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The Function of the Alula in Avian Flight
The alula is a small structure located at the joint between the hand-wing and arm-wing of birds and is known to be used in slow flight with high angles of attack such as landing. It is assumed to function similarly to a leading-edge slat that increases lift and delays stall. However, in spite of its...
Autores principales: | , , , , |
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Formato: | Online Artículo Texto |
Lenguaje: | English |
Publicado: |
Nature Publishing Group
2015
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Materias: | |
Acceso en línea: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4423427/ https://www.ncbi.nlm.nih.gov/pubmed/25951056 http://dx.doi.org/10.1038/srep09914 |
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author | Lee, Sang-im Kim, Jooha Park, Hyungmin Jabłoński, Piotr G. Choi, Haecheon |
author_facet | Lee, Sang-im Kim, Jooha Park, Hyungmin Jabłoński, Piotr G. Choi, Haecheon |
author_sort | Lee, Sang-im |
collection | PubMed |
description | The alula is a small structure located at the joint between the hand-wing and arm-wing of birds and is known to be used in slow flight with high angles of attack such as landing. It is assumed to function similarly to a leading-edge slat that increases lift and delays stall. However, in spite of its universal presence in flying birds and the wide acceptance of stall delay as its main function, how the alula delays the stall and aids the flight of birds remains unclear. Here, we investigated the function of alula on the aerodynamic performance of avian wings based on data from flight tasks and wind-tunnel experiments. With the alula, the birds performed steeper descending flights with greater changes in body orientation. Force measurements revealed that the alula increases the lift and often delays the stall. Digital particle image velocimetry showed that these effects are caused by the streamwise vortex, formed at the tip of the alula, that induces strong downwash and suppresses the flow separation over the wing surface. This is the first experimental evidence that the alula functions as a vortex generator that increases the lift force and enhances manoeuvrability in flights at high angles of attack. |
format | Online Article Text |
id | pubmed-4423427 |
institution | National Center for Biotechnology Information |
language | English |
publishDate | 2015 |
publisher | Nature Publishing Group |
record_format | MEDLINE/PubMed |
spelling | pubmed-44234272015-05-13 The Function of the Alula in Avian Flight Lee, Sang-im Kim, Jooha Park, Hyungmin Jabłoński, Piotr G. Choi, Haecheon Sci Rep Article The alula is a small structure located at the joint between the hand-wing and arm-wing of birds and is known to be used in slow flight with high angles of attack such as landing. It is assumed to function similarly to a leading-edge slat that increases lift and delays stall. However, in spite of its universal presence in flying birds and the wide acceptance of stall delay as its main function, how the alula delays the stall and aids the flight of birds remains unclear. Here, we investigated the function of alula on the aerodynamic performance of avian wings based on data from flight tasks and wind-tunnel experiments. With the alula, the birds performed steeper descending flights with greater changes in body orientation. Force measurements revealed that the alula increases the lift and often delays the stall. Digital particle image velocimetry showed that these effects are caused by the streamwise vortex, formed at the tip of the alula, that induces strong downwash and suppresses the flow separation over the wing surface. This is the first experimental evidence that the alula functions as a vortex generator that increases the lift force and enhances manoeuvrability in flights at high angles of attack. Nature Publishing Group 2015-05-07 /pmc/articles/PMC4423427/ /pubmed/25951056 http://dx.doi.org/10.1038/srep09914 Text en Copyright © 2015, Macmillan Publishers Limited. All rights reserved http://creativecommons.org/licenses/by/4.0/ This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article's Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder in order to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/ |
spellingShingle | Article Lee, Sang-im Kim, Jooha Park, Hyungmin Jabłoński, Piotr G. Choi, Haecheon The Function of the Alula in Avian Flight |
title | The Function of the Alula in Avian Flight |
title_full | The Function of the Alula in Avian Flight |
title_fullStr | The Function of the Alula in Avian Flight |
title_full_unstemmed | The Function of the Alula in Avian Flight |
title_short | The Function of the Alula in Avian Flight |
title_sort | function of the alula in avian flight |
topic | Article |
url | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4423427/ https://www.ncbi.nlm.nih.gov/pubmed/25951056 http://dx.doi.org/10.1038/srep09914 |
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