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 (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).
Author
