Reflex type and performance

[Kidder]

Is there a performance difference between the different designs/locations of reflex all else being equal? To clarify, will there be a performance difference between a longbow with even, consistent reflex and a recurve where the only reflex is at the tips, and all else (length, weight, tip weight, amount of reflex, wood type etc.) is equal?

[Selfbowman]

I think that the more the tips are in front of the handle the more performance. That being said you are creating more stress on the inner limb. Some say deflex the handle area making less stress on that area and being more efficient in the process..But I  don’t completely agree with this design. Yes you need more mass in the outer limbs to hold the reflex and more mass in the inner limbs for the added stress from the reflex in the outer limbs. My thinking is add thickness in the outer limbs and added width in the inner limbs. And yes slight reflex in the entire length. That’s for heavier arrow such as broadhead arrows. What happens in the middle. This is why I have recently divided into a three section in width. First section parallel second section tapered and last section tapered to the tips . I’ll know how this works soon.

[mmattockx]

Is there a performance difference between the different designs/locations of reflex all else being equal? To clarify, will there be a performance difference between a longbow with even, consistent reflex and a recurve where the only reflex is at the tips, and all else (length, weight, tip weight, amount of reflex, wood type etc.) is equal?

This question has been asked many times and is very difficult to answer because so much of the performance resides in the fine details. Assuming the same amount of reflex, bow length, etc. these are some of the things I have found in designing bows using software. These are by no means definitive or comprehensive, just some of the results I have seen:

1) The recurve will store more energy than the long bow.

2) An evenly reflexed limb adds a bit more stress to the wood than a recurved limb.

3) The recurve will provide a smoother draw cycle than the long bow but is significantly harder to tiller. The smoother draw is shown in the analysis, but the tillering difficulty is from practical experience.

4) The recurve usually needs more wood in the limbs towards the tips to keep the limb from twisting through the draw. This increases tip mass and reduces performance. I know you said the same limb/tip weight, but you typically just can't do that and have the recurve work.

None of this really answers your performance question, because modelling that is beyond any software and ability I have. I can calculate stresses and energy storage, but performance is really about maximizing the energy transfer into the arrow. This is why the super recurve FG bows don't perform that much better than a highly optimized more conservative design. They store a significantly higher amount of energy but they struggle to get that into the arrow efficiently. To keep the limbs tracking they need to be quite heavy all the way to the tip and this hurts the performance a great deal.

In general this is why wood bows get so close to the FG bows while using a significantly lower performing material. FG should absolutely blow wood out of the water, but it doesn't because wood is easier to extract most of the potential from while FG is not.

If you want to try adding reflex, I would suggest starting with an evenly reflexed long/flat bow design. It is easy to make a form to heat it into shape or to glue up a simple backed bow on and you can make it a basic pyramid design with nearly even limb thickness that is simpler to tiller, which is always a bonus when trying something new. I wouldn't add more than 2-3" of reflex at most on a 64"-66" bow for a 28" draw. A lot of what reflex does is increase string tension at brace and early draw weight and the extra tension at brace makes it harder to get the string on the bow. The extra difficulty in stringing goes up surprisingly fast with just a little bit of reflex.

Well, I guess that's my novel chapter for Sunday morning...


Mark

[superdav95]

My best performance bows have been reflex in the mid to outer limbs with stiffer out at the recurves.  This is true for static recurves or semi working recurves.  This is mostly what I make for the most part.  I have a bow now that is on the edge of failure as it’s built for flight shooting as per input from Arvin. Very narrow and light out at the tips but just thick enough to not pull out recurves. Highly reflexed and excellent early string tension.    I’ve had many attempts fail and explode in getting to this limit.  To date this is my fastest bow but it is not terribly reliable hunting bow for certain.  Could things be done to make this more conservative?  Yes.  I could do some of the things mention by both Arvin and mark to get a my reliable bow.  Anyway my short answer is yes things can be done to maximize performance and speed but at the expense of some reliability.  I would say the best all round basic design would be the good old pyramid design imho.  Add a slight bit of reflex in the mid limbs and increase gradually with either statics or flipped tips or working recurves.  I have to plug heat treatment here also.  A proper heat treatment will be able to handle the extra stress of this design too with all else being as consistent as possible Re tiller wood quality/ choice and build method.   

[Kidder]

A couple really interesting comments that get me thinking even more. If you need more mass in the tips to avoid twisting does it make building higher performance easier in a longbow than it does simply recurving it?
My questions also really come down to this…I’m working on an HHB bow that has taken some decent reflex right out of the handle. I’m thinking of putting it on a form and heat treating it and adding in even reflex throughout or also debating putting in either short working recurves (just basically flipping the tips) or long graceful working recurves. Their probably isn’t a single right answer, just lots of consideration.

[SLIMBOB]

I don’t know the answer, but I have thought about the question. Everything on these wood bows, in my opinion, is done on a see saw. Adding one element to the bow can often throw things out of balance if not compensated for elsewhere. As Mark mentioned, recurves have a positive effect on stored energy, but unless compensated for with more wood, adding mass, then increased set can have you back where you started. Narrowing the working limb will reduce mass, but you must go thicker, and thicker limbs take more set, bringing you back to where you started. My favorite bow is a 66” inch bendy handle with around 3 inches of natural backset, straight stiff tips. It might not be as fast as some of my recurves, but it is sweet to shoot, quiet, and spine tolerant. Cast is simply one element to measure regarding performance.

[Selfbowman]

I agree slimbob. My hunting and target bows are a bit slower but who cares . Good flight and good speed  gets the job done. But yes you flip the tips about 2” on 68” bow and you have a good smooth shooting bow. The pros would not shoot them if they did not have good cast and pleasant draw. Pretty close to the design straight out of bowyers bible 1., I just tweeted that design a bit with the suggestion of Jim Davis on the forum.

[mmattockx]

A couple really interesting comments that get me thinking even more. If you need more mass in the tips to avoid twisting does it make building higher performance easier in a longbow than it does simply recurving it?
My questions also really come down to this…I’m working on an HHB bow that has taken some decent reflex right out of the handle. I’m thinking of putting it on a form and heat treating it and adding in even reflex throughout or also debating putting in either short working recurves (just basically flipping the tips) or long graceful working recurves. Their probably isn’t a single right answer, just lots of consideration.

For that bow the easiest would be to heat in some even reflex along the limb. Flipping the tips for short static levers would also work well, but will be trickier to tiller. Tillering the long working recurves would be the toughest of the 3 options.


Mark

[Del the cat]

Some good comments.
I think it's pretty much the law of diminishing returns... it's easy to get some improvement on a very basic bow.
But as you strive further it creates almost as many problems as improvements.
Taking a simple ELB design, there are speed improvements to be gained from making the bow narrower or adding reflex or backset, but these can all cause instability.
Bottom line is, it depends what you are trying to build, a flight bow, or a smooth reliable target or hunting bow.
It's noteworthy that Hickman's original R/D glass design had fantastic performance but needed considerable changes to make it smooth and reliable for target shooting.
Del