Foamie aerodynamics.

[GPW]

You know, when considering aerodynamics for a trailer (a box essentially) , you can’t get away from the profile drag , the cross sectional area presented to the wind... So that’s sorta “fixed” . The nose entry is probably the Most important element in smoothing the flow of air over the “Profile”. Ideally a fat smoothly rounded shape , practically for us , more Whale -like than “bullet”.. Rounding of the edges is key to a smooth flow. Easy with foam , as you can always add foam “fillers” under the basic structure to allow much more aggressive Rounding of the nose edges...
There comes a point where Practically bumps heads with Aerodynamics .....fer’ instance.. a fully rounded “Roswell” may look Slippery to the wind, but may not have the Inner space configuration for our needs (the BEER) ... when you severely round “the box” you lose a lot of interior ... So naturally the tendency in such cases is to go BIGGER ... but then you have a larger PROFILE ... the law of diminishing returns... You just have to do what You thinks looks and WORKS correctly for your needs ...

 

[linuxmanxxx]

Most important is merging with and staying in the aero profile of the tow vehicle. You get outside of that vehicle created wind tunnel and rounding and shape won't help much with mileage results.

 

[GPW]

True Dat !!! Like race cars “drafting” ...

 

[GPW]

OK, here’s another idea for a really streamline TD, with wheel fairings and underbody flow smoothing ... and it’s got a galley too ...

 

[angib]

Here is a graphic I did a long time ago about the best shape trailer I could think of to achieve low drag behind a Honda CRV:

And here is a trailer that Honda themselves made to go behind an Insight. It is integral with the car and the bodywork is joined with flexible panels that allow it to steer. By adding the trailer (and also spats on the car's front wheels) they got the drag coefficient Cd down from 0.26 to 0.12 - that is a reduction to 54% less than the car alone.

Minimising the gap between the car and trailer is important, though less so if the gap between the two is realistic for practical considerations like turning and negotiating dips/crests.

 

[Wobbly Wheels]

Angib, that makes a lot of sense. Look at the fairings on tractor trailers to smoth the airflow over the gap. If it didn't have a very real effect on the drag (showing up as fuel economy), you wouldn't ser them on every long-haul rig. If I wind up towing mine as much as I'd like to, I'll definitely be putting a high top canopy on the truck for the same reason.

 

[loaderman]

Been reading on Hypermiling.
http://ecomodder.com/
Lots has to do with driving but also vehicle shape.

 

[angib]

Been reading on Hypermiling.
http://ecomodder.com/
Lots has to do with driving but also vehicle shape.

I find there is so much misunderstanding and plain wrong-ness there that it is too annoying to visit, even for the really interesting stuff that pops up occasionally.

For example, lots of folks there have ScanGuages and think that keeping the instantaneous mpg figure as high as possible all the time is the way to economy - whereas efficient driving is pretty much the opposite, with short bursts of efficient acceleration at low instantaneous mpg figures.

Similarly very few members seem to understand the difference between an aerodynamic shape and aerodynamic styling. Almost everything about reducing aerodynamic drag depends on getting all the details right and copying one 'trick' doesn't do it, particularly if that 'trick' was only styling anyway.

 

[GPW]

Angib , forgive me if I seem to disagree (slightly) ... For our little simple trailers , just cleaning up the shape would add a modicum of efficiency , without having to resort to advanced aerodynamics ... Being a towed vehicle , we’re forced to compromise the design to “better” the efficiency , but towing at reasonable speeds would probably do the same ...

 

[mezmo]

I found this the other day wandering around the internet. It is
a great idea to 'emulate', It's a mostly flat panel design with an aero
frontal shape intended to meld the tow vehicle's airflow onto the trailer,
The back opens wide and the roof lifts if needed. It is as narrow as a VW Polo =
a Euro model that is smaller than the VW Golf. It has a modular two box
kitchenette and a fold-up bed. Various layout setups are possible.

It's the "Cross-Over Trailer" concept by Ross Design, the in-house design function of
the Vohringer Group, a German caravan [wohnwagen] interior component supplier/
manufacturer. It's intended to meld the tow vehicle's air movement into the trailer's
for an aero benefit. It is also light weight and narrow and has a large rear opening:

http://www.voehringer-gmbh.net/rossdesi ... ossdesign/
http://www.v-group.com/uploads/pdfs/CRo ... %20eng.pdf

It could be a TTT or a TTH [TintToyHauler] Foamie or otherwise.

Cheers,
Norm/mezmo

 

[loaderman]

Early rear tapering for aerodynamics.

Article also states teardrops are good.
http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/24077451.cfm

 

[loaderman]

That shape got me thinking about things in nature that use aerodynamics.
Fish - rounded front then taper to back
Birds - basically same idea.

Aeroplanes are rounded front and tapered to the back.

Now none of these are towed, so not sure how that effects it.

 

[ghcoe]

That shape got me thinking about things in nature that use aerodynamics.
Fish - rounded front then taper to back
Birds - basically same idea.

Aeroplanes are rounded front and tapered to the back.

Now none of these are towed, so not sure how that effects it.

Geese/ducks fly in a V formation to cut down on drag.

 

[GPW]

Easiest way to cut down on Drag is to Slow Down !!! Drag increases exponentially with Speed ...

 

[loaderman]

HMMMM - So if one doesn't move at all you get great gas mileage.

which actually is not true if your vehicle is running. An idling stationary vehicle gets 0 mpg.

But I do get your point and it is very true you will get better mileage doing 50 then 65.

 

[linuxmanxxx]

Well yes and no depending on what your vehicle gear ratios are set so that what rpm is the maximum efficiency but then you throw in a towed item and if it's geared too high it will lug the engine at full speed and cause higher consumption vs if it's geared too low you wouldn't see as much dropoff cause the engine wouldn't work as hard pulling the camper.

As said before the most important thing is keeping it within your vehicle's wind tunnel effect for the best efficiency or use a diesel which won't drop mileage until it is massively loaded during a pull.

 

[mezmo]

In case any one is interested:

That Tow Vehicle looks to be a Tatra 87, a Czech car. Quite
a unique vehicle, @ 3000lbs, with an air-cooled V8.

http://en.wikipedia.org/wiki/Tatra_87

The trailer is a Bowlus - the original aircraft style constructed TT, the
actual forerunner of the Airstream. They were very expensive for the times
and went bankrupt. Wally Byam, the founder of Airstream, had
worked for/with them and bought the assets at the bankruptcy sale
and also hired some of the workers... . The trailer is probably a Road
Chief model @ 6ft x 18ft and @ 1100lbs. They used small steel tubing
for the body framing.
http://www.openthinkinc.com/bowlus/index.html

From what I've read on the topic, and for our purposes - as amateur builders -
matching the frontal size of the trailer to the max cross-section of the tow
vehicle and doing somewhat of a kamm-back effect on the rear of the trailer
would seem to be the most beneficial, or the most result for the effort.

Cheers,
Norm/mezmo

 

[atahoekid]

Just a practical note and I really haven't had time to think much about it to evaluate the meaning behind the numbers. I drive a F250 Ford pickup with a diesel engine. The best mileage I've ever gotten is 19.7 mpg on a road trip to SD. No real weight, just myself, my wife, son and our baggage. The worst I've ever gotten is 13.2 while towing a Ford Escape on a trailer back from SD. Normal day to day driving gets me 15.2. My first road trip (1500 miles)with the Road Foamie got me 15.2 mpg.

The Road Foamie fits inside the trucks' envelope pretty well except for maybe 6" on each side sticking out. I did not baby the truck but did try to stay within the posted speed limit. The nose is pretty well sloped but the back is square cut. I'm wondering if the basic shape didn't help my mileage. I was hoping for better.

 

[Wobbly Wheels]

I don't really think it's going to 'help' your mileage: you still have to punch a big square hole in the air to get truck through.
To see that it didn't hurt your mileage much is a good thing.
Imagine if your were pulling a commercially-built travel trailer (a big square box)...

 

[GPW]

Having towed a big commercial trailer , they are like towing a Parachute , and cut my mileage more than half ... From 22MPG to 8MPG ... Big Oil must Love that ...