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Old September 5th 04, 11:54 PM
Nyal Williams
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At 05:42 04 September 2004, Eric Greenwell wrote:
Nyal Williams wrote:
At 18:24 01 September 2004, Chris Ocallaghan wrote:

I'd always assumed there were two factors in choosing
a pattern speed.
First, safety, thus the +5 for turbulence. The other
was to place the
glider at best speed to fly. That way if you have to
put the spoilers
away, you are guaranteed to cover the maximum distance.
If I recall,
the simple formula for best speed was best l/d speed
plus 1/2 the
headwind. Don't recall the second ever being explained
though. Just
seemed to fit.



It appears that if you draw a tangent to your glider's
polar beginning, not at zero, but at any given headwind
speed, the line will touch the polar at a point that
is best L/D plus half that headwind.


I was under the impression it was added to give you
a margin for gusts
and turbulence, which are usually less than the average
wind speed. The
'half' was likely chosen empirically, as something
that was adequate
almost all the time.

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Eric,

Chris already accounted for the safety factor (gusts
and turbulence) with his statement about plus 5 knots.
His second factor was best speed to fly if you have
to close spoilers and need the guaranteed best speed
to fly for maximum distance.

My answer was to that part of his statement. One might
add another 5 knots for the gusts, etc., if desired.