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johnhames
March 4th, 2005, 10:47 PM
No right-left tear, no up-down tear at several different distances with a release ---- does that mean the arrow did not flex? Is it theoretically possible with an over spined arrow and a very precisely tuned bow to shoot an arrow without it flexing? If the energy is imparted to the exact center of the nock, must it flex? Why?

Jorge Oliveira
March 4th, 2005, 11:24 PM
No, if energy is applied to the center of the arrow exactly in the center line and perfectly aligned to it, the arrow will not flex.

I think this may be considered perfect tune.

But then things may not be as perfect, but just a bit off and the stiif arrow has already strightened by the time it hits the paper.

This kind of tuning cannot be achieved with fingers.

johnhames
March 5th, 2005, 12:01 PM
The question is totally theoretical spawned from a disagreement with a friend. He says the arrow must flex because the tip cannot move out from in front of the shaft moving forward fast enough to avoid flexing. I say that since an arrow can tear left or right, there must be a place in the middle, when you are going from stiff to soft, where it does not flex in the horizontal plane. AND, a similar argument exists for the nock high or low condition. As you go from nock high to nock low, there must be a place in the middle where there is no vertical flex. Assuming your string is held vertically to shoot and imparts no horizontal or vertical flex i.e. imparts the energy directly into the center of the nock/shaft, there should be no flex. Am I right???????????

Shawndeer74
March 5th, 2005, 12:37 PM
I'm not going to get into the physics of this, but If you want to test it Your going to have to shoot at more than a few distances through paper. Like try every foot 5 to 10 yards and if you get a perfect bullet hole every time then you have your awnser. My guess is you won't, not because you can't but its nearly impossible. If it was arrow manufacturers would have already done this and passed it on...Good Luck

johnhames
March 5th, 2005, 12:46 PM
I'm not going to get into the physics of this, but If you want to test it Your going to have to shoot at more than a few distances through paper. Like try every foot 5 to 10 yards and if you get a perfect bullet hole every time then you have your awnser. My guess is you won't, not because you can't but its nearly impossible. If it was arrow manufacturers would have already done this and passed it on...Good Luck

I think the different spines are offered because it is increasingly difficult to tune to the exactness necessary to not flex as the bows become more effiecent, bow weight goes up, the arrow becomes longer and as the tip wieght gets greater. I am aware of some archers who won state tournements (before grains per peak bow weight was a factor) with arrows extremely under spined by spending a long time tuning to them and using a great amount of skill to create a repeatable shot with the under spined arrow.

Rat
March 6th, 2005, 03:03 AM
All arrows flex. A perfectly matched arrow will flex on release no matter what.
There isn't "a place in the middle" so to speak, between left and right tears that it is perfectly straight when launched.

Tears are caused when the arrow is SO FAR OUT of spine that it can't recover. A paper tear isn't from the "flexing" of the arrow, it from out of control arrow flight.

So the arrow flexes, but what is important that the "nodes" of the arrow stay parallel with the flight path, when they deviate, you have problems.

I have never seen high speed video where the arrow didn't flex when launched, ever.

Deezlin
March 6th, 2005, 08:07 AM
I'm not going to get into the physics of this, but If you want to test it Your going to have to shoot at more than a few distances through paper. Like try every foot 5 to 10 yards and if you get a perfect bullet hole every time then you have your answer. My guess is you won't, not because you can't but its nearly impossible. If it was arrow manufacturers would have already done this and passed it on...Good Luck

I would tend to agree with this statement, however, for practical purposes this can be accomplished. The down side to using too stiff of a shaft is the physical weight of the shaft for release shooters. But, finger shooters can not shoot too stiff of a shaft and get good accuracy.

As far as the shaft not flexing it would be impossible for it too not flex during launch to some degree. But, for practical purposes, you may be talking about a dimension that may be less that a thirty-second of an inch and the recovery might happen within a couple feet of the string.

I am a mechanical designer and engineer and theoretically, there is no absolute zero. I can make the argument that a pi$$ ant on top of the Sears Tower will deflect the columns. Now, it may take you all day to right the zeros in front of the number, but there is some quantitative deflection!!! :D :D :D Of course, that is why, mathematicians invented scientific notation.

silverback
March 6th, 2005, 09:10 AM
Even if you can impart the force perfectly on the centerline of the arrow, the arrow will not be stable. The more force you put on the centerline, the more likely it is that the arrow shaft will buckle. That means heavier points and heavier draw weights cause more flex. Also longer arrows are less resistant to buckling.

Even if you apply all the force perfectly on the centerline, you can't prevent external factors such as air drafts, contact with the rest (even drop-aways because they contact the arrow up until the rest drops), and asymmetries in the shaft. If the arrow is close to the critical force that will cause it to buckle, very small side forces will cause the center to kick out or flex. The heavier the bow, the more flex for a given arrow.

A good demonstration is to take a plastic ruler. Stand it straight up on your desk. Push straight down on it. Take your other hand and push sideways on the middle. It will buckle. Now push down on it harder. You will find it is easier to cause the ruler to buckle when you push on it sideways.

johnhames
March 6th, 2005, 12:35 PM
I would tend to agree with this statement, however, for practical purposes this can be accomplished. The down side to using too stiff of a shaft is the physical weight of the shaft for release shooters. But, finger shooters can not shoot too stiff of a shaft and get good accuracy.

As far as the shaft not flexing it would be impossible for it too not flex during launch to some degree. But, for practical purposes, you may be talking about a dimension that may be less that a thirty-second of an inch and the recovery might happen within a couple feet of the string.

I am a mechanical designer and engineer and theoretically, there is no absolute zero. I can make the argument that a pi$$ ant on top of the Sears Tower will deflect the columns. Now, it may take you all day to right the zeros in front of the number, but there is some quantitative deflection!!! :D :D :D Of course, that is why, mathematicians invented scientific notation.

If the arrow was a "perfect" cylinder and pressure was applied to the center of the circular cross section perpendicular to the cross section and parallel to the wall of the cylinder. What force would be causing the flex?

FS560
March 6th, 2005, 01:47 PM
The arrow touching the rest is adequate external influence to cause the otherwise "perfect" unsupported column to flex upon "perfect" end loading.

johnhames
March 6th, 2005, 02:08 PM
The arrow touching the rest is adequate external influence to cause the otherwise "perfect" unsupported column to flex upon "perfect" end loading.

Would a fall away rest make any difference? Is that why release shooters find more flex in the vertical plane than in the horizontal one?

silverback
March 6th, 2005, 06:22 PM
a fall away rest would not make a difference because it contacts the arrow for most of the draw cycle.

This also has to do with material science and how the load is transferred from one grain to the next. Since carbon arrows are mostly woven or wrapped, applying a compression force will cause minor twisting that affects the arrow's stability.

Marcus
March 6th, 2005, 06:29 PM
Would a fall away rest make any difference? Is that why release shooters find more flex in the vertical plane than in the horizontal one?
No this is because of nock travel. Drop aways won't make any difference.

silverback
March 6th, 2005, 09:21 PM
No this is because of nock travel. Drop aways won't make any difference.

That brings up a good point. No bows have a truly level nock travel, so none of them will apply force exactly along the centerline. This actually goes back to whether or not you could adjust your rest so perfectly that you are applying the force directly down the center of the shaft. Without perfect nock travel, you can't.