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Strider

NEVER MIND THE BOLLOCKS...HERE'S THE IMPORTANT ISSUE OF THE DAY!

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Spanking...Political Correctness...Intelligent Design...Alien conspiracies...blah blah blah! :blahblah:

Who cares about such trifling matters when there are more important matters to discuss. Fortunately, there was one man who ignored the conventional wisdom and decided to tackle the most important question of our age: WHAT IS THE AIRSPEED VELOCITY OF AN UNLADEN SWALLOW?

Ladies and gentlemen, children of all ages, I give you Jonathan Corum.

Estimating the airspeed velocity of an unladen swallow

Estimating the Airspeed Velocity of an Unladen Swallow by Jonathan Corum

Hashing out the classic question with Strouhal numbers and simplified flight waveforms.

After spending some time last month trying to develop alternate graphic presentations for kinematic ratios in winged flight, I decided to try to answer one of the timeless questions of science: just what is the airspeed velocity of an unladen swallow?

What do you mean, an African or European Swallow?

To begin with, I needed basic kinematic data on African and European swallow species.

Although 47 of the 74 worldwide swallow species are found in Africa,1 only two species are named after the continent: the West African Swallow (Hirundo domicella) and the South African Swallow (Hirundo spilodera), also known as the South African Cave Swallow.

Since the range of the South African Swallow extends only as far north as Zaire,2 I felt fairly confident that this was the non-migratory African species referred to in previous discussions of the comparative and cooperative weight-bearing capabilities of African and European swallows.3

southafricanswallow.gif

South African Swallow

(Hirundo spilodera)

Kinematic data for both African species was difficult to find, but the Barn or European Swallow (Hirundo rustica) has been studied intensively, and kinematic data for that species was readily available.

europeanswallow.gif

European Swallow

(Hirundo rustica)

It’s a simple question of weight ratios

A 54-year survey of 26,285 European Swallows captured and released by the Avian Demography Unit of the University of Capetown finds that the average adult European swallow has a wing length of 12.2 cm and a body mass of 20.3 grams.4

Because wing beat frequency and wing amplitude both scale with body mass,5 and flight kinematic data is available for at least 22 other bird species,6 it should be possible to estimate the frequency (f ) and amplitude (A) of the European Swallow by a comparison with similar species. With those two numbers, it will be possible to estimate airspeed (U).

In order to maintain airspeed velocity, a swallow needs to beat its wings forty-three times every second, right?

Actually, wrong. By comparing the European Swallow with bird species of similar body mass, we can estimate that the swallow beats its wings 18 times a second with an amplitude of 18 cm:

Species Body mass Frequency Amplitude

Zebra Finch 13 g 27 Hz 11 cm

European Swallow 20 g ≈ 18 Hz? ≈ 18 cm?

Downy Woodpecker 27 g 14 Hz 29 cm

Budgerigar 34 g 14 Hz 15 cm

Note that even the tiny Zebra Finch flaps its wings no more than 27 times a second while cruising.

If we ignore body mass and look only at bird species with a similar wingspan, we can estimate an average frequency of 14 beats per second and an amplitude of 23 cm:

Species Wingspan Frequency Amplitude

Budgerigar 27 cm 14 Hz 15 cm

European Swallow ≈ 28–30 cm ≈ 14 Hz? ≈ 23 cm?

Downy Woodpecker 31 cm 14 Hz 29 cm

European Starling 35 cm 14 Hz 26 cm

By averaging all 6 values, we can estimate that an average European Swallow flies at cruising speed with a frequency of roughly 15 beats per second, and an amplitude of roughly 22 cm.

Skip a bit, Brother

Last month’s article on The Strouhal Number in Cruising Flight showed how simplified flight waveforms that graph amplitude versus wavelength can be useful for visualizing the Strouhal ratio (fA/U), a dimensionless parameter that tends to fall in the range of 0.2–0.4 during efficient cruising flight.

For a European Swallow flying with our estimated wingbeat amplitude of 24 cm, the predicted pattern of cruising flight ranges from a Strouhal number (St) of 0.2:

swallow_st2.gif

... to a less efficient 0.4:

swallow_st4.gif

If the first diagram (St = 0.2) is accurate, then the cruising speed of the European Swallow would be roughly 16 meters per second (15 beats per second * 1.1 meters per beat). If the second diagram (St = 0.4) is accurate, then the cruising speed of the European Swallow would be closer to 8 meters per second (15 beats per second * 0.55 meters per beat).

If we settle on an intermediate Strouhal value of 0.3:

swallow_st3.gif

We can estimate the airspeed of the European Swallow to be roughly 11 meters per second (15 beats per second * 0.73 meters per beat).

Three shall be the number thou shalt count

Airspeed can also be predicted using a published formula. By inverting this midpoint Strouhal ratio of 0.3 (fA/U ≈ 0.3), Graham K. Taylor et al. show that as a rule of thumb, the speed of a flying animal is roughly 3 times frequency times amplitude (U ≈ 3fA).5

We now need only plug in the numbers:

U ≈ 3fA

f ≈ 15 (beats per second)

A ≈ 0.22 (meters per beat)

U ≈ 3*15*0.22 ≈ 9.9

... to estimate that the airspeed velocity of an unladen European Swallow is 10 meters per second.

Oh, yeah, I agree with that

With some further study, it became clear that these estimates are accurate, though perhaps coincidental.

An actual study of two European Swallows flying in a low-turbulence wind tunnel in Lund, Sweden, shows that swallows flap their wings much slower than my estimate, at only 7–9 beats per second:

“Compared with other species of similar size, the swallow has quite low wingbeat frequency and relatively long wings.” 7

The maximum speed the birds could maintain was 13–14 meters per second, and although the Lund study does not discuss cruising flight in particular, the most efficient flapping (7 beats per second) occurred at an airspeed in the range of 8–11 meters per second, with an amplitude of 90–100° (17–19 cm).

And there was much rejoicing

Averaging the above numbers and plugging them in to the Strouhal equation for cruising flight (fA/U = 7 beats per second * 0.18 meters per beat / 9.5 meters per second) yields a Strouhal number of roughly 0.13:

swallow_st13.gif

... indicating a surprisingly efficient flight pattern falling well below the expected range of 0.2–0.4.

Although a definitive answer would of course require further measurements, published species-wide averages of wing length and body mass, initial Strouhal estimates based on those averages and cross-species comparisons, the Lund wind tunnel study of birds flying at a range of speeds, and revised Strouhal numbers based on that study all lead me to estimate that the average cruising airspeed velocity of an unladen European Swallow is roughly 11 meters per second, or 24 miles an hour.

What is the capital of Assyria?

For those looking for additional answers, the four capitals of Assyria were Ashur (or Qalat Sherqat), Calah (or Nimrud), the short-lived Dur Sharrukin (or Khorsabad), and Nineveh.8 The ruins of all four ancient cities fall within the modern state of Iraq.

References

Thank to everyone who has written in with comments and questions. Responses are posted here, along with a revised estimate from Dr Graham K. Taylor, and some alternate theories.

1. Chris & Tilde Stuart

Birds of Africa: From Seabirds to Seed-Eaters

MIT Press (1999)

2. G. L. Maclean

Roberts’ Birds of Southern Africa

John Voelcker Bird Book Fund, Cape Town, South Africa (1985)

3. Graham Chapman, John Cleese, Eric Idle, Terry Gilliam, Terry Jones, Michael Palin

Monty Python and the Holy Grail

Python (Monty) Pictures Ltd. (1975)

4. Avian Demography Unit

SAFRING results of the European Swallow (Hirundo rustica)

Department of Statistical Sciences, University of Cape Town (2002)

5. Graham K. Taylor, Robert L. Nudds, Adrian L. R. Thomas

Flying and swimming animals cruise at a Strouhal number tuned for high power efficiency

Nature 425, 707–711 (October 16, 2003)

6. Email correspondence with Graham K. Taylor of the University of Oxford Zoology Department (October 22–23, 2003)

7. Kirsty J. Park, Mikael Rosén, Anders Hedenström

Flight kinematics of the barn swallow (Hirundo rustica) over a wide range of speeds in a wind tunnel

The Journal of Experimental Biology 204, 2741–2750 (2001)

8. Ashur Cherry

Assyrian History

The Mesopotamian Encyclopedia (2001)

November 17, 2003

Jonathan Corum is the founder of 13pt, a design studio. His favorite color is blue.

©2003-11 13pt LLC

Edited by Strider

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The soon to be only "pinned" thread in Ramble On.

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Thanks jabe...unfortunately, it didn't post graphically like I had hoped, so I had to spend time re-editing the post so I could get the graphics arranged properly.

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My bird swallows at a high speed whether laden or not.... :o;):lol:

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My bird swallows at a high speed whether laden or not.... :o;):lol:

Careful, some people might consider that a lecherous, threatening post.

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I had some barn swallows nest under the eaves of my house a few years ago. When they left eventually the mud nest fell off.

The first swallows were reported building their nests in Mission San Juan Capistrano as early as 1776.

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Someone actually made this report?!

The person that made it must be a .. On second thoughts, let's not go there. It is a silly place.

I think I'm gonna whack on Monty Python maybe it'll even cure my insomnia!

Edited by TheStairwayRemainsTheSame

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This thread should be closed. I won't miss it when it's gone.

:blink:

I am an expert on sparrow aerodynamics and avian telemetry, are you?

Strider,

:hysterical:

Sounds like someone needs a spanking.

:lol:

Edited by Strider

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^^^

They're trying to get a swallow to pick up a coconut.

All mods cons...

:whistling:

Edited by Strider

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What I want to know is the airspeed velocity of an unladen spit....GET IT?hysterical.gifSwallow vs. Spit?...I just had to...sorry.bagoverhead.gif

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What I want to know is the airspeed velocity of an unladen spit....GET IT?hysterical.gifSwallow vs. Spit?...I just had to...sorry.bagoverhead.gif

:lol:

CHEEKY CHEEKY! I'm not touching that with a...

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europeanswallow.gif

European Swallow

I made a couple of these in stainless steel cutouts with a plasma torch. They're hanging on the outside of a friends house.

B)

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I made a couple of these in stainless steel cutouts with a plasma torch. They're hanging on the outside of a friends house.

B)

Excellent redrum! Had no idea you were handy with a blowtorch!

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day-11-400x300_v10.gif

That's amazing. Did you design that, Andy? Next time I drop some purple microdot I will have something to look at. ;)

 

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Excellent redrum! Had no idea you were handy with a blowtorch!

A 'slightly late' reply, but here are the ones I made on the outside of the house. Stainless steel.

SWALLOWS.jpg

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