Is 42mpg too low a goal?

[Clev]

Originally Posted by Istas

I'm still a bit leery about doing the aerotabs without having a way to quantify testing them, but I'm going to just take a leap and assume (until I can test them) that having just enough of them to reattach airflow to my rear window will do more good than harm.

Do the MPGuino first. I've not heard positive results on the forums from aerotabs, but if they did work for you, it would be such a subtle change that you probably wouldn't be able to tell just from filling up. Doing a grill block is a no-brainer, but having that instant readout is important to quantify the smaller mods you'll probably have to do to get to 42 mpg.

[NeilBlanchard]

Hi,

Icksnay on the AirTabs-ay -- I doubt they will help, and they probably would hurt your FE. I've tried them, and it was a waste of a fair bit of money...

Here's my sketch of the grill block wedge I'm suggesting -- it's similar to mine:


Some more air may flow to the sides, though probably the difference is subtle. It also would not block (the little bit of) light from the inside edge of the headlights. The blue lines are foam gasket or tape or caulking to seal the air gap -- the front edge of the hood is the more important -- the air flow velocity there is higher and keeping it out from under the hood is important.

Here's my Coroplast grill block:

Your Legacy has less curve to the sides (along the brown line on my drawing) so shedding air to the sides may be less important than on my xA.

[Clev]

Originally Posted by NeilBlanchard

Here's my sketch of the grill block wedge I'm suggesting -- it's similar to mine:

LOL. Make sure you draw the teeth on the finished product. Makes the car look like a hammerhead shark.

[NeilBlanchard]

FYI, that is called tessellation!

[MetroMPG]

Hi, Istas: impressive the way you've jumped in with both feet!

Originally Posted by NeilBlanchard

Icksnay on the AirTabs-ay -- I doubt they will help

FYI, these two "controlled as possible" A-B-A instrumented tests of airtab vortex generators on 4-door sedans showed no significant change in fuel economy:

• Tested: vortex generators (AirTabs) on a Toyota Corolla
  tested at 90 km/h (~55 mph)

• Documenting NHW11 Prius rear window flow separation; testing AirTab vortex generators
  tested at 75 mph

[skyl4rk]

One of these should bump you up to the 40's mpg:

[Istas]

Metro MPG: Thank you!

Yeah, I've read both those articles, but both of those were also done on cars that already had a smoother transition to the rear window, and the window at a more gentle angle. I think both the 2006 Camry and the 2003 Prius are significantly better in this attribute than Car, a 1992 Legacy:

I'm thinking that maybe, maybe, it might be more effective on cars with steeper back windows. However, I won't even think of trying the airtabs until I have an MPGuino installed and calibrated. And maybe when I do, since they didn't work, I can borrow those loners that were floating around? *hint hint*

Thank you for discouraging me from just buying them because I could.

Clev: Hahaha! Yeah, because the first thing people think of when they think fuel efficiency is an upside-down hammerhead shark. *grin*

Neil: Very slick job on your grille block. That's really smooth. And yeah, I can see how it definitely benefits your car, with the swept headlights. It's definitely an interesting idea, and I will keep it in mind, but two things: one, it takes away being able to use the front license plate holes as mounting points and it'd be a lot more complex to secure it by just using the grille alone (somehow), and two, it takes more finesse to shape it the way you have it. I'm going to go with the... hmm, I'm paraphrasing here, but I know I read it somewhere on this forum, "first, do it. Then do it better". I'll make it the simple way, then possibly refine later. I'll definitely keep your shape in mind when I do.

And yeah, I'll be using foam tape or something similar under the front and side edges of the hood, and clear caulk around the edges of the headlights (and possibly the grille blocks).

Thanks to all of you.

[Istas]

skylark: Wow! I hadn't seen that job before. That's your car and mod, right? Is there a thread showing how you built it? Have you tuft-tested the top of it to see where flow rejoins it? Can you still access the trunk?

That looks like a viable option for me (I especially like the way it uses the stock rear window, which will aid in keeping it clean in the wintertime rather than having a homemade plastic viewport, and probably annoy Smokey less). Only thing is I would loathe loss of trunk space. I guess it wouldn't be too hard to just start it after the trunk, or make a panel over the trunk raise up with the trunk lid.

See, I would've never considered that. Never would have thought of a boat-tail that didn't start at the rear edge of the roof. Awesome design.

Edit add: Ahh, it's in your sig. Didn't even look before. *reads*

[Istas]

I likes me some testing with tufts.

The documenting didn't go as smoothly as planned (I do not have video of mirror out, but I do have pictures of mirror out), but I did some tuft testing.

Main goal of the tufting was to see if the flow, once separated from the roof or upper rear window, re-attached at all at the back of the trunk (I had figured it separates from the rear window, and it does)

Another goal was to document the turbulence effects of removing the side-view mirror.

Tufts!

I like tufts.

Mmm, laminar. Nothing out of the ordinary, just wanted to see what it looked like. I do plan on putting a deflector just in front of the wipers.


Rear window. As I thought, total separation. Even the top row of tufts wasn't aiming the right way.



I could use some interpretation help with the trunk. It looks to me like the airflow tentatively rejoins the trunk a bit, but that it's not smooth at all.

That second to last row was swinging left and right, both sorta towards the middle, but not aiming forward (towards the front of the car). I'm not sure if that last row is pushed off the trunk, or if it's being pulled out by the turbulent airflow behind the trunk.

Now, for the side. Mirror in "normal" position.




Lots of movement on all three rows. I guess a 40-square-inch-front-area mirror will do that.

Second, folded in.

Not as bad, but still turbulent down the whole side. Bottom row was calmer than the middle.

Last, mirror off completely.

Mmmm, two smooth rows. The top row, though, is still angled up. The angle gets progressively less, it's barely that way in the back window. That top row's wiggling, but the other two are pretty smooth.

I guess the a-pillar's creating a sort of vortex just behind it against the glass, and that it's pulled along next to the upper windows, so it's angling the tufts up that way. Kinda nifty, actually. This would be worth testing some turbulator tape on the A-pillar, another time.

I didn't see much difference on the rear window or trunk with regard to the different mirror configs.

I have two videos, the mirror off and the mirror folded, neither very high quality and both from inside the car. I've never really posted to Youtube before, but I might try it, maybe. Not just now though. If the quality I got were higher I would be more inclined, but I don't have a video camera, so we went with what we had.

[aerohead]

Istas,I made a thumbnail sketch off the computer screen of the back of your roof/rear deck.From the top of the backlite header to the rear edge of the trunklid,I'm measuring about 18-degrees.That's a bit steep for the air to follow and I don't believe it is re-attaching.You might make a simple rear spoiler which angles up at no steeper than a 30-degree angle ( as measured from the horizon) projecting up and to the rear until it intersects an imaginary line down from the roof at no more than say 13-degrees.It would be a cheap and dirty way to get your flow re-attached without adding adding any significant length,your turbulent wake will be reduced and it should show up at the gas station.