Inner Dialogue

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

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.

South African Swallow (Hirundo spilodera)
European Swallow (Hirundo rustica)

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)

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.

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For the rest of the story, go to http://www.style.org/unladenswallow/