Reflex, Recurve, types of reflex

[beast]

OK. there are many different things we can do to bows to add some energy output in our shots. reflex, recurve siyahs, and such.
right well for now I am trying to clear up some confusion I have about the effects or relfexed limbs. Because, they have a big effect on bows that even are initially deflexed.
Ok first we have bows that start reflexing from the handle section, that look like a flat letter U.
Next we can start the reflex ainbow somewhere near the middle of the limbs.
and next we can do it on the tips, so a recurve. Now the recurve does something that only reflexed limbs don't,  that when the string lifts off the recurves the string angle changes and the bow "elongates' kinda.

Right. But if we were to only bend in some recurves, the rest of the limb will still get stressed more. not just the recurved limb tips get the stress.

Say we have 4 different bows, one that is reflexed from the end of the handle to the tips.
the next one starts the reflex from halfway up the limb
and the last is a normal recurve.

but all have their limb tips 5 inches in front of the handle because its a nice round number.

how would they all compare?

[mmattockx]

That is a much more complicated question than you think. The back profile matters greatly because it affects the thickness profile needed and the optimum tiller shape. I have mathematically modeled a bunch of these variations but it is not completely generic and my results only really apply to the specific designs I looked at.

I used a pyramid back profile on all of my bow designs for consistency. Same length, same draw weight, etc. What I found was that the largest determining factor in stresses was how far the tips are ahead of the handle when unbraced. The fully reflexed bow will have the highest peak stresses, but only by a very small margin over the recurve. They are so close as to be functionally the same. The recurve stored slightly more energy than the reflexed bow and had a smoother draw cycle in terms of stacking. I can't say if one shoots nicer than the other, though. The analysis tools I have are not sophisticated enough to predict how well either design will perform.

I never looked at one that was reflexed from mid-limb so I can't say anything about that design.

Note that 5" of reflex is a lot on a wood bow. You need very high quality bow wood to survive that and the tillering has to be spot on to avoid a large amount of set. Chances of success go up if you make it as a lam bow with woods chosen for the specific loads on the back and belly. 5" of reflex also makes the bow pretty nasty to brace unless you use a stringer. Even a couple inches of plain reflex greatly increases the difficulty of getting a string on it.


Mark

[beast]

hi mark. ya 5 inches does really put more stress on wood. but. 5 inches barely adds performance. it does, but if you would do the math or shoot through chronograph you would only see like an extra 10 fps addition. on average. for a medium weight bow.

[beast]

and so, my logic is, either go hard or make a normal longbow.
but anyways,
as I haven't tested these things to know:
for the same mass and profile, these different types of reflexes and the radius of the reflexes should change something about the bow.

even, siyahs are bloody straight, but they stress the working limb of the bow evenly, right?

[mmattockx]

for the same mass and profile, these different types of reflexes and the radius of the reflexes should change something about the bow.

even, siyahs are bloody straight, but they stress the working limb of the bow evenly, right?

Reflex compared to static recurves does change the stresses in the limb and how the draw feels. The maximum stresses don't vary much between the two but they are distributed differently along the limb. I have compared small recurve hooks with bigger ones but I would have to go back and look at the details to recall the differences. I think bigger hooks increased stresses slightly, but don't quote me on that. The bigger hooks tend to give a less abrupt change in the FD curve as the string lifts off more smoothly over a longer portion of the draw.

I have never modeled anything with siyahs so I can't say much about them, but they should behave very similarly to static recurves overall aside from the step in the FD curve when the string lifts off the siyah.

Tim Baker reached the same conclusions in TBB V4 as you did regarding recurves versus flat bows and decided that it was better to work on reducing tip weight as much as possible on a flat bow instead of using recurves. I don't have enough experience built up to say one way or the other myself, but it is certainly harder to avoid set with the higher stresses of the recurve designs.


Mark

[beast]

ok. let me distil what u said and correct me if I'm wrong tho. reducing tip weight would basically mean make its cross section as closer to a square rather than a longer rectangle.

the wood I'm using a lot of is hickory. that wood has medium elasticity but has great Modulus of rupture, so it can take more stress before it breaks.
it wouldn't be a great idea to put recurves on not great wood, but say one has the materials.

heat-treated hickory is very strong in compression too,

but all that aside, I'm still interested in knowing the difference between all of these types of reflexes. The thing that confuses me tho is how well a reflex deflex bow performs. they shoot better than normal bows but the tips are level with the handles.

that must mean the reflexes do some serious work.

[RyanY]

ok. let me distil what u said and correct me if I'm wrong tho. reducing tip weight would basically mean make its cross section as closer to a square rather than a longer rectangle.

the wood I'm using a lot of is hickory. that wood has medium elasticity but has great Modulus of rupture, so it can take more stress before it breaks.
it wouldn't be a great idea to put recurves on not great wood, but say one has the materials.

heat-treated hickory is very strong in compression too,

but all that aside, I'm still interested in knowing the difference between all of these types of reflexes. The thing that confuses me tho is how well a reflex deflex bow performs. they shoot better than normal bows but the tips are level with the handles.

that must mean the reflexes do some serious work.

Seems there may be a bit of inconsistency with this perception that mild reflex deflex bows significantly outperform straight bows but a 10fps gain with 5” of reflex “barely adds performance”. I can’t speak to all of the nuances of the differences between these bows but at the very least a mild deflex reflex bow will store more energy than a straight bow simply due to string angle and therefore shoot faster.

I will add that hickory is far from “not great wood”. Many records have been set with simple hickory bows. I would caution you to abstain from taking wood species into account till you get a better understanding of design. Design will trump wood species in all but the most experienced hands.

[beast]

no ryan lol, i said hickory is great wood, when I said its not great to focus on putting reflexes into bows on not great wood, I wasn't referring to hickory.
i love hickory, and its very common. and heat treating the belly to a dark brown really makes a difference.

[mmattockx]

ok. let me distil what u said and correct me if I'm wrong tho. reducing tip weight would basically mean make its cross section as closer to a square rather than a longer rectangle.

Yes, the end result is basically a Holmegaard style of lever bow. All the working word is close in to the handle in a wide, flat, thin cross section and then the levers are as narrow as you can make them and survive.

that must mean the reflexes do some serious work.

I can't define why they work well, but R/D bows typically have high string tension at brace and that gives a lot of early draw weight. They do have higher stresses than flat bows, though. As bownarra says, you don't get anything for free. Higher energy storage always equals higher stresses from what I have seen.


Mark

[Selfbowman]

ok. let me distil what u said and correct me if I'm wrong tho. reducing tip weight would basically mean make its cross section as closer to a square rather than a longer rectangle.

Yes, the end result is basically a Holmegaard style of lever bow. All the working word is close in to the handle in a wide, flat, thin cross section and then the levers are as narrow as you can make them and survive.
Mark you are spot on in all you have said.  It I’m not a engineer. Arvin

that must mean the reflexes do some serious work.

I can't define why they work well, but R/D bows typically have high string tension at brace and that gives a lot of early draw weight. They do have higher stresses than flat bows, though. As bownarra says, you don't get anything for free. Higher energy storage always equals higher stresses from what I have seen.


Mark

[RyanY]

no ryan lol, i said hickory is great wood, when I said its not great to focus on putting reflexes into bows on not great wood, I wasn't referring to hickory.
i love hickory, and its very common. and heat treating the belly to a dark brown really makes a difference.

I guess I was confused interpreting “say one has the materials” as if they were not available to you.

[Badger]

When you reflex right out of the handle it gives you higher string angles when braced and even drawn robbing some power.

[Digital Caveman]

I have mathematically modeled a bunch of these variations but it is not completely generic and my results only really apply to the specific designs I looked at.

Are you an engineer by any chance Mark? you've alluded to similar technical points before.  I would love to see the analysis you put together, that's right up my ally. 

[mmattockx]

Are you an engineer by any chance Mark? you've alluded to similar technical points before.  I would love to see the analysis you put together, that's right up my ally. 

Yep, a mechanical engineer. Do most of my work in oilfield equipment and structures in western Canada. I will send a PM to discuss the modeling.


Mark

[Selfbowman]

When you reflex right out of the handle it gives you higher string angles when braced and even drawn robbing some power.

So Steve reflex should achieve better performance the farther it is from the fades?  I was looking at my record bow the other day. It has a very slight reflex starting it about 8” from the fade then the last 8” it has about 2” reflex. My recent static is almost straight limbs till the last 6” where the static hooks start.
Arvin