MetroMPG's Honda Insight boat tail extension (cardboard) tuft video; ABA test +9.7%

[MetroMPG]

A few more pics with a bit of zoom (previous two were from a cell phone with a fair amount of distortion).

You can also see I made a notch in the top of the tail so the center mounted LED brake light is visible.

The plastic wrap came in handy on the weekend: Saturday overnight the car sat out in a torrential downpour. I feared I would find a plastic-wrapped blob of mushy cardboard laying on the ground behind the car on Sunday AM, but it weathered the storm fine.

[Xist]

Nice! The brake-light notch is genius!

[freebeard]

Where you gonna put the MPG Militia logo? The red and white safety tape is a nice touch, too.

[MetroMPG]

I'm going to have to start the Canadian division: but "L/100km Militia" doesn't have the same ring to it, eh?

[jime57]

I wonder if you would consider some tuft testing on the bottom of the boat tail. I've always wondered just how much upward taper angle could be used near the end of the tail. The question has a strong impact on the area of the transom and therefore the drag reduction - I think.

[freebeard]

I'm going to have to start the Canadian division: but "L/100km Militia" doesn't have the same ring to it, eh?

Awww....

[MetroMPG]

Jim - I will do this. I agree it's important to know if the bottom of the tail is working or not.

I was thinking I would wait to put a full coro undertray on before testing, since the bottom of the tail will work better if I deliver the cleanest possible flow to it.

But maybe it would be instructive to see how things look now, with the stock underbody. (Also, I have a pile of other things to do before spending time on an undertray.)

[jime57]

It would probably "advance the art" to have before and after testing on the undertray. From what I've read, I think the undertray is important to the performance of the boat tail. In fact, I think I remember that you found that the case with the Metro tail.

As you know, I don't have much faith in fine grain measurements on the Insight because of lean burn, but I am pretty sure that a full undertray has improved the fuel economy of my experimental unit. I just can't provide a number. Hucho and most of the cutting edge manufacturers, including Honda, seem to think it helps.

If your stock under panels are intact, then you need a fairly small piece of coroplast to complete a full under tray. Because the shape is rather complex, I'd start with a piece of cardboard as template. It is a single plane of about 3-4 degree uptick from the little plastic deflector at front of axel to the bumper cover. Attachments are kinda scarce.

[freebeard]

I like the Difflow diffusers

Perhaps one could add diffuser type fences to the underside of the boattail and see some benefit.

[jime57]

Originally Posted by freebeard

I like the Difflow diffusers

Perhaps one could add diffuser type fences to the underside of the boattail and see some benefit.

Ya know, I've been wondering about that a long time myself. If one could increase the underside angle a bit for ground clearance, and then improve the underside pressure recovery with a diffuser, it might make a great compromise. The diffuser fins could be made of some flimsy sacrificial material like Styrofoam, then ground clearance would not be such a painful issue.