[Shotimes] Do Air Dams, Spoilers, and Wings Work?

[Ron Porter]

In this case, I believe that he is referring to the "skateboard" spoiler on
the Gen 3, which supposedly has a real benefit at higher speeds.

Ron Porter

-----Original Message-----
From: shotimes-admin@autox.team.net
[mailto:shotimes-admin@autox.team.net]On Behalf Of James F. Ryan III
Sent: Saturday, April 12, 2003 11:28 AM
To: shotimes@autox.team.net
Subject: [Shotimes] Do Air Dams, Spoilers, and Wings Work?


Found this excellent article on one of my Fiero sites.  It's from Sept 98
issue of Car and Driver.  It has excellent info AND mentions the SHO!!!

Jim Ryan
Wayne, NJ
91 Plus  all white/mocha with fiberglass hood, rod shifter, & rear spoiler

255 Lph fuel pump, SHO Shop can & horn, 80mm MAF, S&B cone filter, SHO Shop
HiFlow Y-pipe & cat-back exhaust, SHO Shop LPM, SHO Shop underdrive pulleys,
SHO Shop HiRevs Jr clutch & steel billet LiteWeight flywheel, reinforced
engine & trans mounts, SHO Shop TQ limiters, SHO NUT aluminum SFBs, FPS 96
SHO front brakes, Carbotech F brake pads, Nooks full-body SFCs, Koni adj
struts, SHO Shop linear springs, 24mm FSB, 26mm RSB, SHO Shop steel f&r
STBs, Bridgestone Potenza RE-730 225/55-16, CATZ MSP fog lights, police
grille



  When we hear a posh English accent, we assume the speaker
is intelligent. If we see food packaged in a green box labeled "Organic!" we
assume it is healthful. Similarly, when we see a skirtlike air dam on the
front of a car, or a wing or spoiler on it's rear deck, we presume it's a
performance car. But do these devices in fact have an aerodynamic effect on
production cars? Or are they no more functional then a vinyl roof? They come
in so many configurations and sizes, and on so many kinds of cars, that it's
easy to dismiss them as nothing more then eye candy. But that's not always
warranted, as we shall see.
  Aerodynamics is almost as much black art as it is science, and problems
that crop up when air is forced around an object are not easy to fathom. As
a car speeds down the road, for example, it creates a moving obstruction in
the atmosphere. Stationary molecules of air must move up, down, or sideways
to flow around the car as it forges ahead. The air that ends up underneath
the car can be trapped by the various mechanical bits protruding from a
car's undercarriage and end up being dragged along by the moving car. That's
how a car can pick up a scrap of paper as it passes over it and whisk the
paper along in its wake. Dragging this air along requires energy and
comprises a large fraction of a car's aerodynamic drag.
  Moreover, the flow of air underneath the car can build pressure at the
front of the car and in the engine bay, lifting it upward, resulting in less
force pressing the tires to the pavement. That means less grip, which can
adversely affect handling.
  One way to attack these drag and lift problems is by creating a smooth
underbelly. That can be done by installing panels underneath the car to
reduce the likelihood of air being snagged and pressurized by underbody
protrusions. But today, only pricey mid- and rear-engined production cars
such as the Ferrari F355 and the Lotus Esprit use such panels because of the
cost of manufacturing and installing these parts, known as "belly pans."
  A far more common solution is the front air dam, a rigid, skirtlike panel
that extends below the front bumper. This dam diverts air upward over the
hood, or into a grille opening, or around the sides of the vehicle.
  At the rear of the car, the goal is to keep the air flowing smoothly over
the body so that the hole the car punches through the atmosphere closes as
neatly as possible. Airflow that closely follows the contour of the car is
called "attached" or "laminar." The shape that best achieves this laminar
flow is the teardrop---the configuration formed by a drop of rain as it
falls through the air (round end first, for science philistines). GM's
super-efficient EV1 electric car approximates this shape, but more
conventional contours can also maintain laminar flow. The essential contour
is a rear window that is sloped to within 25 or so degrees of horizontal.
Many hatchbacks are so designed, as are such cars as the Chevy Corvette and
the Toyota Supra.
  But keeping the air attached to the vehicle can present a different set of
challenges. When you observe such a hatchback car from the side, it is
curved on top and flat on the bottom---like the cross section of an airplane
wing. When air flows over a shape like this, the air must travel faster over
the top than over the bottom. This phenomenon produces lift and is known as
Bernoulli's principle, which maintains that a pressure drop must when
airflow is accelerated. The pressure over the top of the car might be only a
fraction of a psi less than the pressure on the bottom, but that difference
acts over a large area of the car---from 10 to 20 square feet. The pressure
difference also increases with speed. Traveling at more then 100 mph in some
cars can produce hundreds of pounds of lift. Lift generated this way
typically acts more on the rear of the car. But it has a similarly
destabilizing effect on handling as front-end lift.
  Vehicles with more-vertical rear windows---such as formal sedans, wagons,
and minivans---don't suffer from these lift problems as much, because the
air spills behind their more-upright rear windows in randomly tumbling eddy
currents. This is what's known as turbulence, and although it limits lift,
it's a major contributor to drag.
  The middle ground between these two conditions---between 28 and 32 degrees
of backlight angle---is no solution, either. At this angle, the air can't
decide whether it should stay attached or become turbulent, so it does both
unpredictably. Aerodynamicists  are about as fond of this backlight angle as
they are of a vertical, flat windshield.
  Rear wings and spoilers were invented to address these lift and airflow
issues. Wings come in many shapes and sizes, but they share a common
characteristic---a narrow, horizontal surface, mounted away from the body in
clean, undisturbed air. (Wings mounted close to the body are either
nonfunctional or act more like spoilers, described below.) Wings add
downforce---the opposite of lift. One way to create downforce is to shape
the wing into an airfoil---an airplane wing of sorts---and turn it upside
down. This forces the flow below the wing to travel at a higher velocity
then the air above, creating a downward force. A second way to create such
downforce is to angle the front of the wing slightly downward into the
airflow. This creates more drag then a horizontal airfoil, but it can allow
adjustability of the downforce.
  To differentiate a spoiler from a wing, think of turkey plumage. The
spoiler is an angular, liplike appendage attached to, or designed into, the
rear of the car. It can be used to create downforce like a wing , but it's
more commonly used to reduce lift or drag. On hatchbacks, a lip spoiler can
create a pool of air ahead of the spoiler that separates the airflow from
the backlight, reducing lift. It can also be used at the rear of the car to
launch the airflow cleanly away from the vehicle, preventing its tendency to
remain attached to the car's trailing surfaces. This can decrease drag as
well as reduce the underbody pressure that contributes to lift.
  Automakers were hard at work on drag reduction as far back as the 1930s.
It wasn't until the early 1960s, as both race-car and production-car top
speeds approached 200 mph, that lift became an issue. Ferrari racer Richie
Ginther is credited with inventing the rear spoiler for downforce in 1961,
and discreet rear spoilers started appearing on competition Ferraris soon
thereafter. One of the first cars to use a front air dam was Ford's GT40.
The high snouts of early prototypes produced so much lift at 200 mph that
they were virtually undrivable. Fitting a air dam increased the force on the
front-tire contact patches from 310 pounds to 604 pounds at top speed. The
Dodge Charger Daytona and Plymouth Superbird twins of 1969-70 were among the

first production cars to sport a rear wing. The adjustable wing, supported
high above the rear deck by finlike butresses, combined with changes to the
nose of the car (including an air dam) to increase downforce at both ends of
the car. This allowed test drivers to lap Daytona speedway 5 mph faster.
  Porsche was probably more responsible then any other carmaker for turning
air dams and spoilers into fashion statements. The 1975 Turbo's integrated
front air dam and huge whale-tail spoiler in back cut overall lift on the
cantankerously handling 911 by a whopping 90 percent. The
air-dam-and-plumage look soon became synonymous with the prestigious Porsche
brand. By the late 1970s, just about any car aspiring to a performance image
wore some kind of air dam or spoiler.
  Today, air dams, spoilers, and wings can be found on such supercars as the
Dodge Viper GTS and Acura NSX, where you would expect them. But they also
adorn the exteriors of Dodge Neons, Toyota Corollas, Oldsmobile Intrigues,
and other sedans, many of which are not capable of speeds of much more than
100 mph.
  Which raises an important point; these aerodynamic devices don't do much
if your not going fast. Aerodynamic drag doesn't even exceed tire drag until
you've reached 40 to 50 mph, and you may have to be doing well over 100 mph
for spoilers and wings to have any appreciable effect on lift or downforce.
This is because aerodynamic forces vary with the square of a car from 80 to
160 mph, and if faces a four-fold increase in lift and drag forces.
  Nearly all cars can benefit from the drag-reducing effects of an air-dam.
The Pontiac Grand Prix sedan's front air dam, for example, reduces that
car's overall drag by 5 to 10 percent. Front air dams also help with engine
cooling and can even serve as a useful place to mount fog lights.
  Carmakers don't deny, though, that rear wings and spoilers are often more
show than go. At GM, spoilers are usually added as a marketing-driven item
at the beginning of a car's development, according to John Plonka, an
aerodynamics-development engineer at the company. "From there, we take those
pieces and try to make them aerodynamically useful, with varying success,"
he adds. John Doughty, chief designer of Ford's Advanced Design Studio,
describes a similar story but adds that "if we found that it detracted from
the performance, we wouldn't recommend it." Perhaps such a recommendation
was made, but not heeded, on the Ford Mustang Cobra.
  Some carmakers would rather not install spoilers but offer them simply
because car buyers demand them. "Personally, it hurts to see a Camry with a
[nonfunctioning] spoiler on the back," says Donald W. Brown, former national
product-planning manager for Toyota in the U.S., "but if the dealers are
going to put them on anyway, we would rather supply them to ensure their
compatibility with the car."
  That doesn't mean these devices are never beneficial to workaday cars.
Brown notes that the factory rear spoiler on the Lexus SC trims its
coefficient drag from 0.32 to 0.31, and Ford's Doughty notes a similar
improvement with the rear wing of the Ford Taurus SHO. A future Ford economy
car might end up with a rear spoiler solely for fuel-economy reasons, says
Doughty.
  So, it appears  that front air dams are usually functional, whereas rear
wings and spoilers are as often functional as they are frivolous. Ford
Advanced Studio designer Grant Garrison sums it up this way: "If wings and
spoilers weren't popular, we wouldn't put them on cars. We'd find some other
way to make them aerodynamic."
  In other words, if wings and spoilers are what car buyers want, that's
what they'll get. Whether they work or not.
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