Most People seem to agree that we cannot and do not want to go back to the past, but the reason given is often wrong; that time has moved on and what was can never be again. The truth is that we cannot go back to what we never left. Our home is the earth, our time the Pleistocene Ice Ages. The past is the formula for our being.
(Paul Shepard)

Tuesday, 13 December 2011

ashby and the atlatl

Hi, If you are a bow hunter or atlatl hunter (all two of you) you should be aware of the Natal study by Dr Ashby. The study was to look at the lethality of the bow before bowhunting was legalised in Natal.
Read the study it is really good and stands as pretty much a definitive work on lethality and projectiles As you know bows and darts don't kill larger game by hydrostatic shock so lethality is best determined by the amount of penetration an arrow can attain. Ashby was able to be very specific in his recommendations and nicely for us primitive types it looks like the ancient hunters pretty much had it sorted out way back then. The two downsides are arrow shaft diameter and shaft friction, both of which are harder to get "right" under primitive conditions. I have noticed that atlatl darts get less penetration than standard arrow shafts but they hit with a far greater "whallop"
In a past article I wrote about dart speeds and added the kinetic energy of the darts I will now
add in the momentum calculations.
I am not a mathematics whizz and have been told to work out momentum through mass x velocity I will use grams and MPH as measurements.

- pine dart: 105 gram - 51 mph or 74 fps
- Mark Bracken river cane dart: 118 gram - 56 mph or 82 fps
- Atlatl Bob aluminium dart: 67 gram - 61 mph or 89 fps
- Chris Oberg carbon dart: 91 gram - 64 mph or 93 fps
We found 65 mph for the fastest dart (river cane, 98 gram). Most of the dart speeds were between 55 mph and 60 mph.

My workings for foot pounds

pine dart 20.18 foot pounds

river cane 27.27 Foot pounds

aluminium 18.37 foot pounds

carbon 27.47 foot pounds

momentum

pine dart 5.355
river cane 6,668
aluminium 4,087
carbon, 5,824


for comparison .22lr 38 grain 1050 fps 69 ftlb (100yd) 2. 46 grams 715.9 mph (stats off the ammo box)

momentum
1761.114

so we can see how a .22lr varmint gun while whipping the atlatl in foot pounds compares poorly
in momentum.

A 150 fps stick bow shooting a 600 grain arrow gives us momentum of;
4.097 which (while an heavy arrow) does not compare that well with any save the aluminium dart.

thanks to ken for the formula

No comments:

Post a Comment