Quote:
Originally Posted by tomi_k
Aerohead, thanks ! I think you are referring into Figure 14, on page 10 in the SAE 810185 (Fig, 14 - Influence of rear end slope inclination angle on drag coefficient).
My vehicle (pickup truck) has L0 / L -ratio of 0.3441 (without a tail extension) and L0 / L of 0.4087 (with the tail extension) as of today. For L0, I use trucks bed length (without and with the tail extension).
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I've done a linear interpolation between the 27% aft-body and 36% aft-body, tested and reported in Figure 4.59.
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So you interpolated that range, tested it and results fall into the interpolated line, correct?
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Sorry, I should have been more specific.
It was Buchheim and his associates which did the testing, with their results tabulated in the graphic.
As a first ( and only ) approximation, as if the drag varied monotonically, I just did the simple interpolation, positioning the 18-degrees between the upper and lower known values, as a percentage of the spread between the two values. A 'ballpark' figure.
And these values are for a very crude model, with no roof curvature. Where the downslope angle begins, that's the beginning of the aft-body, in elevation view. FIAT's model had 25-degrees tumblehome as a 'Standard.' Buchheim made no mention of any other conditions.
If your pickup has roof camber, looking from the side, then wherever the roof 'peak' is situated, this location constitutes the 'beginning' of it's aft-body.
If your were going to build a bedcover with a curved top, you'd want to take off from where the trucks cab leaves off, then extend out from there, respecting the cab's roof peak.
You'd need an absolutely flat surface to park on, and you'd want around 300-pounds ( 136-kg ) in the front seats to 'settle' the suspension.
We need to know how much aft-body length you already have for the cab, then add either of your two lengths to that.
And the height from the ground to the roof peak ( with the ballast ). We could design from that if we had to.