Or perhaps a wing like Subaru did with the STi.
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They need to test something like the green Honda SUV. https://us1.webpublications.com.au/st.../3060_13lo.jpg |
I think it would have made sense for them to evaluate the Insight at significantly higher speeds. But as it was, the whole exercise appeared to be pointless on that car.
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As far as the whole "wake fill" idea.... Quote:
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OK, I am sold on the idea of using a turbulator to trip the boundary layer ahead of my hatchback so I don't get held back by suction at highway speeds.
I am going to put a thin zig zagged layer of clear silicone caulk across the roof of my civic hatchback. (I can always scrape 99% of it off later with a razor blade) The question is, how far should I put the caulk "trip" strip ahead of the hatchback? 100mm like Mitsubishi did? |
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I did some tuft testing on my car. There's side view pic of my car in my profile for reference. At 60mph flow started to separate at about 2/3 of the way down the rear hatch, or about 6 inches away from the rear deck. The angle of the glass at the point of separation is about 21 degrees. The flow wasn't completely turbulent, the tufts were still pointed downstream, but they wiggled noticeably more than the tufts just upstream. Now you've got me thinking of using clear silicone caulking to make a zigzag strip! Edit: oh wait, I just saw your car pic in your profile. It's pretty clear where the air would separate. |
DRW- Thanks for the info/help, but my hatch glass is pretty close to vertical. Maybe a 15 degree slope downward (a station wagon would be 0 degrees). So it seems like I need to put the caulk strip on the roof- right?
Its gonna be hard for me to do tuft testing with tufts on the roof unless I can find a volunteer to hang out the window and watch them at 55 mph :D |
Ah! I edited my post at the same time you wrote yours!
Erik, the trailing edge of the roof of your car is similar to the Insight. They both have a gently tapered rooflines terminating with a sharp edge. This is done to give the air a definite point to separate from the body. See part one of the vortex article here www.autospeed.com/A_3058/cms/article.html where they state: " Cars with a two-box shape (eg hatchbacks and wagons) are always stuck with flow separation at the end of the roof, so creating a larger wake. In those cars, and also at the trailing edge of the boot in three-box cars, the separation should be clean – ie the flow shouldn’t wrap around the end of the roof or the boot lid. On hatchbacks and wagons, roof extension spoilers achieve this clean separation, as do sedans by means of the sudden transition from horizontal to vertical at the trailing edges of the boot lid." My interpretation of what that article is saying is that your car already has a nice aero shape at the top of the roof/hatch junction. Sure, it's a large wake, but it has clean separation. VG's might reduce the wake on your car, but it would also make the wake more turbulent. |
DRW- Thanks, that was a great article. I am going to try it just to see if ther eis any change in my mileage, but it looks like a Kamm back is the only aero option to help the back end of my car
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