raulb wrote:
I am no expert (just a dumb electrician), but this is what has always
bothered me about the German glider trailers, the single pole tongue.

Think about it, this single pole has to absorb a lot of movement and
stress:
1. The weight of the trailer and contents (almost a ton) when parked,
often for long periods.

Since you can lift the tongue on the typical trailer, how could the
force be a ton? Unless you are the Hulk, maybe. The force on the nose
wheel is typically about 10% of the total weight. The length of time is
irrelevant, as steel doesn't fatigue or weaken when lightly stressed, as
it is when parked. In fact, the stress on the tongue is less when it's
parked on the nose wheel instead of hitched to a parked tow vehicle.

2. The up and down motion of the trailer as you tow it over bumps and
uneven pavement.

Not a problem, if the tongue is sized properly, regardless of the shape
of the tongue. Cobra trailers can be safely suspended by the coupler and
the rear end, wheels off the ground, which can happen leaving a parking
lot with an extreme dip at the entrance.

3. The sway of the trailer when towed behind your car.

The horizontal forces are much smaller than those in #2, so not a problem.

4. The sideways stress on the tongue when turning, especially short
turns (like U-turns).

Turns put very little stress on the tongue, as you can easily turn the
trailer yourself, by pulling on the tongue by hand. I'm assuming the
trailer doesn't hit the tow vehicle, of course, which can cause damage
to any tongue.

Those are tremendous arm moments. I have never understood why these
trailers have this kind of tongue--or how they have passed DOT and
State regulations.

The kind of tongue is a design choice, and it is up to the designer to
choose the proper materials and sizes to meet the regulations. It is
straight-forward engineering. Perhaps you know a mechanical engineer
that can explain it to you.


Also, are those poles galvanized or just painted?

On the Cobra trailers - galvanized.

If just painted,
they should be inspected carefully before you tow the trailer (a good
idea even if it it galvanized).

Absolutely! All trailers, including (as a minimum) the tongue, brakes,
lights, wheels and lug nuts, should be routinely inspected.

It just takes a pin hole in the paint
to allow rain and dew to seep into the steel where it can rust
unnoticed. This is not to say that galvanizing will not rust,
especially if it is welded, but the chance is considerably less and
the zinc finish will take more abuse than paint will.

I have a Swan trailer (also German) for my LS-1c and it has a
triangular tongue, made of C-channel, more like what we typically see
on American trailers, and it is galvanized. A triangular tongue helps
spread out he load and stresses. You still have a single point where
the trailer hitch is located, but it is rather beefier and the arm is
considerably less than a single 3 or 4 foot pole.

Again, the length of the tongue is a design choice. A longer tongue
increases the forces on it, but increases the trailer stability, and
allows the tow vehicle to turn more tightly without hitting the trailer.
A "pole" tongue allows even tighter turns without hitting the tongue, if
the tongue is long enough that the trailer box doesn't hit first.

I requested a longer than usual tongue on my Cobra trailer, because of
the width of my motorhome and the greater (than a car) distance from the
rear axle to the hitch ball. When I turn tightly, the trailer would hit
the motorhome without that extra tongue length.

You also have a
single point on each leg of the tongue where it attaches to the
trailer, so you still need to be mindful of the up and down loads, but
there should be less risk than with a round pole. I have no proof for
this, but the C-channel cross-section triangular tongue should be
stronger than a round pole in all instances.

And there is no proof! For example, would C-channel out of sheet metal
be stronger than a "pole" out of quarter inch thick steel? The strength
of the tongue is determined not just by the shape, but also by the
material and it's thickness.

--
Eric Greenwell - Washington State, USA
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