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

http://ecomodder.com/imgs/collage-summary.jpg
(Aww, how cute - my second cardboard boat tail.)

I haven't even finished the cosmetic details of the car's new removable/adjustable upper & lower grille blocks. But since I only ever drive this car on the open road, it drives me nuts to be wasting all those extra millilitres of fuel because it doesn't have a boat tail.

I literally think about it ... Every. Time. I. Drive.

Ultimately... eventually... I have in mind a hitch-mounted, "cargo carrier"-based type of tail (along the general lines of this one and this one). But that's quite a big project, and a ways off.

So, until that happens, this quick 'n' dirty prototype will have to tide me over:

• CAD construction (Cardboard Aided Design)
• very small, light internal wood frame (may contain some aluminum tubing also, because aluminum makes it more high tech)
• it'll hang from a bracket through the rear bumper (through factory holes over the licence plate)
• it'll attach via straps to factory tie-down hooks inside the hatchback's cargo area
• 2 more don't-fall-off! straps will run up the rear glass to the top of the hatchback
• the factory hatch will remain openable/accessible with the tail on the car (with the top straps disconnected, obviously)
• a skin of heavy plastic film plus lots & lots & lots of duct & hurricane tape will make it weather proof. And sexy.
• protective film will guard the paint where the tail is in contact with the bumper
• tail lights will be left where they are, exposed in cut-outs, like this coroplast Prius tail -- so only the lic. plate, light, and reflectors will be mounted on the end of the tail (maybe also side marker lights)

I'm basically just winging it (ha), eyeballing the curves & angles.

Ultimately this could also be reproduced in coroplast if it turns out to work OK.

Expectation management: don't expect rapid progress or significant updates to this thread for another week or three. TMP! (Too Many Projects). I just wanted to get it started to get the creative juices flowing. (Fluid dynamics of creative juices?)

And it goes without saying, it won't be nearly as pretty (or as long, or as effective) as Jim's tail:


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Project summary...
updated April 23, 2013

http://ecomodder.com/imgs/tail-wrapped-collage.jpg

http://ecomodder.com/imgs/tail-wrapped-profile.jpg

Dimensions:

Length 79 cm / 31 inches

That makes the car+tail = 4735 mm (186 in.) overall. That's 3 inches shorter than the most popular/best selling car in the U.S. (2012 Toyota Camry).

Weight:

14 kg / 31 lbs

Curves/Angles:

(Approximate)

Top: from ~13 through ~16 degrees
Bottom: from ~6 through ~13 degrees
Sides: ~16 through ~24 degrees

Bottom clearance departure angle: ~18 degrees

Cost:

Duh. It's cardboard, glue, tape & leftover wood, half dozen ratchet straps and heavy duty garbage bag plastic. Maybe 20 bucks in materials.

Test results:

1) Tuft testing video posted on April 22 (post #66) shows smooth, attached flow on top, and attached but turbulent flow toward the rear on the sides.

2) A-B-A testing on April 23 (post #77) showed a 9.7% improvement in fuel economy at 80 km/h (50 mph).

Real world results:

109 mpg (US) / 2.2 L/100 km round trip fuel economy on a ~300 km round trip where my previous average fuel economy was ~95 mpg (US). See post #168 for details.

Tuft testing video:

http://www.youtube.com/watch?v=TmEeiGZwmS8

VERY COOL! :thumbup: I'll be keeping a close eye on your thread! ;)

Here's a material that is essentially coroplast with an aluminum skin on both sides: AlumaCorr. I haven't found a local supplier.

I've started a removable, redwood framed and shrinkwrapped, test boattail. I'm hoping my camera shows up before I get too far along. I intend to do the final version in Polymetal. It's $148 for a 4x8' piece, $104 if I have a shop order it for me.

It sounds like you have six attachment points. I would think with the reduced base pressure there wouldn't be too much suction trying to pull it off. Vibration and tail-wagging must be the bigger problems. I plan on two roof rack style clamps on the driprail and pegs into sockets already in the bumper brackets. With some straps to hold it down.

Ooh, that sounds good. Do you have a thread going that I missed? Feel free to post the link.

- CAD = Kewl
- Aluminum? Get some titanium fasteners, just because

I'll be watching this thread, not because I actually intend to boat-tail something, but more for the watching the build process. :cool:

No thread yet. I'll probably bump an old thread (Project: the Third) but like I said, my camera is probably around here somewhere, I just can't lay my hands on it.

"Pix or it didn't happen."

I've already seen some folks attempting to fix dents with cardboard, using plastic adhesive tape to weatherproof it. Others just used epoxi resin over the cardboard, as a cheaper alternative to fiberglass :eek:

One could run the corrugated cardboard through a paper shredder, then a blender, add in a water soluble glue (or lime) and have paper maché.

I am looking forward to some test results from this mod as I know you will be documenting any changes you see in mpg. I have been planning something similar for my hatchback but I want to keep the taillights functional so the sides would be recessed like yours. I may leave a gap at the top to see out of and have wondered if the air would re-attach.

The ghetto wasn't built in a day...
 

The flow will re-attach if you respect the proper shape (ie. not too "fast" or steep a curve/angle from where you've made the "step").

---

I've been playing with this a bit more:

- Making it up as I go along, I've pieced together a very ghetto wooden 1x2 frame to which both the outer skin and 6 securing straps will attach, and which provides the "contact patches" with the car: carpeted pads that press against non-painted surfaces (or normally hidden, painted surfaces):

http://ecomodder.com/forum/attachmen...1&d=1363717364

(... actual frame is much more ghetto looking than diagram ... but includes more triangulation for strength, not shown)

- Also revising on the fly, I'm no longer going to use external straps over top of the hatchback. Instead, I'm routing the straps from the frame, to the beefy hatchback gas strut mounts inside the car on the "C" pillars.

I'll snap some pics this evening to show how that will work.

Quick 'n' dirty? So much for this being a "quick" project!

I originally envisioned slapping this together in a couple of hours so it could save me a few drops of fuel on a pair of recent highway trips. Instead I've probably got about 5 or 6 hours in it, and the skin isn't even on yet!

It's still "dirty" though. :D

A few more pics to provide the illusion of progress on this project:

http://ecomodder.com/forum/attachmen...1&d=1364864359

Above: ghetto frame mostly completed. In this pic it's very firmly strapped to the car. Five... count 'em! 5 ratchet straps, 2 bungee cords (to be replaced by straps). Still some triangulation to be done.

I've extended a very light 1x1 frame out from the main frame to act as a skeleton. This one won't be a stressed skin structure like the Firefly tail.

http://ecomodder.com/forum/attachmen...1&d=1364864359

Woo.

http://ecomodder.com/forum/attachmen...1&d=1364864359

Starting on the "hip bustles".

How long is it?

I think it sticks out from the rearmost part of the bumper about 36 inches... I'll double-check tomorrow.

EDIT: nope, it's 31 inches.

working on the left hip
 

Correction, Sheepdog: it's 31 inches from the end of the bumper. 7 inches shorter than 3-wheeler's permanent tail.

I hope nobody's copying me, because I'm completely winging this one. We won't know how good my "aero eye" is until it's tuft tested & ABA'd.

Insert tab "A" into slot "B"...

http://ecomodder.com/forum/attachmen...1&d=1364951968

*checks for tail*

I, too, am troubled by my lack of a tail.

I know I am buffeting my way through the atmosphere when I could be slicing through it. I could be saving at least 10% in fuel with a proper trailing edge. I could be passing through the dense fog with far less disturbance to the universe, yet still get where I am going quickly.

I may join thee in this quest for a proper termination of the vehicle body.

Worked on the "hip/bustle" structure on the right side tonight. No pics (mirror image the pic from yesterday if you're having trouble visualizing it).

Ready to start putting the cardboard skin on it next.

Then... tuft testing! We'll see if it needs any tweaking before encapsulating it all in plastic.

Please do!

But... didn't you have a tail already?

hips done
 

http://ecomodder.com/forum/attachmen...1&d=1365381188

http://ecomodder.com/forum/attachmen...1&d=1365381188

Main difference between the Firefly's tail and this one: hot glue gun! Highly recommended for CAD construction.

Both sides are done now. Top skin is next.

looking good! I'll be interested to see the results of the tuft testing

Metro, that is one of the best-looking prototypes that I have seen on this site! Is there any way that you could replace duct\100 MPH\hurricane tape with paper packaging tape? Are you planning on waterproofing that, or would you wait for the next version?

This needs to last 6 months before I start on a "permanent" version (so, more realistically 12 months), so I'll be waterproofing it as best as I can with plastic. If it lasts, it lasts!

I'll tuft test it before wrapping it though, in case I discover I need to make adjustments.

Neat prototype project. Nice curve on the tail from the bumper cover.

Man that looks good. I should make one like that too. Ever consider using balsa wood as a frame?

That's looking really good. I assume the blue tape running off down the side of the car is for alignment purposes?

When you cover the top (he assumes), will you still be able to get to the straps to remove it? I'm curious about the weight.

You could buy one of the those large poster frames, and just use the clear plastic to wrap the tail light section. One good good 3x6 foot poster frame should do it.

I'm curious what the structural requirements of a boat tail are. I tend to over think, and would go for a much heavier construction (some might even think aluminum would be required). But you seem to have done it, first using only cardboard, and then secondly using a light minimal 1x1inch wood frame. I guess a boat tail is shielded from the wind by the car, and only really needs to deal with vacuum pressure and the wind speed parallel to it. Can you share your insight on this?

It looks great. Can't wait to see some tuft testing videos. Hopefully you'll roll something soon.

ready for top skin
 

http://ecomodder.com/forum/attachmen...1&d=1365469364

I ran out of cardboard. :(

I think I'll use an aluminum platform/structure and foam for the "good" version. This cardboard one's not going to be heavy.

Yup, and yup: I'll make a little hatch on top to get at the inside gubbins.

Weight: well, my first tail (hey, I'm a regenerating reptile!), which was much larger but mostly duct tape & cardboard, only weighed ~12 lbs. But with the wood frame inside this one, it's probably more in the 20-25 lbs range (W.A.G.). I'll weigh it when it's done of course!

I don't think I'm going to cover the lights. I'm concerned that in some conditions, reflections could hide the lights inside.

So am I! :D

But seriously, it's not the material, it's the design. You could make the structure from chopsticks if you triangulate enough.

I'm not pretending to be an engineer, but I am triangulating for strength, and the way it's going together, the skin & bulkheads become part of the structure as well. (So as long as it stays dry...)

Also, anyone watching me building this will have seen me at different stages grabbing the frame and wiggling at first, then getting closer to wrenching the rear of the car back and forth as it has gotten stronger. (The tail wagging the car.) Seems strong to me.

Just driving down a smooth road, besides gravity, I don't think there are significant forces at play on a properly shaped tail. The bigger issue (I think) is it also has to withstand a lot of sudden bouncing, jolting, jerking around over bumps.

Sweet, sweet cardboard engineering! it you can just fiberglass over the cardboard (post testing natch!), then you will have a great boattail. Borrow 3-Wheeler's design for the latch cover, and you'll be done.

I'll second that. I've already done it a few times, often using some random cotton fabric scraps to replace a small amount of the fiberglass for budget reasons.

I am also inclined to think that you will have random people stopping in the parking lot and asking out loud "What the heck is that?!"

Then they start poking it with a stick.

You are an artist with cardboard.

When you're ready to move on to the next iteration, hang weight-lifting weights on the end and take it through a traffic-cone slalom in some parking lot.

Hi,

Actually I think your savings would be way higher than 10%.

The "closing edges" of the Insight are way smaller than the typical car already, so comparatively speaking, the Insight has less of a gain by adding the tail.

A typical vehicle however, has more of a "square back-end" which means the addition of a tail has a much greater energy recovery based on the larger closing area before the tail is added.

If one happened to drive on the freeway a lot, then of course the gas savings are even higher based on the higher air speed.

Jim.

You are a cardboard artist. That looks great! I would be ashamed to replace it with anything else. Just fiberglass over it like has been said many times before. I will likely fiberglass the gaps on my trailing edge, but it is not cardboard.....yet :thumbup:

X2! Someone has to do a "proof of concept" in the real world and you are mostly already there. I love the epoxy resin/foam creations on this site but if there was a cheaper, quick and dirty way to get similar results, We need to see it.

If it tuft tests OK, glass it. I think the regulars on this website all cringed a little when the Firefly boat tail ended up in the recycling bin.:(

I have an idea. If you will cover a cardboard with any even cheapest resin that would give it extra strength and additional resistance for weather conditions.

The waterproof wood glue I am using would also work well - no smell and it cleans up with water. It is Titebond III and there is an Elmer's glue that is exterior grade yellow glue that would also work.

I just made another smooth wheel cover yesterday with a scrap piece of cloth and the Titebond III glue. It is dry in under and hour and paints up just fine. The one I made last year is holding up very well.

Re: cardboard artistry.... Let's not get carried away, now. It's pretty easy to look good at 640x480! :D

http://ecomodder.com/forum/attachmen...1&d=1365604855

I'll look into that wood glue idea.

The big issue isn't really the outside surfaces, it's the edges - the corrugation is perfect for wicking up any water that touches it, like a thirsty camel at an oasis.

Also, my plan all along has been to encapsulate the thing in plastic wrap.

This one isn't going to end up in the recycling bin!

That is coming along nicely!:thumbup:

Glad to hear it will be saved.

Wrap the free edges with 1 1/2" masking tape before weatherproofing.

I dragged out my copy of Paper Houses (Sheppard, Threadgill and Holmes. Schocken Books, New York, 1974). It's pretty good on cardboard constructions. The weatherproofing methods they list (p. 74) are:
Nothing
Boiled linseed oil
Copal varnish
Polyurethane paints
Resin-based paints
Fiberglass
Concrete
Other

Use concrete! :P

What manner of plastic wrap will you be using?