A team of scientists and engineers have gained new insight in the aerodynamics of gliding birds – something they think can help develop small and more efficient aircraft.
The team, based at the Royal Veterinary College, Royal Veterinary College filmed owls and hawks gliding through a mist of tiny helium bubbles. Over 20,000 bubbles in the wake were tracked automatically, revealing the ‘aerodynamic footprint’ left by the birds which in turn showed that they use their tails to minimise drag.
Professor Jim Usherwood, Senior Research Fellow at the RVC and lead author of the paper, said: “What was striking at first was the beauty. For many seconds after the bird had landed, the vortices in the wake kept spinning like bath water going down a plughole. Birds appear to be minimising drag, even if this means they are highly unstable and need to constantly make small adjustments just to glide without crashing.”
The RVC scientists found that aerodynamics at the relatively small, slow scales of birds is much more influenced by the air’s viscosity – or ‘stickiness’ – than is the case for airplanes. The form of drag associated with viscosity is minimised if lift is spread evenly across the planform area (effectively the bird’s silhouette) and, as birds have tails that stick out, this means that extra lift from the tail is required to reduce the overall drag.
Professor Richard Bomphrey, co-author of the paper, said: “Our understanding of birds in flight was used to generate the very earliest aircraft designs. Since then, aeronautical engineering has led to aircraft that are larger and faster – where the viscosity of air becomes less important – and birds have been left trailing in their wake. Now, though, as our attention turns back to smaller and more efficient vehicles, it seems that birds might have a new relevance to future aeronautics.”
The work was done in conjunction with engineering company LaVision and is published in The Journal of Experimental Biology.