Author Topic: Flipped Tips or Limb Reflex?  (Read 1735 times)

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Offline mmattockx

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Flipped Tips or Limb Reflex?
« on: November 26, 2020, 11:23:14 am »
Say you have a 67" NTN, ~42lb@28" pyramid profile flat bow and wanted to put the nocks 1.5"-2" ahead of the handle. Stiff tips with very little flex. Would you flip the tips or reflex the whole limb in a smooth arc? Why? Assuming the wood can handle the extra strain either way (ie - no extra set) would you expect one method to outperform the other?


Thanks,
Mark

Offline Allyn T

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Re: Flipped Tips or Limb Reflex?
« Reply #1 on: November 26, 2020, 11:50:10 am »
In TBB3 Tim did a section on this in the bows of the world chapter, it basically said regardless of limb profile bows with nocks equal distance forward of handle would store the same amount of extra energy all else being equal
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Offline Jakesnyder

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Re: Flipped Tips or Limb Reflex?
« Reply #2 on: November 26, 2020, 11:52:33 am »
this is a question I have asked before and has been talked about quite a bit. Reflexing the whole limb puts the most amount of stress on the bow.  I've done it before with white woods and if they are heavy draw weight bows they can be extremely hard to string. Imo. The consensus was/is that recurves are more beneficial than reflexing the whole thing.

Offline mmattockx

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Re: Flipped Tips or Limb Reflex?
« Reply #3 on: November 27, 2020, 10:51:11 am »
Since this appears to have run its course, I will elaborate. I am working on the bow described in the first post and analyzed it as a flatbow, then with flipped tips and a reflexed limb. I wanted to know if my results matched the experience of those here and it appears they do.


In TBB3 Tim did a section on this in the bows of the world chapter, it basically said regardless of limb profile bows with nocks equal distance forward of handle would store the same amount of extra energy all else being equal

My results say they aren't identical, but are close enough that you would never know the difference if you were testing the two on a tree.


this is a question I have asked before and has been talked about quite a bit. Reflexing the whole limb puts the most amount of stress on the bow.  I've done it before with white woods and if they are heavy draw weight bows they can be extremely hard to string. Imo. The consensus was/is that recurves are more beneficial than reflexing the whole thing.

Thanks for this. My analysis results agree that reflexing raises the stresses in the whole limb while recurve tips raise the stresses a touch more than reflexing at the base of the limb, but less as you move towards the tips. By mid limb the recurved limb has lower stresses than the reflexed limb. The recurves give higher string tension throughout the draw and slightly higher early draw weight but finish with a bit lower final draw weight. Stored energy is basically the same, as I mentioned above. Considering the smoother draw and generally lower stresses of the recurves I would say the consensus was correct.


Mark

Offline bownarra

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Re: Flipped Tips or Limb Reflex?
« Reply #4 on: November 27, 2020, 11:59:51 am »
That is all well and good BUT the reflexed limb would take less set :)
Assuming that they would take the same set is wrong. The recurved limb has a shorter woking section opposed to a proper pyramid limb of the same intial length. The pyramid can also have significantly less weight at the tip/last 6 inches or so.
Fresher wood that has taken less set is going to give a greater limb return speed.
Unfortunately in bow making you can't really change one thing without it affecting another area....doesn't half make things interesting though :)

Offline DC

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Re: Flipped Tips or Limb Reflex?
« Reply #5 on: November 27, 2020, 12:16:40 pm »
Are you including string length in your figuring? If you have two bows like you say, at brace height the reflexed bows string will probably be full length ie tip to tip but the recurve string won't have lifted off yet. This will skew your DW at various DL's.

Offline mmattockx

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Re: Flipped Tips or Limb Reflex?
« Reply #6 on: November 27, 2020, 12:53:22 pm »
That is all well and good BUT the reflexed limb would take less set :)
Assuming that they would take the same set is wrong. The recurved limb has a shorter woking section opposed to a proper pyramid limb of the same intial length. The pyramid can also have significantly less weight at the tip/last 6 inches or so.

These were just short flipped tips, not big hooks. The pyramid flatbow I started with has stiff tips. The flipped tips were shorter than the stiff section, so the working limb length was unchanged (unless there is something there I am missing). I agree the tips can be narrowed significantly on a flat pyramid design, but optimizing that wasn't what I was interested in. I wanted to know the effects of reflexing the tips forward and if one method was better than the other overall to achieve that.

The goal of the experiment was to take a flat bow design and modify it exactly as you could in real life with an existing bow in your hand, by either flipping the tips or reflexing the whole limb without any other changes. I changed nothing on the limb thickness or back profile, so the flipped tips were the same weight/width/thickness as before flipping them. As expected with this approach, draw weight increased along with limb stresses. In reality you would likely want to retiller some, to either get back to the original draw weight or fine tune the bend because of the changes made from the original bow.


Are you including string length in your figuring? If you have two bows like you say, at brace height the reflexed bows string will probably be full length ie tip to tip but the recurve string won't have lifted off yet. This will skew your DW at various DL's.

Brace height was kept constant. I would have to look at the string lengths to see how much they differed. The flipped tips didn't touch the string at brace so there was no lift off point to worry about. I just wanted to see what effect the two options had on the outcome, if the string rode the recurves a bit that would have been one of the effects to watch.

In the end the recurved design stored the same energy as the reflexed design at a slightly lower draw weight, had lower overall stresses and a smoother draw with less stack. The differences aren't huge (because I didn't move the tips a huge amount forward), but they are definitely there.


Mark

Offline bassman

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Re: Flipped Tips or Limb Reflex?
« Reply #7 on: November 27, 2020, 01:03:09 pm »
How much lower draw weight ,and what does all this convert into speed in comparison?

Offline Allyn T

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Re: Flipped Tips or Limb Reflex?
« Reply #8 on: November 27, 2020, 08:26:35 pm »
How did you measure stress
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Offline willie

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Re: Flipped Tips or Limb Reflex?
« Reply #9 on: November 27, 2020, 08:56:47 pm »
Quote
In the end the recurved design stored the same energy as the reflexed design at a slightly lower draw weight,

how do the designs compare for stored energy if you adjust up the thickness of the reflexed model to where both bows pull the same weight at full draw?  or are the differences very slight?

Offline mmattockx

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Re: Flipped Tips or Limb Reflex?
« Reply #10 on: November 28, 2020, 12:10:22 am »
How much lower draw weight ,and what does all this convert into speed in comparison?

Draw weight was about 2% lower for the flipped tips than reflexed. No idea on the speed, that is not something that can be analyzed mathematically. Or at least not something I can do with math.


How did you measure stress

The design was analyzed using Super Tiller software.


how do the designs compare for stored energy if you adjust up the thickness of the reflexed model to where both bows pull the same weight at full draw?  or are the differences very slight?

The differences are very slight with the small amount I moved the tips forward. I would expect to see bigger differences with more reflexing, but at that point you would need to design the bow specifically for that side profile. What I was looking at was just the typical small changes people do to an existing bow to hot rod it a bit after it is mostly (or completely) finished.


Mark

Offline bownarra

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Re: Flipped Tips or Limb Reflex?
« Reply #11 on: November 28, 2020, 01:11:38 am »
A pyramid taper for a recurve isn't optimal and stiff tips on a pyramid also isn't optimal. So its a bit like comparing apples and oranges - that is what I was getting at. You are not making a 'fair' comparison. Indeed it is next to impossible to do so and come up with anything meaningful.
An optimised pyramid and an optimised flip tip bow - the pyramid will be faster.

Offline Selfbowman

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Re: Flipped Tips or Limb Reflex?
« Reply #12 on: November 28, 2020, 07:50:40 am »
Mark I have done this with a glass bow it was full of shock . Bad plan to do in glass but may be different with wood. Just flip the tips. Arvin
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Offline Eric Garza

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Re: Flipped Tips or Limb Reflex?
« Reply #13 on: November 28, 2020, 08:28:12 am »
If energy storage is largely a function of how far the nocks are ahead of the handle, what specific benefits does a deflexed handle offer? If any? This assumes that the limbs are reflexed enough to move the tips ahead of the handle.

Offline mmattockx

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Re: Flipped Tips or Limb Reflex?
« Reply #14 on: November 28, 2020, 10:43:01 am »
An optimised pyramid and an optimised flip tip bow - the pyramid will be faster.

When you say an 'optimized pyramid' what is that in your mind? Are you thinking a flat bow, one with lightly reflexed limbs, or something else? Narrowed tips or straight taper to the nock? You are also pretty much the first person here I have seen say that stiff tips aren't desirable on pretty much all bows. I respect your opinion and would like you to elaborate on these a bit if you would.


Mark I have done this with a glass bow it was full of shock . Bad plan to do in glass but may be different with wood. Just flip the tips. Arvin

You built a reflexed limb pyramid with glass? And it was nasty to shoot? Can you PM me more details and a pic or two if you have them?


If energy storage is largely a function of how far the nocks are ahead of the handle, what specific benefits does a deflexed handle offer? If any? This assumes that the limbs are reflexed enough to move the tips ahead of the handle.

I can't make a blanket statement about it, but in the bows I have modeled in this style the deflexing allows you to use a big hook or heavily reflexed limb that gives very high string tension at brace and high early draw weight without overstressing the limbs at full draw. Essentially you have a really stiff limb (or big hooks) that would fail when pulled to full draw on a straight bow, then you rotate them back until they can stand the strain of bending to the full draw position.

As an example, on the bow above I took the flipped tip version and rotated the limbs back until the tips were back to in line with the handle (so the same as the flatbow I started with). With the same brace height this design gives a slightly lower draw weight at full draw and stores a bit more energy than the straight bow. Stresses also go up slightly, but less than the extra energy stored for a gain in efficiency. All the changes are small because I am looking at small recurves and a small amount of deflex, but the gains are there as well with bigger amounts of reflex or recurves and more deflexing.


Mark