Bow balance

[Sea of vapours]

Hi,

I've just returned to archery after a short break of 27 years..... I've therefore been doing lots of reading on current thinking, particularly re equipment set-up.

One thing (well, one of the many things!) on which I can't find a straight answer, other than that it feels right, is that of how the bow should balance (statically). Most people seem to use fairly long v-bar extenders, such that the centre of gravity of the bow is quite a way forward of the pivot point / point of contact with the grip. Intuitively, it seems to me that the bow should balance, such that it moves forwards immediately after the arrow is loosed, hits the sling and then rotates forward; rather than being immediately caused to rotate by the CoG being forward of the pivot point.

I have a couple of theories as to why a forward CoG might be better than a neutral balance, but I'd like to hear if there are any good, theoretical reasons for it (as distinct from 'it feels right') before presuming to suggest why!

Thanks,

Mike

[King Custard]

Originally Posted by Sea of vapours

Hi,

I've just returned to archery after a short break of 27 years..... I've therefore been doing lots of reading on current thinking, particularly re equipment set-up.

One thing (well, one of the many things!) on which I can't find a straight answer, other than that it feels right, is that of how the bow should balance (statically). Most people seem to use fairly long v-bar extenders, such that the centre of gravity of the bow is quite a way forward of the pivot point / point of contact with the grip. Intuitively, it seems to me that the how should balance, such that it moves forwards immediately after the arrow is loosed, hits the sling and then rotates forward; rather than being immediately caused to rotate by the CoG being forward of the pivot point.

I have a couple of theories as to why a forward CoG might be better than a neutral balance, but I'd like to hear if there is any good, theoretical reason for it (as distinct from 'it feels right') before presuming to suggest why!

Thanks,

Mike

depends what you want the 'balance' to achieve.
whats most important? - a nice swing/...or a bow that can be aimed nicely at the x in the center of the gold without wobbling very much atall?

for those of us that would say aiming is more important than aftershot gymnastics it will of course follow that we'd find a Static forward cofg 'better',' feeling good' and scoring higher...
why?...

remember that a statically balanced bow wont/cant have the same cofg when Drawn........the limb tips arching back towards the archer moves the cofg from its forward position to its ideal position, which IMO is at the pivot with forward weight equalling the force of the draw.
Please dont ask for measurements of each or some mathematical equation- as i have none nor would i understand any equation there - but there is a point where the stabilisation counters the force of the draw....and with correct bone alignment and form the 'aim' will become far easier to keep steadier. This is what i am currently finding as i experiment with ' weight '...that even small weights moved around 'outside of the bow' can have a marked effect on the stability of aim.

and do those weights change after shot bow action? ..sure...somewhere you'll find perfect bow action weighting...and perfect aiming weighting...if you look long and hard enough.

Its no so much that the effective cofg improves groups, nor worsens them....its just that a 'better' cog will be steadier over a tournament or an end...easier to hold the sight on the gold and moving in smaller circles around the gold....so those wayward arrows still hit nearer center as they were aimed better, or nearer center when released,
assuming form doesn't detract from the shot of course

now would someone please explain what i meant to say?
__________________________________________________ _____________

understanding is one thing, wisdom another, expounding and explaining - a whole different dimension!

[bkupris]

Yeah, a bow that holds nice and steady, isn't too heavy and goes towards where you are pointing it on release. IMHO of course...

[geoffretired]

If you make your bow balance(static balance) at the grip, it will tip backwards during the power stroke,and you will notice the long rod flicks up at the end. The power stroke creates torque in that direction, that is not there when the bow is at rest. Some archers try to reduce that flick upwards, by adding more weight to the end of the long rod. Having added more weight,the flick up will be almost zero but the bow then has a forward balance and will roll that way after it reaches the sling.

[joetapley]

One thing (well, one of the many things!) on which I can't find a straight answer, other than that it feels right, is that of how the bow should balance (statically). Most people seem to use fairly long v-bar extenders, such that the centre of gravity of the bow is quite a way forward of the pivot point / point of contact with the grip.

The location of the static balance point of a bow is actually quite irrelevant. It is determined mainly by the weight of the riser and partly by the draw weight. The only requirement is that during the power stroke the bow cog exceeds a minimum distance forwards of the grip pressure point (else very bad stability and the upward post shot flick mentioned by Geoff).
In principle the further forward the cog is in front of the grip the higher the rotational stability during the power stroke but there are a number of practical factors that limit this distance .

Intuitively, it seems to me that the bow should balance, such that it moves forwards immediately after the arrow is loosed, hits the sling and then rotates forward; rather than being immediately caused to rotate by the CoG being forward of the pivot point

.

Obviously during the shot you don't want the riser to move at all (rotationally or linearly). When the arrow leaves the string the bow does move forwarded - ideally straight forward with no rotation. The position of the bow centre of gravity is irrelevant to this motion. Once the bow hits the sling limit then of course then things are different.

[Sea of vapours]

Thanks for the replies :-)

To answer King Custard's initial question: I'd like the bow to balance such that I can aim it, primarily! I don't care what it does after the arrow has left the string (other than in so far as it indicates good form or not). So I agree with bkupris's idea of how the bow should feel too. Similarly, it seems a bad thing for the bow to flick either up OR down on release, as geoffretired says. (So, where's the torque coming from at the point of release, to cause the upward flick, if there's no forward CoG? Is that down to tiller? i.e. if tiller is positive, is that what's causing the flick - or is it down to the fact that the arrow is not exactly in the centre of the bow? But then, I thought tiller was trying to compensate for that..... :-\ )

I can definitely see that the ideal is for the bow to move forward without rotation during the power stroke: but it's not obvious (to me!) why the position of the CoG is irrelevant to that. Clearly, it's inevitable that the CoG will move, forwards, between loosing the arrow and the arrow leaving the string, so the bow cannot be balanced around the pivot throughout that, but the CoG surely /must/ be an influence on the bow's behaviour, even if it's a small influence compared to the forces acting on the arrow and bow hand due to the limbs releasing their energy? Maybe that's the answer: that the effect is so small as to be irrelevant, when compared to the much larger forces due to the limbs springing forward?

To take an extreme example: if the CoG of the bow was 10 metres forward of the grip, then the bow would surely start to rotate before the arrow left the string (since the tendency to rotate about the grip would be very high), which would be not a good thing! I suppose the partial answer must be that the CoG needs to be forward / on the grip at full draw, such that it moves forward from there on release, but has minimal effect in making the bow rotate forwards whilst the arrow is still on the string? That sort of makes sense, I think!

[geoffretired]

The back flip is caused by recoil during the power stroke.The power stroke energy is along the line of the arrow, the equal and opposite reaction is along the line of the arrow but acting on the bow,in the opposite direction. As the bow is held below the line of the arrow, the energy causes the bow to rotate, around the point of support at the grip.
You will get almost the same effect if you hold the bow, gently at arm's length, and get a friend to suddenly push the riser towards you at the level of the arrow.

[Sea of vapours]

Originally Posted by geoffretired

The back flip is caused by recoil during the power stroke.The power stroke energy is along the line of the arrow, the equal and opposite reaction is along the line of the arrow but acting on the bow,in the opposite direction. As the bow is held below the line of the arrow, the energy causes the bow to rotate, around the point of support at the grip.
You will get almost the same effect if you hold the bow, gently at arm's length, and get a friend to suddenly push the riser towards you at the level of the arrow.

Ah - yes - that entirely makes sense. And the forward-balanced stabiliser set-up counteracts that. This is beginning to be somewhat clearer. Thanks Geoff!

[joetapley]

To take an extreme example: if the CoG of the bow was 10 metres forward of the grip, then the bow would surely start to rotate before the arrow left the string (since the tendency to rotate about the grip would be very high),

It's actually the complete opposite of what your intuition is telling you. It's much the same (and for the same reason) that people believe a brick falls faster than a feather - "It must do as the force on it is greater"

Reality is the brick and feather fall at the same speed because the mass cancels out, Reality is that the further the cog is forward of the grip the less the bow will rotate in a given time - because the mass cancels out.

e.g the longer a pendulum (the further the cog from the pivot) the slower it swings.

[joetapley]

Originally Posted by Sea of vapours

Ah - yes - that entirely makes sense. And the forward-balanced stabiliser set-up counteracts that. This is beginning to be somewhat clearer. Thanks Geoff!

Geoffs basic idea is correct but this area is somewhat complicated as the recoil force varies over time so you don't just simply counteract a "constant" recoil torque with a "constant" gravity torque.