such as "Introduction", "Conclusion"..etc
According to fundamental aerodynamics the lift force (L) generated on a wing is related to flight speed (U) as:
where ρ is air density, S is wing area, and CL is the lift coefficient [1–3]. In horizontal cruising flight L balances the weight (m × g), and aircraft as well as animals are expected to fly at or near a value of CL giving the maximum efficient lift-drag ratio. Provided that this value of CL is about equal among bird species (as required for dynamical similarity) , it follows that cruising flight speed among bird species is expected to scale with body mass and wing loading (Q = m × g/S) as U m1/6 and U Q1/2, respectively (with the former proportionality based also on the assumption of geometrical similarity; i.e., S varies with m2/3).
These scaling rules have also been used to compare general speeds of a
wide range of flyers, from the smallest insects to the largest aircraft
the absence of reliable measurements of the airspeed of different bird
species in long-distance cruising (migration) flight, theoretically
derived flight speeds for species of different mass and wing morphology
have been used to explore these scaling rules [4,5,7–10].
Deviations from the expected scaling exponent in relation to mass have
been found because of departures from geometrical similarity—larger
birds often tend to have proportionately larger wing area and span [2,5,9–11].
There are additional possible reasons, besides departure from
geometrical similarity, why bird flight speeds may deviate from the
aerodynamic scaling rules. Flight adaptations related to the birds'
ecology and phylogeny may have consequences for their cruising flight
speeds, and different flight modes (continuous or intermittent
flapping) may constrain the birds' speeds [2,10].
full evaluation of the applicability of aerodynamic scaling rules must
be based, not on theoretically derived speeds, but on empirical
measurements of airspeeds of a wide variety of bird species in natural
cruising flight. Here, we present tracking radar measurements of flight
speeds of 138 species from six main monophyletic groups , which were analysed in relation to biometry (m, S, and wingspan b)
and evolutionary origin (as reflected by phylogenetic group). All
speeds reported here refer to flapping flight at cruising speeds of
birds on migration. By restricting the analysis to migration flight we
expect the birds to fly at an airspeed close to that associated with
maximum lift-drag ratio . All speeds designate equivalent airspeeds (Ue) corrected to sea level air density [14,15].
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