What makes some bows more efficient with heavy arrows?

[HATCHCHASER]

Then that means there is not much difference between the performance of bows if you use heavy arrows.  The speed bows only have a noticeable advantage with lighter arrows.  I like heavy arrows so this is good.  I do understand that the more efficient bow loses ground as arrow weight goes up but wouldn't this trend continue?  If the less efficient bow made up 5 to 7 fps in a couple gpp then would it still be behind in a couple more gpp?  Interesting.  Please don't take this as an argument just a thought.

[skarcher]

Originally posted by JimB:
I understand the longer limbs being more effecient but why are they less efficient with the lighter arrow?

I'm wondering if the longer limbed bow has a lower brace height than the other bows.That may help some with heavy arrows.

The brace height on my bows are all 7.25". Limb core on the Whip is bamboo, and on the fastest 58 incher is maple. I don't know enough about woods to tell if this is the difference. The limbs are a different width, the short bow mentioned above is about 3/8 of an inch wider. The Whip has very narrow limbs.

Good discussion folks, thx for the replies.

[LKH]

Lighter arrows will always extract less energy from the bow.  

It's difficult to measure exactly what we get.  Bows are like people, we might be built exactly alike, but our performance will vary.  You'll find different performance in bows of equal weight, even when made by the same bowyer.

[AdamH]

The "Design" of the Bow, That's it ...

[Sixby]

Matchchaser, I have tested hundreds of bows and never seen a bow that was less efficient outperform a more efficient bow no matter the arrow weight. If you have two bows of equal weight and one is more efficient it will always be more efficient even though the numbers come closer together the heavier the arrow. They might get close to even but the less efficient bow will never shoot the arrow faster except occasionally within the margin of error. You may get a few shots faster within the margin of error of the chrono but if you shot 100 arrows the more efficient bow would outperform the lesser bow.

An interesting thing is that the more efficient bow will also be the best mannered bow when shooting lighter arrows because it is transferring the energy into the arrow instead of losing the energy in the form of shock and vibration.

Its an old trick to hide a poorly designed bow by saying it is designed to shoot heavy arrows. Basically it is a smokescreen for a shocky bow.

[skarcher]

Sixby, in all your testing have you ever noticed any statistical difference in efficiency between different lenghts of longbows?

I've only tested my 3 bows so don't have the advantage of the amount of data you must have collected over the course of your testing.

[HATCHCHASER]

How is efficiency measured?  Could one bow be more efficient at 9 gpp and one bow more efficient at 12 gpp? Thanks for the info.

[Jeff Strubberg]

Originally posted by HATCHCHASER:
Then that means there is not much difference between the performance of bows if you use heavy arrows.  The speed bows only have a noticeable advantage with lighter arrows.  I like heavy arrows so this is good.  I do understand that the more efficient bow loses ground as arrow weight goes up but wouldn't this trend continue?  If the less efficient bow made up 5 to 7 fps in a couple gpp then would it still be behind in a couple more gpp?  Interesting.  Please don't take this as an argument just a thought.

The less efficient bow will never take over the more efficient bow.

Look at it this way.  That heavy bow limb will remain a heavy bow limb and will sponge up just as much energy to get it moving no matter how heavy an arrow you put on it.  You can realize some gains by making the arrow stay on the string longer, but the more efficient bow is also gaining.

[George D. Stout]

You can't outstage physics. Rules is rules.  

[Sixby]

Well Said George.
I have not noticed as much difference in efficiency in bow lengths as I have in bow design. Total design including riser ,. Stiffness ect. Some of the most efficient bows I have seen are 64 in D and R longbows.

A couple of bows tested at the WTT last year were in the hi 90s.  

There is a lot of hype put out by some builders about this bow or that bow being the new Valhallah of all bows . That is usually until they are tested under controlled conditions and exact measurements . Some bows are the real deal though and I will give credit where credit is due.
Centaur is the real deal. They were tested against some of the other highly touted bows and although the other bows performed well they were smoked by Centaur. Except for Whippinstick and Sasquatch. They were in that same high 190s class at 10 gpi . those bows were all unbelieveably efficient bows.

 I'm not shilling for any of them and have no stake in them. Except for Kirk at Sasquatch I have not even met any of them. But they are what they are. Finely made efficient bows by master bowyers that understand bow dynamics and physics.

[HATCHCHASER]

So if a bow is more efficient at 9 gpp then it will be more efficient at 12 grains per pound.  The efficiency changes as gpp goes up.  So you can measure efficiency at any gpp? I was reading about dynamic efficiency on the ACS website and the ACS bows DE measures from 80 to 88 percent with arrows from 360 to 700 grains.  Is it not possible for a bow to have it's efficiency maximized for a certain gpp.  Again I am not trying to argue.  Help me understand here.

[freefeet]

I don't class 10 gpp as heavy at all.  Do the same test again with 14-15 gpp - that's heavy.

[Snakeeater]

The only way that a heavier arrow would make the bow more "efficient" is if the arrows greater  mass allowed it to absorb more of the energy being imparted from the bow through the string to the arrow, thus making the arrow faster.

A bow will always produce energy at the same level of efficiency, the difference is how much of it gets into the arrow. What doesn't make it into the arrow turns into vibrations (noise and hand shock).