Circling for rodents?

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

On 04 Jul 2004 18:48:04 GMT, ospam (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 :

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

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

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, ospam
(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 :

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

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 :

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!"

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?

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, ospam (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 :