> I choose not to teach the circulation theory to my students because I
> don't think it exists in the manner the term suggests it does. I
understand
> what people are trying to explain by using the term "circulation"
(basically
> upwash and downwash), but because the airflow does not circulate
completely
> around the wing in a uninterupted circular fa****on round and round (it
stops
> at the stagnation points on the leading and trailing edges) I personally
> think the term "circulation" is misleading and even confusing.
>
> My feeling is that there is no full circulation because it stops at
the
> stagnation points where there is upwash at the leading edge and downwash
at
> the trailing edge BECAUSE of Bernoulli's theory, however Bernoulli's
theory
> alone does not explain lift. For a Cessna 172 to be lifted soley as a
result
> of Bernoulli's theory it would have to be travelling at 400 knots!!!
(from
> http://www.aa.wa****ngton.edu/faculty/eberhardt/lift.htm
an _excellent_
> site).
>
What we need to consider with circulation theory is that the circulation
function is superimposed on the LINEAR flow due to the speed of the
foil through the air, or the air over the foil. With no relative
airflow, there IS NO circulation, so it cannot be considered as the ONLY
flow. It is like studying force vectors on a force at an angle to a
chosen coordinate system. We seperate a single force into two or more
components to ease the mathematics in studying our problem.
Yes, it is a mathematical construct. But airflow around an arbitrary
shape is VERY complex. We could never design good airplanes if we did
not use such mathematical constructs (and even more arcane ones).
