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Old 01-24-2013, 07:04 AM   #15
Miles of Smiles
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Joined: Jul 2009
Location: Tool Shed
Oddometer: 1,712
Originally Posted by mutt2jeff View Post
Agreed. I am usually a big function over form guy, but I cant stand tacked on stuff like that.
I know what you mean. But for me the ride quality improvement, and the fact that the clear Aeroguards kinda disappear from my view with the tank bag on, easily made function win over form.

Nonetheless, the function that they perform is still what has to happen to reduce the buffeting. The low pressure area that is created behind the screen in motion will want to draw air in to balance the pressures. This is what creates the oscillation felt as buffeting.

A bigger shield, with no design to either/both reduce the low pressure and restrict the airflow into that area may not make the difference you want.

Keep this aspect of the aerodynamics in mind while finalizing your design. The problem to solve is the dead air space behind the shield, rather than how the shield parts the wind.

If you can design a shield that has laminar flow on both the front and the back of the shield, that would be optimal in balancing the pressures and forcing the wind up over the rider's head. The front and back airstreams converging together at the top would prevent airflow from trying to roll into the low pressure zone above the dash.

One way to achieve this might be a two-layer design where the back layer has a 1" space between it and the front layer. Then the front layer would have a cutout the width of the shield and an inch or two tall just above the headlight to channel the air into the space between the front and back layers. Sort of a smaller version of what the Aeroflow windshield does.

Anyway, that's just an opinion based on studying windshield designs going back to a 1988 BMW K75S shield that was designed something like this. The only tweak I had to make to eliminate buffeting was to install vortex generators on the top back side of the windscreen to clean up the airflow just before it recombined with that from the front side. It was a eureka! moment for me and helped me better understand just what was going on and how to address it.

Those who have used the brute force method of trying to push more air out of the way haven't met with much success because they often create a greater low pressure zone, thus making the problem worse.

I know you have a lot of enthusiasm and will be putting much effort into the design. Hopefully this might help you visualize what needs to happen to clean up the airflow as it leave the top of the screen.

The Aeroguards change the flow pattern, so the wind doesn't have a direct path into the low pressure zone. Instead it has to come in from farther behind and this helps eliminate an upflow that amplifies the buffeting. It was easier for me to do this than to commit to a fabrication project.

Again, best wishes on the project.

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