a wing is a wing is a wing is a spoiler is a dog is a cat... just so its has the same shape, weight, form, position

Also I don't believe that the stock 968 wing has no real effect on the car. I'm sure just by looking at it that is has less drag and more downforce than the stock 944 wing. (interchange the word wing/spoiler/cat/dog as you wish.)

The only variables with the 968 wing are the mass of air under the wing, mass above it, the size of the wing, the angle of the wing, the thickness of the wing, and the width of the wing and some of these may simplify out of the math when doing the calculations.

Operation

Spoilers generally work by disrupting the airflow going over a car. This disruption has the primary purpose of reducing the amount of lift naturally generated by the shape of the car.

The result is increasing the contact between the tire and the road surface, thereby increasing traction. This increase in traction allows a vehicle in motion to brake, turn, and accelerate with more stability. Additionally, this is accompanied by an increase in aerodynamic drag.

In nearly all cases, drag increases as the speed of the vehicle increases. Thus, some spoilers that are effective at very low speeds often generate excessive drag at high speeds, and spoilers that work well at high speeds are often ineffective while moving slowly.

Science of wings
A Mute swan spreads its wings
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A Mute swan spreads its wings

The science behind how wings work can be complex and is one of the principal applications of the science of aerodynamics. However, at the simplest level, both the upper and lower surfaces of a wing produce lift by deflecting air downward, which propels the flying body upward with an equal and opposite force (see Newton's Third Law).

The air above the wing is also operating at a lower pressure compared to the air below the wing because of Bernoulli's principle. This relates the pressure of air to its local velocity. If the velocity of the air changes as it flows around an object, such as a wing, the pressure of the air also changes. The shape and the angle of attack of the wing cause the air to flow faster above the wing than below, so the pressure above the wing is less than below the wing. This pressure difference causes a force called lift that acts at right angles to the air-flow.

The science of wings applies in other areas beyond conventional fixed-wing aircraft, including:

* Helicopters which use a rotating wing with a variable pitch or angle to provide a directional force
* The space shuttle which uses its wings only for lift during its descent
* Some racing cars, especially Formula One cars, which use upside-down wings to give cars greater adhesion at high speeds
* Sailing boats which use sails as vertical wings with variable fullness and direction to move across water.

Structures with the same purpose as wings, but designed to operate in liquid media, are generally called fins or hydroplanes, with hydrodynamics as the governing science. Applications arise in craft such as hydrofoils and submarines. Interestingly sailing boats use both fins and wings.

In physical aspects the forces acting on the wing and the spoiler are identical, even though people call them different things an engineer or physicist just assigns a variable to them like Fa or such and does the math.

a spoiler also works under the same principles, its just a wing without a body of air moving under it, which is an even simpler equation.

A spoiler on the back of the vehicle is designed to provide a force downwards, arising from air flow along its surface. Since the spoiler is at the read of the car, this down-force is exerted primarily on the rear wheels, increasing the normal force from the road on these wheels. A larger normal force means an increased maximal static frictional force at the read wheels. Meanwhile, the normal force on the front wheels is essentially unchanged. Since the engine power in a front-wheel drive Honda is exerted via the front wheels, the increased frictional forces on the rear tires does not help increase the maximum possible acceleration. In contrast, during turns the down-force does help prevent the rear wheels from sliding outwards.

Downforce - a vertical force directed downward, produced by the airflow
around an object; Down Force is typically created by a device like a wing or front air dam or rear spoiler.

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Drag - a force in opposition to the forward motion of an object, caused by friction

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Rear Spoiler - designed to give or take away down force on the rear of the car. If you raise the rear spoiler, you will create more down force on the rear of the car. The trade off is that the higher spoiler also creates more drag on the back of the car. If you lower the rear spoiler you will have less downforce, but you will also have less drag.

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Newton's Third Law of Motion states that for "every action there is an equal and opposite reaction." A rear spoiler or front air dam is placed on a car to help provide down force or slow the car down. When air hits the rear spoiler, two things happen. First, the air hitting the rear spoiler causes drag on the car. The higher the spoiler, the more the drag. The reaction of the drag on the car is to slow it down. Second, when air hits the spoiler it is deflected up. According to Newton's Third Law, if the air is deflected up, then the car is deflected down. When the air hits the spoiler the other reaction force is drag.

In NASCAR racing the height and angle of the rear spoiler and front air dam is the same for all teams. In many cases, they will raise the spoilers on fast tracks to slow the cars down. On slow tracks they will lower the rear spoiler to slow cars down.

The reason is that on large fast tracks the teams want as little drag on the back of the car as possible. On slow tight tracks teams want as much down force to make it through the turns as fast as possible. By taking away the down force, drivers must go slower around the turns, decreasing speeds.

The front air dam works in just about the same way. The closer the air dam is to the ground, the more down force on the front of the car. If you raise the front air dam, the car will be faster on the straight, but will have less down force on the corners. The same thing applies as the rear spoiler.

In this project Andrew Totolos, host of DIY's Tricked Out, adds some active aerodynamics to a Honda S2000 in the form of a motorized spoiler and retractable canards.

What does "active aerodynamics" mean? In this case it means that, at the touch of a button, the driver is able to alter the way his car moves through the air and have a direct impact on its traction and handling. The motorized spoiler we install on the rear deck can be made to rise and fall to alter down-force. Up front we add motorized canards, also to help keep the car more stable on the track at higher speeds. From the driver's seat, the canards can made to retract for daily driving.

In this first segment, Andrew installs the motorized spoiler to provide down force for added traction when driving at high speeds.

Aside from the shrill whistle in the test car, there’s not much to dislike about driving a Boxster. But lest we miss any, here’s something to concern anyone who’s afraid of another speeding ticket: at 75 mph, a spoiler automatically pops out of the Boxster’s rump, and it doesn’t retract until the car drops back under 50 mph. For the enthusiast who uses radar detectors and was born with a slightly lead foot, forget about avoiding attention from the highway patrol; the speed-sensitive spoiler is like mooning the cops. We can hear it now: "I’m giving you a ticket for operating your spoiler in a 60 mph zone." The spoiler serves to reduce lift and improve ride stability. We just wish it popped up a little earlier.

Increasing speed means little if the car will not take corners. Cornering requires a very precise balance between front and rear downforce to keep centrifugal force from throwing the car into the wall. If the balance is too much to the front of the car, it will tend to turn too easy which will make the rear of the car loose traction and slide out. This is referred to as the car being “loose”. If the balance is too much to the rear of the car, it will not want to turn which will make the front of the car loose traction. This is referred to as the car being “tight” (Woodward). The downforce on the front of the front of the car can be controlled by altering the shape of the nose and by the angle of the front air dam. The amount of rear downforce is determined by the angle of the rear spoiler (Bacque).


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For longer tracks, generally called Super Speedways, speed is the matters more than cornering. These tracks require engine restriction so that the cars cannot run too fast. Since they have less power it is very important to reduce the drag as much as possible. For short tracks, speed is not nearly as important as cornering. To improve cornering teams add more downforce to their cars. When downforce is added so is drag. Since the speeds are lower on short tracks, drag is not as big of a factor. The cars’ engines are also not restricted which allows them to overpower the drag created by increasing downforce (Bacque).

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Dr. James F. Marchman III, a aerospace engineer at Virginia Tech, says, “The biggest problem for race cars usually is simply keeping the rear end on the ground in a turn. People think about drag as the biggest problem, but the biggest problem is the lift. The car develops lift and you don’t want it to” (Bacque). Spoilers and air dams keep the car on the ground when it is going straight, but the major safety issue is when the cars spin sideways. Even though the cars weigh in at 3400 they still produce a lot of lift when traveling at speeds close to 200 mph. As the speed at which the cars ran over the years increased there were more incidences of a car spinning and the lift created would actually make the car fly. This caused the car to roll and tumble injuring drivers and severely damaging many cars (Bacque).

Something had to be done to prevent the cars from creating so much lift in the event of a spin. There were many potential solutions to the problem. Most ideas failed included a 8 inch tall piece of aluminum on the roof of the car from the right front to the back left, a hinging rear spoiler, and a hinging trunk. Some minor changes that were added to the cars included adding glass to the right window, adding side skirts to keep air from getting under the car, and half inch metal strips on the roof to break up the smooth surface that helps to create lift (Nelson).

Dr. James F. Marchman III, a aerospace engineer at Virginia Tech, says, “The biggest problem for race cars usually is simply keeping the rear end on the ground in a turn. People think about drag as the biggest problem, but the biggest problem is the lift. The car develops lift and you don’t want it to” (Bacque). Spoilers and air dams keep the car on the ground when it is going straight, but the major safety issue is when the cars spin sideways.