Designing a tail extension for the first-gen Insight

[RobertSmalls]

Originally Posted by orange4boy

We love the CFD sims. Looking forward to that. Hopefully Trebuchet can give you some pointers. Is he still with us?

I was excited when I found the solver settings that describe my problem. Inflow at Mach 0.088 at the front, outflow at the back, wall below, and farfield BC's elsewhere.

However, the solver won't run because I'm struggling with the mesher. I was hoping to just import my Pro/E .ASM file, and get a viable mesh automatically. But no, I get thousands of invalid polygons. Some of them were able to be repaired, others could be deleted, but 276 invalid polygons remain.

[3-Wheeler]

Originally Posted by RobertSmalls

...So if Honda's curvature is a little too sharp in positions #8,9,10, would the correct response be to make the tail extension a little flatter in those areas?...

Yes, I would definitely agree.

I feel that AeroHead has provided some good tools, with very good data to back it up, so without CFD or other wind tunnel tools, I will take his suggested curvature shape and run with it.

All angles with be designed with the polynomial curve fit found above.

Jim.

[jime57]

Originally Posted by 3-Wheeler

1) Position the car to that it faces straight on the driveway.
a) this was verified by opening the driver door and aligning the step with the edge of the driveway. I had to move the car back and forth manually to accomplish this.
.

Before you get too far along with this data, you should verify that the two door steps are parallel (i.e. they are parallel to the car centerline). You should be able to do this by quickly measuring between the two steps at two different points with a steel tape. Perhaps you have done this already.

[aerohead]

Originally Posted by 3-Wheeler

OK, now this might sound like a dumb question...

Is the intent of the AeroHead Aero Template to be aligned with the underside of the car

OR

should it be set on the ground plane (aka Metro)?



The placement of this template changes the effective length of the tail greatly.

Thanks, Jim.

Jaray's intent was to focus on the aft-body roofline and flanks,as this would govern separation.
So really,the only way the template architecture works,is if we put the wheels even with the 'ground plane' or we totally lose the 'reflection'.
Which requires that the belly end up wherever it is.We know how to fix those,but the roof separation issue can be a tough one.
And remember,the roof can always be longer,with a small skin-friction penalty,but if we make it shorter,we're flirting with separation and a terrific rise in pressure drag.Hope that helps.

[aerohead]

Jim and Robert,I wanted to share a technique I use and it's much like what Jim has shown.
With the vehicle ballasted and on a level slab,I run a 10-ft length of 2" square tubing off the roof and clamped to a step-ladder,with my largest bubble level clamped to the tubing.
You can just 'see' where the roof begins to fall away.I make a witness mark there with tape,and then begin a series of stations at some interval( I use 12-inches) along the tubing,marking each with tape.
From a scale drawing I can transfer the coordinates vertically down,with a carpenter's square/square/speed-square to 'fix' a point above the body with anything handy.
After I've defined the station points,I use a 20-ft length of 1" schedule-40 PVC pipe as a French-curve to connect the points into a smooth curve.
At this point the design is defined and ready for fabrication.
The sides are done likewise after parallel lines are established off the vehicles centerline.

[3-Wheeler]

Originally Posted by jimepting

Before you get too far along with this data, you should verify that the two door steps are parallel (i.e. they are parallel to the car centerline). You should be able to do this by quickly measuring between the two steps at two different points with a steel tape. Perhaps you have done this already.

Actually, I also checked the alignment of the tires.

As you know, the Insight has rear tires that are inset by 2 inches over the front tires.

I moved the car until the rear tires were two inches further away from the edge of the driveway slab that the car was resting on.

When moving the car, I noticed that the rail where the drivers door opens was also in alignment with the driveway edge.

Jim.

[3-Wheeler]

Originally Posted by aerohead

Jim and Robert,I wanted to share a technique I use and it's much like what Jim has shown....

Hi AeroHead,

Actually, the only reason I went ahead and measured the angles of the rear end of car, was to allow fabrication of the extension to proceed before the warm weather arrives.

It was one way that would allow foam blocks to start being glued together at the proper angles to create the overall shape.

Ideally, I always like to have the full scale model available BEFORE any gluing and shaping starts, but the thought of saving several months in the process is quite appealing.

Also, when construction on the car starts, that pretty much means that the motorcycle is used to get to work, rain or shine.

Jim.

[3-Wheeler]

The rear of the car with the extension is small...

It's shown in the blue lines. Just enough room for two round tail lights and a license plate.

To make this legal, there will obviously have to tail lights running along the sides of the extension to show the "true width" of the back of the car, for anyone following the car down the road. These same lights have to act as reflectors when the car is parked on the road at night.

So I will be making a trip to the junkyard for lots of tail light assemblies that are flat on the outside, with no curvature.



Jim.

[RobertSmalls]

How about some 3M reflective strips?

Don't forget to leave room for license plate lights and reverse lights.

I don't like the new narrow width of the rear of the car, and I wish there was room for amber turn signals. I will probably try to leave the original tail lights in place, to supplement the new tail lights.

[3-Wheeler]

Originally Posted by RobertSmalls

How about some 3M reflective strips?

Don't forget to leave room for license plate lights and reverse lights.

I don't like the new narrow width of the rear of the car, and I wish there was room for amber turn signals. I will probably try to leave the original tail lights in place, to supplement the new tail lights.

Robert, good idea about the license plate, which is shown by the rectangle with the X through the middle.

Yes, the backup lights too. Almost forgot about those.

The reflective strips sounds good except for the adhesive. That stuff always seems to peel off after a while. Now if it could be glued on with some expoxy to make it permanent....

Yes, I was also quite thrown back when first seeing just how small the back end looked for the first time.

I definitely don't want to leave the Honda tail lights on the car, as their present location will make an excellent attachment point for the extension to the car.

Jim.