This question is bordering between aviation and biology. I am posting it here, since it is really about aerodynamics.

At first, one would think, that birds should be aerodynamically stable to save themselves the effort of maintaining stable flight. However, even if humans had rigid joints they are in an unstable configuration other than four-legged animals. Thus, stability does not seem to be a must for biology, at least in certain aspects.

So, are birds aerodynamically stable? Are all of them, or are some species which are and some which aren't?

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    $\begingroup$ @Federico why does it have to be (approximately) a rigid body to be aerodynamically stable? I think you could argue if a bird can glide with all muscles relaxed, you could call it aerodynamically stable. $\endgroup$
    – falstro
    May 23, 2016 at 10:27
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    $\begingroup$ @Federico similarly, you could also ask if there is a combination of joint angles in birds that would make them aerodynamically stable if fixed, thus removing the need for constant adjustments to remain in control. $\endgroup$
    – falstro
    May 23, 2016 at 10:29
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    $\begingroup$ Hmm... The on-topic page says that aerodynamics questions related to aircraft are on-topic here. Since a bird does not normally qualify as an aircraft, I'm inclined to agree with the off-topic close votes. Also, I agree with Federico in that you'd need to specify a particular bird and a particular configuration for this to be answerable regardless of what site it's on. You're probably more likely to find bird experts at Biology and the question should be on-topic there, too. $\endgroup$
    – reirab
    May 23, 2016 at 14:00
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    $\begingroup$ I don't agree with the idea that this question is off-topic or more related to biology. Laws of aerodynamics apply equally to aircraft and birds. The question may be impossible to answer because this tight coupling of the aerodynamics and fly-by-wire control system in birds, but the same principles apply. $\endgroup$
    – DeltaLima
    May 23, 2016 at 14:12
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    $\begingroup$ Location and semantics aside, is the answer not terribly obvious for a vast majority of bird species? $\endgroup$ May 23, 2016 at 15:38

1 Answer 1


Birds have integrated active control systems that rely on several sensors to adjust the control surfaces to stabilize the flight. Since it is very difficult (perhaps impossible) to study the aerodynamic properties of the bird independently from its control system it is hard to make any claims on the static or dynamic stability of a bird.

What can be said is that from a control system point of view, most birds are observable, controllable and stabilizable in flight. This does not apply to the class of flightless birds.

If you are interested in the similarities in aerodynamics between insects, birds and aircraft I recommend getting a copy of "The Simple Science of Flight; from insects to jumbo jets" by Henk Tennekes, an Emeritus Professor of Aerospace Engineering at Pennsylvania State University.

After sitting in the garden on a sunny afternoon, observing various bird species and tinkering a bit more on the subject I actually think that many birds are unstable. Especially the smaller species that fly in the garden through bushes and trees, but also those that hunt for flying insects, are capable of extreme rapid changes in direction of flight; they are very agile.

Stability and extreme manoeuvrability are difficult to combine. In fact modern jet fights are designed to be unstable to improve their manoeuvrability. They then need a computerized control system to stabilize them.

An online search showed that some research has been done on the field of flight stability of birds Petter Krus of the Linköping University in Sweden has published an article on Natural methods for Flight Stability in Birds.


There is a stark contrast between the behaviour of flying man-made artifacts and the effortless elegance of bird flight. In this paper, mechanisms are proposed that seems to be at least related to the way birds fly when they are gliding (the no propulsion case). It is recognized that biological structures and actuator systems (muscles) are characterized by a great deal of compliance that produce a completely different dynamic behaviour of flight. In this paper it is demonstrated how this can be applied on a geometrically unstable bird-like configuration. The result is that geometrically unstable configurations can be stabilised without the need of rate gyros and/or accelerometers. Although the bird might have a fast acting control system for flight control, it is unlikely that it is fast enough for active stabilisation of the short period oscillation, and this is unnecessary with the model described here, which only requires stabilisation of the long period oscillation.

In his introduction he also briefly refers to the work of Tennekes, which does not include much about the stability of birds. Also in the introduction he observes that birds have a cambered wing and must have an aft centre of gravity. This combination makes the bird unstable (if it were a rigid body).

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    $\begingroup$ Hi DeltaLima, your garden observation put you on the right path. Birds are indeed unstable, in pitch, yaw and roll. The amount of instability depends on the wing planform and tail incidence, but in no wing position is a bird stable in yaw. $\endgroup$ May 28, 2016 at 7:45
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    $\begingroup$ For gliding, it should be possible to build a replica of the bird and study "the aerodynamic properties of the bird independently from its control system". I wonder if anybody tried. $\endgroup$
    – h22
    May 28, 2016 at 8:29

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