On Mon, 13 Jun 2005 08:15:23 -0700, rolfh wrote:

We're towing a DG-500M in a Cobra trailer, and it has a definite sway,
fortunately it usually damps fairly well. Life was worse with a strong
crosswind. We had 2 thoughts:
1. tonuge weight - are we shooting for tongue weight about 10% of the
total trailer weight?
2. Hitch height - any thoughts?

I used to own a half share in a Nimbus 2. My partner and I had both
previously rolled a glider trailer, writing off the car, in separate
incidents with different trailers. So when we discovered the home built
Nimbus trailer could not be towed over 80km/hr we were determined to fix
it.

Our solution was:

1) We moved the trailer axle back to increase the tow ball weight. We
aimed for 50kg but ended up with close to 60kg. Up from about 20kg. 50kg
is near the limit of most cars, above this and you will need to tow with a
truck.

2) We bought a "Trapezium" towbar stablizer. This is a device which
bolts onto the towbar. It has a mechanism which moves the tow ball from
side to side as the trailer rotates around the tow ball. The effect
of this is to move the pivot point well forward of the tow ball, close to
the rear axle of the tow vehicle. This changes the geometry of the system
and radically reduces the tendency to sway. Google found a writeup on this
device on the bottom of this page.

http://www.swift-owners-club.co.uk/s...abilisers.html

It is a South African invention, originally developed by a glider pilot.
It is VERY effective with a glider trailer due to the length of the
trailer. I don't know whether they are still available, but if you find
one, be sure to know they work.

These two in combination resulted in a trailer which was stable at speeds
over 120 km/hr. I was never brave enough to try towing any faster.

Double axle trailers are also much more stable. If the mod is done
carefully, adding a second axle to a trailer can often provide a permanent
fix.

Of course you must have an appropriate tow car. Beware, modern cars are
lighter, but old glider trailers remain the same.

Many pilots only discover that the car they own is not suitable for towing
the glider that they fly after they have successfully completed their
first outlanding. Worst still, the discovery is often made with an
inexperienced friend driving the car ...

Have fun.

Ian