Rear window fairing (roof extension)

[edbso]

I want to say this cautiously. I am no expert by any means but I am 99.99% certain that the vortex generators are not used to reduce drag on the Lancer. Rather they are used to clean up the airflow into a more laminar flow over the rear spoiler to increase down force.

The IIRC is a small 4 door, 4 cylinder sedan with a huge turbo and the car is designed to go like stink and handle. Look carefully and you can clearly see the vortex generators several times in this movie.

http://www.metacafe.com/watch/342989...tion_mrfq_360/

Trust me, they are for downforce only, you can not even mention fuel economy and the Lancer IIRC in the same sentence with out being laughed at. There are only a very few cars that are faster or handle better than this car and they all cost 3 times as much.

[LostCause]

They definately don't make the flow over the rear more laminar as vortex -generators encourage the opposite of smooth flow, but you may have an argument.

Also, I'm pretty sure that if they did aid the spoiler they would not increase downforce but rather decrease lift. It may be semantics, but they are two different things in my mind. A true spoiler "spoils" the lift of an object, it doesn't generate lift in the opposite direction. Decreasing lift decreases induced drag, which is good for the FE minded, and it also returns the weight of the car to the rear wheels. For example, an airplane spoiler isn't generating down force as much as its returning the aircraft's weight to the wheels for braking.

Race cars definately generate downforce, but they use airfoils rather than spoilers. When it wasn't outlawed, Lotus used a skirt and a specially shaped underside to generate a venturi effect to create downforce. On the other hand, drag racers and cars like the Porsche Carrera use spoilers.

Lastly, while those vortex-generator may not exist for FE, air drag is still an enemy of someone racing their car. While it may not help in slow maneuvers, it should help anywhere high speed runs exist.

- LostCause

[aerohead]

The late-model Corvette uses a glass" fairing" which tapers both in plan and elevation to clean up the wake behind the cabin so air will hit the top of the "trunklid".Since these cars are driven flat-out on the Autobahn they need the downforce and directional stability of the high-drag ,enormous tail,especially in inclement weather.The "boat-tailed" rear windscreen has the shape of the cap on my truck and where Chevy uses it for speed,it cheats the gas pump a bit for me.On a notchback car,such a fairing would block access to the trunk,so provision would have to be made to tackle that animal.

[apgrok1]

OK, so it looks like any fairing that auto makers put on a car, whether is it a notchback, Kammback, or squareback, is used for downforce and not for lowering CofD. So then, any theories on how to reduce CofD by changing the fairing? Why couldn't someone extend the bumper out towards the rear and make a Kammback off the rear of the trunk?

[MetroMPG]

apgrok1 - There are lots of examples of roof extensions (on hatchbacks/wagons) and trunklid lip extensions on sedans which reduce drag. Some of them also happen to reduce lift at the same time. Yet others reduce lift at the expense of higher drag.

adbso - I think you're right in that the goal of the Mitsu engineers was to get more clean airflow to the decklid spoiler on that car. That said, if the spoiler wasn't there, the net effect of the VG's would have been to very slightly improve Cd and reduce fuel consumption.