I agree with this; I know it is more or less the "official" explanation, and that was what I had in mind when I posted on the other thread: the spoiler was introduced on the Boxer to "blow" the boundary layer over the engine bonnet, so it had a purpose on that car. Then it was transfered on the 308 mostly for styling; on this car, I don't think it has any other purpose.
It turns out that the "device" is not a spoiler and wasn't intended to be. What Fioravanti discovered with the BB was a very effective way to reduce drag as a byproduct of stabilizing air motion over the back of the car. It's purpose was to reduce drag on the 3X8s. It came about with the studies done with Dr. Kamm from the earlier models of Ferraris and continued on until today with the F12. I refer back to the other post: "That style of spoiler is more to reduce drag than it is to produce down force. It provides an extension of the roof line that allows the airflow to remain attached to a surface then reach a sharp edge were it is easy for the airflow to separate cleanly. On the natural roof the airflow will try to follow the rear curve of the roof onto the rear glass but it will not be able to turn that sharply. It will then separate from the surface and create a large wake behind the car. This large wake means high drag. By having a slight downward taper to the spoiler the air is able to manage the small change in direction and begin to pull down behind the car before it cleanly separates at the rear edge of the spoiler. This results in a smaller wake, and less drag. Do some study/reading of Kamm rear end, he is the engineer that came up with the concept of a slightly tapered rear surface that cuts off cleanly. What you are doing is tricking the air flow into behaving like the rear of the car has a very long taper to it by getting the airflow moving along that path then cutting it free cleanly at a sharp surface that does not upset the smooth flow. What happens is you form a stable bubble of air that follows the car and creates a shape that acts like a long tapered tail, allowing the airflow to smoothly fill in behind the car instead of tumbling uncontrolled into the big hole you just punched in the air. If you need some downforce at the rear of the car put a small upturned "gurney lip" at the end of the Kamm tail, that will create positive pressure on the top of that Kamm tail extension and give you down force with relatively little drag." ALso in a paper on the Kamm effect: However, Dr. Kamm's wind cheating principle is used in a wide variety of popular vehicles (such as the Citroen CX that was produced from 1974 to 1990), exotic and expensive sports cars (such as the Ferrari 350 GTO), the newer high fuel efficiency and "hybrid" powered cars (such as the Honda Insight with its sharply tapered body resulting in no back seat), as well as specialized race cars (such as the AC Cobra 289 Mk II Daytona coupe). On all of these, the Kamm design enhances their aerodynamic performance. The design trick even works on competition bicycles. Therefore, "all of the above" is really the answer the "What is a Kammback" question. Leonardo Fioravanti devoted his thesis in mechanical engineering while a student at Milan's Polytechnic to 'the study of the engine and bodywork of an aerodynamic six-seater saloon'. For years Fioravanti had been fascinated by aerodynamic design in general and the work of Dr Wunibald Kamm in particular. Fioravanti believed Kamm, the inventor of the Kamm-back theory of design was probably the only person to have understood how to achieve a significant reduction in the drag coefficient of the family car. (from: http://www.landcrab.net/mainframes/main_pinafarina1800.htm) Correct answer 3
The 1965 Renault 16 already had such a wing around 1970 for the TX version. Image Unavailable, Please Login
I'm so far unconvinced of the Kamm theory, but it would be rather easy to test: drive at a steady speed, say 60-80mph, and measure the air pressure at various points over the rear deck with a manometer; repeat the test with the spoiler on versus off the car and report the results. Be sure to repeat each test a number of times to compensate for measurement variation and atmospheric effects.... Good project for a high school science fair, I would think. Any takers? (If a student takes this up, I would be happy to contribute access to some great data visualization software, for presenting the results.) -frank
It turns out that the "device" is not a spoiler and wasn't intended to be. What Fioravanti discovered with the BB was a very effective way to reduce drag as a byproduct of stabilizing air motion over the back of the car. Correct answer 3[/QUOTE] Crowndog, I know that you have devoted a lot of time and efforts in this thread, which gave us a very interesting discussion; I do not supect anything wrong with the discovery and understanding of the Kamm effects by Leonardo Fioravanti, but I still find that it doesn't match the sequence of events. The story goes that the roof spoiler was not designed in the BB concept from the outset, but that it has been added on because test has shown that a boundary layer was stagnating on the engine bonnet and prevented air entenring the carburettors and exiting through the louvres. Should Fioravanti have incorporated the spoiler in the BB design for drag reduction from the outset, why, then, did the 308 GTB (silmilar shaped) enter production without any roof spoiler, not even as a factory option? As far as I know, the roof spoiler only was offered as an option on the 308 GTS, from 1979 if my memory serves me well? Then it was offered as an option on the GTB as well. This four year gap in the spoiler history I find difficult to correlate with the drag-reduction option. Then, as I have already written, the popularity of the spoiler somewhat fluctuated here in Europe. It must have been different in the United States, as it was "standard", and the option was "spoiler delete", for which you had to pay extra. Over here, it was the other way around, and, for 328 GTB, whereas the first years almost all cars were ordered with it, most late 1988 and 1989 GTB were ordered without. So even if I have a deep respect for Leonardo Fioravanti, who did not received in its heyday the praise he deserved, and even if I admit that he might have been at the cutting edge of aerodynamics, I still believe that on the 308/328, the spoiler was just here for style. Perhaps we could ask Fioravanti, who is still alive and well? Best,
Isn't that what car companies use the wind tunnel for? Virtually every new car design spends considerable time in the wind tunnel, studying the flow of air over, under and around the car at all different speeds. Even with computer-aided design these days, they still need to see how air actually flows around a car, and determine whether the coefficient of drag will adversely effect performance and gas mileage. The more "slippery" a car is, from the point of view of drag, the better the gas mileage, especially at highway speeds. It would be interesting to know if there are any videos of wind tunnel tests on the 3x8 cars with and without the spoiler. I'm sure it was done -- Ferrari would not have simply slapped on a spoiler for the fun of it. And I'm sure that they tested different configurations before settling on the design that they used. It would be interesting to see the wind tunnel test, probably stored away some where on film.
Great thing about forums, we get to express our individual opinions. I certainly respect all those that are presented here. This outcome was not suspected by me at all. Afterall I was wondering at first just what purpose this reversed upsidedown appendage was doing on my car? I made all sorts of inqueries all over the place including Pininfarina. In fact I learned how to make international calls on my cell phone just to do some research. The person that I spoke to under conditions of anonimity and surprise was very familiar with the whole affair. That individual's comments in addition to some helpful insights into the whole Kamm thing pointed out articles and other sources for me to conduct my own investigation. I am only reporting here the fruits of my efforts. My intent is not to change anyone's opinion but to simply report this most unexpected outcome. It is up to each person I suppose to accept or not. I am fully convinced that the "air splitter" was a very sophisticated device that was used for one purpose that then morphed into another as a result of the effects that it produced. Drag reduction, something that was always a reoccurring theme in the designs from the 350 GTO to the Daytona to the BB to the 308, 288, 348 ,355, F40, F50, 458 and F12. Who would of thought? Certainly not me.
That's great for you Chris, but if you don't know what the car is like without it, how can you attribute its function?
I have no idea what is the right answer, but if you feel the weight of the rear lid, it is heavy. My gut feeling is that the "spoiler" was put on to provide a "strut" to support the lid when it is opened up. It probably needed it, and the "spoiler" was a way to do it without redesigning the whole rear end.
Steve, yes, of course! But full-size car-size wind tunnel time is seriously expensive; I was merely pointing out a way to use a poor-man's wind tunnel - a nice stretch of interstate - to make the relevant measurements. I think the investigation would be super interesting.... -frank
Resurrection of this old post just to add information. In this article the Ferraris are listed as some of the first cars to use Kamm tails. https://en.m.wikipedia.org/wiki/Kammback
the front spoiler doesn't work with Kamm effect but the most correct answer is the No.3. It reduces drag by lowering the nose and above all sweeping out air from the car bottom, where there is a very bad aerodinamic. It then increases a bit the downforce, by reducing the lift effect due to the wing shape of the body. So it's not "downforce" but "much less upforce" It works ciao
Ok...if it wasn't designed to remove heat (as I always believed) then why was it OEM on the hotter running U.S. cars and an option on the Euro cars? If it was there to reduce drag, then wouldn't it be standard across all cars regardless of market?
It would have been really nice if we can see the 308 with the rear spoiler inside a wind tunnel and with smoke.
Guys, seriously, that thing isn't a cooling apparatus. QV's, like every other model 308 run normal temps at speed. It's only slow stop and go they get "hot" and that wing thing ain't doing **** when you're sitting still
