Anyone every used these to reduce drag?

They're vortex generators (typically used on commercial jet airlines). Available from amazon in a kit of nine fins.

AeroHance GasPods Project – Be Atmospheric

I am a little skeptical about their effectiveness as a DIY kit, as I believe angle and positioning of these need to be professionally engineered and installed for optimal performance - tailored to the specific vehicle. On the other hand Amazon reviews, though limited in number, are generally positive (tho one comment stated that they provided "zero" improvement in gas mileage).

I suspect that their claim of "11% better mileage" (see link above) is a theoretical (possible, not guaranteed) improvement and should probably be read as "up to 11% better mileage", depending upon installation. However, I myself, am intrigued enough to consider purchasing a kit just to see how well they work (awaiting other comments here). At $60 per kit, at the very least they would make an interesting, if not cosmetic, conversation piece.

I believe these are similar to the vortex generators krmcg uses on his Prius Four.

 

i have never heard of anyone using them, so no opinion on effectiveness.

toyota does a pretty good job of reducing drag, right out of the factory.

 

How critical is the placement of those things? I am by no means an aero expert but I would think that the correct placement is important.

 

Depends on what you are trying to do. For aerodynamics it's primarily used to tweak wing design - often to improve stall characteristics and aircraft safety.

In the image below, the small fins are vortex generators, shown here to improve low velocity stall performance of an Navy A-4 wing leading edge slat. The vortex generators, produce small vortices that help delay the onset airflow detachment from the wing surface, keeping it from stalling prematurely during low speed/high angle of attack flight (landings). The large two fins at the front of the slats are call "fences" used to restrict lateral airflow (also for improved stall performance).

File:Vortex Generators (942583271).jpg - Wikimedia Commons

For automotive application, it's more of a gimmick than anything else. Basically, they reduce the size of a vehicle's slip-stream, by the same technique, described above, for aircraft. Although, vortex generators can theoretically reduce aerodynamic drag this way, bisco's comment, above, pertains: Toyota has already optimized the Prius body for minimum drag, so I would not expect much of an improvement, if any, with the use of vortex generators on a Prius. For automobiles, it has no impact on safety.

 

If it were real, I just cannot imagine that the major automakers would pass up such an easy and cheap-to-implement gain.

 

It doesn't look good to most consumers so manufacturers will probably be very cautious with such modifications.

 

I'm kind of chuckling at that 11% better mileage claim. So, at low speeds around town, where aerodynamics has little if any impact and where the Prius gets the best mpg, it will raise the mpg from maybe 60-70 mpg to maybe 66-77 mpg by improving the aerodynamics that don't really matter at those speeds.

And at highway speeds, where aerodynamics have a major effect, it will raise the mpg from maybe 50 mpg to maybe 55.

And it will do that on a design that one of the best car companies in the world worked very hard to make as slippery as possible.

On a box-like truck, I think it might be a big help. But I'm skeptical about how much it would help a Prius. As already pointed out, Toyota went to a lot of effort to reduce drag, and some of that was at the expense of attractiveness, so they would almost certainly used vortex generators if they would have gained an 11% improvement rather than investing millions in the next generation transaxle.

 

Yeah. Also, I am certain that the 11% did not have the Prius in mind... ...More like a semi-trailer rig going 100 mph. Then I could believe it.

 

Funny. We're saying the same thing.

 

They don't look so bad that no major car models at all are built with them.

No, not even a commercial trailer.

Trailer skirts between the wheels are saving 4-8%. Trailer tails, at $2k each, are saving 1-4%. Absent hard evidence up front, I'm not going to believe that a much smaller and cheaper set of vortex generators are going to save 11%. The industry should have already tried that, and if it worked, adopted it much faster and more extensively than skirts and tails.

 

I'll take your work for that.

 

There are a few of these on our Prius c. It seems that Toyota did find some sense in including them on the side view mirror trim and on the sides of the rear taillight lenses.

Honestly they seem like great little gadgets, as long as you have access to a wind tunnel and a smoke machine for long enough to figure out exactly where they should be placed.

 

My Prime has small rounded ones on the trim in front of the mirrors. I read somewhere that they were not just cosmetic. But I don't remember where I read it or if it's accurate information.

 

We had a thread about these years back. Or a very similar product.

Do what you want.

I have a really hard time believing they would be of any benefit to a standard vehicle, especially a Prius.
Yes, I default to the idea that with Toyota trying to create as much MPG benefit as possible, and countless hours put into aerodynamic design, if a significant MPG % could be obtained with something as basic as this? They would do it in design and from the factory.

I'm HIGHLY skeptical.
But if you want to buy em, and try em, go right ahead. I also feel they probably aren't going to do any harm. And Placebo affect is nice for a while.

 

Small enough and round enough to hide in plain sight and not be knocked off by a car wash or de-icing session… could be that Toyota is sensitive to more than just aerodynamic effects.

 

We all know that vortex-reducing devices can save some, like 3-5% of fuel (not 11%), that's why we are seeing them as wing-/sharklets in many airplanes.

I am not specialist in these things, but I'd assume that in cars the air resistance is not quite as prominent a factor as in airplanes, so I find it hard to believe 11% can be achieved.

 

It can’t be that hard to find a juicy 11% stat to cherry-pick… Probably just a specific band of speeds is good enough. i.e. “This prius got an 11% improvement in back-to-back 95mph runs…"

 

I think we're a little distracted by the 11% claim.

I'm highly skeptical of much if any advantage- period.

11% imo, is ridiculous. If I could get an 11% increase in fuel efficiency, I'd strap Roseanne Barr to my car.

This presentation just seems too much like snake oil and miracle cures.

Again, I trust in design. Original design.
How many hours did Toyota claim they spent in the wind tunnel with the Gen 3 Prius trying to improve and minimize drag? Hard for me to believe they would miss any significant possible gains by just attaching pods to various areas on the vehicle.

Like...hey this pretty good....
Then John the technician tapes a few pods to the spoiler...11% gain!

I just don't buy it.

If you want to buy it?
Well go ahead.

 

depending on your annual mileage you might be able to get somebody to flat out pay for 11% of your fuel just to see this.

…there have been worse comedy tours