Dual Cams do like hitch weight - they work by positioning the equalizing weight bars in a saddle that's attached to the trailer A-frame.? When the trailer is straight ahead, the indentations in the end of the equalizing bars are centered on the humps (or cams) in the saddle.? If the trailer turns to one side or the other, the bars ride up on the sides of the cams and the downward pressure of the arms against the side of the cams tries to make the trailer return to a straight-ahead position.
The important point to the dual-cam arrangement is the hitch opposes movement away from a straight ahead position, and aids in returning the tow vehicle and trailer to a straight line.? The tighter you crank the weight distribution arms, the more self-centering force the hitch exerts, so it works best with trailers that have a lot of hitch weight.
You're right - it's the trailer pressing sideways (to the right) against the hitch that makes the front of your rig turn left.? ?The blast of air from the truck's bow wave hits the front half of the trailer, pushing it to the right.? ?At the same time the partial vacuum is pulling the rear of the trailer towards the truck.? Both of these combine to make the front of the trailer lean to the right.? This pushes the hitch to the right, the tow vehicle pivots around it's rear axle and it's front end moves left.? The longer the distance between the tow vehicle's rear axle and the hitch, the more leverage the trailer can exert on the rig's direction of travel.? ?That's why 5th wheels are inherently more stable without needing any kind of sway control devices - their pivot point is directly over the tow vehicle's rear axle.? Side forces from the trailer press directly against the rear axle so they don't have any leverage to affect the direction of the tow vehicle.
A friction bar sway control simply dampens the side to side rotation around the hitch.? ?When you tighten down on the sway bar, you're stiffening the joint between the tow vehicle and the trailer.? ?The hitch opposes the trailer moving off-axis, but once the car and trailer are at an angle, it also resists them getting back into a straight line by the same amount of force.? ?This is why the manufacturers recommend loosening up the sway control if the road is wet, or if there's anything thing else that might reduce traction.? In an extreme case, if the car's front tires lose traction at the beginning of a turn, the sway bar will prevent the rig from turning.? Or if the front wheels lose traction in the middle of a turn, the car and trailer can stay locked into an angle and will continue turning instead of straightening back out.
I like the dual-cam.? I use it to tow an Artic Fox 26X with a 3/4 ton pickup.? Loaded the Arctic Fox weighs about 8500 lbs and has 800-900 lbs of hitch weight.? The dual cam works extremely well for me - the trailer feels almost like a 5th wheel.? Passing trucks and side winds have little or no effect on the rig.
But again, it's anti-sway effectiveness is proportional to the amount of hitch weight - or more precisely, the amount of countering force the equalizing bars are exerting against the hitch.