Source data on Crossbows

[clawrenc at cup.hp.com]

I found the following at:

  http://www.gci-net.com/~users/w/wolfsoul/medieval/crossbow/cross_l_v_c.html

                        The Crossbow in the Medieval Period


Revised 1 March 1997

The crossbow played an important role in the late Medieval period. The
crossbow was really the first hand-held weapon that could be used by
an untrained soldier to injure or kill a knight in plate armour. The
most powerful crossbows could penetrate armour and kill at 200 yards.
Longbowmen could certainly penetrate plate mail (though perhaps not at
such a great distance), but longbowman were generally highly trained
soldiers. This meant that they were also expensive, and that they
could not be replaced easily. (Many bowmen were recruited at a young
age to master their craft.)

Anyone could use a crossbow though. Crossbows are easier to aim than
longbows because the crossbowman doesn't have to use a hand to hold
the string back while aiming. On a similar note, a crossbow can be
loaded long before the bowman might need to fire. In this way, the
bowman would be able to fire immediately if surprised. Crossbows
require less upper body strength to operate as well. One can use both
arms to span (draw back) a crossbow. Crossbows do, of course, come
with a price. That price is in efficiency and in the firing rate.
Longbowman could fire 2-5 times more frequently in a given time than a
crossbowman. Efficiency is a more technical problem.

Although it is impossible for any bow to be perfectly efficient,
crossbows are particularly inefficient when compared to longbows. The
reason for this is that the draw length and the lath (also called a
prod) of crossbows are much shorter than those of longbows. So even
though a crossbow may have more stored energy when spanned, the tips
of the lathe do not have enough time to reach the maximum velocity
that the amount of stored energy would otherwise allow. It is the
lathe tip velocity that determines the speed of the bolt that is
loosed. (Crossbows are not "fired", which is a term related to
gunpowder.)  W.F. Paterson (1990) published data from Stephen V.
Grancsay about an experiment comparing a longbow and a crossbow that
was spanned with a cranequin.

 Type of Weapon   Draw weight    Bolt weight    Speed of bolt 
Difference

 Longbow            68 lbs.        2.5 oz        133.7 fps      Not
much!!
 Crossbow          740 lbs        1.25 oz.       138.7 fps      Not
much!!


This problem could have been alleviated with a longer draw length or a
longer lath, but that would increase the weight and bulkiness of the
crossbow, which are already two distinct disadvantages of crossbows.
In the above example, it should be stated that the bolt loosed by the
crossbow could have been heavier without experiencing much of a
decrease in exit velocity. A heavier arrow loosed by the longbow would
have had a significantly reduced exit velocity.

NOTE: through the use of modern engineering and advanced materials,
modern crossbows are now much more efficient. The Excalibur Exomag has
a draw weight of 185 pounds, and is able to send a bolt at 290 fps.
The 165 pound draw weight Excalibur Exocet looses bolts at 270 fps,
and the 150 pound draw weight Excalibur Vixen looses bolts at 250 fps.
Special thanks to Excalibur Crossbows for the use of crossbow specs.

--
J C Lawrence                           Internet: claw at null.net
(Contractor)                           Internet: coder at ibm.net
---------------(*)               Internet: clawrenc at cup.hp.com
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