[VACList] re: hitch analysis

[Warren Little <wlittle@xxxxxxxxx>]

In response to inquiries for more info on my hitch analysis, I offer the
following.
First some definitions:
ff	upward force on truck at front wheels
fr	upward force on truck at back wheels
fw	downward force on truck at center of gravity due to gravity
	(ie weight of truck)
fb	downward force on truck at the ball
	upward force on trailer at the ball
fc	upward force on truck due to chain of hitch
	downward force on trailer due to chain of hitch
fa	downward force on trailer at center of gravity due to gravity
	(weight of trailer)
ft	upward force on trailer at mid point between wheels
L	wheelbase of truck
C	distance from rear wheels of truck to center of gravity of truck
B	distance from rear wheels of truck to ball
D	distance from ball to chains of hitch
E	distance from ball to center of gravity of trailer
F	distance from ball to mid point between wheels of trailer

For my rig fw=5000 lbs, fa=7000 lbs, L=13.2 ft, C=6.6 ft, B=4.5 ft, D=2
ft,
E=18 ft, F=19 ft.

The force and torque equations are

1:	fw + fb - ff - fr -fc = 0

2:	Cfw - Lff = Bfb - (B +D)fc

3:	fc + fa = fb + ft

4:	(F -E)fa + (F - D)fc = Ffb

We have 4 equations for the 4 unknowns fb, ff, fr, ft.

The solutions of the equations are:

fb = ((F - E)fa + (F - D)fc)/F

ft = fc + fa - fb

ff = (Cfw + (B + D)fc - Bfb)/L

fr = fb - ff - fc + fw

I programmed these four equations into the Excel spreadsheet to get the
tables I gave in my last posting to the list.

Please feel free to use the equations in your own spreadsheet if you
wish.

Jon Fitz suggested to me that a user friendly interface to these, or
perhaps even more detailed equations, might be of interest.

If anyone would like my Excel spreadsheet as an attachment I would be
pleased to send it. I don't believe I can just send it to the list for
people to download.

Warren Little #9302
31 ft 76 Sovereign
92 F250 longbox supercab