
comparative purposes.



--
martin@ : Martin Gregorie
gregorie : Harlow, UK
demon :
co : Zappa fan & glider pilot
uk :

[Mike Lindsay]

In article >, Robert Ehrlich
>I can't believe that, except for very low heights. The elevator experience
>you mention mention is for such heights, or at least when something (the
>building itself) is very near.
>
>The best processing system (e.g. the bird's brain) cannot infer anything
>from missing or non significative input. In the case of climbing, the only
>information on which you say they rely is the change in the apparent size
>of ground features. I didn't do the computation, but I bet that the change
>during one full turn is below the optical resolution of a bird's eye. In
>this domain, we are better equiped than they are, our eyes are larger.

On the other hand, do you think you'd be able to spot a mouse from
3000ft? No problem for some birds of prey.
--
Mike Lindsay

[Bill Daniels]

> In article >, Robert Ehrlich
> >I can't believe that, except for very low heights. The elevator
experience
> >you mention mention is for such heights, or at least when something (the
> >building itself) is very near.
> >
> >The best processing system (e.g. the bird's brain) cannot infer anything
> >from missing or non significative input. In the case of climbing, the
only
> >information on which you say they rely is the change in the apparent size
> >of ground features. I didn't do the computation, but I bet that the
change
> >during one full turn is below the optical resolution of a bird's eye. In
> >this domain, we are better equiped than they are, our eyes are larger.
>

You don't look down to see height changes, you look out at an angle. You're
not looking for changes in the size of objects, you look for changes in
angles. It's just like we judge height on final approach to landing. I can
judge the strength of thermals visually up to 1000 meters or so and I bet
the birds can do a lot better.

Bill Daniels

[Tony Verhulst]

??Back in my hang gliding days I participated in a competition at ?Grandfather Mountain in North Carolina - about an 800 foot cliff ?followed by another 800 feet of mountain Ð and the cliff was part of a ?soarable ridge. Grandfather mountain is a tourist attraction with a road ?to the top and a gift shop at the summit. We knew we weren't going to ?soar that day because we had trouble walking into the gift shop. The ?weather station inside was reporting winds in excess of 90 mph. But the ?wind direction was perfect - dead on the ridge.??We didn't soar that day but the local residents did. They have ravens at ?Grandfather mountain - lots of ravens. We were literally hanging on to ?any thing we could because we were afraid of being blown off the ?mountain. And, walking across that suspension bridge between the 2 peaks ?was probably not the smartest move. Anyway, the ravens were soaring the ?flippin' ridge. They had their wings tucked in real close and were just ?zipping along. T
hey were at ridge top level about 30 feet in front of us ?and it was just amazing. I can only guess at what their airspeed was, ?but they were probably moving across the ridge at 20 to 30mph and so ?when you factor in the 90+ mph wind speed, their ASIs were probably ?hitting near 130. You'll never convince me they were flying to catch ?lunch - they were flying because they were having a blast. Of this I ?have absolutely no doubt.??Tony V. LS6-b "6N"?

[Robert Ehrlich]

Bill Daniels wrote:
>
> You don't look down to see height changes, you look out at an angle. You're
> not looking for changes in the size of objects, you look for changes in
> angles. It's just like we judge height on final approach to landing. I can
> judge the strength of thermals visually up to 1000 meters or so and I bet
> the birds can do a lot better.
>
> Bill Daniels

Well, the changes in (apparent) size of objets is nothing else than a change
in an angle. I agree that looking for such an angle just below the glider is
not what will maximize the change for a given height change. If your method
is by watching the change in the angle of the directions of some fixed ground
feature and the horizon, it can easily be shown that the maximum rate of change
is obtained by looking at some feature at 45 degrees below the horizon. In this
case, the change rate, in radians per climbing meter, is 1/(2*height), at 1000
meters the rate of change is of 1.7 minute per meter, in order to see a 1
degree change when climbing at 2 m/s, you have to wait 35 seconds.
Difficult but workable. I should try it in my next flight, although I think I
will not be able to perceive changes below 10 degrees, when looking at 45 degrees.
Looking toward a more horizontal direction should provide better senitivity, as
the fixed feature and the horizon are together in the visual field, but the
rate of change of the angle is much lower. When looking in the same direction
as on final approach, i.e. the direction of the 1/10 slope, the rate of change
is 1/(10*height) radians per climbing meter, 5 times lower than at 45 degrees,
you have to wait nearly 3 minutes climbing at 2 m/s to see a 1 degree change
at 1000 m.

[Mike Lindsay]

In article >, Tony Verhulst
>flippin' ridge. They had
>their wings tucked in real close and were just ?zipping along. T
>hey were at ridge top level about 30 feet in front of us ?and it was just
>amazing. I can only guess at what their airspeed was, ?but they were probably
>moving across the ridge at 20 to 30mph and so ?when you factor in the 90+ mph
>wind speed, their ASIs were probably ?hitting near 130. You'll never convince me
>they were flying to catch ?lunch - they were flying because they were having a
>blast. Of this I ?have absolutely no doubt.??Tony V. LS6-b "6N"?
>
I wonder what Vne is for a raven?
--
Mike Lindsay

[Tony Verhulst]

> I wonder what Vne is for a raven?

African or European? :-)

Tony


--

All good things arrive unto them that wait -
and don't die in the meantime.

Mark Twain

[BllFs6]

>> I wonder what Vne is for a raven?
>
>African or European? :-)
>
>Tony

And is it carrying coconuts shells? :)

take care

Blll

[Stewart Kissel]

For that matter, what the heck are red-tails doing
up at FL180 in the middle of the summer. They sure
are not spotting food or migrating. And what sort
of O2 saturation levels are they maintaining?








At 15:36 16 July 2004, Bllfs6 wrote:
>>> I wonder what Vne is for a raven?
>>
>>African or European? :-)
>>
>>Tony
>
>And is it carrying coconuts shells? :)
>
>take care
>
>Blll
>

[Don Johnstone]

Although Ravens are corvids not raptors they do take
live prey as well as carrion. There is no reason in
the world why they should not be hunting for food.
Flying takes a great deal of energy and like most animals
birds fly for a reason, they don't waste energy which
requires more food. Whether they enjoy themselves at
the same time is debateable. Ravens are also renowned
for their intelligence, in the brid sense, but that
is not saying a great deal. The description 'birdbrain'
was coined for a reason and most of a birds brain is
taken up in processing it's senses. This does not leave
a lot for thinking.

Come to think of it.................. no, better not
go there :-)

At 18:48 12 July 2004, Tony Verhulst wrote:
>??Back in my hang gliding days I participated in a
>competition at ?Grandfather Mountain in North Carolina
- about an 800 foot cliff ?followed by another 800
feet of mountain Ð and the cliff was part of a ?soarable
ridge. Grandfather mountain is a tourist attraction
with a road ?to the top and a gift shop at the summit.
We knew we weren't going to ?soar that day because
we had trouble walking into the gift shop. The ?weather
station inside was reporting winds in excess of 90
mph. But the ?wind direction was perfect - dead on
the ridge.??We didn't soar that day but the local residents
did. They have ravens at ?Grandfather mountain - lots
of ravens. We were literally hanging on to ?any thing
we could because we were afraid of being blown off
the ?mountain. And, walking across that suspension
bridge between the 2 peaks ?was probably not the smartest
move. Anyway, the ravens were soaring the ?flippin'
ridge. They had their wings tucked in real close and
were just ?zipping along. T
>hey were at ridge top level about 30 feet in front
>of us ?and it was just amazing. I can only guess at
what their airspeed was, ?but they were probably moving
across the ridge at 20 to 30mph and so ?when you factor
in the 90+ mph wind speed, their ASIs were probably
?hitting near 130. You'll never convince me they were
flying to catch ?lunch - they were flying because they
were having a blast. Of this I ?have absolutely no
doubt.??Tony V. LS6-b '6N'?
>
>

[David]

A few years back I drove out to Dead Horse Point in southeast Utah
late on a summer day. For a week it had been hot with overdevelopment
which didn't actually produce rain or even much wind. But it was
gonna do it this evening. You could smell ozone. Hell, you could
practically smell the ocean for how much water the thunderheads were
packing.

I walked to the edge and looked out over the lodge-pole fence into a
breeze that was freshening around 25kts. There were two big ravens
soaring the cliff face. That experience put all doubt behind me.

The rain was coming, and life was easy, if just for that little while.
They skidded, stalled and dropped out front. They tucked and raced
along the edge. They got high way back and zoomed through the
compression zone.

They played.

When the rain came I ran to my truck. There was so much wind that my
shocks lurched just sitting in the parking lot. I suppose the birds
left. I couldn't see them for the downpour. But I thought about a
couple hotshots kicking back in a hanger somewhere smiling and trading
"there I was" stories.

[David]

One time I went hang gliding on the ridge out at Randolf, Utah. This
ridge is perhaps 5-10 miles long and a big rookery for buzzards. I
flew lazily that evening for a couple hours enjoying the avian company
and then landed at the bottom with the zillion mosquitos, because I
feared that if I top-landed and hurt myself it might be a long time
before someone found me.

Anyway, that meant I had to walk back up to get my truck. A fer
piece.

So I was walking this dirt road close to twilight, and I was thinking
about the nice flight and how when it's good it's really good, when I
spotted a jack rabbit sitting up ahead maybe 20 yards. And BAM!

A Red Tail hawk slammed into the rabbit and crashed in a rolling dusty
heap of wings and fur. But he didn't let go! And in a second he
righted himself on top of the stunned or dead bunny and flapped like
there was no tomorrow until he'd cleared the sage and the stupid human
walking his way. I lost sight of him as he cleared the mouth of the
canyon.

Incredible. I had this notion that they could just pick 'em off like
the proverbial surgical strike. But hell no. I walked away
thinking... undignified.

[Jack]

David wrote:

> I had this notion that they could just pick 'em off like
> the proverbial surgical strike. But hell no. I walked away
> thinking... undignified.

All surgical strikes look like that from the rabbit's point of view.


--
Jack

"Cave ab homine unius libri"