Quote:
Originally Posted by ThomCat316
I'm in the "thinking about it" stage of designing and building an aerodynamically slippery ultralight fifth-wheel travel trailer. One thing I'm not finding in the wild is information about turbulent drag over side-to-roof corners.
The simplest build for the center section of the trailer would be a rectangular box, or I could (almost as easily) put a radiused (anywhere from "sharp" to 6") edge on it. Any references, information or educated opinions about which way I should go?
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Radius degree is found on any Airstream, Avion, Silver Streak or Streamline travel trailer circa 1970-1990 for ease of comparison. Every edge meeting every other edge. 12-22 degrees.
And why a fiver? Turns the tow vehicle into a one trick pony. The money is in the TV drivetrain. Turbo diesel is king. Fit the trailer to that. VW Jetta pulling an 20' A/S trailer today is solidly in the twenties as to mpg. Solo, the sky is the limit for mpg. And a fiver is compromised by a higher COG. As is the truck to pull it.
KamperBob has a small aero fiver he pulls with a small truck. His mpg is the same as my 63' long combined rig of one ton truck and 35' travel trailer. The difference is the drivetrain.
And how many miles annually is the rig supposed to travel? This is what kills putative savings as a travel trailer is mainly stationary. And economy depends MOST on not having to move it or the TV in order to re-supply.
My usual wet blanket set of questions. Thus, apologies. When I look at my fuel cost of operation, solo is presently at 11-cpm solo, and around 17-cpm towing. ($2.70/gl diesel). If this question is not answered (asked rhetorically) then the rest is only an exercise unbalanced in its approach.
So the percentage deduction between solo and towing mpg is key. 30-40% is the general range. What savings are possible for a sub-30 deduction, and was it done where the towed vehicle was compromised?
An Oliver or Casita trailer behind nearly any small TD car is already a winner. And weight is not relevant except for acceleration/deceleration events. Which are minimized by trip planning. In other words, best trip planning is worth more than hundreds if not a few thousand pounds of trailer weight (given a decent aero shape as is already present in production trailers past and present).
The real question to answer is capacities. Water, fuel and food (in that order).
As to shapes, look to the Avion and Silver Streak 5'ers of the mid/late 1980s. Pics on this site as well as on web. Those were reported to be as good in FE as the conventional trailers, but with the 5'er advantage of shorter OAL and with onboard generator. Greater battery capacity as well.
A good basic shape to handle wind loads, and which has comparably good capacities, is the winner. FE is a second order consideration.
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