Honda Insight Tail Extension Project

[RobertSmalls]

I saw a few Insights on the road in and near Madison this weekend, and now I can really appreciate their quirky looks. I think this is going to complete the look, not just the aerodynamics, of the AlienMobile.

[3-Wheeler]

Originally Posted by RobertSmalls

I saw a few Insights on the road in and near Madison this weekend, and now I can really appreciate their quirky looks. I think this is going to complete the look, not just the aerodynamics, of the AlienMobile.

Hi Robert,

I've always thought that the stock Insight rear looked like it was truncated too early by the original designers.

It's almost as if the car begs to have it extended to complete what was originally started by the Honda design team.

I hope the tail extension does justice to their original conception!

Jim.

[jime57]

Jim, I have been studying your latest pictures with great interest. I "think" I see a "possible" problem that you might want to think about. In the most complete picture, fourth from last thumbnail, I see that you have mounted the foam right against the upper edge of the vertical hatch section, the area with the little plastic "spoiler." I did some testing tonight and I see that the lowest edge of the hatch needs about 5 inches of clearance to swing the opening arc. Are you planning some sort of access door to accomodate this geometric requirement? Obviously this would be a very good area, along the front top of the boattail, for a hatch allowing access to the latch handle and the keylock. Just thinking out loud. Wish I had time to do it right like you are doing.

[ac7ss]

Also, with jimepting's remark: how will you access the trunk catch? or will you wire a switch up front to release the trunk? (It really is just an electrical switch.)

[3-Wheeler]

Originally Posted by jimepting

....I did some testing tonight and I see that the lowest edge of the hatch needs about 5 inches of clearance to swing the opening arc. Are you planning some sort of access door to accomodate this geometric requirement?.....

Hi

You are right about the need for extra arc clearance on the hatchback.

When designing and installing the wood framework for the mounting system, it became apparent that extra clearance would be needed for opening the hatch.

Yes, there will be a section, I don't know, maybe 6 inches or so that will have to flip up out of the way for opening the hatch.

It's kind of nice to engineer some of this stuff as the design progresses, and this is one area where this is true.

__________________________________________________ ___

Also made a decision that I was putting off up until now, and that is the angle of the underside of the tail extension.

Adding more foam blocks to the sides of the extension were getting pretty floppy with no underside support, and so the CAD model was again analyzed.



I decided to go with an underside angle of 13° which is shown in the picture above. This angle was chosen as a compromise between good air flow and scraping driveway aprons.

This angle also keeps the license plate at the same height as the stock Insight. Making the underside angle shallower would get the plate even closer to the ground, and I think the license plate and lights are getting pretty low already, thus the 13° angle.

Jim.

[jime57]

Originally Posted by 3-Wheeler

Hi





I decided to go with an underside angle of 13° which is shown in the picture above. This angle was chosen as a compromise between good air flow and scraping driveway aprons.

This angle also keeps the license plate at the same height as the stock Insight. Making the underside angle shallower would get the plate even closer to the ground, and I think the license plate and lights are getting pretty low already, thus the 13° angle.

Jim.

Yep, the practical does seem to intrude If tuft testing shows too much separation, then you can simply add foam and fiberglas as a fix. The added weight will be small. You would even have the option of fabricating several rather simple "add on" bottom pieces of differing angles. Basjoos had rather steep bottom angles also, and has highly satisfactory reported results. Of course, he has gone well beyond boat tails, so it is a bit difficult to sort out the various improvement contributions.

On the question of underside angle, I have wondered if better results would be obtained by keeping the angle small and doing something a bit more fancy with the bottom rear edge. Several things come to mind. First, the bottom rear could be shortened and rolled up to create a bit more ground clearance. Another option would be to try some sort of captured vortex effect like I think is going on with the stock under bumper shroud. Or, maybe just build the rear transom at an angle of about 30 degrees, with a recessed license plate plane. Just thinking out loud. Hucho showed three "unconventional [termination] methods" in section 4.7.3, but he was not particularly positive about any of the three. I'm not seeing much encouragement on any of the more fancy meaures.

[3-Wheeler]

A vise and several pieces of wood are adjusted to an angle of 13° in preparation of glueing the underside foam at this angle.



This shows a large piece of foam being glued at the same angle as the wood support.



The garage door is closed and a single lamp is turned to illuminate the foam, with the purpose of creating shadows across the surface.



This allows the shadows to reveal low/high spots for further smoothing.



The master curvature template is used to ensure that the proper curvature is being shaped across the length of the tail extension. I look for the same amount of light shinning through, across the entire length of the template.

This sometimes takes an hour or so just to sand small increments here and there to ensure everything is smooth. Use of the template can detect a low/high spot of 0.015 inches (1/64th inch). A couple strokes of sand-paper can easily remove this much material, so careful sanding is in order.

In the process of sanding all surfaces, the template is moved hundreds of times to ensure the entire area is curved at the same curvature. Very tedious work.



Look at the far end of the master template. Notice how tightly the curvature of the stock body work is. Honda's curvature is quite a bit higher than the AeroHead airfoil template in this area.



Here is another shot in the same area. I would estimate that Honda used at least double the curvature in this area.



An end shot showing smoothed foam in the background and new blocks in the foreground.



Notice the hacksaw blade protruding from the side of this foam?

The author glued this section with too steep of a curvature, and the piece needs to be cut-out and reglued at the proper angle. Whoops! Stuff happens once in a while!



Here is the piece cut-out. Looks kind of sad!

Nice thing about the foam; it's relatively easy to glue back into place.



The two last support wood blocks are now mounted in place.



And the start of the foam support system in this area.



You can see that there is clearance in front of the foam block for the trunk to open.



The little dents in the center of the picture are locations where excess glue was picked from the surface. The excess glue makes it harder to sand the finish smooth in this area.

The dents are filled with light-weight spackling, which is much easier to sand than the glue. I've gone through two quart containers at this point. Very handy stuff!



Jim.

[silverinsight2]

This is sooo cool. I can't wait to see the finished product.

[jime57]

Just too cool for words

Here is an old trick from an old shade tree bodywork guy (actually an old race car driver). To eliminate dips from bondo work, not much different from your problem, I used a full 8 1/2 x 11 sheet of sandpaper stapled to a dressed 1 x 4 x 11" block. Cut the block to the long dimension of the sandpaper, 11". Wrap the sandpaper tightly around the block and staple it along the edge of the block. A standard sheet of sandpaper just exactly fits without any trimming. The longer length of the block is much more effective eliminating dips than the shorter sanding blocks.

Also, once you have the fiberglas covering into place, you will be able to add small quantities of bondo to smooth any remaining dips, so it isn't ultra critical.

I wonder a bit about that sharp edge on the bottom outsides. As I think I remember from Darin's Metro tail, there is flow "down" the lower tail to repressurize the diffusion area underneath. As I'm sure you have noticed, there is a bit of a problem extending the stock Insight line since it is quite sharp on the fender skirts and bumper. I wondered just what to do with this problelm myself, but it would seem that continuing the sharp line through the length of the boattail would not be correct. Clearly you can round this area considerably by installing extra foam inside the corner. What do you think?

I see from the photos that you had a very productive weekend

[3-Wheeler]

Originally Posted by jimepting

....To eliminate dips from bondo work, not much different from your problem, I used a full 8 1/2 x 11 sheet of sandpaper stapled to a dressed 1 x 4 x 11" block....

.....Also, once you have the fiberglas covering into place, you will be able to add small quantities of bondo to smooth any remaining dips, so it isn't ultra critical.....

Your large sheet sanding approach has been also mentioned by my brother, who has painted many car bodies over the years, so I hear you on that one.

In my working with foam, there two options to get the body work really smooth.

1) Roughly finish the foam work and then cover with fiberglass/resin, and THEN start the smoothing process, using Bondo and so on.

2) Finely finish the foam work, add cloth/resin and only apply glazing putting to fill around the glass seams, which are inevitable with glass work.

The second approach ends up in a body shape that is just as smooth, but weighs less because adding foam and/or light weight spackling weighs less than any body filler, and costs less too.

So the objective is to get things as smooth as possible before any cloth is added!! This goes so far as sanding with only a "shading light" on, in a dark garage. It's amazing how easy it is to see small defects in the curvature using this method.

Originally Posted by jimepting

....I wonder a bit about that sharp edge on the bottom outsides. As I think I remember from Darin's Metro tail, there is flow "down" the lower tail to repressurize the diffusion area underneath. As I'm sure you have noticed, there is a bit of a problem extending the stock Insight line since it is quite sharp on the fender skirts and bumper. I wondered just what to do with this problelm myself, but it would seem that continuing the sharp line through the length of the boattail would not be correct. Clearly you can round this area considerably by installing extra foam inside the corner. What do you think?...

I agree!!

Actually this came to mind this last weekend when "eye-ball engineering" the situation. It dawned on me that holding this Honda feature to the end of the tail extension is not at all ideal.

Instead, what is needed is to blend this feature, and "roll" the curvature just as you described, so it disappears into a smoothing curvature more like Basjoos has on his design.

And yes, working out the details may take adding more foam to accomplish this.

Jim.