To: Magnet
The most common application of a wiffeltree is on a wagon that is drawn by two horses.
It is a bar that pivots at the center and is attached to a draw bar which is in turn attached to the wagon. The horses are usually attached to the wiffeltree and actually push against it and cause the wagon to move forward. If one horse walks faster or exerts more force than the other horse the bar will pivot and the forces will balance out. There is a variartion of this and it is called a double tree and is used when four horses are in the hitch. It is also used in some aircraft flight control systems. I know it was used in the S-58 tail roitor servo and, I believe it is used in the CH47 flight control system.
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The Cat