On May 8, 1:58*am, Ramy wrote:
Say overall speed is not an issue (you are not racing) and the only objective is to achieve best glide to make it home with a marginal final glide. Also lets assume you fail to maintain the correct speed and deviate +/- 10 knots. Which will have less penalty, flying 10 knots too fast or too slow than best glide? so for example, if best glide is 60 knots, which speed will have better chance to get you home, 70 knots or 50 knots?
Assuming stable air with no wind, but will be interested to hear opinions for other conditions.

Ramy

You can easily answer the theoretical question visually. Open your
glider manual to the polar page. Draw a line from the origin to the
tangent of the polar. This is the best glide line; the intersection of
straight line and polar gives your best glide speed and sink rate at
that speed. The slope of the line is your glide ratio. Now draw lines
from the origin to a point on the polar 10 knots slower and 10 knots
faster. Those lines represent directly your glide angle, which ever
one is flatter is the better glide angle.

Now to reality... The chance that you are doing this in exactly still
air is pretty small. And if it's perfectly still air, anyone can
actually hit their best glide speed, typically more like 55 dry, no?
So, if you're struggling to make it home, you're likely going through
rising and sinking air. Now, if there were any rising air around,
you'd stop and thermal in it. So that means you're managing to neatly
follow the sink.

So now ask the question, in gentle sink, are you better off at "best
glide" + or - 10 knots? You'll see that the 50 knot (really 45 knot)
answer is a disaster. Unless you have a really good speed to fly vario
set up, knowing that you're in 1 knot sink and what to do about that
will escape you.

So, my 2 cents: when in doubt, fly a little faster, because if you're
not in lift you're in sink, and getting out of sink is important.
Equivalently, fly the Mc 1 speed not the Mc 0 speed if there is any
motion to the air

John Cochrane