Virtual Mass revisited

[sleek]

Didn't we decide that you can't get part of a limb to bend first? More or less, yes but not first or last. If you take any snape limb and move the tip 1/4" the inner part of the limb will move, maybe not much but it will move. Like the Parsons carriage.

I haven't abandoned the thought because I simply haven't fount a convincing reason to doubt it. Perhaps instead if saying "bending first"  if i were to say, bending faster in terms of release, that could get you closer to my side of the fence? If an arrow relieving a stiff kick in the rear by way of string release will cause the arrow to flex, setting up a wave, then the same logic should apply to the bows limbs. When the arrow is shot, the nock moves either first or faster than the point, i cant say which, causing the arrow to bend until the tip catches up in speed with the nock. I feel strongly this same principle can me made to apply to a bows limbs and do my best to tiller with that in mind.

 Id love to be prove wrong, because if so, that means I became more knowledgeable than I am right now as I sit thinking over a bowl of oatmeal. But as I currently sit, I just can't convince myself that it doesn't work that way. This may just continue to be a case where you and I must agree to disagree, and thats ok. Id like to get acess to a super slow mo camera as mentioned to prove this theory, which at this point, is all it is.

[sleek]

I'm reading the words, but not quite grasping what they are referring to.

Badger: I have always suspected that a tiller where the limb bent progressively from outer to inner could also help to control this vibration by simply returning to brace over a more extended period.

Sleek: So I tiller the working limb closer to the tips to bend first as I draw it the bow, and the inner limb to bend last. The inner limb is last to bend on draw but first to release its energy upon string release. This flows like a wave all the way to the tips allowing the most energy efficient delivery of energy possible.

To me, they appear to be saying the opposites. Am I wrong?

No, he and I are in agreement on the points you are confused about. We just look at it from different ends of the bow for a reference point. His thoughts start from tips to inner limb, mine start from inner limb to tips. Either way, its the progression of energy transfer thats key. Steve, if I misrepresented/understand what you are saying please correct me.

[bownarra]

Right DC. At least on any bow where the string doesn't touch the belly at brace.
The only design I know of to act differently is the Duoflex. Of course this is because the string is sat on the belly of a significant proportion of the limb at brace and this changes as the bow is drawn.
These different limb profiles only work when tied into width taper. Tiller shape is dictated by width profile.
For a straight limb bow eg non recurve the way to the minimum limb distorsion losses is to concentrate the bend in the inner limbs, stiff, narrowed past pyramid taper outer limbs. Tillered like Willies last tiller picture. This tiller gives the longest return path for the tips.

[DC]

Didn't we decide that you can't get part of a limb to bend first? More or less, yes but not first or last. If you take any snape limb and move the tip 1/4" the inner part of the limb will move, maybe not much but it will move. Like the Parsons carriage.

I haven't abandoned the thought because I simply haven't fount a convincing reason to doubt it. Perhaps instead if saying "bending first"  if i were to say, bending faster in terms of release, that could get you closer to my side of the fence? If an arrow relieving a stiff kick in the rear by way of string release will cause the arrow to flex, setting up a wave, then the same logic should apply to the bows limbs. When the arrow is shot, the nock moves either first or faster than the point, i cant say which, causing the arrow to bend until the tip catches up in speed with the nock. I feel strongly this same principle can me made to apply to a bows limbs and do my best to tiller with that in mind.

 Id love to be prove wrong, because if so, that means I became more knowledgeable than I am right now as I sit thinking over a bowl of oatmeal. But as I currently sit, I just can't convince myself that it doesn't work that way. This may just continue to be a case where you and I must agree to disagree, and thats ok. Id like to get acess to a super slow mo camera as mentioned to prove this theory, which at this point, is all it is.

I like the arrow analogy but I still don't think the nock moves first, slower, yes but not first. Anyway That's getting to be semantics.
 So the bow is held bent by the string, so the "pressure" is released at the tip. I can see a wave being propagated down the limb. I have to think about what happens next

[DC]

Right DC. At least on any bow where the string doesn't touch the belly at brace.
The only design I know of to act differently is the Duoflex. Of course this is because the string is sat on the belly of a significant proportion of the limb at brace and this changes as the bow is drawn.
These different limb profiles only work when tied into width taper. Tiller shape is dictated by width profile.
For a straight limb bow eg non recurve the way to the minimum limb distorsion losses is to concentrate the bend in the inner limbs, stiff, narrowed past pyramid taper outer limbs. Tillered like Willies last tiller picture. This tiller gives the longest return path for the tips.

Oh yeah, I'll add that to my thought list.

[willie]

 @tradecraftsman
nice well written description of the energy losses associated with accelerating the limb at release. limb energy losses do seem like they would be predictable for a given design, and a graph might be plotted to project losses at other velocities.

This might be a way to get a handle on the separation of hysteresis losses from limb kinematic losses.

[Badger]

Vibration losses don't seem to change as radically as Hysteresis losses.

[Yooper Bowyer]

You know more about this than I do, (you came up with the mass principal, right?), but handshock is also the result of the limb kinetic energy. 

By the way, how do you distinguish between losses for hysteresis and limb kinetic energy in the lab?  I'm getting the urge to start experiments myself.

[Badger]

  Virtual mass is based on Limb KE.

[bownarra]

By the way guys - what exactly is it you are trying to work out?

[willie]

Mike,
I brought this discussion on virtual mass to a dedicated post, because we were getting off track in    http://www.primitivearcher.com/smf/index.php/topic,68878.0.html
over there, Badger commented....

A glass bow has very little hysteresis so once the virtual mass is established it will remain fairly constant regardless of arrow weight even though efficiency will continue to drop with arrow weight. A wood bow that has taken set will display more hysteresis and because set is time sensitive it increases rapidly as arrow weights go down.

Calculating Virtual Mass does seem useful when hysteresis is constant, and was useful for comparing different glass limb designs when Norb Mulaney made his contributions to the industry, but how useful is calculating VM for natural materiel bows if we need to tease the different losses apart to make improvements?

I think we have learned (or relearned) a lot about limb geometry since klopsteg introduced the VM concept , so our challenge is to use VM or something like it, to learn more about hysteresis.

[DC]

I'm trying, I'm really trying but I just seemed to get bogged down. I can't see the direction this is taking me. I know it all works because otherwise you guys wouldn't use it. How about if I was to take a bunch of measurements could someone do whatever it is that you do and tell me a bunch of stuff about my bow? Maybe then I could see what we're trying to do. I'm just taking the last scrapes on a bow so I could use that one. Don't be afraid of saying no

[sleek]

By the way guys - what exactly is it you are trying to work out?

I WAS WRONG IN THE STATEMENT BELOW, BUT AM LEAVING IT BECAUSE IT WAS REFERENCED IN OTHER REPLIES. sorry for yelling

Exactly how much wood is required to make a bow. Or more specifically, how little we can get away with.

[Badger]

By the way guys - what exactly is it you are trying to work out?

Exactly how much wood is required to make a bow. Or more specifically, how little we can get away with.

  Virtual mass has very little relation to actual mass

[willie]

Virtual mass has very little relation to actual mass

I think kevin has a good point, Steve. My guess is that you are pointing out that arrow mass, or the virtual arrow mass,  is not directly comparable to bow mass, as in grains and ounces.