[DeTomaso] Jr. Wilson Pantera wing

[Daniel C Jones]

> How well versed are the those who opine in aero?

I was awarded "Outstanding Aerospace Engineeer" in 1986 at the University
of Cincinnati.  I still remember some of it.  Does that count? :-)

> A properly shaped wing will generate downforce with the top side of the
wing parallel to the ground.
> The cord angle will still be angled down giving you the downforce
desired.

I think you mean the airfoil camber line, not the wing chord (wing chord is
just the imaginary straight line joining the airfoil leading and trailing
edges).  Camber can provide lift (or downforce) at zero angle-of-attack.

> While tipping the nose of the wing down will increase downforce, it
increases drag as well limiting top speed.

Lift generated by either camber or angle-of-attack comes at the expense of
induced drag.

Dan Jones

P.S. Here's a segment of an earlier post I made on automobile aerodynamics
that covers camber:

Also, the path the air actually travels may be quite different from the
contour of the vehicle.  For instance, a flat shape with equal distances
over
and under can produce a lot of lift.  If you don't believe me, try this
experiment at home (just don't sue me if you do).  Step into the bed of a
pick-up truck and lift a 4'x8' sheet of plywood over your head.  Be careful
to hold the sheet of plywood parallel to the ground, while the driver slowly
accelerates to 60 mph or so.  Now comes the fun part.  Grip tightly to the
sides of the plywood and quickly tilt the leading edge upward.  What
happens?
Instant lift (and an impressive, if short lived, Peter Pan imitation).

What you've just experienced is the influence angle-of-attack has on lift.
Take a symmetric (top-to-bottom) airfoil shape that does not produce lift
when it is aligned parallel to the air flow (i.e. is at zero angle of
attack)
and point it up.  It produces lift.  Point it down and it produces
downforce.
While the physical distance over the top and bottom of the plywood are the
same, the distance the airflow travels is not.  Likewise, you don't need
angle of attack or even thickness to produce lift/downforce.  A thin curved
shape like a Venetian blind slat will also produce lift.  This is an extreme
example of wing camber.

A little wing theory and several definitions are in order here.  This would
be easier to explain with illustrations, but I'll give it a shot with words.
An airfoil is the 2-dimensional cross-sectional shape obtained by the
intersection of a wing and a perpendicular plane.  The mean camber line of
an
airfoil is the locus of points halfway between the upper and lower surfaces
(measured perpendicular to the mean camber line itself).  The chord of an
airfoil is the straight line connecting its leading edge to its trailing
edge.  Camber is the maximum distance between the mean camber line and the
chord line, measured perpendicular to the chord line.

An airfoil's angle of attack is the angle between the relative wind (the
local airflow direction) and the airfoil's chord line.  Drag is the
component
of aerodynamic force parallel to the relative wind and lift is the
perpendicular component.

If an airfoil is symmetric (top-to-bottom), it has no camber.  A sheet of
plywood has no camber.  A Venetian blind slat is a shape that has camber but
(practically) no thickness.  The camber, the shape of the mean camber line,
and the thickness distribution of an airfoil determine its lift and moment
characteristics.  Surface roughness also plays a roll but is usually treated
as a separate design issue.

Because of camber, wings can have lift at zero degrees angle of attack and
because of angle of attack, wings (and sheets of plywood) with no camber can
still produce lift.  To separate these effects, aerodynamicists break an
airfoil's lift into two components:

    Cl = Clo + (Cla * alpha)

  where:

    Cl = coefficient of lift
    Clo = coefficient of lift at zero angle of attack
    Cla = lift curve slope (the slope of Cl versus alpha)
    alpha = angle of attack

On low speed circuits where downforce is very important, Formula 1 race cars
will have multiple, highly cambered, wings, oriented at a relatively large
negative angle of attack.  All of this is done in an attempt to generate
downforce.  Since this approach is a relatively high drag method of
generating lift, you won't see similar set-ups on aircraft (they are not
limited by wing size rules).

Wings are not drag reducing devices, they are lift (negative lift or
downforce, in the case of automobiles) producing devices and will generate
substantial drag if they are effective.  Wings produce drag as a direct
consequence of generating lift/downforce.  This drag is in addition to the
wing's basic profile drag (the drag at zero lift) and is termed induced
drag.  Induced drag is proportional to the square of the lift/downforce
produced:

   Cdi = Cl**2/(pi*e*AR)

 where:

   Cdi = induced drag coefficient
   Cl  = coefficient of lift
   AR  = the aspect ratio (wing span squared/wing area) of the wing
   pi  = mathematical constant (approximately 3.14159)
   e   = wing efficiency factor (1 for an elliptical wing planform like
         that used on the WWII Spitfire fighter planes, less than 1 for
         other planforms)

When they are not strictly cosmetic, wings are added to cars for stability
and downforce reasons.  The wings on a Formula 1 race car generate
incredible amounts of drag because they generate equally incredible amounts
of downforce (4 to 5 times the weight of the vehicle - the primary reason
these cars are able to pull 4 to 5 lateral g's on high speed corners).
Obviously, F1 cars are willing to trade a lot of top speed for increased
corner speeds.
-------------- next part --------------
   > How well versed are the those who opine in aero?A
   I was awarded "Outstanding Aerospace Engineeer" in 1986 at the
   University of Cincinnati.A  I still remember some of it.A  Does that
   count? :-)
   > A properly shaped wing will generate downforce with the top side of
   the wing parallel to the ground.A
   > The cord angle will still be angled down giving you the downforce
   desired.
   I think you mean the airfoil camber line, not the wing chord (wing
   chord is just the imaginary straight line joining the airfoil leading
   and trailing edges).A  Camber can provide lift (or downforce) at zero
   angle-of-attack.A
   > While tipping the nose of the wing down will increase downforce, it
   increases drag as well limiting top speed.
   Lift generated by either camber or angle-of-attack comes at the expense
   of induced drag.
   Dan Jones
   P.S. Here's a segment of an earlier post I made on automobile
   aerodynamics that covers camber:
   Also, the path the air actually travels may be quite different from the
   contour of the vehicle.A  For instance, a flat shape with equal
   distances over
   and under can produce a lot of lift.A  If you don't believe me, try
   this
   experiment at home (just don't sue me if you do).A  Step into the bed
   of a
   pick-up truck and lift a 4'x8' sheet of plywood over your head.A  Be
   careful
   to hold the sheet of plywood parallel to the ground, while the driver
   slowly
   accelerates to 60 mph or so.A  Now comes the fun part.A  Grip tightly
   to the
   sides of the plywood and quickly tilt the leading edge upward.A  What
   happens?
   Instant lift (and an impressive, if short lived, Peter Pan imitation).
   What you've just experienced is the influence angle-of-attack has on
   lift.
   Take a symmetric (top-to-bottom) airfoil shape that does not produce
   lift
   when it is aligned parallel to the air flow (i.e. is at zero angle of
   attack)
   and point it up.A  It produces lift.A  Point it down and it produces
   downforce.
   While the physical distance over the top and bottom of the plywood are
   the
   same, the distance the airflow travels is not.A  Likewise, you don't
   need
   angle of attack or even thickness to produce lift/downforce.A  A thin
   curved
   shape like a Venetian blind slat will also produce lift.A  This is an
   extreme
   example of wing camber.
   A little wing theory and several definitions are in order here.A  This
   would
   be easier to explain with illustrations, but I'll give it a shot with
   words.
   An airfoil is the 2-dimensional cross-sectional shape obtained by the
   intersection of a wing and a perpendicular plane.A  The mean camber
   line of an
   airfoil is the locus of points halfway between the upper and lower
   surfaces
   (measured perpendicular to the mean camber line itself).A  The chord of
   an
   airfoil is the straight line connecting its leading edge to its
   trailing
   edge.A  Camber is the maximum distance between the mean camber line and
   the
   chord line, measured perpendicular to the chord line.
   An airfoil's angle of attack is the angle between the relative wind
   (the
   local airflow direction) and the airfoil's chord line.A  Drag is the
   component
   of aerodynamic force parallel to the relative wind and lift is the
   perpendicular component.
   If an airfoil is symmetric (top-to-bottom), it has no camber.A  A sheet
   of
   plywood has no camber.A  A Venetian blind slat is a shape that has
   camber but
   (practically) no thickness.A  The camber, the shape of the mean camber
   line,
   and the thickness distribution of an airfoil determine its lift and
   moment
   characteristics.A  Surface roughness also plays a roll but is usually
   treated
   as a separate design issue.
   Because of camber, wings can have lift at zero degrees angle of attack
   and
   because of angle of attack, wings (and sheets of plywood) with no
   camber can
   still produce lift.A  To separate these effects, aerodynamicists break
   an
   airfoil's lift into two components:
   A A A  Cl = Clo + (Cla * alpha)
   A  where:
   A A A  Cl = coefficient of lift
   A A A  Clo = coefficient of lift at zero angle of attack
   A A A  Cla = lift curve slope (the slope of Cl versus alpha)
   A A A  alpha = angle of attack
   On low speed circuits where downforce is very important, Formula 1 race
   cars
   will have multiple, highly cambered, wings, oriented at a relatively
   large
   negative angle of attack.A  All of this is done in an attempt to
   generate
   downforce.A  Since this approach is a relatively high drag method of
   generating lift, you won't see similar set-ups on aircraft (they are
   not
   limited by wing size rules).
   Wings are not drag reducing devices, they are lift (negative lift or
   downforce, in the case of automobiles) producing devices and will
   generate
   substantial drag if they are effective.A  Wings produce drag as a
   direct
   consequence of generating lift/downforce.A  This drag is in addition to
   the
   wing's basic profile drag (the drag at zero lift) and is termed induced
   drag.A  Induced drag is proportional to the square of the
   lift/downforce
   produced:
   A A  Cdi = Cl**2/(pi*e*AR)
   A where:
   A A  Cdi = induced drag coefficient
   A A  ClA  = coefficient of lift
   A A  ARA  = the aspect ratio (wing span squared/wing area) of the wing
   A A  piA  = mathematical constant (approximately 3.14159)
   A A  eA A  = wing efficiency factor (1 for an elliptical wing planform
   like
   A A A A A A A A  that used on the WWII Spitfire fighter planes, less
   than 1 for
   A A A A A A A A  other planforms)
   When they are not strictly cosmetic, wings are added to cars for
   stability
   and downforce reasons.A  The wings on a Formula 1 race car generate
   incredible amounts of drag because they generate equally incredible
   amounts
   of downforce (4 to 5 times the weight of the vehicle - the primary
   reason
   these cars are able to pull 4 to 5 lateral g's on high speed corners).
   Obviously, F1 cars are willing to trade a lot of top speed for
   increased
   corner speeds.