[drkarrow]

I was looking at boat tails and such and thinking about optimum trailing angles. Most of the designs I have seen typically have no consideration for cross winds. I was wondering how much cross wind is typical and what the effects are. I've been a long time lurker here and I've never seen this covered.

I pulled the last year of wind speed data from weather underground for my area. I get 6.5mph average daily average wind speed, stdev of 3.4mph. So I take that and randomize the direction and calculate the angle of attack of my car (Lets just call it yaw angle like a plane) going 70mph. Absolute the results so that my values are a deviation from 0. It makes a neat distribution, and it shows an average yaw angle at 3.4deg, with the worst condition being a wind at around 85deg from the direction of travel resulting in at 5.3deg yaw.

So on an average day my car driving down the freeway sees a 3.4deg yaw angle on the wind. I'm thinking perhaps boat tails and general side of vehicle angles should be 3.4deg less than optimal taper to compensate?

But that's only average, so half of the days of the year should be better, half worse.

+1stdev on the average wind speed which should be around 60 days a year will be at or worse than 5.3deg yaw average, 8.3deg max yaw. +2stdev on average wind should be around 8 days a year at or worse than 7.1deg yaw average, 11.2deg max yaw.

Now I realize 70mph is probably far above my average speed, and the yaw numbers are larger for a vehicle going slower. So In the end to get myself to a comfortable level, I'm thinking a side taper for a boat tail should be ~5deg less than theoretical optimal on each side to deal with typical cross winds. For anyone who made it through this rambling, does that sound right? Part of me is starting to think that it may be best just to keep the sides parallel like a typical sports racer body.