Gliding swifts attain laminar flow over rough wings.
Swifts are among the most aerodynamically refined gliding birds. However, the overlapping vanes and protruding shafts of their primary feathers make swift wings remarkably rough for their size. Wing roughness height is 1-2% of chord length on the upper surface--10,000 times rougher than sailplane wi...
| Main Authors: | , |
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| Format: | Article |
| Language: | English |
| Published: |
Public Library of Science (PLoS)
2014-01-01
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| Series: | PLoS ONE |
| Online Access: | http://europepmc.org/articles/PMC4070913?pdf=render |
| _version_ | 1818962597305647104 |
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| author | David Lentink Roeland de Kat |
| author_facet | David Lentink Roeland de Kat |
| author_sort | David Lentink |
| collection | DOAJ |
| description | Swifts are among the most aerodynamically refined gliding birds. However, the overlapping vanes and protruding shafts of their primary feathers make swift wings remarkably rough for their size. Wing roughness height is 1-2% of chord length on the upper surface--10,000 times rougher than sailplane wings. Sailplanes depend on extreme wing smoothness to increase the area of laminar flow on the wing surface and minimize drag for extended glides. To understand why the swift does not rely on smooth wings, we used a stethoscope to map laminar flow over preserved wings in a low-turbulence wind tunnel. By combining laminar area, lift, and drag measurements, we show that average area of laminar flow on swift wings is 69% (n = 3; std 13%) of their total area during glides that maximize flight distance and duration--similar to high-performance sailplanes. Our aerodynamic analysis indicates that swifts attain laminar flow over their rough wings because their wing size is comparable to the distance the air travels (after a roughness-induced perturbation) before it transitions from laminar to turbulent. To interpret the function of swift wing roughness, we simulated its effect on smooth model wings using physical models. This manipulation shows that laminar flow is reduced and drag increased at high speeds. At the speeds at which swifts cruise, however, swift-like roughness prolongs laminar flow and reduces drag. This feature gives small birds with rudimentary wings an edge during the evolution of glide performance. |
| first_indexed | 2024-12-20T12:31:51Z |
| format | Article |
| id | doaj.art-cb2056be03214c66a4da18025156d8d7 |
| institution | Directory Open Access Journal |
| issn | 1932-6203 |
| language | English |
| last_indexed | 2024-12-20T12:31:51Z |
| publishDate | 2014-01-01 |
| publisher | Public Library of Science (PLoS) |
| record_format | Article |
| series | PLoS ONE |
| spelling | doaj.art-cb2056be03214c66a4da18025156d8d72022-12-21T19:40:42ZengPublic Library of Science (PLoS)PLoS ONE1932-62032014-01-0196e9990110.1371/journal.pone.0099901Gliding swifts attain laminar flow over rough wings.David LentinkRoeland de KatSwifts are among the most aerodynamically refined gliding birds. However, the overlapping vanes and protruding shafts of their primary feathers make swift wings remarkably rough for their size. Wing roughness height is 1-2% of chord length on the upper surface--10,000 times rougher than sailplane wings. Sailplanes depend on extreme wing smoothness to increase the area of laminar flow on the wing surface and minimize drag for extended glides. To understand why the swift does not rely on smooth wings, we used a stethoscope to map laminar flow over preserved wings in a low-turbulence wind tunnel. By combining laminar area, lift, and drag measurements, we show that average area of laminar flow on swift wings is 69% (n = 3; std 13%) of their total area during glides that maximize flight distance and duration--similar to high-performance sailplanes. Our aerodynamic analysis indicates that swifts attain laminar flow over their rough wings because their wing size is comparable to the distance the air travels (after a roughness-induced perturbation) before it transitions from laminar to turbulent. To interpret the function of swift wing roughness, we simulated its effect on smooth model wings using physical models. This manipulation shows that laminar flow is reduced and drag increased at high speeds. At the speeds at which swifts cruise, however, swift-like roughness prolongs laminar flow and reduces drag. This feature gives small birds with rudimentary wings an edge during the evolution of glide performance.http://europepmc.org/articles/PMC4070913?pdf=render |
| spellingShingle | David Lentink Roeland de Kat Gliding swifts attain laminar flow over rough wings. PLoS ONE |
| title | Gliding swifts attain laminar flow over rough wings. |
| title_full | Gliding swifts attain laminar flow over rough wings. |
| title_fullStr | Gliding swifts attain laminar flow over rough wings. |
| title_full_unstemmed | Gliding swifts attain laminar flow over rough wings. |
| title_short | Gliding swifts attain laminar flow over rough wings. |
| title_sort | gliding swifts attain laminar flow over rough wings |
| url | http://europepmc.org/articles/PMC4070913?pdf=render |
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