Cobra Limbs Tweak...

[Mad Max]

Nice bends Rich

Here is a good picture of unstable at 1st brace off the form
the left limb is stronger and it's not braced high enough, needs tiller and braced higher.
If you grab the string and push it to the left the left limb will lay on the string and the right limb will bend more.
This bow was fine and stable after I finished the tiller

[Appalachian Hillbilly]

Mad max, do those tips act like siyahs?
How much faster do they make it?

[Mad Max]

They are Siyah's,  and yes

Let's stay on the Topic of Cobra limbs

[Shredd]

DFC of 2018

[Shredd]

  DFC of 2021

[Shredd]

 Comparison of 2018 and 2021

[Flem]

Shredd, do you experiment with different woods in those limbs, or do you try to keep that factor consistent?

[Shredd]

  I most always use Hard Maple...

  Sorry...  I tried to increase the size of the pics to make more readable...  Maybe good ol' Roy can lend a hand...

[Mad Max]

[OldRawhide42]

So what did you change from 2018 to 2021

[Shredd]

I am gonna explain DFC's when I get some time...  I just wanted to get them up on the forum...  Took me about 45 minutes to do that and I still could not get the right size...   

[Shredd]

Anything I post on here is open for discussion...  Do some of you have thoughts on floppy and vertically unstable limbs and shootability??

  Do any of you experienced bowyers have any opinion on floppy, vertically unstable limbs???  I am repeating the question because you all may have been busy with Christmas stuff...

[Appalachian Hillbilly]

What is a "cobra" limb? Is that just what you call your design or?
pardon my ignorance.

[Shredd]

  Yes...  It's the design...  I posted pics of it on the first page...

[Shredd]

   As a general rule a bow with higher numbers in the beginning of the DFC (10")  and low numbers at the end of the DFC  (28") is usually the faster bow...  When the difference is extreme between two different bows this will usually apply...  If the numbers are close and you have two different types of limbs or the same kind of limbs this rule does not always apply...  As in this case the numbers on the 2018 bow ( 10.84 & 5.00% ) and the 2021 bow ( 11.07 & 4.84% )...  2021 should be the faster bow...  But it is not...  2018 edges it out by about 2 fps... I believe it is because the 2018 has shorter, snappier limbs... If you look at the curve on 2018 at the 28" mark the curve starts pulling away from the line in a more vertical direction...  I have been told in the past by a bowyer or two that you want the bow to start stacking right after where you draw the bow for good performance...  This theory seems to hold true with this DFC...  Now when I make my new limbs I will make them similar to bow 2018...  I am not sure how I will tweak them yet...  I will post that when I decide...

    When you are comparing two sets of limbs of the same design and you want a smooth draw...  It is simple...  Just go by the numbers... Big in the beginning of the draw and small at the end...  If you want performance it is more of a balancing act...  You want an optimal curve on the DFC graph... It's all about  how those limbs are gonna unfurl during the shot cycle to transfer their energy to that arrow...  I think it is about keeping a nice even pressure on that arrow during the whole shot cycle...  I believe a straight limbed bow will have most of the pressure on the arrow at the beginning or the shot cycle...

  Below is a DFC of those big oversize hooked recurve limbs...  I drew a line on the graph from the first to last point...  A lot of people say that space between the line and the curve is stored energy...  I am not sure I believe that...  And if it is stored energy they did not do the best job at delivering it to the arrow...  I know of a few bows with a lot flatter DFC that goes just as fast or faster than one of these type bows...  Granted they are fast but going by the theory that the DFC shows almost twice as much stored energy you would think it would be a whole lot faster...

[mmattockx]

   As a general rule a bow with higher numbers in the beginning of the DFC (10")  and low numbers at the end of the DFC  (28") is usually the faster bow...

This is why compounds are the kings of speed, they draw very heavy at the start and then drop off  at the end for easy holding at anchor. Their DFC's are hugely pumped up with that high early weight for lots of energy storage and the limbs are super short and stout for minimal energy loss during the shot.

I drew a line on the graph from the first to last point...  A lot of people say that space between the line and the curve is stored energy...  I am not sure I believe that... 

The area under the DFC curve down to the x-axis is indeed the energy stored. The big hook recurves lose out by needing heavy outer limbs to keep stability and through a lot of noise and vibration eating up energy during the shot.


Mark

[Longcruise]

The area under the DFC curve down to the x-axis is indeed the energy stored. The big hook recurves lose out by needing heavy outer limbs to keep stability and through a lot of noise and vibration eating up energy during the shot.

I agree.  However,  it's easy to doubt that since there are other effects that can influence the dynamics such as hysteresis,  weight of the limb material and (not certain on this one) location of the neutral plane.

[Appalachian Hillbilly]

So...draw weight does not translate directly to speed. How fast can a limb get rid of the stored energy? This reminds me of the torque vs horsepower scenario.

How do you quantify or translate DFC to speed or efficiency? Could the are under the curve between the linear blue line be efficiency loss?

I think what we really would like to see, is not necessarily Draw Weight Curves, but a "map" of the energy being released into the arrow per inch upon release,  then draw a correlation between the two.

[mmattockx]

How do you quantify or translate DFC to speed or efficiency?

There is no way to that I know of (not that that means much overall...). All the DFC gives you is the energy stored and how smooth the draw cycle is. Efficiency not only depends on how much energy the bow wastes due to excess limb weight and vibration, but also the weight of the arrow. Heavy arrows increase bow efficiency because they absorb more of the energy in the shot, leaving less behind in the limbs to be wasted.

I think you can get some idea of the inherent bow efficiency separate from the arrow weight by working with dry fire speeds, but I have not looked at them yet and am not that familiar with them. The flight shooters care a great deal about this because it is very important with their light arrows.


Mark

[Stagmitis]

Good stuff Rich! One other factior I would consider you look at is the physical weigh of the limbs