How to simply determine the L/D of your glider

On Jan 10, 12:07*pm, jan wrote:
Hi Gang
* 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 (manufacturer claimed 51.5.
How the hell could DG claim a half percentage point in 51???? That
represents a 1% accuracy! What nonsense!) - 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.
Dave

just out of curiosity I went through my OLC flights from last year.
Looking at the E value and averaging it between 9 flights resulted in
an average L/D of 20.25 for my Cherokee which I flight tested in
perfect smooth air conditions at 23.5. Sounds about right.