RECURVES ARE NOT FAST!

[aero86]

thats the summary i was thinking of aries..  you need to plot out two different bows, to see the energy stored. 

[toomanyknots]

@Badger

"R/d bows I believe have the potential to be just about as fast and I think in most cases are faster because they will usually have lower mass outer limbs and be more efficient."

I totally did not even think about reflexing in any way shape or form,   Reflexing definitely makes a faster bow. But I firmly believe the smaller the bow the faster the bow, and not just because of less mass. Maybe it's a mix of less mass, and a more strained bow, like a reflexed bow, say a typical reflexed laminate for example, would strain the material more than a bow of the same length and draw weight. Evident in that the unreflexed bow of the same draw weight would be thicker/or just more material to reach the same weight than the reflexed bow. The extra energy comes from the extra stain. Just like in a smaller bow, the extra energy comes from the extra strain if pulled at the same drawlength of a larger bow. Or, in case of a turkish composite, you have a very small bow, and a very heavily reflexed bow. How do those perform now? I really don't buy the "every design performs as well as you accompany it to the wood" quote.

"Good post here!"

Thank ya, it's the only way I really learn is to discuss stuff. Thanks for the reply. Totally didn't think about reflexing,

@ Justin

"You are right in that they are leavers. BUT..... leavers are often used to increase speed. Put a ruler on a pencil to make a little teeter totter. First put the pencil in the middle of the ruler. Put something on one end then smack the other end down. The object will fly. Now try it with the pencil 2 inches away from the end you will smack. It will fly a lot farther. WHY?? ?? ?? Because the leaver made it travel faster."

I would probably just say that moving down made it travel further. That doesn't make too much sence to me, comparing the ruler flipping the pencil to the string taking the arrow as I would not think the string cares how it get back to brace, as long as it gets back fast. Less mass, or no recurves, would take the string home faster, wouldn't they? If the arrow was shot by tip of the bow like a pencil on a ruler I would see your arguement... But no, I really don't undertand what your saying.

"Reflex equates to early draw weight. If the recurve (leaver) makes the tips 4" reflexed how can it not add early weight."

Totally true and not very thought out on my part. I would have to admit that my argument could only be applied fully toward static nonworking recurves on a unreflexed bow. My point is that the recurves shrinking the working bow part down (hense a recurve being more stressed, because it's bent more, because it's essentially become a smaller bow that is overdrawn. Making it faster.) Yes, most selfbow recurves, like the style associated with osage so much, kinda would be like an even mixture of recurve and reflex, although we just call it a "recurve"?, especially if the recurves uncurl when drawn it would be alot to do with reflex making higher early draw weight. But compare it to a static recurve of the same length nock to nock and I would bet the static would beat it, only for the fact of being over drawn.

"But by reducing stacking you increase energy put back into the arrow and increase speed."

Do you mean because the energy gets distributed out more evenly for the draw it gets put into the arrow more? How would that work? Because if you mean early draw weight being higher you could reflex the bow or brace it higher than normal and get higher early draw weight, right?

@hammertime

"Just throwing out a couple other questions does a set back-in -the handle or reverse riser add anything to speed?"

Well if I think about, I would say that it would add speed by working the limbs more. Like if the bow was smaller.

@aero86

I didn't mean to sound like a duesh, I just wanting to point out something that is probably obvious to everyone else but for me was not, which is that recurves, as well as reflex with working recurves, but recurves/siyahs/levers all make a faster bow because of  shrinking a bow really, stressing the limbs more because less of the length of a bow is working. Not that recurves by them selfs make a faster bow, (what I thought at first, even though it didn't make sence ). Like if you had two 70" bows that both pulled 50#. And on one you added 5" recurves, but instead of recurving back the limbs, you just added the 5" recurves onto the ends of one bow, making it a 80" bow nock to nock. Which would most likely shoot alot slower than the bow without the siyahs.

[Justin Snyder]

@ Justin
 That doesn't make too much sence to me, comparing the ruler flipping the pencil to the string taking the arrow as I would not think the string cares how it get back to brace, as long as it gets back fast.



"But by reducing stacking you increase energy put back into the arrow and increase speed."

Do you mean because the energy gets distributed out more evenly for the draw it gets put into the arrow more? How would that work? Because if you mean early draw weight being higher you could reflex the bow or brace it higher than normal and get higher early draw weight, right?

A ruler is a leaver and a perfect example of physics. The laws of physics don't care if it is a string attached to a recurve, a ruler on a desk or a dart on an atlatl.

It is using leavers to eliminate histersis (the loss of energy from stacking) in the limbs and transfer the energy that would be lost into the arrow.

[toomanyknots]

@ justin

Oh, thank you for clarifying that. I still don't fully understand exactly how it works but I am sure you are right, I think I am just thinking too hard...

[NTD]

I think you are misunderstanding a lot of the physics at play.  Justin's reference about the pencil and ruler is about leverage.  Bow limbs are just levers...that's it.  Short bows in straight profiles are not faster than longer bows.  Of course there is a point of diminishing returns but typically longer straight profile bows are faster at least according to the info in TBB4.  Also you seem to think that strain equals more speed according to the TBB's this isn't true either.  The more you can reduce stress to the wood the better the bow performs.  "Perry" Reflex is an example of this.  The theory is that by gluing the bow up in reflex you are taking strain off the wood and placing it in the glue line.

"One of the cruel realities of bow design is that shorter straight bows can't be as fast per pound as longer straight bows even at equal draw length.  Bewteen 35" and 60" possible performance rises roughly 1 fps per inch of bow length.  Cast rises slowly from there to around 68" then only minor improvement from there to 80" and only then if given a more elliptical tiller."

-Tim Baker
Traditional Bowyer's Bible IV

[NTD]

I was typing while you were posting..

[toomanyknots]

"One of the cruel realities of bow design is that shorter straight bows can't be as fast per pound as longer straight bows even at equal draw length.  Bewteen 35" and 60" possible performance rises roughly 1 fps per inch of bow length.  Cast rises slowly from there to around 68" then only minor imporvement from there to 80" and only then if given a more elliptical tiller."

Whaaaaaaaaaaaaaa? Way ta turn my world upside down... 

[Lombard]

@ justin

Oh, thank you for clarifying that. I still don't fully understand exactly how it works but I am sure you are right, I think I am just thinking too hard...

Toomanyknots, to bring home what Justin is saying about levers, take yourself an apple in your hand raised to shoulder height and flick you wrist. See how far your apple goes. Now take your apple and poke it onto the end of a two foot long stick, raise your hand to the same level as before, only now you are holding the stick with the apple on the end. Flick your wrist with the same force as before, and note how much further your apple went. What changed? Same energy, same weight, but the mechanical advantage of a lever has increased your cast. You moved that same weight over a greater distance in the same time period. And if you want to test the diminishing returns factor, just keep launching your apple with a longer and longer stick, remember to apply the same amount of force each time. Eventually due to the weight/mass of your stick, you will not be  able to maintain the same time period with the same amount of force, thus losing cast. The experiment will clarify for you the advantage of the lever, and the point at which you get diminishing returns.

[aero86]

wow, good example lombard!

[medicinewheel]

.... But I firmly believe the smaller the bow the faster the bow, and not just because of less mass.
...

Well, if a bow is too short, it will simply not have enough mass to store energy; I - with my little experience - do also believe, that a stacking bow is slower that a no-stacking bow. I also believe that early draw weight means an elongated acceleration to the arrow, which means a faster flight, which MIGHT have to do with recurves. Sure, the recurves themselves don't store energy.

JMO

[TBod]

Steve

Why do you think r/d bows are faster than slightly reflexed. If the total amount of reflex is the same is the r/d still faster?

[Badger]

   Bows are not complicated but they do follow certain rules of physics. A longer bow will always store more energy because it maintains lower string angles. Very little of the weight gain you experience when drawing back a bow has to do with the wood compressing, almost all of it is due to increasing string angle and lowering your leverage.
    For the most part it seems straight bows betwen about 66" and 68" have recorded the fastest speeds for straight bows. Longer bows do store more energy but the efficency starts dropping off at this point when you are testing with a 10 grain per pound arrow. As the arrow weight goes up so does the efficiency so bows shooting heavier arrows are better off to concentrate on storing more energy, either through making the bow longer or adding recurves for instance and lowering the string angles.
    Flight bows that shoot very light arrows can be built much shorter and made to store less energy as they are more concerned with efficiency and higher dry fire speeds. Most of us don't concern ourselves with something called virtual mass, but virtual mass refers to how much more the arrow could have weighed to attain the same speed if it were 100% efficient. Flight bows like to have a very low virtual mass figure.
    After testing out literaly hundreds of bows I still could not tell you what I think is the best design. Elbs, mollies, pyramids and regular old american long bows all built with just a hint of reflex and refined a bit in design will all perform about the same at around 172 fps if everything goes just right. There will alwasy be exceptions that will out do this but for the most part this seems to be about it. Laminates will average about 8 fps faster and r/d and recurve designs will bump that up another 8 or so fps if everything is just perfect.
     Besides light outer limbs the most important thing in performance is to minimise the damage you do to the wood when tillering. Damage will start happening even before set becomes apparent. A perfect bow ( almost non existent) will spring back to it's pre braised shape the instant is is unstrung. Excersising in a bend after wood removal becomes unneccessary because if you have to excersize it in it is because you are crushing cells. A perfect bow would have no memory of ever being bent. I have only succeeded in doing this one time but the closer you come the better. This is the advantage fiberglass has on wood, fiberglass cells don't crush. Steve

[medicinewheel]

...This is the advantage fiberglass has on wood, fiberglass cells don't crush. Steve

Steve, it seems that cells heat treated bamboo crush very little (at least for quite a long time, or for many many shots...); would you say that is true from your experience??

[medicinewheel]

PS: this is a really good discussion going on here!

[Kegan]

NTD- I was refering to his reflexed static recurves, not the R/D ones. Like the one he did in his article "The Burnt Offering".

How much energy a bow stores and how well the bow transfers that energy to the arrow seem to be the only two things that affect performance. Which Steve explained, illustrated, and made very clear

Short bows are slower. All they have going for them is lower mass than longer bows, so slightly higher efficiency. Of course, since they store less energy because the cells are crushed so much more, there's no net gain. The converse being true for longer bows. More stored energy, but more mass. Most bows balance it out, get leverage, low mass, and low vibration working on the limbs to increase the mechanical efficiency while making sure there's a little reflex or as little string follow as possible to maximize energy storage without overstressing the limbs. The result being a good performer (if done right).

All of that is just a summation of the vast amount of info from the Bow-experts who contributed to TBB vol. 4. Once accepted, or even just tested, becomes readily apparent. "Black Betty", "Expectations", and even "Talea" were built with this in mind over the lsat few months and their performance exceeded most of the bows I'd been building for years prior