Comet trailer near catastrophe

A longer tongue increases the forces on it...

Lengthening the tongue can increase the bending moment (and the
applied stresses if the diameter and wall thickness remain the same).
But I don't think it's accurate to say that it increases the forces
acting on the tongue.

...but increases the trailer stability...

Definitely! I've never met a trailer stability problem that couldn't
be fix by adding more tongue.

*Hydraulic surge brakes seem like the modern
choice (versus pure mechanical).

If I understand correctly, the most frequently encountered reason for
using a mechanical surge brake is the parking brake feature, which is
so convenient on our glider trailers. A mechanical parking brake can
be left engaged indefinitely without harm or loss of effectiveness (at
least until the brake shoes attach themselves to the drums through
rusting/corrosion of the drums or actuating hardware which, from
experience, can occur in a relatively short period of time if it's
damp). There are some hydraulic parking brake systems that trap the
pressure in the system and leave the brakes engaged but I don't know
how well they work [can anyone comment?]. As a result, it's relatively
easy to replace the German mechanical surge brake and axle on Komet/
Cobra trailers with a hydraulic version that brakes the trailer and
provides a breakaway emergency feature. But it's far more difficult to
provide the parking brake feature. Without knowing the relative cost,
and having had to make this decision before, I'd generally recommend
rebuilding/replacing components of the existing system if you want to
keep a surge/parking brake.

Chip Bearden
ASW 24 "JB"
USA

All of the above does also apply to home-built trailers. I own an all
Aluminum Schreder-type trailer, which was built very well. A few years
ago, I inspected the tow bar, which was a 2" square steel tubing. I
took a ball-peen hammer and could easily bash in the walls in several
spots! The walls were very thin to begin with but had corroded from
the inside outwards.
I replaced the tow bar with a 2" stainless steel tube with a slightly
thicker wall. The added weight was neglible. I also ran a loop of
stainless steel cable through the inside around the bolts connecting
the tow bar to the trailer and those connecting the coupler to the
bar. Should the tow bar break, there is still the cable inside, which
will keep the trailer from completely getting away and wandering off
into the oncoming traffic.

Safe flying and trailering

U. Neumann

[quote=GM;611857
I replaced the tow bar with a 2" stainless steel tube with a slightly
thicker wall. The added weight was neglible. I also ran a loop of
stainless steel cable through the inside around the bolts connecting
the tow bar to the trailer and those connecting the coupler to the
bar. Should the tow bar break, there is still the cable inside, which
will keep the trailer from completely getting away and wandering off
into the oncoming traffic.

Safe flying and trailering

U. Neumann[/QUOTE]


The cable is a great idea!
The choice of stainless, however, I wouldnt take. Stainless will work harden from continual heat/cool cycles or vibration (like every bump you go over) and crack at the stressed points.

Please check your stainless bar on a regular basis at its stressed points for VERY small cracks, once there, they will grow and split, probably on the same trip. The section will fail under tension, not compression.

A better choice of towbar material would be mild steel with a heavy galvanic (hot dip) coating. The wall section does not have to be that heavy, its better to use a larger section, especially in the vertical direction. Do not seal the ends before gal dipping, this will ensure the coating goes inside as well and leaves a great protected spot for wiring runs. Do not weld to the assembly after gal dipping.

If this style of towbar/tongue needs to be retrofitted to an existing trailer, use as many bolt points as possible to reduce the stress point.

Bagger

On Mar 15, 8:28*pm, bagmaker
wrote:
GM;611857
I replaced the tow bar with a 2" stainless steel tube with a slightly
thicker wall. The added weight was neglible. I also ran a loop of
stainless steel cable through the inside around the bolts connecting
the tow bar to the trailer and those connecting the coupler to the
bar. Should the tow bar break, there is still the cable inside, which
will keep the trailer from completely getting away and wandering off
into the oncoming traffic.

Safe flying and trailering

U. Neumann[/QUOTE Wrote:







The cable is a great idea!
The choice of stainless, however, I wouldnt take. Stainless will work
harden from continual heat/cool cycles or vibration (like every bump
you go over) and crack at the stressed points.

Please check your stainless bar on a regular basis at its stressed
points for VERY small cracks, once there, they will grow and split,
probably on the same trip. The section will fail under tension, not
compression.

A better choice of towbar material would be mild steel with a heavy
galvanic (hot dip) coating. The wall section does not have to be that
heavy, its better to use a larger section, especially in the vertical
direction. Do not seal the ends before gal dipping, this will ensure
the coating goes inside as well and leaves a great protected spot for
wiring runs. Do not weld to the assembly after gal dipping.

If this style of towbar/tongue needs to be retrofitted to an existing
trailer, use as many bolt points as possible to reduce the stress
point.

Bagger

--
bagmaker- Hide quoted text -

- Show quoted text -

Bagger,

points well taken - you must be a ME, too!
I have inspected my tow bar closly (magnifying glass) on a regular
basis since I do tow quite a bit with my old motor-home. The longer
the distance between the rear axle and the hitch-ball, the greater the
amplitude as you go over a bump hence the greater the whip-lash for
the trailer. I have not detected any cracks so far - will do a dye-
penetration test the next time.
One other thing I have done to lower the stress in the bolting points
under the trailer and the coupler is to insert heavy wall bushings on
the inside of the tube. The bolt is now no longer able to crush or bow
inwards the wall of the tube.
To reduce the possibility of galvanic corrosion between the aluminum
structure and the stainless tube, I applied a layer of heavy clear
packaging tape over the tube in the areas of contact. Just don't count
on using the tow bar as a vehicle ground lead anymore.
It all sounds like a design overkill, but if its worth doing, it is
worth overdoing, right? ;-)

Uli Neumann