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Old 05-15-2009, 04:57 PM   #1 (permalink)
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Frontal Area vs Frontal Curve Smoothness

Just a general question about aerodynamics. Here, im referring to the general teardrop shape.

Is smaller frontal area more important than keeping the front curve smooth over the guts of the vehicle?

I am working on a new fairing design for my kawasaki ninja 250. I am wondering if it would be more beneficial to keep frontal area small, or should the fairing extend out past the handlebars? It seems as though a full exterior fairing is what most people aim for (looking at HPV designs).

Furthermore, is there some sort of equation or rule for figuring out the best front curve angle (length vs width)? Is it better to have a perfect semicircular front (from a top down view)

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Old 05-15-2009, 05:03 PM   #2 (permalink)
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Curvature... There is - and it's a ratio of curvature/width (or something like that).... Alas, I don't have it available at the moment but it's in Hucho's book on road vehicle aerodynamics. Having more curvature beyond this critical ratio has diminishing returns.

The question of more FA versus not covering handlebars is an exercise in optimization. You want to minimize FA, but protrusions (handlebars) are never a good thing...
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Old 05-15-2009, 09:07 PM   #3 (permalink)
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Quote:
Is smaller frontal area more important than keeping the front curve smooth over the guts of the vehicle?

I am working on a new fairing design for my kawasaki ninja 250. I am wondering if it would be more beneficial to keep frontal area small, or should the fairing extend out past the handlebars?
You are only going to be able to guess at which is better. If the extended fairing is aerodynamic enough, it can reduce drag even if it increases total frontal area, but without a windtunnel or CFG there is no way to tell for sure whether you've achieved this.

Remember, the frontal area of the fairing itself is not important; the amount of frontal area the fairing adds to the whole bike is what you have to consider. So if the fairing covers the handlebars (and where your arms are), but just barely so as not to add much FA, and the fairing is quite a bit more aerodynamic than the handlebars—which it should be if designed properly, it will likely reduce drag.
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Old 05-15-2009, 09:22 PM   #4 (permalink)
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I'm not sure what you are asking, but it is OK to have a fairly sharp transition between front and side, rather than one continuous frontal curve. As long as you are pushing into the air, it is inclined to behave.
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Old 05-15-2009, 10:41 PM   #5 (permalink)
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The big problems are at the rear anyway.
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Old 05-17-2009, 03:38 PM   #6 (permalink)
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Quote:
Originally Posted by Frank Lee View Post
The big problems are at the rear anyway.
That is kind of moot, unless he makes some kind of fiberglass monstrosity that conforms to the back of his body and forms a boattail.




The practical place to aeromod on a bike would be the front end. Think of it like a kamm back to suppress your "it would be better going backwards" reflex
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Old 05-17-2009, 04:28 PM   #7 (permalink)
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It's not moot at all.

He can make the slickest forward fairing ever and the aero will still suck.
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Old 05-17-2009, 04:36 PM   #8 (permalink)
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I understand that the tail is very important.... that is not the question i asked.... this topic is strictly based on front end design. My question was also pretty straight forward. If you notice, i said "Here, im referring to the general teardrop shape."
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Old 05-17-2009, 05:56 PM   #9 (permalink)
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Quote:
Originally Posted by Frank Lee View Post
It's not moot at all.

He can make the slickest forward fairing ever and the aero will still suck.
A bike with a faired front end is going to be better than one without. Just because you're preoccupied with the idea of rear end aerodynamics being the most important doesn't mean that the front doesn't matter. Like I said, think of it as a kamm back
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Old 05-17-2009, 06:41 PM   #10 (permalink)
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Quote:
Originally Posted by winkosmosis View Post
That is kind of moot, unless he makes some kind of fiberglass monstrosity that conforms to the back of his body and forms a boattail.
Tail Boxes Can be beautiful - and not monstrous or fiberglass... Big benefit just requires more work and thought





I do agree with lee... There's a reason aero textbooks spend more time on the back end. Here's a cool picture I took awhile back showing these awesome rings in the water tunnel.



But it doesn't change my original answer - it's an exercise in optimization

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