Author Topic: Question about takedown bows (Read 1583 times)

Naphtali · « **on:** March 17, 2005, 04:37:33 AM »

I have a question that pertains to takedown bows.

Were a bow to have identical limb sets -- IDENTICAL -- one long bow and one recurve, would one limb set store more energy or yield higher arrow velocities with arrows heavier than 450 grains? If yes, please identify which is which. If possible, briefly explain why.

Mac11700 · « **Reply #1 on:** March 17, 2005, 05:32:27 AM »

Depending on how it is built and what matarials is used...the recurve set gennerally will store more energy within the limbs therby transfering it to the arrow...you can gain arrow speed faster...lb for lb. of draw weight...it's the design of the limb that allows it...that is with all things being equal...same material...same width...same poundage of draw weight...I haven't seen to-many true recurved limbed longbows...nor have I seen too many recurves with the amount of deflex in the limbs like what some of the fastest longbows are coming with these days...each design has it's advantages..and distractions...you can have some encredbly fast long bows built these days...and they are a far cry from what was on the market 25 years ago...same too for the recurves...but thru better materials used in them...to the no-stretch strings...they are shooting as fast as a-lot of the mechanical bows on the market...

Mac

Naphtali · « **Reply #2 on:** March 17, 2005, 07:54:39 AM »

I was attempting to avoid all variables except limb shape by referring to the bows as otherwise identical.
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Bob Lee Archery, for example, makes five different models of takedown bow that you can get with "longbow" limb set or recurve limb set.
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I make an assumption here, though, that the recurve is a working one rather than decorative. I have no idea if this makes a difference, though.

I'm of two minds on this. Since there is no gearing à la compound bows, if limb sets are otherwise identical, energy stored should be identical. This makes sense to me.

But if this is a true deduction, there is no purpose for the recurving limb. Stored energy is stored energy.

Except perhaps same energy storage in shorter limbs. But this makes no sense. Just create limbs without a recurve that store the energy you want to store. . . . So I'm back where I began.

I am confident that many, many other neophytes have asked this question, and that more than one person has tested identical limb sets (same draw weight, draw length, etc.) to conclusive answer.

Woodbutcher · « **Reply #3 on:** March 18, 2005, 01:48:16 PM »

Dear Naphtali:
I hear ya. Been there myself. Trying to determine the best based on a formula or a comparison of data. All I ever got was confused. ( I admit that isn't really difficult for me to do! ) Ain't no real answer, cause as soon as you get one something changes, or someone changes something. Someone develops something new or more questions are asked. Is stored energy the proper direction to look, or how the energy is released? I'm asking, not arguing.
Target shooters strive for the ultimate whatever, cause they're working at long range, and anything that might help is wanted.
Hunting, on the other hand is a twenty yard game, ( insert your own yardage here ) and the needs differ from target work. Now I stated those things to ask, what do you want to do with the answer you want? How will it help you to select a bow for the job you want to do? That's been my question! I'm asking, not preachin', cause I've been there and I don't have an answer, and maybe you'll help me learn sumpin. Oh, the times I've agonized over questions lke yours!
Had the opportunity to make a hands on comparison between a bunch of bows, once. Settled on what "felt comfortable" and have stuck with that standard since. That way there's no confusion. Discovered that what felt good to me wasn't necessarily so for someone else.
People are taking game of all kinds, and formal target shooting with bows made from floorboards to the latest, and most cutting edge laminated materials. Designs of all kind abound, wide, long, short, reflex, deflex...I'm so confused!!! And every one is really great, especially if the guy that made the bow, is writing about it!
Neophyte, you say? Who ain't? How long have people been shootin bows, and comparing designs and materials, ect? When you get a satisfactory and definitive answer to your question, please tell me! Please do enjoy your quest in the meantime, cause it's all part of the game.
Woodbutcher

Naphtali · « **Reply #4 on:** March 19, 2005, 03:53:34 AM »

Hi Guys. Here's my reply:

You would think that there are formulae for calculating spring storage (might need to do multiple calculations on working recurve because it might be two springs working together/sequentially??). The mathematics would zero out all the variables, I suspect. But I'm not a structural/mechanical engineer.

Mac11700 · « **Reply #5 on:** March 23, 2005, 07:54:46 PM »

If you take the typical measurement of a recurve...and built a flat/longbow to the same over-all lenght dimensions...the recurve will store more energy in the limbs...they are already prestressed...by their shape...now...if your taking the physical lenght of each limb from the riser block...then magically flattened out the curve to come up with the same lenght...they would have the same energy...but you really splitting hairs...they are both different...and react differently...put recurved limbs on a long-bow...and you have a long recurve...the recurve was built to be shorter than a long bow..more maneuverable...and even though they can built some awsome long bows...none match what has been accomplished with the recurve

Mac

handirifle · « **Reply #6 on:** April 03, 2005, 11:37:59 PM »

Having shot all sorts of bows over the last 40+ years and building them for about 10 I am convinced it is not really about the power stored. Compounds use this as a measurement of effeciency but I think it is incorrectly applied to recurves and longbows.

First off, recurve and longbow limbs CANNOT be identical. If they are, they are both recurves or longbows.

The real power and speed (and advantage over longbows) of the recurve is in how QUICKLY that energy is released via the recurve. I have yet to see a MODERN recurve bow that was not a working recurve. Many factors play a role. The width, weight and materials in the limb itself.

The faster the recurve tip can unfurl, the faster the bow will be. Narrow, lightweight limbs usually will produce more speed than wide heavy ones drawing the same weight.

Type of string material plays a role too, since it is the final contact with the arrow. Newer materials will send a greater amount of the bows energy into the arrow, but at a price.

My 66" Martin recurve was factory 60lb with wide limbs. I reduced the draw weight by narrowing the limbs from 2" in the middle to 1 3/8". I also added phonelic material to the tips and installed a fastflight string. All told I ended up 10fps faster than when it was 60lb and now it draws 55lb.

Naphtali · « **Reply #7 on:** April 04, 2005, 04:11:36 AM »

Handirifle:

You went right for the throat of the query. I was doubtful that my question was a meaningful one after Mac11700's responses. I invested some time with a patent (USPTO) search plus several Internet search engine queries.

Bob Kooi, et.al., through Joe Tapley's URL, have several articles and a doctoral thesis pertaining to bow mechanics and design.

One thing that surprised me is that Kooi concludes that initial velocity is about the same for all types of non-compound bows [compounds not studied] under similar conditions that is, same draw weight, draw length and mass of limbs, while the mass of the arrow and string and stiffness of the string are also the same. This means longbows, recurves, etc. have same potential. ("An Approach to the Study of Ancient Archery using Mathematical Modelling," Kooi and Bergman, page 6.) Working recurve bow designs are easier from which to create stated result using shorter bow.

I identified several patents among whose claims two were important: significant improvement in energy storage -- that is, greater bow efficiency for the same draw weight; and let-off in draw weight for non-compound bow designs.

The claims for improved energy storage make good sense. And at least two bowyers appear to use techniques described in patents. The methods are so similar that I question most of the patents' claims for original concepts.

Claims for draw weight let-off are touchier. I understand how each intends to achieve a let-off of an essentially traditional bow. Without exception let-off is nowhere as great as a run-of-the-mill compound (6580 percent). The claims are, for example, that a 70-pound draw weight will become in the high 40s, the plateau beginning about inch fifteen and remaining static through inch 30-something.

Were any of these to function more or less as diagrammed, the results are still remarkable -- a "normal" longbow or recurve that incorporates much of the benefit of a Buck Rogers Personal Model compound bow without its excessive complexity, weight, and clumsiness.

But, as I said, I question whether any claim for let-off is valid. Does it matter, though? By achieving same amount of stored energy, delivering the same arrow ballistics from substantially lower draw weight, doesn't this achieve somewhat similar result? If I get a 650-gr arrow to leave the bow at 190 ft/sec, isn't it a good result if my draw weight is 45 pounds rather than 60 pounds?
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Next step is to find a bowyer willing to try some more conservative methods at a price I can afford. Notice how the final step is always the BIG one?

Mac11700 · « **Reply #8 on:** May 31, 2005, 09:42:24 PM »

Handi...put a regular dacron string back on it...and you will loose velocity over what it was at 60lbs...your increase came from having less stretch in the string. which increased flex in the limbs....not all because you reduced the mass in the limbs...

A pre-stressed limb at rest...has no energy in it...once energy..(pulling the string) starts...the energy that is stored in the limbs (flex) can be imparted to the arrow. and it is stored earlier in the draw..inch for inch.....and throw in a string that doesn't stretch...and you've gained additional flex in the limbs...thus you have more stored energy....to be applied to the arrow..Now...go 1 step futher if you will...switch to a metal riser recurve...such as my Skybow...it's limbs are perfectly matched...at it's widest 1.730"...and .805 thick in the pocket...tapering to .770" wide and .345" thick at the string groove...my bow...as compared to an identicle solid wood bow...is 35fps faster...I know...I shot both thru a chronograph...several times. before I settled on my current one.....the reason it's faster is lack of flex of the riser...and allowing all of the energy to go into the limbs...stiffen the riser...you make a faster recurve.. ...the faster the limbs unstress...the faster the arrow...

Mac

handirifle · « **Reply #9 on:** July 09, 2005, 07:46:22 PM »

Actually Mac my post was incomplete, the 10fps gain came with a dacron string. The Fast Flight gave me about 8 more, so it is really 18fps but I forgot to mention that in the earlier post.

The Fast Flight came later on as well. Tim Meigs did the weight and limb reduction on it. Even he commented on how much quicker the bow recovered. Less limb width and mass equals quicker recovery.

I agree with you partially. The faster they recover the faster the bow but I'd bet if you were able to put those limbs from the all wood bow (I assume you mean the riser is all wood) on the metal riser, it would still be the same outcome.

Limb design, materials, layup, type of glue, curing temperature of the limbs, thickness of glass vs wood in the limbs, direction of the grain in the wood (edge grain vs flat grain) and more, can ALL add up to effect the speed of the limb recovery, as well as noise, shock etc. I have made quite a few all wood, wood laminated and fiberglass laminated, one piece and takedown bows. Sold them for a bit. Have seen considerable changes come from minor changes in the design/layup of a bow.

I've never measured but I doubt there is enough flex in most of the recurve risers put out today to make more than 1 or 2fps difference over metal.

My risers were most often laminated with 2 pieces of glas through them, in addition to several different types of hard wood, all in the same riser.

Here is one pic of a bow I made for one of my sons with the above design.

Mac11700 · « **Reply #10 on:** July 10, 2005, 06:42:37 PM »

Handi:

Very nice bow...I bet your boy is proud of it :agree:

On the amount of flex difference...there is actually enough to make a significant difference...this is one of the reasons Earl Hoyt insisted on using metal risers for the US Olympic teams he built bows for......he was maticulous in his approach and designs of his bows...and made a science out of it.I got to shoot several diffferent designs of his the day we set mine up...both the wood and the metal riser type...with the same limbs...The difference was dramitic to say the least...and the speed difference was about 7-10fps...not to mention the feel from the shock difference...the metal helps dampen the feel...not a true tradtional recurve mind you...but one combining the essence of everything in archery...at least for me.........We lost a great one when he passed...

Mac

handirifle · « **Reply #11 on:** July 22, 2005, 02:08:26 PM »

Mac
Yep he is and thanks for the compliment.

I AM suprised there was that much gain with just a change of riser. Hard to argue with the like of Hoyt, I'd bet he has a few more days building bows than I :grin: .