Cee Bailey's® Windshield ( ST1300 )

[KoTAOW]

Contributed by Scott Fairchild, STOC #4728.
Original article can be found here: http://www.thefairchilds.org/bikes/

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Cee Bailey's® Windshield ( ST1300 )

The windshield of the ST1300 is very nice, and this is coming from a guy who normally doesn't like windshields. It's electrically adjustable on the fly and can be a great way to create a pocket of smooth air to increase comfort for the rider and passenger on long trips. Plus, it can really do the job of deflecting bugs and other hazards from reaching your face.

That said, there is a shortcoming. One general complaint with the shield is that when it's at its highest setting, the vortex vacuum that is created from the resulting "dead air" pocket can tend to curl the air flowing over the shield and blow it back on the rider and passenger from the back. This resulting "back pressure" tends to be uncomfortable in that it keeps shoving you forward into the handlebars.

I chose to upgrade my shield to the Cee Bailey's® windshield shield for the ST1300. They offer aircraft-quality acrylic shields that start out at stock height and width, which is equal to the windshield that comes with the bike. You can then choose to modify the dimensions by adding (or removing) inches. I chose to go with the +2" higher and +4" wider model. The bigger shield reduces your mileage a bit, but it also creates a bigger (huge) comfort pocket when it's at full mast. Another thing to note is that the shield is a full 1/4" thick, which I believe is the thickest shield you can commercially get. Installation is straightforward and easy and takes about 10 minutes with a #2 phillips screwdriver and an 8mm nut driver.

There is a level of visual distortion when using this shield. If you've used the stock windshield at full height, you already know what I'm talking about. On the Cee Baily it's a bit more pronounced at the corners. After all, this is a thicker shield. I will admit it was a bit disorienting at first, but frankly I don't even notice it anymore. Other than that, from a visibility standpoint, this is one of the clearest pieces of acrylic Plexiglass® I have ever seen.

I also chose to add the NACA aerospace vent option they offer. This vent allows air to flow into the pocket just enough to offset the back-pressure. Frankly, I couldn't imagine getting this shield without the vent, as the resulting laminar flow would create some massive back pressure. Be aware, at mid-height (my favorite setting, just below eye level) the vent will begin to whistle at around 85mph. If you hit 100 or more it'll be a windy scream...er so I'm told. Anyway, you shoudn't be going that fast anyway, so it shouldn't matter.

The shield even came with a small bottle of their Plexiglass® cleaner and some wipes, which I thought was nice. It seems to work pretty well too, I might buy more in the future.

Shield up...



Shield down...



What to do with the older windshield? You could be like me and just keep it around as a spare, or you could sell it on ebay.

Fluid Dynamics 101
I'm a mechanical engineer, so it's fun to actually use my degree for things. This is one of them. The question you're probably asking at this point is why. Why is there back-pressure from using the stock windshield? It really all comes down to friction.

When the air flows over the shield (and I'm just concentrating on the shield here) it comes in at a relatively straight line. When it hits the shield, it begins to flow over the top. While it's flowing along the shield, the entire cross-section of the air stream is not traveling at the same speed. As you get closer to the shield surface, the air begins to to slow down. This is due to friction of the shield on the air, culminating in a thickness of air on the shield that is known as the boundary layer. Usually very thin - microscopically thin at highway speeds, the boundary layer is a region where there is no air flow, because the friction of the shield is holding onto the air molecules. As you get further from the shield, the air speeds up until it reaches the speed of the bike traveling through still air.



Now, seeing as friction is the cause, what's the effect? Due to the difference in speed, the slower moving air nearer the surface of the shield is at a lower pressure than the air that is moving faster. This is not really a big deal until the air flow moves off the edge of the windshield. At that point, the high pressure side (top) pushes down on the low pressure side (bottom) causing the flow to curl over downward into a vortex. This effectively rotates the air flow partially onto your back, shoving you forward. This is the back-pressure you feel, and its strength is directly proportional with your bike's speed. You usually only feel this when the shield is fully up, forcing the vortex to form above your helmet. When the shield is lower, you also have direct flow of the air onto your body and helmet. This counteracts the back flow vortex, giving you relatively even pressure across your entire torso.

Cause, effect, now solution. It's all about the vent. The function of the vent is to provide a layer of air flow through and up the back side of the windshield. This acts to prevent the formation of the vortex because the flow on the underside of the shield will curl upwards, counteracting the downward curl of the air over the top of the shield. The stream then flows over your body smoothly.

The below diagram helps illustrate the effect of the air stream as it flows onto the bike in different configurations.



Frankly, I feel Honda was shortsighted to not include a vent (they do on the GoldWing), especially after hearing the complaints from the 2003 model owners. They made an awesome bike, no doubt, but it's got some shortcomings, this being one of them.

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Thank You again for your contribution Scott Fairchild, STOC #4728