Virtual Mass revisited

[DC]

Up until now I have just used two carbons with a variety of tip weights and it's worked just fine. I just ignored the spine. Now I've got this one arrow that seems faster for some reason and it's opened a can of worms. I did try scraping the middle to lower the spine but it did affect the weight enough to make me doubt whether it was the weight or the spine that was making the improvement. I wasn't expecting that. It may be the Tiger arrows. They are heat treated I believe and maybe that makes them less responsive to scraping. I dunno. Anyway the shooting machine is all packed in the trailer for the Gathering so it's all stop for a few days. I'll be making a good old knotty yew self bow. It will be nice not to think about speed for a few days.

[willie]

the virtual mass may increase with less arrow weight and then reverse and start decreasing, or sometimes it is the other way around.
Alan

Alan, would you be willing to speculate or comment about any limb designs features that may affect these harmonics? or how one could "tune" their design to a particular weight arrow?  This goes a bit beyond making tips lighter  or stiffer I presume.

[DC]

When you think about it all you can do is leave wood on or take it off. The question is where?
Oh, I guess you can prebend it or not.

[sleek]

the virtual mass may increase with less arrow weight and then reverse and start decreasing, or sometimes it is the other way around.
Alan

Alan, would you be willing to speculate or comment about any limb designs features that may affect these harmonics? or how one could "tune" their design to a particular weight arrow?  This goes a bit beyond making tips lighter  or stiffer I presume.

I know 6ou weren't asking me, but as far as I've got so far in my wave theory is that the wave exists and the best flying arrow weight needs to be found for the bow, I haven't figured a way to tune the bow to the arrow yet, though I'd imagine it has to do with bow length or working limb length as it  applies to wave length. I doubt its that simple, and im certain its going to take a lot of experimentation to find what arrow works best, why, and how to duplicate that across a spectrum of arrow weighta/spines/draw lengths.

[willie]

I doubt its that simple, and im certain its going to take a lot of experimentation to find what arrow works best, why, and how to duplicate that across a spectrum of arrow weighta/spines/draw lengths.

How about trying to see the limbs in action with some sort of way to "record" an arrow release?

[sleek]

I doubt its that simple, and im certain its going to take a lot of experimentation to find what arrow works best, why, and how to duplicate that across a spectrum of arrow weighta/spines/draw lengths.

How about trying to see the limbs in action with some sort of way to "record" an arrow release?

I want to go to a college with a high speed camera and do some recording with different weight arrows to see how they affect the harmonics of the bows limb.

[willie]

Tuomo did a lot of work with HS photography, maybe he can comment if something as subtle as a wave in a returning limb is  something he has seen, or could be detected with photography.

https://www.youtube.com/channel/UCmVczwYUfq6sQQjCmKd2q5Q/videos

[sleek]

Maybe if I make the bow large enough, like, ridiculous proportions,  the wave would be large enough and slow enough to see easily.

[Badger]

Maybe if I make the bow large enough, like, ridiculous proportions,  the wave would be large enough and slow enough to see easily.

  I don't thin a very efficient bow would have much of a wave. It is usually just refereed to as vibration but I think of it more as dis torsion. Unless you are talking about a wave that occurs during the power stroke before the arrow has left the bow. I estimated DC's stored energy at 55# more of a guess than an estimate. But based on that he only has about 125 grains of virtual mass which is almost nothing. Extremely efficient bow.

[willie]

Unless you are talking about a wave that occurs during the power stroke before the arrow has left the bow. I estimated DC's stored energy at 55# more of a guess than an estimate. But based on that he only has about 125 grains of virtual mass which is almost nothing. Extremely efficient bow.

It is my understanding Kevin is proposing a "wave" during the powerstroke, but an investigation might detect it as a vibration or low frequency sound. Sonar is just a reflected sound wave, and you would be surprised what can be learned from looking at the returned "picture". It is not at all a pic that looks anything like the real thing, but can be quite useful if interpreted correctly.

[sleek]

The power stroke wave is exactly what I am referring to. I think I will refer to it as a power stroke wave theory to provide clarification from now on, PSW for short.

Willie, I like your thought process and would like to engage every possible way to disprove my idea as possible to be certain I dont look for false positives due to my own bias.


Badger, in my line of thought, the limb distortion that undoubtedly exists as we all see it often, in my opinion, can come from a frustrated wave, or, dirty wave, due to improper arrow weight, and more commonly,  poor tiller that instead of setting up a proper wave on release, sends out instead, a blast of.... static? Maybe I'll just call it noise. So then, instead of the bow limbs being properly tuned, like a harmonically tuned exhaust in a car, its just wasted power getting released in an chaotic way.

Again, as usual,  I reserve the right to be wrong and would welcome it.

[Badger]

  If the arrow doesn't use all the energy the remaining energy has to go somewhere. Low string angles make the arrow effectively heavier and help it to sap more energy out of the bow and I think we both agree that tiller shape can have an effect on that also. If set can be avoided shorter working areas in the limb will usually solve that problem.

[Tuomo]

Tuomo did a lot of work with HS photography, maybe he can comment if something as subtle as a wave in a returning limb is  something he has seen, or could be detected with photography.

Yes, I made a videos of shooting heavy and light arrows but it was very difficult to see any kind of valuable information, except that with heavy arrows bow limbs are returning slower. I think this video can tell something, at least about the importance of tiller:

https://www.youtube.com/watch?v=xGgWZYny9RM

This is an very good analogy and very true. You will see this if you very carefully test a bow over a wide range of arrow weights.  In a plot of virtual mass versus arrow weight, the virtual mass may increase with less arrow weight and then reverse and start decreasing, or sometimes it is the other way around.
Alan

Weight may be one thing but I believe that spine and the properties of the arrows are also very important. I made some years ago testing and found that same weight bamboo arrows were about 1 fps faster than wood (pine) arrows. Maybe CF arrows are also ittle faster than wooden arrows? But, there seems to be three arrow variables: arrow mass, arrow (dynamic) spine and arrow material stiffness (elastic modulus).

[DC]

If there is a wave you would want it to dissipate by the time it reached the end of the limb? Somehow when I think of the wave I always think of it as starting at the tip and running toward the handle. If it's not dissipated you get hand shock.

[willie]

Sleek, have you considered the possibility there might be more going on with the arrow than the bow if one arrow outshines the others on the graph?

Arrows have the primary flexing or "wave" deflection we see in slow motion where spine seems to be the biggest factor, but a close examination of the arrow shows a number of different things going on.  Click the settings gear icon in this video and lower the playback speed to .25.  Starting at 5:12 you will see the arrow doing a variety of flexing before it leaves the bow.

How the bow transfers the energy into the arrow might make a difference in how the limbs react and ultimately how effectively the energy is transferred.

https://www.youtube.com/watch?v=96KGWC0PB6s