When you bend the arms of your boomerang either up or downwards, you are adjusting the dihedral, which is the angle above or below the straight/neutral position. In general, bending the arms will modify the distance, hover, and trajectory of your boomerang. Remember even a few degress in change will alter the flight of your boomerang significantly.
Bending Up
Bending up is generally recommened to increase the catchability in situations where there is no wind. By bending one or more of the arms of your boomerang up you are adding dihedral to the wings. This generally results in a higher trajectory, earlier lying down (shorter circle), and a longer hover. When you add dihedral to the lift arm the boomerang will tend to lie-down sooner in the flight and then zoom higher. This requires the thrower to alter the throw to a more vertical and higher release. You will get a higher and more circular flight with a nice hover at the end of the flight, making the boomerang easier to catch. Adding dihedral to the dingle arm (trailing arm) will result in a higher trajectory and a great hover, but at the expense of a lot of distance.
Bending Downward
Bending down the arms of your boomerang is recommended for long distance, throwing in wind, or fast catch. Bending the arms of your boomerang downward will decrease the dihedral of the wings and will result in: a lower trajectory, a reduced hover, and lying down later in the flight, which produces more distance. By reducing the lie-down of the flight the boomerang will tend to fly in a figure-eight shape helping to increase distance. Since the boomerang is flying lower it is less effected by the wind, which combined with the reduced hover makes bending downwards a great tuning idea for windy conditions. It is suggested that the throw be adjusted accordingly by holding the boomerang with more tilt (flatter), throw lower, harder, and at times, more into the wind.
