Everything an amateur bowyer does to turn a log into a bow throughout the year.
Making bows, longbows and primitive bows with all the tips, tricks and problems.
Monday, 6 August 2012
Bow Geometry Explanation
I mentioned how adding a riser section changes the bow geometry in an earlier post, here's an attempt at a 'proof'
The diagram is just the top half of the bow, I'm assuming its lower half is completely symmetrical.
The black limbs at the top represent the upper limb of a bow at brace and full draw.(BOW 1)
The string is length L. and the full draw length is at B (On the big fat red horizontal centre line).
If we now extend the limb downwards into a rigid riser section, also of length L (BOW 2), we see the string is now length 2L. The limb bends exactly as it did before to point A (not strictly true, due to the slight change of string angle, but this is my simplified model)
Now drawing an arc for the string of radius 2L centred on point A, we see it intersects the new horizontal centre line at point D which is our new draw length.
So you can see it is drawing further.
If the limbs return to brace at the same time, then the arrow is travelling further in the same time and is thus faster!
Blimey, my brain hurts now.