How to simply determine the L/D of your glider

On Jan 11, 8:43*am, Eric Greenwell wrote:
On 1/11/2011 3:13 AM, BruceGreeff wrote:

Then ask yourself whether it is significant.

Best L/D is just one number that has dominated marketing for gliders.
Like most things marketing it is subject to a lot of creativity....

Actual performance, how well a wing uses energy from vertical gusts, how
it climbs, how sensitive it is to contamination, whether it gets
distorted over time. All these will affect how far and fast you fly -
Best L/D is a useful "summary" but it is a generalisation and subject to
a deplorable level of hype and exaggeration.

snip

* you would soon discover the vast difference in

achievable XC performance between the two.

This posting gets my vote for "best overall view of the situation".

I routinely exceed Schleicher's 50:1 claim for my ASH 26 E by 10% to
40%, flying 15 to 20 knots higher than best L/D. That's "Mean L/D" from
SeeYou statistics. It's easy in good conditions with plenty of lift,
cloud streets, or ridge lift. If the Mean L/D drops under 50:1, it's
almost always been a bad day with lift hard to find. So, I really doubt
this L/D statistic has any value for determining a point on your
glider's polar.

It is instructive to compare your statistics for the day to another
pilot flying a comparable glider. I've been surprised at how different
they can be, particularly the number of thermals taken, how fast they
cruise on average, and the percentage of circling times.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)

My mean L/D is always much better than that. I routinely make flights
of 150-250 miles with a net loss of altitude of 2000 ft or less.
That's an achieved L/D (if we want to persist in using that term out
of context) of about 450/1. Pretty impressive for a standard class
glider. The manufacturer only claims 44/1.

Why do we want to continue using the terms L/D, and best L/D, out of
context?

Andy