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Hi Marv,
Just back from a nice glider flight, fully refreshed
to attack the subject once again.
On our club's glider, the airspeed for best glide is
50 knots. The airspeed for minimum sink is 45 knots.
Therefore, given a certain amount of energy, let's say
10000 feet of altitude, if you fly at L/D Max (50
knots) you will cover the greatest distance (max
range). If however you fly at minimum sink speed (45
knots) you might not go as far, but you will stay in
the air longer (max endurance). Replace the energy we
had (altitude) with a different kind of energy (fuel)
and using the same logic you get the same result. I
realize that by AOA the difference between the two
airspeeds might be imperceptible, but the fact
nevertheless remains that L/D Max gives max range.
'Stick and Rudder' (by Wolfgang Langewiesche), a book
every pilot should have describes this very well.
In the event of an engine failure L/D Max is the first
airspeed (or AOA) you want to maintain because it is
the one that will give you the biggest range and
therefore make more fields available to you. However,
once you have made the field and are still busy trying
to restart your engine, the airspeed you would want to
maintain is the one that gives you the minimum sink
rate, as that is the one that will keep you in the air
for the longest amount of time, therefore allowing you
more time to fiddle/restart your engine and run
through your checklists. The airspeed you want to
touch down at is definitely the minimum sink rate
airspeed since that's when you carry minimum
forward/downward speed, therefore allowing a 'softer'
impact.
I however realize that the exact point where we differ
is that you think that at a higher AOA than L/D Max
you are already behind the power curve. I think that
the back side of the power curve not just round the
corner but still a ways below that airspeed, and it is
possible to maintain altitude with a slower power
setting. How do we find out ? Maybe someone with an
AOA could go try it out, or one of the experts on the
list could put in their 2 cents worth.
Disclaimer: I am only discussing theory here, I
realize that the two airspeeds (or AOA) might in some
airplanes be so close that you could not tell them
apart. Also, wind is not taken into consideration
right now.
Regards, fili
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Please send your photos and drawings to marvkaye@olsusa.com.
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