Hood splitter for my vw

[winkosmosis]

Originally Posted by Frank Lee

Look at any wind tunnel image with the smoke trails... they sure look to be arcing smoothly up at the hood/windshield to me...

Yeah and at the rear the smoke stream always follows a nice smooth gradual curve downward and rearward. Put a brick in the wind tunnel and you'll see the same thing. Works great for advertising materials!

[Frank Lee]

Guess I'm not missing anything by not having access to a wind tunnel.

http://inter.action.free.fr/images/a...t-aerodyne.jpg

[winkosmosis]

If the VW didn't have that steep windshield making air pile up, I bet it would have attached flow with a small bubble at the edge of the windshield/hood.

[Varn]

Interesting smoke around the beetle. A top down view would be interesting considering the external fenders.

Nice thing about the multiple lines is that you can see compression by noticing the spacing of the lines at the front of the car
Since lowering the windshield might be prohibitive filling in front of there might be a start to lower the pressure over the roof of car. The smoke trail is moving upward at about 20 degrees.

On the 86 jetta the trunk lid is pretty high but still might be a bit low to be ideal. Thankfully it is squared and not rounded like the early model vw. unfortunately the front of the jetta is also very square. The hood angle is 7 degrees.

[Christ]

It's pretty easy to grab a good rear angle with a sedan body: lay something off the roof at 15 ish degrees, and measure the height that it sits 2" past the deck lid.start from there, frame it out with a good taper, cover it with chicken wire and a couple old white tees, and apply elmers mixed 70/30 with clan water vigorously. Good enough for test purposes, anyway.

The nice thing is that it doesn't make a sedan any longer.

[fjasper]

I was looking at one of these this last weekend and I noticed that, based on the dirt streamlines, airflow starts to spill off the hood maybe 2/3 of the way back (about even with the top of the wheel arches), and continues over the well-rounded hood-fender transition and onto the sides.

I don't know how much this contributes to the low drag number, but it seems like the same sort of thing a big hood-bulge might induce.

It appears that even with the relatively flat windshield (compared to, say, an old Saab), they've found a way to get the air to go (partly) around the sides of the passenger compartment instead of going over it. Seems like this would reduce lift (span-wise flow tends to do that) to a small degree as well.

The B5 Passat, which has a Cd of something like 0.27:

[Varn]

Chicken wire, (ah "You first" ) Makes coroplast look good.

Originally Posted by Christ

It's pretty easy to grab a good rear angle with a sedan body: lay something off the roof at 15 ish degrees, and measure the height that it sits 2" past the deck lid.start from there, frame it out with a good taper, cover it with chicken wire and a couple old white tees, and apply elmers mixed 70/30 with clan water vigorously. Good enough for test purposes, anyway.

The nice thing is that it doesn't make a sedan any longer.

[euromodder]

Originally Posted by Christ

That's not really a deflector... The hood just happens to cover up the wipers in the parked position.

That Camaro already has a very raked windshield, so the hood-windshield transition is smooth.

Getting the wipers out of the airstream has both aerodynamic and safety advantages as it cuts down on drag and pedestrian injuries, while it costs next to nothing to do.

[Frank Lee]

The base of the windshield is the point where the cross sectional area begins a greater increase than ahead of it. From the bottom of the windshield to the top of it is basically the zone where we go from some portion (2/3?) of max frontal area to full frontal area. When you go from smaller frontal area to larger frontal area there will be a "pressure" increase, no doubt about it. The operating theory here seems to be that making this increase in pressure from the base to the top of the winshield more gradual somehow decreases drag. What I'm trying to say is, why would that be? If you're going from 2/3 frontal area to 1/1 frontal area in that general zone anyway, and if the flow ahead of the zone is basically unaltered (non turbulent, as before), and the flow past the A-pillars is basically unaltered (non turbulent, as before), then... WHAT? What's the difference? I say, none.

[winkosmosis]

Originally Posted by Frank Lee

The base of the windshield is the point where the cross sectional area begins a greater increase than ahead of it. From the bottom of the windshield to the top of it is basically the zone where we go from some portion (2/3?) of max frontal area to full frontal area. When you go from smaller frontal area to larger frontal area there will be a "pressure" increase, no doubt about it. The operating theory here seems to be that making this increase in pressure from the base to the top of the winshield more gradual somehow decreases drag. What I'm trying to say is, why would that be? If you're going from 2/3 frontal area to 1/1 frontal area in that general zone anyway, and if the flow ahead of the zone is basically unaltered (non turbulent, as before), and the flow past the A-pillars is basically unaltered (non turbulent, as before), then... WHAT? What's the difference? I say, none.

It always takes less energy to change direction with a larger radius... compare coasting your car through a 90 degree corner vs a wide sweeping curve.