Bamboo-maple-horn, 98#@28"

[mmattockx]

      You are wrong the best predictor of speed over an assortment of different weight arrows is virtual mass, which is based on stored energy and efficiency. The lower the virtual mass the less drop in ke as arrows get lighter.

I assure you that the laws of physics say what I wrote is 100% correct. The only question is how much the efficiency (as defined by what percentage of the stored energy is transferred into the arrow) changes between the two arrows.

Is there somewhere that explains how you calculate virtual mass?

I would also enjoy seeing OP test a few different arrow weights (if possible). It would make for an interesting experiment.


Mark

[willie]

Is there somewhere that explains how you calculate virtual mass?

Mark,
If this is the definition that Steve is refering to, it seems to be a derived unit of measure describing bows.

[Badger]

   Virtual mass is easy to calculate. It helps if you know the stored energy but if you don't you can usually get it by shooting a few different weight arrows.
Here is how to calculate it. His bow shot 256 fps with a 463 grain arrow. You go to a KE chart and look it up It shows 67.39 ft pounds. Lets say I estimate the bow is storing 93% of draw force. So it would be 93% X draw weight ( 98# )  That would give me 91# of stored energy. So now I simply add enough imaginary weight to the arrow that we know the speed of which is 256 fps to give me 100% efficincy. On the icase if I add 160 grains to the 463 grain arrow and then check the ke at 256 fps it will give me about 91 Ft#. So to check speeds of arrows I have not shot simply add 160 grains to the arrow I want to the know the speed of. So if I want to know how fast a 320 grain arrow would be I add 160 to 320 and see what speed gives me 91 ft#. So 320 + 160 + 480. How fast would a 480 grain arrow have to be to get 91.  The answer would be 292 fps.

   I am guessing at the stored energy in this case because I only hvae 1 arrow sample. If I had two samples I could be a lot closer. A 250 grain arrow should do about 316 fps.