Which Tow Vehicle

On Oct 9, 5:30 pm, Mike the Strike wrote:
Bob:

As a physicist, I am also a great believer in Newton's laws.

I once towed a trailer containing my Jantar-1 (19 meters) with a VW
bug, or rather I should say the trailer propelled my bug down the road
only marginally under control. I terminated that experiment very
quickly!

Since that attempt, I have used larger vehicles (station wagons in the
old days) or SUVs more recently.

I now use the moderately-sized Toyota 4Runner (Prado Land Cruiser to
the rest of the world), which has a V8 gasoline engine as an option
here in the USA. It's the perfect size, weight and power for towing a
single-place sailplane ( I tow a Discus 2). The standard gasoline
engine here or the diesel available in much of the rest of the world
would be OK at sea level, but in my view you need both sufficient mass
and power in the tow vehicle to maintain control and stability.

Yes, I know we'll get posts from the guys who'll tell us they towed
their Duo Discus over the alps using a Fiat 500. That doesn't meant
that it is necessarily a good idea!

Mike

Sadly, some of us remember what a Fiat 500 is (I even owned one)...
See ya, Dave "YO"

wrote:
Sadly, some of us remember what a Fiat 500 is (I even owned one)...
See ya, Dave "YO"

Cheer up! Fiat has started making them again, there is even talk of
bringing them to the US to compete with the Mini. Should be perfect for
towing around an Antares...

On Oct 9, 10:30 pm, Mike the Strike wrote:
Yes, I know we'll get posts from the guys who'll tell us they towed
their Duo Discus over the alps using a Fiat 500. That doesn't meant
that it is necessarily a good idea!

Nobody has ever suggested that - I believe that is a "strawman"
argument.

Towing is simple. Follow these rules, and your rig will be stable in
all conditions and not need stabiliser hitch.

*Make sure that the laden mass of the trailer does not exceed 85% of
the laden mass of the tow car, and preferably less.

*Have 7% of the trailer's actual mass on the hitch. Measure with some
bathroom scales and a length of wood cut to the correct height to fit
between hitch and the scales. It's important to get this number right
- no more, no less. If the 7% value is more than the car's noseweight
limit, you'll just have to keep within that limit and accept a less
than optimum noseweight.

*Carry heavy items in the car, not the trailer, but make sure you
don't exceed the maximum axle load (or end up with your car dragging
its arse along the road). I often put the heaviest
items in the passenger footwell if I'm travelling alone.

*Look after your tyres on both car and trailer. Blow-outs can really
ruin your trip (and your glider!). Trailer tyres should be replaced
every five years and definitely every seven - rubber ages naturally,
whether you use them or not. In winter ideally take the wheels off
and
store them level in a cool dry place wrapped in hessian (not
plastic),
or at least wrap the tyres in hessian on the trailer to keep the UV
off.

*Make sure you run the correct tyre pressures all round. Check before
you set off on every trip. A tyre with low pressure will run hot and
could blow.

Now, I didn't want to mention this earlier as it sounds like willy-
waving, but I once performed a maximum-effort stop from 70 mph in a
light Euro car with an Astir on the back in pretty old trailer (no
Cobra). The car and trailer were well maintained and pulled-up very
quickly in a perfectly straight line. I could have probably let go of
the wheel.


Dan

Dan G wrote:


*Have 7% of the trailer's actual mass on the hitch. Measure with some
bathroom scales and a length of wood cut to the correct height to fit
between hitch and the scales. It's important to get this number right
- no more, no less. If the 7% value is more than the car's noseweight
limit, you'll just have to keep within that limit and accept a less
than optimum noseweight.

We've discussed this one before, and there is no evidence suggesting 7%
is appropriate for glider trailers, as the number comes from a study of
caravans (travel trailers). The more common numbers are 10%-15%, also
with the requirement to stay within the vehicle and hitch load
specifications.

The list does not include the most important factor: speed. Every tow
vehicle and trailer is stable below some speed; unfortunately, there
isn't any safe and easy way to determine this that I know of. I do
suspect most trailer accidents from loss of control could be avoided if
the driver had paid attention to signs of instability in the past, and
drove more slowly as a result.

--
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 11, 9:51 pm, Eric Greenwell wrote:
Dan G wrote:
We've discussed this one before, and there is no evidence suggesting 7%
is appropriate for glider trailers, as the number comes from a study of
caravans (travel trailers). The more common numbers are 10%-15%, also
with the requirement to stay within the vehicle and hitch load
specifications.

I won't disagree, though I'm not sure glider trailers and caravans are
*that* different. I guess the real "rule" is simply having plenty of
weight on the hitch, but not more than the tow vehicle is rated for.


The list does not include the most important factor: speed. Every tow
vehicle and trailer is stable below some speed; unfortunately, there
isn't any safe and easy way to determine this that I know of. I do
suspect most trailer accidents from loss of control could be avoided if
the driver had paid attention to signs of instability in the past, and
drove more slowly as a result.

Isn't that common sense, really?


Dan

Dan G wrote:
On Oct 11, 9:51 pm, Eric Greenwell wrote:
Dan G wrote:
We've discussed this one before, and there is no evidence suggesting 7%
is appropriate for glider trailers, as the number comes from a study of
caravans (travel trailers). The more common numbers are 10%-15%, also
with the requirement to stay within the vehicle and hitch load
specifications.

I won't disagree, though I'm not sure glider trailers and caravans are
*that* different.

Even glider trailers can differ markedly from one another, so it's no
stretch to imagine caravans (less than half the length, 30% wider, and
twice as tall as a glider trailer of the same weight) might act very
differently behind the same tow vehicle.

--
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

Hmmm... where to begin in response to this, Dan. First you claim that a
previous poster was using a "strawman" argument and then you immediately
begin to use the Reductive Fallacy (oversimplification) argument.



It would be nice if we could apply a few simple rules to any problem and
have it solved. However, a vehicle towing a trailer is a _very_ complex
system requiring much more than a few "shoulds" or "Do these x things
and everything will be fine" approaches. In addition to the obvious
things that have been written about in this thread (vehicle weights,
tongue weights, tires and tire pressures, etc.) there are _many_ other
significant factors in play. To name a few (very incomplete list):



--moment arm of the hitch ball to rear axle of the car (one of the most
significant from my experience)

--suspension dynamics of tow vehicle

--aerodynamic shape of the trailer

--combined aerodynamic interactions between tow vehicle and trailer

--environmental considerations where you tow ( prevailing wind, etc.)

--proximity to field effects of passing vehicles, etc.

--necessary or desired speed for trip

-- on and on.......



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.



Larry

"zero one"

USA















"Dan G" wrote in message
ups.com:

On Oct 9, 10:30 pm, Mike the Strike wrote:
Yes, I know we'll get posts from the guys who'll tell us they towed
their Duo Discus over the alps using a Fiat 500. That doesn't meant
that it is necessarily a good idea!

Nobody has ever suggested that - I believe that is a "strawman"
argument.

Towing is simple. Follow these rules, and your rig will be stable in
all conditions and not need stabiliser hitch.

*Make sure that the laden mass of the trailer does not exceed 85% of
the laden mass of the tow car, and preferably less.

*Have 7% of the trailer's actual mass on the hitch. Measure with some
bathroom scales and a length of wood cut to the correct height to fit
between hitch and the scales. It's important to get this number right
- no more, no less. If the 7% value is more than the car's noseweight
limit, you'll just have to keep within that limit and accept a less
than optimum noseweight.

*Carry heavy items in the car, not the trailer, but make sure you
don't exceed the maximum axle load (or end up with your car dragging
its arse along the road). I often put the heaviest
items in the passenger footwell if I'm travelling alone.

*Look after your tyres on both car and trailer. Blow-outs can really
ruin your trip (and your glider!). Trailer tyres should be replaced
every five years and definitely every seven - rubber ages naturally,
whether you use them or not. In winter ideally take the wheels off
and
store them level in a cool dry place wrapped in hessian (not
plastic),
or at least wrap the tyres in hessian on the trailer to keep the UV
off.

*Make sure you run the correct tyre pressures all round. Check before
you set off on every trip. A tyre with low pressure will run hot and
could blow.

Now, I didn't want to mention this earlier as it sounds like willy-
waving, but I once performed a maximum-effort stop from 70 mph in a
light Euro car with an Astir on the back in pretty old trailer (no
Cobra). The car and trailer were well maintained and pulled-up very
quickly in a perfectly straight line. I could have probably let go of
the wheel.


Dan

Larry, I agree.
I drove at one point an extended version of the old Aero Star. This
combination was good for about 60m/h max no wind, with the same sort
of trailers I am towing now. This was ok for the odd retrieve and
contest.


The points you raised were also the things I was looking for in a new
Mini Van. But only one Mini Van met those criteria, the Honda Odyssey.
Low C of G, short coupled between ball hitch and rear independent
suspension. Powerful and fun to drive, comfortable and reasonably good
on gas. In any case I found it handled the Schreder trailer as well as
a Cobra unit, The Schreder trailer Van combination use more gas then
the cobra trailer combo.

With the currant cobra trailer I noted a difference, even though this
one is newer and has shocks. It was not as stable as the other cobra
trailer. Lucky for me I marked my drive way for my first cobra
trailer wheels. I noticed that the trailer was to close to the
garage door. It turns out the wheels are to far forward by at least
10". Also the trailer hitch would not stay down when the trailer is
empty, which all other trailers did with about 15 lb down force
empty. I think that would explain the slightly less stable set-up
In time I will move the axle.

Udo


and everything will be fine" approaches. In addition to the obvious
things that have been written about in this thread (vehicle weights,
tongue weights, tires and tire pressures, etc.) there are _many_ other
significant factors in play. To name a few (very incomplete list):

--moment arm of the hitch ball to rear axle of the car (one of the most
significant from my experience)

--suspension dynamics of tow vehicle

--aerodynamic shape of the trailer

--combined aerodynamic interactions between tow vehicle and trailer

--environmental considerations where you tow ( prevailing wind, etc.)

--proximity to field effects of passing vehicles, etc.

--necessary or desired speed for trip

-- on and on.......

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.

Larry
-

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