Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - Project Slipster: Streamlining the Kawasaki Ninja 250 (WIP Thread)

theycallmeebryan · 12-17-2009, 06:27 PM

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?

12-17-2009, 06:27 PM	#28 (permalink)
theycallmeebryan Master EcoModder Join Date: May 2009 Location: New Jersey Posts: 389 2003 Ninja EX250 - '03 Kawasaki Ninja EX250 90 day: 78.57 mpg (US) Saturn - '99 Saturn SL1 Base 90 day: 47.27 mpg (US) Thanks: 25 Thanked 58 Times in 37 Posts	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? __________________ Doing my part to reduce dependence on OIL Doing my part to reduce congestion And enjoying it! If you have to use your brakes, you are driving too fast! My 101.5 MPG 2003 Kawasaki Ninja 250 Crude Oil Price Today