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Whippletree (mechanism)

File:Leader bars.jpg
A set of whippletrees or leader-bars for the two leaders of a four-horse team.

A whippletree (or whiffletree) is a mechanism to distribute force evenly through linkages. It consists of a bar pivoted at or near the centre, with force applied from one direction to the pivot, and from the other direction to the tips. Several whippletrees may be used in series to distribute the force further. Whippletrees may be used either in compression or tension.


Draught whippletrees

A single horse ploughing – the whippletree is the horizontal wooden bar just in front of the plough.
Whippletrees are used in tension to distribute forces from a point load to the traces of draught animals (the traces are the chains or straps on each side of the harness, on which the animal pulls). For these, the whippletree consists of a loose horizontal bar between the draught animal and its load. The centre of the bar is connected to the load, and the traces attach to its ends. Whippletrees are used especially when pulling a dragged load such as a plough, harrow, log or canal boat or for pulling a vehicle (by the leaders in a team with more than one row of animals).

A swingletree (or singletree) is a special kind of whippletree used for a horse-drawn vehicle, and the term swingletree is sometimes used for draught whippletrees generally.

A whippletree balances the pull from each side of the animal, preventing the load from tugging alternately on each side. It also keeps a point load from pulling the traces in onto the sides of the animal.

If several animals are used abreast, further whippletrees may be used behind the first. Thus, with two animals, each will have its own whippletree, then a further whippletree will balance the loads from their two whippletrees – this arrangement is sometimes known as a double-tree, or for the leaders in a larger team, leader-bars. With three or more animals abreast, even more whippletrees are needed; some may be made asymmetrical to balance odd numbers of animals. Multiple whippletrees balance the pulls from the different animals, ensuring that each takes a fair share of the work.

File:Triple whippletree set.svg
A set of whippletrees for a three-animal team.

Other agricultural whippletrees

Whippletrees may also be used in modern agriculture, for example to link several ganged agricultural implements such as harrows, mowers or rollers to a tractor. In this case the effect is to combine several small loads to a single load at the tractor hitch (the reverse of the use for draught animals).

Windscreen (windshield) wipers

File:Heckscheibenwischer kl.jpg
A standard automobile windscreen wiper uses whippletrees to distribute the force of the wiper arm evenly across the blade.

A series of whippletrees are used in compression in a standard windscreen wiper, to distribute the point force of the sprung wiper arm evenly along the wiper blade.


Some designs for large telescopes use whiffletrees, attributed to Grubb [1], to support the optical elements. The tree provides for distributed mechanical support, thereby reduces localised mechanical deflections, which in turn reduces optical distortion. Unlike the applications described above, which are two dimensional, these whiffletrees are 3D designs[2] since the tree has to support multiple points.

See also

  • Boat trailer, which uses this mechanism to evenly distribute force across the hull of the boats it carries.
  • Differential (mechanical device), which does for torque what each layer of a whippletree does for force.
  • Draught animal
  • Mobile (sculpture), similar principles applied in art.
  • Paraglider wing, in which a load is distributed by multiple strings, but without rigid elements.
  • PLate OPtimizer, CAD program for distribution of whiffltree support elements in telescope mirror cell design
  • Proteus (WAM-V), catamaran with whippletree suspension


External links


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