One or two axles

My impression, having towed many glider trailers over the years, is
that trailers where the heavy wing roots are at the front of the
trailer tow better than those where they are at the back. This is
irrespective of nose weight and number of wheels, and would make sense
in that such trailers would have a smaller moment of inertia behind
the car. The disadvantage is that (assuming the axle is in the right
place for weight balance) you have a greater overhang behind the
wheels, so are more likely to sideswipe things when manoeuvring in
tight situations.

Accurate alignment of the trailer wheels and using the correct springs
and dampers for the weight of the trailer are also important. One four
wheel trailer I used to tow was known to have a slightly bent front
axle stub after an argument with a stone gatepost and was a bitch to
tow.

Derek Copeland


On Nov 5, 3:14*pm, Andy wrote:
On Nov 4, 9:09*am, Eric Greenwell wrote:

glider wrote:
My 18M ASH 26 E Cobra trailer has the 1300 kg (2870 pounds) Al-Ko axle,
which is adequate for even an Open Class motorglider like the Nimbus 4M
a friend has. Al-Ko offers the same style axles up to 8000 pound
capacity, but I don't know what capacities Cobra offers. I suspect the
major reason for choosing the dual axle trailer is for more stability.

--

*I have a big *heavy trailer for a vintage two place. The trailer had
dual axles and would sway at normal cruise speeds. Add a lot of weight
in front and it made no difference. Increase tyre pressure and still
no improvement.
*Converted to single axle and problem is solved.

Do you have a guess as to why it's stability improved?

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* "A Guide to Self-launching Sailplane Operation" atwww.motorglider.org

I can imagine why people think a dual axle would be more stable but
this was never my experience. I found when my dual axle trailer got
pushed off line (as by a passing 18-wheeler) it was slightly more
persistent in trying to shove the car around - I suspect because it
wanted to keep going where the dual wheels were pointed. I recall more
shimmy-ing and vibration, but never more stability.

The only change I've ever made to the whole vehicle-trailer system
that improved stability was to get a heavier vehicle with a large tire
contact patch and a short distance between the rear wheels to the ball
(in my case a VW Tourareg). That made a huge difference - I've never
had the least amount of sway towing - all the way up to 105 mph. (No,
I don't tow that fast normally). My two generations prior tow vehicle
(a VW Scirocco) actually got spun around backwards by a glider trailer
on straight dirt road by a 20 mph tailwind.

The vehicle and trailer is a dynamic system - so the sway
characteristics are determined by the combination. Given the long
moment arms and significant rotational inertias of a glider trailer, I
believe the biggest stabilizing force is the way that rotational
inertia is transmitted into the tow vehicle and how the tow vehicle's
weight, geometry, suspension and tires damp it all out. I've never
found changing tongue weight or the number of axles to have anything
but minor effects on stability. Since glider trailers are more alike
than they are different when compared to other types of trailers I
suspect you can find out a lot about what works by talking to glider
owners with different tow vehicles more than different trailer
configurations.

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