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

[James F. Ryan III]

> From: 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.

That's what I figured since the article is from '98 and I remember reading
that (about the Gen3 skateboard) on the list a while back.

It's amazing that the big wing on the Superbird/Daytona only gave an extra
5mph.  If that's true then the spoiler on my '91+ doesn't do squat.  (I
never thought it did anything anyhow.)


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, Nook's 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

 

 

 


> Sent: Saturday, April 12, 2003 1:15 PM
> To: shotimes@autox.team.net
> Subject: RE: [Shotimes] Do Air Dams, Spoilers, and Wings Work?
> 
> 
> 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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