Mirror designs, if we can't use cameras yet.

[Vekke]

Some rough calculations:
stock mirror = 5,2 l/100km@97 km/h or 45.27 MPG us @60mph:Aerodynamic & rolling resistance, power & MPG calculator - EcoModder.com

My mirror desing rough estimation:
- delta Cd= 0,010 ( no mirror at all =0,012 drop in cd)
- Frontal area reduction 0,0298m2=calculation based on my lupo 3l mirror frontal area drop
-->5,01l/100km@97 km/h or 46.98 MPG us @60 mph
http://ecomodder.com/forum/tool-aero...ToStep=5-200-5

That is roughly 0,19 liter or 3,7% difference FE at 60 MPH

Take mirrors out:
delta cd in CFD program =0,012 (0,017 in wind tunnel test)
Frontal area drop = 0,0456m2
--> 4.95 l/100km@97 km/h or 47.5 mpg us @ 60 mph
http://ecomodder.com/forum/tool-aero...ToStep=5-200-5

That is 0,25 liter drop from start or 4,9% effect at high speed driving.

Cd estimations are made based on this wind tunnel study: http://publications.lib.chalmers.se/...ext/143193.pdf

I would say my mirror design has even bigger impact to cd than that 0,010 but that is a safe bet as not all cars are the same aero wise...

[OG VX]

I came up with a contraption I called the "R.A.M. Mirror" for my VX.

See my post here.

I love it and it works great! I've capped the inside for colder weather.

[aerohead]

Purists would probably slam you for not using a NACA submerged inlet,but compared to AC on,or windows down,I suspect that you don't pay much of a penalty.
And having it away from the body is good,since it's in slower air.
'suppose the aft-body could be faired.(don't you love how others want to spend your time!)

[cowmeat]

And having it away from the body is good,since it's in slower air.

Okay, that confuses me. Can you explain what you mean?

Being a noob to aeromodding, it seems like the air traveling right down the length of the car would slow down as it met resistance and follow along with the car a bit, and that the air farther away from the car would be at a standstill, making it "faster" by creating more resistance.

Everybody school me here, I'm interested but ignorant!

[aerohead]

Originally Posted by cowmeat

Okay, that confuses me. Can you explain what you mean?

Being a noob to aeromodding, it seems like the air traveling right down the length of the car would slow down as it met resistance and follow along with the car a bit, and that the air farther away from the car would be at a standstill, making it "faster" by creating more resistance.

Everybody school me here, I'm interested but ignorant!

*As the car attacks the stationary air mass,the imaginary streamline filaments which comprise the air must accelerate from a standstill,to whatever velocity they'll reach,as a function of displacement.
*Around the windshield,the air can be up to twice your driving speed,depending how the air is divided by the cars body.
*As you can see in the photo of the Golf/Rabbit,the streamlines are crowded together near the top of the windshield

*From Daniel Bernoulli's research we know that this displacement requires the increased velocity.
*The farther and farther we move away from the body,the displacement effect of the body diminishes,and the air moves at lower velocity and higher static pressure.
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*The air around the A-pillars is fast,just as at the windshield header,and by moving a structure away from the body sides,it encounters slower air,reducing its drag due to the velocity-cubed relationship to aerodynamic power,and also interference drag associated with it.
*Subaru,during the development of their 1986 XT sport coupe,was able to eliminate the drag of the side-view mirrors by moving them 80mm outboard of the doors.
*This can also reduce aero-acoustic effects,minimizing wind noise.

[cowmeat]

got it, thanks for the explanation without me having to read through 20 separate threads!

I understand the windshield dynamics from the pic, but does it do the same thing in the mirror area? I don't ever remember seeing a wind tunnel pic from a kind of 45 degree-ish angle to where you could see what happens right at the junction of the lower windshield and the pillar where the mirror sits. All the pics I can find just show the side view.

[aerohead]

Originally Posted by cowmeat

got it, thanks for the explanation without me having to read through 20 separate threads!

I understand the windshield dynamics from the pic, but does it do the same thing in the mirror area? I don't ever remember seeing a wind tunnel pic from a kind of 45 degree-ish angle to where you could see what happens right at the junction of the lower windshield and the pillar where the mirror sits. All the pics I can find just show the side view.

We don't get a bunch of plan-view images for this sort of thing.
I'm gonna try a link to the Masters Thesis on Mirror Drag from Sweden which Vekke shared with us.
In the text,some plan-view CFD velocity/pressure profiles are provided for a Mercedes-Benz A-Class car
http://publications.lib.chalmers.se/...ext/143193.pdf

[cowmeat]

Awesome, thanks for the link, I found some good pics in it to kind of use for a template.

Here's where I'm confused about as far as moving the mirror way out to the side (see pic below), and what I was asking in the first place. It seems like there's an eddy right created at the base of the pillar, so tucking a small mirror in right there seemed to me to be the best idea for placement.

Or is that eddy created from the mirror and the mirror stalk?

Thanks for the help!

[aerohead]

Originally Posted by cowmeat

Awesome, thanks for the link, I found some good pics in it to kind of use for a template.

Here's where I'm confused about as far as moving the mirror way out to the side (see pic below), and what I was asking in the first place. It seems like there's an eddy right created at the base of the pillar, so tucking a small mirror in right there seemed to me to be the best idea for placement.

Or is that eddy created from the mirror and the mirror stalk?

Thanks for the help!

That is an A-pillar Vortex,and it's created by the discrepancy in pressures and velocities between the A-pillar area itself (very fast-moving low-pressure air) and slower/higher-pressure air on the side of the car.
The high-pressure side flow bleeds into the low-pressure A-pillar flow,attempting to reach equilibrium pressure, and shearing forces within the viscous air create the rolled-up cyclonic flow exactly as warm moist Gulf air rising off a Colorado plain meets fast-moving air in the jet-stream above creating the meso-cyclone super-storms which will set down later as tornadoes in Kansas.
Again,the very fast A-pillar flow is the culprit.You don't want anything near it.

[cowmeat]

Thanks for the explanation! I understood about a third of it, but I'm taking your word for it cause nobody goes to those lengths to explain something wrongly!

In light of that, I think what I really need is a camera driven projected holographic mirror to replace my plastic one! Wonder if that would technically be legal since it would be outside of the car?