For arguments sake:
Would it be more meaningful to include the length of the blade's cutting surface (i.e. blade's length) into the calculation of the total cutting surface? This to me would be logical since this has an effect on penetration due to friction of a longer blade versus a shorter blade.

A steeply angled short blade such as the nitron or the slick trick might have the same cutting diameter as say a less steep thunderhead, but the thunderhead has a longer blade and therefore technically a greater "cutting surface." One would theorize, if ferrule diameter and weight were the same for each, that a thunderhead would penetrate less and we could perhaps prove it mathematically.

Mabe have two factors: Cutting surface and Cutting area? Or something like that?

Great stuff btw 5-shot!

As always 5shot, keep up the great work and thanks.

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The way I look at it, blade surface area and total cutting surface are different. What I was looking for was the size of the wound channel. While I agree that longer blades do have more "surface area" they don't always have more cutting ability or larger wound channels. I could include both, but I think that the actual penetration testing kind of "proves out" how the heads penetrate, so it works out in the end. Of course I know it's still not an exact science, but at least I think it makes for better more accurate comparisons between heads.

Well, I don't know how else to figure total cut, each blade has 1/2 the cutting diameter, so you have to divide the cutting diameter by 2 then multiply by the number of blades. I agree that some heads like the old NAP razorback, ( the rocky mtn razor was actually a pretty good head) can get a boost, but when the fragile head hit's a steel drum or plywood those blades breat off pretty quick. The razorbacks did fly well though.