Boomerangs were the world's first heavier than air flying machines, used most famously by the Australian Aborigines, but also found in other ancient cultures in Egypt, stone age Europe and the Indian Sub Continent. No-one knows how they were first invented and even though they look simple, they use a very complex combination of physics and aerodynamics to perform their amazing returning flights.
A returning boomerang is basically two wings joined at an angle of between 80o and 120o, although it can have more than two wings. The wings are arranged so they work best when the boomerang is rotating rather than flying straight like an aeroplane. The combination of spin with forward motion causes uneven lift on the wings because at any given time, one wing is rotating forward in the same direction as the flight, while the other is rotating backwards, against the direction of flight. This means the air flow over the wing on one side of the disk of rotation has a higher airspeed than the other wing and so generates more lift. The uneven lift tries to tip the boomerang over, but just like leaning a moving bike over makes it turn, the boomerang's spin twists the tipping force at right angles and gives the boomerang a curving flight. Another tipping force, caused by the centre of lift being forward of the centre of gravity, is also twisted to make the boomerang "lie down" in flight. The name for both these twisting motions is gyroscopic precession. The illustration above shows how it all comes together to make the boomerang fly in a circle and (given some skill) come back. Click here for a view of a flight path from above. Click here to see a boomerang movie.