MINIMUM WIND STRENGTH REQUIRED FOR DYNAMI C SOARING OF ALBATROSSES

Authors
Citation
G. Sachs, MINIMUM WIND STRENGTH REQUIRED FOR DYNAMI C SOARING OF ALBATROSSES, Journal fur Ornithologie, 134(4), 1993, pp. 435-445
Citations number
17
Language
TEDESCO
art.tipo
Article
Categorie Soggetti
Ornithology
Journal title
ISSN journal
0021-8375
Volume
134
Issue
4
Year of publication
1993
Pages
435 - 445
Database
ISI
SICI code
0021-8375(1993)134:4<435:MWSRFD>2.0.ZU;2-W
Abstract
The problem of minimum wind strength required for dynamic soaring of a lbatrosses is considered and it is shown with a flight mechanics inves tigation which is the flight profile for maximum energy gain for the b ird. As a starting point, basic considerations for the energy transfer between moving air and a bird are presented. A mathematical model is then developed for describing the bird motion taking horizontally movi ng air into account. This includes a model for the wind boundary layer within which dynamic soaring is performed. Computations of flight tra jectories yield the mimimum wind strength with the use of which dynami c soaring in the boundary layer is possible for albatrosses. Furthermo re, the flight profiles as well as the history of speed and altitude a re shown. Other quantities presented are the lift coefficient and bank angle with the use of which the bird controls the flight path. A more detailed investigation of the energy transfer between moving air and bird in the course of the flight path shows that there is a certain ph ase which is of primary significance. This phase is the upper turn whe re the bird changes its flight direction from a course against the win d into a course with the wind. The upper turn may be understood as a c haracteristic element of dynamic soaring of albatrosses to achieve an energy gain. Besides a double-S shaped trajectory which represents fro m an energy transfer standpoint the best flight path, albatrosses also perform a spiral type of flight path. This case is also considered an d a trajectory is presented which requires the minimum shear wind stre ngth for this type of flight path.