JoeS wrote:Here's a report they did on a Honda Civic, where they festooned the sides with the Airtab vortex generators, resulting in a 4% reduction in horsepower required at 55mph. They extrapolated the data to say that a further reduction of 2% could be had if they had put the Airtabs across the roof, yielding a total horsepower reduction of 6%.
I'm a *little* suspicious - This test was run by the makers of the AirTabs as a way to advertise how well they work and thereby generate sales. They rented the wind tunnel, likely had boxes of the tabs which don't take 5 minutes to install, yet they have to 'extrapolate' how well they might work if added to the roof?
I understand it's hard to generate real world data, so using a wind tunnel is easier, but I also wonder about the changes you would see if the wheels were actually turning 55 mph as opposed to being stationary in a wind tunnel, and the car was moving over real pavement as opposed to the slick smooth bottom of the wind tunnel? In short, I'd be quite suspicious that the 6% figure would be accurate for any given body shape in real world conditions
All other things being equal, a 6% power reduction translates into a roughly 3.6mile range increase. Why didn't Mitsubishi install these, or did the marketeers say that would look too dorky?
No doubt they don't make the vehicle look better and that alone would probably turn off a few buyers. I do not doubt for a second that there is some benefit to using Vortex Generators as the lions share of vehicle drag is that pocket of turbulent air you're dragging around behind you - Boats have the same problem and you can design to minimize that drag if that's something you truly want to do. The extended Kamback (which looks a lot like the aft end of many sailboat hulls) would go a long way toward lessening that drag, but oh boy, what a price you'd pay - A.) Who wants that fugly tail hanging back there and B.) What a pain in the neck when it comes to parking, or loading/unloading cargo for an urban commuter car. If the negatives didn't outweigh the positives, I think you'd see lots more of this sort of technology out there in the real world
You'd think all the BEV manufacturers would be implementing something like this, if it really worked...
I think it's the minimal gain vs the change to the look of the car - You quoted a 3.6 mile range extension (2 to 2.5 might be more realistic for our body shape in real world conditions) but that assumes running 55 mph for the total duration of a full battery charge. How often does that happen in the real world? Mitsu thought they were designing an urban commuter car, not a (very short) freeway runner. I've never come close to running 55 for even a third of a charge, so the actual gain for me would be much less - Probably less than one mile. Not worth the 'dorky look' alone, even if the tabs were free, IMO
While it doesn't make much sense for the factory to do it, if an individual thinks there's a real benefit there, I guess it makes sense for them to add something like this - I've seen much less beneficial things sell to 'believers' over the years. 30 years ago if you bought every gizmo from the JC Whitney catalog which guaranteed you a 5 or 10% improvement in mileage, you'd be getting 200 mpg or better!!