One man's DIY wind protection
I wanted to have the benefits of a taller windscreen- less buffeting, protection from the weather, etc... but I wanted to address what I found to be the primary functional (aesthetics aside) drawback of the taller screen - wind roar. I wanted to significantly reduce the wind roar; given a tall enough windscreen, this is doable. I upped the level of challenge by adding one additional element. I did not want to have to look through the windscreen, but would rather be able to look over it, for better visibility at night, in the rain, or when the windscreen wasn't so clean.
I have been able to achieve most of my objectives. Wind roar is reduced dramatically at highway speeds (not easy to quantify, but I would guess by >90%). I am 6'3" and have the top set to a height where I can sit up straight and look over it (still benefiting from major noise reduction), or I can hunch down just a tad and look thru the lip at highway speeds and reduce noise even more.
I used an 18"x24" sheet of .093 Lexan from Home Depot (about $14). The screen is 24" tall, plus a couple of extra inches with the Laminar Lip. That is very tall for a Ninjette. The problem is that a tall and flat screen really wants to bend back at speed, so I added bracing to add strength and to also introduce a cylindrical curve, thus adding much more resistance to bending back.
One of my goals (especially with the Laminar Lip) was to raise the airflow as high as possible. I have read that negative pressure behind the windscreen can pull the airstream back down. I wanted to let some air in behind the screen, so I cut a duct. I could have simply cut a round hole, but for non-scientific reasons I went with a NACA style duct. My instincts suggested that my goal should be to create an updraft on the backside of the screen. For that reason, I put another piece of Lexan behind the duct to deflect the draft upwards. You can see it a little in these two pictures.
I was not sure if I was adding unnecessary complexity with the ducting, so I tried covering the hole with (what else?) duct tape. Without the ducting in play wind roar did increase, so I feel the ducting does make a positive contribution in raising the airstream.
This shows a couple of things: the windscreen has a bit of a cylindrical curve, and I have a cross brace just above the midpoint that 'pulls' the two sides together to give more curve. The top does flatten back out a bit. The Lip is more curved. I took some steps to curve the top to match the Lip, but went back, as this way seems to work better.
Going this tall presents way more surface area. The screen wants to bend back, and will also place great stress on the mounting points in the fairing. I added substantial bracing. I used simple flat stock painted black. I also tied the bracing to the fairing with some diagonal pieces. It does help make the whole structure significantly less fluttery and flexy at higher (80 - 90 mph indicated) cruising speeds.
I normally am not that concerned with appearance, but I did find the bracing to be somewhat unsightly. To hide it a bit, I tinted the bottom portion of the screen. I was never crazy about paint that had a hard cutoff line, so I tried for a bit more of a tapered gradient effect. I used VHT Nightshades tint, used mostly for tinting plastic taillight covers on cars. The bottom is dark, but I wanted to taper off to make the top quarter or so clear where I might want to look thru it at very low speeds. On the road, I rarely even look through the main body, instead just looking through the Laminar Lip, which has good optical qualities, with little distortion.
I am going to continue my experiments, but for the moment I am fairly pleased.
About the wind
It seems like there are two aspects to wind: the main wind stream, and then the little random licks and eddies of wind. Also related to the size and shape of the 'still pocket' of air are road speed and external wind, both natural and unnatural (such as from 18 wheelers).
Looking over the lip at moderate speeds (such as 70 mph) with little ambient wind, I get no significant buffeting to the torso or the helmet. The main airstream does start to touch the outer portion of my shoulders and the top of the helmet. Depending on your size, it is not terribly difficult to get the wind off your torso. Again, my main goal is wind roar abatement, so getting the main windstream off the bottom of the helmet and away from the face shield are the next goal after protecting the torso. The last and most difficult factor to address is the little licks and eddies of air. While still mostly predictable, they are somewhat more random than the main airstream. I would have to get the wind stream much further away from the torso and helmet to completely eliminate the little eddies, so unless I want an even more huge screen (twice the square footage or more), I will settle for getting rid of the majority of the little odd bits of wind that might find me.
When I go faster, the 'quiet envelope' shrinks, but I can hunch down maybe 3 or 4 inches and look through the lip, still having a fairly quiet ride. Of course, all this is built around my size, standard bars, and the seat the bike came with (lowered for a woman rider with some padding removed). I have recently swapped to a more standard seat, so I am sitting a little higher, but the current setup still works ok, even if I am moved a little further from the sweet spot.
Again, if noise reduction is your goal, using engine noise (stock pipes and airbox) is a good measure of comparison. Before, I could not hear the engine at all at 70 mph, unless I downshifted or was really heavy on the throttle. The wind completely drowned the motor out. Now I would put the wind noise roughly equal to the (stock) motor.