ArthurP, Just finished reading Dr. Ashby's paper. Thanks again! When reading the paper in its entirety it is clear that he points out that neither momentum or KE alone are direct indicators of potential penetration. Without considering the arrow/broadhead combination you don't have much indication. I agree completely. My only issue with the paper is a minor one but I will point it out anyway as it relates to KE in this thread and of course because I find it "fun" to discuss such things! I think you and I tend to bore people with our technical blathering but here goes anyway...
Ashby writes:
As applied to an arrow in motion, K.E. includes such things as: radial energy due to arrow flexion, rotational energy due to arrow spin, sonic energy due to vibration, heat energy due to friction, and potential energy (all other remaining energy).
In the way we all refer to KE this is not correct. Like I said before when we talk about KE in an arrow it can be considered to be a vector quantity in that it is calculated from the forward motion of the arrow
only. KE =1/2mv^2. The rotaional energy for example is not included but rather is "drained" from the forward KE as the arrow moves towards the target. The other "energies" that he talks about are the reason you have less KE as the arrow moves farther and farther down range. The
total energy reamains a constant and is equal to what we normally call KE + these others. The "others" are not inlcluded in the KE number. They are of course all "present" and manifested in the arrow but are not included in the number we all call KE.
In the manner we talk of KE in an arrow a tuning fork KE would be 0 not a high value as Ashby says. A tuning fork has no forward motion so if you plug that in to KE = 1/2mv^2 you get 0.
I think a lot of the disagreement regarding these issues is a result of definition and context and of course sometimes people say things and they just don't know what they are talking about.