Quote:
Originally Posted by ChazInMT
Here's what I'd do to the design. Everyone gets all geeked up over 20° rear angle, but I think that is too aggressive. Based on a paper I read by a Cal State Masters Thesis candidate exploring pickup truck aerodynamics, you get 97% of your aero gain by going only 10°, but you maximize lift reduction. The usable space is way better with the design I illustrate here too. So in a sense, you get the best of everything, huge drag reduction, big lift reduction, and a usable design. Win Win Winny Win.
Reason you don't want to get too aggressive on the top taper, is that you start to create a large area of low pressure that wants to get filled in from the sides, this sets you up for a vortex generation situation which produces a lot of drag.
The paper I reference is here. Paper The table on pg. 85 sums it up.
Why this paper isn't the gold standard for truck aerodynamics is beyond me. The author Feysal Adem clearly put a huge amount of VERY knowledgeable effort into its creation, yet somehow everyone bases their opinions on what looks right to them instead of the real science Feysal did.
I can only take credit for putting 2 & 2 together here on this concept. All due credit rests with Feysal.
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This looks good as to use-ability. The central assumption about a trailer is that it has work to do. And is not likely to be constantly underway, so "mpg improvements" can actually work against one.
Trailer suspension is critical. Not ever as sophisticated as the tow vehicle (as passengers are not allowed), and market economics place
terrible suspensions aboard as a result. The exception is in fully independent suspensions such as DEXTER "Tor-Flex". And the wheel center (face) using that type should be no further inboard than the outer trailer wall. For leaf sprung, the leaf spring itself should be at trailer wall. These are not to be compromised. Note U-Haul trailers in this regard as they are very good.
I would not ever use 15" or smaller wheels/tires with ST ratings, but would automatically upsize to 16" and LT-spec tires. Disc brakes (and anti-lock) are also a no-brainer (cost impediment usually cited).
A page taken from 1940's travel trailer design (Wally Byam, et. al.) is that sidewall radius to roof
and undercarriage should be 12-22 degrees. The longer the trailer, the more the sidewall pressure of winds increases along the length. Side winds are what roll trailers. This radius was used by travel trailer makers where the cost was the same or higher than the average American house circa 1960, and by Airstream to this day.
Thanks,
ChazInMT
.