The Search for Fuel Economy

Pages from a Designers' Notebook Readers comments

Chap. 3: Road Testing the Long Tail Mar 28, 08

This thing is 10 feet long. It has slab sides. If everybody is right, it should be a handful in blasting sidewinds.

Time to find out. I headed out to Big Sur and Hurricane Point, about a half hour from my shop in Carmel.

I love this stuff.

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Forty miles down Coast Highway 1 and forty miles back told me this:

Since the foamboard is so light, weight has no effect on the "feel". This is good.

Since the cutout is big enough that I don't snag on it, the streamlining does not affect my use of the bike. More good.

This was a good day for gusty winds.

But, I hardly felt them. At first, I thought there were no side winds. But there were. What I did notice first was:

No wind was coming from behind (which happens on touring fairings when the air tries to fill in the hole you just made) The wind cannot come in from the back because of the tail. No wind from the back is really good.

Bottom Line: Even with slab sides... assumed to be the "kiss of death" for side winds, side winds were not noticeable. I believe it is because the long tail steers the bike into the wind. I think the bike pivots around the rear wheel in gusts and is automatically self correcting.

My rides have convinced me that it is OK to proceed...

I also realize that the original streamlined fairing from the 1980s is not close enough to what I want today. Too much cutting and fitting. Therefore, I have decided to begin from scratch on a new design.

Next step: Lay the final shape out on one foot grids to cut out a plywood profile.
Making a new streamlined body

My personal design process

It is is time to make a "Pattern" with the perfect, streamlined shape that will completely enclose me and my machine.

Until I am able to ride with the smooth, continuous shape, I am not going to be streamlined. Until I am streamlined, mileage will not be improved.

I sketch out the shape over a photo in Photoshop.

I know that the actual machine is 9'8" from tip to tail. Now I am able to draw 6" grids on a layer in PhotoShop over the streamlined shape I want. The grid will allow me to scale it up onto a sheet of plywood. PAD - Plywood Aided Design. I will make one side first and when I am satisfied, will generate the other side.

There may be other ways to do this, but my way is fast, cheap and I can do it all myself.

Translating to plywood:

Now I draw out a smooth shape, full size on plywood. I use 1/4" tape to make the line smoother, checking all the time to see that the shape conforms to the PhotoShop grid.

At 10 feet long it will not fit on a single sheet of 4 x 8 plywood. I must add a 2 foot piece.
Establish a cross section:

I noticed that the widest section of the foamboard body was about 24" wide in a line from my shoulders to my toes. So, with CAD, cardboard-aided-design, I generated that section, drew a line around it and cut it out of plywood as my main bulkhead.

Now I had the minimum cross section that I fit into. Not too big.. not to small.

Notice the new, close-to-the rider windshield
It is a simple job to eyeball the section when viewed from the top. It is round at the front and pointed at the rear. But will the new clear the front wheel at full lock? We won't know until we make the shell.
The major cross-section bulkheads:

The bulkhead for the major cross section is put in place. The shape for the lengthwise section is being generated in cardboard and then cut out of plywood.

Everything is screwed and glued together on my 4 x 8 foot granite stone slab. This is how I know things are made flat.

Trimming the rest of the outside edge with a saber saw, making the curves match up. These outlines in plywood represent the smallest, streamlined shape I can fit into. They also determine what this thing will look like.

As far as I am concerned, in a good design, nothing is arbitrary.

As we go along, the shape will be generated. "Popular style" has no place here.

Now I touch it up with my body grinder, making all the curves flow together. It is ready to fill it in with foam to generate one, smooth continuous shape.
This page posted Mar 28, 08

Udated April 18, 2008