Gravity may play a part here. The upper arm has an upward component of movement when it springs back. The lower arm has a downward component.
Might be immeasurably small effect in practical terms, I guess.
How does this work with distinctly asymmetrical bows, like Japanese yumi?
It actually works out fine, Yumi bows are shot with what they call a thumb ring so they are drawn back very close to the arrow nocking point. They simply tiller the bow to draw straight back from this point. Symmetry is not all that important as long as the limbs are tillered accordingly.
The arrow shelf on the bow is usually about 1 1/4" above center anyway so the top limb is normally tillered just slightly weaker than the bottom.
Am I the only one unduly amused by this typo?
And yeah, pretty much whenever the question is “where did the energy go”, the answer is almost always “heat”. The really interesting question is not where the energy goes; it’s how it gets there.
What is the difference in accuracy/etc between an expertly tillered bow, a raw untillered bow, and an actively anti-tillered bow meant to bring out the worst performance?
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Many tiller the bow shape according to how the bow is held. I contend it should be tillered according to how the arrow is shot.
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What is the difference between “how the bow is held” and “how the arrow is shot?” To me (I know nothing), the holding of the bow includes the archer’s fully drawn back grip style (how many fingers above/below the arrow and where along the string). To me, how the archer shoots the arrow implies all of that as well.
So (1), a bow balanced at the nocking point won’t “feel right” when drawn below the balanced point, but (2), the arrow won’t fire right if it sits high above the balanced point, but but (3), even if the nocking point is at the balanced point, it still won’t be fired correctly if the draw sits low beneath the balance & nocking point.
I’m imagining a balanced draw bow with the arrow nocked up somewhere near the top attachment point, and I’m imaginiing a balanced fire bow drawn from somewhere down near the bottom. Obviously, both of these are going to fail.
I think you’ve got a fundamental limitation of the design: My week intuition is that you get around the same amount of energy either way: either you have a less efective draw, or you have a less effective push.
Is the portion that goes to “sound” (acoustic energy) considered negligible/unmeasurable?
Energy is always one part of the key. Momentum is usually the other.
Going back to the OP, the idea that a bow will retrace its deformation on being loosed is, in general, trivially wrong.
When being drawn the path is controlled by the bow and the force applied by the archer. On loosing, the bow path is controlled by the mass distribution of the bow and the fired mass, and the energy stored in the bow. Simple point - attach a 100 gram mass to one end of the bow. This mass will not materially affect the draw path. However on release it will clearly make a huge difference to the path the system takes, and that path will not be the one it was drawn on.
Any mass asymmetry in the bow will mean unequal momentum in the arms. Even without worrying about energy loss (for instance from hysteresis ) in the arms, even with equal energy stored in each arm of the bow, the movement will not be symmetric.
If you ignore hysteresis losses, the path of a bow that is released slowly should retrace its draw path. Here, again, the path is not controlled by the mass of the bow. Once asymmetric energy losses occur, even the slow release path will not be the same.
Usually, yes. And even if you do account for it, the sound will also dissipate to heat quickly enough.
Bows are actually very quiet if made properly, no real string twang. The limbs don’t really slam home as a lot of folks think. The arrow sucks about 80% of the available energy out of them. In many cases even more. The theory is that if limbs could not vibrate bows would be almost 100% efficient. I find that reducing the amount of working limb used also reduces the opportunity for vibration so I try to minimise it.
I think I get what you’re saying ( I have a take down recurve that I miss targets with regularly…) and I agree with it. Wouldn’t you be able to easily determine which way is right be intentionally having a noticeably weaker limb on one(say a 35 lb limb lower and 40 upper) and then setting up both ways to see which way works better?
The fact is not so much which is right or wrong as we know it works fine both ways. We simply call it tuning and adjust the arrow knocking point on the string to where we get good arrow flight on release. The actual issue is just the fact that I feel the return path of the bow relates entirely to where the arrow is placed as opposed to how it was pulled back. I feel it forgets all about being pulled back as soon as it is released.
But if it’s not tuned to the pull back point, the bow isn’t drawn correctly. Imagine it is drawn at a point *very far * from the tuning point. Yes, the arrow only feels the return path: but if the bow was misdrawn, the energy transfer to the arrow won’t be effieient.
I think you’ve reached a fundamental limitation of the design.
I’ll chime in with my less than 2 cents again.
The arrow rests above the point at which you are holding the bow. Then your arrow knock point is at some variable point on the string. You may have your fingers, in various number above and or below the arrow knock. Or, a mechanical release, dead center behind the arrow center. The limbs may be in equal or unequal balance. Then. The arrow in it’s particular construction, and combination, has all sorts of variables.
Ideally. The limbs are balanced. The knock point places the center of the arrow shaft, dead center between equally balanced limbs.
But! Where are you holding the bow? Usually, the arrow is above your hand, by quite a bit. When you draw and hold the bow. Your are not fighting to hold the bow as if the arrow was level from all the perfect balanced geometry, that is messed up by holding the bow at a point well below the arrow. If the bow were balanced evenly and the knock point dead center on the arrow shaft. When you draw it. The whole rig, tilts upward, from knock point, to arrow shelf. Not good. Because it will be driving the knock end forward, not in line with the arrow shelf. Severely warping the arrow. Which already warps a lot. So you need to do all these complex tillering, knock point adjustments, to lessen that quite violent flexing and waste of energy. Trying to deliver the energy of the string knock point, in as direct a line as possible, to the arrow rest or shelf. Which is above the point you are holding the bow. So you tiller the bow, to make the knock point draw straight back, and return straight forward, even though you are holding the drawn bow canted off off it’s top to bottom energy center, if it was evenly tuned.
The ideal, would be a bow where the pivot point against it’s draw, was exactly in line with the arrow shelf and knock. All energy delivered directly forward.
Best case for the bow, hold point, shelf, knock point. Is to try and make them as in line as possible. Then tiller to perfect it, and select arrows based from that, for best speed. Then sight that in.
You seemed to have grasped the dynamics pretty well. Because the knocking point on the string can be raised or lowered to accommodate tiller I think a lot of bowers tend to tiller for the hold rather than the arrow. They feel it is more stable when holding on a shot. I find the small amount of pressure needed to adjust for the slight imbalance of hold pressure is almost undetectable. I choose to tiller mine so the arrow moves straight back with the hook at the bottom side of the nock.
It is surprising how many guys seem to believe that the string will return along the same path it was drawn.