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3-Wheeler 06-11-2010 01:37 PM

Honda Insight Tail Extension Project
2 Attachment(s)
Honda Insight Tail Extension Summary Page

Quick-Links To Various Aspects of Project

Mounting System Framework 1

Mounting System Framework 2

First Piece of Foam in Place

Rough CAD model of Extension

Absolutely Beautiful Aptera Photograph

Making Use of the AeroHead Streamlining Template 1

Making Use of the AeroHead Streamlining Template 2

Making Use of the AeroHead Streamlining Template 3

Extension Removed From Car for First Time

Rear Hatch Hardware

Verifying Top Angle of Extension
More Info on Hatch Mounting System

Adjusting Top Angle of Extension

Beautiful Rendering of Tail Extension by Botsapper

Question About Vortex Generators Under Tail

More on Rear Hatch Construction

Design Concepts for the VW 1L

SiverInsight2's Spy Photo

Final Stages of Build for 2010

Side Marker Details
Rear Hatch Clearance

Wiring Loom Inside Extension

First Impressions After Driving With Extension

Pictures of Extension

MetroMPG's Ingenious WebCam

First Severe Weather Test on Extension

Summary Table for Build

Limited Run Gas Mileage Test

Center of Pressure from Side Winds

You can see the full array of pictures at:

Picasa Web Albums - Jim - Honda Insight...


Honda Insight Under-Body Smoothing Panel Project



See also: MetroMPG's Insight boat tail project ...

MetroMPG's boat tail thread details:
  • design / construction
  • tuft testing (video)
  • A-B-A testing, showing 9.7% better mileage at 80 km/h (50 mph)
  • 110+ mpg (US) sustained at 80 km/h (50 mph) on a level road, warm weather
  • best ever trip mileage on a frequently driven route


3-Wheeler 06-11-2010 08:10 PM

5 Attachment(s)

Originally Posted by RobertSmalls (Post 178361)
...I am curious about what methods you're using to keep your tail extension straight and true to the equations you developed. I've been using cardboard templates, but I'm not satisfied that I can align them accurately enough....

A little more incentive for adding a tail...

I used a cheap and old CAD program to layout the shape of a template that has the curvature of the side skirts to the tail.

It turns out that the template shape can be estimated by drawing a straight line, then indenting the line by 5/8" in the middle to form an ellipse.

This elliptical shape was then transferred to a large piece of foam, to form the template.

The foam dimensions are:

2" x 8" x 42"

The template is cut with a hacksaw blade, then sanded smooth so it "looks" consistent in curvature.

I have yet to layout and make a template for the curvature from the top of the glass to the tail.

This is a picture of the tail light socket. It shows what we have to work with regarding sheet metal.

This is a view showing where the trunk lid stops are. When the rear plastic bumper shroud comes, these stops will need to be replicated.

A wood block is being fashioned using a hacksaw blade into the compound shape required to fit against the sheet metal of the light socket.

The wood blocks are fitted tightly against the shape of the socket sheet metal.

Thickened epoxy resin was added to the wood pieces to mimic the exact shape of the sheet metal. Grease was used as a mold release to get the pieces back off after hardening.

The reason for the tight fit on the sheet metal will be apparent later on...


mtgeekman 06-13-2010 10:34 PM

Can't wait to see some more updates. been wanting to do this to my insight for a while though I don't have the funds/time at the moment.

jime57 06-14-2010 06:44 AM


Originally Posted by mtgeekman (Post 178852)
Can't wait to see some more updates. been wanting to do this to my insight for a while though I don't have the funds/time at the moment.

Me either. Time gets very tight around here during the summer:(

3-Wheeler 06-15-2010 10:11 PM

7 Attachment(s)
The next picture shows the rear end of the car with the plastic bumper guard removed. This is down by the rear of the tire skirt.

This shows that the rear air vents are actually protected by one way valves, made in a soft rubber material. Every time the trunk or door is shut, the vent valve opens briefly to relieve the cabin pressure.

Here is another chunk of wood that has been added to attach the previously separate pieces of wood.

This shows the rear of the wheel well guard. This will have to be attached to the rear extension at some point.

This picture shows many more blocks added to create a solid support in the tail light area.

Here's another view with the back hatch open.

This picture shows probably the most important feature of the mounting block:

Smooth surfaces in which to mount the block assembly to the car when the time comes. All the attachment points are placed in areas where the sheet metal is naturally stronger based on the inherent curvature of the tail light socket.

This is the most critical mounting point in the entire tail extension project. If this area looses adhesion, the entire tail will try to fall away from the car.

I'm planning on using silicone adhesive to hold this assembly to the tail light socket. This will accomplish two things:

1) Hold the assembly tightly to the sheet metal
2) Allow the assembly to be "pried" from the car, and the stock tail light returned to it's location, if need be.

Anyone have any other ideas for strong, yet removable adhesives?


RobertSmalls 06-15-2010 10:55 PM

You're right, that will be the point that's under the most stress in a crosswind, when hitting a pothole, or just supporting the weight of the extension.

Do you plan to add some kind of access door to get at the hatch switch and lock cylinder? If so, you could use the same door to drive screws through the extension and into sheet metal. I don't know of any adhesives I'd trust with this job.

It might be easier to drive wood screws through the sheet metal and into the tail extension from the inside. The rear bulkhead carpet would hide the evidence, too.

3-Wheeler 06-16-2010 09:50 AM


Originally Posted by RobertSmalls (Post 179214)
...Do you plan to add some kind of access door to get at the hatch switch and lock cylinder?...


The goal is to keep the car as stock as possible when making any of these changes, so they can more easily be undone if necessary.

So there will be a hatch that opens to the rear of the car and gain access to the normal hatchback and key-lock.

Unless someone has any other ideas, the plan is to use silicone caulk to create a tight fitting assembly into the tail light socket area that is held in with various screws.

The wood screws are mounted almost 90 to the normal force direction, and that should keep these fasteners in "shear" more than in "tension". This orientation will minimize the possibility of simply pulling the fastener right through the sheet metal under high force.

I do like your idea of getting more sheet metal involved though.

It makes sense to look at options that would mount a 2x4 piece of lumber sideways across the sheet metal that runs under the rear hatch glass in the area where the top of the plastic bumper guard ran.

If the wood in the tail light socket area were to come loose, at least the long 2x4 wood would hopefully give enough support to still keep the extension attached to the car.


3-Wheeler 06-18-2010 08:16 PM

5 Attachment(s)

Your comments about getting good mechanical strength on the upper portion of the tail extension caused me to decide to beef up the mounting system dramatically.

This also means that the extension will not be used for trunk space, as you shall see in later photos that access to the "trunk" will be limited due to the beefy mounting system.

This first picture shows one way of getting more mechanical strength from thin sheet metal. The Insight is designed to be lightweight, and this also applies the sheet metal in the rear of the car.

Unfortunately, this also means that attempting to mount a lever arm off the back of the car means possible trouble if not done carefully.

The panels are thin enough that they easily "oil-can" when pushed in various locations. Because of this, any place there are transitions in the sheet metal, the ribbing causes the panel to be stronger in that location. We have to utilize this feature when mounting strengtheners to the car.

To this end, the back of the Insight is going to be beefed up to allow adequate mounting strength for the tail extension.

Here is another view of a way to strengthen the sheet metal. Any place were there are creases in the sheet metal, this is also an area where lumber can be used to aid in the stiffness of the assembly.

This shows the reverse side of the mounting lumber, and shows how smooth the finish is here. This was done by mixing thick epoxy and adding to the back side of the lumber and attaching it to the car and allowing to setup. Grease was used as a mold release, and even then, some areas stuck and had to be carefully pried apart after the epoxy setup.

This shows reinforcements being added to this "tab", which will later be used as one of the main structures to hold the tail extension.

This picture shows the embedded 5/8 inch fastener that was epoxied in place for good strength. This 5/8 threaded rod was drilled and tapped with a 1/4-20 thread for later attaching to a 5 inch long bolt.


RobertSmalls 06-18-2010 10:56 PM

I'm taking notes and planning my own boattail construction in my head. There are large areas at the back of the Insight that have little structure, but there's pretty good stiffness around the perimeter of the hatch.

I think I will unbolt the center bumper cover retainer and attach the frame of my tail extension there. I will also get the bumper rebar involved. A few pieces of aluminium angle attached to those two components should be plenty to support a 3' long cargo floor with a 150lb weight capacity. This sturdy cargo area will give me plenty of rigid attachment points for the frame of the tail extension.

That lower piece of lumber looks like it's designed to fit under the original bumper cover. I take it that allows you to use lots of fasteners and never worry about how to remove it from the car?

3-Wheeler 06-19-2010 10:37 PM


Originally Posted by RobertSmalls (Post 179671)
That lower piece of lumber looks like it's designed to fit under the original bumper cover. I take it that allows you to use lots of fasteners and never worry about how to remove it from the car?

Hi Robert,

As usual, your observational powers are correct.

Yes, the lower lumber is slowly being prepared to be "semi-permanently" mounted on the car with silicone adhesive.

Several days ago, the wood was trimmed here and there to fit under the bumper cover.

By using silicone adhesive, IF NECESSARY, it can still be removed, but will take a lot of digging/prying with a plaster knife.

The wood will be prepared for "permanent" mounting by drilling more through holes and mounting with lots of wood screws.


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