Main Discussion Area > Arrows

Energy storage and light arrows

<< < (2/4) > >>

Badger:
     There are actually a few different reasons at play why heavy arrows are more efficient. With wooden bows they have a double wammy because they also have hysteresis which is time sensitive. So the faster the limbs are moving the more hysteresis they have. Another big reason is that heavy arrows have more leverage against the momentum of the moving bow limbs especially in the final few inches of the power stroke. Bow limbs do not reach a dry fire speed until they are actually dry fired, any amount of weight will slow the limbs. We often use a number called virtual mass when attempting to extrapolate speed potential. It really only works with bows that don't have hysteresis. But suppose a bow didn't have hysteresis. If a bows virtual mass is 200 grains it will stay 200 grains regardless of arrow weight. This means that a 500 grain arrow will shoot the same speed as a 700 grain arrow if the bow were 100% efficient. The same bow would shoot a 200 grain arrow the same speed as a 400 grain arrow if it were 100% efficient. As you can see 200 grains is 1/2 of 400 grains so it will drop down to 50% efficiency. The same 200 grains is less that 1/3 of 700 grains so the bow will be 74% efficient.

willie:
 you start shooting a heavy arrow over a chrono,
then as you successively lighten it, it leaves the bow faster and faster up to the point the limbs can go no faster

isn't that more to do with the bow than the anything else? how does the 28" arithmetic work?

I think I am beginning to understand virtual mass... a little bit anyway  ???... thanks steve

Badger:
  Willie, there is no point the limbs will stop going faster, all the way until there is no arrow. They will never reach a dry fire speed before they are actually dry firing

willie:

--- Quote ---With an arrow so light, the max speed will be reached before the end of the power stoke of the bow.
--- End quote ---
from sleeks explanation.  sounds reasonable.........    but is this different from your experience, Steve?

sleek:

--- Quote from: Badger on December 03, 2017, 10:47:42 pm ---  Willie, there is no point the limbs will stop going faster, all the way until there is no arrow. They will never reach a dry fire speed before they are actually dry firing

--- End quote ---

I know there is more to it than I wrote, but to explain it completely would have required almost a book. I know hysteresis is a friction factor that slows down a limb, and the angle the limb is at relative to the load ( leverage ) which is why a bows limb changes its speed due to levearge agaimst its own weigh on a dry fire ( i reserve the right to be wrong ). I just wanted to say there is a max speed without going into the detail of why and the factors involved. Also the max speed of the limb does change as a heavier arrow is used, speed is not a consyant in this, it is a variable,  changing with the arrows weight. There is probably more to that than I understand.  So, Willie, i dont think Steves point disagrees with mine, only he is further explaining a part of it I didnt go into at all, and clarifying  ( where he mentions dryfire speed and arrow speed will never be the same  ) things i didnt go into detail about.

If im wong on anything, i sure hope he points it out. And any disagreement between me and him, defere to him, he has forgotten more than I know probaly, and I doubt he forgets much.

Navigation

[0] Message Index

[#] Next page

[*] Previous page