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

[NeilBlanchard]

Are you going *all the way* and adding wheel strakes, too?

Looking quite clean and crisp!

[MetroMPG]

No immediate plans to boat tail behind the wheels. I may later on though, if this works out OK.

EDIT: also, the rear wheels are more exposed than normal in these pics - the back of the car is jacked up.

Reminder: everything looks good at 640 x 480! In person, it's clearly not a factory cardboard boat tail.

[MetroMPG]

Originally Posted by ECOHondaOdyssey

Great job!

Thanks. Put one on that van!

[Rokeby]

Re: waterproofing cardboard structures... a non-intuitive method

I've had very good success waterproofing cardboard boats with
contact cement, either the original or new water-based formulas.

Just apply with a roller and let it dry thoroughly. It really soaks
into and grabs onto the cardboard. When dry it remains flexible
which is a good thing as the cardboard has a lot of "give."

It is an excellent substrate for water based paint. Although it
might seem like overkill, I recommend finishing as per: contact
cement-primer-paint to get the best film adhesion. One boat
that I designed for and directed building of for a corporate client
was used for three cosecutive years with no waterproofing/paint
failures. (We used triple corugated refridgerator box cardboard.)

I wish that I had see this thread earlier, there are many little
construction tips that lead to a stronger, longer lived cardboard
structure.

For example, it is very difficult to get a good solid glued joint
where the edge of a piece meets a flat surface. The end of the
corrugation just doesn't provide enough surface area. This can
be overcome by including a folded-over flange on the edge-on
piece.

The additional surface area thus created provides a much
stronger joint in two ways: first, it provides greater area for
the joint between the two pieces. It also spreads out shear and
tension forces in the smooth face ply of the flat surface. This
helps prevent the separation of the face ply and interior
corrugations, which are simple glued joints,easily pulled apart
in tension.

At any rate, it looks like you've done a good job. I look forward
to seeing how your work holds up and what aero benefits it
provides.

[orange4boy]

I like how you resolved the lines. Looks stock.

Another water resistance idea is acrylic concrete sealer. It can be sprayed on with a household spray bottle so you would be able to get in between all the ribs and stuff. And it's water based. I have not tried this myself but I'll bet you it would work really well.

[AndrzejM]

Awesome job!

[YeahPete]

Love this. I started working on a front bumper for my cavalier out of cardboard right before winter. But had to stop because of TMP. But it was looking good as well. Since my front bumper is now slightly damaged from hitting already dead animals in the road I was going to use rivots and screws to attach the cardboard bumper.

I was going to seal the cardboard using 1 layer of duct tape and 2 layers of heavy duty trash bags shrink wrapped on using hot glue and heat gun. The bumper was going to be fastened using screws / rivots.

Setting 4x 12'x4' raised beds out of cinderblocks for a square foot garden and babysitting my daughter while the wife is at school is taking up all my time right now.

[MetroMPG]

Video coming later or tomorrow.

The good news:

1) The top side tufts look very happy, right to the tip of the tail.
2) We have flow re-attachment at about half of the way along in the pocket/notch behind the tail light (so, "trapped" turbulence bubble behind the light). I was a bit worried about how messy things might have turned out if the bubble wasn't completely captured.

The less good news: I think the side curvature is a bit too aggressive. There's quite a bit of turbulence in those last 3 tuft columns. They dance around quite a bit, sometimes off the surface, though they never point "in to" the flow, so we don't have reversal (worst case scenario).

I don't think it's so bad that it has to be rebuilt/modified. But I'll mull it over a bit.

[tayjo22]

FYI. Scotch makes a product to tape over boxes that makes them look new so you can cover old writing and whatnot. Might be good to cover the edges with that so you don't have it wick up moisture. Or you could apply it prior to fiberglass sing or whatever. I know it's sold at office max. We use it on old boxes that are still good but have too much shipping info on them.

[NeilBlanchard]

Darin, You can be modest and self-effacing all you want - but that is sharp looking!

Paint it in glue at least, or fiberglass it - or heck just glue on an old bed sheet and paint it and call it done!

Are the side tufts lifting up, or up and down? I'm wondering if wheel strakes would help tame that turbulence, or maybe clear lens covers over the notches?