Bio-inspired Wing Based on the Primary Feather of Birds
Wing of bird is composed of a lot of feathers. Typical example is a primary feather. There are three kinds of primary feathers. First primary feathers are the longest and the largest fethers in a bird wing. About ten pieces of the first primary feathers allign anteroposteriorly at the wing tip. The second and the
third primary feathers are smaller than the first primary feathers and exist between the first primary feather and the body. In addition, wing coverts cover the wing surface making it smooth.
We are investigating the function of primary feathers focusing on the stability enhancement. The first primary feathers are elastic and bend upwards under the aerodynamic force while the bird is flying. The function of this elasticity is not known in detail. So, we are conducting wind tunnel tests using hard and elastic wing models and compare the results..
Frimary feather model Deformation of elastic wing
In consequence, the deformation of elastic wing could make a lage registance force and a restoring moment to a side slip and thus had a better straight foreward moving stabiliry than the hard wing. This is because the upward bending of elastic wing can increase the dehidral angle of the wing and thus enhance the dehidral angle effect which generates a restoring moment to inhibit the side slip. The upward bending also increases the side area of the wing thus generating the large resistance force to the side slip.
Large land birds like hawks or eagles usually fly with its primary feathers bent upwards. So they may be utilyzing the large straight forward moving stability and explore the prey correctly.
Wing model (hard) set at the wing tunnel
Wing model (elastic) set at the wing tunnel