Birds gliding through bubbles reveal aerodynamic trick


As this barn owl glides through the darkness a sudden flash of light illuminates
over 20,000 helium filled soap bubbles, suspended in the air. Researchers can track the bubbles as they
swirl in the owl’s wake, and they’re using this to study the bird’s flight in unprecedented
levels of detail, revealing unexpected ways in which
birds generate lift and reduce drag while gliding. The first task is to persuade the birds
to fly through the cloud of bubbles. If they can see the bubbles,
they try and avoid them, so the researchers have to snap
the lights on right at the last minute. That’s the idea anyway. When the birds do glide through smoothly, they leave vortices swirling in the air behind them. The movement of each bubble is then tracked
and recorded by a computer to visualise the air flow. As expected, the researchers saw vortices
spinning down from the wing tips. This helps provide lift. But the swirling bubbles
revealed something surprising: a second pair of vortices
coming down from the tail. These also generate lift and because they come from the tail,
the lift is spread more evenly over the bird’s body, reducing overall drag. This is different from the way something
like this toy plane works. It has fixed, solid wings
and uses its tail for stabilisation. A tail that generated lift
would make it very unstable. But birds are able to constantly move and
adjust their bodies for stability, so they can use their tails to make extra
lift and decrease drag. Engineers might be able to copy this trick for use in aircraft that
actively stabilise themselves. It wouldn’t work in the same way in
something like a passenger plane, which is much larger and faster, but for small, slow-flying craft,
like a gliding drone, designers could make good use of this
aerodynamic trick borrowed from birds.

15 thoughts on “Birds gliding through bubbles reveal aerodynamic trick

  1. wait what, so birds use there tail to produce lift! stop the presses every one need to to know this.
    o wait no…. how is this news?
    how did the researchers not know this!

    just look at a owl glide and land, u will see that the wings are more to the front wile gliding. this needs to be offset by the tail providing lift.

    o and the fact that tail wings don't produce lift is the hole point.
    if u make them as small as possible at the greatest distance from the center of balance u have very little drag.if u wand to use the tail plain to produce lift u will need to move the center of balance of the entire aircraft.u want to move the 2 main FIXED wings forward so u can use the tail for lift but cant use it for control anymore?

    this vid is so dumb and the writers don't know what they are talking about.

  2. Beautiful! For anyone interested in aerodynamics this is really interesting, and of course birds of prey like the owl are amazing and fascinating. However, people can see this for themselves, by watching seagulls as they ride onshore winds on the coast. They use their tail feathers constantly whilst flying, helping them turn and out manoeuvre their rivals. When they come into land, they spread their tail feathers out into a wide 'delta' shape and angle them down, so as to generate extra lift and bleed off airspeed, so they can land at walking pace. Conversely, whilst they are in flight, they can tuck all of their tail feathers into a very minimal, streamlined shape for extra speed, making fine adjustments to their flight with their wings only.
    Aircraft designers have long wanted to emulate this astonishingly fine tuned control system for agile, efficient flight, but it is expensive and very challenging to implement. Computerised, 'fly-by-wire' control systems make it possible, but stability is still an issue for 'tail-less' high performance aircraft. Research aircraft have been built with wings that actually twist in a controlled way, but no aircraft in service uses this technology.
    The current designs that are widely used may seem mundane, but they are stable, safe, and easy to build.

  3. Nice video. I in particular liked the part when the LED was turned on too early and the bird saw a white "wall" and tried to land on it. This was not (of course) involved in the original paper and I appreciate this footage. I'd like to point out 3 things on the video, though: (1) The wingtip vortices do not "helps provide lift". They are unavoidable byproduct of producing lift with a finite span wing, and they actually cause the induced drag. (2) It's not the lift but the lift coefficient that is distributed more evenly over the body (spanwise). Please see the red lines in figure 5 of the paper. This is the whole point of the paper… (3) The video acknowledges 2 professors but not the 2 postdocs who played the major roles in the experiments and analysis. No mentioning on the LaVision (equipment company) people either, who not only provided the software/hardware but actively involved in the experiments.

  4. The vortices from the wings do NOT generate lift. They are an effect of lift. They generate induced drag and reduce the effectiveness of wings.

  5. "Canard" aircraft do this as well, but they look weird, because the stabilizer is in the front, and also adds lift as it does its job. Rutan's odd looking, but beautiful airplanes are like that. They don't require active stabilization. The other extreme is helicopters and drones, which require a lot of active stabilization, and it was impossible to build one on a small scale until we had the technology to miniaturize the electronics and position sensing devices needed to do that.

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