First off, don’t try tuning a boomerang until you can throw decently, and consistently (unless you KNOW the boomerang is poorly tuned). You will not be able to assess the effect of your tuning if there is no consistency between your throws. Concentrating on tuning to the detriment of throwing technique will get you nowhere.
There are two main things you can do to tune a boomerang — change the dihedral, or change the angle of attack (if these terms don’t make sense to you, look in our boomerang glossary). For a two-armed boomerang, and considering the two directions the bend or twist can be made, you therefore have a total of eight potential changes.
Luckily the superimposition method of tuning, as initially described by American Dr. Fred Malmberg, makes those eight possible changes easy to remember. Here’s how it works:
Hold the tips of a two-armed boomerang, top facing up, in your hands. Now imagine the bend of the boomerang represents the flight pattern. Then, simply, bend the rang to more closely match the flight pattern you want!
To make the boomerang turn around quicker at the start (and hence have a shorter range), twist extra angle-of-attack into the lead (right) wing. To make it straighten out at the end, reduce the angle of attack of the trailing (left) wing.
There’s four of the possibilities; you should be able to easily work out what the four reverse bends and twists will do, and, more importantly, find it impossible to forget.
Of course, that’s a simplification; if, for example, you increase the angle of attack on the leading wing, you’re likely to introduce a bit of extra lift as well. So to “simply” reduce the range, you might need to bend down that leading wing as well. Having said that, try to do your tunings one at a time until you’re relatively expert at it.
Of course, sometimes it’s easier to “tune your throw” to get a different effect (ie. if the wind dies off, throwing with a little extra layover).
Also, before you start breaking your boomerangs with that little bit too much tweaking, remember that different materials accept and hold tune differently. A thicker paxolin rang will take, and hold moderately well, just about any tune you might want to bend in; but be careful with thinner sections of it, as well as some of the more brittle plastics, especially in the cold.
If you want to tune a plywood boomerang in a more permanent way, try heating it for up to ten seconds above a steaming saucepan, or in a microwave. This momentarily softens the glue between the plys — bend the boomerang to the desired shape and hold for the five or so minutes it takes to cool down and re-set the glue. Again, caution is recommended, and don’t be too attached to the paint job as it may get damaged in doing this; and if you put a boomerang with metal weights into your microwave, consider it an interesting science experiment if things go bang.
Above all, experiment to see what works for you!