Designing a tail extension for the first-gen Insight

[RobertSmalls]

I was working on the car today, and I noticed something very interesting. The underside of the car slopes upward, starting near the gas tank. 25" from the end of the car (in line with the wheel centers), there is 7" ground clearance. 4" from the back of the car, where the boattail would need to begin, there is 10" ground clearance. That gives an overall angle of 8° in this region.

I don't know if a stock Insight has attached flow in this region, or if it could have attached flow with an undertray installed upwind. But it does seem plausible. I would tuft-test it, but I don't have a webcam or an undertray.

I just watched the footage of MetroMPG's tuft testing of the underside of his boat tail, which starts at 5:00 at

http://www.youtube.com/watch?v=Mjff5NDREkQ

[aerohead]

Originally Posted by RobertSmalls

I was working on the car today, and I noticed something very interesting. The underside of the car slopes upward, starting near the gas tank. 25" from the end of the car (in line with the wheel centers), there is 7" ground clearance. 4" from the back of the car, where the boattail would need to begin, there is 10" ground clearance. That gives an overall angle of 8° in this region.

I don't know if a stock Insight has attached flow in this region, or if it could have attached flow with an undertray installed upwind. But it does seem plausible. I would tuft-test it, but I don't have a webcam or an undertray.

I just watched the footage of MetroMPG's tuft testing of the underside of his boat tail, which starts at 5:00 at

The big-dogs say that aft-body mods are a wash if the fore-body isn't real sweet.The diffuser is one of these areas which won't function without a good bellypan ahead of it.

[ilusnforc]

Just a small idea for what to do with those rear air vents. The Aptera has a great design for cabin exhaust air. If someone would be so kind as to repost this picture, I don't have enough posts to do pictures or links yet.

htt p://100stax.com/Joomla1/images/stories/aptera2.jpg

[Nevyn]

[botsapper]

A little late for the party. I've always been interested with modding the first gen Insight. It was EV1's design contemporary in terms of clean sheet aero designs. Unfortunately that design direction has been deferred by the more popular SUV box design language of the time. Now your project & efforts have peaked everyone's attention & interest. Everyone's contribution has been helpful in finding the 3dmax files of the Insight model.
Please don't ask for accurate 'cutting' models or templates because this should only be used for an inspiration or aesthetic concept. I've taken a basic 3D model & applied different peoples' ideas for discussions' sake.
The sample has a grafted 'tail' blending into the body line before the bumper & rear light parting lines. It is more integrated & cleaner. There is a pronounced 'shoulder' side contour at the rear wheel cover, this complicates the symmetrical tail taper. This necessitates to continue the line all the way to the rear. The rear window has a clean taper shape. The rear bulkhead design may depend on rear light assemblies available. (A 90's Honda Accord 2dr may have these triangular lamps). I've added front & rear tire spats to clean up vortices & helps balance the 'heavier' rear proportions. Let's starting cutting...

[botsapper]

Just use for discussion:

[jime57]

It is beautiful, and would appear to be practical for street use. I think you will get some arguement on the upsweep angle of the underside, but we shall see. I like it!

[botsapper]

The visible side upsweep is the rear wheel spat angle. There is a shallower upsweep under the tail. It should begin clean and integrated with the full length belly pan.

[RobertSmalls]

Those are some nice renders. And look, babes are not afraid of it!

You've given it plenty of character. However, I have to reconcile that character with aerodynamics. Foremost, it looks like you've added about two feet of lenghth to the car, while I plan to add 3.5' for a more complete tail. Therefore, the region above the "shoulder" will disappear before or near the end of the tail. But continuing the Insight's distinctive rear shoulders backwards until they disappear is an aesthetic must-do.

I have a feeling the shoulder itself should be tapered very slightly downward. Also, as Jim pointed out, the debate has been between 2° and 7° angle at the rear. Although yours will have separated flow, yours has the advantage of having the same departure angle as stock.

You menion "heavier rear proportions". That would contribute to a boat-tailed car looking odd, wouldn't it? How can this be offset? I wonder if anything can be done with the black vinyl stripe that runs up the rocker panels and rear wheel skirts to visually diminish or explain the tail extension.

I've contemplated painting streamlines on the tail extension so passers by might get an idea of its purpose.

Can you export a .3ds file to a .DXF solid model? If so, I'd be very interested in acquiring a .DXF version of the stock Insight.

[botsapper]

RS,
You're correct. I've added only 30" to the existing stock length. It was an arbitrary but 'balanced' decision. Your project has it's own desired engineering criteria. Mine was based on the the boat tail extension not to exceed the car's wheelbase. Anything longer would make an uneasy visual 'weight' proportion. Creating a heavy tail-dragging appearance. By continuing the original Honda designers' solution, the material (black color) change of the lower wheel spats help lessen the visual 'weight' at the rear section of the vehicle. An intrinsic & desired Insight design characteristic. Conversely by adding (aero helpful too) large body-colored front wheel spats help bring more visual 'weight' to the front of the car & helps balance the overall proportion. As for your planned 2° - 7° 'downward' curve of the shoulder, might create unwanted lift instead of obvious 'zero' lift if it stays with the flow of originally designed flatter or nearly horizontal character line.

What is 'painting' streamlines? Sometimes creating a 'design' flourish creates more attention to it instead of diminishing it. Then again you are trying to create an aero design statement...