Poundage Efficiency of Modern Recurves

[LYONEL]

If all things were equal on a modern recurve other than poundage etc

Same model bow
Same materials
Same bow length
Same draw length

All bows shooting 9 GPP with identical made up arrows other than bare shaft weight which poundage range would be the most efficient.
Examples.

40#bow 360grain arrow 170fps =4.25fps per pound of bow weight

Would these next two weights be as efficient (Idon't think they would be)etc

50#bow 450grain arrow 212.5fps =4.25fps per pound of bow weight

60#bow 540grain arrow 255fps =4.25fps per pound of bow weight

(I don't know of a 60# recurve shooting 255fps with 9gpp)

At what point would inceases in poundage cause a bows efficiency to take a big drop rather than slight decreases.

[Ragnarok Forge]

The example you use actually has all three bows being equally efficient.   There is a point where the increase in bow weight is offset by the mass of the limbs.   Each bow design hits the maximum efficiency at a different point depending on design.  The real measure is when a set bow design firing matching gpp arrows reaches its maximum velocity. Unless of course you want to use penetration as your measure of efficiency.  You can plug the numbers into the impulse momentum equation to determine that answer.

[Forrest Halley]

It appears to me that the velocity increases are a bit ambitious. Forty fps for every ten pounds draw increase is an awesome dream, but if it were true all 100# bows would be laser flat and everybody would be gutting it out for the benefit. I'd say that benefits of draw weight efficiency must stabilize in the high sixties to mid eighties depending on the bow design. Every 100# design I have seen has an instantly recognizable bludgeoning potential. As such one can assume that while the KE is increased from that of an 80 or 90 pounder the efficiency is not as increased as say a 70 vs. a 50 or 60.

[LYONEL]

The examples shown are based on all bows being equally  efficient , we all know this is not the case hence my question what poundage in a modern recurve would be considered to be the most efficient. In other words at what poundage would the foot per second for each pound of bow weight start to decrease instead of increase.This question pertains to speed  only. I know there are a lot of other equally or probably more important aspects to a bows performance & shooting characteristics.This question is purely just out of curiosity as I see a lot of people are shooting  quite low poundage bows.

[LYONEL]

Sorry I said in my previous post " at what poundage would the foot per second for each pound of bow weight start to decrease instead of increase. I didn't mean decrease what I meant was at what poundage would the gains in speed be minimal enough to be considered  not worth while.

[Glunt]

The lighter bow would "win" by far when judged the way you have it layed out.

If the 40# bow does 170fps with 9gpp, the 50# and 60# would probably also be very close to 170fps with 9gpp.  That would make the "fps per pound of draw" keep getting lower as weight increases.  But I would consider them equally efficient if they all went 170fps with 9gpp.

Its a little different way of looking at efficiency.  When I think of efficiency vs draw weight, I would want to know at what draw weight does a certain design go faster or slower with a 9gpp arrow.  I have no idea.

[MikeM]

Jack Howard (bowyer) use to say that you reached maximum "efficiency" somewhere around 55#

[LYONEL]

That was the kind of answer I was trying to find. I wonder if this would apply to any design of traditional bow

Jack Howard told me the same thing, and he added that the poundage would be less for a 27" draw than for a 28" draw with his bow.  I think that a Hill style longbow the peak will vary depending on bow length, draw length and how lean the bow was made, but the peak can be higher at times than the Jet recurve as far pounds go, I have only ever seen one longbow shoot the same hunting weight arrow faster than the 55 pound Gamemaster Jet, my Schulz Legend and it's 64 pounds at my draw. Personally, I would never get a recurve that was heavier than 55 pounds at my draw, no point to it.

[wingnut]

The math is flawed in the real world.  What you will find is that the identical bows will shoot the 9gpp arrow the same speed.  So if the 40# bow shoots it at 170, the 55# bow will also shoot it at 170 or pretty danged close.

Now you need a bow that will shoot the 9 gpp at 195+.

Mike

[bow_man_66]

I agree with wingnut, my experience has been that most bows shooting the same gpp arrow will shoot approx the same fps. I have been lowering my poundage I shoot, matching the gpp and still maintaining close to the same fps. And my shooting has improved from shooting less poundage.

Scott

[John Havard]

Mike is 100% correct.  Bows of precisely the same design shooting precisely the same grains per pound will shoot precisely the same speed with one caveat.  A 40# bow with a 100 grain string might be a half-foot per second slower than a 60# bow with the same 100 grain string.  You must use a shooting machine to notice such things.  So a 40# bow shooting a 360 grain arrow will shoot X fps and the same bow design at 60# will shoot a 540 grain arrow the same X fps.

Maybe this link will help:
 http://dryadbows.com/Defining%20Bow%20Performance%20Dryad.pdf

[Sixby]

No Diminishing returns guys? I have to admit that I have always thought that suing exaactly the same design and shooting say 550 gr arrow,  55 lb bow , 190 fps. That when I got up to 80 lb same design and shot an 800 gr arrow I would be blessed to get 180. But I may be wrong. I can honestly say I have not chronographed higher poundage bows agains same design medium weight bows. I used these poundages and speeds only as an example.
God bless and Merry Christmas to all, Steve

[LYONEL]

Thanks John, For That Link.
It made very interesting reading.I have printed it out & will read it several more times.I think it will take me a month to get my head around it all.Do Dryad build a non ILF Takedown? Also I see you don't use foam in any of your limbs on the Dryad
Website is there any reason for this?

[John Havard]

Lyonel,

Thanks for the kind words.  We're going to introduce our three-piece ACS recurve and three-piece ACS longbows in bolt-down (non-ILF) versions this January (in less than a month).

Regarding foam cores, I still have an open mind but I've tested two sets of our limbs we built with foam and have found that both were noticeably slower (like 5-6 fps slower) than the same exact limbs made with our bamboo.  That's not to say that foam cores might not work well for others in their bow designs.  But in the ACS carbon limbs, foam cores are actually a step backward in performance when compared with our bamboo cores.

[LYONEL]

Look Forward to seeing them

[**DONOTDELETE**]

Originally posted by John Havard:
[qb] Mike is 100% correct.  Bows of precisely the same design shooting precisely the same grains per pound will shoot precisely the same speed with one caveat.  A 40# bow with a 100 grain string might be a half-foot per second slower than a 60# bow with the same 100 grain string.  You must use a shooting machine to notice such things.  So a 40# bow shooting a 360 grain arrow will shoot X fps and the same bow design at 60# will shoot a 540 grain arrow the same X fps.

Maybe this link will help:

Well guys... I respectfully disagree with this line of thinking. it's one of those things that looks good on paper, but doesn't test out the same.


In order to get a 35 pound bow shooting 350 grains the same as a 60 pound bow shooting 600 grains requires close attention to keeping the core to glass ratios the same for one. and secondly the working portion of the limb needs to be shorter on the lower poundage bow to get enough pre-load to stop the limbs. It can be done if everything is scaled down proportionately, but not if the bow limbs use the same glass thickness and width profile, and working limb length.  

The 50 pound bow shooting 500 and the 60 pounder shooting 600 is going to be a lot closer to the same, but the lower poundage bows are just not going to be as efficient if they are built exactly like the higher poundage bows because they will not transfer the energy to the arrows the same.

i pulled my hair out for a long time working out a formula to keep lower poundage bows performing as well as heavier bows, and my testing proved it requires altering your core lay up, as well as core to glass ratios right to pull it off.

[LYONEL]

Thanks for your observations  Kirk , the different thoughts on this subject are interesting for me & worth more research.Just one question, is there really a particular bow weight that would be considered most efficient. I'm starting to think its the heaviest weight that you can shoot comfortably with whichever design of bow you choose to shoot.

[Blaino]

Really interesting stuff... way above my pay grade though  :confused:    

[John Havard]

Kirk, I'd be interested to know what your testing of the lighter bows shows the drop off in performance to be when precisely tested with the same gpp arrows and shot out of a shooting machine.  My experience backs up exactly what I said earlier, although I must admit that I've never tested one of your bows.

I have only tested a few bows down in the 35# range (because we don't build many there) but when we build bows that light we normally alter the amount of hard outside stuff as well as the amount of core.  Otherwise we can't get the limbs to be light enough.  I don't see that as an alteration of the basic design of the bow.  Anyway, based on many many tests I've never found a light bow any slower than a heavier bow ceteris paribus.