Wagon aero trials
 

Update: wool tuft pics and video in the Aero section here:
https://www.gassavers.org/showthread.php?t=7519

Long story short, Geo's dead, and I'm driving my Volvo wagon everyday now. And using more gas. I read a thread a couple days ago that had a request for some info on the aero effects of a wagon with the sunroof up vs down. I haven't seen anything pop up yet, so I decided to get started on it. Anyone interested in results can watch my gas logs.

(I'm young here, but not a total noob. My old user name was only synonymous with the Geo which is gone, so I've been reborn so to speak)

Tilting the sunroof up will aid in reducing the low pressure area just behind the top of the windshield. This can have an effect on reducing the turbulence on top. With roof rails this 'filling in the vacuum' may or may not be a desired result.
Tipping up the sunroof aids in producing air flow inside the cabin which can mean allowing reduction in fan speed.
Leaving any sun shade nearly closed will limit solar gain in summer, reducing air flow 'wind-chill' requirements for occupant comfort.
But when it's hot...close the roof, close the shade, fire up the A/C!

and be glad that the "box-it-came-in" square shape of Volvos went out with the 700 series. My 760 GLE with the odd-fire B28 V6, not the later even-firing B280F, got an average of 20 mpg (with an 11 gallon tank!) Cheap to fill, but the frequency....!

Depending on the particular wagon and particular position and angle of the sunroof, there is a possibility that the airflow may take a more curved path over the roof, resulting in less base drag at the rear. What works on one, might not work on a different one.

Thanks for the input. It feels good to be back in experiment mode. Too bad I don't have someone that can follow me to work and take pictures of wool tufts the whole way. I could do it as a weekend experiment, but burning gas just for the sake of finding out how to burn less gas is completely bass-ackwards to me. My findings will be slow and steady, but maybe I'll have some real data by the time this wagon chalks up another 100k miles.

Yeah, I find it hard to do testing for the sake of testing. Gotta work it into the necessary trips. However, some of the very cheap digital cameras will do 640x480 video... I have one I could potentially use... and I'm pondering the idea of strapping it to the vehicle somewhere to record tuft behavior...

What happened to the Geo? Rust? :(

Road Warrior, I think you're on to something. I actually have a friend who duct taped his camera to the side of his motorcycle to create an on board camera. Although, the camera probably causes aero glitches of it's own, and I don't know how I'd get shots of the rear end. Trailer?

BamZipPow, you're ID basically describes the old Geo. It was more like a Feo though (fake). It was just a Prizm (Corolla), automatic, 1.8L, been in at least 3 wrecks before I got it. Bought it from my boss 2 years ago for $600 and drove it every day for 2 years. That I can't complain about. But I only kept it as an extra car so we'd always have transportation when I was working on one of the other cars. It paid for itself several times over (just having it to drive while I replaced the Volvo's turbo myself saved me $1000.) But as soon as IT needed repairs, the savings were gone. It still runs, in fact I sold it to another guy who was going to fix it and drive the thing. But it only got 27-ish mpg, and all the little glitches were going to cost ~$1200 to fix MYSELF. And even if I did, I'd still have a rattly, rusted Geo in the end. The Volvo's much more fun to drive, more utilitarian, more fun to work on, no rust, and the insurance is less than 2/3 what it was for the Geo. (Not to mention the sleeper quality - it will hang with Mustang GTs of the same year and tops out at 155, which of course is the optimal speed for FE)

Wool tufts are bad for gas mileage! I tufted my rear windows this morning (I'll have pictures up when I get home. Forgot my camera USB cable) and my avg was 2mpg lower than usual. Interesting. It was fun to see the tufts at the top of the window be sucked up out of view. I think a hatch back spoiler back there would work wonders for this vehicle. Also interesting was that with the sunroof up, it seemed to create more lift on the tufts. With it up, the top row of tufts wasn't even in sight. With it down, they'd flutter around where I could see the tips. I got video too that I'll share.

bump (new info)