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Tuning
Nov 17, 2005, 10:57

Condensed Know-How  (for more detailed information, cf. our ld book)

We compiled a few hints derived from other throwers and based upon our own knowledge regarding the tuning of LD boomerangs (aoa = angle of attack):
  • Adding a positive dihedral generally results in a higher and shorter flightpath with the boom having a larger laydown rate, and you risk of obtaining a screw* flight pattern.
  • With a negative dihedral on the other hand you obtain a boom that flies fa,rther and stays lower. Besides, the laydown rate is smaller, so the boomerang flies a more circular, left** flight path.
  • A positive aoa on the leading arm gives more drag and provokes a shorter, more circular flightpath with less laydown. A negative aoa lets the boom travel out straight farther.
  • Adding a positive aoa at the dingle wing renders a more circular flightpath with a hover at the end. With a negative aoa you obtain a more elliptical flightpath and provoke the boom to perform an s-curve on its way back.
REMEMBER: Be careful with your tuning. Make only small changes!

* screw flightpath: boomerang (right-handed) precesses to fast and keels over to the right
** left flightpath: opposite from screw, boomerang does not precess (tilt axis of rotation) sufficiently, it makes a large curve to the left and always lands left, no matter how flat you throw.

Flight path
Nov 21, 2005, 11:29

Compared to the flightpath of conventional boomerangs (which the exception of MTA), the trajectory of a correctly thrown LD boomerang is much more stretched, i.e. elliptic. Although different LD boomerangs may follow slighlty different flightpaths that will all yield a correct return, there are a number of general features:
  • Elliptic trajectory
  • High altitude at farthest point
  • Highest point reached shortly after the farthest point
  • Diving on the way back
  • S-shaped curve at the end

The drawing shows one possible, yet commonly observed LD flightpath. The thin line is the imaginary projection on the ground. The boomerang is launched almost flat (60-80 deg off the vertical), so that the low lift may just balance gravity. The boomerang is usually launched with a slight positive angle to the ground so that it will climb steadily on its way out, going almost in a straight line in this first phase. As the boomerang's altitude increases, its forward velocity diminishes, and the gyroscopic forces begin to dominate. This results in a more pronounced soaring and rather narrow hairpin curve in the region of the farthest point. When the boomerang reaches its highest point, it should already have passed the apex and steer towards its way back. It will then dive while picking up speed, again in an almost straight line. This is the most critical part of the flightpath: will the boom crash ? Will it dive low enough to pick up sufficient momentum to make it all the way back to the baseline ? In a perfect throw, the boom will come surfing in low over the baseline (Attention ! It may not be seen and be very dangerous due to its possible high speed. Duck if necessary and warn your companions !) and land a few meters behind. Often, boomerangs slightly tilt over in this last phase, giving an S-shaped trajectory.

We can summarize that a well built, balanced, tuned and correctly thrown LD boom goes almost straight out, then converts its forward velocity to altitude, turns around in a narrow hairpin, and comes surfing back on a low trajectory.

Smith Picture

By the way, Herb Smith made a diagramm of his record throw of 108 yards. Similar flightpath features can be seen here, although he had to throw his boomerang low (into the ground), an indicator of not very aggressive airfoiling (undercut was not used at that time). Still, the boomerang went far due to its heavy weight (240g).
© 2005 BAGGRESSiVE
www.baggressive.com provides information for boomerang throwers and interested parties. You'll find all the info you need to successfully throw a boomerang over 100m and have it return over your head.
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