MOMENTUM • VIRGINIA TECH MECHANICAL ENGINEERING 11 that these transitions work only if the water isn ’ t allowed to get all the way to the bottom of the porous feather structure .”
Boreyko remained intrigued with how the balance was struck , curious about the mechanisms that allow a duck to hold water in its feathers without sinking completely . He brought Farzad Ahmadi into his lab in 2014 as a graduate student , sharing that intrigue in one of their early meetings . Ahmadi picked up the project and dove into the finer details . Their first approach was simple – they attempted to force a single drop of water through a natural duck feather .
“ It didn ’ t work ,” said Ahmadi . “ Then we had the idea to build a pressure chamber to force a pool of water through several layers of feathers .”
they sealed one feather at a time , leaving only a small area exposed . The researchers sealed each layer , leaving an area exposed in the same place on each surface . This allowed them to create a column of exposed feather surfaces upward through the stack . A thin pool of water was poured over the top exposed surface . The stack was placed in a pressure chamber , and gas pressure was employed to push the water downward through the feathers . A camera was placed at the bottom to observe the water as it passed through the layers .
Feathers have micro-sized openings in them , tiny slots that allow pressurized water to pass through . A duck sitting on the surface of a pond isn ’ t encountering any water pressure , so the water penetration is negligible . A duck diving downward , however ,
A synthetic feather in the pressure chamber created by Boreyko ’ s team .
Under pressure
The team first needed to ensure the water could only penetrate directly through the feathers , as opposed to simply leaking around their outer edges . To achieve this , encounters a steady increase in hydrostatic pressure , something familiar to anyone taking a dive into the deep end of a pool .
Ahmadi discovered that as the number of feather layers increases , the pressure required to push water through all the lay-