The Search for Fuel Economy

Pages from a Designers' Notebook

Sept 1, 08, 2008

updated Sep 2

Chap. 16: Results of adding weight to front
Those of you who have been following the development of this project know that I have been concerned about the effects of side winds on a streamlined shape such as this. After all, the long tail is necessary for streamlining. We are in uncharted waters. So far, I have concluded that as long as it is ultra light (3 pounds) the tail seems to be unaffected by winds.

The nose is a different story. It has become clear that with the addition of the nose, I have begun to feel the wind. Many of you offered suggestions, such as shortening and rounding it off more. Others suggested adding "anti-lift" spoilers. One person thinks adding a front wing to induce a downforce might help.

After thousands of miles of riding with the nose and tail, I reasoned that if I added a large mass to the very front, the wind would not be able to move it so easily. It would be like "Kicking a boulder." The idea would be easy to test.

Bar bell weight tucked up front in the nose
I peeled open the front and found a place for an 18 pound bar bell weight. I made a mounting bracket for it to make sure it would not fall out and get tangled in the front wheel. There was not room for two bar bell weights, so I tie-wrapped two, 5 pound lead balls in for good measure. The new weight adding up to 28 pounds.
The Real Test: A 300 mile trip down the Pacific Coast

We headed for Big Sur and Arroyo Grande, Carol riding her GS650 with #3 prototype aluminum (un named) fairing. I rode the Helix Streamliner. Immediately, I noticed that the Helix felt more "substantial" than before. To get to the main road, we must pass over an open grid metal bridge, the kind that always makes motorcycles squirm. This time my Streamliner did not even notice the grid. This was a dramatic change. I always thought it was the tire pattern that caused this. Now I know it is weight on the Helix.

At the beginning in Carmel, there were no winds, but by noon, the winds built up to become very powerful - blowing from the ocean side (right) and a little from the rear. We rode 55-65 mph along the Pacific Ocean passing the devastating fire damage. 70 mph, closer to SanLuis Obispo. The effects of the wind on the Streamliner had ben dramatically reduced. This was a new machine! We rode the exact same way and recorded our mileage. 131 miles later in Arroyo Grande, where it was 100 degrees, we filled up.

The trip to Arroyo Grande: The weight works!
Mileage down, from Big Sur to Arroyo Grande: 131miles. Fuel used: 3.967 gallons @ $3.979/gal = $15.78 total for both bikes

Craig on Streamliner: 1.93 gallons = 67.87 mpg or 5.86¢ a mile

Carol on BMW: 2.037 gallons = 64.31 mpg or 6.18¢ a mile

This mileage is not particularly good or bad. Keep in mind that I do not expect any mileage gains until the streamlining is complete. This is the time to deal with wind problems. My Helix Streamliner now felt like a regular motorcycle in side winds. The weight up front was doing what I hoped it would. Side winds? I never felt them. Burning less fuel than Carol made me feel pretty good. Things were about to change.
The trip back to Carmel: Horrible winds! The weight still works

The afternoon winds from the north, heading north in Salinas Valley are always the most powerful headwinds I have ever experienced. I am not kidding. After Paso Robles, they blow at least 40 mph. After King city, they get worse. Would the 18 hp of my Helix be enough to maintain posted speeds? How would Carol's 40* hp BMW fare?

The 50 miles of freeway above Paso are posted at 70 mph. The Helix was able to go 70 about half way. In the last half, as the winds increased, it could only muster 65-7 mph, wide open. Carol had no problem running 70 and flaunted the fact, "dancing" around me on the freeway. My only consolation was that, inside my streamlining, I had absolutely no sensation of the winds. It was only when I stuck my hands out that I could feel it.

Mileage back, from Arroyo Grande to King City: 101 miles. Fuel used: 3.745 gallons @ $4.119 /gal = $15.43 total for both bikes

Craig on Streamliner: 2.08 gallons = 48.55 mpg

Carol on BMW: 1.707 gallons = 59.168 mpg

Into the winds, Carol beat me in fuel economy! Substantially! What is going on? Didn't I have the right power? The answer will come only when I have completed the streamlining on my Helix. We had to put our warm clothes back on because the temp was dropping quickly. It always does that.

Back to the road...

Past King City, riders on bikes are hammered and most bike traffic slows into the wind. It is just too painful. We passed many bikes who had slowed down to avoid the torture. The wind was maddening but we were on a mission. At the gas fillup, Carol told me that my tail was waving back and forth, as if it was waving at traffic. I could not feel that. Farther on as the wind got stronger and came mostly from the front and a little from the right side, I began passing semi trucks. Slowly, because I did not have the power to pass quickly. Besides I figure it is my job to be learning what will happen. Now I could feel the violent winds. anybody on a motorcycle could.

In the awful wake of semis, I began to feel some unusual vibration... like a wheel out of balance, but sort of sideways. I cannot see the tail in my rear view mirrors. Carol pulled up next to me with her eyes wide like saucers. I knew something was not right . Fortunately, our turnoff was just a few miles ahead, so we pulled off and de briefed.

Carol said that my inflatable tail was going crazy... fluttering so much it scared her. I discovered that it was low on air pressure and had gone limp. Had it sprung a leak? No. The temp had dropped 50 degrees and the air in the tail had contracted, causing it to go limp. I blew it up tight and continued home just fine

Conclusions, Sept 1, 2008:

I am convinced that true streamlining - round at the front, pointed at the tail - is feasible on single track vehicles, in the worst wind conditions.

The rider comfort inside real streamlining is unmatched.

I can carry anything I want and it is inside, safe and streamlined.

I still do not know if we will burn less fuel with a bigger engine running slower - or - a smaller engine running faster. I won't know until I am as streamlined as I can get. Right now, it is looking like a bigger engine, like Carol's BMW turning slower may have better potential.

A too-flexible tail is not a great idea.

Keep in mind, my goal is to go 70 mph, into a 20 mph headwind, carrring 4 bags of groceries and get 100 mpg. (that is 4¢ a mile, by the way.) With its 40 mph head winds, Highway 101 is a lot tougher than my goal.

It is time to pack up and go to BUB Speed Trials at Bonneville where I hope to discuss streamlining changes with FIM officials. It is time to reconsider the bans on real streamlining that the FIM has had in place since 1957.

* I am suspicious of internet reporting about the GS650's horsepower. My KLR is reported to have 37 hp, at the rear wheel, 43 at the engine. Less power. But in reality, my KLR seems much more powerful than the BMW. In any case, Until proven wrong, I will believe that horsepower is more important than engine size for determining the right size for fuel economy.
Read this very interesting E mail from Paul in the UK, Sep 2, 08: I am sure you have these same comments. Thanks for your kind note, Paul.

My comments are in bold

Craig, I've been considering why your fuel consumption hasn't improved as much as it might.

My first thought was the CVT. The simple rubber band type in particular suffer from poor part load efficiency, so to some extent you just swap aero drag for transmission drag. You also have a fixed loss from hysteresis in the belt. If you really have significantly lowered the aero drag, then you might want to consider changing the Variator springs and weights to raise the average gearing (since you can't do anything about peak at the moment).

I don't know if mileage has improved or not since I have not been riding next to a stock Helix. But, mileage probably has not improved. I don't expect it to until I am really streamlined... all smooth.

I agree that the CVT is not real efficient. But the Helix is an easy place to begin. If it comes to it, I am prepared to have two shafts machined to raise the gearing inside the engine. But not yet. ( look at my 300 mile ride into the winds... the Helix is geared pretty good for these really tough conditions) We have other problems to address first. I will probably have changed the power plant long before that. Either electric or Diesel. My friend, Fred Hayes wants me to install one of his 34 hp Diesel KLR engines which would come with a tranny. Fred is already in the 80 mpg range with no streamlining!

Secondly, I wonder if your shell simply isn't smooth enough. Conventional car design sometimes shows how little shape matters , most of the aerodynamic improvements come from detail design; Better shut lines, flush fitting glass, smaller radiator openings. Have you done any wool tuft tests to see what kind of airflow you're getting?

This is what I call a "Quick and dirty" design to to learn what the problems actually are with a big, streamlined, sit up single-track vehicle. This is the smallest shape I can fit into and be comfortable. All those unresolved holes in the streamlining are hurting for sure. But first, I must figure out how big and where they need to be before dealing with covering them over.

The whole point of my efforts to date are to find out if it will be safe in real riding and traffic conditions. How will I get my feet out? How will I keep the air smooth around the things that must stick out? Like the wheels, rear view mirrors, the turning handlebars, my head... How will I get on and off and keep the surface smooth? I will figure all these out in this Quick and dirty version.

For me, design means riding. Riding in all the kinds of conditions we normally encounter. I can do this with rough and incomplete streamlining. Now is the time to catch problems so I can deal with them, not after it is all smooth and pretty.

The truth is, this is the shape we are stuck with and the wind likes to have its way with it. The truth is now is the time to resolve these issues, not later. The truth is that weight in the nose tames sidewinds.

This is all pretty exciting to know, isn't it?

How would we know this unless I ride and experiment?

I deal with these problems philosophically. I want to get the big parts right before attending to the little parts. I am sure that I can make it smooth. I am not sure about the things I have mentioned above. These problems have never been addressed and solved in a manner that is not "More trouble than it is worth."

In a garage of vehicles, I want this one to be the first choice.

I love working in unknown territory. We must question popular beliefs, be fearless in accepting the truth and addressing those truths.

I hope you are not discouraged. I certainly am not. I cannot wait to get up and work on this thing! But first, I am going to BUB Speed trials at Bonneville to talk of these things with people more experienced than me.

Stay tuned.

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This page updated Sep 2, 2008