Low drag mirrors

[Idahotom]

Am I the only one to fold the side mirrors back? I'm talking middle of Wyoming, and into a 30 mph headwind. I was always in the right hand lane, (interstate) traffic was very light, like none. My neck still can turn, and I have a rear view mirror. As I neared a town, I'd flip them back out. Safe enough, probably not legal. I havn't done it since, just that long stretch with the headwind and it was getting real boring. Can't say I could see a difference on the scangauge, and I only did it for a couple hundred miles.

[MUSKOKA800]

I'd rather have full visibility than be obsessed over the drag, if any, they add.
I'd think the envelope that the front of the car creates going through the air at highway speeds extends out past the side mirrors. If it didn't, wouldn't the manufacturers see this in the wind tunnel and tune the mirror size/shape accordingly???

[Klink10]

Tune the size accordingly? You would think but then they can't even come up with a quality waterpump.

[why?]

actually mirrors are tuned for visibility first, and drag is accepted in that area.

You can buy racing style mirrors if you'd like, they are much smaller. Garm has a set mounted on his yaris.

and so a few waterpumps aren't perfect. That stinks, but there are always a few stupid problems with cars. Thank God the Yaris is one of the best in this category.

[Idahotom]

After hearing about guys who remove the windshield wipers for less drag, folding back the mirrors seemed pretty minor. A one time deal for me, though I do like how they hold their adjustment through the folding process. Maybe the next time I'm driving through Wyoming I'll do it again!

During that leg of the drive, I saw a state trooper had pulled over a Prius, and I had to wonder for what, too fast, too slow??? Drafting semi's maybe?

[why?]

prius drivers are usually snobs who forget the rules apply to them as well.

[derickveliz2]

I would like ti see some smaller rear view mirrors that not only have less drag but generate less "wind noise"

[Midnight Drifter]

prius drivers are usually snobs who forget the rules apply to them as well.

Oh, please. When I was coming home from Georgia, one of the fastest cars I drafted before the VA border was a Prius with the Virginia plate SAVN GRN. She averaged 95 mph and had a Greenpeace sticker on the back of her car.

...yeah, that's totally what you're supposed to do in a Prius. Floor it the whole way home to save gas.:clap:

[Toyota_Yaris]

Tune the size accordingly? You would think but then they can't even come up with a quality waterpump.

hahahahaha x's 2

62k miles on mine and I just went through my first waterpump

[cali yaris]

Prius bashing = :thumbdown:

[cfeng]

i dont see how adjusting the mirrors will make a difference at normal driving speeds. sometimes drag is even beneficial. for example, the antennae, which seemingly produces unnecessary drag, helps to trip a turbulent boundary layer for higher efficiency and lower overall drag.

[Idahotom]

i dont see how adjusting the mirrors will make a difference at normal driving speeds. sometimes drag is even beneficial. for example, the antennae, which seemingly produces unnecessary drag, helps to trip a turbulent boundary layer for higher efficiency and lower overall drag.

What...you wind tunnel testing the Yaris with smoke streams or something?
The antenna is drag, though not much. As are the mirrors, less so when folded but who wants to drive around with no mirrors, besides me, one time!

[cfeng]

i use a water tunnel in my lab. i've been thinking about this. with a properly designed rear wing on the hatchback, it may be possible to increase fuel economy.

http://www.sinhatech.com/Auto-02.gif

the top picture is similar to a stock yaris, air swirls in vortex patterns, which means that not only does the yaris need to propel itself forward, but spend considerable energy into moving air. with the correct rear wing, there could be less separation in flow at end and less movement in the air, similar to the bottom picture. i found this picture online, the second picture is misleading because it represents an ideal case with virtually no separation in flow.

the antennae will disturb how the eddies are shed, reducing wasteful swirling of air (reduce a little). similarly, if a wing is designed to reduce the size and number of eddies from forming by increasing turbulence at the rear of the car, the car will have less drag and overall better efficiency.

[derickveliz2]

What about the Sedan?

D.

[cfeng]

can't say for sure. it would seem that a sedan will have separation in the back as well, however it may not be as defined. since the wing might help reduce the effects of separation, i'm not sure how much benefit you have if the separation is already less than the hatchback. however, i dont have much experience on aerodynamics of cars, i work on fish.

[daf62757]

Really? Fold the mirror in to save on drag?

If you a rocket scientist for NASA, I would understand.

[TLyttle]

What does rocket science and NASA have to do with drag? Aerodynamics can be a hobby as well as a science: more than once I have been involved in tufting a car in order to find a source of gas-eating turbulence, it ain't that hard, and the results are worth the time and effort.

Re the sedan: just the mud patterns on a sedan give you a hint, ie, there is far less mud on the back of a sedan after driving in crappy weather. This means that the air stays stuck, and the turbulence and rotors are smaller, ie, less drag. I consistently get better fuel mileage than my buddy's hatch, and we both drive about the same.

Folding in the mirrors may or may not make a difference, depending on the shape presented by the folded mirror, and the turbulence generated. Somehow, I don't think the difference would be easily measured. Now, skinning the underside should change things a lot, but not always for the better...

[slow.yaris]

Aerodynamics can be a hobby as well as a science:

I don't think the difference would be easily measured.

Sentence number 2 is why sentence number 1 is false.

I think what he is trying to say is, unless you have access to a wind tunnel, the difference is near impossible to measure, kind of defeating the whole point of trying to become more aerodynamic. Its just like VG's - sure the theory is there and you can experiment, but unless you have wind tunnel data to back up that they are decreasing drag by stopping flow separation, you could be hurting your drag as much as you are helping.

[sickpuppy1]

dont have much experience on aerodynamics of cars, i work on fish.


So are you creating more hydrodynamic fish? LOL

[cfeng]

haha. almost. i'm studying what allows fish to accelerate at such high speeds, over 20g. maybe one of these days ill try a miniature yaris in the water tunnel for fun.

[TLyttle]

I build and fly model sailplanes for a hobby, yet I study aerodynamics much of the time, trying to cheat a slightly better L/D ratio out of a model. Science or hobby?

As far as wind tunnels are concerned, many of us model builders have built tunnels and discovered a lot in the process, particularly in the low Reynolds numbers we work with, stuff seldom dealt with by "scientists".

Also, a simple tuft test around the side of the vehicle with the mirrors in and out would show the difference in turbulence, and a camera would record the info. The actual drag coefficient would be measured in the usual way, the numbers proving any differences between the two, but again I don't think the differences would would be large enough to measure.

Drag coefficient is a strange beast: there is a model of Freightliner that shows a lower C/D than a Corvette; lots of factors in there...

[Idahotom]

I was just pointing out that any significant drag reduction on the rear end would have to be accomplished with some sort of spoiler or vortex generator full span: across the entire rear of the roof left to right. The antenna, just in the middle, may have some effect, but only on a small percent of the total area. At one time a few years ago, I saw some research being done on tractor trailers using vg's to break up the rear end suction, but I guess it didn't catch on, havn' seen any lately. I have noticed the big white plastic fairings under the trailer, it looks like to clean up the running gear drag, I see LOTS of those these days, must work.

Ain't nothing more streamlined then fish! I'd think that research would be very helpfull in general drag reduction thinking...I'm into building and flying airplanes myself, and you quickly realize less drag is always better then more power, effciency wins everytime. One reason I drive a Yaris instead of a Suburban....

[Yaristeve]

i use a water tunnel in my lab. i've been thinking about this. with a properly designed rear wing on the hatchback, it may be possible to increase fuel economy.

http://www.sinhatech.com/Auto-02.gif

the top picture is similar to a stock yaris, air swirls in vortex patterns, which means that not only does the yaris need to propel itself forward, but spend considerable energy into moving air. with the correct rear wing, there could be less separation in flow at end and less movement in the air, similar to the bottom picture. i found this picture online, the second picture is misleading because it represents an ideal case with virtually no separation in flow.

the antennae will disturb how the eddies are shed, reducing wasteful swirling of air (reduce a little). similarly, if a wing is designed to reduce the size and number of eddies from forming by increasing turbulence at the rear of the car, the car will have less drag and overall better efficiency.

Intersting drawings. What do you think (as in "do you think they work?") of those little "shark fin" vortex generators and Air Tabs? I was thinking of sticking on a row of the latter on the top of my hatch door but not on the sides as they recommend.

[derickveliz2]

talking about log drag mirrors... LoL

http://image.motortrend.com/f/35263470+w750/subaru-impreza-concept-front-three-quarters.jpg

D.

[TLyttle]

Any drag generator has to be there for a purpose; the point is to find out if indeed the generator needs to be there, and can it justify itself in lowering the C/D?

The water tank would certainly prove the worth of mirrors in/out. I like the position of the mirrors on the auto above; they are mostly out of the main airstream. It would take a bit of time to get used to the position: they remind me of the old peep mirrors from the 40s-50s, or the wink mirrors from the 60s.

The trucking industry have been ignoring aerodynamics for decades. I suggested changes when I worked in a truck plant in the 70s, and was told first, to mind my own business, and that second, service techs would never accept their presence. That was then and this is now: in my mind, they still have a long way to go.

[kustom play]

http://www.maxspeed-motorsport.com/catalog/images/bomex%20body%204.jpg

i have these mirrors on my MR2, bomex type 2's

i would love something like that for our yaris. Visibility is great with them.

[cfeng]

What do you think (as in "do you think they work?") of those little "shark fin" vortex generators and Air Tabs? I was thinking of sticking on a row of the latter on the top of my hatch door but not on the sides as they recommend.

Its difficult to get something like this done right through trial and error. Unless if you have access to a full scale wind tunnel. I know that they are used on other cars already, I think one of the earlier evos had something similar.

The reason I was thinking about a wing is that it is larger and easier to test in the water tunnel at my lab. The job is the same, to trip turbulence that will be helpful in reducing drag. The equipment I use has lasers measuring the movement of small aluminum particles in water to visualize the flow on a computer. However, unless if the changes are drastic, this equipment probably wont accurately show the influence of tabs on a miniature yaris.

BTW, does anyone know where i can find a model yaris?

[cfeng]

http://hikickracing.blogspot.com/2011/01/effects-of-vortex-generators.html

Its related, but his test procedure is bs.

[TLyttle]

Yeah, the test procedure leaves a bit to be desired, but us amateurs do the best we can. C/D is an easy test (regardless of the 5th wheel that the magazines use) for our purposes: results are often quite clear, like the difference between windows up or down. Besides, there seems to be a lot of confusion between drag reduction and stuff like downforce in the results of modifications. These mad machines with air dams, wings, and all the folderol on something with 100+ horses makes me laugh heartily.

Just changing brands of tires can affect C/D, hence fuel mileage. Skinning the underside has a big effect on C/D, but can also radically change handling in crosswinds, sometimes NOT for the better. Even air management at the rear has its interesting effects on drag; go to F1 to find out how far one can go with this!

C/D is a huge subject with an amazing number of variables AND solutions. Keep with it, guys, it CAN be fun...

[dogsridewith]

(Idahotom wrote:
"Vortex generators on rear of roof! I'm an airplane guy and had them laying around, and damn if they didn't make it track better at freeway speeds, my theory is that they keep the airflow more attached at the rear and not so turbulent. I wrote about it here, if you search.")

I once drove some 300 miles on PA interstates covered with inches of snow because road crews were off for Christmas day. Sharp skinny 155-80/13 tires (new, but not aggressive tread pattern) on 89 Tercel EZ Hatchback w/ rear seat removed. Car wagged it's tail continuously at speed, which was disconcerting until I determined it was otherwise well planted and controllable. There were SUV's etc. that ran off the road every mile or so. Maybe 2 vehicles passed me the whole day.

Idahotom: That's all advanced search here gave w/ "Idahotom" and "vortex generator." Did you post anything more about this mod?

[JimKellyfan]

folded, they probably drag worse, really, less smooth parts that a way