The Search for Fuel Economy

Pages from a Designers' Notebook Readers comments

Chap. 2: CAD Streamlined Body Mar 8, 08

Before I begin designing a slippery body, I want to rebend the handlebars to fit me. Honda has pulled the bars back so as to not hit the windshield at full lock. I don't like the feel so I bent the handlebars into a comfortable position for me.   You can see that I had to grind notches out of the windshield. That is OK... I plan to replace whe windshield with a smaller one closer to me.

Over a period of a week, I bent the bars- rode it -and rebent the bars until they felt right to me. I like fatter grips, too. This is all subjective. These little revisions make the Helix feel right to me.  You may like Helix bars as is.  

Rebent handlebars
Streamlined shape: Air likes to go around this Demo

Air likes to go around one smooth shape, round at the front, pointed at the rear.  The perfect streamlined body would be exactly that.  But we have to get on and off our cycle, which means we need some kind of cut-out.  The air does not like to go around gaps or cut-outs. It causes fuel burning drag. Now it is time to determine the smallest cut-out necessary to get on and get off without affecting the streamlining too much.

I will make a mockup streamlined body from industrial foam board, made for sheathing walls of houses.  It is similar to the white foam board we can buy at art stores, but a lot cheaper and comes in 4’ x 8’ x 1/4” sheets, which is good. See my Cardboard muffler of 1965

Tha long tail is absoultely necessary for decent streamlining. But it is generally believed that a tail is responsible for handling problems in sidewinds. See Joe Petrali's experience with his tail in 1936. Read my analysis.

I want to get on the road as soon as possible to see what happens with a long tail. If it affects handling in a negative way, I need to know now, before I waste any more time.

All we need is a hot melt glue gun, foam board and a razor blade. I am trying to generate a smooth, continuous shape that has a streamlined profile: round at the front - pointed at the rear.
After tacking together the final shape from little pieces, I trace around it and cut a single piece from a fresh piece of foam board. Tracing is an easy way to cut two pieces... one for each side. I get on and off  all the time to be sure I will be able to ride this. No CAD (computer aided design) here. 
It is easier to leave the Helix windshield in place so I can go for a ride and see what we have. All the foam board has been hot melted to the Helix and attached with screws and tape.  
This page posted Mar 8, 08

Updated Nov 28, 2009