>> I guess I'm not getting the picture of why the angle of attack
>> goes to zero as the plate is rotated at 90 degrees "sweep."
> AoA goes to zero at 90 degree sweep assuming no dihedral/anhedral (I
hope I
> said that before).
> Imagine a rectangular plate with zero dihedral and zero sweep at some
AoA.
> If you sweep it 90 degrees, what was originally the end of the plate is
now
> the leading edge...the airflow is going straight "sideways" along the
> original wing. That will be true regardless of original AoA. It's not
an
> aerodynamics thing, it's a geometry thing.
OK, I guess I was assuming the plate was rotated about a
vertical axis...but in any case we can cause an angle of attack
in the situation of a plate held edgewise to the flow, and it
will produce some lift.
>> But let me pose a question that seems equivalent to me: suppose
>> we have two flat plates of the same area, one rectangular and one
>> circular, held at the same angle of attack. Will they produce the
>> same or different lift?
> Different. Areas and spanwise chord variation are different for the two
> plates. Lift coefficient should be sort of close, as they're both flat
> plates, but the induced drag will make it somewhat different.
I agree that the lift will not be identical for the rectangular
and circular plates. But it's second order effects such as induced
drag. We don't have lift reduction of each spanwise element
pro****tional to the (square of the) local angle between the flow and
the leading edge--which seems to me to be analogous to the sweep
angle. So if a small spanwise element doesn't suffer a lift dropoff
according to its apparent sweep, why does an entire wing?
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