Boomerangs were not meant to come back

Groovy boomerangs were the best fliers, says a University of New South Wales researcher, who suggests markings on traditional Australian boomerangs may have more than a decorative or ceremonial importance.

Ray Nelson, senior lecturer in the school of civil engineering at University College, University of New South Wales, believes the regular pattern of parallel grooves and flutes found along the length of boomerangs and throwing sticks from the central and western Australian deserts may have more to do with enhanced aerodynamic performance than decoration.

"Until now people thought the grooves, which are 5mm wide and a fifth of a millimetre deep and are found on lots of boomerangs, were for decoration or some ceremonial reason," explains Dr Nelson, who normally specialises in coastal and ocean engineering.

Dr Nelson has tested artefacts, collected by his wife, in wind tunnel experiments and has found the grooves are, in some instances, crucial to flight.

"These are non-returning boomerangs used for hunting," says Dr Nelson, who adds that returning boomerangs were very rare and might have been seen as toys.

"A casual observer may think that the boomerang would fly better without fluting, but the grooves actually make them fly better. They make a boundary layer of turbulent air right from the leading edge of the boomerang, which allows the air to stick to the curvature for longer, giving a narrower wake, and resulting in more lift."

Dr Nelson says that this layer of turbulent air would also develop on a flat wing, but normally some 100 to 400 mm behind the leading edge. "Boomerangs are only 50 mm wide, so you need some artificial roughness. The boomerang tests showed that the uplift provided by the grooves on the top surface was, when thrown at more than 30 metres per second, approximately equal to the weight of the boomerang. So,while it maintained its speed, the boomerang tended to travel straight, without dropping. As it was usually made of mulga wood, which is hard and heavy, it could kill a person at 50 metres."

Dr Nelson adds that the flutes, which probably date back several thousand years, are analogous to the dimples on golf balls, which, he says, increase the latters' range by about 50 per cent.