Sorry about the very delayed response on this one, I've been
away from my email for quite some time now.
The now old launch height thread kind of reminds me of the
early threads on DS. I remember the initial posts that I got in
response to my first DS posts. Most of which had comments
that were disbelieving, uncertain, or showed a lack of the
underlying physical realities.
I'm seeing the same trend with the HLG heights. A few years ago,
I did a HLG launch simulation to better understand the underlying
mechanics. My results indicated that in calm air I should be able
to get about 70 feet of altitude, and with 20 ft/sec of wind, I
should get about 100 feet. This is assuming an 80 ft/sec throw
speed, wind tunnel airfoil data, and a standard build up for the
remaining drag elements.
The 80 ft/sec initial throw speed was a number that I estimated
based on a good softball throw, and other SWAGs. It turned out
to be fairly accurate, as two different radar guns have consistently
clocked me at 50 to 55 mph.
Another comment, the better HLGs out there at present have minimum
sink values in the 1 ft/sec range, at least based on analysis using the
wind tunnel, as well as the predicted, airfoil performance. This is
consistent with the 1:10 to 1:15 "dead" air hang times that have been
recorded, if one assumes the ~70 feet initial launch altitude.
An interesting trade here is to add drag to the airframe to bring the
calm air launch height down to the only 40' - 50' "claimed" possible.
I had to triple the total profile drag to get down to 50'. To achieve only
40', the drag had to go to 5x the wind tunnel + build-up profile drag.
One more comment on the laser range finder toy. It, by itself, seems to
be quite accurate. It seems to agree very well with our previously
hand-measured 145 m F3J lines. And, I know of other applications
that use them repeatably and reliably. So, I'm pretty confident of
their absolute range readings. Whether there is a slant range
component is up to the users capability to figure out what is
vertical. I'm not too worried, as 15 degrees of vertical error (a lot),
only shows a 3.5% absolute altitude error. This is about the
scatter error that we noted when throwing in stable air, although
the scatter was undoubtedly due to variations in the individual
throws.
Joe Wurts
PS and BTW, If you cannot do at least two or more loops after
a throw around the power lines on the west of the Visalia field,
I would recommend getting into tip launch, as your conventional launch
is not up to par.
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