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Re: ? Tail-Heavy Trailer Sway
Joe wrote:
> I got really curious about this, and studied it for a long time (I'm an
> engineer). There was a good thread on this at woodall's RV forum. I have
> found no frank discussion of it by anybody who has broken it down into its
> component forces. It's hard to explain it using ASCII here. But my opinion
> is this:
>
> First off, it's clear that trailers can amplify their swaying until you
> crash. They don't do it all the time, but they can, and that's what
> interests me. They have no power of their own to bring to the table. The
> energy to do this comes from the tow vehicle. The trailer sways like a
> pendulum, sort of (I admit the forces holding a trailer back are not exactly
> like gravity in this analogy). A pendulum can be powered by a wide variety
> of motions. One of those motions is moving the pendulum's pivot point side
> to side. I think this is the motion we want.
>
> The forces on the trailer come from its tires and the tow vehicle. I was not
> interested in any other forces. "front loaded" trailers are trailers where
> the center of gravity is in front of the tires. When the tires are pushing
> the trailer sideways (during sway), the center of gravity is in front of
> that force. Since the side force doesn't go exactly through the center of
> gravity, the weight of the trailer pushes sideways on the tow vehicle.
>
> The inertia of the swaying trailer pushes the tow vehicle from side to side.
> The difference in loading is simply this. If the center of gravity is in
> front of the wheels, it pushed the tow vehicle one way, and if it's behind
> the wheels, it pushes the two vehicle the other way. One cancels the sway,
> and the other amplifies it.
>
I don't know if amplification is the correct term. Poor loading will
increase the sensitivity of a tow vehicle and trailer to winds and side
drafts from big trucks, but I don't understand how the forces could
actually be amplified. In my experience the side-to-side swaying is
amplified or increased by the driver trying to offset the swaying by
steering out of it.
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