Metro aerodynamics

[SVOboy]

Fixed it!

[MetroMPG]

Hmm. Vertical winglets or not, that Celica wing would be about as helpful for aerodynamics as a ram implosion device or a set of roof racks!

[zpiloto]

Originally Posted by MetroMPG

Hmm. Vertical winglets or not, that Celica wing would be about as helpful for aerodynamics as a ram implosion device or a set of roof racks!

That was funny.

[MetroMPG]

Well, I should have said "as useful for fuel economy...", but you got what I meant.

[ZugyNA]

Originally Posted by MetroMPG

Well, I should have said "as useful for fuel economy...", but you got what I meant.

I disagree...as per usual. Remember the "science fair project" or whatever where the guy claimed an mpg gain from vertical wings....angled inwards?

The VW wing with verticals angled outwards?

It's my contention that SOME of these wings increase mpg, acting like LARGE vgs.

The Mitsubishi vg research also worked WITH a wing? With all the attention they paid to CD values...do you think the wing caused overall drag?

How do they work? My guess is that wings and vgs create a strong focused flow that breaks up large/inefficient vortexes that form at the back of vehicles.

On a trip last summer I was trailing a big rig pulling one of those container boxes on a trailer...I could move up close and then back out some...I could feel the big rolling vortexes coming off this truck...each one sucking it backwards...and about blowing my car off the road.

BIG BAD UNCONTROLLED ROLLING VORTEXES are evil.

Small controlled vortexes and larger directed flows are GOOD!

Of course...a properly formed boat tail is HEAVEN ON EARTH.......

[Silveredwings]

Originally Posted by ZugyNA

I disagree...as per usual. Remember the "science fair project" or whatever where the guy claimed an mpg gain from vertical wings....angled inwards?

Winglets on planes are used to reduce lift-induced drag caused by wingtip vortices by increasing a wing's aspect ratio without increasing its span. Though most of the 2 winglets' horizontal lift vectors cancel each other out, the net is a small amount of forward lift or 'thrust' thereby reducing drag a little more. Here's the problem: where there is lift, there is induced drag (and parasitic drag) that opposes thrust. The drag likely exceeds the thrust gain but so its just a small side benefit to the planes.

I don't imagine winglets are giong to be very effective in decreasing a car's Cd.

Originally Posted by ZugyNA

It's my contention that SOME of these wings increase mpg, acting like LARGE vgs.

The Mitsubishi vg research also worked WITH a wing?

As I understand VGs, they are used along a curve of a surface with the intent of extending the area of laminar flow along that surface. They had a small effect on a sedan shape when placed on the back part of the roof near but not on the knee of the curve. This made air flow a little more smoothly over the back window. I don't think the 2 big winglets on the back (with no surface behind them) will work the same way as the VGs are used.

It's still possible they could reduce the turbulence behind the car but at what cost in terms of drag? In that respect, I agree with you about designing for the "boattail effect."

[MetroMPG]

Originally Posted by ZugyNA

I disagree...as per usual. Remember the "science fair project" or whatever where the guy claimed an mpg gain from vertical wings....angled inwards?

But they were minus the giant horizontal trunk wing.

The Mitsubishi vg research also worked WITH a wing? ... do you think the wing caused overall drag?

Unquestionably. You just have to have a look at the CFD images in the PDF to see it. In both the "with" and "without VG" examples, the wing extends into clean (unseparated) airflow, which increases drag. Don't forget: this car is a turbo high-performance AWD racing machine, not a fuel-sipper, and its wing is there to generate downforce.

In fact, I think it's likely that they put the VGs there in the first place to get more downforce from the wing, rather than cleaning up the overall Cd, and the tiny reduction in Cd was a happy accident:

CFD results in Fig. 10 also show
that the velocity of the airflow along the bottom surface
of the rear spoiler increases by addition of VGs, which
reveals that a decrease in lift (an increase in down-force)
did occur.

...

Originally Posted by ZugyNA

With all the attention they paid to CD values...

I think that's an overstatement. The Mitsu is a brick, and their interest in Cd is more about road-holding than efficiency. If they just wanted more FE, there wouldn't be a wing on the back.

[ZugyNA]

Originally Posted by MetroMPG

I think that's an overstatement. The Mitsu is a brick, and their interest in Cd is more about road-holding than efficiency. If they just wanted more FE, there wouldn't be a wing on the back.

And yet...there is the page you found showing the advantages from a small lip at the back of a vehicle...I see them on most newer cars...there is the VW wing with angled surfaces...there is the 2 angled vertical fins science fair project...ALL made for increased FE.

So it looks like...DESPITE...the drag caused by these angled surfaces...they reduce overall drag.

Yes...many wings are designed to produce downforce or for decoration...but I'm saying that if they are designed for FE...they work for FE.

And...I'm always right.

[MetroMPG]

Originally Posted by ZugyNA

Yes...many wings are designed to produce downforce or for decoration...but I'm saying that if they are designed for FE...they work for FE.

On that point, we are in violent agreement.

I was only answering the issue you raised of the Mitsu wing being a FE instrument, which it definitely isn't.

[ZugyNA]

Ok...you win.