The ferret_imp said:
Steve for the benefit of our knowledge, does your company do any wind tunnel or smoke testing and try and get the wind managed in any particular way? Or is it mostly a styling excercise which has some benefit?
In other words do you know how high above the windscreen the majority of the wind hits at a given speed? Would a 5'6" guy catch the wind in the face and a 6'2" guy catch it mid chest? Or is that even a design criteria?
Good questions Ferret, and deserving of a proper answer. So here goes…
Taking the second question first, my priority is function. There’s no point in adding to the bike unless some functional benefit is attained. After that come appearance and aesthetics. So both are important, but it’s in the opposite order to your question.
We don’t do wind tunnel testing, but we do test on the road and make adjustments accordingly. To achieve the quality I require, each screen design requires a large investment in injection moulding tooling, so a lot of thought and testing goes into it: once the tooling is produced, that’s it - we can’t make changes so it’s important to get it right.
The reason we don’t do wind tunnel testing is that (apart from the fact that it’s expensive) there’s not much point. Unless you’re designing a big tourer or a race bike, you simply don’t have enough control over the aerodynamics of the overall bike and rider And therein lies the Dart philosophy… we make small screens because I believe they provide the greatest benefit to most riders.
It’s my belief that you either want a flyscreen or a fully-faired bike. The middle ground - large handlebar-mounted screens - is where you get the most problems with buffeting and instability, for little reward.
The point of a flyscreen is not to provide a bubble of still air over the rider. It can’t possibly do this. The intention is twofold - to smooth out the airflow over the instrument area (which otherwise is susceptible to a lot of turbulence) and to provide a cone of relatively still air in front of the rider’s chest. In this way, the rider (who on a naked bike resembles a parachute) is relieved of a good proportion of wind blast, making riding less of a strain at speed. A well-designed flyscreen will not affect airflow at head height.
As for height differences, it’s not that critical. The main difference between a tall guy and a short one is in the limbs - there’s generally only a couple of inches or so in the torso.
Hope this is helpful, and apologies for the length of the essay!
Steve
