Projectile Throwing Engines
Sir Ralph Payne-Gallwey
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PART III THE BALLISTA

BALLISTA  FOR  DISCHARGING  HEAVY  ARROWS OR JAVELINS
FIG.13. BALLISTA FOR DISCHARGING HEAVY ARROWS OR JAVELINS. Approximate scale : .in. = 1 foot.

THIS engine is here shown ready for discharge with its bow-string drawn to its full extent by the windlass.

The heavy iron-tipped arrow rests in the shallow wooden trough or groove which travels along the stock.

The trough has a strip of wood, in the form of a keel, fixed beneath it. This keel travels to or fro in a dove-tailed slot cut along the upper surface of the stock for the greater part of its length. ( F, fig. 14.)

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THE BALLISTA

The arrow is laid in the trough before the bow-string is stretched. (A, B, fig. 14.)

The ballista is made ready for use by turning the windlass. The windlass pulls back the sliding trough, and the arrow resting in it, along the stock of the engine, till the bow-string is at its proper tension for discharging the projectile. ( Fig.13.).

As the trough and the arrow are drawn back together, the arrow can be safely laid in position before the engine is prepared for action.

The catch for holding the bow-string, and the trigger for releasing it, are fixed to the solid after-end of the wooden trough. ( Fig. 14.)

The two ratchets at the sides of the after-end of the trough travel over and engage, as they pass along, the metal cogs fixed on either side of the stock. ( Fig.14. )1

By this arrangement the trough can be securely retained, in transit, at any point between the one it started from and the one it attains when drawn back to its full extent by the windlass.

As the lock and trigger of the ballista are fixed to the after-end of the sliding trough ( fig. 14. ), it will be realized that the arrow could be discharged at any moment required in warfare, whether the bow-string was fully or only partially stretched.

In this respect the ballista differed from the crossbow, which it somewhat resembled, as in a crossbow the bow-string cannot be set free by the trigger at an intermediate point, but only when it is drawn to the lock of the weapon. It will be seen that the ballista derives its power from two arms ; each with its separate skein of cord and pair of winches.

These parts of the ballista are the same in their action and mechanism as those of the catapult.

FIG. 14 The Mechanism of the Stock of an Arrow Throwing Ballista. (Previous Page).

A. Side view of the stock, with the arrow in the sliding trough before the bow-string is stretched.

B. Surface view of the stock, with the arrow in the sliding trough before the bow-string is stretched.

C. Section of the fore-end of the stock, and of the trough which slides in and along it.

1 When the bow-string has been released and the arrow discharged, the ratchets are lifted clear of the cogs on the stock of the engine. This allows the trough to be slid forward to its first position as shown in A, B, Fig. 14. It is then ready to be drawn back again for the next shot.

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THE BALLISTA

THE MECHANISM  OF  THE   STOCK   OF  AN   ARROW- THROWING   BALLISTA

FIG. 14 THE MECHANISM OF THE STOCK OF AN ARROW- THROWING BALLISTA

D. Surface view of the trough, with the trigger and catch for the bow- string.

E. Side view, showing the keel (F) which slides along the slot cut in the surface of the stock as the trough is drawn back by the windlass.

G. Enlarged view of the solid end of the trough. This sketch shows the catch for the bow-string, the trigger which sets it free, the ratchets which engage the cogs on the sides of the stock, and the slot cut in the stock for the dove-tailed keel of the trough to travel in.

Ballistas were constructed of different sizes for the various purposes of siege and field warfare. The smallest of these engines was not much larger than a heavy crossbow, though it more than equaled the latter in power and range. The small ballistas were chiefly used for shooting through loopholes and from battlemented walls at an enemy assaulting with scaling ladders and movable towers.

The largest had arms of 3 ft. to 4 ft. in length, and skeins of twisted sinew of 6 in. to 8 in. in diameter.

Judging from models I have made and carefully experimented with, it is certain that the more powerful ballistas of the ancients could cast arrows, or rather feathered javelins, of from 5 to 6 lbs. weight, to a range of from 450 to 500 yards.

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