Closing the trailer gap - Ideas & Theory

[euromodder]

Whatever its merits, I've always felt Phil's solution was way too complex to work IRL.

It's got to be done the easy way to work - KISS.

* Optimised for straight line duty and slight turns, i.e. highway style driving.
--- Don't bother about streamlining in slow hard turns

* Gap filling plates hinged on the tow vehicle
--- outboard movement to be restrained by bungee cords
--- inboard movement physically restricted by solid stops, yes, this will leave a gap on the outboard side in a hard turn - that's not an issue
--- downward movement of the top plate to be physically stopped by the sideplates , upward restrained by bungees
--- bungees might be fixed to the physical stops for the gap-filling plates, but not too far aft on the plates in order not to bend these.

* front side and top of the trailer to be rounded
--- helps even without the gap-filling plates
--- rear end of the gap-filling plates to rest on the rounded front, using teflon wheels on the plates
--- small, locally applied teflon plates on the trailer where the above wheels go as the plates slide over the front of the trailer

[darcane]

Not sure if there is value in copying it, but the Seattle area buses look like this:

It's basically a permenantly attached trailer on the back of a bus, so there are three total axles and it articulates in the middle. The front and rear are connected with an accordian-like material.

I've thought about building a triangular shaped plywood box on the tongue of my travel trailer. My thought is that is would improve aerodynamics while towing, but also provide some storage space for trailer related items that I could get out of the cabinets in the trailer (it is somewhat light on storage space). There may not be a lot of gain economy-wise, but the dual-purpose nature would make up for that.

I've also put some thought into lowering the trailer, as it sits quite high. I think this was done to keep the fenders from intruding so much into the trailer, but the overall height are much higher than most of the other trailers I see at the campgrounds.

[aerohead]

Originally Posted by euromodder

Whatever its merits, I've always felt Phil's solution was way too complex to work IRL.

It's got to be done the easy way to work - KISS.

* Optimised for straight line duty and slight turns, i.e. highway style driving.
--- Don't bother about streamlining in slow hard turns

* Gap filling plates hinged on the tow vehicle
--- outboard movement to be restrained by bungee cords
--- inboard movement physically restricted by solid stops, yes, this will leave a gap on the outboard side in a hard turn - that's not an issue
--- downward movement of the top plate to be physically stopped by the sideplates , upward restrained by bungees
--- bungees might be fixed to the physical stops for the gap-filling plates, but not too far aft on the plates in order not to bend these.

* front side and top of the trailer to be rounded
--- helps even without the gap-filling plates
--- rear end of the gap-filling plates to rest on the rounded front, using teflon wheels on the plates
--- small, locally applied teflon plates on the trailer where the above wheels go as the plates slide over the front of the trailer

The most challenging hurdle I ran into was when in a low speed turn,with trailer cocked,and on the sloping crown of the roadway,and the tow vehicle was ascending a laterally-level up-slope.
With only aluminum skins on the outside of steel-truss skeleton plate frames,the side plates would snag underneath the top plate and destroy it as it was displaced span-wise.
By moving the side plates onto the trailer by use of the lolly-shafted C-frame,the side plates cannot bind against the trailer during any type of orientation,nor the integrator on the back of the tow rig.
The upper frame has skids and rollers which are in constant contact with the trailer.As soon as the trailer displaces in any manner,the upper plate can raise to clear.An upward displacement of the trailers tail causes no interference.
I've yet to finish the lower plate(s).Those will have to wait 'til after the A2 Wind Tunnel.
As far as bungees or springs,I found that the side plates would be required to swing a full 90-degrees to clear the trailer face at 'full-lock',and no bungee or spring could maintain tension while 'straight',without being stretched beyond it's elastic limit and permanently deform when at full 'turn.'
I ended up with something akin to cable/pulley/double-hung window sash weights, riding vertically inside no-snag elevator shafts.These can handle the entire range of motion without damage.
It is complicated but has survived over 5,000 test miles without a hitch.
I recommend that the nose of the trailer be just as close to the tow ball as possible to allow the side plates to be as short and as light as possible.
When you strike a pothole or pressure ridge in the roadway it causes 'jerk,' which is an instantaneous acceleration,and can easily destroy structures who's inertia/momentum loads can be overcome during these 'instant' transient loads.

[aerohead]

Originally Posted by darcane

Not sure if there is value in copying it, but the Seattle area buses look like this:

It's basically a permenantly attached trailer on the back of a bus, so there are three total axles and it articulates in the middle. The front and rear are connected with an accordian-like material.

I've thought about building a triangular shaped plywood box on the tongue of my travel trailer. My thought is that is would improve aerodynamics while towing, but also provide some storage space for trailer related items that I could get out of the cabinets in the trailer (it is somewhat light on storage space). There may not be a lot of gain economy-wise, but the dual-purpose nature would make up for that.

I've also put some thought into lowering the trailer, as it sits quite high. I think this was done to keep the fenders from intruding so much into the trailer, but the overall height are much higher than most of the other trailers I see at the campgrounds.

I like the accordian type integration very much.I do not know how they do when torsion is introduced.
The Monorail at Disney Land in Anaheim,California has used it since the 1950s.But it runs on a track and experiences no torsional loading.
Bus systems typically stay on the streets without dealing with driveway slopes and the like.
Same for passenger trains.
I remain shy of it,as I cannot fathom how they would perform with radical,multi-orientations thrown at them when in passenger car/trailer applications.

[slowmover]

The most challenging hurdle I ran into was when in a low speed turn,with trailer cocked,and on the sloping crown of the roadway,and the tow vehicle was ascending a laterally-level up-slope.

A problem for any of us with low ground clearance trailers. My TT (travel trailer; a longer one than in my current sig pic) has a very long rear overhang and not much clearance. So, fuel stops and the rest are best planned in advance (reference materials and Google Map confirmation).

One must also (with Texas law and other states) pulll over at a "safe place" to allow traffic around one. So, one is always scanning the road shoulder on two-lane highways to recognize those places. There is a pretty good burden in being a draft horse out on a race course. It cannot be ignored. (In the same vein: mirrors on the TV must allow visual convergence on an object 200' to ones rear. This is not optional. What is past (behind one) is (actually) "future".


I recommend that the nose of the trailer be just as close to the tow ball as possible to allow the side plates to be as short and as light as possible.

For purposes of tow vehicle stability (steering gradient index, and braking) keeping yaw to a minimum, the tow vehicle hitch receiver and the trailer coupler are ideally as short as possible. Shorter than what most off-the-shelf stuff measures to (givens are that one must be able to clear a 90-degree turn; in backing one WILL hit the trailer with the tow vehicle otherwise). There is nearly always room to shorten by a few inches.

Custom hitch builders still take this into account.

IMO, this is where the money is as combined vehicle dynamics are vital. Reducing driver inputs to maintain lane-centeredness is the first goal. Aero is secondary . . icing on the cake that is a well-chosen pair of vehicles, well-hitched, and on a well-planned trip. Aero won't mean much without those first done.

.

[freebeard]

For purposes of tow vehicle stability (steering gradient index, and braking) keeping yaw to a minimum, the tow vehicle hitch receiver and the trailer coupler are ideally as short as possible. Shorter than what most off-the-shelf stuff measures to (givens are that one must be able to clear a 90-degree turn; in backing one WILL hit the trailer with the tow vehicle otherwise). There is nearly always room to shorten by a few inches.

You're in a better position to know, but I thought the significant ratio was tow-vehicle rear axle centerline to hitch vs hitch to trailer axle centerline. I'm not picturing how to shorten the hitch/coupler.

[slowmover]

1] Hitch receiver design. Inches count

2] Length of drawbar. Inches count

For any given tow vehicle.

Shortest rear overhang -- from tow vehicle axle center to hitch ball -- is best, as you note, but separate from the above.

The "best" trailer for a given use (shape + weight, first; second are road performance issues such as COG, ground clearance, suspension and brake type) drives the design for best tow vehicle. "Given use" drives the length of the trailer (among other dimensions).

The more choices one has in appropriate tow vehicles, the "better" is the trailer design, IOW. A Euro turbodiesel SUV or sedan may return all the best numbers . . but how affordable, in main? Avoiding the need for a pickup truck ought to drive things -- so to speak -- for a non-dedicated combination (where solo miles predominate).

If HP demand can be settled to the comfort of the owner, then the lash-up can be optimized for a given tow vehicle.

It's circular, but the trailer drives all other decisions. Trailer weight is secondary to trailer shape, on the one hand, but climate & terrain (mainly altitude) are the tow vehicle limiting factors. Paved, or unpaved. Etc.

Subsidized roads and subsidized fuel are the largest picture. Without them this is an exercise in futility.

More closely, we might say that the scaled weight of the payload, and it's shape, is what is at stake.

How quickly or slowly, and at what cost it arrives at it's destination is what needs sorting as secondary concerns (that folks often assume as being primary).

Shipping that same load by rail or truck versus transporting it ourselves reveals that we find convenience to be of a higher value than true lowest cost. Where do we draw a line? What are the upper and lower limits of payload shapes and weights. Etc.

Hitch rigging (lash up) comes down to specifics of the vehicles chosen. Aero is simply unknown until that point.

A pickup with the bed removed pulling gooseneck-hitched trailer may well be the best candidate for an aero trailer "package". But how useful is that tow vehicle to a non-commercial user in solo miles?

Etc.

.

[freebeard]

The 'fifth-wheel' hitch needs to be at approximately the axle line, right? I know with farm tractors if the drawbar is above the axle line bad things happen.

1] Hitch receiver design. Inches count

2] Length of drawbar. Inches count

For any given tow vehicle.

Shortest rear overhang -- from tow vehicle axle center to hitch ball -- is best, as you note, but separate from the above.

Suppose the hitch is drawn up under the body, which terminates in a convex spherical sector that is centered on the hitch ball. Then a trailer with a long tongue and a concave front bulkhead could make torsional and angular excursions without impacting the tow vehicle.

[slowmover]

The PULLRITE hitch essentially replicates the 5'er / gooseneck advantage. Is this what you were thinking? (As to "safety" -- minimizing / eliminating trailer sway -- it is an excellent choice).

.

[freebeard]

Is this what you were thinking?

Since I'd never seen it before, no. But it does point up a problem with what I *was* thinking. Which was the tow vehicle (or a profile extension) shaped as a quarter sphere with a half cone carved out of the bottom center for a single tongue to fit into. (How do you latch the hitch onto the ball?)

The Class III and IV hitches the Pullrite is intended for use an A-frame on the trailer, which pretty much kills the idea for me.

I tend to think of the lighter end of the scale.

But it seems to scale up:

http://www.youtube.com/watch?v=dgJ3lSbOqqw