COBRA Anti-Sway Coupler

On Monday, September 7, 2020 at 4:36:06 PM UTC-7, Eric Greenwell wrote:
wrote on 9/7/2020 2:51 PM:
On Monday, September 7, 2020 at 11:30:06 AM UTC-6, Nick Hoare wrote:
To get back to the original posters question the only thing I would say is
that really they are for make a good combination better not a bad
combination good. If it is not safe without an anti-sway hitch it probably
won't be safe with one, you will just be going a bit faster when it all
goes wrong.

Nick is entirely correct. You can't fix an unstable trailer with an antisway device, but you can make up for a (slightly) unsatisfactory tow vehicle. Once again, MASS + longer wheelbase = better stability. And adding weight to the tow vehicle does NOTHING to increase the stability of the trailer, and the higher loading on the vehicle's rear wheels is likely to make a sway problem worse. (Think: Moment of Inertia.)

That being said, some weight on a lightly loaded rear axle will help with traction, but not stability.

Generally, it's the characteristics of the tow vehicle and trailer that determines
the stability of the combination. We all know a trailer might tow better with one
vehicle but not the other one. My motorhome and mini-van illustrate this principle
well: the motorhome can tow the trailer much faster for the same wiggle than the
van can.

So, by adding weight to the tow vehicle (usually between the axles but favoring
the rear axle), then raising the tire pressures to match the new weight, can yield
a more stable combination. Using a friction damping device like the Cobra clamp
coupler can also increase the stability of the combination. There are other
devices to increase the damping that are frequently used on travel trailers, but
the Cobra unit is easy to use.


--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorg...ad-the-guide-1

Adding weight to the tow vehicle won't much difference except to slow down its rate of acceleration. This is because the suspension and tires aren't designed to handle this extra weight. A trailer-vehicle combination is a very complex spring-mass mechanical system. Such systems will have a natural resonant frequency. This paper gives an idea of just how complex these systems a
https://tinyurl.com/yylt9uj3
The bottom line is that the critical speed, above which the car-trailer combination becomes unstable, is determined by:
1. mass of the car.
2. mass of the trailer.
3. distance of the hitch from the CG of the car.
4. damping provided by the car and trailer suspension.
The car's manufacturer has already taken all of this into account to come up with (2) the maximum mass of the trailer (they will have to estimate the trailer's suspension damping). Eric's suggestion was to add weight to the car to move the CG rearward. This is a self-limiting trick because you are always dealing with the maximum combined vehicle weight, which you will be pushing with these smaller cars.

There are suspension mods you can make to increase the stiffness (damping) of the suspension. Of course, increasing tire pressure increases their stiffness, which is important. Personally, I have added airbags to my F250 pickup for towing a travel trailer that can weigh upwards of 10,000 lb fully loaded.

Ultimately, there is a speed above which the car-trailer combination becomes unstable. Driving at this speed means you have no stability margin and a disturbance (wind gust, sudden steering movement, passing truck) will make you unstable. You can't recover from this - it happens too fast and steering/braking inputs just make it worse (see the videos). So you need to drive at a slower speed to give yourself some margin, probably at least 10 mph slower.

Tom

One adisional factor is the distance of the hitch from the rear axle. Less is more. In a perfect world you would put the pivot point between the rear wheels of the tow vehicle. There are two hitches for travel trailers that atempt to achive/simulate this. The Hensley does it with some fancy linkages, but eliminates the tow ball as a result. But in any event, some tow vehicle mass can be replaced with tow geometry. Not that I am recommending this, but I have seen a duo towed with a VW bottle. I towed a 304cz with a bottle, and the safe speed iwas about 10mph slower than my ukonxl. The upon was 2 x the mass, but much farther from the axle to the hitch

You REALLY need to get glasses. Or a bigger keyboard. Some parts of this post looks like a Google Translation from Klingon.

VW bottle?

2G wrote on 9/7/2020 9:31 PM:
On Monday, September 7, 2020 at 4:36:06 PM UTC-7, Eric Greenwell wrote:
wrote on 9/7/2020 2:51 PM:
On Monday, September 7, 2020 at 11:30:06 AM UTC-6, Nick Hoare wrote:
To get back to the original posters question the only thing I would say is
that really they are for make a good combination better not a bad
combination good. If it is not safe without an anti-sway hitch it probably
won't be safe with one, you will just be going a bit faster when it all
goes wrong.

Nick is entirely correct. You can't fix an unstable trailer with an antisway device, but you can make up for a (slightly) unsatisfactory tow vehicle. Once again, MASS + longer wheelbase = better stability. And adding weight to the tow vehicle does NOTHING to increase the stability of the trailer, and the higher loading on the vehicle's rear wheels is likely to make a sway problem worse. (Think: Moment of Inertia.)

That being said, some weight on a lightly loaded rear axle will help with traction, but not stability.

Generally, it's the characteristics of the tow vehicle and trailer that determines
the stability of the combination. We all know a trailer might tow better with one
vehicle but not the other one. My motorhome and mini-van illustrate this principle
well: the motorhome can tow the trailer much faster for the same wiggle than the
van can.

So, by adding weight to the tow vehicle (usually between the axles but favoring
the rear axle), then raising the tire pressures to match the new weight, can yield
a more stable combination. Using a friction damping device like the Cobra clamp
coupler can also increase the stability of the combination. There are other
devices to increase the damping that are frequently used on travel trailers, but
the Cobra unit is easy to use.
https://sites.google.com/site/motorg...ad-the-guide-1

Adding weight to the tow vehicle won't much difference except to slow down its rate of acceleration. This is because the suspension and tires aren't designed to handle this extra weight. A trailer-vehicle combination is a very complex spring-mass mechanical system. Such systems will have a natural

... Eric's suggestion was to add weight to the car to move the CG rearward. This
is a self-limiting trick because you are always dealing with the maximum combined
vehicle weight, which you will be pushing with these smaller cars.

My suggestion was in the context of towing with a pickup or a minivan, both of
which can have a wide range of weight from empty to fully laden; for my minivan,
that is over 1000 pounds, and the pickups I've owned it can be as much as 3000
lbs. So, it is possible to add significant weight to these vehicles, which can aid
in increasing the stability of the vehicle/trailer combination, and still obey the
vehicle weight ratings. Please note I'm not saying this is the best way to achieve
higher-speed stability, but only that it is a workable method.


--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorg...ad-the-guide-1

I wonder if this would sway... https://www.youtube.com/watch?v=o6HOXghLG94

On 9/8/2020 5:08 AM, RR wrote:
One adisional factor is the distance of the hitch from the rear axle. Less is more. In a perfect world you would put the pivot point between the rear wheels of the tow vehicle. There are two hitches for travel trailers that atempt to achive/simulate this. The Hensley does it with some fancy linkages, but eliminates the tow ball as a result. But in any event, some tow vehicle mass can be replaced with tow geometry. Not that I am recommending this, but I have seen a duo towed with a VW bottle. I towed a 304cz with a bottle, and the safe speed iwas about 10mph slower than my ukonxl. The upon was 2 x the mass, but much farther from the axle to the hitch

--
Dan, 5J

On Tuesday, September 8, 2020 at 9:02:37 AM UTC-7, Eric Greenwell wrote:
2G wrote on 9/7/2020 9:31 PM:
On Monday, September 7, 2020 at 4:36:06 PM UTC-7, Eric Greenwell wrote:
wrote on 9/7/2020 2:51 PM:
On Monday, September 7, 2020 at 11:30:06 AM UTC-6, Nick Hoare wrote:
To get back to the original posters question the only thing I would say is
that really they are for make a good combination better not a bad
combination good. If it is not safe without an anti-sway hitch it probably
won't be safe with one, you will just be going a bit faster when it all
goes wrong.

Nick is entirely correct. You can't fix an unstable trailer with an antisway device, but you can make up for a (slightly) unsatisfactory tow vehicle. Once again, MASS + longer wheelbase = better stability. And adding weight to the tow vehicle does NOTHING to increase the stability of the trailer, and the higher loading on the vehicle's rear wheels is likely to make a sway problem worse. (Think: Moment of Inertia.)

That being said, some weight on a lightly loaded rear axle will help with traction, but not stability.

Generally, it's the characteristics of the tow vehicle and trailer that determines
the stability of the combination. We all know a trailer might tow better with one
vehicle but not the other one. My motorhome and mini-van illustrate this principle
well: the motorhome can tow the trailer much faster for the same wiggle than the
van can.

So, by adding weight to the tow vehicle (usually between the axles but favoring
the rear axle), then raising the tire pressures to match the new weight, can yield
a more stable combination. Using a friction damping device like the Cobra clamp
coupler can also increase the stability of the combination. There are other
devices to increase the damping that are frequently used on travel trailers, but
the Cobra unit is easy to use.
https://sites.google.com/site/motorg...ad-the-guide-1

Adding weight to the tow vehicle won't much difference except to slow down its rate of acceleration. This is because the suspension and tires aren't designed to handle this extra weight. A trailer-vehicle combination is a very complex spring-mass mechanical system. Such systems will have a natural

... Eric's suggestion was to add weight to the car to move the CG rearward. This
is a self-limiting trick because you are always dealing with the maximum combined
vehicle weight, which you will be pushing with these smaller cars.

My suggestion was in the context of towing with a pickup or a minivan, both of
which can have a wide range of weight from empty to fully laden; for my minivan,
that is over 1000 pounds, and the pickups I've owned it can be as much as 3000
lbs. So, it is possible to add significant weight to these vehicles, which can aid
in increasing the stability of the vehicle/trailer combination, and still obey the
vehicle weight ratings. Please note I'm not saying this is the best way to achieve
higher-speed stability, but only that it is a workable method.


--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorg...ad-the-guide-1

It is important to actually weigh the loaded tow vehicle and trailer to ensure that you are within the GCVW - most people don't. This rating is NOT arbitrary. I actually had one manager of an RV trailer dealership tell me I could exceed the rated tow capacity by a large amount!

Tom

On Tuesday, September 8, 2020 at 10:26:49 AM UTC-7, Dan Marotta wrote:
I wonder if this would sway... https://www.youtube.com/watch?v=o6HOXghLG94

On 9/8/2020 5:08 AM, RR wrote:
One adisional factor is the distance of the hitch from the rear axle. Less is more. In a perfect world you would put the pivot point between the rear wheels of the tow vehicle. There are two hitches for travel trailers that atempt to achive/simulate this. The Hensley does it with some fancy linkages, but eliminates the tow ball as a result. But in any event, some tow vehicle mass can be replaced with tow geometry. Not that I am recommending this, but I have seen a duo towed with a VW bottle. I towed a 304cz with a bottle, and the safe speed iwas about 10mph slower than my ukonxl. The upon was 2 x the mass, but much farther from the axle to the hitch

--
Dan, 5J

At only 50 hp I wouldn't be taking it in the mountains (or hills, for that matter).

Tom

Gotta admit, it's a pretty cute idea. (Horsepower deficiency aside.)