Research>Flight dynamics>Model-based animation of flapping flight

Background

The motion of animals in flight is perhaps one of the most intriguing phenomena observable in nature. Underlying the grace and elegance of flying creatures, are a variety of complicated scientific principles that are still undergoing research. However, strategic simplifications can lead to the development of physics-based methods of modelling flight. The work introduced here aims to produce physics-based simulations of flapping bird flight for the purposes of real time animation.

The flow around flapping wings is highly complex; however a reasonable approximation to the forces developed can be obtained using blade element theory. In this technique, a wing or other lifting body is spilt in to a number of chordwise strips and the local angle of attack of each strip is calculated based on the relative motion of the strip with respect to the surrounding air. The angle of attack is then used to determine the strip lift and drag coefficients and hence the aerodynamic forces acting on the strip. The overall force on the body is then determined by summing up the forces from all the strips.

The overall bird animation problem not involves aerodynamic modelling: it is also necessary to develop appropriate guidance and control laws to produce realistic flight trajectories. A particularly challenging aspect of bird flight involves the transition between hovering and forward flight (thrust-based weight support and lift based weight support). The type of flapping motion, or 'gait' required for the different modes of flight are quite different (in an analogous way to the difference between walking and running) and it is not energetically efficient to transition smoothly between these modes. This presents an interesting challenge when trying to animate a bird landing or taking off.

Publications

Parslew, B. 'Low Order Modelling of Flapping Wing Aerodynamics for Real-Time Model Based Animation of Flapping Flight', MSc dissertation, University of Manchester, 2005

Hovering birdbot, Ben Parslew

RoboPigeon (Neil Watson)

RoboPigeon, accelerating flight