Like you all I have questioned what the best L/D of my 3 (now 1)
gliders - DB800B, Stemme S10-VT and SparrowHawk were in reality
suspecting that real L/Ds would be lower than the manufacturers
published values. I have used a PDA for many years switching it
between gliders. Software is GN11. After each flight I usually
download the log and review on a PC using SeeYou. Now GL11 calculates
an average L/D which can be viewed with the stats for each flight.
Also one can straight edge any glide from a flight and calculate that
effective glide ratio. Especially on a non thermic day one can get a
feel for a gliders' performance. So what I have I found after crudely
averaging in my brain 10 years of flying these 3 glider. Fairly
consistently the DG800B came out around 43

The above describes one way to develop what I think of as a 'working L/D' for
your glider, your soaring style and 'typical conditions.' I developed my own
w/o benefit of electronics/GPS/software, and it was something over 30:1 for my
never-detailed 15-meter glider, which model Dick Johnson measured at
37.something. Given the relative crudity of my measurements, the
routinely-in-motion atmosphere through which the measurements were taken, and
the fact I 'rarely' flew at max L/D, the disparity between numbers seems
entirely sensible to me. I'd hope (expect?) anyone desiring to fly XC does
something similar before heading out while boldly depending on their glide
computer to get them home sans risk of a landout. That noted, don't mistake a
lower number (and I *have* experienced 30+ mile glides in the PM exceeding
60:1 L/D) for manufacturers' 'brochuresmanship.' In the absence of controlled
test conditions, you are NOT evaluating your ship's max L/D.

(manufacturer claimed 51.5.
How the hell could DG claim a half percentage point in 51???? That
represents a 1% accuracy! What nonsense!)

Um...how the hell did whomever evaluated Robert Harris' former world altitude
record determine he soared to 49,009 feet? Nine feet?!? 9/49,000 = .018%
accuracy. Bogus? Not a bit; it simply 'fell out in the wash' when doing the
evaluative arithmetic. No need to impute sinister motives to anyone...

- the Stemme around 42
(claim approaching 50) almost comparable with the DG and the
SparrowHawk around 29 (claim 35)

If you haven't done these seat of the pants measurements with your
own gliders I would suggest you all do them. It takes a little
practice and time to do the averaging over many flights. Interestingly
after a time and with practice you will find the measurements become
quite consistent which suggests that they might represent something
close to reality.

We're in agreement here, but don't mistake the numbers for anything other than
what your ship delivers, with your flying style, in 'typical conditions.' Then
be happy, don't worry!!! (Oh... and be prepared for the occasional landout,
too, I don't care WHAT your computer may have told you ' a while back!')

Regards,
Bob W.