An inverse windshield top spoiler for convertibles when top down?

[Big time]

From the Mercedes photos it looks like separation is increased when the aircap spoiler is raised.
Wouldn't this actually increase drag?

[botsapper]

The Mercedes Benz Aircap spoiler for its cabriolets is primarily designed for less passenger compartment wind buffeting, a more luxurious, and quieter conversation-friendly open air driving. Along with its Airscarf, a heating system for your neck, the spoiler also keeps the outside air blast away from the driver/passenger in fall/winter open air driving. Indeed more drag.

[serialk11r]

Originally Posted by whatmaycome14

Somewhere along the lines, I heard that the Lexus SC430 convertable had the same Cd when the top was down as when it was up. I've always thought this was quite impressive.

Actually, I wouldn't be surprised if this happened in a lot of convertibles. The convertible top tends to have an awkward shape (since it needs to fold) and this could push the airflow over the top so that it doesn't reattach to the rear. I'm no aero expert, maybe someone else can chime in on this but I suspect it's more important to have surfaces following the airflow where the car is tapering. Afterall, a 2 door pickup truck has a very long bed but they have pretty crap drag coefficient.

In my own car, top down with wind screen up it's actually very civilized in the cabin, and sticking my hand into the air I can kind of feel the air moving at full velocity just a few inches above the wind deflector. I wouldn't be surprised if the drag were the same with top down, and I wouldn't be surprised if the drag were lower in a Z4 or Boxster with top down, seeing how short and low their tails are.

[Big time]

Looks like the pickup truck spoiler might be just what the doctor ordered for convertible windshields

This one


So it would make air flow go and head lower for a less tall windshield wake.
While lower this flow wouldn't be so low IMO as to be directed to the drivers head.
Even for the aerodynamically state of the art E-class convertible the normal flow is well above the drivers head, even for tall drivers.




Even if air were directed to the drivers head (with increadible drag reduction by doing so) the pickup truck spoiler might be tilted to redirect air upwards


In a similar line of thinking this pickup truck spoiler might be used in the A-pillars to redirect flow inside the car reducing the windshield wake when viewed from above.

Any ideas for pickup truck spoiler angle?
Would boundary layer suction and/or blowing allow to use more dramatic spoiler angles?
Mods?
Is this spoiler already patented?

[freebeard]

Are you suggesting having it behind the windshield with the airflow in the same direction or before the windshield with the flow in reverse?

[Big time]

Originally Posted by freebeard

Are you suggesting having it behind the windshield with the airflow in the same direction or before the windshield with the flow in reverse?

It would neet to be over/behind the windshield

i.e. for the yellow spoiler image


The car would be facing to the right with the big yellow block, the one with the X-Z axis letters being the windshield header

[freebeard]

Maybe... The design relies on the body being closed to below F. It is a divergent duct, which will slow the air down and appears to rely on the Coanda effect to change direction at D.

IMHO it would work better ahead of the windshield with the airflow reversed. See the Air Curtain the 2014 BMW M5 uses to bridge over the front wheelwells.

[Big time]

Originally Posted by freebeard

Maybe... The design relies on the body being closed to below F. It is a divergent duct, which will slow the air down and appears to rely on the Coanda effect to change direction at D.

IMHO it would work better ahead of the windshield with the airflow reversed. See the Air Curtain the 2014 BMW M5 uses to bridge over the front wheelwells.

Why reversed? Can you please elaborate?
I don't see it working in reverse as its purpose is to make the trailing wake smaller.

[freebeard]

Let's review what you're trying to do. Redirect airflow around the top and/or sides to reduce the wake behind the windshield, without impacting the driver's comfort—yes? The traditional solution down through the years is to just chop the windshield. What kind of vehicle are we talking about?

To elaborate: A convergent duct ahead of the windshield [read: sun visor] w/ a large opening at the front, maybe 6" horizontally taking air off the top of the windshield with the exit a vertical slot maybe 1" tall that blows over a Coanda nozzle at the back of the windshield header. This passive duct, like BMW uses, would not be as effective as pumped air. An augmented Coanda nozzle would look like this:



The thing is, if it works the driver would need goggles.