Which Tow Vehicle

On Oct 12, 3:57 pm, "01-- Zero One" wrote:
So to say that "Towing is simple. Follow these rules, and your rig will
be stable in all conditions and not need stabiliser hitch." is in my
experience a gross oversimplification.

Think we'll have to agree to disagree - but I'd like to know of
examples where these guidelines were met, but the rig was still
unstable.

One thing I don't mention which could be called an
"oversimplification" is weight distribution within the trailer, mass
should be concentrated low and over the axle. However you don't
usually have much choice about that with a glider.


Dan

OK--I'll supply one.

1999 Chev Tahoe
1999 ASW27 + Cobra
Tongue weight about 9%
all tires new

Begins sway at 68mph--diverging oscillation above 70 mph.
Tried spoilers on vertical fin--no help
Used nails as wedges to stabilize hitch in the receiver--no help.

Attached same setup to a Ford Expedition--stable at up to 110 mph!

Bought 2003 Chev Avalanche
Stable at any speed traffic allowed!

The difference---The 1999 Tahoe had a soft suspension and "vague" steering.
The Avalance and the Expedition are much more stiffly suspended and the
steering more precise. All three vehicles are massive compared to the
Cobra+'27

The answer--IMO the "natural frequency" of the suspension no longer
resonated with the trailer suspension "natural frequency" at highway speed.

--
Hartley Falbaum
"KF" USA


"Dan G" wrote in message
ps.com...
On Oct 12, 3:57 pm, "01-- Zero One" wrote:
So to say that "Towing is simple. Follow these rules, and your rig will
be stable in all conditions and not need stabiliser hitch." is in my
experience a gross oversimplification.

Think we'll have to agree to disagree - but I'd like to know of
examples where these guidelines were met, but the rig was still
unstable.

One thing I don't mention which could be called an
"oversimplification" is weight distribution within the trailer, mass
should be concentrated low and over the axle. However you don't
usually have much choice about that with a glider.


Dan

Dan,
Indeed, from reading many posts on the stability issue, it seems that
a precise, stiff suspension is what makes the rig stable. I recall one
poster saying his rig was not very stable till he fixed a somewhat
worn and loose joint in the front suspension that was barely
noticeable when driving normally, but it improved the stability of the
rig enormously.

I suspect that when the tow vehicle itself is heavily loaded, making
it less stable, it can have the same effect and cause the rig to be
less stable than when the tow vehicle is more lightly loaded.

The Honda Accord I used to tow had a Iow cg and a fairly stiff
suspension compared to many large tow vehicles. The Astir CS and heavy
trailer were clearly stable to 80MPH, which is as fast as I ever
went. Never tried faster as I never trusted the small tires on the
trailer too much.

I doubt stability is about the weight of the tow vehicle.

tommytoyz wrote:

Indeed, from reading many posts on the stability issue, it seems that
a precise, stiff suspension is what makes the rig stable.

And this explains partly why Americans tend to think they use trucks to
tow. US cars have had a reputation for poor suspensions. Poor suspension
means poor towing stability. Imagine someone towing with a large V8 with
poor suspension. The tow will be unstable. Now try to tell that guy that
towing with a smaller car will yield more stable results! No way, his
logic will tell him he needs an even bigger car, i.e. a truck.

As my girlfriend always said: It's not the size, it's the stiffness
which matters.

On Oct 16, 3:35 am, "HL Falbaum" wrote:
OK--I'll supply one.

1999 Chev Tahoe
1999 ASW27 + Cobra
Tongue weight about 9%
all tires new

Begins sway at 68mph--diverging oscillation above 70 mph.
Tried spoilers on vertical fin--no help
Used nails as wedges to stabilize hitch in the receiver--no help.

Attached same setup to a Ford Expedition--stable at up to 110 mph!

Bought 2003 Chev Avalanche
Stable at any speed traffic allowed!

The difference---The 1999 Tahoe had a soft suspension and "vague" steering.
The Avalance and the Expedition are much more stiffly suspended and the
steering more precise. All three vehicles are massive compared to the
Cobra+'27

The answer--IMO the "natural frequency" of the suspension no longer
resonated with the trailer suspension "natural frequency" at highway speed.

Of course different tow vehicles will tow differently, particularly
with SUVs, many of which use suspension which can only be described
politely as being "agricultural". My point (which I did not explain
clearly) was that I doubt that if you had, for example, tried a
negative noseweight or stuck a bunch of lead acid batteries in the end
of the trailer your Tahoe would have towed at high-speed with
stability.


Dan

Dan G wrote:
On Oct 12, 3:57 pm, "01-- Zero One" wrote:
So to say that "Towing is simple. Follow these rules, and your rig will
be stable in all conditions and not need stabiliser hitch." is in my
experience a gross oversimplification.

Think we'll have to agree to disagree - but I'd like to know of
examples where these guidelines were met, but the rig was still
unstable.

My '89 Dodge Caravan and ASH 26 E trailer meets all your rules and is
stable at 60 mph. At 70 mph, it's starting to quiver, and I've never
dared go faster. So, is the rig "stable" or "unstable"?

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly
* "Transponders in Sailplanes" http://tinyurl.com/y739x4
* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

On Oct 16, 4:46 am, Eric Greenwell wrote:
Dan G wrote:
On Oct 12, 3:57 pm, "01-- Zero One" wrote:
So to say that "Towing is simple. Follow these rules, and your rig will
be stable in all conditions and not need stabiliser hitch." is in my
experience a gross oversimplification.

Think we'll have to agree to disagree - but I'd like to know of
examples where these guidelines were met, but the rig was still
unstable.

My '89 Dodge Caravan and ASH 26 E trailer meets all your rules and is
stable at 60 mph. At 70 mph, it's starting to quiver, and I've never
dared go faster. So, is the rig "stable" or "unstable"?

What's the speed limit for a towing vehicle in the US? In the UK it's
60, so your rig would be "stable", though of course it would be
preferable to have a higher safety margin in the event of cross-winds
etc.

Let me try and explain this another way:

*if your trailer is trying to lift the rear of your tow vehicle when
hitched, it will have reduced stability than if it's pressing down.

*If your trailer has a heavy mass at the far end, it will have reduced
stability compared to if it had that mass in low down over the axle.

*If your trailer has underinflated tyres, it will have reduced
stability compared to if it had correctly inflated tyres (and they
might go "bang", too)

*If your trailer weighs more than your towcar, it will have reduced
stability compared to if the towcar was heavier than the trailer.

I hope that's clearer. The Bath University guidelines were also
developed using average Euro cars - I would not expect an tall,
unstable American SUV or pickup with ancient suspension to be
particularly stable in many circumstances, even when not towing. More
recent models with relatively modern suspension should, of course,
fare better.


Dan

"Dan G" wrote in message
ups.com...
On Oct 16, 4:46 am, Eric Greenwell wrote:
Dan G wrote:
On Oct 12, 3:57 pm, "01-- Zero One" wrote:
So to say that "Towing is simple. Follow these rules, and your rig
will
be stable in all conditions and not need stabiliser hitch." is in my
experience a gross oversimplification.

Think we'll have to agree to disagree - but I'd like to know of
examples where these guidelines were met, but the rig was still
unstable.

My '89 Dodge Caravan and ASH 26 E trailer meets all your rules and is
stable at 60 mph. At 70 mph, it's starting to quiver, and I've never
dared go faster. So, is the rig "stable" or "unstable"?

What's the speed limit for a towing vehicle in the US? In the UK it's
60, so your rig would be "stable", though of course it would be
preferable to have a higher safety margin in the event of cross-winds
etc.

Let me try and explain this another way:

*if your trailer is trying to lift the rear of your tow vehicle when
hitched, it will have reduced stability than if it's pressing down.

*If your trailer has a heavy mass at the far end, it will have reduced
stability compared to if it had that mass in low down over the axle.

*If your trailer has underinflated tyres, it will have reduced
stability compared to if it had correctly inflated tyres (and they
might go "bang", too)

*If your trailer weighs more than your towcar, it will have reduced
stability compared to if the towcar was heavier than the trailer.

I hope that's clearer. The Bath University guidelines were also
developed using average Euro cars - I would not expect an tall,
unstable American SUV or pickup with ancient suspension to be
particularly stable in many circumstances, even when not towing. More
recent models with relatively modern suspension should, of course,
fare better.


Dan


On our USA Interstate Highways, speeds tend to average 75mph. Speed limits
are lower, but not usually enforced until above 80 mph or more. Even the
Semi trailers (18 Wheel trucks) are doing 70-75 or more. If you drive 65,
you are continually passed by these trucks, each producing "bow waves" that
induce more sway. So stability up to 80 mph is highly desirable.

The above noted points all contribute to stability, but I tried them all,
and then some, one at a time, and in combinations. There was no dramatic
improvement until I changed vehicles. The Tahoe and the Avalanche weigh
about the same. The Avalanche has a longer wheelbase. They both have live
rear axles and use the same tires.

IMO the best way to improve a tow vehichle is with "helper springs" to
stiffen the rear, and if needed, the front, suspension. These are easy to
add, relatively inexpensive, and can improve the handling even without the
trailer. Of course, this is after bringing the suspension up to "specs"
first. Shortening the distance between the hitch and the rear axle, where
possible, helps too. Two inches can make a difference.


Hartley Falbaum
"KF" USA

Regarding safety in collisions:

Linked bellow is a report from the institute for Highway safety that
shows that a car colliding with a heavy SUV favors the occupants of
the SUV enormously. These are death statistics.

However, in Solo acciddents, like spin outs and collisions with
immovable objects, the car is far better and the statistics support
this.

Because in cars, 42% of deaths are in solo accidents. In SUVs, 63% of
deaths are in solo accidents. So basically, don't loose control of an
SUV or hit anything. In cars, only 27% of deaths occur when cars are
involved with something bigger than themselves, including buses.

The report concludes that by far, the most deaths occur in solo
crashes in both cars and SUVs. This speaks against SUVs being safer
overall.

Overall, except for slow city driving, I doubt the SUV is safer and I
personally don't feel safer in one cruising on a country road or
freeway, especially towing something.

Report:
http://www.iihs.org/sr/pdfs/sr4005.pdf

Dan G wrote:

My '89 Dodge Caravan and ASH 26 E trailer meets all your rules and is
stable at 60 mph. At 70 mph, it's starting to quiver, and I've never
dared go faster. So, is the rig "stable" or "unstable"?

What's the speed limit for a towing vehicle in the US?

The highest speeds are on the Interstates. In California, it's 55 mph;
in Montana, it's 75 mph. Other states are between these two.

In the UK it's
60, so your rig would be "stable", though of course it would be
preferable to have a higher safety margin in the event of cross-winds
etc.

So, the study investigated relatively short, wide, and tall trailers
towed no faster than 60 mph. It doesn't seem likely to have much to
offer the typical glider pilot!

The point I'm trying to make is most of the glider towing combinations
can go fast enough to become unstable, and following the "rules" doesn't
ensure stability at even legal speeds, much less at the speeds many
pilots want to tow.



Let me try and explain this another way:

*if your trailer is trying to lift the rear of your tow vehicle when
hitched, it will have reduced stability than if it's pressing down.

*If your trailer has a heavy mass at the far end, it will have reduced
stability compared to if it had that mass in low down over the axle.

*If your trailer has underinflated tyres, it will have reduced
stability compared to if it had correctly inflated tyres (and they
might go "bang", too)

*If your trailer weighs more than your towcar, it will have reduced
stability compared to if the towcar was heavier than the trailer.

I think we all agreed from the start that the "rules" were sensible;
what some of us have pointed out is they are not sufficient. If pilots
never towed over 60 mph, we'd have far fewer trailer towing discussions!
And a lot fewer accidents, too.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly
* "Transponders in Sailplanes" http://tinyurl.com/y739x4
* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org