(sorry if this thread has already been beaten to death; I'm still 9 days behind
in
reading the postings)---on the subject of fishtailing trailers,
>Ray Gibbons writes"This is almost guaranteed to cause fishtailing. When you
>load the
>trailer, load it so that you maintain at least 10% of the total weight on
>the tongue. When towing a car, this generally would mean having the
>middle of the car somewhat forward of the trailer axle(s) and the engine
>of the car in the front of the trailer. "
He's right--and I think the best way to put it is to make sure that the mass
center
(center of gravity) of the trailer+payload is forward of the trailer axle. (If
dual
axle, I don't know exactly what is required for stability). I believe that
problem to
be similar to that of tricycle vs conventional (tail wheel) landing gear on
aircraft.
The (older) tailwheel variety are prone to the unstable behavior known as
ground
looping. Cause of that instability is fact that the mass center is aft of the
main
(front) gear. The (newer) tricycle gear (nose gear) aircraft have mass center
fwd of
main gear, and are stable on rollout. A free-body diagram (plan view) during
rollout
(assuming a small crab angle) will convince you that this instablity
exists--the
restoring moment is in opposite directions in the two cases. Same principle
applies
to the trailer if loaded so that the mass center is aft of the axle.
Note that if some dunderhead loads the (single axle) trailer so that the mass
center
is behind the axle, then tries to hook it up to the car, he will realize that
something is amiss--has to push the tongue down to connect. But if the hitch
is
already connected and the lbc/new deepfreeze/hoss is loaded into the aft
portion of
the trailer, it isn't so obvious. The subsequent behavior of the trailer may
be
obvious though, and can and has caused seriour accidents.
Move ole dobbin forward, Ray.
A reminder--someone pointed out earler that there would be some vintage car
races
sunday 27 Nov. at 5:00 pm (time zone?) on ESPN.
Best regards, and happy turkey day!
-------------------------------------
Name: Ray W. James
Texas Transportation Institute
Civil Engineering Department, Texas A&M University
E-mail: Ray James <rwj4123@sigma.tamu.edu>
Date: 11/22/94
Time: 17:41:45
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