Rotational Flight... Energy Lost?

[royden]

Jan 1, 2009 20:54:01 GMT -5 BT said:

Thats gonna be very hard to do and thats why (at times) questions to be answered must be answered based on the physics rather than actual physical evidence.

true BT - that is why I put it out now (as soon as I caught back up to where ya'll where at).

arrow's leaving the bow at the same speed but arriving at different speeds have at least two different variables - therefor only assumptions can be made - nothing concrete. Chronying the arrow at impact and adjusting #'age to compensate and create equal arrival speeds is the only way I see to accurately determine what affect rotation has on penetration.
Then with that info in hand a person can again shoot at the same poundage and see the two-fold impact rotation may have.

[Buckshot06]

Jan 2, 2009 14:50:52 GMT -5 royden said:

Jan 1, 2009 20:54:01 GMT -5 BT said:

Thats gonna be very hard to do and thats why (at times) questions to be answered must be answered based on the physics rather than actual physical evidence.

true BT - that is why I put it out now (as soon as I caught back up to where ya'll where at).

arrow's leaving the bow at the same speed but arriving at different speeds have at least two different variables - therefor only assumptions can be made - nothing concrete. Chronying the arrow at impact and adjusting #'age to compensate and create equal arrival speeds is the only way I see to accurately determine what affect rotation has on penetration.
Then with that info in hand a person can again shoot at the same poundage and see the two-fold impact rotation may have.

That is an excellent point you have royden. So you want to find out the difference at impact with the shafts at the same speed putting rotation against a non rotating shaft. That would be good, so then you can take the shots and deduct the difference you came up with from the first test and determine how much friction loss there is in flight. We would want to know the whole not just part of the friction loss. This would be good to determine how much drag there is in different types of fletching (feather/ vanes). Now we are into a whole different test and a new thread needs to be started ;D ;D ;D.

[BT]

You cant adjust the poundage or you skew the test results based on differing K.E. outputs at the bow.
But your following the right logic which is why I said that there is no way I have the time or seasonal temperatures that will allow me to do this test now.

What you would have to do to is compare results before a speed loss occurs
In other words....point blank more or less....perhaps 5 yards?.

You cant effect change by moving the target distance either....or you will effect the same changes in K.E. at the time of impact.
I am suggesting a hard helical that will get the shaft spinning well before speed loss.

[royden]

explain to me BT .... how two exact same arrows traveling at the exact same speed at impact have different KE at impact.

The deer don't care if a 47# bow shot the arrow or a 49# bow did it.

Of course your idea of point blank ... ever seen a highspeed video of the arrow oscillating but not spinning yet? Even at 10 yards, the arrow may not be up to rotation speed - I don't know on that one, only that I have read it takes time for the fletch to get the arrow rotating.

After you have shown the seperate affect of rotation on the ability of a broadhead to penetrate, then test again with arrow velocity the same at the bow and you can see the overall affect of rotation on penetration - speed loss and friction.

[BT]

Jan 3, 2009 0:09:34 GMT -5 royden said:

explain to me BT .... how two exact same arrows traveling at the exact same speed at impact have different KE at impact.

IMO...2#added wouldn't make the needed change for downrange velocity (in my experience and based on the pictured evidence provided so far) within the area that was previously tested.
By the time you got to the range of weight gain, you would skew flight unless you re-tuned for flight and you would still need to be within the same spine range.
I am talking K.E. at the bow which would effect flight and stored energy in the arrow throughout it's effective range.
Just as stored energy can be effected by spine, arrow density, weight, taper, ect....tune also effects stored energy.
The more Bow weight (on the same cam) that you add, the more stored energy you add to the same arrow.

Of course your idea of point blank ... ever seen a highspeed video of the arrow oscillating but not spinning yet? Even at 10 yards, the arrow may not be up to rotation speed - I don't know on that one, only that I have read it takes time for the fletch to get the arrow rotating.

As I said earlier....
"I am suggesting a hard helical that will get the shaft spinning well before speed loss."
The old Tourney twist vanes could easily effect instant rotation within a yard of travel.
That might be the better choice so as not to have to fight the drag and therefore end up too close to the back stop.

[royden]

good points BT ... I assumed speed loss wouldn't be that much yet at 20 yards. I can see where if it is too much the adjustments needed to get good flight would be excessive.

[BT]

What about distance?
You can leave the bows set and just vary distance.
The speed X arrow eight would keep K.E. same.
Also...that would allow the rotational effect to be confirmed rather than having to believe it.

As I said....good summer job or maybe one for those in the south

[firenock]

This is all very interesting, but with Aerovane II, what you said is even more true on cut. I have done quite a bit of shooting for the last 2 days. You are not going to imagine an arrow going full spin at only about 1 foot off the bow! I am working on getting a slow motion video camera for it will be the only way to explain this and FORCE people to at least acknowledge that it is happening.

This is what I believe is happening. With the arrow at full speed DRILLING just about 1 foot off the bow. The arrow actually behave more like a bullet than a traditional arrow! The arrow with its full spin/drill now want to go into a gyro spin which means the force is going into the center instead of out! By having a weaker spine, the arrow will recover faster which achieve full spin faster. That is why a 400 spine arrow shoot better than what I use to use a goldtip 75/95 or carbon tech Rhino 45/70.

I also believe the spin have force open a void on the impact point on the target which make penetration deeper, like what a drill bit would do compare to a straight pointed knife. As the arrow when impact is preventer from spinning, the energy of that rotation have to go somewhere, which can only lead me to believe it is move into cutting energy.

This is getting exoteric fast, but I am having more fun for I do not believe anyone beside my self had ever observe this. I just feel very privileged. To think that all this happen because I asked "why not"!

[smj]

It takes a bit of time to catch up on this thread! Then more time to think through your reply - prior to posting...

For measuring force at impact - seems like a chrono about an arrows length off the target, whether the target is 10 feet away or 100 yards away, and then adjusting distance to keep the energy measured the same at an equally close distance to the target. This is assuming arrow mass is the same for both spinning and non spinning arrows. Probably two sets ups - one at two or three arrows length, and then one at 20 yards. On the longer shot, if the spinning arrow gives up energy due to fletching drag, then you should move half a step or so closer to the target until the two arrows energy's match when slightly more than an arrows length away from the target. Penetration differences should be just the difference from rotation. Although, having said that, one should probably consider the rate at which the arrow is slowing down, and is it significant over the distance from the chrono to the target. This is why I think the chrono should be as close as possible to the point of impact. Trying to match up as closely as possible the energy that each arrow has to expend on penetration. (Seems like this has already been suggested...)

When you measure the KE of an arrow by weight and speed, any energy that has gone in to rotational force is not measured. If the arrow spins, there is energy stored there. Hence, if there is a difference between spinning and non spinning arrows, penetration wise, it is obviously due to that energy being used in some way to enhance the penetration... Or used against the arrows travel, reducing penetration. If it went against arrow penetration, I would think at worst case, it would result in the cancellation of an equal amount of KE taken from forward travel of the shaft. Hence, on longer shots if a spinning arrow hits lower, the energy difference reflected in the velocity delta - is in part stored in rotational energy of the shaft. The remaining difference is lost in fletching drag that did not effectively convert to rotational energy. How much energy would be stored in the rotating shaft - I expect a very small number. Would it be enough to open a void, as firenock suggests above??? I don't know. Maybe in soft tissue, I would not think so in bone. Maybe a slightly positive effect in soft tissue, and a slightly negative effect in bone?? For the longer shot, measure the KE of the arrow spinning, and one not spinning when shot at the exact same distance, and then subtract the two measured KE values. Now assume 100% efficiency of the fletching (Not true, but so what?) having converted that KE energy difference in to rotational energy in the spinning shaft. Then that difference would be the best case amount of energy the arrow would have to work with, or work against, during penetration. Which, when you come right down to it, its probably a fairly small fraction of that energy that will actually be stored in the spinning shaft. Still, if full rotation is in effect at one foot off the bow - a more efficient fletching would allow for a better transfer of energy, with less impact on trajectory/velocity and more KE left in the forward travel of the arrow. (A good thing!) The actual energy stored in the shaft would depend on rotational velocity and shaft mass (a cylinder) and tip style (a big yuck to calculate, and different for each broadhead style.)

Maybe its time to wrap some steaks with plastic wrap, shoot some arrows, see what can be seen, and have a BBQ ! ;D

[BT]

Very nice SMJ

Dorge's (firenock) vane exhibits speed enhancement due to the fact that this vane of his is mounted straight and that the vane itself operates on zero drag.
The bonus of the Aerovane is that it spins the areo based on airflow over the curvature of the vane rather than over the stance of the vane on the shaft.
This is the same (sort of) concept as was used to design the Crimson Talon, with the difference being that the AerovaneII puts guidance where it is most beneficial.