>> You're getting mixed up between lift and lift coefficient. Forget the
>> second order effects...the area of a circular and rectangular plate is
>> different (assuming same max chord) so the lift is different.
>
> The assumption was the same area, hence the span and/or max chord
> must be different. Let's assume the same chord and that the max chord
> is lower on the rectangular plate.
OK, that makes a difference. For equal area, I suspect the circular plate
actually has higher lift coefficient (and lift) because it concentrates
its
area near the center where the downdraft isn't as bad...it's closer to
being
an ideal elliptic wing than the square plate. I did some quick digging on
the web and my reference books and didn't find this though, so I could be
wrong. I'm sure the Cl of a square plate and a circular plate have been
tested and do***ented somewhere.
> That's the point I was trying to make...how does the airflow
> "know" where the chord is? All it "knows" is the angle between itself
> and the leading edge. (And I think we are agreeing that that
> shouldn't make a difference...)
The airflow doesn't know or care where the chord is. However, the wing
does. The wing only generates lift from chordwise flow. As you sweep the
wing, the chord sweeps with it. Therefore the chordwise airflow drops and
the spanwise airflow increases. Since the wing can't "see" the spanwise
airflow it generates lift like an unswept wing flying at a lower speed
(ignoring other sweep effects, like dutch roll).
You can look at it a whole different way and get the same result. If you
define the chord as being parallel to the airflow, then as you sweep the
wing the chord increases and the airfoil section that the air sees gets
longer and thinner. Long and thin airfoils generate less left than short
fat ones (all other things being equal).
>From the wings' point of view, sweeping drops the airflow velocity. From
the air's point of view, sweeping makes the wing shorter and the airfoil
longer and thinner (finer). Either way, the lift goes down.
I agree that the angle between the freestream the leading edge doesn't
make
a difference, as far as this discussion goes.
Tom.
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