Originally Posted by SteveSueMac
I agree with his conclusion and love the demo but agree its a little flawed.
Steve, Benjamin Hu's Lego Hensley Arrow is more than a little flawed. It is significantly flawed, and flawed in favor of the HA versus the conventional hitch.
If we assume the model TV represents a wheelbase of 130" (e.g. a Suburban), the model of the HA would represent a Virtual Pivot Point located about 26" ahead
of the Suburban's rear axle instead of about 25" behind
the rear axle where it should be.
This means the model TV is much less
influenced by lateral force applied via the Lego HA hitch than a real TV would be.
The ball of the "conventional" hitch scales to be about 140" behind the Suburban's rear axle versus an actual distance of about 65".
This means the model TV is much more
influenced by lateral force applied via the Lego"conventional" hitch than a real TV would be.
The ball-to-axle distance for the TT towed by the Lego HA scales to about 90" -- which would correspond to a TT with a body length of about 7'.
The ball-to-axle distance for the TT towed by the Lego "conventional" hitch scales to about 175" -- which would correspond to a TT with a body length of about 18'.
Again, this scaling flaw gives the HA hitch a very large perceived advantage over the "conventional" hitch.
The biggest misrepresentation in the video is the act of simulating a yaw-axis torque applied to the Lego trailer.
And, I'm not talking about whether Mr. Hu applied a greater amount of twist when the TT was connected with the "conventional" hitch.
The misrepresentation is the fact that a real TT is not subjected to a pure yaw-axis torque.
A real TT is subjected to lateral forces which tend to make the TT pivot about its pivot point -- the ball, for a "conventional" hitch, and the VPP, for a HA.
Furthermore, when the TT is moving down the highway, there is no lateral resistance provided by its tires unless the TT swings so that the tires are pointed at an angle to the direction of travel.
Applying a yaw-axis torque to the model TT is an unrealistic simulation of how the HA (or PP) responds in a sway event.
A realistic simulation would be to have the TT tires on a friction-free surface, and load the TT with a lateral force instead of a "twist".
Given the right external loading, a TT will exert a lateral force on the rear of the TV.
With a "conventional" hitch, the force will be exerted on the ball which might be about 65" behind the TV's rear axle.
With a HA or PP, the lateral force will be exerted at the VPP which might be about 25" behind the rear axle.
The shorter moment arm means that less steering torque will be imposed on the TV when the TT is connected via a HA or PP.
Less steering torque means there is less tendency for the driver to overcorrect, and that means there should be less likelihood of loss of control.
The concept is pretty simple, and it has not been simulated correctly by any of the video models I've seen.