How to simply determine the L/D of your glider

On Jan 10, 12:13*pm, Andy wrote:

Do you really spend all your flight time at best L/D. You must fly in
really crappy conditions. *I feel sorry for you.

Andy

I was going to say something similar, but without the pathos.

The glide angle I most need to know is at around 80 knots dry / 90
knots wet. I rarely fly at best L/D as it is generally not useful for
X-C flying and certainly not for racing except under extreme
circumstances. Even when I am low and scratching I generally fly 10
kts above best L/D as the tradeoff between glide angle and forward
progress argues for biasing towards a higher speed in the flat part of
the polar.

When I am flying slow I don't count on achieving the quoted L/D. At
that flat a glide angle any air motion will blow the glide out of the
water. Think about a 50:1 glide over 25 miles - if you experience 500
fpm in sink for 60 seconds you will all of a sudden need an L/D of
62:1. Generally I won't fly a final glide at less that 3-4 knots
McCready. If I do that then I can set the computer to read out arrival
altitude and modulate my speed depending on whether the arrival
altitude is going up or down over time. My experience is that I need
to fly around 8-10 knots below the calculated speed to fly to arrive
at the intended altitude. With this technique it pretty much doesn't
matter how accurate the polar in my computer is.

While cruising on course my achieved L/Ds as calculated by SeeYou run
anywhere from the high 40s in to the 100s at cruising speeds of 85
knots and up. This is way above the polar so the polar's not really of
any use unless I'm trying to cross a big blue hole in which case I
revert to the technique in the above paragraph.

9B