Ke and flight characteristics
 

The mechanical thread has gone long enough so I am going to continue something that got me thinking from that thread.[:o]


I have often felt that ke will allow a person to get by with less foc if they have higher amounts of ke.The reason I feel this way is because of the mechanical definition of ke is.

The motion of a body may be one of pure translation,pure rotation,or a combination of rotation and translation.By tranlation is meant motion in wich every line in the body remains parallel to its original position throughout the motion,that is no rotation is associated with the motion of the body.

This to me states that an arrow would have more ability to remain traveling in a straight line toward the target and through the target as the ke goes up.Both are characteristics that foc can help with.

To take it a step further,wouldn't an arrow be more forgiving to outside forces such as wind and torque if it has more ability built in to remain traveling in a straight line.I am not just talking about sheer weight because we can most likely agree that weight will make an arrow more stable.But isn't it the actuall ke that helps makes the arrow more stable.Therefore if you have higher ke,you can have a more forgiving setup.


This is helpfull when choosing a head,knowing you have more ke will allow you to shoot more aggresive fixed blade heads.Of course speed is a consideration.



I know that most traditional equipment doesn't produce high ke but they do have a lot of weight(momentum),slower speeds, and high foc.This is counteracting the low ke.Isn't it?:eek:


I probably should have posted this in the technical forum but it is a bit late now.


I was just wondering what everyone else had to say about it.


Come on Arthur,I know you will have an opinion on this subject.;)

RE: Ke and flight characteristics
 

Yep. Here I is. :D

No. Momentum is actually what makes an arrow more stable. By definition, momentum is force applied in a specific direction. KE is a non-directional factor. The more momentum, the more it resists any change in it's direction. That is why a heavier arrow is more stable.

Increased FOC is another factor that enhances stability. Aircraft that are too light in the front end will not fly at all. Drag on the back end of the shaft enhances stability. Also, spin around the longitudinal axis of the arrow is a huge stabilizing factor.

Bullets have plenty of KE and most of their weight is in the back (back of center balance). But if they don't have enough spin to stabilize them, they begin to tumble.

RE: Ke and flight characteristics
 

But isn't momentum the object is moving in a direction,ke is the force within the object.

Yes,I agree that foc does play a role but why do you need more foc to get good flight when using heavy arrows than you do when using lighter arrows with higher ke.


Doesn't ke and momentum both play a role? We all know the penetration argument but this is another twist to the old argument.



A bullet has many other variables.Speed is one.The lack of foc would explain the tumbling but speed allows it to continue in a straight path.

RE: Ke and flight characteristics
 

Too many of today's bowhunters are a victim of the Internet. They have too much access to too much information, much of which they do not comprehend and will never comprehend. Most are average shooters and average hunters that may shoot only during the pre-season and season period. If they try to understand and apply the sciences, they end up with an information overload and are left totally confused as to what is relevant (what they need to know) and what is not.

All the study of science of matter and motion, the endless scientific research, and the intellectual theories regarding what an arrow does in flight and what arrow setup will do the job can be reduced to this BOTTOM LINE statement I read in an article concerning arrow speed and KE.

"Any bow at 45 lbs. or better, within 20-30 yards will do the job nicely if the arrow is placed right and the broad heads are sharp."

In other words; (just) use an arrow that has weight to it, fletch it with ample 5" to 5.5" fletching to quickly and efficiently stabilize the flight, mount a sharp broadhead that will penetrate even at a low KE, shoot the arrows for accuracy and grouping, and go hunting.

RE: Ke and flight characteristics
 

It depends on what the meaning of the word "is" is.:)

RE: Ke and flight characteristics
 

TFOX, Maybe this will help, KE is the amount of stored energy within the arrow. It takes more energy to propell a 400 gr. arrow to lets say 250 fps than it does to propell a 300 gr. arrow to 250 fps. The energy is stored within the arrow. Where FOC comes into play is that with an extremely heavy FOC the arrow will tend to nosedive. When the arrow begins to nose dive the fletchings will have more pressure on the air. Causing them to dig into the air. This starts to slow the arrow down. With a reduction in speed the kinetic energy will also reduce accordingly. You can get too light FOC and the arrow will loose its stearability because the fletchings aren't "digging in" the air. Thats where the FOC recommendations come from. It will give you the optimum steerability with the minimum drop. As far as wind being a factor. It takes more wind energy to blow a heavier object the same distance than it does to blow a lighter object. Thats where the heavier arrow will be more stable in the wind. I shoot alot of 3-D competitions and choose to go with a heavier arrow(423gr.), by 3-D standards. I do much of my shooting in the wind. The guys with the 350 grain arrows have alot of problems when it gets windy. I can usually get everyone of them because the wind is less factor for me. Shooting at 280 fps. I find that I can still run with them on a calm day. But in the wind I can usually pull away. Hope this helps you understand.

RE: Ke and flight characteristics
 

Elk ,I know all that.I was wanting to take it a step further and get into the actuall physics behind it.


Like when an arrow front does get out of shape(like from torque).I know that fletching and foc will play a huge role in getting it back into shape but will an arrow with the same foc and the same fletching but one has 5 more ft/lb's of ke.The one with 5 more ft/lb will straighten out faster,OR WILL IT ?,Why is that?Is it because of momentum or is it because of ke.


Heavier arrows are more stable in wind and foc is a huge advantage.Why is it that a light arrow does great at 10% and you see traditional guys using upward to 16%-18% on their really heavy,slow arrows.They do nose dive but they seem to need the heavy foc along with the huge fletching.

Heavy arrow will need more stabilization on the back than a light.As speed increases,the need for huge fletching decreases.Just check Easton site on this.Is this because of the lack of ke in the traditional equipment?



See where I am going,much deeper than you need between 10%-15% foc and 4"-5" vanes.Or a certain arrow weight.



I know most don't give a rats %$# but it interest me.

RE: Ke and flight characteristics
 

As I stated in my last post the higher the FOC the more the vanes will dig into the air with the arrow nosediving more. Most of the traditional arrows are heavier and thus it causes more force to straighten the arrow out. If you have more down force on the front of the arrow it will make the vanes more effective. The bigger the vanes are the more surface area there is to work on the arrow. If an arrow has higher KE that means it has more speed thus meaning that there are more forces working to stabilize the arrow. Thats why the need for the bigger vanes. Also with shooting fingers. You get a less than perfect release and more fishtailing in return needing aditional stabilization.

RE: Ke and flight characteristics
 

I honestly have to say, I don't know. But if you're talking shooting the same weight arrow faster in order to pick up the extra 5 ft lbs of KE, you gotta remember you're also picking up more momentum at the same time.

If you want to get into fluid dynamics there is something else to consider... Since resistance increases by the cube of speed (speed X speed X speed) then the fletching is going to have more air resistance and so will have a bit more effect on the faster arrow than it will on the slower arrow. And so will the broadhead blades on a poorly tuned arrow.

To pick up 5 fps, that's like shooting a 400 grain arrow at 290 fps vs the same arrow at 281 fps. The 3% increase in speed gives you a 9% increase in resistance. In theory, the arrow could stabilize 9% sooner at 290 than it would at 281. Hardly worth the effort, in the grand scheme of things.

What would happen if you dropped arrow weight to 350 grains and drove it at 310 fps to get 75 ft lbs of ke? Resistance would increase by 26%. Possible it would stabilize 26% faster? Maybe. Maybe you could get the same stabilizing effect with 26% less fletching area. I dunno.

On the other hand, you've sacrificed some momentum at the same time you've increased resistance to the broadhead, so what would that do to penetration?

Anybody besides me confused all to heck yet? LOL :)

RE: Ke and flight characteristics
 

Not yet Arthur P, but lets not get into drag co-efficients. My head is starting to hurt.

RE: Ke and flight characteristics
 

Oh crap! Yet another variable.[:'(]

RE: Ke and flight characteristics
 

Arthur,

I think I am following what you are saying but it would seem like there was a point of deminishing returns considering the fact that broadheads typically get more eradic at higher speeds. Since the resistance on the broadhead and the fletching would theoretically increase proportionally I can't help but think there is a belle curve in the effectiveness of increased drag? Would you agree?

RE: Ke and flight characteristics
 

I agree silent,there will be a point that there will be so much turbulence that stabilization would be next to impossible.


Elk,you are on the money with foc,I agree but if the heavy,slow arrow has the same foc as a lighter one it will still need more Fletching.Slow arrow will become unstable in flight unless their is sufficient stabilization on the back.The speed will actually help stabilize a light arrow to a point.


I do not agree with you that speed needs to be increased to increase ke,you increase momentum AND ke when shooting a heavier arrow out of a bow.The speed decreases but ke increases.


Arthur,you are catching on to what my question is.Yes there are many other variables beyond foc,momentum and ke.Drag coefficients is one.Diameter is another.How about spine,that is another huge variable.Imo their is no 1 thing that does everything,they all are needed and should be taken into account when setting up equipment.


All of these variables is why I have always said to get a well balanced arrow and stay within the parameters that Easton gives you on their hunting charts for arrows.


Aluminum needs some thicker walls to be effective,imo so naturally they will be on the heavy side and carbon doesn't need to be as heavy,IMO to do the same job .As to how much,that is debatable,heaven knows we have debated it.;)
But maintaining a good foc and a proper spine will always be at the top of my list.

RE: Ke and flight characteristics
 

I certainly believe there is a point of diminishing returns, but a bell curve? I doubt it's so. If it were a nice bell curve, someone could sit down and come up with a foolproof mathematical formula to plug numbers into and always come up with the perfect arrow setup for whatever speed you were looking to get. So, if it really was that easy, I'm sure some brainiac would've already figured it out and we'd all be using calculators to make arrow/fletching/broadhead/FOC selections.

You know, TFOX, there are so many things going on with arrows that it really boggles the mind. And I am one that is easily boggled. ;) That's probably why I like my slow old logs so much. They're easy to tune, outside forces don't affect them as much as they do light, fast arrows. And even with my imperfect form and tuning skills, I can still get great arrow flight and accuracy.

RE: Ke and flight characteristics
 

Arthur,I am not just talking about the time it takes but how much easier that it might stabilize.Meaning that an arrow with more ke could starighten back out EASIER than one with less,making it more forgiving to torque.



Please don't take any of this too serious,I am just being a bit out there right now.

RE: Ke and flight characteristics
 

Yea Arthur,when throwing logs it is simple,IF you get enough fletching and foc.;)

RE: Ke and flight characteristics
 

In case anyone was wondering, yes, I did say "I am not a good enough archer to shoot a super speedy setup." And I am perfectly comfortable with that. :D

TFOX, simple has it's virtues. ;)

RE: Ke and flight characteristics
 

Simpleton ;):D[8D] Some how I don't think that is the case.

RE: Ke and flight characteristics
 

TFOX. there is a website that calculates everything for you. You put in the fletching info. Arrow weight and length, tip weight etc. and it spits out the drag co-efficients etc. It is kinda interesting even if a person never uses it. Your are absolutly correct. Every thing that you mention has its part in arrow flight. Whether it is neccessary to the average archer, probably not. But it gives us something to think about when we are not hunting!!!!