This informative document was shared with me on the Airstream Forums in response to some questions about the Model X -- travel trailer linkage distance. It includes much more information that is applicable to our topic, and I found it fascinating.
Regarding the linkage question, the yaw angle (angle of air travel across the roadway) changes the coefficient of drag significantly. This situation is exacerbated by hard edges on the trailer and by the tow vehicle-trailer gap. See the following diagram (apologies about the resolution) for the effects at yaw angles up to 20° (
source: Hammache, Michaelian, Browand). This provides support for radius edges like on the Airstream and also minimization of the gap between the tow vehicle and travel trailer.
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