If taller is better, then too tall is just right, right? Not necessarily. There is a lot of VooDoo surrounding windshield design and modification, but the air is not going to follow the arrows on the designers pad. Instead, it is going to stubbornly follow the laws of fluid dynamics. Well, the guys at CalSci have done the math, and unless you want to derive and solve your own simultaneous differential equations, you might read here for the Readers' Digest version, especially if you are incined to think that you are going to install a small edge deflector and "throw the air over your head"...
Motorcycle Fairings and Windshields
I disagree with a little of what they have said, but they have done the math and I have not, so I am probably wrong. I do agree with them that artistic little "flips" at the end of the windshield do more harm than good. All they accomplish is increased turbulence. My new Givi windscreen, in addition to being too tall, had this little artistic flourish as well. By cutting it off, I will eliminate its spoiling effect as well as the excessive height. A "spoiler" operates by increasing the amount of turbulence flowing over a shape, thus "spoiling" the laminar flow and providing a cushion for the laminar boundary layer. While this will serve to reduce drag on a race car, what it will mostly do at the top of a motorcycle windshield is create noise. It will widen the area of turbulence of the windshield. What I want to do is narrow the area of turbulence and place it at a position below my helmet base.
Why not over my head? The sad fact, is that in order to place the airstream completely over your head, you just about have to be looking through the shield, which I do not like. Lots of Gold Wingers do it. My father was one. I could not stand to ride his motorcycle, especially in the rain. He got volume discounts at the Rain-X store but what he really needed was a windshield wiper. Those in search of quiet air that don't want to look through the windscreen often try to size the shield to be nearly in the line of sight. CalSci gives a good method for determining this "best" height for your windscreen by using 30 ft. and 60 ft. sightline targets. Dodging the bullet in this manner (especially with the 60 ft. target) has you forever dealing with the line at the top of the windscreen. Slump a bit and it is in your field of vision. My own personal preference is to have the top edge well below my line of sight. In order to beat the noise devil, the turbulent region needs to be reduced in width and placed about mid-chest on the rider. CalSci's scientific method of determining this height is to measure to a 12-15 ft. distant target.
So, if you believe all that, I now need to cut about 2 inches off of the brand-new Givi windscreen that I just shelled out good money for. Here is one method. The CalSci literature gives another. They and I disagree on the fineness of the saw blade to use and they make use of a MAP fueled torch to create a glass-like edge whereas I use the craftsman's approach of filing and sanding. Well, actually, they do both. I have not used the MAP torch, but I find the concept interesting. Give it a try and let me know if you destroy your windscreen! I'd love to know. I am satisfied with the matte edge effect I get with fine wet-sanding. I also take some different measures because my method is for working alone with the shield on the motorcycle. Here goes...
Motorcycle Fairings and Windshields
I disagree with a little of what they have said, but they have done the math and I have not, so I am probably wrong. I do agree with them that artistic little "flips" at the end of the windshield do more harm than good. All they accomplish is increased turbulence. My new Givi windscreen, in addition to being too tall, had this little artistic flourish as well. By cutting it off, I will eliminate its spoiling effect as well as the excessive height. A "spoiler" operates by increasing the amount of turbulence flowing over a shape, thus "spoiling" the laminar flow and providing a cushion for the laminar boundary layer. While this will serve to reduce drag on a race car, what it will mostly do at the top of a motorcycle windshield is create noise. It will widen the area of turbulence of the windshield. What I want to do is narrow the area of turbulence and place it at a position below my helmet base.
Why not over my head? The sad fact, is that in order to place the airstream completely over your head, you just about have to be looking through the shield, which I do not like. Lots of Gold Wingers do it. My father was one. I could not stand to ride his motorcycle, especially in the rain. He got volume discounts at the Rain-X store but what he really needed was a windshield wiper. Those in search of quiet air that don't want to look through the windscreen often try to size the shield to be nearly in the line of sight. CalSci gives a good method for determining this "best" height for your windscreen by using 30 ft. and 60 ft. sightline targets. Dodging the bullet in this manner (especially with the 60 ft. target) has you forever dealing with the line at the top of the windscreen. Slump a bit and it is in your field of vision. My own personal preference is to have the top edge well below my line of sight. In order to beat the noise devil, the turbulent region needs to be reduced in width and placed about mid-chest on the rider. CalSci's scientific method of determining this height is to measure to a 12-15 ft. distant target.
So, if you believe all that, I now need to cut about 2 inches off of the brand-new Givi windscreen that I just shelled out good money for. Here is one method. The CalSci literature gives another. They and I disagree on the fineness of the saw blade to use and they make use of a MAP fueled torch to create a glass-like edge whereas I use the craftsman's approach of filing and sanding. Well, actually, they do both. I have not used the MAP torch, but I find the concept interesting. Give it a try and let me know if you destroy your windscreen! I'd love to know. I am satisfied with the matte edge effect I get with fine wet-sanding. I also take some different measures because my method is for working alone with the shield on the motorcycle. Here goes...
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