Trebuchet03's JettKamm (2000 VW Jetta)

[wyatt]

As requested! I tried to get this done last night, but I don't think an iPod Touch has the ability to do a simple "Copy Paste"... and I didn't feel like typing in the link very bad...

As you can see, not a very good picture by any means, but it illustrates the point. The upper provides some downforce with the "lip" at the back end, and the lower one is more optimized for flow. I would guess the lower one could cut off around 15 degrees or so, and not have the lip. In practice, you could put the spoiler on the two sides of the car vertically to help a little more... that is if they don't interfere with the brake lights (make out of plexiglass?). Let me know what you think.

[Christ]

Ah.. it was different than I was picturing in my head.

What I'm thinking right now is that complexity of mounting/angling might negate any actual gains... I might be wrong, and it would take a fluid dynamics test to prove one way or the other, but I'm sure I could mount it if it were something I was doing.

Top, bottom, and sides... so basically you want to build an inside-out venturi around the rear end of the car?

Although, I think the lower spoiler might interfere more than help... I'm pretty sure the angle is much too high, and will cause more drag than what it negates by re-joining flow.

[dichotomous]

I think you would be better off going with ground effects under the car, tapered slots that grow in width and dept to the back of the car, they create downforce from the descreased pressure, but you could make them to be reversed or something, I dont think you would encounter lift, not at 55mph, and it could jettison some higher pressure air into that rear area. or, cut pressure vent holes in the top of your rear bumper, which would do something very similar

[Christ]

I've seen people putting louvered panels in the rear bumper of their race cars, showing a marked improvement in 1/4 mile times, because instead of the rear bumper being a parachute of sorts, it allows some of the air out... better airflow.

I think a belly pan would do better, but hey, it's easy enough.

[drudis]

To: trebuchet03

I see that you are busy... but if/when you get a chance sometime in future, I would like to pick your brain for a flow of the rear roofline off my racecar.

I have done wing profile calculations, yet dont have a good overall flow over the roof and onto the hatch approximation (angle of attack for wing). Maybe over the holidays, we could work on something. Willing to help your college fund... ($$$ hint, hint).







email me directly if you wish: DRudis@DariusRudis.com

[kafer65]

Wonder how my idea would fly. I wanted to start a little higher than the attachment shows at the point were you say the boundry layer seperates on the rear window and come back from there just above the back edge of the trunk on back about 4 ft with a gentle taper ending with a small kammback about three feet wide and maybe a foot tall. I also was wondering how a grill block would effect the front flow. I've blocked all of the central grills except for the bottom most opening to help with early warmups. Blocking the additional bottom one didn't seem to help warmups and I didn't want to risk overheating on a hot day.

[Christ]

I'm pretty sure you're better off blocking the lowest grilles over the higher ones, especially if the lower ones are perpendicular to the ground... they would present a higher open area for air to flow into.

[mfor4x4]

Hey I'm new to these forums, I really like some of the ideas too.

I am curious if anyone here is familiar with the Formula 1 cars that were banned for being too quick? They had radiator fan motors mounted on the underside of the cars to actually suck the car to the track. Why not use this similar principle to improve rear aero on your car but have a tube coming out of the center of the back of your car pushing air out. Has anyone tried to model this or tried it? Would something like this help to smooth out the aero on the back of the car?

[Bicycle Bob]

You could reduce the wake that way, but you'd never save enough to power the fan. Secondary, pumped air paths are only beneficial to preserve laminar flow, which is seldom seen on a car.

[Christ]

I had actually thought about this while discussing the benefits of centering the exhaust pipes in the wake of a vehicle (a la Pagani Zonda).

I don't believe a radiator fan would even pump enough air to actually create any kind of real vacuum under the car anyway.... it would require a much larger, higher flow apparatus.