Aero trunk lid project
 

This idea comes from a response by aerohead to my spoiler tests (http://ecomodder.com/forum/showthrea...tml#post242653). But I think it needs its own thread since it is not a "Bonneville" spoiler--or even a spoiler.

The current lid mod (see photo) lifts the trunk 2.75-3.0" and keeps or slightly increases its downslope. It extends a "lip" out to the bumper. It is sealed to the oncoming air with duct-tape on the read window and magnets on the sides of the body. It is ugly. Made of coroplast, reused cardboard, black duct tape, reused styrofoam, and a 1/8" steel support rod at the lip's edge to prevent wind from contorting the shape. If it has a good effect, I'll build a better one entirely of coroplast using this prototype's parts as a template for the cuts.

I want to do my test differently than the ABA type. I have a 6 mile stretch of freeway on my regular commute. I want to use it as the test track, recording the data of my commute for a couple weeks. I'll record very carefully by setting up a video camera on a tripod in the former back seat area. The camera would record 7-8mins of video daily. What Ultra Gauge data would be of most interest? I'll put throttle position, trip g/h, MPH and trip ave MPH, InstaMPG and trip average MPG, trip distance. That's six, all the space I have on one window. Substitutions?

BTW, the terrain has two sustained, significant half mile inclines. But I am practiced already at hitting steady throttle positions as I climb them.

You do plan to tuft it right ?
Why not add a vertical 'spine' that meets up with the rear window? ( At the center of the car ) You could add tufts to it and get a better idea of where the airflow is going.

( Basically just a rectangular piece of coroplast / cardboard that would have one edge cut at an angle to meet up with the back window. Rather than taping the tufts, you could even poke holes in the thing and sew the yarn into it. This would keep the yarn from sticking to the tape or being affected by it )


Also, the edges of the sides look like they will cause considerable drag ( my guess ).
Any plans on taping the sides flush with the car ( at the B-pillar )

I know I need to. But I have never done it and when I looked it up on this site, I did not find what I felt I needed: what's the best tuft length and what's the best spacing?

So you mean attach tufts to either side of a vertical section bisecting the trunk lid and rear window from the top of the window to the end of the lid?

( Basically just a rectangular piece of coroplast / cardboard that would have one edge cut at an angle to meet up with the back window.

That's a clever idea.

I would need duct tape and that would leave awful residue on the paint. Instead, I just taped up the edges of the cardboard and tightened the assembly so it fits more snugly. That, I think and hope, can be sufficient.

On Volvo sedans (S60/S80/S40 Mk.2), you can see the higher trunk line toe in as it gets further aft, reducing the wake area of the upper half of the car.
At the same time the higher trunk line reduces the apparent rear angle, so it'll match the streamlining template closer.

Cd and euromodder, thanks for your comments. I made changes based on Cd's earlier ideas. Mostly changing to all coroplast and cutting a more contoured line to try and avoid drag. But I now think I might need to do more. Any ideas that don't involve tape to the body? The plan is to make it easily and quickly removable (magnets). I also plan to taper more now, based on these ideas from you, euromodder. Here is an update and a hope you and others might further advise:

I tested the below design (see pics) last night in a situation of low traffic but dropping ambient temps. My not-so-reliable results suggest a possible gain of .65mpg, or no gain at all, but no loss likely. I need to retest it, having learned not to test between 10pm and midnight. I found MetroMPG's old excellent tuft testing for his vortex generator experiment, and I plan to copy his spacing and length of tufts. I'll try and build this vertical tuft thing too, Cd. I'll take and post video.

But first how might I improve the tapering, the trailing edge, and other drag contributors. I should curve the ends of the "lip"?

tapering
 

With respect to the taper,you might increase the tumblehome of the spoiler sides slightly from beginning to end.
You'll see this on say the Honda Fit,as you stand behind the car to one side looking forward.Looking at the A,B,C,and D-pillars,you notice that each falls in towards the center of the Fit a little more than the one in front,the further back you go.
It would put a little twist into the sides,reducing the plan form area of the top of the extending panel while maintaining the curve of the 'base' which is less affected by the downwash off the roof.

the Fit has an impressive amount of taper. i notice it every time i'm behind one.

I was unfamiliar with the term "tumblehome" though now that I have looked it up online I realize I understood what was meant already. Funny. It's the taper from the beltline of the vehicle to the top, making protrusions in the upper portion not stick out much beyond the maximum width of the car. I understand the point about taper too. So, I'm going to redesign according to these ideas. One priority was not to cut the main long flat section of coroplast until I was fully confident I was honing in on a proper design. I'm at that point. Gotta cut a mildly curved line into the flat lid surface, on each side to carry the tumblehome and the taper to their logical finish. Below is a great set of Honda Fit images that make your points more clearly than most photos people post on the web.

tuft test 1
 

I should have done this earlier. Now I have, and I think what it tells me is that the angle of the rear window may not be all that bad for air flow. In the linked video, you will see what I think is mostly pretty good flow down the window. A little turbulent, maybe? But down low, in the center, you'll see tufts that are being sucked-up the windowpane. That movement was very consistent, at 40 as much as 65 mph. The bottom row of tufts would be under my trunk lid if it were attached. http://www.youtube.com/watch?v=KLQeoV831aU

Thoughts anyone?

I'm also working on the rear trunk area on my 96 civic hx it currently has a fastback flow thru design that makes it ideal for riding with the ac off windows down. there is no back window no trunk lid no trunk whatsoever, tailights have been relocated into the bumpercover. I'm pretty sure this might get some attention. would love to post pics but I'm hadicapped when it comes to computer prowess, tried to attached pic to this reply promt ask for url adress I'm lost there any help maybe?