Advanced

Flight in Ground Effect Dramatically Reduces Aerodynamic Costs in Bats

Johansson, L. Christoffer LU ; Jakobsen, Lasse LU and Hedenström, Anders LU (2018) In Current Biology 28(21). p.3502-3507
Abstract

Most flying animals, from insects to seabirds [1], perform flights close to ground or water when taking off or landing [2], drinking, and feeding [3-5] or when traveling near water surfaces [1, 6, 7]. When flying close to a surface within approximately one wingspan, the surface acts as an aerodynamic mirror, interrupting the downwash [8, 9], resulting in increased pressure underneath the wing and suppression of wingtip vortex development [10]. This aerodynamic interaction lowers the energy added to the air by the animal, reducing the cost of flying. Modeling suggests that flapping wings in ground effect can affect the expected power savings compared to gliding flight, either positively or negatively, depending on the wing motion... (More)

Most flying animals, from insects to seabirds [1], perform flights close to ground or water when taking off or landing [2], drinking, and feeding [3-5] or when traveling near water surfaces [1, 6, 7]. When flying close to a surface within approximately one wingspan, the surface acts as an aerodynamic mirror, interrupting the downwash [8, 9], resulting in increased pressure underneath the wing and suppression of wingtip vortex development [10]. This aerodynamic interaction lowers the energy added to the air by the animal, reducing the cost of flying. Modeling suggests that flapping wings in ground effect can affect the expected power savings compared to gliding flight, either positively or negatively, depending on the wing motion [11-13]. Although aerodynamic theory predicts substantial power reductions when animals fly in ground effect [4-6, 9, 11, 12], quantitative measurements of savings are lacking. Here, we show, through wake-based power measurements, that Daubenton's bats utilize 29% less aerodynamic power when flying in compared to out of ground effect, which is twice the predicted savings. Contrary to theoretical predictions [4-6, 9, 11, 12] we find no variation in savings with distance above ground when in ground effect. Given alterations in kinematics with ground proximity, we hypothesize that modulation of wing kinematics raises the achievable benefit from ground effect relative to current model predictions. The savings from ground effect are comparable to formation flight [14, 15] but are not limited to large bird species. Instead, ground effect is experienced by most flying animals and may have facilitated the evolution of powered animal flight.

(Less)
Please use this url to cite or link to this publication:
author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
aerodynamic power, aerodynamics, animal flight, bats, Chiroptera, energy savings, evolution of flight, ground effect
in
Current Biology
volume
28
issue
21
pages
6 pages
publisher
Elsevier
external identifiers
  • pmid:30344122
  • scopus:85056256374
ISSN
1879-0445
DOI
10.1016/j.cub.2018.09.011
project
Centre for Animal Movement Research
language
English
LU publication?
yes
id
f3bb8f5a-88cb-4015-b852-7dd1e5ede998
date added to LUP
2018-11-22 10:43:47
date last changed
2020-09-16 04:01:47
@article{f3bb8f5a-88cb-4015-b852-7dd1e5ede998,
  abstract     = {<p>Most flying animals, from insects to seabirds [1], perform flights close to ground or water when taking off or landing [2], drinking, and feeding [3-5] or when traveling near water surfaces [1, 6, 7]. When flying close to a surface within approximately one wingspan, the surface acts as an aerodynamic mirror, interrupting the downwash [8, 9], resulting in increased pressure underneath the wing and suppression of wingtip vortex development [10]. This aerodynamic interaction lowers the energy added to the air by the animal, reducing the cost of flying. Modeling suggests that flapping wings in ground effect can affect the expected power savings compared to gliding flight, either positively or negatively, depending on the wing motion [11-13]. Although aerodynamic theory predicts substantial power reductions when animals fly in ground effect [4-6, 9, 11, 12], quantitative measurements of savings are lacking. Here, we show, through wake-based power measurements, that Daubenton's bats utilize 29% less aerodynamic power when flying in compared to out of ground effect, which is twice the predicted savings. Contrary to theoretical predictions [4-6, 9, 11, 12] we find no variation in savings with distance above ground when in ground effect. Given alterations in kinematics with ground proximity, we hypothesize that modulation of wing kinematics raises the achievable benefit from ground effect relative to current model predictions. The savings from ground effect are comparable to formation flight [14, 15] but are not limited to large bird species. Instead, ground effect is experienced by most flying animals and may have facilitated the evolution of powered animal flight.</p>},
  author       = {Johansson, L. Christoffer and Jakobsen, Lasse and Hedenström, Anders},
  issn         = {1879-0445},
  language     = {eng},
  month        = {11},
  number       = {21},
  pages        = {3502--3507},
  publisher    = {Elsevier},
  series       = {Current Biology},
  title        = {Flight in Ground Effect Dramatically Reduces Aerodynamic Costs in Bats},
  url          = {http://dx.doi.org/10.1016/j.cub.2018.09.011},
  doi          = {10.1016/j.cub.2018.09.011},
  volume       = {28},
  year         = {2018},
}