Quote:
Originally Posted by khafra
I'm interested to hear how the comparison goes. From what I've heard so far, a clean separation at the back of the car is better, and "energizing the boundary layer," like vortex generators do, essentially gives up a laminar boundary layer in order to make the boundary layer more reluctant to separate from the surface.
So, it'd be applicable mainly where the angle between the roof and the back window is steep enough that you get separation, but shallow enough that some vortexes would make the air cling better. Not so much applicable when there's nothing behind them to cling to.
When Autospeed did an informal test of trailing-edge VGs on an Insight, they made fuel consumption worse: Browser Warning -- and there's an old thread here taking all that into account, and looking for hard data: http://ecomodder.com/forum/showthrea...nefits-97.html
That thread points out that tank to tank testing may not help, although some A/B drag tests would be cool. |
Thanks for your post. My last car was a 2006 Insight so I can appreciate the temptation to add VG's to that in hopes of benefits. I suspect the negative result they reported with the Insight is more about the small surface area of the rear of a GenI Insight (hence less surface area for any low pressure wake to act upon) plus the extreme aero tweaking that went into the Insight at the factory. They likely squeezed about as much as possible out of the Insight's CD short of the full boat-tail treatment our fellow ecomodder in Wisconsin has done.
Not a big fan of A/B drag tests. Personally, I don't trust short distance A-B-A testing which is why I'm doing a controlled tank to tank test. Really, "tank to tank" is a misnomer. I'm accumulating several tanks worth of fuel consumption data. My driving route, speed, air temperatures and number of warm-ups per tank are close enough that I have reasonable confidence that a significant improvement in MPG will be detectable. I keep exacting fuel consumption records so I have a solid benchmark for my Mini's fuel consumption. Thus far my first full tank refill (525 miles worth of driving) after installing the AirTabs has increased my fuel economy by 1.5 mpg. This is about what I was expecting. It works out to about a 3% improvement over no VG's. We'll see how I fare on the next tank. The improvement might completely disappear.
