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Old 06-02-2020, 07:39 PM   #17 (permalink)
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Join Date: Oct 2017
Location: USA
Posts: 32

Accord - '12 Honda Accord sedan EX-L
90 day: 25.99 mpg (US)
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I wish I was studying this.. it would be more fun. It's just a hobby.

Originally Posted by JulianEdgar View Post
1. Car stability is most determined by the lateral centre of pressure location. If the car turns away from wind gusts (most common), you need to move the centre of pressure rearwards. Rear fins are the easiest way of doing this, and in my testing on a Gen 1 Insight, have worked extremely well.

2. Separated flow on the downwind side of the car will, however also cause instability (as you earlier indicated). The yaw angle at which downwind side separation occurs depends on:

- the shape of the front corner of the car
- the shape of the A pillar
- the surface roughness of the side of the car

The only thing that your vortex generators could impact on this list is the behaviour of the A pillar - and the hood location is a long way from the A pillar.

I'd try the VGs on the A pillars and the front corners of the car.
So, from #1 I understand that VGs will "attract" the center of pressure toward their downstream area.
And from #2 I understand that what I was going to do could easily (when overdone) worsen the crosswind instability by keeping the center of pressure even more off.

I was also considering directly placing them on the A-pillar which would also deal with the buffeting with open window at medium to high speeds. So I start at the bottom of A-pillar and where should I stop? For some reason I feel putting them on the roof between the top of B and C-pillars would be effective.

Speaking of 1G Insight, are you the person who wrote Autospeed blog? That's where I read about the idea to place airtabs under the car.

Originally Posted by gregersonke View Post
I don't see why it wouldn't work. Just adding two of them to my 2020 prius prime in the back on the black plasic piece behind the shark wing at an angle increased my fuel mileage about 4-8 percent in two different speed ranges 60-67 and 78+ but also drastically reduced my crosswind issues. Also I installed them with the high side of the vg facing forward to center of the car rather than backwards away from center.
Feel free to consider this fairy tale but I have experienced surprisingly good mpg as I increased crusing speed a bit which made my rpm higher so the BSFC was actually lowered more than the increased drag so I got better MPG going faster than usual.

I recognize those VGs. I considered them at one point but they were too big and thick for my taste so I passed and then they went out of business so yeah.

I tend to believe VGs near trailing edges of box shapes reducing drag (probably due to reading Airtab marketing material too much) but trying to work with a sedan I feel there are a lot more that I should consider but don't even know.

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