Honda Insight Tail Extension Project

[3-Wheeler]

Originally Posted by RobertSmalls

...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....

Robert,

Is it possible to sketch up something as to what you are thinking here?

I'm having a hard time visualizing some of what you are saying.

I can imagine someone removing the aluminum bumper and attaching beams to the same points were the bumper used to be, but would also imagine that this support would act somewhat like a diving board and flex up/down over bumps in the road, especially if it were 3 feet long.

This flex would then mean that the normal gap between the extension and existing bodywork at the tail would need to be larger to accommodate the movement.

Maybe you have something else in mind to make the assembly more rigid?

Jim.

[Funny]

This appears to be one of those threads that will get very interesting, very quickly. Keep up the great work, and I look forward to more pictures. I am fascinated at the usage of lumber in the construction of aero mods.

[RobertSmalls]

I will definitely be leaving all of the original crash structure in place, including the bumper rebar. Instead of removing it that bar, I'm going to drill into it and attach a three foot long cargo floor, framed in 0.125"x1" Al L-channel. Interestingly, the bumper rebar is already at the end of a three foot long "diving board" of aluminium honeycomb, so a three foot extension would make a six foot cantilevered beam. To add rigidity to it, I will make a few triangles between it and the strong location just above your center lumber, where Honda has provided three threaded holes in strong sheet metal.

Additional truss members will be required to give the desired result. I'll just have to keep adding until it feels rigid enough.

Originally Posted by Funny

This appears to be one of those threads that will get very interesting, very quickly. Keep up the great work, and I look forward to more pictures. I am fascinated at the usage of lumber in the construction of aero mods.

I am anxiously awaiting the completion of an Insight tail extension, whether Jim's meticulous work in fiberglass, Jim E's cardboard prototype, or my own coroplast + Al tail. What kind of fuel economy is an Insight really capable of?

[3-Wheeler]

Originally Posted by RobertSmalls

...Interestingly, the bumper rebar is already at the end of a three foot long "diving board" of aluminium honeycomb, so a three foot extension would make a six foot cantilevered beam....

You are correct, but when looking at the Uni-body construction under the car, one can also make out lots of sheet metal around the "center" beam, which makes this incredible in strength, much more than just a beam by itself. No need to calculate the moment of inertia here (Z-section if you like math).

Originally Posted by RobertSmalls

...To add rigidity to it, I will make a few triangles between it and the strong location just above your center lumber, where Honda has provided three threaded holes in strong sheet metal....

I was looking at those three fasteners as well, and will use some small aluminum L-brackets to tie those points to the lumber.

Originally Posted by RobertSmalls

....I am anxiously awaiting the completion of an Insight tail extension, whether Jim's meticulous work in fiberglass, Jim E's cardboard prototype, or my own coroplast + Al tail....

I would just like to wrap things up before the weather gets real cold, just like last year with the under-body panels.

Originally Posted by RobertSmalls

...What kind of fuel economy is an Insight really capable of?...

Well I don't know for sure, but I think that over 100 mpg is possible with my turtle driving style. How about you guys? Any guesses?

Jim.

[jime57]

Originally Posted by RobertSmalls

I am anxiously awaiting the completion of an Insight tail extension, whether Jim's meticulous work in fiberglass, Jim E's cardboard prototype, or my own coroplast + Al tail. What kind of fuel economy is an Insight really capable of?

Well the fuel economy is pretty well studied over on CleanMPG. In the warm months, with grill guard and block heater, at 36-38 mph, the car can fairly easily achieve 100 mpg on a no traffic type road.


Of course, that speed is too low for aero work. My own testing leads me to believe that the baseline fuel economy on my 06 MT is about 95 mpg at 55mph on an interstate round trip circuit. I've pretty much commited to 60 MPH testing, so I still have some testing to do.

[3-Wheeler]

Originally Posted by RobertSmalls

...To add rigidity to it, I will make a few triangles between it and the strong location just above your center lumber, where Honda has provided three threaded holes in strong sheet metal.....

Robert,

Last night I did the "metal tap test" where one goes around tapping on the metal to listen for "dead sounding" spots.

Those three faster holes that you describe above are not all that solid sounding, but still the best we have to work with in that area of the tail.

If you compare that area to where the aluminum bumper protrudes through, the bumper area sounds extremely dead and solid in contrast.

I can't imagine not adding some type of reinforcement in the area of the three bolts to increase the stiffness there.

Jim.

[3-Wheeler]

Here's a view of the new mounts below the aluminum bumper, made from 2x4's.



The bottom edge of the lumber is cut at the same angle as the under-body smoothing panels.



Small spacers were machined from 3/8 inch tubing and are mounted on all four bolts on the lower part of the bumper, due to the high curvature of the bumper in this area.



This view shows the spacers on the bolts, and stabilizing wood between the four 2x4's. The stabilizing wood maintains the same spacing between the lumber if removed from the car. This is important, otherwise the bolts and screws that hold the tail extension may not line-up properly.



Here the foam is being trimmed away from the muffler pipe as part of the heat control in this area. That's the nice thing about foam; it's easily carved.



A thin piece of lumber is machined for thickness and will be used as a spacer later on. The two thicknesses will be cut into two separate spacers.



One of the wood spacers is shown in this view, and being glued in place. After the epoxy set's-up, wood screws will make sure it stays put.



This shows the spacers being glued in place with epoxy. You can start to see part of the extension taking form.



Jim.

[aerohead]

Jim,I don't know about 100 mpg.
The best single 1-way run at 55-mph in the CRX was 84-mpg.That was downhill with a South-westerly from Cloudcroft,NM,@ 8,600-feet,to Denton @ around 620-feet,over around 565 miles if I remember correctly.
I think basjoos has seen north of 90 mpg with AeroCivic.I'd pester him and see If he can give you some real-world prediction for your car.
I thought 90-mpg would be reasonable for an Insight,but that was with the full tadpole gap-filled trailer as is in the photo archive.I estimated Cd 0.12 with that rig.And that was based on a 70-mpg baseline from a local businessman who bought a fleet of Insights for his employees.
Renault claimed 138-mpg for it's Cd 0.19,approx 18.5 ft-sq.,27-Bhp,1987 Vesta II,at a constant 100 km/h from Paris to Bordeax.
It's just hard to know.

[Daox]

People have already broken 100 mpg on a tank of gas in the insight w/o mods. Its completely doable.

[aerohead]

Originally Posted by Daox

People have already broken 100 mpg on a tank of gas in the insight w/o mods. Its completely doable.

Daox,were they hypermiling,or just driving down the highway at a reasonable speed,say,100 km/h ?
Honda has extremely good quality control from car to car,and on coast-to coast runs with
fleets' of cars,they return virtually 'identical' performance.
It's hard for me to wrap my brain around a 30-40 + mpg variance between like vehicles.
If that's what they can do,it's great,just hard to explain and to design around.