Flight feather aerodynamics and its dependence on morphology and material properties

Abstract

For some bird species the outermost part of the wings, the feathers can separate from each other and the wing, in such cases each feather must act as an independent aerodynamic unit. In addition to regular function of flight feathers such as colouring and overall aerodynamic and structural capabilities, these separated feathers must withstand the aeroelastic demands on their own using the complex surface the microstructures of the feather create. It is known from the fossil record that the feather microstructures have evolved over time and that modern flight feathers differ from the first birds. This thesis is a first step into exploring the behaviour of a feather and the impact on the air flow from its microstructures, using computational models. The computational models were based on a Jackdaw (Corvus monedula) ninth primary flight feather.

First, two papers examine the aerodynamics of a profile of a feather section and focus on how profile shape and microstructures of the feather impact aerodynamic performance, using both the layout of microstructures found in Jackdaw today, as well as modified ones. Modifications are done by changing the microstructures relation to each other. Second, two papers examine the fluid-structure interaction effects of the entire outermost part of the feather. Material properties and overall shape are under consideration by tracking the general behaviour of the aeroelastic response.

The findings from the first two papers indicate that the feather profile in its current configuration operates at a local aerodynamic performance maximum. However, there are indications that flow predictability and shaft structural integrity are prioritized before aerodynamic efficiency. Suggesting that a trade-off between differing selection pressures (aerodynamic efficiency, aerodynamic stability and structural integrity) and developmental constraints exists. The findings of the third paper suggest that bend and angle of attack is governed by the material and structural properties, whilst the backwards sweep is also dependent on the relative movement of the barb and barbules. In the fourth paper the inherent twist of the feather does seem to have an aerodynamic advantage, and further studies are needed to fully understand its function.

In summary, the aim of this thesis was to take a first step to better understand feather behaviour in an air stream. The results suggest that trade-off between aerodynamic and structural functions have been made and that more studies are needed to fully understand the complex nature of the feather. The results in this thesis could also be of interest when constructing low Re wings, especially those with highly flexible blades.

Abstract (Swedish)

For some bird species the outermost part of the wings, the feathers can separate from each other and the wing, in such cases each feather must act as an independent aerodynamic unit. In addition to regular function of flight feathers such as colouring and overall aerodynamic and structural capabilities, these separated feathers must withstand the aeroelastic demands on their own using the complex surface the microstructures of the feather create. It is known from the fossil record that the feather microstructures have evolved over time and that modern flight feathers differ from the first birds. This thesis is a first step into exploring the behaviour of a feather and the impact on the air flow from its microstructures, using computational models. The computational models were based on a Jackdaw (Corvus monedula) ninth primary flight feather.

First, two papers examine the aerodynamics of a profile of a feather section and focus on how profile shape and microstructures of the feather impact aerodynamic performance, using both the layout of microstructures found in Jackdaw today, as well as modified ones. Modifications are done by changing the microstructures relation to each other. Second, two papers examine the fluid-structure interaction effects of the entire outermost part of the feather. Material properties and overall shape are under consideration by tracking the general behaviour of the aeroelastic response.

The findings from the first two papers indicate that the feather profile in its current configuration operates at a local aerodynamic performance maximum. However, there are indications that flow predictability and shaft structural integrity are prioritized before aerodynamic efficiency. Suggesting that a trade-off between differing selection pressures (aerodynamic efficiency, aerodynamic stability and structural integrity) and developmental constraints exists. The findings of the third paper suggest that bend and angle of attack is governed by the material and structural properties, whilst the backwards sweep is also dependent on the relative movement of the barb and barbules. In the fourth paper the inherent twist of the feather does seem to have an aerodynamic advantage, and further studies are needed to fully understand its function.

In summary, the aim of this thesis was to take a first step to better understand feather behaviour in an air stream. The results suggest that trade-off between aerodynamic and structural functions have been made and that more studies are needed to fully understand the complex nature of the feather. The results in this thesis could also be of interest when constructing low Re wings, especially those with highly flexible blades.

• author: Alenius, Frida
• supervisor: Christoffer Johansson; Johan Revstedt; Kent Persson
• opponent: Associate Professor Nakata, Toshiyuki, Graduate School of Engineering, Chiba University.
• organization: eSSENCE: The e-Science Collaboration; Animal Flight Lab (research group); Evolutionary Ecology and Infection Biology
• publishing date: 2026
• type: Thesis
• publication status: published
• subject: Biological Sciences; Mechanical Engineering; Other Biological Topics
• keywords: Aerodynamics, Feather evolution, Computational fluid dynamic, Functional morphology, fluid structure interaction, Flow stability, Bird flight, Material properties
• pages: 200 pages
• defense location: Blå Hallen, Ekologihuset, Biologiska institutionen
• defense date: 2026-10-02 09:00:00
• ISBN: 978-91-90202-50-0
• ISBN: 978-91-90202-49-4
• language: English
• LU publication?: yes
• id: bc3f6deb-eb4a-4b3c-8b1f-ee51db7fd621
• date added to LUP: 2026-09-02 16:33:11
• date last changed: 2026-09-04 15:04:37