I’ve lived in or near 3 different cities (DC, Philly, and Trenton) and all of their local metro trains have had flat fronts. Wouldn’t it make more sense for them to be shaped more like cars or Amtrak trains when it comes to aerodynamics? I don’t understand how the flat front design could be efficient.
In: Engineering
There are 2 main kinds of air resistance or drag at low speeds: form drag and skin drag. Form drag refers to drag resulting from a objects geometry on the front/leading or end/trailing edges while skin drag is caused by friction with the air along the objects length as air moves over its surfaces.
It turns out that for aspect ratios greater than 100:1 (an object 100 times longer than it is wide) that the skin drag will always be more significant that the form drag, so no matter what the front or end of the train looks like, the shape along the sides matters more. Thus if you are going to sink time and effort into reducing one, skin drag is the best bang for your buck and the flat front really isn’t that bad. This doesn’t mean a pointed end isn’t helpful though, especially as the average speed of the train increases.
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