Air Tabs

[ChazInMT]

Here is what I have seen when I followed a Beetle in the rain, it stood out like crazy, these 2 very active vortices. The thing to keep in mind about these devils is this, the air was not moving (Let's assume a calm day here) before the car rams through it, but at the back of the car, you have created 2 horizontal tornadoes......these do NOT follow you.....This is the tough part to understand, you are constantly generating them, it requires power all the time to keep the air moving like that. Imagine how much energy it would take to spin two 30 inch tornados constantly using say, a fan. It would be a fairly large fan and some large motors driving it. This is the energy your engine must create to keep those going, thus, less MPG.

I hope that makes sense.

[ecomodded]

I could make a fiberglass spoiler that will fit on to the lip of the bottom of my hatch, so when i opened the hatch the spoiler goes up with it.
It looks like my only hope, with those vortexes and my hatches steep angle.
If i do that then mounting VG's above the hatch could help send the air onto the hatch lip spoiler. A three part aero system, the vg's the glass spoiler and the hatch lip spoiler.
That should change my cars rear aerodynamic attitude.
And boy does it need it,thanks for the art work and the introspection ChazInMT

[ecomodded]

Originally Posted by redorchestra

i thinkI might have proof of airtabs working for me. I drive about89km each direction to work everyday. Last week my tank to tank was 36.28mpg that pretty stock as I removed my airdam and grill block. This weeki added 6 airtabs that I made and mounted on magnetic sheets. My mileage for this week was 37.69mpg. I will remove them again for next week and see what happens.

Could you post a photo of your tabs on the car ?
So far the numbers are hopeful,1 mile a gallon gain is large,looking forward to the weeks results.
With your commute consistency the results should be repeatable the following week, might be good to note temperature differences or lack of as the temp variation will have an effect. Maybe vary the VG's duty time from the mornings one day to nights the next to try and even out the temperature variations in your findings.
This mod will need to be retested to factor out all the variables that could sway results. The VG's need to be tested to death, they have a lot of convincing to do for the perfectionist or anyone really who wants hard evidence. The longer the drive with cruise control the better,which is great you are using it, its hard to sway cruise control results over the same route day after day.
I have a preconceived notion as to the amount of gas saved, your findings will be interesting,to say the least.

[euromodder]

Originally Posted by ChazInMT

Here is what I have seen when I followed a Beetle in the rain, it stood out like crazy, these 2 very active vortices.
I hope that makes sense.

They way it's drawn might suggest they come from the bottom of the car, while AFAIK it's the air flowing in from the sides, above the bulging rear fender.

On a Beetle, I'd seperate these 2 flows from the flow over the roof, and give the side-flows hard edges to detach from.

A hard edge under the rear bumper / extending a belly pan somewhat beyond the lower bumper line might not be a bad idea either.

[ChazInMT]

It really looks like 2 large round spinning trash cans counter rotating behind the car, so maybe the below illustration makes it a bit more clear.

The main point to take away is that these vortices require constant power input to be generated, it has no "Inertial Mass", so you can't think of it as something that moves with the car. It is constantly being created and dissipates as the car goes by.

[ecomodded]

I think what is happening is the air off the roof is coming down to meet the side air streams, when it does it sets a spin in motion by pushing on each side of each air stream, making a whirl wind, or vortex. The roofs air stream is pumping the vortexes, I am not to confidant that a lower hatch spoiler will stop them, but it will slightly change the flow as well adding the VG's upstream. If the rear hatch spoiler is made to extend to the tail lights it could deflect a lot of the top airflow off the back at that point, instead of joining the airstream further down the body.
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A hard edge under the rear bumper / extending a belly pan somewhat beyond the lower bumper line might not be a bad idea either.

Good ideas, i am going to look into that, give the air leaving the underside a purposeful flow,perhaps even filling the low pressure area behind the car.

[redorchestra]

Well here are my findings after one day using my instant read out on my android tablet with torque.
On my way to work with air tabs 6.2 l/100 without air tabs 6.4 l/100
On my way home with air tabs 6.4 l/100 without air tabs 6.9 l/100

My tank to tank is going to wait a bit because I am getting new tires today so I need to start my Aba testing at the beginning.