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