GMMAT

Let me get this straight, Bob. If somebody's shooting a smoking fast bow.....and his numbers are staggering (arrow speed/KE/etc...)......but his bow is technically not as efficient as a person shooting 100fps slower.....and shooting 50fp's of KE less.....

The guy shooting the second bow can claim (and rightfully so.....don't get me wrong).....that his bow is superior.....because it's "more efficient"?

When we're talking about the modern companies producing compound bows......is this that big of a concern?

I've only been shooting a bow for a little over two years. I hope this is a fair question.

MeanV2

I have been extremely impressed with the speeds and KE my Allegiances have given me in 05, 06, and 07. I know the 07 at 60#, 28" draw was producing more than 68# KE and it looks like for 08 the Airbornes both the 82 and the 101 will best that.
Quite Impressive!

Dan

quiksilver

One thing that alwaysamuses me about the claimed"efficiency" numbers is this: Different arrow spines absorb different amounts of energy, and they flex differently with every different force-draw curve.So unless you're 100% certain that the tester took the time to find an arrow that worked best with the bow... Then the "efficiency" numbers that he's spitting out - they aren't exactly reflecting that bow's actual maximum efficiency.

That wouldn't matter in general terms - but when you're splitting hairs, saying that Bow X is more efficient than Bow Y, because it is .5% more "efficient" - thearrow of choicecould be skewing the results.

Just thought thiswhole conversation was incomplete withoutat least mentioning that the ARROW has a lot to do with a bow'sstated "efficiency."

BobCo19-65

Let me put it a different way.

You can take any compound bow design and increasethe poundage (of course you may need stronger limbs, risers, string, etc) to reach KE energy levels at mentioned.So the KE alone mentioned doesn't impress me.

The most efficient bow will reach these KE levels with more energy of the bow going to the arrow instead of being dispensed otherwise and will take less work from the archer. That does impress me.

Im not getting into commenting onsuperior claims etc. I also won't get into claiming what people look for in a bow is right/wrong either.

I would think effeciency would be a concern for the little as well as big company when designing a modern compound bow.

BobCo19-65

The weight of the arrow will also have an effect.

Arthur P

IF the archer can handle the draw weight. Sometimes that IF can be awfully big. It's one thing to be able to handle it standing flat footed on the ground at the range in 90 degree weather. It's quite another to be able to handle it infreezingweather when you're cold and stiff from sitting still in the stand for several hours.

What Sylvan is getting at is it's not possible - with current technology anyway - to get more out of the bow than you put into it. The energy stored in the bow is equal to the amount of work you did to draw it. (Actually, the bow won't store all that work because you have to subtract for friction, inertia and other inefficiencies, but let's not worry about that. Just take in the general concept.)

But, if we want to know how easy a bow's draw weight would be to handle, we need tolook at draw cycle, not just draw weight. And to do that, we need to know the bow's force draw curve.

When you graph the draw weight at every inch, from brace to full draw - that's what the force draw curve is - you can figure the stored energy. When you figure the stored energy, you know how much work you did to draw the bow. Count the squares that are under your graph line. Everything under that line is the stored energy.

The ultimate in energy storage is for a bow to jump straight up to max draw weight in the first inch and not let off until you hit full draw. If your bow is set at 70 pounds, then you're drawing 70 pounds each inch of the draw. Say the bow has a 7" brace and your draw length is 30", so you're drawing 70 pounds each inch for 23". 23" is 1.917 feet. 1.917 feet times 70 pounds yields 134 ft lbs of stored energy (if you actually counted the squares under the line on your graph, there would be 134 of 'em), which means you did 134 ft pounds of work to draw that 70 pound bow. (There are no bows with this draw cycle because they would be particularly nasty to pull. Most speed bows have a short slope up to peak, a very long dwell at peak, then a very short slope into the let-off. As close as they can get to this 'ideal' but still maintain at least some level of comfort during the draw.)

Say you take off those cams and replace them with round wheels. They give a curve that starts an easy slope up to peak weight about midway though the draw cycle,with a very short dwell at peak, then they break over and give a gentle slope down into to the valley. The slopes on the front and back of peak weightmeans you have less squares under the line onyour graph. Less squares = less stored energy. Let's assume this setup stores 80 ft lbs of energy, which would be about typical for a round wheel bow. You'vedone 80 ft lbs of work to draw that 70 pound bow.

The same draw weight, but it'd be easier to handle because you've done 54 ft lbs less work to draw the round wheel bow.

The force draw curve shows whatmakes one 70 pound bow feel smooth and easy to draw and another feel like you're trying to pull a pickup out of the mud.




- for the reason Frank stated below

PABowhntr

Nice explanation Arthur. Understanding something and being able to articulate it are two entirely different things. You obviously do both quite well.

Glad you are still around.

Sylvan

Don't you want to be "most" efficient at whatever draw you can handle? It seems to me that for what ever amount of energy you expend drawing the bow back, ideally you'd not want to waste a bit of it. You'd like all of your effort converted to arrow velocity wouldn't you?I certaily do. Ofcourse any bow made by man is imperfect and some amount of your effort will inevitably wind up wasted. My point was merely that some bows will waste less of your efforts than others and that is what is important to me. I want to get the biggest bang for my "effort expended" buck so to speak.

I will never shoot an arrow that carries 97.3 ft/lbs of ke simply because I'm not physically capable of expending that much energy drawing any bow over my draw length. But I want to be as efficient as I can be with what God gave me.

c_str

Yes it has a bigeffect because kinetic energy essentially is massx speed x speed.But what has a huge effect is speed, so if you can lower the weight in something, throw it faster because it weighs less, you have much more kinetic energy.

Killing an animal needs enough weight to be effective. (to plow through bones, tissue, etc) Would you rather get hit in the face with a plastic hockey ball, or an NHL puck that is much heavier?

I'm not knocking KE at all, just saying that when killing animals it's not the end all be all. What really it all boils down to as the other poster mentioned, in my humble opinion, is what the individual archer can handle.

BobCo19-65

c-str

In my quote, I was referring to efficiency, not KE.

Personally, I would use momentum as a better indicator of penetration (if that was what you were referring to in your post) then KE. But that would sure open up a whole nother can of worms.