February 9th 2009

Will my boomerang come back?      

                   

     given by the President, Richard Aldridge

Inclement weather prevented the advertised speaker making the long journey up to Norwich. Our President, Richard Aldridge, stepped in and gave a talk about the flight of the boomerang, an old (if not the oldest!) flying machine developed by man.

After a brief historical introduction that demonstrated that boomerangs and boomerang like objects had a long and diverse history across the globe (not just in Australia!), Richard explored the basic physics of flight with particular relevence to boomerangs. Clearly to get an object to fly through the air a force, called lift, has to exist that counterbalances, if not exceeds, gravitational attraction and this lift has to be provided so that flight is stable.

The normal source of unstable motion for flying objects is the self interaction between the moving object and the forces produced by the vortex stream that are caused by the consequential circulatory motion of the airflow around the object itself.

Appropriate methods have to be found for a boomerang, which do not have the fins and flaps of conventional aircraft, to overcome these destabilising effects

                     A typical boomerang geometry                                                                A boomerang 'returning' path

In the case of the boomerang and similar flying objects, such as the frisbee, discus and flying disc, use is made of the inherent stability of rotation about an axis. The classic example of such stability is the motion of a spinning top.

The geometry of the boomerang together with its rotation has the consequence that, under certain circumstances, it will fly in closed paths that includes the launch point later on after launch on its trajectory i.e. the boomerang is said to ‘return’.

The talk as well as discussing lift and angular motion included several live demonstrations such as an examination of the stability of real gyros and the flying of several different indoor boomerangs and frisbees.The audience were particularly amused when one of the 4 armed boomerangs returned and landed on the speakers head! He had completely lost sight of this particular boomerang after launch!! Richard was thanked by our Vice President, Dick Abbott, for stepping in at the last moment.

A pdf copy of the slides used in this talk can launched by clicking here