Why a Boomerang flies
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The first correct explanation of the boomerang's flight was given by an anonymous author in a Dublin University Magazine in 1838. This explanation was subsequently forgotten for more than a century.
For a long time scientists were baffled by the boomerang's flight. Popular literature was peppered with unproven theories. One theory held that the slight twist of its arms was vital to its performance. This idea gained wide acceptance, since it reduced the explanation to an analogy with the workings of the then well-understood propeller. However, the boomerang does not work like a propeller at all.
It was not until the 1970's that a complete mathematical model was worked out. Since then neither scholars nor the general public need be misinformed. Yet explaining the intricacies of the boomerang's behaviour in everyday language has proved difficult. This task was best achieved by the Dutch scientist Felix Hess, in his 1975 book Boomerang, Aerodynamics and Motion.
The vital boomerang attributes: convex top surface, distinctive curve, thin body and wide surface area are essential to the boomerang's aerodynamic properties. With these features in place the boomerang stands out as a rare example of a non-ballistic missile.
Most missiles, such as throwing clubs, spears or stones, are ballistic. So are arrows, mortars, artillery shells and a wide range of rockets. That is, they travel in an upwards arc and then come down again. This means ballistic missiles must be thrust upwards, travelling in a vertically curved path. If a spear was thrown parallel to the ground it would be soon brought down by gravity. The time allowed for its flight on a parallel path is roughly equivalent to the time needed for its free fall, as if dropped. So, if not for its ballistic path, the spear would barely stay more than two seconds in the air, not nearly enough to travel, as it does, about seventy metres. By contrast, boomerangs fly roughly parallel to the ground and as long as they maintain sufficient speed and rotation, they can resist the force of gravity.
There are a few minor technical aspects which increase these self-supporting abilities. Again, aeroplane wings provide us with a useful analogy. The large surface area in relation to the boomerang's mass gives it a greater capacity to stay in the air. For this reason the best flying boomerangs tend to be small, thin and light, but also broad, creating a large surface area. In much the same way, modern aeroplanes unfold their wings to make the largest surface area possible, so they achieve a speedy takeoff.
Just a slight upwards tilt of the wings will further increase a boomerang's flying ability. This is achieved by a small twist of the surface which means the leading edge is slightly above the trailing edge. In the past this twist was seen as vital for the returning boomerang, to provide it with a propeller-like quality. However, the purpose of a twist is only to enhance, not to create, the boomerang's ability to fly. For the same reason the wings of aeroplane are inclined to increase its aerodynamic capability.
Flying ability can be further improved if the leading edge is steep and the trailing edge less so. Again, this design is used in aeroplane wings and can be seen in some boomerangs.