Tuft Testing on Insight Hatch Glass (2006 Honda Insight, 1st gen.)

[aerohead]

On GOOGLE IMAGES there is a wind tunnel image of the North American Solar Challenge-winning car from the University of Michigan.
It's just a still photo of smoke going over the solar cars body.
The thing that gets me,is that the smoke is literally trying to grind the finish right off the car,all the way down the aft-body to the trailing edge.
This is my interpretation of perfectly attached flow,with the smoke hugging right at the surface.No wiggling.Perfect surface contact.
I believe that this is our objective,however there's is not a lot of 'science' to draw on.
Renault's Vest II is significantly shorter than the 1st-gen Insight and is credited with Cd 0.187 vs 0.25 for Insight.
Vesta's roofline is very close to the Template.I do not have a proper plan-view of the car so I can't really address that,except that it appears to have significant plan-taper as with EV-1.
Mercedes Boxfish is also shorter,appears to be right on Template,and also has Cd 0.19.
So to Jim's question about raising the hatch,I think it would be worth the investigation,although I don't like to play fast and lose with other's time and resources,as I myself would not be doing all the work.
There are many 2012 cars out now with Template roofs of various lengths and some a year away from showrooms.
My gut feeling is that raising the roof on the HONDA would 'show' at the gas pump.
You would in all likelyhood lose total rearward vision.( you'll notice that Bugatti uses an upright backlight reminiscent of the 1967 Lotus Europa for their Veyron.

[aerohead]

I went to GOOGLE IMAGES,typed in wind tunnel testing,on page 11 I found the photo of U. of Michigan's solar racer.

[Quasimoto]

Originally Posted by aerohead

I went to GOOGLE IMAGES,typed in wind tunnel testing,on page 11 I found the photo of U. of Michigan's solar racer.

Phil is this the same car?

http://www.youtube.com/watch?v=CUZ9O7bVmZc

[Xringer]

I'll bet the PV on their car cost more than a new Prius..

[Webskippergone]

Originally Posted by jimepting

Later, I'm going to raise the hatch a couple of inches and see if the flow improves,

I used to haul big boxes in my hatch and I'll tell ya, as soon as that hatch is opened up a few inches, the mpg just drops and the battery drains.

Maybe its because I had the windows cracked to overcome the fumes or the AIR fans on high. No A/C on just Econ Off mode for forcing fresh air in.

[jime57]

Originally Posted by aerohead

Renault's Vest II is significantly shorter than the 1st-gen Insight and is credited with Cd 0.187 vs 0.25 for Insight.
Vesta's roofline is very close to the Template.I do not have a proper plan-view of the car so I can't really address that,except that it appears to have significant plan-taper as with EV-1.
Mercedes Boxfish is also shorter,appears to be right on Template,and also has Cd 0.19.

I'm seeing more and more vehicles which "appear" to have roof taper very close to template. Perhaps more modern windtunnel testing is showing that for a given length, better aero is achieved by keeping template taper and increasing transom area wake. I've always been a bit suspicious that these folks were just maximizing internal room.

Honda pretty clearly put the insight just on the ragged edge, a different approach. Since they were commited to a 2 seater they had options.

The

[PaleMelanesian]

I agree. I to am seeing more cars with closer to ideal rear aerodynamics.

Like the Altima Coupe, with both a plan and profile taper.

[COcyclist]

Originally Posted by aerohead

My gut feeling is that raising the roof on the HONDA would 'show' at the gas pump. You would in all likelyhood lose total rearward vision.( you'll notice that Bugatti uses an upright backlight reminiscent of the 1967 Lotus Europa for their Veyron.

For testing purposes on the rear glass, would it be possible to jack up the rear suspension with spacers, to video the change in the tufts? Seems that would be quicker and easier than redoing the bodywork to smoothly raise and fill and seal the back hatch.

[aerohead]

Originally Posted by Quasimoto

Phil is this the same car?

Quasimoto,that's the beast! And your video trumps the still image.Fantastic!
I'll watch again with sound and catch up with the rest of members.
Thanks mucho!

[aerohead]

Originally Posted by jimepting

I'm seeing more and more vehicles which "appear" to have roof taper very close to template. Perhaps more modern windtunnel testing is showing that for a given length, better aero is achieved by keeping template taper and increasing transom area wake. I've always been a bit suspicious that these folks were just maximizing internal room.

Honda pretty clearly put the insight just on the ragged edge, a different approach. Since they were commited to a 2 seater they had options.

The

With the higher CAFE standards they may be choosing some length,and then by doing a good K-form roofline,they get the lowest drag per unit length.
This is exactly what Fachsenfeld and Kamm and Korff advocated.
Kamm and Korff recommended that cars be chopped off at 50% frontal area.
Todays Bugatti Veyron does exactly that.It ends at 49% aft-body which if it also had the plan-taper,would end up at 50% area.
They keep the broad rear to help keep it earthbound at 258-mph.
If we extend out to the full enchilada we get Cd 0.13.
If we streamline the wheels we can go below Cd 0.10.