Trailer weight distribution demonstration

On Tuesday, October 4, 2016 at 8:22:12 PM UTC-4, waremark wrote:
So what is the message? We are normally told not to have much weight on the nose of the trailer, which presumably would adversely affect the balance of the car. To achieve that I have to put luggage etc at the back of my trailer (I tow an Arcus M in a Cobra trailer). What should I do? How much weight should I have on the hook?

The video is a good illustration of the effect of adding mass far away from the pivot point. Anything that adds to the polar moment about the pivot point reduces stability.
The concept of having enough tongue weight is mostly a result of experience that shows tail heavy trailers tow worse than ones that are not.
Consider adding and using a center drawer to stow some heavier stuff near the axle.
Maybe put a few heavy things in the vehicle between the axles.
Also look at what is in the trailer that may not really be needed.
I move the tail weight(13lb for fatty) from the tail to the cockpit when towing my '29. Even that adds a small amount of added stability.
FWIW
UH

I've wondered if adding a small (1/4" - 3/8") anti sway bar to the trailer axle would help in most situations. Granted, proper weight is best, but the anti sway bar may widen the margin.
Thoughts?

At 14:59 05 October 2016, Charlie M. UH & 002 owner/pilot wrote:
I've wondered if adding a small (1/4" - 3/8") anti sway bar to the
trailer
axle would help in most situations. Granted, proper weight is best, but
the
anti sway bar may widen the margin.
Thoughts?

Weighting is important, no doubt. Reducing the weight and therefore the
inertia on the anchored end of the trailer does reduce the possibility of
any swing increasing by increasing the ability of the towing vehicle to
damp the oscillations. The trigger for these oscillations is aerodynamic
caused by the low pressure area between two vehicles as they overtake/are
overtaken. The situation is made worse if the vertical surface is the same
or more than the area in front of the axle. Cobras and Komets are designed
to reduce the side area behind the axle.
I towed a trailer, containing a Grob 103 back from Holland. The nose weight
was close to the maximum limit allowed for my car, theoretically the best
situation to improve stability, however it swayed readily. I have just
towed the same combination over 300miles. Before leaving I increased the
tyre pressures on the trailer from 35psi to 55psi (Max 65psi). The trailer
now tows with no swaying up to the maximum speed limit in the UK (70mph).
It does allow towing at just below 60mph which means I can avoid being
overtaken by large trucks, the condition which is most likely to trigger
swaying. Tyre pressure appears to have a large influence on the stability
of the trailer, greater than loading. Vertical instability is now the major
problem, easily fixed by a stabiliser.

In the early 1970s, my father and I loaded our damaged 201 Libelle into a tall, straight-topped, corrugated-aluminum-and-steel-tube trailer meant for a 16.5M Diamant. Almost unbelievably given the weight of the Diamant wing, it was set up to load wingtips first from the rear. So that's how we loaded the Libelle wings: i.e., spars aft. The fuselage we just rolled into the trailer and tied it down as best we could using the tail tiedown bracket that was in place.

As you can imagine with our short-span bird sitting well aft of where the Diamant would be, the trailer was somewhat tail heavy. Off we went in the family Chevy station wagon (read: heavy, full-size American car from that era) from Cincinnati to the Gehrleins' repair facility in Erie, PA, a 350 mile journey that should have taken about 5 hours.

I have long since suppressed most memories of that terrifying trip but not the lessons of that masters-level, crash course (no pun intended, fortunately) in trailer control. Everything I know about keeping uncooperative trailers in line I learned that day. I almost had to pry my fingers off the steering wheel when we arrived.

I learned how to slow going uphill so I could avoid slowing (not good) or braking (really bad!), and even accelerate slightly if needed on the way down the hill. How to accelerate slightly when being passed by a large truck. Or anything larger than a motorcycle, for that matter. How to watch in the mirror to make certain there were no large trucks overtaking as we reached the top of a hill.

How never to touch the brakes going around a curve. How to hit the throttle to straighten out an incipient tail wag, including when going downhill being passed by a large truck (see "how to slow going uphill", above).

I don't know why we didn't just stop and move things forward, or pile a bunch of stuff in the front of the trailer to get some tongue load. I guess we didn't know any better. Or assumed it was some fundamental flaw in trailer stability. The empty trailer towed fine on the way home, unsurprisingly. If I recall correctly, the subsequent owner of that glider moved the axle back to get some more weight on the tongue even with the heavier, longer-span Diamant in the box, and it towed fine.

To this day, almost 45 years later, I'm still wary of the little twitch in the steering wheel that signals the trailer is moving around and could get squirrelly.

Chip Bearden

On Wednesday, October 5, 2016 at 4:50:51 PM UTC-4, wrote:
In the early 1970s, my father and I loaded our damaged 201 Libelle into a tall, straight-topped, corrugated-aluminum-and-steel-tube trailer meant for a 16.5M Diamant. Almost unbelievably given the weight of the Diamant wing, it was set up to load wingtips first from the rear. So that's how we loaded the Libelle wings: i.e., spars aft. The fuselage we just rolled into the trailer and tied it down as best we could using the tail tiedown bracket that was in place.

As you can imagine with our short-span bird sitting well aft of where the Diamant would be, the trailer was somewhat tail heavy. Off we went in the family Chevy station wagon (read: heavy, full-size American car from that era) from Cincinnati to the Gehrleins' repair facility in Erie, PA, a 350 mile journey that should have taken about 5 hours.

I have long since suppressed most memories of that terrifying trip but not the lessons of that masters-level, crash course (no pun intended, fortunately) in trailer control. Everything I know about keeping uncooperative trailers in line I learned that day. I almost had to pry my fingers off the steering wheel when we arrived.

I learned how to slow going uphill so I could avoid slowing (not good) or braking (really bad!), and even accelerate slightly if needed on the way down the hill. How to accelerate slightly when being passed by a large truck.. Or anything larger than a motorcycle, for that matter. How to watch in the mirror to make certain there were no large trucks overtaking as we reached the top of a hill.

How never to touch the brakes going around a curve. How to hit the throttle to straighten out an incipient tail wag, including when going downhill being passed by a large truck (see "how to slow going uphill", above).

I don't know why we didn't just stop and move things forward, or pile a bunch of stuff in the front of the trailer to get some tongue load. I guess we didn't know any better. Or assumed it was some fundamental flaw in trailer stability. The empty trailer towed fine on the way home, unsurprisingly. If I recall correctly, the subsequent owner of that glider moved the axle back to get some more weight on the tongue even with the heavier, longer-span Diamant in the box, and it towed fine.

To this day, almost 45 years later, I'm still wary of the little twitch in the steering wheel that signals the trailer is moving around and could get squirrelly.

Chip Bearden

My PIK trailer was a bit wiggly when pulling with my little Triumph TR7. It did get rolled when we got run off the road by a truck and ended up with an uncontrollable divergent oscillation.
The glider did not get hurt and flew in my first Nationals 2 days later(another story).
When repairing the trailer I replaced the front frame members with one size larger tubing and extended the tongue area about 8 inches. It was like a different trailer and never wiggled again. Tongue weight was almost exactly the same so my theory was that the longer arm from the tow ball to the oscillation dampers(wheels) was enough to entirely change the dynamics.
FWIW
UH

On 10/5/2016 2:50 PM, wrote:
In the early 1970s...
Snip...
I have long since suppressed most memories of that terrifying trip but not
the lessons of that masters-level, crash course (no pun intended,
fortunately) in trailer control. Everything I know about keeping
uncooperative trailers in line I learned that day.

I learned how to slow going uphill so I could avoid slowing (not good) or
braking (really bad!), and even accelerate slightly if needed on the way
down the hill. How to accelerate slightly when being passed by a large
truck. Or anything larger than a motorcycle, for that matter. How to watch
in the mirror to make certain there were no large trucks overtaking as we
reached the top of a hill.

How never to touch the brakes going around a curve. How to hit the throttle
to straighten out an incipient tail wag, including when going downhill
being passed by a large truck (see "how to slow going uphill", above).

For readers not yet personally acquainted with the need "to hit the throttle
to straighten out an incipient tail wag, including going downhill..." well,
you ain't yet lived life to its fullest. (BTDT!) Kinda like being over VNE and
concluding it would be faster to stop airframe flutter by INcreasing speed
rather than slowing down. Really bad place to be.

Should it happen to you, if you have any sense at all it'll be the sort of
"getting religion" experience that'll stick with you for the rest of your
life! Thanks for sharing, Chip. Yeow!

Bob W.

P.S. Another poster mentioned the good success he obtained by simply
increasing his trailer tire pressures. FWIW, unless you're sufficiently into
higher-performance vehicle handling so's to benefit from
tire-temperature-taking probe technology (and interpretation), another
"sensible rule of thumb" regarding towing glider trailers behind passenger
vehicles is simply to start out by ensuring every tire in contact with the
road is at its recommended (tire, not vehicle) maximum...and *screw* any
misplaced concern about "abbienormal tread wear" or "violating the vehicle's
owner's manual's recommendations." You won't get the former (in the absence of
running "bicycle-width" or "gumball" tires, of course), and no manual writer
can see into a vehicle's future, insofar as what sort of tires with which
it'll eventually be shod. Given today's tires, I'll wager Big Money far more
accidents are contributed to by "too low" tire pressures than "too high." As
always, YMMV...

Bob, I can't tell whether you're questioning my sanity or confessing to having a similar experience. Obviously you can get yourself in a world of trouble very quickly. But we had 350 miles with a barely controllable trailer to try every possible technique and, once the swings passed a certain point, the only thing that worked was to ease on the accelerator. That meant topping the hills quite slowly, keeping a sharp eye for trucks to avoid being overtaken on the downhills, and not using this technique if a lot of downhill remained ahead (the alternative being trundling down the hill much slower than prevailing traffic, which caused other problems, including being overtaken much more often. I should have been more careful in relating the story.

Plus because the trailer was so unstable, all of the excitement began at slower speeds than usual, giving us a little more time to react.

Yeah, it was exciting at times. Kind of like when I was easing down a hill in the snow many years ago and the rear end of my small, rear-wheel-drive car swung out. I wasn't on the brakes but the deceleration from holding it in a lower gear was enough to trigger the skid. I steered into it but that didn't help a bit, even at full lock. I had to gently feather the throttle to straighten it out, at which point I was moving downhill a LOT faster. Fortunately I was almost at the bottom and was able to steer straight and slow it down safely on level ground.

We should have just stopped and redistributed the load that day. Not to be repeated. I will say that some years later, a crew member driving my trailer home was overtaken by a big rig while going downhill on the freeway. When the trailer started oscillating, she didn't hit the brakes but just got off the throttle. That was enough to exacerbate the swings and she ended up jack knifing and sliding off the road, fortunately with no injury and very minor damage.

I'm not sure this posting is going to sound any less crazy than my first one. But, hey, it works for me, although my Cobra trailer with the right tire pressures is hardly felt behind my full-size van.

Chip Bearden

Funny.
I find when my trailers (2 Cobras and a Solaire) starts to oscillate that a quick hard jab on the brakes stops all the bad motions. Doesn't make any difference whether the oscillations are started by an 18 wheeler passing me or by my increasing my speed too much. Acceleration just seems to amplify the swings.

I do find that making sure the trailer is very tongue heavy makes it stable and that tongue light makes it unpredictable.

Technical information for only $26
http://papers.sae.org/2008-01-1228/
Stability and Control Considerations of Vehicle-Trailer Combination.
Hac, A., Fulk, D., and Chen, H., "Stability and Control Considerations of Vehicle-Trailer Combination," SAE Int. J. Passeng. Cars - Mech. Syst. 1(1):925-937, 2009, doi:10.4271/2008-01-1228.

Or http://proceedings.asmedigitalcollec...icleid=1645010
The Effect of Longitudinal Center of Gravity Position on the Sway Stability of a Small Cargo Trailer
Michael G. Gilbert, Daniel A. Godrick and Richard H. Klein
Paper No. IMECE2008-66022, pp. 295-305; 11 pages
doi:10.1115/IMECE2008-66022

Or http://www.scientific.net/AMM.29-32.1420
Study on High-Speed Lateral Stability of Car-Trailer Combination

And many more, courtesy of scholar.Google.com (exclude patents at first)

Oh, and at no cost, there's Nelson Funston's classic OSTIV article
http://journals.sfu.ca/ts/index.php/...e/view/779/737
The Influence of Design Parameters on Glider Trailer Towing Behavior