String angle

[DC]

Yes, that's the problem Pat. As another example in this picture what angle are the boards meeting at. You could measure the angle right where they touch and get about 1 degree. Or you could stand back and squint a bit and get about 15 degrees(I'm guessing). What it boils down to is there is no way of doing it. But there must be an "effective angle" or something.

[gfugal]

I didn't say  siyah because a lot of the diagrams are showing tips inclined back and clearly changing string angle.
People still have this weird thought that a siyah is somehow different from a one piece tip.  It seems they still do.
Tim Baker introduced the retroflexed tip term I think to create a generic term for all the types.

I don't consider siyahs inherently different from recurves. They are after all just different approaches to accomplish the same thing. The only difference is one is made from the limb and thus shortens it, while the other is added on usually lengthening it. But if you plan ahead and design accordingly shortening and lengthening shouldn't be an issue as you get what you wanted anyway.

[PatM]

  So despite all of this nobody seems to be willing to actually come up with a string angle for the recurve in the diagram.

Is that the correct diagram you're looking for? I need pull up my image measuring app to get the actual angles but I don't think that's what you're looking for. If that's incorrect you should enlighten us with your own drawing.

  That's exactly what I mean and I tried to say that when the first diagram was shown.   That I think represents the "functional"l string angle.
     I think you still need to draw them differently come to think of it more but the basic idea won't be different. You'll still get those two different angles.

[George Tsoukalas]

That's close to 90 degrees.. from the drawn string to the limb provided you measure the way string angle has been measured for decades. It is the right triangle I have been mentioning since yesterday afternoon.
BTW I have yet to see a recurve with that large a string angle. I understand the photo is for illustrative purposes though.
Jawge

[PatM]

   Can you just ease away from repeating the straight bow limb angle which nobody has argued and venture an opinion on how you establish recurve angle?

[Badger]

  Pat, you never do establish a firm string angle because it varies over the entire limb, the longer the recurve or straight area at full draw the lower the string angle obviously but there is no set string angle unless you are talking only about a specific portion of limb which we usually talk about toward the tips. When we have a slow build in final inches we simply attribute it to low string angles but no one I have ever known has tried to pin it down to something exact.

[George Tsoukalas]

Yes, it is represented by the first red line on the top extending to the string. It is the angle between string and red line.

[PatM]

With a bit of study I would think establishing an effective string angle would be feasible.  If you scribe an arc from the recurve tip so that it merges with around mid-limb, it's probably pretty close to what your perception of the string angle is.

[PatM]

Yes, it is represented by the first red line on the top extending to the string. It is the angle between string and red line.

 Which diagram?  I can't see the one on Greg's post anymore.

[George Tsoukalas]

PatM, you could but that would mean leaving the bow full draw for quite a long while. Not something I would do.
Taking an eyeball estimate is sufficient for me.
Jawge

[PatM]

 I meant on a diagram or picture of course.

[George Tsoukalas]

"Which diagram?  I can't see the one on Greg's post anymore."

When I defined it I looked at the first diagram in this thread, PatM.

Way back on Pg 1.
Jawge

[joachimM]

if I have a 64" straight bow and a 64" recurved bow, the recurve bow doesn't END it's draw longer, it begins the draw as a shorter bow.

So,  say the recurve takes effectively 2" out of the braced bow length.  As a proportion of the total, slightly shorter limb applies LESS leverage at the limb base than before, but the midlimb feels a LOT less.....at first.  Then, when the limb effectively lengthens later in the draw, the BOW is still getting shorter, but less dramatically because of the recurve.  The recurved tip thus continues to apply good leverage to the limb base, and BETTER leverage to the midlimb than early in the draw.  This is where the F/D benefits and lower "stacking" come in to play.  Non-contact recurves and R/D bows share this benefit, just less so and at lower angles.

+1
It's the net length of the lever from the string contact point that counts. Basically, a recurve "stacks" early in the draw: it has a higher draw weight than its length suggests, because early in the draw the recurve doesn't contribute to the effective lever length. (hence the high early draw weight: you're drawing a shorter bow, but it lengthens during the draw).

Basically, you can view the realized lever length (if you keep the bow vertically) as the net vertical projection of the bow arms (including recurves if any). Moment = force times lever length. The shape of the lever (recurved or not) doesn't matter for a particular draw length. Since a recurve opens up during the lever length changes in a different manner than with a straight bow, as explained by Springbuck.

[PatM]

"Which diagram?  I can't see the one on Greg's post anymore."

When I defined it I looked at the first diagram in this thread, PatM.

Way back on Pg 1.
Jawge

   For the recurve....

[gfugal]

Yes, it is represented by the first red line on the top extending to the string. It is the angle between string and red line.

 Which diagram?  I can't see the one on Greg's post anymore.

Sorry I edited it so I could put the actual angles in. The image address changed thus breaking the link. I modified the original message so you can see it on my post, but your quote still won't show it. Here it is again


So the Recurve string angle in the above photo is less than the straight limb, at around 72° compared to 79°. That is a difference of around 7°, which is more than what DC was estimating, but still not a lot. However, I noticed that this depiction is far from accurate since the string lengths between the non-recurved bow and recurved bow are not the same. The recurve has a longer string as depicted. Therefore that is not the correct position it would be in for that draw length since would most likely have a string length similar to the non-recurve bow, thus the string angle would be different. If we use my first sketch I think it is a little more accurate. here it is.


Look at the bottom limbs. Notice that it is drawn so both have the same string length, and draw length. This causes the tip position to be in the same spot. I can't say this would be the case in every instance but they would be much closer in practice than what was depicted in the image above. Assuming the tips are in the same position as I drew them here, what does that do to the string angle if the reference point is the average or "net reference point PatM, and Tim Baker use? It's the same sting angle for both the recurve and the straight limb! (see the black angle at the bottom which is 64°) This is because both tips are at the same spot. However, if you measured the recurve string angle from the limb before the recurve, it gives a much higher string angle (76°). Therefore the recurve is bending the limb to a (potentially higher string angle of 76°, but it does so in actuality with a lower string angle of 64°). Hence you can get better bend out of a limb but with better string angle too. If you tried to get that same bend in the straight limb the string angle would increase much higher than the 64° it is at now.  So to summarize: recurves bend the working limbs farther at similar draw lengths while still maintaining good string angle, thus creating more stored energy. I don't know if that made sense to anyone else but it does to me.