Black Frog

Why wouldn't that be a valid analogy? If two arrows spend the same amount of time in a crosswind starting from a static position, the heavier one will get moved a lesser amount (from the crosswind) due to the greater inertia of the arrow. That assumes same shaft diameter and fletching style.

You could easily prove this by dropping two arrows of the same shaft diamter, but with different weights from a tower of some sort. Since they will fall at the same rate due to gravity, the lighter one will be carried farther with the crosswind.

Of course when looking at this situation from a shooting from a bow with these two arrows- to have them spend the same amount of time in the crosswind to the target, the heavier one would need to be launched at a higher initial velocity to keep the "air time" the same as the lighter arrow. The higher speed would cause a difference in drag numbers and throw a wrench in this idea. But do you account for nothing when looking at arrow weight inertia in a crosswind?

Edited by - Black Frog on 01/08/2002 13:57:31

sajackson

The issue concerns much more than arrow mass is the reason. A better FOC may actually allow less drift for the lighter arrow due to weathervaning, although starting from zero velocity(the exact opposite if being launched from a bow), this would be much tougher to pull off in s short time, but gravity is a rocket engine given enough time. In addition, if the heavier arrow presented a much higher cross section for side drag, that force may overcome any inertial advantage.

Drag varies as the square with area, so much more force can be directed on a larger arrow pushing it further in the same amount of time. Because of the mass inertia, neither arrow will start drifting with the same velocity as the crosswind but will generally ramp up as time in the wind increases.

Black Frog

SA-

I realize that there is MUCH more to this situation than mass of the arrow comparisons, but I don't think it can be neglected. I agree with you on the drag being the major contributor to determining the amount of drift- that's why I had stated arrows of equal diameter and fletching style. Then the only variables left are arrow mass and FOC.

Doesn't your last sentence describe my river analogy a couple of posts ago? They won't ramp up at the same rate though, the lighter one will ramp faster than the heavier one.

Thanks for the input on this thread- fun reading as usual!



Edited by - Black Frog on 01/08/2002 14:43:46

sajackson

It describes the river analogy only to the point of ignoring everything else, assuming no FOC and no forward velocity/momentum. Your river analogy didn't consider the force of current/water over the area of the vessel to weight ratio in figuring how fast each would be brought up to speed. It's concievable the drum might be brought up to speed faster, since the cork has so little area exposed to the current, just bouncing long on top.

If one did the drop test from 10 meters then repeated from 50 meters, based on drift alone you'd probably come to 2 different conclusions. That would not be explainable by inertia, FOC, or arrow velocity/momentum alone.

DeerThug

Holy FOC batman! All I can say is that FLHunter and sajackson you got some real mojo going on. I asked about FOC on the bowhunting fourm and didn't learn nothing like you two have taught!! THANKS!!!!!!

sajackson

Black Frog,

I just wanted to make clear, that I wasn't disagreeing that inertial effects be taken into account. I agree 100%. My main point above was that when viewed by itself could lead to wrong assumptions.

Black Frog

SA-

I agree with you as well- I just didn't see any mention of the inertial effects in some of the posts and was wondering if it should at least be addressed.

Good stuff!

FLHunter

I don't think the inertial effects apply greatly here in regards to a free flying object moving within an air mass. There could be some consideration, but the arrows accelleration is almost instantaneous out of the bow to the top velocity for that given setup. The drift on a piper cub is the same as it is on a 747 in a given period of time given no course correction. I think where the confusion lies is that a cork and a barrel have a certain amount of displacement because they float. But if both items were submerged in the water they would drift at the same constant rate of the water flow(current); the same as what happens in the air. In the military we used to use computations in the air sea rescue business where we would compute drift considering currents like the Gulfstream, the wind component factoring in the size of the vessel, its freeboard and such to establish our search areas over day periods of time from a best estimate of the last know position. I think the major factors for amount of drift in archery are the speed of the arrow equating to time airborne, and the geometry (drag) of the arrow which factors the amount of weathervaning during its short flight.

Edited by - FLHunter on 01/09/2002 09:34:49

sajackson

FL,

The acceleration we're talking about isn't from the bow, but the wind. The amount of area will largely determine what force a given wind velocity will exert on the arrow, this force locks in the amount of acceleration the arrow "feels" and so how quickly it ramps up to match the wind speed, neglecting weathervaning effects.

From the arrow's point of view, if you suspended it in a wind tunnel and blew air over it, or shot it out of a bow, the drag effects would be the same, the higher the velocity or the more area equals more resistive force. From the front this would de-accelerate it, from the side accleration would be felt(again neglecting weathervaning).

FLHunter

Steve,

Thanks for the clarification, I understand the premise.