Hi Russell,

You probably have thought of this already but my understanding is
that, to "first order", a flat plate is just an "airflow deflector",
so that it gets maximum L/D at 45 deg AOA, and at that point, L=D.
Furthermore, a stalled airfoil approximates a flat plate.

The most satisfying explanation of lift I've found is the Coanda
effect (wiki has a decent article IIRC). The typical "air passes
faster over the curved surface than over the flat one" explanation is
wrong or at least reverses cause and effect as I understand it.

Basically, the Coanda effect says that airflow will tend to stick to
surfaces unless the surface geometry would require too abrupt a
momentum change, in which case it separates and causes turbulence. So,
an airfoil is a device for smoothly directing airflow. With an
asymmetrical airfoil or a symmetrical one with an AOA > 0, the net
airflow off the back of the wing is DOWN, producing an upward reaction
force on the aircraft.

Sean


On Tue, Apr 29, 2008 at 8:04 AM, Apptech <apptech@paradise.net.nz> wrote:
> Airfoil and flat plate lift.
>
>  I'm trying to understand flat-plate lift well enough to
>  model "bent flat plate" vertical axis wind turbines. While I
>  started off thinking that these were a trivial or simplified
>  version of a Savonius Rotor it appears that they are a
>  combination lift and drag machine.
>
>  Simple to build. Not so simple to understand. One approach
>  is "just build them and bend the 'blades' for best
>  performance". Hopefully a modicum of theoretical
>  appreciation will help at least a little.
>
>  Target application is an alternator driver.
>
>  ____________________
>
>
>  AIRFOIL NASA Glenn FoilSim II-Vers_1_4 - Airfoils
>  Beta testing version - let NASA know what's wrong with it.
>  Online airfoil simulator
>
>         http://www.auf.asn.au/FoilSim/FoilSim.html
>
>
>  Lift from flow turning
>  Downloadable applet simulator
>
>         http://www.grc.nasa.gov/WWW/K-12/airplane/right2.html
>
>  Lift
>
>     http://en.wikipedia.org/wiki/Lift_(force)
>
>  Foil
>
>         http://en.wikipedia.org/wiki/Foil_(fluid_mechanics)
>
>  Flat plate lift at small aoa
>
>         http://books.google.co.nz/books?id=yV2QSl92TzcC&pg=PA66&lpg=PA66&dq=flat+plate+lift&source=web&ots=08MIDR3FqI&sig=EmP4yz4I12Ray11meRciPgOBjx4&hl=en#PPA67,M1
>
>
>  Fly Light Groundschool theory of flight
>  Airfoils and wings module
>
>         http://www.auf.asn.au/groundschool/umodule4.html
>
>
>
>
>  Tutorial - Circulation theory of lift.
>
>         http://www.onemetre.net/Design/Downwash/Circul/Circul.htm
>
>  Momentum theory of lift
>
>         http://www.onemetre.net/Design/Downwash/Momentum/Momentum.htm
>
>  Lifting line theory of lift
>
>         http://www.onemetre.net/Design/Downwash/LiftLine/Liftline.htm
>
>  Airfoils at high angles of attack
>  Design your own Mig 29 / F22
>
>         http://www.aerospaceweb.org/question/airfoils/q0150b.shtml
>
>
>  Kite lift equations
>
>         http://www.grc.nasa.gov/WWW/K-12/airplane/kitelift.html
>
>  Interactive kite modeller
>
>         http://www.grc.nasa.gov/WWW/K-12/airplane/kiteprog.html
>
>  Aaaaaagh!
>
>         http://www.google.co.nz/search?hl=en&q=flat+plate+lift&meta=
>
>
>
>
>  --
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>  View/change your membership options at
>  http://mailman.mit.edu/mailman/listinfo/piclist
>
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