What makes some bows more efficient with heavy arrows?

[skarcher]

Cronographed all 3 of my bows lately and came up with some interesting results. Had correctly spined shafts for all of them and had 2 weights of arrows, 410gr and 520 gr which equated to 8 gpi and a little over 10 gpi.

My shorter 58" bows averaged 7 and 10 fps faster than the 62" with the light arrows, but with the heavier ones they all shot statistically the same.

The 62" is a Toelke Whip, one of the 58" bows is a Thunderstick Mag, and the other one is quite similar to the Mag but made for me by a friend and a bit faster.

Maybe it's just cabin fever, but I would be very interested in some insight in this unexpected surprise.

[Sixby]

Nothing. The most efficient bow will always be the most efficient. At higher arrows weights they will come much closer together but the one that is slower at 7gpi will be slower at 12 gpi. That is if the bows are identicle weights and drawn exactly same length each time.

[skarcher]

I did actually measure all my bows, and they are all within 1 lb of each other on the scale I was using. Can't guarantee that my draw is totally consistent, but the averages I mentioned were over 20 arrows for each weight for each bow.

That's why I thought it so curious, as I shot a lot of arrows. Even had a buddy try my bows. He draws an inch longer than me so his speeds were a little higher, but the differences remained the same. Short bows faster than longer bow with light arrows, same speed with heavy.

[Earthdog]

I find my recurves usualy do better with light arrows,and my longbows to best with heavier arrows.
That's just a general thing though,and my current 50lb Hoyt riser with Tradtech limbs seems to be able to handle any arrow wheight I put across it very well.
My target arrows are 350g and my hunting arrows 610g,,it smokes the target arrows and still shoots the heavies at mid 180's.
The only difference I know of with this set up over most of my other bows is "carbon" in the  limbs.

[Benny Nganabbarru]

Just a no-idea stab in the dark: thicker limbs?

[EzArcher]

with the longer limbs there is more energy stored in the limbs using a heavier arrow uses more of that energy.
with the shorter limbs less energy is stored however they are much lighter so more of the energy is used by the arrow

english longbows were made extremely long so they could shoot heavy arrows that would penetrate armor

[GREASEMAN]

Very good explanations.
Thanks

[George D. Stout]

EzArcher,  English longbows were made long so they wouldn't break so easily.  A short longbow of English Yew, or any other wood, would struggle to stay alive unless built long.  The arrows were heavy, and so were the bodkins, wedge type points, which mostly "rained down" on the enemy and penetrated because they had mass and a very narrow point.  

The old bodkin point would penetrate mail armor, but not plate armor at those long distances.

[LongStick64]

Then how can we compare the English longbow to the Turking/Asian Horn bow. Those little shorties could really zip an arrow and do possibly more damage than an English longbow.

[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.

[George D. Stout]

The comparison isn't necessary since the fighting was conducted differently with each bow.  The English (Celts) could put thousands of arrows in the air at a time, and that created havoc among the enemy forces....read Agincourt if you get a chance.

The little bows of the mounted archers...Mongols, were deadly at close range from full gallop, and were much more of a precise weapon.  I think the biggest difference in the success rate was the horse, as much as the bow 8^).

[Jeff Strubberg]

I wrote one very long, very wordy paper comparing the archery equipment and the techniques of the Persians and the English during the medieval period.  Bottom line, the English warbow was a rugged, reasonably accurate and interchangeable field weapon, while the Persian bows were heighly tuned, personally fitted and finicky weapons.  You could dunk an English longbow in the Thames, string it up and grab any arrow off of a supply wagon and get fair results.  With a Persian bow you had to get up early and warm the limbs over a brazier of coals in order to string it.  Having a partner help didn't hurt, either.

It's also intersting to note that most trick shooting in Persia was done with detuned bows that were much longer and much less curved/recurved than those you see in museums.

[robtattoo]

The English Warbow, don't forget, was an artillery weapon & not a precise 'target' weapon.
It's effectiveness as a military weapon was based solely on the massed volley shots that we (the English, NOT the Celts. Sorry George) perfected during the Hundred Year's War & most famously used at the battles of Crécy & Agincourt. As George correctly states, the lenght of the English longbow & warbow is a byproduct of the inefficiency of the design. A highly crowned belly will chrysal very easily if compressed too far. Adding length decreases the amount of compression on any single point along it's length.

As Sixby correctly posted above, the most efficient bow is the most efficient, regardless of arrow weight. If it's faster at 8gpp it will be faster at 12gpp

[EzArcher]

very good point that english longbows were also made longer to support the 120#+ draw weight and 32 inch draw. Let me rephrase my statement above to 'One of the reasons English longbows were made longer were to use  heavier arrows.'
 there is a good bit of info in The Traditional Boyers Bible Volume 1 pgs. 66-71 about mass placement and bow length.
heres a couple paragraphs from page 66
"Much of the energy stored in long and heavy limbs remains in the limbs after release, becoming hand shock, string twang, and limb vibration.  This is why slower moving, very heavy arrows leave the bow quietly.  Heavy arrows make bows more efficient because more of the bow's energy has time to leave with them.

[EzArcher]

..."This is why flight bows are golf club-like:short,low mass, fast-reacting limbs. Flight arrows, arrows light enough not to impede these fast limbs, can be shot much faster than normal weight arrows.  The same flight arrow shot from an english war bow of equal weight would be considerably slower."

[MercilessMing]

What I am thinking is the energy stored on 3 bows are about the same providing they drew to the same length with the same weight.  However those shorter bows have less total mass weight (arrow+limb+string) to move in the light arrow situation.  Once shooting the heavier arrows, the effect from the less (limb+string) weight is no longer significant.

[LongStick64]

Thanks all for the education, good stuff here as always.

[HATCHCHASER]

If the most efficient bow is faster regardless of weight, then why is there a 7 to 10 fps difference at the lower weight and the same speed at the higher weight.  I know it is not a scientific study just a thought.  

I know one bowyer I talked with said that if you wanted to shoot heavy arrows then use a heavier limb core like osage.  If you plan on shooting light arrows then use a lighter core like bamboo.  I don't know if this is accurate but I do know that mass moves mass.

[Jeff Strubberg]

I don't think bad bows pass up good bows just by adding arrow weight.  I think bad bows have farther to go, so they seem to improve more as arrow weight goes up.

[Sixby]

Matchchaser , great question but already answered in some of the posts. the heavier arrow uses the energy in the heavy limb more efficiently. thus as you go up in arrow weight the two bows get closer and closer to same speed. However the more efficient bow will still be the better performing bow. If only by a half ft per second. The less efficeint bow will never surpass the performance of the more efficient bow of the same poundage. No matter the conformation of the limb.