RE: arrow speed and distance
 

ArthurP and reylamp, you guys both make some valid points so I did some conceptual physics research and have identified a variable that I did not consider, which in a round about way you both did. Momentum. Your right check this out.

The only tricky part of the equation, like that for kinetic energy, is determining mass. Rather than taking the weight of your arrow and multiplying it by the velocity, you must first take the weight in grains and divide by 7,000 to determine the weight in pounds. After determining the weight in pounds, you must then divide that result by 32 (for the force of gravity). The result from that equation is expressed in " slugs" and is then multiplied by the speed of the arrow to determine the momentum, expressed in " slug-feet per second."

Lets take a look at the arrow to see how well it penetrates:
wt. = 550 gr.
Vel.= 200 fps.
For the equation:

mass = 550/7000 = .079 lbs.
Then .079/32 = .0025 slug
finally
.0025 x 200 = 0.5 slug/fps momentum

Now, what happens when we reduce arrow wt. By 190 grains to the AMO recommended minimum for a 60 pound bow, 360 grains, and gain 80 fps in speed?
Wt = 360
Vel = 280
mass = 360/7000 = .051 lb.
Then .051/32 = .0016 slug
finally
.0016 x 280 = 0.448 s/fps momentum

Now, given broadheads of identical design, cutting width and sharpness, the combination with .500 slug-feet per second momentum will penetrate better than the faster but lighter combination at .448 slug-feet per second.

If we had used the formula for kinetic energy, the lighter arrow would show a definite advantage at 62.7 foot pounds of kinetic energy versus the 49 foot pounds for the heavy arrow!

Just some food for thought. Thanks for keeping me honest.

RE: arrow speed and distance
 

Capt Ray.Yes momentum is a big part of penetration but you still totally aren' t getting the point.The light arrow DOES NOT have more ke.PERIOD.nor does it have more momentum,which you agree on.This isn' t a matter of opinions but a matter of FACT.The only way it produces more ke is to increase the draw length or bow poundage.And it still doesn' t have more momentum,unless you do some major increasing of the draw length or weight.

You must account for efficiency of the arrow bow combination.Do you not believe my arrow speeds and weights?my light arrow has 53.3 ft/lb ke and the heavy arrow has 54.5 ft/lb.This is a fact and will be the same results on 99.9% of the bows in the world.I changed nothing but arrows.My archery program said the heavy arrow should be shooting 263 fps and the chrono said it was shooting 262 fps.Might be the untuned setup.The fact remains that the heavy arrow is more efficient,even from an untune setup.

RE: arrow speed and distance
 

Capt Ray,I just run your arrow weights through my program and you can see by my previous post that it is very close to real life #' s.


Out of my hunting bow a 550 gr arrow will shoot 220 fps @ 59.12 ft/lb ke
the 360 gr arrow shoots 262 fps @ 54.8 ft/lb ke

You can try to discredit the program if you want but I have shot literally hundreds
of arrows trying to prove it wrong and it is always very close.

For some reason you believe your velocity will go up much more than it really does.I' m not trying to get on you but merely trying to explain what is happening.You are not alone with this misconception and I' m am just trying to help.

RE: arrow speed and distance
 

Capt Ray, I' m very much a fan of momentum. My hunting arrows are never less than 550 grains because they have BOTH, an advantage in KE and an advantage in momentum, over a lighter arrow from my bow. Since I shoot instinctive for hunting, with stickbows and compounds, and limit my shots to 30 yards and less, trajectory is a non issue.

If TFOX is up to the task, I' d ask him to run one of my bows thru the program for an example. Hoyt ProTec, LXPro limbs, Accuwheels, fingers release, 60 pounds draw weight, 33" draw. Arrows are 32" long, 470 grains for carbons and 580 grains for my 2315' s. 4" vanes on the carbons and 5" feathers on the 2315' s.

RE: arrow speed and distance
 

Arthur,I just gave it a run.Now I don' t know how efficient your bow is so the fps might be off.

My 2001 Hoyt catalog said the bow should shoot 255 ibo.My program agreed.So that is what I used but this may be different than what you actually get but the relationship should be close.Seems like I remember you saying you were getting 220 at one time but who knows.


470 gr carbon-216 fps @ 48.7 ft/lb ke
580 gr aluminum-198 fps@ 50.5 ft/lb ke.

To tell you the truth I have never been able to actually test anything against the program out that far in draw length.The program might be off when you get out to those crazy draw lengths.I am still amazed when I see you type it.[&:]


I was having a hard time getting the same weight out of the carbons.I was using evolutions but they were not adding up.Were these a real setup or just imaginary.

RE: arrow speed and distance
 

OOPS! I think the atypical draw length might have over-amped the system. :D The chronograph said I am getting right at 220 with the 2315' s and close to 240 with the carbons. But that was never double checked with a different chrony, and you know how chronographs can lie. ;)

RE: arrow speed and distance
 

Like I said,the program needs to know how efficient the bow is.The ibo of the bow may be 275 fps.I do not know.I can adjust accordingly.But like you said,if the chrony hasn' t been checked, who knows.Also,it helps to take actuall measurements and plug them into the program and not from a catalog




When I build a bow with the program I can give it an actuall chrono reading and the force draw curve is created from that.If you do not know this # for sure then everything is just a guestimate.You can also shoot the bow and use site clicks on a sight bar and count clicks from different yardages and get accurate speeds.

RE: arrow speed and distance
 

Arthur.Are you sure the poundage is correct.Usually round wheels come out right.At least at shorter draws they do.;)You said 60#' s.70#' s keeps coming out exactly what you are getting. I guess this is why you can build in the efficiency yourself.I was using round wheels.Soft 2 cams come out with your numbers also.

RE: arrow speed and distance
 

Capt Ray.Just so you know.My bow is built on my program with an actuall real life efficiency rating.my bow will give much more accurate numbers because I have checked every measurement and speed and inserted them into the program.Like I showed you earlier.262 on chrono and 263 on program.


I just wahted to say this because I can already see the rebutle.;)

RE: arrow speed and distance
 

I don' t know for sure, TFOX, but I think the Accuwheels could technically be called a soft cam, because they' ve got a pretty healthy lobe on the cable side. I did put a little extra pre-bend in the limbs last time I twisted up the rigging, but I' m sure I didn' t pump an extra 10 pounds into them!