Low drag mirrors

[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]

Originally Posted by TLyttle

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.

[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....

[derickveliz2]

talking about log drag mirrors... LoL



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]

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]

http://hikickracing.blogspot.com/201...enerators.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