trailer sway

I finally installed an Alko AKS 1300 (shown at the
same web site) on my Toyota 4 Runner and Cobra (DG808)
after trying everything else short of relocating the
axle and it worked. Expensive but much less trouble
than reworking the trailer.



At 04:48 15 June 2005, Ian wrote:
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

Gary Evans wrote:
I finally installed an Alko AKS 1300 (shown at the
same web site) on my Toyota 4 Runner and Cobra (DG808)
after trying everything else short of relocating the
axle and it worked. Expensive but much less trouble
than reworking the trailer.

I presume the standard ball won't work, because this device would slowly
unscrew it?

The standard ball works fine if....

Most standard balls have flat sides so they can be gripped by a wrench while
the nut on the bottom is being tightened. Carefully mark where these flats
lie on the hitch, and have two small bars welded onto the hitch. This will
keep the ball from turning.


On 6/16/05 7:57 PM, in article Nlose.222$SF5.199@fed1read07, "Greg Arnold"
wrote:

Gary Evans wrote:
I finally installed an Alko AKS 1300 (shown at the
same web site) on my Toyota 4 Runner and Cobra (DG808)
after trying everything else short of relocating the
axle and it worked. Expensive but much less trouble
than reworking the trailer.

I presume the standard ball won't work, because this device would slowly
unscrew it?


--
Bob
bobgreenblattATmsnDOTcom --fix this before responding

Agree with a little weight in the front of the trailer. Add a tool kit,
you may use it. Don't severely overload the trailer tongue, this takes
weight off your steering axle (bad idea).
Agree on using trailer tires, they take more pressure!
Also:
Check tow vehicle shocks, change to heavy duty.
Check tow vehicle front end alignment.
Check tow vehicle and trailer tire pressure.
Fiberglass top trailers may need spoilers added to the vertical fin.
Jim

Dear Rolf
You are up against the basic fact that the weight distribution with such two
seater trailers can be really terrible with regard to forcing excessive rear
overhang. Yes the configuration with fuselage and wing roots to the front
produces the best ease of rigging, but with a serious compromise in towing
stability in that the axle(s) are further forward than desirable. There is
nothing better that you can do than get the axle(s) well back, but too far
and then of course the tongue weight goes up unacceptably. You may still be
able to get some weight out of the front of the trailer and redistribute it
to the rear. The more you can do this the more you can move the axle(s)
back maintaining a constant drawbar weight. Just because a spare wheel
seems not important at 15 to 18 kg, it is actually useful if you can
relocate it from the front end to the rear end somehow, or at least to the
side and rear of the trailer wheel mudguard. Can you fit a stowage tray/box,
sideways pullout on rails, behind the axle and underfloor? This may get
some of the miscellaneous stuff out of the front of the trailer and help get
weight to the rear such that you can then relocate the axle(s) aftwards.

You do not say whether your trailer is single axle or dual axle. If single
axle then you can fit dual axles which, even if the centre position of the
axle set is the same as for single axle, will get some rubber contact with
the road at further back distance than before. I know of so much hassle
with two seaters towed on a single axle, I would never go down that path.
Always double axle for me. Yes the trailer quote to me for such a Cobra
German trailer three years included the suggestion that the dual axle axle
requirement I included was unnecessary. Rubbish I say.

Getting the axles back also helps reduce side area aft of the wheels. To
understand this issue better, go to the rear of your trailer when attached
to your car. Push sideways against the rear end and feel how soft it is in
comparison to when you go to the front end and do the same. Pushing at the
rear causes sway, whereas when you push sideways against the front you feel
the lateral resistance of all the tyres, car plus trailer. So the bow wave
from the passing truck or cross wind through the trees can cause large
trailer sway angles because of the low resistance at the rear to side force.
Side area and rear overhang are tails that wag the dog.

I have had good results with a Hayman Reese sway stabiliser. I have looked
at the ALKO product as on the face of it potentially better. Someone has
commented on this list on the sway stabiliser from Alko and noted the need
to anchor the tow ball. I seem to recollect that on the ALKO website here
in Australia I recently saw this device (which I have seen also in the real
world) AND also shown was the additional ALKO part required to hold the ball
to the tow tongue and prevent the ball being turned by the sway stabiliser.

Fit tyres with stiffer sidewalls.

See also article by Funston in Technical Soaring July 1989, p90-95. If you
want it and can't get it closer to home send me a direct email with a real
world address.

Cheers
Roger Druce
Australia

wrote in message
oups.com...
Howdy -

I know this topic has come up before, but we're searching for the
latest theories:
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?

Thanks!
Rolf