Bumblebee aerodynamics
Chris Elmore
aerodynamically impossible for a bumblebee to fly. Does
anyone know the origin of this statement? Has anyone "proven"
that a bumblebee *can* fly?
[Moderator's note: Well, the bumblebees have, obviously. MFS]
Thanks,
Chris Elmore
Don Stauffer
Has anyone REALLY proven it can't? I am getting very interested in
history of technology (plan to return to school and get a history
degree when I retire in about seven years). Anyway, I have heard this
story so many times, but I suspect it is urban legend. I think it
would be a good thing if we can debunk it, because it is used a lot by
people to denigrate engineers and engineering.
Can ANY of us professional engineers and aerodynamists find ANY
evidence that anyone ever "proved" that bumblebees cannot fly?
Michael Carley
>Can ANY of us professional engineers and aerodynamists find ANY
>evidence that anyone ever "proved" that bumblebees cannot fly?
I certainly remember finding evidence that birds can't fly. It's in
a history of NACA called "Engineer in Charge". Apparently somone stuck
a bird in a wind tunnel and found that it was unstable.
[Moderator's note: Evidence that birds can't fly or that dead birds
are unstable? MFS]
--
Survivors Describe A320 Flight As `Normal' (Aviation Week)
m.ca...@leoleo.mme.tcd.ie 353-1-6081134
Michael Carley, Mechanical Engineering, Trinity College, Dublin
<A HREF="http://leoleo.mme.tcd.ie/~m.carley/Welcome.html">Home page</A>
dple...@genb.cca.rockwell.com
|>The other day I heard someone repeat the legend that it was
|>aerodynamically impossible for a bumblebee to fly. Does
|>anyone know the origin of this statement? Has anyone "proven"
|>that a bumblebee *can* fly?
I remember reading about that a long time ago. Evidently scientists
underestimated the physical capabilities that insects were capable of.
Unfortunately that is too long ago for me to remember the reference
but I think that once they realized that bumblebees did not just rely
on nuerotransmissions to flap their wings but had a physical mechanism
that worked even faster then the aerodynamic equations worked out.
I hope this helps. I'll see if I can find any information in my books
at home.
Rockwell has nothing to do with these facts or opinions and takes no
responsibility for them. But then again, you already knew that.
- David Leemon
rjre...@delphi.com
>>The other day I heard someone repeat the legend that it was
>>aerodynamically impossible for a bumblebee to fly. Does
>>anyone know the origin of this statement? Has anyone "proven"
for engineering. My take on it was always that perhaps someone,
somewhere tried to look at bumblebee aerodynamics as a fixed wing
operation rather than the continuous dynamic nature of insect flight.
As a fixed wing device I suspect that the bumblebee might have the L/D
of a ring of car keys. Perhaps that could be constured as not being
able to fly, in the broadest sense of flight. Of course, there's
always the Shuttle!
[Moderator's note: Lifting bodies fly perfectly well. MFS]
Reilly
Brent Wellman
: In article <950522204...@nasp.dfrc.nasa.gov>,
: ch...@andy.hssc.scarolina.edu (Chris Elmore) says:
: >
: >The other day I heard someone repeat the legend that it was
: >aerodynamically impossible for a bumblebee to fly.
: >
: >[Moderator's note: Well, the bumblebees have, obviously. MFS]
: Has anyone REALLY proven it can't?
<snip>
: Anyway, I have heard this
: story so many times, but I suspect it is urban legend.
Well, I don't know if I can debunk the urban legend, because I have
heard several versions regarding its origin. I can, though, explain
why it is easy to come to the improper conclusions with regard to
bumblebee aerodynamics.
The apocyphal story I have with regard to the legend is that an
aerodynamicist worked up the aerodynamics of the bumblebee on a lark,
and found, based on his assumptions (i.e. flat plate aerodynamics over
the wing, a certain beat frequency and airspeed [indicating an
oscillatory angle of attack on the wings], imposition of the Kutta
condition, etc), that the power requirements were far beyond the
capacity of bumblebee flight muscles to provide. Moreover, the wings
were stalled through a large percent of their flap cycle, yielding
horrendous L/D penalties. He confided his result to another during a
reception to which the press had been invited; it was overheard by a
member of the press, and the rest was media history. The
aerodynamicist was reported to have realized an error in his [tacit]
assumptions later during the event, but the damage had been done.
As I said, an apocryphal tale.
The key to understanding bumblebee (and dragonfly and butterfly and
mosquito) aerodynamics is in understanding bumblebee airfoils. If you
imagine a bee's wing, with its veins and undulations in cross section,
the first question that comes to mind is, "why would anyone pick such
a horrible airfoil and try to fly with it?" Of course, individual
bumblebees have little choice in the matter, but mother nature *could*
have chosen another design. Bees have been part of the biosphere since
the late Cretaceous (they coevolved with the flowering plants). If
another insect were to develop, which could fly and pollenate flowers
with greater ease than the bee, it would have had a survival advantage
and taken over (it should be noted that bees have several other
survival advantages as well).
So why isn't there a bee-sized insect out there with a NACA 64-series
airfoil?
The answer is scaling. At the sizes of bee wings, the bumpy-looking
wing cross section is actually a very efficient airfoil. The key is to
recognize that at bee dimensions, Reynolds numbers are low! Many of
the fluid dynamic assumptions students use in the study of airfoils do
not hold up (since few airliners are built to bee dimensions, the
assumptions are still fine for most of us aerocritters). Once you have
a higher Cl airfoil, the L/D goes up and power requirements go down.
And, voila! the bee flies!
This is what our hapless hero realized, too late to hold the presses
(if you believe this version of the story).
Actually, at small scale, and low Reynolds numbers, a surprising
variety of structures become quite good flying machines. Perhaps one
of the oddest is gossamer. Certain species of spiders have taken to
the air by spinning web and holding it aloft. Once picked up by the
breeze, these spiders can travel great distances and achieve fairly
respectable altitudes. Often, these spiders travel en masse, and meld
their webs into a flying spider colony (a few cases of UFO sightings
in the 50's were attributed to gossamer).
Airborne bacteria have developed even stranger schemes...
Brent Wellman
U.S. Army Aeroflightdynamics Directorate, Ames Research Center
Richard Isakson
>Apparently somone stuck a bird in a wind tunnel and found that it was
>unstable.
relative to his MAC. His tail is fanned out and down. This makes his
tail is a lifting surface resulting in a lower landing speed.
However, to achieve this configuration the duck must be statically
unstable. Of course, he can compensate for that through the use of an
excellent active control system.
--
Rich (r...@whidbey.com)
Frank Manning
the last couple of years or so.
[Moderator's note: In alt.folklore.urban, perhaps? MFS]
In that version of the story, a researcher (German, I think), wondered
whether bumblebees have rigid or flexible wings. After working through
the calculations, the researcher found that rigid wings wouldn't work.
So the result was not that bumblebees can't fly -- the result was they
must have flexible wings.
Anyway, that's the version I heard. Don't quote me :)
-- Frank
Johannes Schoon
: Well, I don't know if I can debunk the urban legend, because I have
: heard several versions regarding its origin. I can, though, explain
: why it is easy to come to the improper conclusions with regard to
: bumblebee aerodynamics.
<rest deleted>
I guess most of us say the same. Since I love to hate the bumblebee
'paradox' (or is it the people that manage to be amused by junk like
that I can't stand??), I find it very satisfying that it more and more
looks like a pure legend. That is, with no connection to science and
engineering at all, not even flawed sci. and eng.!
Well, if anyone of you, prompted by this self-satisfied followup,
manage to dig up the original source of this legend, I would only be
half disappointed. It would give me something to stick under the noses
of everone that dares to mention the good-ol' bublebee 'paradox'
within earsight of me.
By the way, there is a similar legend concerning dolphins, but there
the source of the problem is known (albeit not to the public)...
Cheers
Johannes Schoeoen
dept. of Naval Architecture and Ocean Engineering
Chalmers University of Technology
Gothenburg, Sweden
Patrick Erk
Lighthill on insect/bird aerodynamics. An old one, somtimes in the
70's, Ann. Rev. Fluid Mech. or so ?
I think the bumblebee aerodynamics were as follows:
According to ordinary stationary aerodynamics, the shape and the area
of the bb are not producing enough lift (or rather: lift to drag ratio
of a bb is pretty bad): A bb is definitely a bad glider!
However, the wing movement of a bb is pretty elaborated and produces
an instationary effect called dynamic stall: an upward pitching
airfoil is stalling at higher AOAs than an airfoil where AOA is
increased in a quasistationary manner. A good reference to look here
are the flow visualizations by Freymuth. Anyway, helicopter people
know also about these things, I think they call it the retreating
blade phenomenon (?).
--------------------------------------------------------------------------------
Dipl.-Ing. Patrick P. Erk, M.Sc. Patri...@pi.tu-berlin.de
Hermann-Foettinger Institut
Technische Universitaet Berlin
Mueller-Breslau Str. 8 Tel.: +49-(0)30-314-24531
D-10623 Berlin (12) Sec.: -23359
Fed. Rep. Germany FAX : -21101
--------------------------------------------------------------------------------
Andrew Goldfinger
Recently, I was looking for a reference to the bumblebee calculation
for a book I am writing. I consulted with Dr. Alvin Eaton here at the
Johns Hopkins University/Applied Physics Laboratory. He told me that
he was involved with the study, although he does not remember when it
was done or where it was published. (He did say that there was an
article in Collier's magazine). He stated that the original
calculation did not take into account the flapping of the wings. He
also stated that he was the one who did the calculation correctly and
proved that the bee could indeed fly.
Merlin Dorfman
: By the way, there is a similar legend concerning dolphins, but there
: the source of the problem is known (albeit not to the public)...
Dolphins can't swim???
Merlin Dorfman
DOR...@NETCOM.COM
Merlin Preuss
>However, the wing movement of a bb is pretty elaborated and produces
>an instationary effect called dynamic stall: an upward pitching
>airfoil is stalling at higher AOAs than an airfoil where AOA is
>increased in a quasistationary manner. A good reference to look here
>are the flow visualizations by Freymuth. Anyway, helicopter people
>know also about these things, I think they call it the retreating
>blade phenomenon (?).
Does a hummingbird use the same science when it is "parked" in a flower?
Merlin
mh...@freenet.vcu.edu
>the source of the problem is known (albeit not to the public)...
Dolphin legend? Tell us about this one. I've never heard of
it (and I'd rather be underwater than airborne).
Carry on. With a good L/D ratio.
--
---------------------------|------------------------------------------------
Michael B. Holt | [This is test of the signature feature]
Richmond, Virginia, U.S.A. | [If this were not a test,
| something pithy would be quoted here.]
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Brent Wellman
: Hmmm, as far as I remember there was a re-/overview article by James
: Lighthill on insect/bird aerodynamics. An old one, somtimes in the
: 70's, Ann. Rev. Fluid Mech. or so ?
I have become intrigued enough by this thread to spend some time at
the library...
: However, the wing movement of a bb is pretty elaborated and produces
Far more elaborate than a bird's. The bee uses a figure 8 motion,
especially in hover (as does the hummingbird).
: an instationary effect called dynamic stall: an upward pitching
: airfoil is stalling at higher AOAs than an airfoil where AOA is
: increased in a quasistationary manner. A good reference to look here
The airfoil fails to stall, basically because it hasn't time to. Lift
continues to build beyond the normal stall limit of the airfoil
(remember also, that at these scales, Reynolds numbers are low, and so
viscous forces play a larger role here). the situation would not last
long, and the wing would stall out, but by then, the wing is on
another stroke.
Bee instantaneous angles of attack are affected by the motion of the
wing(s), the airspeed of the bee and an induced flow generated by the
downwash. Also keep in mind that bees are also bipes, and as the
biplane is a simple case of cascaded airfoils, you must keep in mind
that the second set of wings flies in the wake of the first...
: are the flow visualizations by Freymuth. Anyway, helicopter people
: know also about these things, I think they call it the retreating
: blade phenomenon (?).
Indeed we helicopter people do! It is one of the bigger bugaboos of
high speed helicopters. Most [surviving] pilots who experience a
dynamic stall event do not hunger to repeat the experience...
Klaus Kaiser
> : By the way, there is a similar legend concerning dolphins, but there
> : the source of the problem is known (albeit not to the public)...
>
No, they swim faster than allowed. Their body have less drag than
the 3D-profile. The fat has an influence on the laminar/turbulen
behaviour.
[Moderator's note: I remember reading something about trying to skin
submarines with "adaptive" skin, emulating dolphin skin/fat, some
years ago. As I recall, the dolphin's skin, and the fat layer
beneath, somehow molded to the streamlines or something. This is
obviously a vaguely-remembered interpretation of the article, but is
probably related to the paradox mentioned above. Anyone with a better
memory and/or more information about this dolphin skin? MFS]
Klaus Kaiser
workgroup windturbines
Technical University Berlin
Germany
http://keynes.fb12.tu-berlin.de/luftraum/konst/engwindkraft.html
Mike Elgersma
Klaus Kaiser <kl...@zwirbel.fb12.tu-berlin.de> wrote:
>Merlin Dorfman wrote:
>> : By the way, there is a similar legend concerning dolphins, but there
>> : the source of the problem is known (albeit not to the public)...
>>
>> Dolphins can't swim???
>
>No, they swim faster than allowed. Their body have less drag than
>the 3D-profile. The fat has an influence on the laminar/turbulen
>behaviour.
I thought "the source of the problem" was that people watched dolphins
effortlessly ride (surf) for many hours just ahead of the top of the
crest of the wave put up by the front of a ship. These people then
incorrectly concluded that in order to "swim" that far that fast for
that long a time, the dolphin must have an incredibly low drag
coefficient.
Mike Elgersma
Richard Isakson
>
>No, they swim faster than allowed. Their body have less drag than the
3D-profile.
at NASA Ames. In one of the smaller tunnels (4' x 6')(?) there was a
wooden dolphin they were testing. I never got to see any of the
result but they said that they were trying to test a theory on
adaptive skin.
--
Rich (r...@whidbey.com)
Klaus Kaiser
> Anyway, helicopter people
> know also about these things, I think they call it the retreating
> blade phenomenon (?).
The windturbine aerodynamics learned something from the helicopter
people. Maybe we can start a research project together?
regards
Klaus
Klaus Kaiser
Workgroup Windturbines
Technical University Berlin
Germany
http://keynes.fb12.tu-berlin.de/luftraum/konst/personen/engklaus.html
rjre...@delphi.com
>[Moderator's note: I remember reading something about trying to skin
>submarines with "adaptive" skin, emulating dolphin skin/fat, some
>years ago. As I recall, the dolphin's skin, and the fat layer
organization at Mississippi State fooling around with a mohair-like
surface on laminar flow surfaces. I believe the theory was that the
friction normal to the stream- line flow (in the fuzz) was to damp out
the Tollmein-Schlichting waves in the boundary layer that are
ultimately amplified to cause transition. Maybe some of Gus's old
colleagues could comment on the existence of this program and any
intermediate results. Some theories of dolphin drag also concentrate
on the T-S aspects of transition.
XSF
kl...@zwirbel.fb12.tu-berlin.de (Klaus Kaiser) writes:
>[Moderator's note: I remember reading something about trying to skin
>submarines with "adaptive" skin, emulating dolphin skin/fat, some
>years ago. As I recall, the dolphin's skin, and the fat layer
>beneath, somehow molded to the streamlines or something. This is
>obviously a vaguely-remembered interpretation of the article, but is
>probably related to the paradox mentioned above. Anyone with a better
>memory and/or more information about this dolphin skin? MFS]
There was an article in Scientific American within the last six months
about a robotic fish, and it talked some about this effect. BTW the
submarine skin was theoretically sound, but someone asked how many
drydocks we have in the Navy, because the boat would have to be
drydocked at every mooring to keep the growies off.
In article <950609191...@nasp.dfrc.nasa.gov>,
elge...@src.honeywell.com (Mike Elgersma) writes:
>I thought "the source of the problem" was that people watched dolphins
>effortlessly ride (surf) for many hours just ahead of the top of the
>crest of the wave put up by the front of a ship. These people then
>incorrectly concluded that in order to "swim" that far that fast for
>that long a time, the dolphin must have an incredibly low drag
>coefficient.
I have some experince wathcing these animals from the bridge of my
sub, they are really cooking. They don't spend a lot of time in the
bow wake, they mostly take advantage of it as a discontinuity to jump
from, they get mor 'hang time'. I have wathced schools, literally
swimming circles around my ship, and calculated rough speeds of 30 kts
peak sustained for at least twenty minutes.
Justin Lawler
>No, they swim faster than allowed. Their body have less drag than
>the 3D-profile. The fat has an influence on the laminar/turbulen
>behaviour.
>[Moderator's note: I remember reading something about trying to skin
>submarines with "adaptive" skin, emulating dolphin skin/fat, some
>years ago. As I recall, the dolphin's skin, and the fat layer
>beneath, somehow molded to the streamlines or something. This is
>obviously a vaguely-remembered interpretation of the article, but is
>probably related to the paradox mentioned above. Anyone with a better
>memory and/or more information about this dolphin skin? MFS]
If I remember correctly (in a book called Biophysics) the Dolphins
skin and fat layers are formed in such a way that when moving through
the water a series of oscillations occur in the skin and sub layers
which form ripples that travel along the dolphins body (these are
quite small I think).The effect of these is to keep the turbulent
boundry layer attached and thus reducing drag.
Justin
J M V Rayner
vorticity in some insects (and birds as well), but as far as I know
not in bumblebees. It is essential to lap the wings together dorsally,
so that air flowing into the opening wings already has appropriate
momentum to generate bound vortices when the wings are drawn apart.
This mechanism does not work if the wings do not contact or approach
closely.
But the explanation is probably in the right direction. The bumblebee
problem was that steady state blade element theory would not work: the
mean lift coefficient would be large, perhaps as big as 10. This
happens in many flying animals, especially in slow flight. Blade
element and quasi-steady lifting line models forget the large forces
to be obtained from time-varying bound circulation, inertial and
virtuall masses, and induced thrust from a complex 3d wake. It is not
difficult to suppose that forces of this kind can propel and support a
flying animal. What is difficult is seeing how the appropriate
crculation patterns are maintained on wings with complex geometric
movements in complex flow fields. A solution to that problem is still
eluding us, though we are getting there.
Jeremy Rayner
--
Dr Jeremy M. V. Rayner
School of Biological Sciences
University of Bristol
Woodland Road
Bristol BS8 1UG UK
tel. +44 117 928 8111, messages +44 117 928 7476, fax +44 117 925 7374
e-mail J.M.V....@bristol.ac.uk
Patrick Erk
magic word here: The skin gives way to pressure oscillations, ie.
disturbances, in the free stream and thus dampens the growth of
Tollmien-Schlichting waves. But I think this direction of research
is also gone from the list of grand-winners.
Steven Vogel
natural technologies ...
drag was discovered and mimicked. According to Sir James Gray's
calculations in the mid 1930's, only if flow around it were smooth and
laminar could a dolphin's muscles move it at the speeds it attains.
About twenty years later, Max Kramer claimed that dolphins manage to
maintain laminarity with a compliant skin that damps incipient
turbulence, and he devised a coating system that achieved the same
impressive effect. Unfortunately, the story doesn't hold water.
First, Gray's calculations were based on what's now clearly an
underestimate of the maximal aerobic output of mammalian muscle as
well as a slight overestimate of the dolphin's maximum sustainable
speed it could manage quite well if flow were turbulent, as is normal
for streamlined bodies of its size and speed. Second, no one has
succeeded in demonstrating conclusively that dolphins worked as Kramer
suggested. Finally, the "Lamiflo" coating has proven a
disappointment.
I give a more elaborate version in "Life in Moving Fluids" (1981, 1994
- Princeton University Press.)