Research>Flight dynamics>Flocking

Background

Flocking is a set of behaviours by which groups of flying organisms or aircraft coordinate their motion to achieve collective goals. The two basic rules of flocking are:

• Cohesion: fly towards your neighbours
• Alignment: match your velocity vector with your neighbours

In order to prevent over crowding, the cohesion rule is replaced with a separation rule when two flock members get too close. Furthermore, if a collision is imminent then an evasion rule takes priority. Another useful rule for flock management is migration: this is like cohesion, except this time flock members all fly towards a specific point, rather than towards their local flock centroid.

What is the difference between flocking and swarming? Definitions vary, however swarming tends to be associated with collective motion driven more by migration than by cohesion or alignment. This may be linked towards the sophistication of sensing and information processing available to the flock members: groups of insects can respond to global stimuli and pheromone gradients but probably can not perform the information processing necessary for alignment. Another view is that for lift bourne flight as opposed to thrust borne flight (hovering), manoeuvering topology is relatively limited, e.g. you have to turn to reverse your direction of motion. So, in order to obtain collective motion for wing borne flight, alignment is essential, leading to flocking-like behaviour. for hovering creatures or vehicles, alignment is not so essential, leading to swarming like behaviours. Schooling (of fish) can be either swarming-like for low speed swimming or flocking-like for high speed swimming.

Publications

Watson, N.R., John, N.W. and Crowther, W.J., ‘Simulation of unmanned air vehicle flocking’, Theory and practice of computer graphics conference, Birmingham, 2003.

Crowther, W.J., ‘Flocking of autonomous unmanned air vehicles’,  Aeronautical Journal, Vol. 107, No. 1068, pp. 99-110, February 2003.

Crowther, W.J., ‘Rule-based guidance for flight vehicle flocking’, Proc. Instn. Mech. Engrs Part G (Journal of Aerospace Engineering), Vol. 107, no. 2, pp. 111-124, April 2004.

“..and the thousands of fishes moved as a huge beast, piercing the water. They appeared united, inexorably bound to a common fate. How comes this unity?” Anonymous, 17th century

The two fundamental rules of flocking