is Circulation theory "wrong" ???? (fwd)

[brian whatcott <inet@INTELLISYS.NET>]

> Date: Sun, 17 Jan 1999 09:44:39 -0600 (CST)
> From: David_Anderson <dfa@fnal.gov>

>     <PHYS-L@LISTS.NAU.EDU>,
>    tap-l <tap-l@listserv.appstate.edu>, scott@aa.washington.edu,
>    Jan-Olov Newborg <newborg@algonet.se>, jefraskin@aol, jsd@monmouth.com
> Subject: Re: PHYS-L: is Circulation theory "wrong" ????
>
> ... an aerofoil obtains lift essentially by imparting
> downward momentum to the oncoming airstream.  In the case of a single
> aerofoil, in an infinite expanse of fluid this elementary truth is
> disguised, perhaps, by the way that the deflection of the airstream tends
> to zero at infinity.
>
> There should be no question that the net result of lift is that air is
> given vertical momentum and energy.  The confusion comes from the 2D
> simulations of the aeronautical engineers.  I think you will have an
> easier time visualizing the 2D situation if you keep in mind that a 2D
> airfoil is really an airfoil of infinite length.  This fact is often lost
> and is the cause of much of the confusion.  As Scott and I discussed in
> our paper, the efficiency for lift of a wing is proportional to its
> length.  A wing of infinite length diverts an infinite amount of air down
> at zero velocity.  Since the work done is proportional to the vertical
> velocity of the air (squared), the infinite wing develops lift without
> doing work.....
> ___________________________________________________________________________
____
>                               David F. Anderson

While sympathizing completely with Anderson's approach, I had better
tighten up an assertion of his which is not quite sturdy enough to
serve as a stick for beating aero engineers, namely:
"A wing of infinite length diverts an infinite amount of air down
at zero velocity."

 This assertion would doubtless be true for any wing of finite weight.
If, however, the wing loading were given in force ( or weight) per
 unit length of span, then the weight to be reacted, also being infinite
would need finite net downwards velocity.

I hope and believe that Anderson and his associates would heartily concur
with my position. I have copied him on this note as a courtesy.


brian whatcott <inet@intellisys.net>
Altus OK