Projectile Throwing Engines
Sir Ralph Payne-Gallwey
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THE CATAPULT

This spindle passes through the center of the roller and through the sides of 
the frame.

The small cogged wheels, with their checks, which are fitted to the ends of 
the spindle GG, prevent the roller from reversing as the arm is being wound down. 
(Fig. 6.)

HH.  The hollows in the sides of the frame which receive the lower tenons 
of  the  two  uprights.  Between  the  tops  of  these  uprights  the  cross-beam is  fixed against which the arm of the catapult strikes when it is released.  (Fig. 6.)

KK.  The hollows for the lower tenons of the two sloping supports which 
prevent the uprights, and the cross-beam between them, from giving way when the 
arm recoils.  (Fig. 6.)

FIG. 9.-ONE OF  THE  PAIR OF  WINCHES OF A CATAPULT. Scale : 1/16 in. = 1 in

FIG. 9.—ONE OF  THE  PAIR OF  WINCHES OF A CATAPULT.
Scale : 1/16 in. = 1 in

I.  Surface view of one of the winches and of the thick iron plate in which 
the socket of the large winding wheel of the winch revolves.

II.  View of a winch (from above) as fitted into one of the sides of the frame 
of the catapult.  One end of the twisted skein may be seen turned round the cross-
bar of the large wheel.

III.  Side view of the large wheel of a winch.

IV.  The cross-bar of one of the large wheels.  These pieces fit like wedges 
into  tapering  slots  cut  down  the  barrels,  or  inside  surfaces,  of  their  respective wheels.

V.  Perspective view of the wheels of a winch. The  winches  are  the  vital  parts  of  the  catapult  as  they  generate  its projectile  power.

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THE CATAPULT

They  are  employed  to  twist  tightly  the  skein  of  cord  between  which  the 
butt-end of the arm of the engine is placed.

The cord composing the skein is stretched to and fro across and through the 
sides  of  the  catapult,  and  alternately  through  the  insides  of  the  large  wheels  and over their cross-bars ; as show in fig. 8.

THE IRON SLIP HOOK
FIG. 10.  THE IRON SLIP HOOK

This simple contrivance not only pulled down the arm of  a  catapult  but  was  also  the  means  of  setting  it  free.  However  great  the  strain  on  the  slip-hook,  it  will,  if  properly  shaped,  easily effect the release of the arm.

The trajectory of the missile can be regulated by this form  of release,  as  the longer  the  distance  the  arm  is  pulled down the  higher  the  angle  at  which  the  projectile  is  thrown.

On the other hand, the shorter the distance the arm is drawn back, the lower 
the trajectory of its missile.

The slip-hook will release the arm of the engine at any moment, whether it 
is fully or only partially wound down by the windlass.

The slip-hook of the large catapult shown in fig. 6. , has a handle, i.e. 
lever,  10 inches  long,  the  point  of  the  hook,  which  passes  through  the  eye-bolt  secured to the arm, being one inch in diameter.

A SPRING ENGINE WITH A SLING ATTACHED TO ITS ARM, WHICH CAST TWO STONES AT THE SAME TIME.

FIG. II. – A SPRING ENGINE WITH A SLING ATTACHED TO ITS ARM, WHICH CAST
TWO STONES AT THE SAME TIME.
From ‘ II Codice Atlantico, ‘  Leonardo da Vinci.  1445-1520.

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THE CATAPULT 

THE SKEIN OF CORD

Fig. 12.-- THE SKEIN OF CORD

A.  The  skein  as  first  wound  over  the  cross-bars  of  the  large  wheels 
(shown in section) of the winches.

B.  The  skein  with  the  butt-end  of  the  arm  (shown  in  section)  placed 
between its halves.

C.  The  skein  as  it  appears  when  tightly  twisted  up  by  the  winches. 
Compare with AA, fig. 8.

Cord of Italian hemp, about . in. thick, is excellent for small catapults. For 
large  ones,  horsehair  rope, . in.  thick,  is  the  best  and  most  elastic. Whatever  is used,  the  material  of  the  skein  must  be  thoroughly  soaked  in  neats-foot  oil  for some days previously, or it is sure to fray and cut under the friction of being very 
tightly  twisted.  Oil  will  also  preserve  the  skein  from  damp  and  decay  for  many years.

HOW TO WORK THE CATAPULT

There  is  little  to  write  under  this  heading  ;  as  the  plans,  details  of 
construction and illustrations will, I trust, elucidate its management.
The skein should never remain in a tightly twisted condition, but should be 
untwisted when the engine is not in use.

Previous  to  using  the  catapult  its  winches  should  be  turned  with  the  long 
spanner, fig. 6, first the winch on one side of the engine and then the one on 
the other side of it, and each to exactly the same amount.

Small  numerals  painted  on  the  surfaces  of  the  large  wheels  near  their

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THE CATAPULT

edges, will show how much they have been revolved ; in this way their rotation 
can be easily arranged to correspond.

As the skein of cord is being twisted by the very powerful winches, the arm 
will  gradually  press  with  increasing  force  against  the  cross-beam  between  the 
uprights.  The arm should be so tightly pressed against the fender, or cushion of 
straw, attached to the centre of this beam, that, whether large or small, it cannot be 
pulled back the least distance by hand.

If  the  skein  of  my  largest  catapult  is  fully  tightened  up  by  the  winches, 
three strong men are unable to draw the arm back with a rope even an inch from 
the cross-beam,  though  the  windlass  has  to  pull  it  down  from  six  to  seven  feet when the engine is made ready for action.

When the skein is as tight as it should be, attach the slip-hook to the ring-
bolt in the arm and place the stone in the sling suspended from the top of the arm.
The arm can now be drawn down by means of long spanners fitted to the 
windlass.  Directly the arm is as low as it should be, or as is desired, it should be 
instantly released by pulling the cord fastened to the lever of the slip-hook.
The least delay in doing this, and the resulting continuation of the immense 
strain on the arm, may cause it to fracture when it would not otherwise have done 
so.

The plans I have given are those of my largest engine, which, ponderous as 
it seems—(it weighs two tons)—is, however, less than half the size of the catapult 
used by the ancients for throwing stones of from forty to fifty pounds in weight.
As  the  plans  are  accurately  drawn  to  scale,  the  engine  can  easily  be 
reproduced in a smaller size.

An interesting  model  can  be  constructed  that  has  an  arm 3 feet  in  length, 
and a skein of cord about 4 inches in diameter.  It can be worked by one man and 
will throw a stone, the size of an orange, to a range of 300 yards.
The sling, when suspended with the stone in position, should be one third 
the length of the arm, as shown in fig. 7
.
If the sling is shortened, the ball will be thrown at a high elevation.  If the 
sling  is  lengthened,  the  ball  will  travel  at  a  lower  angle  and  with  much  more 
velocity.

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