High gear/low gear

[lonbow]

Very interesting videos! I think the biggest reason for the limb vibration is mass inertia. The limbs move forward and when reaching the brace hight, they are suddenly stopped. The mid limbs still have some kinetic energy due to their mass. I think a bow with no mass wouldn´t vibrate at all!

[avcase]

Very interesting videos! I think the biggest reason for the limb vibration is mass inertia. The limbs move forward and when reaching the brace hight, they are suddenly stopped. The mid limbs still have some kinetic energy due to their mass. I think a bow with no mass wouldn´t vibrate at all!

The limbs reach their maximum speed around 2/3 the way through the shot and then the tips start decelerating even though the arrow is still accelerating all the way to the end.  So it isn’t a sudden stop, but it is a rapid slowing. If the limb flexes between the handle and limb nock during this phase of the shot, then the center portion of the limb hangs on to a portion of that forward momentum rather than transfer it to the arrow.

One possible experiment is to clamp the handle and the limb tip down to something solid, then tap the mid-limb and listen to the frequency.  A design that rings at a higher frequency between the nock and handle should be the better light arrow bow.  A bow limb design with stiffer tips should have a higher natural frequency with with this vibration mode.

Alan

[willie]

  I made what I called a hinge bow several years ago with very extreme recurves and reflex, something like 12". The bow was about 4" wide in the bending area which I think was no more than about 8" long up close to the handle. It broke down quickly because of set and hysterisis but in the initial shots it was the fastest bow I had ever seen bar none with a 10 grain per pound arrow. I think it was like 212 fps on the first shot. And dropped with every shot until it stabilized after about a dozen shots. Once it stabilized it had no real performance left but it did confirm what is possible if the right materials were used. Short working areas solve a multitude of design problems with bows. The stored energy was over 125% of peak draw force.

Steve, i gotta ask if you built a follow up bow to that hinge bow, and where you took the idea?

[DC]

If the limb flexes between the handle and limb nock during this phase of the shot,

This is confusing me a bit. What kind of flex are you talking about here. The bow is bending, that's flex, but I don't think that's what you're talking about.

[Badger]

  I made what I called a hinge bow several years ago with very extreme recurves and reflex, something like 12". The bow was about 4" wide in the bending area which I think was no more than about 8" long up close to the handle. It broke down quickly because of set and hysterisis but in the initial shots it was the fastest bow I had ever seen bar none with a 10 grain per pound arrow. I think it was like 212 fps on the first shot. And dropped with every shot until it stabilized after about a dozen shots. Once it stabilized it had no real performance left but it did confirm what is possible if the right materials were used. Short working areas solve a multitude of design problems with bows. The stored energy was over 125% of peak draw force.

Steve, i gotta ask if you built a follow up bow to that hinge bow, and where you took the idea?

   I never did, I was trying to find some fiberglass builders to build the bow but none that I know of took interest. the new border bows closley resemble the design. The main thing I was trying to estalish was the amount of design problems that can be solved by simply using shorter working limb areas. Stability at brace for highly reflexed bows has always been a major issue, as well as the distorsion in the limbs that Allen described above. It solves both of those issue. Bows built from wood just cannot tolerate that short of a working area unless they are drawn much shorter. This particular bow could have tolerated a 24" draw pretty well without breaking down.

[avcase]

Steve,
A Sinew-wood-Horn composite should be capable of handling the high bending strains of your design. If you recreated your bow and really thinned down the area of hinge-like bending, then used that as the core. The horn and Sinew would not have to extend all the way to the tips.

A Drake flight bow might be most similar to your design. The latest Border “Hex 8 super recurve” designs are a full working Recurve. A 35# bow stores almost as much energy as a 50# bow with a more conventional design. There is one major drawback as far a small flight shooting is concerned, the efficiency is relatively low and it starts to run into a wall below 8-9ggp. This is one design where the faster bow with heavy arrows is not the fastest with lighter arrows.

Alan

[Badger]

  I don't like the full working recurves especially with light arrows.

[Tuomo]

There is one major drawback as far a small flight shooting is concerned, the efficiency is relatively low and it starts to run into a wall below 8-9ggp. This is one design where the faster bow with heavy arrows is not the fastest with lighter arrows. Alan

Why? What are the physical reasons of that?

[DC]

I'm trying to wrap my head around that too. This bow will still shoot a lighter arrow faster than it will shoot a heavier arrow, right? But compared with other bows, not so good? Hard to get a piece of yew to bend like that though

[sleek]

I'm trying to wrap my head around that too. This bow will still shoot a lighter arrow faster than it will shoot a heavier arrow, right? But compared with other bows, not so good? Hard to get a piece of yew to bend like that though

The efficiency can drop while arrow speed increases. They are not the same. Just as an example:
A 10 gpp fires at 180 fps
9 gpp hits 190
8 gpp hits 195
7 gpp hits 199
6 gpp is 203

These are not real numbers but its showing how the energy ( velocity x mass )  of the arrow is decreasing as the arrow weight drops, making the bow less effecient in putting its energy into an arrow.

You can see that the lower weight arrow, though it is faster, its actually storing less energy because of its decrease in weight.  An arrow at 10gpp may have X number of jules in kenetic energy,  an arrow at 5 gpp would still have X Jules if the bow were 100 % effecient, but that would require the speed of the arrow to be MUCH higher for its weight,  and the bow simply doesnt get more effecient as arrow weight drops, rather, less so. The difference in speed between arrows may be only 1 fps, if any difference, even if the 2nd arrow were only half the weight of the first, when the first weighs 2 grains, and the second weighs 1 grain.

[DC]

But a bow that shoots a 2 grain arrow at 250 fps will always shoot a 1 grain arrow a little faster. Right?

[Del the cat]

But a bow that shoots a 2 grain arrow at 250 fps will always shoot a 1 grain arrow a little faster. Right?

I got pretty light (about 15 grains  ) in this test (see link) and you can see the velocity goes up pretty damn quick as you get really light.
But there will come a point where it is too light to do much good (e.g very little kinetic energy or momentum.
https://bowyersdiary.blogspot.com/2011/11/mass-velocity-and-energy.html
Del

[DC]

I'm going off on a bit of a tangent but why do we care if the energy drops off as long as the speed is still increasing? It's the speed of the arrow once it leaves the string that's the bottom line isn't? Is there something we can do with the energy information?

[Del the cat]

I'm going off on a bit of a tangent but why do we care if the energy drops off as long as the speed is still increasing? It's the speed of the arrow once it leaves the string that's the bottom line isn't? Is there something we can do with the energy information?

Nope, if it is too light the drag will overpower it's momentum/kinetic energy.
I't the old ping pong ball vs golf ball thing.
Fastest tabletennis ball smash is about 70 mph, but it wouldn't go as far as a golf ball travelling at 70 mph.
Del

[sleek]

I'm going off on a bit of a tangent but why do we care if the energy drops off as long as the speed is still increasing? It's the speed of the arrow once it leaves the string that's the bottom line isn't? Is there something we can do with the energy information?

Nope, if it is too light the drag will overpower it's momentum/kinetic energy.
I't the old ping pong ball vs golf ball thing.
Fastest tabletennis ball smash is about 70 mph, but it wouldn't go as far as a golf ball travelling at 70 mph.
Del

That and the point is to get a bow to deliver the most energy into an arrow. Just because the arrow goes 300 fps it doesnt mean anything if the bow is only putting 50% its energy into it. Say, you hit 400 fps, big deal, it took a 400 pound bow to do it. Thats bad effeciency. Now 400 fps with a 40 pounder, now we are talking.