A new paper by Johansson, Jakobsen and Hendenstram 2018
introduces the benefit of ground effect (the surface acts as an aerodynamic mirror, interrupting the downwash, resulting in increased pressure underneath the wing and suppression of wingtip vortex development) in the origin of bat flight.
This is something every student pilot learns.
Ground effect is basic aerodynamics whether applied to bats, airplanes or flying fish.
Even so, it is measured here for bats for the first time.
You might remember, an earlier hypothesis first published here proposed an origin of bat flight associated with dropping out of trees while frantically flapping to break the fall in order to attack insects heard in the leaf litter (Fig. 1). The benefit of such unprofessional flapping increases as the ground gets closer and closer. In bats this frantic flapping while parachuting evolved to hovering before ground contact (with the help of ground effect). And this evolved to powered flight in bat-fashion, distinct from bird and pterosaur flight origins.
Highlights of the Johansson, Jakobsen and Hendenstram 2018 paper:
- Aerodynamic power is 29% lower when bats fly close to rather than far from ground
- Measured savings are twice the savings expected from models
- Wing motion is varied with distance to ground, which may modulate ground effect
- The results challenge our understanding of how animals use ground effect
Johansson LC, Jakobsen L and Hendenstram A 2018. Flight in ground effect dramatically reduces aerodynamic costs in bats. Current Biology. DOI: https://doi.org/10.1016/j.cub.2018.09.011