Circling for rodents?

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?

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!

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, 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 :

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 ?

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

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

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

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
news
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 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.

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