Few Questions About Aerodynamics of DIY Travel Trailer

[slowmover]

Whats there to know about DEXTER? Most dealers I’ve dealt with are good. Now that both HENSCHEN and AL-KO are out of business, the less desirable DEXTER is the only torsion axle left.

There are other suspension designs, but I would stick with tried & true until weight justified the use of MORryde independent suspension.

[slowmover]

Travel trailers are about two things:

1). X-number of people aboard without re-supply for Y-nights. (Include -3-season bad weather for habitability issues: one is sick or injured).

2). FE is nice, but pales in comparison to cross-wind handling. Low COG (and floor low to ground) are central to that. All surfaces covered, and ALL edges radiused. Independent suspension with anti-lock disc brakes. (An auto wreck is like being gunshot: life-changing or -ending. TAKES BUT ONE INCIDENT. Talk about skill at the wheel is laughable).

— From this PRIMARY design factor comes a shape where interior space utilization is the FAIL of 99.5% of DIY. The balance of things is the difficulty.

Rounded exterior walls AREN'T a requirement. Aero Nose & Tail look great, but fail the interior test of “Useful”. (Not enough gain in fuel burn reduction to justify far more difficult construction. And of no real use, again, in what’s most important: Cross-wind handling

Airstream had it put together with the addition of IS by 1963. Past ABS, nothing before or since is an improvement, per se.



The Shell is the value. Double-shell on Silver Streak, Streamline $ Avion are what set them farther upmarket.

Fuel burn per mile just isn’t the holy grail. How long one can remain in place without using tow vehicle for re-Supply is where the action is. The trade-offs of changing trailer capacities from factory limits. (Really, just food storage).

This is elimination of cold start, in dramatic detail. That is the long term fuel savings

The average RV’er vacations about 5k miles annually. Against an average of 15K regular miles. What percentage gain in FE justifies expenditure?

If one has one of the above and a FAMILY vehicle set to tow, the gains are vanishingly low.

At the drivetrain end, it’s the usual: combining all errands and practiced trip routing. After which, gains are, again, vanishingly low.

The REAL economy is in the trailers indefinite lifespan, AND the family vehicle in use from brand-new out to 12-yrs or more and/or 250k miles.

What causes confusion (emotional upset) is in using a months worth of fuel in a week while on vacation.

Get that problem out of the way by the use of FUELLY or a more detailed paper journal recording fuel burn PARTICULARS. Which is Average MPH against AVERAGE MPG.

Once one understands that relationship — while in typical solo duty against typical vacation towing duty — the rest clears up.

FWIW, expect FE while Towing to show a MPG decrease of 40% as baseline. Fix problems with rig until this is standard at 60-mph versus solo at 60-mph.

A well-sorted rig with an AS type TT can trend down to 30%.

The hard number doesn’t mean much. But two person combined-vehicle rigs seeing above twenty are not hard to assemble. (Even though it’s the wrong target)

[slowmover]

If it wasn’t clear, I’m not interested in dissuading a DIY build. Some guys need to.

A homebuilt canoe, for example, can be a work of art.

But a TT could also be a lifetime of after-hours effort when a re-habbed TT can also be art.

What is the point to camping? This needs a list of What & Why.

[ennored]

If you search this site with my username, you'll find lots of stuff about aerodynamics and boxes. I post mostly about trailers and motorhomes. Might find some stuff you haven't read yet.

I will add something I have said before about basic aerodynamics. Starting with a square box, round the front edges until the aero doesn't improve anymore (4% of the width radius is commonly accepted as enough) then taper the tail (per the template) as much as your requirements can tolerate. Done.

[freebeard]

Starting with a square box, round the front edges until the aero doesn't improve anymore (4% of the width radius is commonly accepted as enough) then taper the tail (per the template) as much as your requirements can tolerate. Done.

Plasma actuators