Dual axle sway

The big enclosed trailer was made in the UK and the running gear was
from Germany. The big Tundra did a good job towing until about 60
MPH when the trailer would start to sway. I'll fix that...easy. I toss
in a couple of bags of crushed rocks in front. No change. Another bag
was added to the front for a total of 120 pounds as I recall.
Amazingly, there was no additional tongue weight. How can that be?
The sway was just as exciting.
I'll fix that! Now it has a new single axle and all is well.
GA

On 27 Feb, 23:07, glider wrote:
*The big enclosed trailer was made in the UK and the running gear was
from Germany. * The big Tundra did a good job towing until about 60
MPH when the trailer would start to sway. I'll fix that...easy. I toss
in a couple of bags of crushed rocks in front. No change. Another bag
was added to the front for a total of 120 pounds as I recall.
Amazingly, there was no additional tongue weight. How can that be?
*The sway was just as exciting.
* I'll fix that! Now it has a new single axle and all is well.
*GA

There was a misalignment of the twin axles on the trailer and an
oscillation set up by the conflict between that making the tail of the
trailer sit out slightly and the aerodynamic forces trying to
straighten it up? I had a trailer delivered with a misaligned axle
so it can happen.

John Galloway

"glider" wrote

The big enclosed trailer was made in the UK and the running gear was
from Germany. The big Tundra did a good job towing until about 60
MPH when the trailer would start to sway. I'll fix that...easy. I toss
in a couple of bags of crushed rocks in front. No change. Another bag
was added to the front for a total of 120 pounds as I recall.
Amazingly, there was no additional tongue weight. How can that be?
The sway was just as exciting.
I'll fix that! Now it has a new single axle and all is well.

It is not possible to add weight in the front of a trailer, without making
the tongue weight higher. Perhaps your measuring ability was not able to
detect a change, but I guarantee there was some change. Depending on the
weight of the trailer, and the percentage of total load that is on the ball,
170 pounds may not have been enough to change the percentage of tongue
weight far enough to make much difference.

If you had real numbers, such as starting tongue weight, distance of the
axles from the ball, total trailer weight, added amount of weight and
distance from the ball, we could tell you exactly how much different
conditions changed, and what the percentage of the total load was on the
tongue.

Dual axles set up correctly are more stable than single axles, if
percentages of tongue weight to axle/s weight it the same for both cases.
Every time. No debate. To argue differently is to say you do not
understand the variables and the physics of trailer set-up.

By removing the front axle and making it into a single axle, you have
increased the percentage of tongue weight, and eliminated the possibility of
poor dual axle alignment, and poor dual axle suspension set-up.

I am appalled by the tales of poor towing glider trailers. If the trailer
manufactures can not get thing right, they have no business making trailers,
at all. Trying to make the tongue weight so light that a huge trailer can
be towed with a compact car with no beefed up rear suspension using a flimsy
bumper hitch or such, is near criminal.

Even though a person should not want to, or for safety reasons never tow a
trailer at 85 MPH, a trailer should be able to go those speeds and have no
stability problems. If it can't do that, the trailer is not stable enough,
and the manufacturer should go back to the drawing board.

How much of the problem is caused by the person putting the trailer in the
glider? By that question, I mean deciding how the glider is placed, What
particular glider is placed, and how the wings are stowed in what location
and in what supports?

I do not know the answer to the above questions. If problems are arising by
people selecting a certain glider vs. another for a generic trailer, and how
they place the load and come up with tongue weight percentages, then the
problem is the person, not the manufacturer. I don't know how the blame
goes, or if the trailer manufacturer is off the hook.

Summarizing, line up your axles, put at least 15 percent of the total
trailer weight on the tongue, and tow as safe as you can steer and stop.
Sway should never be a factor.
--
Jim in NC

Summarizing, line up your axles, put at least 15 percent of the total
trailer weight on the tongue, and tow as safe as you can steer and stop.
Sway should never be a factor.
--
Jim in NC

I'm certainly not an expert, but I've never heard a recommendation as
high as 15% of gross on the tongue. My Komet single axls has a squeek
under 10% (175 lbs on the tongue, 1,876 gross), and is rock steady at
all legal towing speeds (and well beyond).

"Grider Pirate" wrote in message
...


Summarizing, line up your axles, put at least 15 percent of the total
trailer weight on the tongue, and tow as safe as you can steer and stop.
Sway should never be a factor.
--
Jim in NC

I'm certainly not an expert, but I've never heard a recommendation as
high as 15% of gross on the tongue. My Komet single axls has a squeek
under 10% (175 lbs on the tongue, 1,876 gross), and is rock steady at
all legal towing speeds (and well beyond).

I went online and found a few sites as documentation, quickly. It would
seem you are at the lower recommended tongue weight, and I was using the
higher limit. As long as glider trailers are, that contribute to poor
handling, I would think being closer to the upper limit would be wise. It
seems as though you have found your weight to be satisfactory, though. I
won't argue with your success, but will argue with people using ridiculous
light tongue weights, then wondering why they have sway problems when they
push the driving speeds.

Again, I will say that you (everyone) should be able to drive a trailer
faster than you feel comfortable driving for the traffic and highway
conditions, and never experience sway. There is no reason to put up with it
when it is so easy to prevent, totally.

**From an online travel trailer site
http://changingears.com/rv-sec-tow-vehicles-understand.shtml#_tongue

Tongue Weight or King Pin Weight
Tongue Weight (also called Tongue Load) is the actual weight pressing down
on the hitch ball by the trailer. The recommended amount of Tongue Weight is
10-15% of the GTW.

**From "How Stuff Works"
http://www.howstuffworks.com/auto-parts/towing/towing-capacity/information/tongue-weight.htm

Most experts agree that an acceptable tongue weight for any trailer is
somewhere between 9 and 15 percent of the gross trailer weight (GTW).

***From a Sherline Products web site
http://www.sherline.com/lmbook.htm#refrn9

RECOMMENDED HITCH WEIGHT PERCENTAGES
TYPE OF TRAILER
PERCENT OF WT. ON TONGUE

Single Axle
10% minimum/15% maximum

Tandem Axle
9% to 15%

Travel Trailer
11% to 12%

5th Wheel
15% to 25%

On Feb 27, 4:07*pm, glider wrote:
*The big enclosed trailer was made in the UK and the running gear was
from Germany. * The big Tundra did a good job towing until about 60
MPH when the trailer would start to sway. I'll fix that...easy. I toss
in a couple of bags of crushed rocks in front. No change. Another bag
was added to the front for a total of 120 pounds as I recall.
Amazingly, there was no additional tongue weight. How can that be?
*The sway was just as exciting.
* I'll fix that! Now it has a new single axle and all is well.
*GA

I'd bet there's a lot more to it than just tongue weight.

Tires on both the trailer and towing car matter a lot.
A towing vehicle with soft lateral suspension compliance and/or high
CG. (Think Jeep)
Trailer with a high moment of inertia. (lots of weight in front AND
back.)

"bildan" wrote

I'd bet there's a lot more to it than just tongue weight.

Tires on both the trailer and towing car matter a lot.
A towing vehicle with soft lateral suspension compliance and/or high
CG. (Think Jeep)
Trailer with a high moment of inertia. (lots of weight in front AND
back.)

The factors mentioned do come into play, but don't discount the very large
effect that tongue weight does have on towing.

I have towed many trailers, and occasionally had a load that was too large
to get the tongue weight I wanted. I am talking about one specific load
here, a very large utility building, that I even had to get oversized load
permits to tow. It very heavy, had a high center of gravity, lots of weight
in front and way in the back, bad vortex generating capability, and much
wider than the axle, making it lean very easily with sway or sideways road
inclines. Probably many times worse than any glider trailer could ever be.

After deciding I could not tow it fast enough to keep from creating a
traffic hazard, I got about 20 concrete blocks and put them in the very
front of the building. This trailer that would not tow straight at 25 mph
suddenly was straight as an arrow at 50 mph, and probably would be even
faster.

So yes, do all you can to get good tires, suspension, and improve all the
factors you can with your trailer.

Then, get some scales, or use good estimating, and get between 10 and 15
percent of the gross trailer weight onto the trailer hitch. It really isn't
magic, but it is as close as it comes!
--
Jim in NC

Morgans wrote:
"bildan" wrote

I'd bet there's a lot more to it than just tongue weight.

Tires on both the trailer and towing car matter a lot.
A towing vehicle with soft lateral suspension compliance and/or high
CG. (Think Jeep)
Trailer with a high moment of inertia. (lots of weight in front AND
back.)


The factors mentioned do come into play, but don't discount the very large
effect that tongue weight does have on towing.
There have been plenty of glider trailers that swayed, even with high
tongue weights, and plenty of glider trailers that were stable without
high tongue weights. The tow vehicle is a critical component in the
equation, and going to 15% tongue weight simply will not be good enough
for some combinations to go the speeds the owners want to drive. Tires
are known to make huge differences in some situations.

Note that none of those recommendations you link to are based on
trailers anything like our glider trailers, and are somewhat suspect for
that reason.

It is certainly worth trying higher tongue loads, particularly if you
achieve it by moving the axle towards the back, or by moving stuff from
behind the axle to ahead of it. It is important that tongue load not
exceed the trailer manufacturers ratings, the tow vehicles ratings, or
the hitch ratings.

--
Eric Greenwell - Washington State, USA (netto to net to email me)

- "Transponders in Sailplanes - Feb/2010" also ADS-B, PCAS, Flarm http://tinyurl.com/yb3xywl

- "A Guide to Self-launching Sailplane Operation Mar/2004" Much of what you need to know tinyurl.com/yfs7tnz