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

[thatguitarguy]

Originally Posted by 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.


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?

I think you're right about the air traveling much more around the sides than up and over the bike. It's different in a car, because the car is so wide.

I think that the NACA shapes are a good starting point, but don't be locked into it. Be ready and willing to change your shape as tuft testing with your CAD fairings as more guidance than NACA theory.

And the first thing I'd be wary of is the length after the rear wheel. You're not making a straightline Bonneville speed bike, and with that short wheelbase, you're looking at some handling problems. I'd chop it off not far past where your photo ends in a Kamm shape, or at the very least, have a sharper upsweep, and bring the tail into a cone shape, rather than a fin.

You see the longer boattails on cars because of the inherent stability of 4 wheels on the ground. Having a long tail on a bike is going to give you the same type of weathervaning problems as an independently faired front wheel, especially with that short wheelbase.

Take it slow, use a lot of cardboard, and be very ready to change your design if it doesn't feel stable.

Stay safe!!

[3-Wheeler]

Originally Posted by 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.

Brian,

Here is confirmation that you indeed, do not want to add a fairing to the front wheel by itself...

... The fairing around the front wheel needs to be supported by the frame...

Ask me how I know!!

Picasa Web Albums - jsmosher - Motorcycle-Fa...

Needless to say, the beautiful work on the front fairing did not last. The fairing however, is still going strong.

P.S. It took a while to find these old photos from 1988.

Jim.

[thatguitarguy]

You might also consider borrowing from modern bicycle technology:




Lightning F-40: World's Fastest Production Bicycle

[theycallmeebryan]

So i was doing some modeling in Blender to see what this beast would look like using a NACA 0030-93..... and MAN it looks so cool!!!!!! I still have to add a tail section, but everything in this picture is exactly to scale how it would be on the bike (of course, with smoother edges). I could have added a couple more vertices on the top of the canopy to make it smoother, but you get the idea.





And a rider view shot!


Heres a side view showing a picture of me on the bike behind the model. You can see where my head is oriented in relation to everything.

[theycallmeebryan]

Ok i finished the tail modeling.







I dont know about you guys, but i think this mock up looks absolutely BEAUTIFUL.

One thing to note: in that model, the dimensions are base on me sitting on my bike with the suspension compressed in an idle state. I dont think i would be able to have the underside of the fairing that low to the ground as it is in the model. Ill have to do some testing to see how low my bike can get with the suspension fully compressed.

Now i have to figure out if i can get this model into SolidWorks for some CFD testing

[Jethro]

It looks like a blimp that was stretched in Photoshop with 2 wheels below it.

I don't think a flat front end is 'ideal' shouldn't it be more rain droppish?

[thatguitarguy]

Looks like a pointy baby carriage in reverse.

Sorry.

It would be pretty hard to cover the bike inside with a teardrop shape, and blunt in front is good.

I'd still be concerned about the length of that tail, though.

[Christ]

Originally Posted by Jethro

It looks like a blimp that was stretched in Photoshop with 2 wheels below it.

I don't think a flat front end is 'ideal' shouldn't it be more rain droppish?

Refer to Mr. Vetter's "Rifle" body fairing.

The nose isn't quite blunt in that design, but the wind isn't really concerned about where it separates, so much as how it comes back together.

While a more rounded nose would be more "ideal", the design doesn't lend itself to use in this case, at least not as easily.

I'm sure there will be refining and tweaking as the design goes from digital to real.

[theycallmeebryan]

Chopped tail anyone?

Originally Posted by Jethro

It looks like a blimp that was stretched in Photoshop with 2 wheels below it.

I don't think a flat front end is 'ideal' shouldn't it be more rain droppish?

A blimp is aerodynamically designed for its purpose. Cool!

About the front end bluntness, i had mentioned this a few posts back. Most of the air will flow to the sides of the fairing since that is the most parsimonic path. Motorcycles are taller than they are wider (opposite of what you would find in most cars), so more concentration should be made on the sides of the fairing than the top. Having a blunt front end is not necessarily detrimental, and as Christ mentioned, its the ass that matters .

That having been said, these pictures are a first take at a possible plan for the fairing. I will try some other things to improve the aesthetics.

[thatguitarguy]

It looks safer. But just chopping it off so abruptly leaves a good sized void for the air to rush in and pull you back. I think if you tighten your taper before the rear axle a little bit you can bring all the surfaces much closer together, still within that framework, and keep enough air attached that you won't have nearly as big a void. It may seem like a compromise, but safety shouldn't be compromised. Good work and good luck!