Designing a tail extension for the first-gen Insight

[RobertSmalls]

YKYAEM if you've been checking out other people's taillights in traffic, trying to find ones to stick on the back of your boat tail.

The Saturn SL || SC has a three-bulb cluster like the Tercel's, but smaller. I think what I'm looking for is something that's not much taller than a license plate.

As for the thread slowing down, I'm pretty much satisfied that we've come up with a good design with an equation that partially describes its geometry. I'm just going to procrastinate until spring, then I'm going to try to get the thing roadworthy in a weekend.

A few details still need to be worked out. Opening the hatch requires maybe 20lbf depending on the temperature and condition of your hatch shocks. That's probably too much force to apply to the spoiler, but I wonder if there are any good attachment points for a handle behind the third brake light.



I thought of something else that the transom needs: holes! I believe this picture shows one of the two primary air exits for the passenger cabin, and I suppose there should be holes of comparable size in the transom and/or on the underside of the tail.

Another feature I'd like the Insight to have is a push/pull handle. The easiest way for me to move the Insight in and out of the garage is by pushing/pulling it. I've been popping the hatch and using the back of the car as a handle, but I'd like something easier to grasp. Maybe I'll find room for a handle on my tail extension.

[jime57]

Originally Posted by RobertSmalls

Another feature I'd like the Insight to have is a push/pull handle. The easiest way for me to move the Insight in and out of the garage is by pushing/pulling it. I've been popping the hatch and using the back of the car as a handle, but I'd like something easier to grasp. Maybe I'll find room for a handle on my tail extension.

I usually just roll down the drivers window and grasp both pieces of the seatbelt at the upper B pillar attachment. Works for me

[3-Wheeler]

Originally Posted by RobertSmalls

...I thought of something else that the transom needs: holes! I believe this picture shows one of the two primary air exits for the passenger cabin, and I suppose there should be holes of comparable size in the transom and/or on the underside of the tail...

Robert, I forgot about those as well.

Basjoos has two small holes inside the rear portion of his extension, and has coarse mesh screen to keep bugs out.

It looks like the holes are about 1.5 inches in diameter.

As for extension construction, I'm getting close to starting, but it certainly won't be done over a weekend!! I had a pretty good laugh after reading that Robert!!

Jim.

[RobertSmalls]

Well, you're going with a fiberglass monocoque. I'm still planning to try skin-on-frame construction. I am going to try to get parabolic curves out of 1"x.125" Al bar stock, probably riveted or screwed together. The plan is to strip down the car and lay up a frame on a Saturday, apply cardboard skin and tuft test on Sunday, and have the frame welded together on Monday. A fiberglass skin would certainly be preferable, and maybe I'll build one, piece by piece, but coroplast will suffice until I do that.

If I don't finish by that Sunday evening, the frame will be removed and the original bumper and taillights will be put back in place.

[jime57]

Originally Posted by RobertSmalls

Well, you're going with a fiberglass monocoque. I'm still planning to try skin-on-frame construction. I am going to try to get parabolic curves out of 1"x.125" Al bar stock, probably riveted or screwed together. The plan is to strip down the car and lay up a frame on a Saturday, apply cardboard skin and tuft test on Sunday, and have the frame welded together on Monday. A fiberglass skin would certainly be preferable, and maybe I'll build one, piece by piece, but coroplast will suffice until I do that.

Great

The small Aluminum shapes are pretty easy to bend into gentle curves. Did it myself with earlier Echo rear underbelly. I've though through the next steps some myself. The cardboard outter skin, if you use corrugated, will be a bit difficult to shape in two dimensions, but you can cut out some gores and do it I think. Obviously you can also make your work easier by making good decisions when to divide the sections, and the direction of the cardboard ribs. It will bend slightly even across the ribs. One way to "stabilize" its shape, if you bend across the ribs, is to push a small steel rod into a section edge. These little rods are also available at Lowes/HD. Lots of duct tape will probably be required.

The final step of laying on fiberglas is probably the most difficult. Since fiberglas cloth with resin is rather heavy and needs support as it hardens, that necessity must be considered. I had contemplated forming the boattain shape with sytrofoam and laying the fiberglas over, but laying down over cardboard lowers the complexity and work load, not to mention cost. Both the inside and outside of the tail would have to be fiberglassed, since the cardboard is obviously not immune to water.

I envy you being able to proceed now. We are all anxiously awaiting some pictures and results

[RobertSmalls]

Just to be clear, I will try to complete the project in "a weekend", but not "this weekend". My garage isn't heated, so I will wait until some time in April. The Green Grand Prix is the second weekend in May, and I'll have the tail extension in place before then.

If Jim is close to starting, he may finish before me.

[3-Wheeler]

Originally Posted by jimepting

...I had contemplated forming the boattain shape with sytrofoam and laying the fiberglas over, but laying down over cardboard lowers the complexity and work load, not to mention cost. Both the inside and outside of the tail would have to be fiberglassed, since the cardboard is obviously not immune to water....

Actually the cost of cardboard/fiberglass versus foam/fiberglass is almost the same.

The glass will cost about $30.
The foam board will cost about $30 (1-1/2 sheets at 2in thick)
The epoxy resin will cost about $100 (one gallon)

So the only difference in price is the cost of the cardboard.

Really, most of the cost for me, is labor. Figure three months. I can start now or later when the weather gets warmer, but it will still take that many hours for me to get a nice fit and finish.

The finished paint job will not be done this year, as getting a class A finish on the fiberglass takes another two months or so, then many coats of automotive quality paint, and finally the clear coat. So this fall, I will driving the car with primer colored paint, and that's fine with me.

Years ago, I did the motorcycle fairing over the winter, with the bike in the basement. Used a boat winch to get it up/down the basement stairs.

Robert, you will most likely finish before I do.

Jim.

[3-Wheeler]

Robert,

As for the vent holes in the extension, you got me thinking...

How about putting a small and appropriately sized hole behind the license plate. Then cover the hole with screen mesh to keep bugs out. You can't see the hole, water will not splash into it, and still does it's job.

Put spacers behind the plate to offset it away from the bodywork slightly, to allow adequate air flow through the hole.

That's how I will tackle the venting issue.

Jim.

[COcyclist]

I hope you both will give us pictures and updates as things progress. I plan to start on my detachable tail soon but haven't decided on the construction method yet.

jimepting, will you take the tail off the car and stand it up to fiberglass it or does it need to be attached so it doesn't change shape as it cures?

[jime57]

I really don't have any experience with cardboard/fiberglass or foam/fiberglass material mixes. I think that one might want to do some material testing before getting too far along - assuming lack of experience like mine.

I know that fiberglas cloth/resin needs support to hold any shape while hardening. Therefore, it must be laid down over some sort of full support. I also know from personal experience that resin is not compatible with styrofoam. I have tried to mix it in syrofoam cups and it just disolves the cup. A while back I discussed this with someone in the ecomodding community who indicated that this problem could be sidestepped by painting the finished styrofoam shape with a water based latex paint before fiberglas overlayment. No direct experience, but I've heard it.

Regarding cardboard/fiberglass, there may be shape shifts (ala Star Trek ;-)) when the resin soaks into the top layer of cardboard. I think that I would certainly do some quick testing on this approach before I got very far along. In addition, it is going to be difficult to get finish quality smoothness with just cardboard and fiberglas. It will probably suffice for testing, but it's gonna be difficult to get it smooth. Perhaps the addition of some exterior bondo will facilitate the shaping of finish quality curves.

All this is just thinking out loud. I also want to build a boattail, but getting the materials tested before I start is definitely on my agenda. Too much work and expense to gamble of bad material mixes. Perhaps a two step process, with cardboard over frame, followed by something more permanent, would be the best way to go, but that is really slow. I'm still rolling it all over in my mind. Perhaps someone else will go first ;-)