Comet trailer near catastrophe

[e***@ventureassociates.com]

Trailering my DG-300 home after a Saturday flight, I was on the
highway within a few miles of home when someone pulled up beside me,
gesturing back towards my trailer (never a good sign).

I immediately pulled over and was stunned to find the tongue of my 25
year old Comet trailer snapped almost in two! It was more than 95%
severed, sagging mid-span, hinged and hanging by a mere thread of
metal. That had activated the trailer's surge brakes as I drove and
they were HOT, barely touchable at the hubs.

I called AAA who told me that they'll help with my car, but not with
trailer problems. So I thanked the agent (not really) and called back
to report my "car" problems, asking that they send a flat bed truck.
The driver arrived shortly thereafter, put the trailer up on the flat
bed, and delivered the trailer a few miles away to the repair shop
that recently repacked the wheel bearings.

I consider this a gift that a) it happened near home instead of
central Nevada and b) that it didn't break all the way off,
doubtlessly causing me to get on the brakes and bash the trailer into
the back of my SUV!

If you've got a similar vintage Comet trailer, you might want to
inspect for this - though, from the looks of my failed tongue, I'm not
sure there'd be any outward signs...

Has anybody heard of this kind of (near) catastrophic tongue failure
before? Now what?

Eric
ER

[nimbusgb]

Post by e***@ventureassociates.com
Trailering my DG-300 home after a Saturday flight, I was on the
highway within a few miles of home when someone pulled up beside me,
gesturing back towards my trailer (never a good sign).
I immediately pulled over and was stunned to find the tongue of my 25
year old Comet trailer snapped almost in two! It was more than 95%
severed, sagging mid-span, hinged and hanging by a mere thread of
metal. That had activated the trailer's surge brakes as I drove and
they were HOT, barely touchable at the hubs.
I called AAA who told me that they'll help with my car, but not with
trailer problems. So I thanked the agent (not really) and called back
to report my "car" problems, asking that they send a flat bed truck.
The driver arrived shortly thereafter, put the trailer up on the flat
bed, and delivered the trailer a few miles away to the repair shop
that recently repacked the wheel bearings.
I consider this a gift that a) it happened near home instead of
central Nevada and b) that it didn't break all the way off,
doubtlessly causing me to get on the brakes and bash the trailer into
the back of my SUV!
If you've got a similar vintage Comet trailer, you might want to
inspect for this - though, from the looks of my failed tongue, I'm not
sure there'd be any outward signs...
Has anybody heard of this kind of (near) catastrophic tongue failure
before? Now what?
Eric
ER

Yup. My Komet II with its Ventus Bt inside started to fold just behind
the axle. I was in Jaca in Spain at the time and about 900 km from
home. When the lid was opened the tail sagged to within about 2 inches
of the hardtop. On inspection the lower longitudinal stringers ( 25mm
square steel tubing ) had stress fractures almost completely through
just behind the rear axle attachment points.

The local agricultural mechanic in Santa Cila took the trailer into
his shed and I had it back about 3 days later with a really 'robust'
repair and a measly repair bill for I think about Euro 150. That
trailer is still on our airfield and has been to Spain several times
subsequently.

If you have any old trailer I'd keep an eye on those stringers. The
weight of the aft fuselage, wing stands, tail dolly, ramp and other
stuff that tends to get put in there on long trips all that distance
from the fulcrum must put some serious loads on the metalwork!

Ian

[Chip Bearden]

You're lucky in more ways than you know. At 25 years, you were overdue
for some drama. :)

http://groups.google.com/group/rec.aviation.soaring/browse_thread/thread/db0e9e4360529d6d/e70a2398cd9ec225?lnk=gst&q=Komet+trailer+failed#e70a2398cd9ec225

http://groups.google.com/group/rec.aviation.soaring/browse_thread/thread/37316dd2e384dee8/fea7dce06c960dff?lnk=gst&q=Komet+trailer+failed+floor#fea7dce06c960dff

These URLs/links may be too long to work. Either copy/paste them into
your browser window or just go to groups.google.com,
rec.aviation.soaring, and then search for Komet+failure+ either tongue
or floor. It's happened before. It will happen again.

Chip Bearden
ASW 24 "JB"
USA

[raulb]

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.
2. The up and down motion of the trailer as you tow it over bumps and
uneven pavement.
3. The sway of the trailer when towed behind your car.
4. The sideways stress on the tongue when turning, especially short
turns (like U-turns).

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.

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

The idea of putting the chains on the trailer instead of the tongue is
a good one and even though I have more confidence in the Swan tongue,
I think I am going to investigate this idea.

Post by e***@ventureassociates.com
Trailering my DG-300 home after a Saturday flight, I was on the
highway within a few miles of home when someone pulled up beside me,
gesturing back towards my trailer (never a good sign).
I immediately pulled over and was stunned to find the tongue of my 25
year old Comet trailer snapped almost in two!  It was more than 95%
severed, sagging mid-span, hinged and hanging by a mere thread of
metal.  That had activated the trailer's surge brakes as I drove and
they were HOT, barely touchable at the hubs.
I called AAA who told me that they'll help with my car, but not with
trailer problems.  So I thanked the agent (not really) and called back
to report my "car" problems, asking that they send a flat bed truck.
The driver arrived shortly thereafter, put the trailer up on the flat
bed, and delivered the trailer a few miles away to the repair shop
that recently repacked the wheel bearings.
I consider this a gift that a) it happened near home instead of
central Nevada and b) that it didn't break all the way off,
doubtlessly causing me to get on the brakes and bash the trailer into
the back of my SUV!
If you've got a similar vintage Comet trailer, you might want to
inspect for this - though, from the looks of my failed tongue, I'm not
sure there'd be any outward signs...
Has anybody heard of this kind of (near) catastrophic tongue failure
before?  Now what?
Eric
ER

[JJ Sinclair]

Post by raulb
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
1.  The weight of the trailer and contents (almost a ton) when parked,
often for long periods.
2.  The up and down motion of the trailer as you tow it over bumps and
uneven pavement.
3.  The sway of the trailer when towed behind your car.
4.  The sideways stress on the tongue when turning, especially short
turns (like U-turns).
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.
Also, are those poles galvanized or just painted?  If just painted,
they should be inspected carefully before you tow the trailer (a good
idea even if it it galvanized).  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.  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.
The idea of putting the chains on the trailer instead of the tongue is
a good one and even though I have more confidence in the Swan tongue,
I think I am going to investigate this idea.

Post by e***@ventureassociates.com
Trailering my DG-300 home after a Saturday flight, I was on the
highway within a few miles of home when someone pulled up beside me,
gesturing back towards my trailer (never a good sign).
I immediately pulled over and was stunned to find the tongue of my 25
year old Comet trailer snapped almost in two!  It was more than 95%
severed, sagging mid-span, hinged and hanging by a mere thread of
metal.  That had activated the trailer's surge brakes as I drove and
they were HOT, barely touchable at the hubs.
I called AAA who told me that they'll help with my car, but not with
trailer problems.  So I thanked the agent (not really) and called back
to report my "car" problems, asking that they send a flat bed truck.
The driver arrived shortly thereafter, put the trailer up on the flat
bed, and delivered the trailer a few miles away to the repair shop
that recently repacked the wheel bearings.
I consider this a gift that a) it happened near home instead of
central Nevada and b) that it didn't break all the way off,
doubtlessly causing me to get on the brakes and bash the trailer into
the back of my SUV!
If you've got a similar vintage Comet trailer, you might want to
inspect for this - though, from the looks of my failed tongue, I'm not
sure there'd be any outward signs...
Has anybody heard of this kind of (near) catastrophic tongue failure
before?  Now what?
Eric
ER- Hide quoted text -

- Show quoted text -

I believe the single pole tongue comes from the surge brake inside,
but there's no reason it couldn't be supported with triangular braces
and still allow the surge brake to do its thing. There is a gas strut
inside which should be removed before you start welding on the tongue.
JJ

[rlovinggood]

JJ,

I too have a Swan with an LS1-c/d inside. The triangular shaped frame
does have a surge brake. The tongue and axle are all from Al-Ko,
which I believe supplies tongues and axles to Cobra and possibly
Komet. (???)

The main web page for Swan is
www.swan-trailer.de

and you can see a photo of their tongue at
http://swan-trailer.de/eng/swandetaildeichsel.htm

The shape of the tongue and frame makes it appear as if the trailer is
a "tilt bed" design, but it is not.

Ray Lovinggood
Carrboro, North Carolina, USA

[Eric Greenwell]

Post by raulb
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
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.

Post by raulb
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.

Post by raulb
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.

Post by raulb
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.

Post by raulb
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.

Post by raulb
Also, are those poles galvanized or just painted?

On the Cobra trailers - galvanized.

Post by raulb
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.

Post by raulb
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.

Post by raulb
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.

[Bob Kuykendall]

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.

[Fred the Red Shirt]

Post by raulb
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.

Well I'm a physicist who considers electricity to be
dangerous black magic so I'm strongly disinclined
to think of any electrician who has survived his
choice of profession as being 'dumb'.

Post by raulb
Think about it, this single pole has to absorb a lot of movement and
1. The weight of the trailer and contents (almost a ton) when parked,
often for long periods.
2. The up and down motion of the trailer as you tow it over bumps and
uneven pavement.
3. The sway of the trailer when towed behind your car.
4. The sideways stress on the tongue when turning, especially short
turns (like U-turns).

If I understand the design and use correctly the
weight being supported by the tongue when
properly parked is about the same as when
hitched and is only a fraction of the wieight of
the trailer itself. Most of the weight is carried
to the ground through the suspension, axle.
wheels, and tires--always.

Well, almost always:

http://www.altavista.com/image/results?itag=ody&q=strong+hitch&kgs=1&kls=0

'Parked' implies a static load, except when loading
or unloading. For Structural metals, which typically
do not creep, the length of time over which a static
load is borne is not relevant to the life expectancy
of the part. It is the process of cycling a load that
causes fatigue, that is why fatigue life is measured
in terms of cycles, not time. By contrast, a
cantelevered wing spar undergoes reverse stress
at least once each flight, supporting the weight
of the wing, in one direction on the ground and
half the weight of the entire aircraft, plus half the
down force of the epenage, in the opposite direction
when airborne (canards excepted of course).

Of course in real flight the load varies constantly
with up/down movement, banking, and bumps
in the air.

Lightweight construction motivates designs with
a relatively load fatigue life, despite a high factor of
safety for static loads, which is one of many good
reasons to avoid flying in turbulence even with a
wing rated for 9 gs or more. But I digress.

The typical ball hitch allows the tongue to pivot
up, down, left, and right, so that the load on
the tongue is predominantly pure tension, or
when slowing down or driving downhill, pure
compression, with minimal bending moment.

As you note, tight turns are probably the most
stressful operation and should be minimized.

Post by raulb
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.

They are approved because they work well,
they are most likely to fail during those tight
turns, as when backing, parking or doing a uey,
(low speed manouvers) and also, being ductile
metal, tend to fail gradually enough that the
problem is noticed before rupture.

That said, they are a single point of failure,
never a good engineering practice,and i's
personally opt for the triangular bracing and
a safety chain, whenever possible.

Post by raulb
Also, are those poles galvanized or just painted? If just painted,
they should be inspected carefully before you tow the trailer (a good
idea even if it it galvanized). 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.

Yes, unfortunately zinc reacts readily with acid.
Rainwater is naturally slightly acidic, in part due
to nitric acid created in the atmosphere by lighting,
an effect dwarfed by the ubiquitous acid rain we
have heard so much about in recent decades.

Painting galvanized steel may help it to last longer
but makes it much harder to evaluate the condition
of the underlying metal.

Post by raulb
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. 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.
The idea of putting the chains on the trailer instead of the tongue is
a good one and even though I have more confidence in the Swan tongue,
I think I am going to investigate this idea.

Yes, the safety chain then spans what would otherwise be
single point of failure, giving you redundancy.

Post by raulb
...

Post by e***@ventureassociates.com
I called AAA who told me that they'll help with my car, but not with
trailer problems. So I thanked the agent (not really) and called back
to report my "car" problems, asking that they send a flat bed truck.
The driver arrived shortly thereafter, put the trailer up on the flat
bed, and delivered the trailer a few miles away to the repair shop
that recently repacked the wheel bearings.

I'm extremely impressed that you actually got through to
the AAA, not once, but twice, in the same day!

--

FF

[e***@ventureassociates.com]

To update my initial posting on my Komet (not Comet!) trailer...

Boy, that was a close one! I'm lucky to have made it safely off the
highway! Closer inspection revealed a small hole in the bottom part
of the tongue, with corrosion. This might have been visible upon
inspection. (Go inspect yours.)

I've not gotten a response after a few calls and messages to Entech
Techincal Services, Komet 's "sole North American representative" per
their website at http://entec.soaringweb.net/. Does anyone know if
they're active or where else I should inquire? I'll be needing a new
tongue, etc.

Inspecting the trailer more closely, the local trailer shop pointed
out another problem. The rear axle's suspension arms were down,
resting on the frame -- there is no shock absorbtion except for the
tires. With this information, a new strategy could be to replace the
axle with an American made, easy to get axle (though a custom length,
made by Dexter). I'd also replace the brakes and go with hydraulic
brakes. Finally, they trailer shop would fabricate a new tongue that
uses the hydraulic surge brake. Cost: $2000, ouch.

I could get this done in 3 weeks (spring soaring's almost here!!!) and
everything will be standard and replaceable. So far it's making sense
to stick with a surge brake (versus electric) so that I can use
various vehicles to tow my trailer (and avoid installing the electric
controller in my SUV). Hydraulic surge brakes seem like the modern
choice (versus pure mechanical).

I've not pulled the trigger on this yet -- I'll await a few comments
here to make sure this is the best option.

Thanks,

Eric
ER

[rlovinggood]

From Paul Remde's website:

http://www.anschau.de/englishversion.htm


Ray Lovinggood
Carrboro, North Carolina, USA

[Chip Bearden]

 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

[GM]

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

[bagmaker]

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

The cable is a great idea!
The choice of stainless, however, I wouldnt take. Stainless will wor
harden from continual heat/cool cycles or vibration (like every bum
you go over) and crack at the stressed points.
Please check your stainless bar on a regular basis at its stresse
points for VERY small cracks, once there, they will grow and split
probably on the same trip. The section will fail under tension, no
compression.
A better choice of towbar material would be mild steel with a heav
galvanic (hot dip) coating. The wall section does not have to be tha
heavy, its better to use a larger section, especially in the vertica
direction. Do not seal the ends before gal dipping, this will ensur
the coating goes inside as well and leaves a great protected spot fo
wiring runs. Do not weld to the assembly after gal dipping.
If this style of towbar/tongue needs to be retrofitted to an existin
trailer, use as many bolt points as possible to reduce the stres
point.
Bagge

--
bagmaker

[GM]

Post by bagmaker
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

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