In article ,
Rory O'Conor wrote:

Subject: Aerodynamics of carrying water
Author:
Date/Time: 17:30 16 October 2005
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l/d max occurs when induced and pressure drag are the same, not at 75%
induced. (interference drag is (per definition) negociated)

When 75% of the drag is induced you`r flying at Vy-min (min sink)

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I stand corrected. Apologies.

http://www.av8n.com/how/htm/4forces.html#sec-powers

Both the 50% and 75% numbers are "wrong" in the sense that either one
could be correct for some particular aircraft, but neither is correct
for all aircraft.


The correct statement is that l/d max occurs at the speed at which a
small change of speed (a small increase, say) causes an increase in the
parasitic drag and an exactly equal decrease in the induced drag. In
graphical terms, it is the point where the slope of one curve is the
same as the clope of the other, but one is going up and the other is
going down. And in the Fig 4.15 in in the link above that is pretty
clearly right around 65 knots or so.

And, yes, it appears that that is at the point, for that aircraft, where
about 75% of the drag is induced drag. But you could make some
modification to the aircraft that moved one (or both) of the curves up
or down (if you could do that without changing the shape of the curve)
and the minimum would still be at the same speed, but the proportion of
induced to total drag could be almost anything.

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Bruce | 41.1670S | \ spoken | -+-
Hoult | 174.8263E | /\ here. | ----------O----------