Metro aerodynamics

[The Toecutter]

Someone in the early days of the site posted a link to a guy who had added a foot to the back of my car and was getting 80+ mpg (he was doing other stuff, too, of course, )

You're probably thinking of Phil Knox. He heavily modified his Honda CRX for fuel economy. Boattail, rear wheel skirts, bellypan, side skirts, front air dam, and lots of other modifications. He only used aeromods, and never touched synthetic transmission oil, LRR tires, and other significant modifications in order to get that fuel economy. Got 90 mpg highway, just by aeromods, no engine change or anything.

[95metro]

I'm glad you found that. I had seen it once and couldn't find it again. That Rex looks good from the front - nose piece is reminiscent of an IROC Camaro - but I think the back is a little odd looking.

However, for 90 mpg highway...wow!

Still no front skirts though. It almost makes me wonder if people have tried them and had stability issues or they just can get a decent working model.

[The Toecutter]

Front skirts are very difficult to implement. So much so that even experts in aerodynamics don't find them worth the effort to properly implement.

If you use rounded skirts like that chopped/tandem Geo Metro that got near 80 mpg, you increase frontal area enough to cancel out the reduction in drag coefficient. It is difficult to make front skirts that allow you to turn, without wheels or tires rubbing them.

I think the only practical way to get front skirts is to make them turn along with your wheels. That would be difficult and/or expensive to properly implement. But I'm no expert, so I am likely wrong.

[Mighty Mira]

Originally Posted by 95metro

Well, there's a mockup of the adjusted spoiler/boattail. It only extends back the same distance as the rear bumper (but it could go maybe 6" over) and it shouldn't (knock on wood) impair vision through the mirror.

Damn, that's nice!

You sure are a much more talented photoshopper than I am with MS Paint, heh. Looks like it would work well.

But of course, testing will triumph over all.

It reminds me of the time that we were streamlining balloons back in grade school. We had these balloons attached to strings and we had to modify them with paper to see which would go the fastest, as a science experiment.

My idea was to make the front end to be a cone, with the rear just being the back of the balloon. I recall that someone tried it the other way, and knowing what we know now, of course it won, but at the time I thought it must have been some sort of mistake.

Hopefully I have learned from that experience. Trust the scientific method, it works.

[Mighty Mira]

Originally Posted by The Toecutter

Front skirts are very difficult to implement. So much so that even experts in aerodynamics don't find them worth the effort to properly implement.

Only those as hardcore as the team that made the Prove V tried the front skirts. And got rewarded with a 0.13 something Cd for it.

I think that it's not the difficulty so much as that it's a fairly out-of-the-box kind of idea that stops it getting implemented.

[Mighty Mira]

Originally Posted by The Toecutter

You're probably thinking of Phil Knox.

Hey, thanks for those pictures, I've wanted to see them for a long while now!

The only anomaly to my eyes is that spoiler at the back... unless it is somehow covered with perspex on both the top and sides, and was done for visibility reasons. Other than that, beautiful.

[The Toecutter]

If you want to get in touch with Phil Knox, you can find him at the following yahoo group:

http://autos.groups.yahoo.com/group/maxmpg/

He goes by the name aero1898head.

Only those as hardcore as the team that made the Prove V tried the front skirts. And got rewarded with a 0.13 something Cd for it.

.137 to be exact. Damn that's smooth.

[Mighty Mira]

Originally Posted by The Toecutter

.137 to be exact. Damn that's smooth.

Thanks for the info!

A bit OT, but you can kind of get a feel where car aerodynamics is going by looking at aircraft. That pulse autocycle was designed by Jim Bede, who has designed some of the most efficient aircraft in the world. He employed a guy by the name of Burt Rutan, who designed the long-ez. The velocity looks almost identical to it, seats 4, and gets something like 8l/100km, which is like a car!



Strip off the wings and canards, and you can see which direction cars will go for minimizing drag and weight. Since it already has to fit 4 people, two side by side, it already has some of the compromises necessary to seat them comfortably.

In fact, if you bought the top and bottom part of the kit, you might be able to graft it onto a car like mine.

[95metro]

Originally Posted by Mighty Mira

Damn, that's nice!

You sure are a much more talented photoshopper than I am with MS Paint, heh. Looks like it would work well.

Thanks. Photoshop (I prefer Corel Photo-Paint) is part of my everyday job. It comes in handy for these type of things. And I kind of cheated since I have the tools. I drew the side-profile in CorelDraw, then opened up 3D Studio and made a 3D version from there.

I only know the basics of 3D Studio, but it does have some physics capabilities. If I could develop a 3D wind tunnel...

[Mighty Mira]

Originally Posted by 95metro

Thanks. Photoshop (I prefer Corel Photo-Paint) is part of my everyday job. It comes in handy for these type of things. And I kind of cheated since I have the tools. I drew the side-profile in CorelDraw, then opened up 3D Studio and made a 3D version from there.

I only know the basics of 3D Studio, but it does have some physics capabilities. If I could develop a 3D wind tunnel...

*cough* emule *cough* fluent...

Of course, you'd have to figure out how to use it...

Meanwhile, I found this while googling:

The Supermileage? competition provides engineering and technology students with a challenging design project that involves the development and construction of a single-person, fuel-efficient vehicle. Vehicles are powered by a small four-cycle engine. Students have the opportunity to set a world fuel economy record and increase public awareness of fuel economy. The engines are donated by Briggs & Stratton.
In 2003 and 2004, the University of British Columbia Supermileage Team (UBCST) won the Supermileage competition with mileages of 927 and 1747 miles per gallon (US), respectively. Their current goal is to continue to improve their designs and manufacturing methods through innovative and effective ideas.
Besides the engine, an efficient drive train, a well-designed yet light frame, and an aerodynamic car body are vital components for low mileage consumption. Because the cars at the Supermileage competition run at low speeds (with a minimum average of 15 mph), the aerodynamic shapes are extremely important. For this reason, the UBCST spent a great deal of time on the design and development of the 2004 body using wind tunnel testing (with 1/4 and 1/2 scale models) and CFD analysis using FLUENT.

What a retarded competition... how about a competition to make an actual car that can accelerate to highway speeds and do everything that normal cars do? If I wanted to travel at 15mph, I'd get a recumbent bicycle.