This is just too fascinating because it ties in what
how a medium (air, water, aether, etc.) is entrained
by a rapidly moving mass that suddenly STOPS.
The medium continues to flow for a brief period due to
entrainment.
If this rapid motion and sudden stopping is fast
enough, the mass moves through the medium.
Totally cool, thanks Dan Davidson for sharing this
with the discussion list;
------------------------
The Strange Case Of The Bumble Bee Which Flew
Ken Zetie, Clarendon Laboratory, University of Oxford
I get many strange reactions from people when I tell
them I am a scientist. Frequently I'll be told by my
new acquaintance that they were hopeless at science at
school, or I'll be asked if I make atom bombs.
People, it seems, are frightened of science, so they
take every opportunity to belittle it. They'd like to
believe that science is all very well in the lab, and
for making bombs, but it doesn't apply to "real life".
Michael Flanders summed it up beautifully when he said
that he cannot understand scientists and they cannot
understand anyone else; they must be spoken to in
their own language:
"H2SO4 Professor! Don't synthesise anything I wouldn't
synthesise! And the reciprocal of pi to your good
wife!". Like most great humour, painfully close to the
truth.
One favourite subject people raise is the old line
about scientists having proved that the bumble bee
cannot fly, a much-beloved piece of urban folklore.
There it is, the humble Bombus Terristris, plainly
flying around us all through the summer and those
crazy know-all scientists with their noses in their
test-tubes say it cannot possibly fly. What utter
nonsense!
It is obvious to any scientist that the bumble bee can
fly as experiment proves it. So what is this business
about proving bees cannot fly? And who started it?
First let's look at the physics behind the story. If
you are asked about flight the first thing you do is
to use the equations which describe how much lift an
object has. You compare the lift to the weight of the
object.
If the lift is greater than weight then the thing can
fly. Bumble bees are pretty big, weighing almost a
gram, and have a wing area of about a square
centimetre. Tot up all the figures and you find that
it cannot generate enough lift at its typical flying
speed of about one meter per second. But that doesn't
prove bees cannot fly. It proves that bees with
smooth, rigid wings cannot glide. Experiment has
proven this too.
With the aid of dead bees and a little lacquer it is
easy to show that they really cannot glide.
So how do they fly? Actually that turns out to be a
very interesting question and one that reveals a lot
of physics. Why do bees flap while jumbo jets have
fixed wings? It is a question of size and this is
revealed in a figure called the Reynolds Number.
Osborne Reynolds was a Victorian engineer who was
interested in what happens when you place an object in
a stream of liquid or gas. The number named after him
is a ratio which tells us, for a particular object,
how much lift you get compared to how much drag or
resistance you get. A low Reynolds number means little
lift for a lot of drag and a large Reynolds number
means a lot of lift.
The Reynolds Number depends on the size of the wing.
Bigger wings give bigger Reynolds numbers. Now if,
again, you put in all the numbers you find that bees
work at very low Reynolds Numbers (1000 or so for a
honeybee, as little as 15 for the aphid-eating chalcid
wasp).
This means that their flight is very inefficient
because as a wing starts to move to create lift the
drag holds it back.
It is fairly straightforward to show that birds can
generate enough lift to fly once they are in motion
with air flowing smoothly over their wings, but many
of them would have great difficulty taking off. Small
insects, according to this model, cannot fly at all.
(Reynolds did far more than simply develop the
'Reynolds number', he also has a fascinating theory
about then the nature of the aether as being a
'dilatant' matrix, like wet sand which responds to
matter in motion by loosening up..as matter slows its
motion, the sand particles regather to hold it in
place...totally beautiful and why the Reynolds files
were posted at KeelyNet years ago, check out;
http://www.keelynet.com/energy/reynold1.txt
http://www.keelynet.com/energy/reynold2.txt
http://www.keelynet.com/energy/reynold3.txt )
Of course, all this proves is that the model is
incomplete.
Some brilliant work by Torkel Weis-Fogh has shown us
how small insects do fly and it has led to some rather
neat insights into nature's cunning.
If you are small and want to fly you have a problem.
The Reynolds Number is against you so you cannot glide
and flapping is very hard work. A wing is a device
which encourages the air to flow over it so that when
it leaves the rear wing edge, the air moves downwards.
That produces a thrust upwards on the wing. A
smoke-filled wind tunnel shows this beautifully with
curling eddies of smoke flicking off the wing edges.
Unfortunately to make a good eddy takes time. The wing
has to move a few times its own length to get things
started. This makes it tricky if you are going to flap
as the maximum travel of a wing is about its own
length
and very little lift is generated for most of the
stroke.
Nature has come up with a number of interesting
solutions to this problem of which the "clap-fling" is
a good example.
When a small bird or insect wants to take off it needs
a lot of lift. What it does is bring its wings
together above its back so they clap, expelling air
from between them.
As the wings are separated, air is drawn quickly in to
fill the void. The wings are flung apart and lift is
generated immediately as the air is already in motion
in the correct way. You can hear the clap.
The characteristic whirring of a pheasant taking off
is caused by its wings clapping. Almost 2000 years ago
Virgil recorded in The Aeneid that a rock dove claps
its wings as it takes off - a passage he stole from
Homer but he added the bit about the clapping.
So in asking how bees fly we find that they are
remarkably clever about it.
Aircraft can generate enough lift that they do not
need such tricks, but they do need long runways. Birds
get enough lift to fly but for take-off need a boost.
Just the poor old bee and about a million different
species of winged insect need some extra trickery to
stay aloft.
But how did it all start? Where does the story date
back to? J.H.Mcmasters states that the story was
prevalent in the German technical universities in
the 1930's, starting with the students of the
aerodynamicist Ludwig Prandtl at Göttingen.
The story he tells is that a noted Swiss
aerodynamicist, whom he does not name, was talking to
a biologist at dinner. The biologist asked about the
flight of bees and the Swiss gentleman did a
back-of-the-napkin calculation of the kind I
described. Assume a rigid, smooth wing and so on. Of
course, he found
that there was insufficient lift and went away to find
out the correct answer.
In the meantime the biologist put the word around,
presumably to show that nature was greater than
engineering, and the media picked it up. The truth,
as now, wasn't newsworthy so a correction has never
been publicised.
The man on the Clapham omnibus, therefore, continues
to tell me that science is a load of crock because
it once proved that bumble bees cannot fly. And he
will not hear otherwise, especially not from a
scientist. Perhaps if I became a journalist he might
listen?
---------------------------
The Strange Case Of The Bumblebee Which Flew
---------------------------
Animals/fruit flies
The AFU and Urban Legend Archive
Newsgroups: alt.folklore.urban,alt.folkore.science
Subject: Bumblebees can't fly, say physicists!
Date: Thu, 16 May 1996 13:53:39 -0700
I was reading the a.f.u. FAQ, and came across this: F.
Scientists once concluded that bumblebees couldn't
fly.
I don't know about bumblebees, but I did attend a
great talk last year about why Drosophila (fruit
flies) theoretically can't fly. According to the
models used to describe their flight, their energy
output isn't high enough to generate flight. They
built a virtual reality flight simulator and found
that elasticity in the wing support structure creates
rebound allowing them to fly more efficiently than
predicted.
See: 1. Alexander RM. Springs for wings [comment]
[published erratum appears in Science 1995 May
5;268(5211):625]. Science, 1995 Apr 7, 268(5207):50-1.
2. Dickinson MH; Lighton JR.
Muscle efficiency and elastic storage in the flight
motor of Drosophila [see comments]. Science, 1995 Apr
7, 268(5207):87-90.
Note: I don't read this group so 1) I apologize if
this has been gone over before and 2) e-mail if you
have comments.
Jon Singer
singer@biovx1.biology.ucla.edu
http://www.urbanlegends.com/
Copyright Information
---------------------------
Letter to naturalSCIENCE about bumblebees
From: Ilffili@aol.com
Date: Sun, 14 Dec 1997 06:10:19 EST
To: publisher@naturalscience.com
Subject: Bumblebees
Organization: AOL (http://www.aol.com)
The flight of the bumblebee
Someone has said that, in theory, a bumblebee should
not be able to fly. Can you provide any information
about who said this and why?
* * * * * * * * * * * * * * * * * * * *
Many people must have said it because it is true. And
it is true not only of bumblebees, but of most, if not
all, flying insects. That is to say, it is true
according to the conventional aerodynamic principles
employed in the design of fixed wing aircraft. But
since bumblebees can fly--after a fashion, clearly
some other aerodynamic theory is needed to account for
the fact.
Conventional aerodynamics generally deals with steady
motions, such as a wing moving in a straight line at a
constant speed. Thus, it is assumed that for a given
portion of an insect wing, the lift generated at a
particular moment is indentical to that generated by a
wing moving uniformly at the same speed and in the
same direction (McNeill, 1996).
But insect wings do not move in a straight line at
constant speed. They flap up and down, which means
that they continually change in both direction and
speed. They also rotate axially with each change
between upward and downward motion. According to a
study by Ellington and others (1996), it is the
constant change in motion that explains the ability of
insects to generate the lift necessary for flight.
These authors photographed streaks of smoke flowing
past both a tethered hawkmoth, and also a mechanical
insect model, or "flapper," located in a wind tunnel.
The pictures revealed an intense leading edge vortex
created during the down-stroke. The vortex developed
first adjacent to the body of the insect at the
beginning of the downs-stroke and extended along the
wing to spill off at the end.
Apparently, the vortex constitutes an area of reduced
pressure above the wing and adds sufficient lift to
make flight possible not only for hawkmoths but,
presumably, for bumblebees as well.
But what have others to say?
Editor.
References
Ellington, C.P., Coen van den Berg, Alexander P.
Willmot and Adrian
L.R. Thomas. 1996. Leading-edge vortices in insect
flight. Nature 384:626-630.
Alexander, R. McNeill. 1996. Smokescreen lifted on
insect flight. Nature 384:609-610.
---------------------
Also see a prior entry on the Interact list at;
http://www.escribe.com/science/keelynet/index.html?mID=6382
---------------------
On thinking about this clapping effect, and I could be
wrong but the clapping occurs when the wings slap
together on the full upstroke.
So we'd have air being sucked into the area under the
wing to create a higher pressure zone because as air
rushes in to fill the void, it entrains other air with
it, like a wide angle venturi to produce this higher
pressure.
When the wing comes back down against this higher
pressure zone, it has a 'harder' surface to push
against...does that make sense?
I'm probably way off on this but the idea intrigues me
about this clapping of wings in insects or birds that
engineering wise, can't fly, yet they do, and how it
could possibly be applied to other, even the fantasy
of the aether..<g>....just kidding...
=====
=================================
Please respond to jdecker@keelynet.com
as I am writing from my work email of
jwdatwork@yahoo.com.........thanks!
=================================
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