Horn bows and stacking

[sleek]

Its on my mind, how do short 48 50 inch hirn bows with siyahs etc... fair when it comes to stacking at 28 inches of draw?

[loon]

The following bow, "T-35" by Francesco Alessi, is 110cm ntn (<44").



it begins stacking slightly at 25-26". so such a bow scaled up to 50" wouldn't stack at all at 28". if my math is right, drawing a scaled-up 50" version to 28" is like drawing this one to 24.36", and a 48" one to 25.67". still an insignificant amount of stacking. plus, such a less stressed bow would be able to hold more reflex

[Aaron H]

 

[sleek]

Loon, you are amazing sometimes. Thank you.

[mikekeswick]

I draw my 48 inch Turkish bow to 30 with no real stacking and it doesn't show much string follow even if strung for a few days.
A standard length for a 28 inch draw Turkish bow would be around 42 inch. Of course you can modify any design to suit.
if you take the length of the bow and divide by 1.5 you will get its potential drawlength. So my 48 inch bow could go to 32 inch draw.   48/1.5 = 32.
Stacking in isolation is down to the design of the tips (angles) more than the length of the bow.

[gfugal]

I draw my 48 inch Turkish bow to 30 with no real stacking and it doesn't show much string follow even if strung for a few days.
A standard length for a 28 inch draw Turkish bow would be around 42 inch. Of course you can modify any design to suit.
if you take the length of the bow and divide by 1.5 you will get its potential drawlength. So my 48 inch bow could go to 32 inch draw.   48/1.5 = 32.
Stacking in isolation is down to the design of the tips (angles) more than the length of the bow.

I concur that it's not just about length. If you have sharp angled recurves or siyahs you can avoid stack regardless of length as long as the material can handle it. It's just about making the right string angle and not related to the material bending. But if the recurve angle is low, or it's straight limbed I would stick to a draw around half the length maybe  less but I wouldn't go more than 1.8 unless you got some sharp and/or large levers such as in a Turkish bow.

[sleek]

With time to have thought about this i realused there is another component to stack and string angle. I havent seen it mentioned but perhaps its already understood. Either way, i just recently realized it.

String angle is not what matters with stack. It is tip leverage and that alone. String angle is a bi product of leverage, not the cause of it. For example, the longer the bow the more leverage the limbs provide, as a result string angle is low at the tips.

Lets take this further. A short bow with standard recurves. Whats standard, I dont know dont be so difficult, just humor me. Now the recurves provide more leverage at the tips and as a result, the strung angle is low.

But lets complicate things. Why? Because I like to be difficult, and you arw still reading this so it must be ok with you too. Lets say for illustrative purposes only we have a short straight limb bow with no recurves. We know what to expect with string angle at its tips and stacking already regardless of how long the short bow is you just imagined. Now lets tie on a recurve the diameter of a basketball, and make it so the tip ends 90 degrees. When strung, the stack reduces as well as string angle. Lets now untie the basketball sized recurves and tie on soup can ones, same 90 degrees. All else being equal, the stack will increase compared to the basketball, even though string angle is identical. Now lets tie on a recurve the size of a golf ball. Once again all else equal, the stack will increase compared to the soupcan, but string angle is the same.

The take away here is, with tips, its a leverage function. With recurves, the leverage increases with radius. The string angle is just along for the ride.

Now the next stwp is to realose, there is an optimum radius and angle for any bow. Find that and you have a winning combination. Im certain there is a ratio or formula to be made to calculate the perfect tips for any bow.

[gfugal]

String angle is not what matters with stack. It is tip leverage and that alone. String angle is a bi product of leverage, not the cause of it. For example, the longer the bow the more leverage the limbs provide, as a result string angle is low at the tips.

I think you're on to something sleek. Yes, we only care about string angle because it is related to leverage which is what really matters. I would have to disagree with you that string angle is a bi-product of leverage, but rather the inverse is true. Good string angle allows better leverage on the limb. However, like you mentioned it's not just string angle that can effect leverage. Lever length is also very important, if not more. So you could potentially have a better string angle on a short recurve due to its sharp bend but a longer lever in a siyah, for example, would produce more leverage despite having a worse string angle.

...lets tie on a recurve the diameter of a basketball, and make it so the tip ends 90 degrees. When strung, the stack reduces as well as string angle. Lets now untie the basketball sized recurves and tie on soup can ones, same 90 degrees. All else being equal, the stack will increase compared to the basketball, even though string angle is identical. Now lets tie on a recurve the size of a golf ball. Once again all else equal, the stack will increase compared to the soupcan, but string angle is the same.

This is some good creative thinking, again you're on to something. But I would have to disagree that it's the radius that matters. I don't think its the radius but the fulcrum length of the lever. a larger radius will naturally give a longer fulcrum, thus better leverage.

[sleek]

I disagree very respectfully.  I believe it has everything to do with leverage and i believe I can prove it.

Simply putting the long post i made,  the bigger the gap in distance, between the string nock, and the back of the bow, the more leverage. It has ZERO to do with string angle.  String angle is a bi product not a cause of leverage.

[sleek]

A bow could be built with tips thay shoot straight down, creating 0 degrees string angle,  and still have leverage as long as the nock is at or above the back of the bow.

[gfugal]

A bow could be built with tips thay shoot straight down, creating 0 degrees string angle,  and still have leverage as long as the nock is at or above the back of the bow.

What do you mean by 0° string angle? It all depends on your reference point.

here you have three separate reference points (1st which is verticle, probably in reference to the handle, 2nd reference point doesn't make sense to me but apparently it's been used in discussion before in the other thread on the bow forum, 3rd reference point is in reference to the tip of the limb which happens to be horizontal in the picture I drew). It also depends on where the string is and I have three potential string locations (1 verticle, 2 most like what we see, and 3 exactly horizontal to the tip). The colored angle arcs belong to one of the three reference points: blue to the 3nd (tip), orange to the 2nd, and purple to the 1st (handle). In all of these situations, I can only think of one that would have a string angle of 0° and that is a verticle string in reference to the verticle plane of the handle. But even in that situation the leverage does not equal 0 just because that string angle is 0°. while it is 0° in reference to the handle it is 90° in reference to the tip which gives a lot of leverage. So the fact that the bow isn't linear, but a curved arc really throws stuff like this off since there are so many potential reference points.


I personally like to think of string angle in reference to the tip, but the handle could work too. I downright don't get why you would use a diagonal reference point that seems to be hovering theoretically in space not connected to anything.

[sleek]

Im glad you are giving this some thought. I will reply with pictures of what I am talking about when i get home. Im on a cross country trip right now,  be home tomorrow.

[gfugal]

I disagree very respectfully.  I believe it has everything to do with leverage and i believe I can prove it.

Simply putting the long post i made,  the bigger the gap in distance, between the string nock, and the back of the bow, the more leverage. It has ZERO to do with string angle.  String angle is a bi-product not a cause of leverage.

Yes the larger that gap the greater the leverage. This is what I was saying before when I was talking about the length of the lever, it's not just about string angle. But I think I was (and maybe you too) confusing leverage and torque. I was also misusing the word fulcrum before.

You get more leverage when you have a longer lever length from tip to the fulcrum. Greater leverage gives you more torque. More torque is what we want because we can get more stored energy with less effort on our part (greater speeds for the same draw weight). But leverage is not the only thing that affects torque. The direction of the force is also important. In this simple example, that doesn't translate well to the bow, the best direction for torque is perpendicular to the lever arm. if we imagine the thing applying this force is a string, then you can think of it as string angle. Thus, in this case, the optimal string angle is 90°. As you can see both levers may have the same string angle but the lower lever will move much easier with less force due to its leverage. likewise, you could have a different string angle than 90° with the same leverage, as depicted by the different colors, but again just because the string angles are the same between the two does not mean the torque is. So yes you're right, string angle may not be as important as leverage. But string angle is not the bi-product of leverage. leverage is independent of the direction the force is applied. Torque is not independent, but leverage is. In the lower image, the limb has great leverage regardless of either of those three potential string angles. Those three separate string angles could all potentially happen too so, therefore, it is not dependent on how long the lever is. So the amount of torque is a byproduct of the combination of leverage and force. The amount of force applied to the lever is a byproduct of string angle. It's also true that changing the lever shape on the limb may change the string angle (maybe this is what you're referring too). I agree with that. By changing the shape to increase the lever length and thus the leverage you may also change the string angle, but theoretically, they are independent things as depicted in my image.