I've read from a few places that around 50-55# is max efficiency for most modern recurve bows that are glass backed. How does this translate to arrow speed?
If one is shooting a 30# bow or 40# bow at 10gpp and jumped up to a 50 or 55# bow with 10gpp arrows would the 50 or 55# bow cast a 10gpp arrow at a faster speed since it's more efficient?
I've also heard Byron state that he shoots a 70# longbow for the same reason, at 70# for modern glass/carbon backed longbows max efficiency is supposedly reached and gives the fastest cast.
I'm just curious because it seems like to me as this may be the case but just wanted to make sure.
It's theorized that kinetic energy is a reasonably good way of assessing overall efficiency. Arrow speed X arrow weight in grains divided by 450,240 gives foot lbs. of kinetic energy. I'll leave the plug-in math up to you.
Put simply, if you want to maximize efficiency then shoot heavier arrows.
a better method than KE would be momentum. The resistance to stopping...a layman's imagery for the measurement might be-
Using a machine, throw a ping pong ball and a golf ball using the same force- at a snowbank.
Which will go deeper into the snow?
Forestdeweller, Don't think you could generalize all recurves like that since there are several designs in recurves, standard, semi-static, static super curve for example. That is to say limb design will effect efficiency. The bowyer would usually know what his design maxes out at.
As Katman said, it really comes down to the particular bow.
What happens is that at a certain weight, the stiffness of the limbs causes additional flex through the riser, which lowers the efficiency.
On the other side, you will lose efficiency to extra string mass, limb and tip mass, etc. on lighter models. This also depends on the design, which is why many bows have a "sweet spot".
They're very small differences, usually, and normally anyone shooting 45-60# will be pretty darn close to "optimal".
QuoteOriginally posted by katman:
Forestdeweller, Don't think you could generalize all recurves like that since there are several designs in recurves, standard, semi-static, static super curve for example. That is to say limb design will effect efficiency. The bowyer would usually know what his design maxes out at.
Well when I said recurve I'm talking about the modern recurve used in Olympic Style archery and the likes.
Shoot as much weight as you can handle, for both bows and arrows...these days I mostly hunt with 60 pounds bows and 900 grain arrows
DDave
QuoteOriginally posted by Ray Hammond:
a better method than KE would be momentum. The resistance to stopping...a layman's imagery for the measurement might be-
Using a machine, throw a ping pong ball and a golf ball using the same force- at a snowbank.
Which will go deeper into the snow?
+++1
very good saying :)
Ray, please explain something for me. Is not KE (and the resultant momentum) a function of mass and velocity? Therefore, if an arrow of a given weight is shot at the maximum achievable velocity, is that not just another way to express maximum momentum. I'm not being argumentative, I just don't know the "science" of physics, but the "English" seems to essentially be saying the result is basically the same thing.
I'm getting a lot of posts about momentum and KE but what I was asking for was is there a particular draw weight at which a bow will cast an arrow the fastest independent of arrow weight for a particular bow?
Sorry for the confusion!
If you mean maintaining a consistent GPP all through the various draw weights, then my answer is the heavier the bow the higher the efficiency rating. My guess on this (and it's only a not very scientific wild ass guess) is that draw weight is going to rise at a higher rate than limb mass allowing more energy to be imparted to the arrow.
QuoteOriginally posted by monterey:
If you mean maintaining a consistent GPP all through the various draw weights, then my answer is the heavier the bow the higher the efficiency rating. My guess on this (and it's only a not very scientific wild ass guess) is that draw weight is going to rise at a higher rate than limb mass allowing more energy to be imparted to the arrow.
Thank you that's what I was asking for.
I figured this was the case since if you took a 20lb bow with a 200 grain arrow and shot with it I'd imagine if you took the same bow design and made it 50# instead with a 500 grain arrow that the 50# bow with the 10gpp arrow would be significantly faster.
You might try this is the bowyers bench for a more technical answer. I also remember reading something like your op but don't know your answer.
http://tradgang.com/cgi-bin/ultimatebb.cgi?ubb=forum;f=125
Didn't Fred Bear say that there was a weight at which increasing a bow's weight would become counterproductive, due to the increasing mass and weight of the limbs? I thought that was around 60-65#.
I'm paraphrasing, since I've always heard that fact second hand.
Be careful with theory and math and the like. Whatever the answer is, I am gonna go on the line and say if you took a bow in 45# and a SAME bow in 60# and shot arrows of 10 gpp out of each, there may be a winner in terms of speed, but it will not be a huge win. Certainly not something worth worrying about.
The difference will be in momentum gained by making a heavier arrow go the same speed as a lighter arrow.
Chuck
QuoteOriginally posted by monterey:
If you mean maintaining a consistent GPP all through the various draw weights, then my answer is the heavier the bow the higher the efficiency rating. My guess on this (and it's only a not very scientific wild ass guess) is that draw weight is going to rise at a higher rate than limb mass allowing more energy to be imparted to the arrow.
To a point, which as I said before varies between bows. When you reach a certain level of stiffness to the limbs, it becomes great enough to begin inducing flex through the riser, which lowers the efficiency.
There is a broad "sweet spot" but it depends entirely on the bow as to what the exact range is. For the most part though, most bows will reach that point around 45-60#, though.
Too heavy, and you lose efficiency to flex and vibration. Too little draw weight, and you lose efficiency to too much mass.
Yes, you had me thinking about riser flex when I saw it in your first post. Not sure I can see my way to agreement with that. The construction of the riser and the wood or other materials incorporated into the riser I think would make a significant difference in the riser flex effect.
It may not be within the scope of the OP's question, but chuckc's point about the advantage of an ever increasing arrow weight in terms of terminal penetration would be very noticeable.
That's why I said it depends on the bow. The Hoyt Excel ILF riser is a good example of a riser where you can feel the flex and vibration with the heavier limbs. Most wooden recurves and longbows have short, stout risers but a thin, narrow grip or one without sufficient lamination will flex there. The rest of the riser can be made of thick steel, but a small throat will become the focal point of flex.
I've built bows from 10# up to 100# and unless your riser is significantly overbuilt, there is a point of diminishing returns. As a matter of fact, flight shooters found that the most efficient bows were in the 35# class, not the unlimited. Of course, this means little to hunters, who just need delivered energy regardless of how they get it.
You're making this much more complicated than it is...but I guess that's the norm for internet archery.
How am I making things complicated? We all strive for maximum performance from our equipment.
Even Byron has talked about the reasons behind him shooting a 72# bow before and in his own words "that's when his bow style reaches maximum efficiency and gives the flattest trajectory".
He shoots the classic D shaped longbow so it requires a lot more wood to increase the draw weight on them which means they reach peak efficiency at a higher draw weight than say a recurve which already has thin limbs.
Maximum effcinecy = flatter trajectory
the most efficient bow and arrow setup is the one that you can well control and exhibit consistent accuracy at sane shooting distances.
as to the details of bow weight and arrow weight with regards to hunting critters, all that will matter is that the arrow, which is Far more important than the bow, is of a weight that will insure good penetration when a razor sharp cut-on-contact broadhead is employed.
the 10gpp rule of thumb is quite apropos. as to the bow's holding weight, that's up to the operator, with regards to local trad archery hunt regulations, the type of game hunted, the typical kill distance, and absolutely the archer's abilities (or lack thereof).
let all of the above rule the absolute specifications for bow holding weight and arrow total weight.
I believe Byron has also said that he shoots 70# because he has a bad release. The truth might be that he just likes shooting 70# and it has nothing to due with engineering or releasing.
Searching for optimal efficiency like this is not a single numerical answer. There are too many other variables that you will have to take into account.
No. It all depends on the bow design by the bowyer. Most modern day bows are probably designed for max efficiency around 50# because that is the most requested bow weight. But if a bowyer was so inclined, he could design a bow to max efficient at any draw weight. Its just 50# is the best weight to design at because I would wager 90% of the bows ordered today fall within +/- 5# of 50. But again, its all in the design. You can't generalize all recurves into the same pot.
A machine (bow) is designed to do certain things. Each is designed differently. Each is designed ( whether on purpose or not) to react in different manners, fast, slower, shorter longer, whatever.
It is not so easy to assign a simple answer to this question because there are variables, especially with "stick bows" which have no actual "stop" like a compound machine. Drawing a heavy bow to its best draw length will equal certain response, but drawing it further may or may not improve upon that response even though it is then heavier.
Adding arrows to the discussion, the weight of the projectile will greatly influence the amount of energy transferred from the bow to the arrow as will resultant imperfections in the arrow flight and recovery from any deflection of the shaft upon release.
Also, from everything I have read, the math calculation for KE ( kinetic energy) involves velocity squared or multiplied by itself, giving greater weight to the speed of an object than to its mass.
As stated above several times.... too many variables
ChuckC
Shoot what you can handle accurately. Accurately means that when you shoot that bow you can shoot groups of arrows tightly at the max distance you will hunt.
QuoteOriginally posted by KeganM:
I believe Byron has also said that he shoots 70# because he has a bad release. The truth might be that he just likes shooting 70# and it has nothing to due with engineering or releasing.
Searching for optimal efficiency like this is not a single numerical answer. There are too many other variables that you will have to take into account.
Oh yea I agree that is not a single numerical answer but we can get a general ballpark figure.
I know I shot a 22# recurve once and the arrow speed.
I don't believe for a second that Byron has a bad release though.
Interesting discussion though.
I think Jack Howard said 57# was optimal.After 65# your putting more in than you getting out.
QuoteOriginally posted by ChuckC:
Be careful with theory and math and the like. Whatever the answer is, I am gonna go on the line and say if you took a bow in 45# and a SAME bow in 60# and shot arrows of 10 gpp out of each, there may be a winner in terms of speed, but it will not be a huge win. Certainly not something worth worrying about.
The difference will be in momentum gained by making a heavier arrow go the same speed as a lighter arrow.
Chuck
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