Project Slipster: Streamlining the Kawasaki Ninja 250 (WIP Thread)

[3-Wheeler]

Originally Posted by theycallmeebryan

.... Shes now sitting next to me giving me the eye....

Brian,

My wife gives me the same look. LOL

And I respond, "It's just the engineer's curse"!!

Jim.

[Christ]

From the streamlined bike page:

The front wheel fairing has to go to. I was quite confident that it would work and not affect the steering to much.

It turned out to be very scary to ride even with as little as 3 beaufort (about 10mph) side wind I did not dare to go over 35mph. It is a pity I made a mould and all without ever testing with a cardboard model.

Now I am forced to change the design drastically

I guess that's a warning for ya!

Coincidentally, Googling "Slipster" places this page in the search results at #5.

[thatguitarguy]

Originally Posted by Christ

I saw a phone book earlier today with a computer mouse on the back... it had a guy sitting in it with a aero windshield and it actually looked quite streamlined. It was odd. Maybe someone should build one?

One ball bearing on the ground - less RR!

[3-Wheeler]

Originally Posted by Christ

...I guess that's a warning for ya!...

You know your on to something here...

About 10 years ago, I had the crazy (cool) idea of covering the entire front wheel on the Honda VF500 with a small foam/fiberglass fairing. Similar to a Suzuki Hayabusa, but with *full* coverage. Just a portion of the tire sticking out next to the ground.

And after spending a large portion of the winter working on it in the basement, I was delighted to find out it worked great.... As long as I was not behind a semi trucks draft....

It turns out the air turbulence coming off the back side of the semi trailer creates a buffeting air movement at about 4 Hz.

....It also pretty much meant that I had about zilch for handlebar control of the front wheel while in that draft....

Needless to say, the beautiful and delightful front wheel fairing disappeared from the motorcycle, never to return.

Jim.

[theycallmeebryan]

I plan to extend the front fairing over top and around the front wheel, not have it actually attached to the forks.....much like you see in the aero recumbent on the previous page.

The problem seems to be that turbulence is causing instability in the steering when a fairing is attached to the forks. Air hits this rotating object and simply wants to move it.

[Christ]

Well, I was mostly referring to CAD design before really using materials, but the front wheel thing is a lesson well learned as well. I ate dirt road for nearly 500 feet on a pedal bike because I lost front stability.. I don't think I'd ever do anything that intentionally caused the effect.

[thatguitarguy]

I think you are going to have "weathervaning" problems any time you increase the lateral surface area of anything on the front fork, whether it be a wheel fairing, or even a headlight or headlight fairing. These should all be mounted to the frame - not the fork. The balance and control of the bike are dependent on your relationship with the front wheel through the fork and bars. It's strictly 1:1, with no mechanical advantage or separation like in a car. And when you try to shorten the bars for better aerodynamics, any problem is going to be more pronounced.


This may look cool, but I think that any turbulence is going to be amplified by all that extra surface area on the front wheel.


Here the front wheel is protected from those turbulent forces. The frontal area may be larger, but control of the bike is paramount.

The great thing about designing bikes is that it costs a lot less money than designing cars, and you have fewer rules and regulations that you have to deal with in getting it on the road.

You may be able to shortcut the laws of man - but you still have to abide by the laws of physics. And what you don't pay for with money, you may end up paying for with your body if you don't get it right the first time.

[theycallmeebryan]

Just trying to make a plan of attack for this project. Tomorrow i think i'll pick up the framing supplies and try to find some cardboard for some CAD testing. I figure i can start by making the frame adjustable (ex: Be able to elongate the tail if i need to), overlaying cardboard, and tuft testing to find a good shape.

Let me see if i have this right:

From what i understand, the objective for stability is to keep the center of pressure behind the center of gravity, if possible (this is Rocket Science!). The Center of Pressure wants to follow the Center of Gravity through the air. The entire mass will want to rotate around the center of gravity, so having that more forward would be beneficial for stability. Also, it seems that the more you can separate the distance between the CP and CG the better because variances in turbulence across the fairing would try to turn a shorter distance faster (harsher).

So if i have this correctly, i want to choose a fairing shape that will keep the CP as far back as possible while maintaining an aerodynamic shape.

Today I did some measurements on my bike. The fairing at the widest point will be 32-34" wide at the handlebars in order to give me about 2-3 inches of room on the sides of the bars. From the handlebars back will be the tail section. With this in mind, i tried to find a good shape in DesignFoil. I figured that the chord width will be a 30% profile,which would make the fairing about 9 1/4 feet long (A total extension of about 3 feet).

In DesignFoil, i tried to find a shape that in itself (in a 2d world), had a Cd under .01 with a chord of 9.5 feet and a width of 30%, all while having a CP as rearward as possible. It seems like the NACA 0030-93 looks like the best bet. It indicates a CP of about 88% the chord length.



So i took this shape and overlayed it on a top view of the Ninja and this is what it looks like.



What do you guys think of this?

Also... I was thinking about the Side view of the bike, and it came to me that MOST of the air ill be pushing through will travel to the sides of the fairing and not overtop. Would it be safe to say that the shape of the side view doesnt matter TOO much? I know a 10-15* taper from the back of my helmet to the edge of the tail would be beneficial.

Would it be better to have the bottom half of the fairing the same exact shape? Here's what i mean visually.



So in other words, that whole black area (in side view) would be the NACA 0030-93 shape (in top view).

What do you guys think?

[COcyclist]

I thought De Ligmotor should have kept the full fairing for rain and foot protection inside the fairing. He says he kept some of it to keep his feet out of the wheel but he's going to get some wet legs if he rides that in the rain. I can tell you that there is a lot of water that sprays out sideways after it impacts the fender. If the fully faired wheel is inside the outer fairing it shouldn't affect handling adversely even in crosswinds. The wind can't get to it, right? Inspiring work though, great link

[thatguitarguy]

Originally Posted by COcyclist

I thought De Ligmotor should have kept the full fairing for rain and foot protection inside the fairing. He says he kept some of it to keep his feet out of the wheel but he's going to get some wet legs if he rides that in the rain. I can tell you that there is a lot of water that sprays out sideways after it impacts the fender. If the fully faired wheel is inside the outer fairing it shouldn't affect handling adversely even in crosswinds. The wind can't get to it, right? Inspiring work though, great link

He's clearly a smart guy. It won't take him long to figure out that he'll want that front wheel enclosed inside the fairing. It'll be interesting to see how he encloses the suspended front wheel. That'll help to quiet it down a bit. I'd think that eventually he'd want to isolate the noise of the engine also, but he'll still need airflow to cool it. His helmeted head is above the fairing, but still the noise inside that thing must sound amplified.

It is a great link, and I hope he keeps it updated for us vicarious inventors.